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Insects are the most numerous of all living animal species. The reasons for their success are many and varied but can be directly related to adaptations found not only in the adult, but also in the various life cycle stages. In particular, those adaptations which enable survival during a period of severe environmental adversity are of considerable importance as the survival of the species depends to a large extent upon the success of these particular adaptations. Foremost among these are the overwintering adaptations which enable survival during the rigours of winter. For a large majority of species these include not only sub-optimal temperatures, frosts, and snow, but often the absence of the food source or host, so that normal growth, development and reproductive activity are inhibited. Many species of animals and plants faced with such environmental problems during winter have evolved a variety of survival mechanisms loosely referred to as dormancies, all of which involve either the slowing down or even the complete cessation of normal metabolic and behavioural activity. For such insects, the only alternative to evolving an overwintering survival stage (or dormancy mechanism) is migration out of the region for the duration of the winter, and in fact many insect species rely on this strategy instead of a period of dormancy.
Specific overwintering mechanisms such as diapause in insects, or its equivalent in plants — deciduousness — are presumed to have evolved during the Pliocene-Pleistocene Ice Ages in the Northern Hemisphere, when the selection pressures of severe climatic adversity brought about either the extinction of many species, or the development of overwintering survival mechanisms such as diapause. In the Southern Hemisphere, however, and particularly in New Zealand, the severity of this period is thought to have been sufficiently modified by our maritime climate so that relatively few insect or plant species were eliminated. As a result, we not only have a very high percentage of endemic plant and animal species, but there is also considered to
However, diapause is not solely an adaptive outcome of severe climatic selection pressures; it may also evolve in response to a number of other limiting factors in the life cycle such as periodic absences of food, or water (or even an excess of water in certain tropical latitudes). In some cases, in which the life cycle of the individual is closely related to that of a host species (animal or plant) a diapause stage may result which synchronises the insect with the seasonal cycle of the host species. According to the ‘Dumbleton hypothesis’, examples of climatically induced diapause in New Zealand insects should be rare or even absent; and any example of a diapause stage can therefore be presumed to have two probable sources: either it evolved in response to environmental pressures other than climate (such as have already been referred to); or the mechanism was evolved elsewhere and imported into this country along with the insect in question. Problems associated with the latter can be easily solved in those cases where the recent arrival of the insect has been observed and recorded. Difficulties can occur, however, in those cases in which the insects' antiquity in this country cannot be accurately determined.
The major objectives involved in overwintering studies are thus three-fold. The first involves detailed field studies, noting in particular how many, and which particular stage(s) are present during the winter months and their state of activity. This may range from normal daily activity to various degrees of inactivity or dormancy. Observations on adult activity during winter also involve examination of the state of the reproductive organs, as imaginal reproductive diapause is known in many insects. Identification of any possible environmental limiting factors operating in the field during the winter will assist the second objective which is a laboratory study of the factors that induce and terminate the state of dormancy. Finally interpretations of the findings from both field and laboratory observations have to be based upon a clear understanding of the meaning and definition of the various types of dormancy states commonly referred to in the literature. Unfortunately several of these terms are often used synonomously, i.e. hibernation, diapause and dormancy may all be used with reference to the same overwintering mechanism. Generally, the term dormancy can be used to encompass all types and degrees of growth arrest, which range from briefly and directly induced states of cold torpor to progressively intensifying states of inactivity including quiescence, through to the advanced and physiologically complex adaptation called diapause.
Many attempts have been made to define these terms and in particular to identify the environmental factors which are involved in their induction (or onset). Recent literature on the subject (e.g. Way 1962; Lees 1962; Danilevskii 1964; Norris 1970; Mansingh 1971) reveal a consensus of opinion that two basic types of dormancy can be distinguished: quiescence and diapause. The former can be defined as cessation of activity for indeterminate lengths of time, in direct response to adverse environmental conditions (commonly temperature) with a correspondingly direct return to normal activity upon termination of the adversity. Quiescence can be found in any or in all stages of the life cycle which are subjected to the adverse conditions. By contrast, diapause is known to occur in only one species specific stage of the life cycle, in almost all known diapausing insects (Beck 1968). This stage, therefore, is the only one which is present and able to survive the period of seasonal adversity. Secondly, it can be distinguished from quiescence by being induced in advance of (i.e. in anticipation of) the seasonal adversity, and then continuing to proceed for a definite period regardless of changes in the external environment. Only when this period of ‘diapause development’ is completed will the diapause be terminated. Observations in the field on the anticipatory nature of diapause and of its ‘timing’ in order to synchronise a particular life cycle stage with the seasonal adversity, have led to the conclusion that an innate ‘clock’ mechanism is involved in this process. While temperature has long been known to influence both the incidence and intensity of diapause, its actual timing has been shown to be based on seasonal information received from the daily photoperiod. This provides an extremely stable and accurate environmental ‘time cue’ as to the time of year, and thus enables the insect to anticipate the onset of the unfavourable season and hence enter diapause before its arrival.
An interesting aspect of this discovery is that this reliance on photoperiod by diapausing insects has led to the observation that this photoperiodic process is latitudinally related, and in fact many examples of geographical ‘clines’ in a population of the same diapausing species are known to occur. This is particularly true in facultatively diapausing species in the Northern Hemisphere which can show a gradation in the percentage of diapausing individuals in any one generation ranging from virtually nil at low latitudes, through an increasing percentage with increasing latitude until at very high latitudes an apparently obligate diapause of 100% in every generation is manifested.
A survey of the literature concerning overwintering studies in New Zealand insects highlights most of the aspects already mentioned, i.e. problems concerning the introduced or endemic status of some insects; problems in the lack of parallel field and laboratory investigations into the nature of the overwintering stage(s); and problems in the interpretation of the type of dormancy stage. A good variety
According to Wilkinson (1964) the tiger-moth, Metacrias strategica, in Otago (47° S) appears to overwinter in the larval and pupal stages, the adults having only a very brief life span (approximately 21 days) confined to the summer months. Early instar larval feeding during warm periods then gives way in the cold winter months of June to August to an inactive ‘quiescent’ last larval instar, which overwinters until the approach of warmer spring weather. Because of individual variations in the duration of the larval instars, pupae too may overwinter, and Wilkinson noted that the duration of the pupal instars increased with decreasing winter monthly temperatures. Although no experimental investigations were carried out to determine the nature of the stimuli(s) involved in the onset of this ‘quiescence’, the absence of a total arrest in the life cycle prior to the onset of winter, and of a single specific overwintering stage, along with the observations concerning the relationship of the length of the pupal stage to temperature, are all strongly suggestive of a temperature induced quiescence rather than a diapause. (Unfortunately Dumbleton (1967) cited this as one of the two known examples of a winter diapause in New Zealand.) Spitzer (1970) looked specifically for evidence of either winter quiescence or diapause in the Manawatu (40° S) as indicated by the presence or absence, respectively, of all or only one stage of the life cycle during the winter months. Of at least 23 species of Noctuidae examined, in most the adults, although not numerous, could be found during the winter and in all cases they were reproductively mature. The larval and pupal stages during winter remained active but growth was slowed, and pupal quiescence was ‘probable’ in at least one case. Spitzer concludes that ‘at low altitudes in the North Island diapause does not occur’ (either in the adults, as reproductive diapause) or ‘even in the immature stages although … development may be somewhat retarded’ — this state of growth retardation he terms ‘quiescence’. Because of the low altitude and more northerly latitude of this study, Horak-Kaenel's (1969/70) investigation into the overwintering of Proteodes carnifex is of particular interest as it was carried out on an alpine species at high altitudes and latitudes (41° S at the St. Arnaud Range in Nelson, and 45° S at Te Anau). In the Northern Hemisphere at such latitudes and in a known univoltine species, diapause could be expected to occur. In fact, however, although P. carnifex constructed a protective winter hibernaculum, it only remained inactive within this cocoon for short spells during heavy snowfalls when feeding was impossible. At every favourable opportunity it emerged to feed on Nothofagus cliffortiodes. It appears that despite the high latitude
The 10 species of Lepidopteran Crambini studied by Gaskin (1975) included both uni- and bi-voltine species, and even geographical races within the one species, which vary according to latitude as to the number of generations per year. The life cycle of Orocrambus simplex, a uni-voltine species inhabiting sub-alpine tussock grasslands, is illustrative of the general overwintering trends in this group. The adults and eggs are both present during the summer months while the first four larval feeding stages can be found during autumn. The sixth larval instar appears to be the overwintering stage, remaining inactive (and non-feeding) from April to October. No adults of any of the 10 species were recorded during August and September. In O. flexuosellus (on which the greatest number of observations of each stage were made) there is a definite trend within each particular stage of the life cycle for an increase in its duration to occur with the approach of winter: e.g. January egg duration (9-10 days); July egg duration (24-29 days); larval stages 1-4 in March (14-30 days); in May (25-50 days). Without conclusive experimental evidence it is not possible to state categorically that the last larval overwintering stage represents a quiescent rather than a diapausing dormancy stage. However, the evidence of progressive growth retardation in all stages with the onset of lower winter temperatures, along with the overlap in several species of both late larval and pupal stages during winter months are again suggestive of a quiescent rather than a winter diapause mechanism.
It is important at this point to emphasise that all insects so far cited are not only endemic but are phytophagous, on evergreen host plants. The existence and the importance of such a year-round food supply for so many of our endemic insects is realised only from comparison with studies on insects lacking such a continuous food supply; in which case this can possible become the limiting factor promoting the evolution of a diapause overwintering mechanism. In the remaining studies, this and other potential diapause-producing factors are considered.
The Pompilidae (‘spider-wasps’) studied by Harris (1974) are a case in point. Unfortunately although a large number of these species were studied in considerable detail, only one life cycle is described. Priocnemis nitida is a uni-voltine insect present in the adult stage only during the summer months when, because of its strongly positive heliotropism, it is active only in full sunlight. The eggs are laid in summer (e.g. February) and along with a single spider to which each egg is attached, they are placed individually into a protective nest. Within two weeks the larva passes through its feeding stages, completely consuming the spider food supply before spinning the cocoon of the last larval (fifth) instar. Inside this, the
Praeolepra unifomis. This insect displays a close relationship with the seasonal phenology of its host plant Coprosma lucida. The eggs are laid in March in the axil of the green fruit and stem, and the developing larvae burrows into the fleshy mesocarp where the first instar feeds externally, while the second instar tunnels in through the hard endocarp and continues to feed inside the seed case on the carpels, and inner walls of the seed coat. The prepupa then overwinters inside the maturing fruit until emergence 16 to 18 months later (i.e. in July and September respectively of the following winter). (B. M. May, pers. comm.)
Although details of the degree of host specificity and the adult foodplant of this weevil are not certain, it is possible that the winter emergence of the adults is related to the winter flowering of the Coprosma plant. The interesting feature of this life cycle is that it illustrates another environmental factor which is known to contribute to the evolution of a winter diapause mechanism, and that is where the life cycle of the insect is closely adapted to the phenology of the host plant for food and/or shelter. Danilevskii (1964) cites as a ‘typical example’ of this situation the apple blossom weevil whose entire development occurs in the buds of the apple blossom. The adult beetle after emergence enters a diapause state for 10 to 11 months until the following spring flowering of the apple tree. It is quite possible that Praeolepra uniformis may have evolved a prepupal diapause for similar reasons; as Danilevskii (1964) notes, ‘such cycles are characteristic of many carpophagous insects.’ Alternatively, the lengthy period inside the Coprosma fruit may be spent in a combined larval feeding and prepupal quiescence.
The life cycle of Pericoptus truncatus, an endemic scarab beetle (Dale, 1963) provides another example which poses interesting ecological problems concerning the existence of a diapause or quiescent stage in the life cycle. This beetle spends its entire life, including mating and reproduction (except for an adult dispersal flight shortly before death), beneath the ground on sandy beaches.
The remaining overwintering studies worthy of note concern those insects which (unlike the endemic species previously mentioned) are of more doubtful, or of recently introduced origin. In such insects it is not surprising to encounter instances of diapausing mechanisms; the problem lies in determining whether they evolved in this country or were introduced with the arrival of the insect.
Hardwick (1965) reports a winter pupal diapause in Helicoverpa armigera conferta (of the corn earworm complex), varying from 19% at Rotorua (39° S) to 82% in the Nelson (41° S) population. The published status of this insect as a South Pacific sub-species is indicative of its lengthy presence in the area, but the origin of its diapause mechanism was most probably imported along with its adventitious spread into the Pacific. (J. S. Dugdale, pers. comm.)
Similarly, the codling moth, Cydia pomonella, is of known recent introduction, and it also exhibits a diapause in which the percentage variations in incidence per generation (and hence the occurrence of uni or bi-voltinism) are correlated with different latitudinal locations. (H. C. Waring, pers. comm.)
The cricket species in New Zealand represent the most interesting and problematical of overwintering studies, and indeed one species, Teleogryllus commodus, is the second of the two examples of winter ‘diapause’ cited by Dumbleton (1967). However, two major problems present themselves when trying to determine the exact nature of the overwintering mechanism in the Gryllidae; one is the uncertainty of origin (particularly of Teleogryllus commodus) and the other is (once again) the lack of experimental evidence concerning the environmental stimuli responsible for the timing and induction of the ‘diapause’. It is commonly observable that the uni-voltine life cycle of T. commodus in the field, even in Auckland (37° S)
Pteronemobius sp. and concluded that they represent distinct ecological races, with the Christchurch egg diapause being ‘obligate’ and of ‘high intensity’ while in the Kaikoura population it was of ‘lower intensity’ and ‘facultative’. Comments on diapause formed only a minor part of McIntyre's investigation and were based on insufficient evidence to verify this conclusion. However, her work, together with evidence from cultures of Pteronemobius bigelowi and P. nigrovus at Victoria University (
Parkes (1972) also examined two populations of Pteronemobius sp. at Hamilton, and the more coastal Kawhia (38° S). Here field studies showed that adults were present throughout the winter months in the Hamilton population, while at Kawhia ‘both adults and nymphs could be found during most of the year’. Parkes concludes that in the Hamilton population a partial second generation may occur in favourable years while at Kawhia, ‘continuous year-round breeding probably occurs’ — which rules out any diapause mechanism at least in the latter population. By contrast T. commodus populations at both locations had only a single generation/year, the adults dying out in autumn and only the eggs overwintering in diapause.
Although Bigelow (1964) points out that certain morphological differences exist between the New Zealand and Australian populations of T. commodus, suggesting its long standing in this country, Parkes (1972) comments that both Gryllinae species (T. commodus and Modicogryllus tepidus) are of introduced origin.
In conclusion it appears that to date the investigations into overwintering mechanisms of endemic New Zealand insects do not indicate the existence of a diapause state as distinct from other forms of dormancy, such as quiescence. However, possible exceptions may be the zoophagous ‘spider wasps’, the carpophagous weevil Praeolepra uniformis, and the sand-inhabiting scarab Pericoptus truncatus. It is interesting to note that each of these insects introduces ecological factors other than that of severe macro-climatic adversities which more commonly promote the evolution of a diapause mechanism.
It thus appears that Dumbleton's (1967) thesis relating the lack of a sufficiently severe Pliocene-Pleistocene with the presence of a high
Optical Apparatus Technician, Department of Zoology, Victoria University of Wellington
These practical notes on the microscope are intended for the biologist, who uses a microscope as an analytical tool in his research work. It is not necessary to become a full-time professional research microscopist in order to get the best out of a microscope. For this reason these notes do not go into the laws of optics as applied to microscopy.
The ‘biological microscope’ discussed here includes all types in general use in teaching laboratories that employ bright field illumination. The parts of a typical instrument are shown in Fig. 1. Low-power dissecting microscopes, i.e. stereo microscopes, have been omitted as they are easily set up and hence less likely to be used incorrectly.
The optical information which can be obtained from a biological microscope (also known as a compound microscope) is sufficient for most biological demands. However, it has its limitations as a bright field observation microscope. Its utilisation can be enhanced by adaptation for dark field, phase contrast, polarised light, differential interference-contrast and U.V. fluorescence microscopy. It should be noted that only modern high quality microscopes can be converted from one phase of observation to another. In fact each one then becomes a specialist instrument. In order not to confuse the beginner this article will deal only with the basic compound microscope. The higher facets of microscopy are nevertheless built on these foundations.
Magnification in the microscope is collectively produced by two independent optical systems — objective and eyepiece. The image formed is inverted and reversed, i.e. it is seen upside down, and left to right is also reversed. The objective projects an image which is located below the eyepiece at a point which falls in the front focal plane of the eyepiece (known as the aerial image). The eyepiece, because it is acting as magnifier, enlarges the already greatly magnified image coming from the objective to produce at the exit pupil of the eyepiece an even wider visual angle and thus higher magnification.
The objective and eyepiece have been designed to work together to give best results at a particular tube length. 160 mm is one of the standardised tube lengths. This length is the distance from the flanged shoulder of the objective to the upper end of the eyepiece tube.
Resolving power is the ability of an eye or lens system to differentiate between extremely fine lines. When two adjacent objects become so small in apparent size that further reduction results in the eye's failure to separate them, the angle of maximum resolution has been reached. The image-forming power in the optical system of a microscope is naturally much greater than the unaided eye.
Figure 1
A Generalised Bright-FIELD Microscope
(1) A, eyepiece; B, diopta ring; C, eyepiece interpupillary slide. (2) Binocular inclined tube. (3) Revolving objective nosepiece. (4) Mechanical stage. (5) Sub-stage condenser assembly: A, swing-out top lens; B, centering screw (one each side of condenser carrier); C, aperture iris; D, filter carrier; E, auxiliary condenser lens. (6) Field stop diaphragm. (7) Lamp mount. (8) Base plate. (9) Coarse focus adjustment. (10) Fine focus adjustment. (11) Sub-stage condenser drive. (12) Operating knob for mechanical stage. (13) Stand with tube carrier.
It should be noted that a limiting factor that is generally termed ‘useful magnification’, namely the limit of resolving power, is also to be found at a specific point. Beyond this limit further resolution of fine detail is no longer accomplished even when magnification is further increased by the use of a higher-powered eyepiece. To do so would only increase the initial magnification without resolving any new detail. We can calculate the limits of ‘useful magnification’ by knowing the numerical aperture of a particular objective.
The useful magnification of an objective is found by multiplying the N.A. by a minimum of 500 and a maximum of 1000. An eyepiece must then be selected to produce the appropriate magnification up to, or within, these two limits. The numerical aperture is engraved on most objectives. For example, we may find ‘40/0.65′ engraved on a typical ‘medium power’ objective. This indicates that 40x is the objective's magnification and 0.65 is the maximum numerical aperture of its front lens. Multiplying 0.65 by 500 and 1000 gives a useful magnification range from 325x - 650x. As the magnification of the objective is 40x in our example and as total magnification of a microscope is found by multiplying objective and eyepiece magnifications, we can calculate that to remain within the limits of useful magnification an eyepiece should be selected which has a magnification within the range of 325/40 to 650/40— that is, between about 8x and 16x magnification. Eyepiece magnification is normally engraved on top of the eyepiece. To exceed (as many beginner microscopists do) the useful magnification range of an objective by using an eyepiece of too high a magnification only distracts from the excellence of the objective.
We have seen that resolving power is the measurement of the degree to which an optical system can create separate images of two points closely set together. This ability to distinguish fine detail is thus not governed by magnification alone but rather by the N.A. value. The higher the N.A. the greater the, resolving power.
To help understand the theory behind the formula which determines the N.A. value, one must firstly comprehend that any light entering the optical system of a microscope manifests itself in the form of waves (the fundamental restricting element in all optical microscopes). These light waves have a natural spreading tendency. Furthermore, as they traverse through the specimen and cover glass, they become refracted from the optical axis, i.e. the cone of rays originating at the object. The outermost rays thus fall in intensity as their angle of refraction is increased. Conversely the central area of light is concentrated because of the smaller refracted angle.
As Fig. 2 shows, the refractive index of air has been given a numerical value of 1. Objectives which do not employ a refractive medium such as some liquid between the cover glass and the front lens are referred to as ‘dry systems’. Objectives so designed cannot have an N.A. value greater than 1.
Figure 2
Schematic diagram showing how a ‘dry ‘objective fails to absorb all the diffraction of light rays. By using a liquid, e.g. oil, between the cover glass and objective, the numerical aperture is increased so that the lens can resolve all of the diffraction aperture.
In practical terms it is impossible to achieve a figure greater than 0.95 for dry systems. This is due to the failure of the aperture angle within the objective to attain a half-angle of 90°, a limiting factor governed by optical theory. If a medium which has a greater refractive power than air is used between the front lens and cover glass (e.g. immersion oil, N.A. = 1.515) a greater angle of acceptance is achieved. Consequently this type of objective, known as an ‘immersion system’, has a superior ability to resolve through the gain in numerical aperture. Immersion objectives are therefore assigned higher N.A. values than those designated to dry systems — and are used to obtain higher magnifications. At this point it is important to stress the influence of illumination and the sub-stage condenser on the microscope's total resolving capability.
There are various kinds of illumination on biological microscopes.
An improvement on daylight illumination is to use a desk lamp with an opalescent bulb. Place it about 25cm from the plane side of the mirror.
Note: Generally use the plane mirror in (a) and (b). However, when the microscope has no sub-stage condenser or you wish to remove unwanted images cast by the plane mirror, use the concave side.
This assembly has a very important role to play in the total balance of microscope illumination. Its task is to collect as much
A basic bright-field condenser can be vertically racked up and down. It consists of a fixed lens and an iris diaphragm. More sophisticated condensers incorporate a swing-out top lens or one which can be screwed off and interchanged. Most microscopes with this type of unit also have the extra facility whereby the condsenser can be centred in the horizontal plane. This is a prerequisite for Kohler illumination unless the light source itself can be centred.
Basic preparatory points are often neglected by the student microscopist.
Firstly, it is important to avoid the use of mismatched components on your microscope. Do not use different makes of objectives and eyepieces. They may work and produce a somewhat satisfactory image. However, they are usually not ‘parfocal’ with the other objectives. (Each objective must have the same focal length to the mechanical tube length.) It is important that when the nosepiece is revolved to a different objective, the focal plane does not deviate from the last objective used — a significant factor when changing from low power to an oil immersion system when damage to the objective and specimen can occur if parfocalisation is not maintained. When revolving the nosepiece make sure that it positions itself at the click stop. Failure to do this will cause the objective to be out of alignment with the optical axis. Check, too, that the objectives are fully screwed in. A dirty or finger-printed front lens will give an upsharp image lacking in contrast. When the lamp collector, condenser lens or eyepiece are dirty, this will usually be indicated as blurred spots or flecks which remain in the field of view as the preparation is moved. Their location can be easily found by rotating either the eyepiece, objective or by moving the sub-stage condenser. When using a microscope with a monocular body tube, it is recommended that you keep the unused eye open to lessen eye fatigue. In order not to harm the muscles by this form of ‘disconnection’, the eyes should be used alternately. This problem does not apply to binocular microscopes. However, it is important to adjust the eyepieces for individual interpupillary distance. This is accomplished by lateral movement of the eyepieces until only a single image is seen in union with both eyes. Also the eyepiece must be adjusted to suit the operator's individual eyesight. This is done by focusing sharply on to the specimen while observing only through the fixed eyepiece (the other eye remaining closed). Now open the closed eye and bring into focus the image seen in this eyepiece, by adjustment
Often the novice does not correctly relax his eyes while focusing the instrument. The image should be imagined to be set at infinity. Invariably this is mistakenly viewed as if it were closely set inside the eyepiece. This form of accommodation by the eye will be found to be very tiresome. If one is working in a laboratory that has a window, a good practice is to periodically glance at some distant object. You should be able to look from the window back to the specimen image without refocusing. Another good practice is to constantly alternate the focus by means of the fine motion adjustment. This will prevent your eyes from accommodating a fixed point, thus alleviating eye strain.
As stated earlier, the most basic illumination device found on microscopes consists of a mirror, either utilising daylight or some form of artificial illumination. For the sake of convenience this has generally been substituted by a fixed light source mounted on the base plate. For this reason we will describe the adjustments required for the latter system. The manner of operation will, of course, also apply to other bright field observation instruments, irrespective of what system is used.
Place the microscope in a convenient working position. Switch on the light source, then check that all optical components are clean and that the rest of the instrument is functioning correctly. Before placing a specimen slide on the stage, the following important points must be observed:
Never try to set a slide under the objective without firstly either lowering the stage assembly so that there is some distance between slide and objective (on some microscopes the stage is fixed and the body tube is the moving part) or, alternatively, if you do not wish to lose your focused setting, you may turn the objective away from the optical path. e.g. slanting it halfway between click stops. However, this is not recommended when using oil immersion objectives, i.e. unless they are of the spring-mounted type (pushed up and locked).
The above prictice, if adopted, will safeguard the objective's front lens from being inadvertently scratched by the sharp edge of the slide. The importance of this exercise cannot be overstressed and should in time become second nature to the operator.
Finally, rotate the nosepiece to the required objective that is to be used for observation. Remove the eyepiece and look down the tube at the objective. Take care when doing this so that dust does not enter the tube or eyepiece. By using the aperture iris, mask the visible field by approximately one third. It is important to remember that each time a different objective is used the aperture must be correspondingly adjusted.
A point of caution here. — Never control the light intensity by using the iris diaphragm on the condenser as the resolving power will be adversely affected. Should the image be too bright, regulate the lamp voltage or insert a filter (e.g. neutral density or blue) between condenser and light source.
Observe and carry out steps 1 and 2 as previously described under Critical Illumination'.
Then carry out step 5 as described under ‘Critical Illumination’.
Remove dust and dirt from the microscope body, i.e. painted surfaces, with a damp cloth (never use harsh or abrasive solvents on any part of the microscope) and if required use a small amount of hand soap. Dry and polish with a soft linen cloth. When the above exercise is carried out always remove the objectives and eyepieces (replace with dust plugs).
The optical components of the microscope such as eyepieces, objectives and condenser should never be attempted to be dismantled. Clean only the outer surfaces in the following manner:
Remove loose dust with a degreased (in ether) camel-hair brush or a soft ‘brush-blower’. However, check that the inside of the ‘blower’ is of a type that is chalk-free. Rigid and encrusted dirt should be removed by firstly breathing on to the lens surface and then cleaning with a clean, lint-free cloth. Avoid using circular motions that produce harmful ‘sandpaper’ effects. Lateral movement is far better as it minimises the risk of scratching the lens surface. Should a closer inspection (e.g. with a magnifier) reveal still some residual dirt, try using a cotton wool applicator moistened with a little xylol. (Never use alcohol as this may dissolve the cement between lens elements.) Note of caution here is to remember that xylol is carcinogenic so that inhalation or contact with the skin must be avoided. This also applies to benzene which is frequently used as a cleaner. If possible safer alternative solvents should be used, e.g. diethyl ether. It goes without saying that all chemicals should be used sparingly and with care.
Never attempt to oil any part of the microscope. Special lubricants have been used in its manufacture. If it requires servicing due to a stiff focusing mechanism, condenser drive or a tight mechanical stage, take the microscope to an authorised workshop.
Finally, protect the instrument against dust by covering it when not in use, e.g. plastic cover or placed in a cabinet.
In conclusion, remember that the microscope is only as good as the operator and its performance will be dictated by the user's own technique.
The zoogeography of moas is compared with that of other bird groups within New Zealand. Moa species tend to be restricted to one or other of the two main islands, whereas the other birds, flightless as well as flying, tend to occur on both islands. The ecology of moas provides no explanation for the contrast. Rather, the anomaly probably reflects faulty taxonomy, several subspecies of moas having been ranked as true species.
In 1873 Haast, drawing largely on the descriptions of Owen, made the first serious attempt to classify the moas. Subsequently, Lydekker (1891) and Parker (1895) refined the generic definitions, and in 1930 Oliver produced a fully integrated taxonomy. It was further improved by Archey (1941) and Scarlett (1972). There would be general agreement with this skeletal history of the evolution of moa taxonomy. Other writers might add a few more names and dates — they are unlikely to subtract any — but they would recognise the progression I have listed. It passed through a descriptive phase powered by Owen's genius, to a classificatory phase dominated by Parker and Oliver, to a consolidatory phase in which Archey and Scarlett rationalised and economised the previous classifications.
Meanwhile, Fleming (1962) placed the extinction of moas in ecological and historic perspective. Far from being a puzzling and protracted episode reflecting an obscure conjunction of unknowable circumstances in the early Holocene, the extinction stood revealed as an event modern in its timing and abrupt in its duration. Most species of moas were still extant in 1600: while Cromwell was making Ireland safe for potatoes the Polynesians were making New Zealand safe for kumaras.
Classification of incomplete specimens usually goes through a stage when species proliferate. The moas provide no exception. The trend reached its apogee with Rothschild's (1907) 38 described species, many of them based on single bones. Oliver (1930) reduced the number to 22 which he divided between two families, the Dinornithidae and the Anomalopterygidae. Subsequently Archey (1941), who had access to a wider range of material, continued this rationalisation by reducing the number of species to 19. His sensible scheme was made possible by his study of variation within species, thereby enabling him to reject those taxa that fell within the range of variation of others. He accepted Oliver's (1930) families, and subdivided the Anomalopterygidae into the sub-families Anomalopteryginae and Emeinae.
Oliver's classification of 1949 is based largely on Archey's (1941) scheme. Into this he injected a further nine species required by study
McDowall (1973) complained that there were still too many species for his liking. He looked at the problem as a zoogeographer rather than as a taxonomist, pointing out that the late tertiary history of New Zealand did not provide the necessary conditions for a radiation of this magnitude, and that none of the other groups of birds radiated in this way.
I have another complaint. It might appear to be opposed to McDowall's, but actually it comes down to much the same thing: there are not enough subspecies. Table 2 divides four classifications of the moas, and two groupings of extant birds, into three categories: those species occurring only in the North Island, those common to both islands, and those only in the South Island. The extant birds (which for the purpose of this analysis are defined as species alive within the last 150 years) are divided into flying and flightless forms. They include only those species peculiar to New Zealand. Offshore island forms and all sea birds, shore birds and water birds are excluded. The data of Table 2 reveal no significant difference between the distributional patterns of flying and flightless extant species, but both of these groups differ significantly from the moas in the ratio of North Island: common: South Island species. Moa species, as presently recognised, tend to be restricted to one or other of the main islands whereas the extant species tend to be on both, usually with one subspecies on each island.
Taken at face value Table 2 suggests that the zoogeography and hence ecology of moas was quite different from that of the other birds. Circumstantial evidence as to the ecology of moas is thin, but what data are available on distribution, diet and the species of birds associated with them in sub-fossil deposits, suggest that most forms, if not all of them, lived in forest and along the forest edge (Simmons 1968, Gregg, 1972). Moas ranged from sea level to the upper timber line and penetrated the alpine grassland beyond. Habitat requirements for most species were probably generalised in much the same way as are those of kiwis today. Ecological counterparts of the moas are more likely to be found with the forest-dwelling cassowaries of northern Australia and New Guinea than with grassland forms such as emus and ostriches. There is no evidence to suggest that the ecology of moas was in any way strange or remarkable; ecology provides no explanation for the strange zoogeography implied by their current taxonomy.
A more likely explanation is that the zoogeography of moas is much the same as that of the rest of the New Zealand avifauna but that this is not reflected in their current classification. The dearth of species occurring on both islands need reflect no more than an unwarranted assigning of species status to North Island and South Island subspecies. Interestingly enough, Archey (1941, p. 62) came within a whisker of this interpretation in his treatment of the genus These are not the names used by Archey or by Oliver. In 1954 the International Commission of Zoological Nomenclature replaced Dinornis. He remarked that the series in the South Island — D. torosus, D. robustus, D. maximus, ranked in ascending size — was paralleled by the analogous series D. struthoides,* D. novaezealandiae and novaezealandiae, as used by Archey and Oliver, with struthoide, and their ingens then became novaezealandiae.D. giganteus in the North Island. Scarlett (1972) explicitly invoked subspeciation to explain these similarities, but then awarded species status to all six forms in his informal list of species. Since, in each case, the South Island form is a little more robust than its North Island equivalent, there seems little reason to suspect anything more than straight-forward subspeciation conforming to Bergman's rule. Similar comparisons can be made with species-pairs of the other genera.
I am actively dissatisfied with the checklist classification, but my dissatisfaction is founded on distributional anomalies rather than on morphology. Hopefully taxonomists will take a closer look at the taxonomic relationships deduced from the size and shape of bones. Luckily they are not entirely satisfied with the prevailing scheme witness, for example, Scarlett's (1972) drubbing of Oliver's (1949) genus Zelornis and Cracraft's (1976) conclusion that only 13 species should be recognised. As Dwyer (1976) and others have argued, if it is to have any evolutionary meaning a classification must make sense according to ecological and zoogeographic criteria as well as according to morphological criteria. My considerable fund of osteological ignorance does not, of itself, disallow a critical interest in the classification of moas. Nor does it disqualify me or any other ecologist from questioning the biological reality of this or that ‘species’ which, although perhaps morphologically distinct, is ecologically anomalous.
There are four areas in which ecology can say something useful about the classification of moas:
Sexual dimorphism: We know from extant species that ratites can be sexually dimorphic, particularly with regard to size. So far no bimodality of size has been detected within any species of moa. Strange? An ecologist would suspect strongly that he was dealing with sexual differences if two forms shared a common distribution and were found together consistently in ratios not significantly more disparate than 1:4.
Subspeciation: If two forms, one on each of the main islands, are morphologically closer than is either to other species of that genus with which it is sympatric, then subspecies status is the most economic and conservative interpretation.
Misclassification: If a form is well represented on one island but occurs rarely on the other we can reasonably question its occurrence on the latter island. It may be misidentified there or the locality label may be in error. Neither circumstance is unprecedented.
The one-off problem: If a species is erected on a single specimen (e.g. Dinornis gazella, Pachyornis murihiku, and Megalapteryx benhami), or a particular bone (Dinornis hercules), we should wonder why, with the wealth of material available, further specimens have not been discovered. Does the specimen represent a morphological extreme of some well-known species? Ecologists tend to distrust this kind of data for two reasons: they are conditioned to question the significance of an unreplicated event, and they would view as anomalous the corollate implication that several species of moa were extraordinarily rare. It might be as well to keep these ‘species’ on a suspense list, transferring them to the list of species we are sure of only after further material is unearthed in support of the original diagnosis.
Probably the most efficient instrument for tightening up the current classification is a multivariate analysis of a large number of bones collected, without judgement as to species, from both islands. The first question we might ask of it is how many distinct morphological groups (clusters) can be recognised within the moas. These groups would then be investigated further to determine which are sexes, which races and which species, by use of distributional criteria similar to those listed above. The problem of deciding which bones belong to which specimen can be avoided by restricting the analysis to one bone (femur, tibia) or a single fused bone sequence (cranium, pelvis, sternum, metatarsus).
As a means of determining how large a sample might be required for this exercise I ran a preliminary analysis on the measurements of 60 pelves and 85 crania recorded by Oliver (1949). Three multivariate techniques (Principal Component, MULTBET, MULCLAS) generated clusters mainly on the basis of the absolute size of specimens. The measurements were therefore converted to ratios and re-analysed. This time the clusters produced interesting relationships at and above the level of genus, but these samples were too small to allow resolution at the level of species. A sample of around 500 is needed, and that requirement rules out crania, and probably also pelves. The answer seems to lie with leg bones, but if these were used the sample size should be increased further or the number of measurements taken from each should be expanded well beyond the standard set.
But does it all really matter? Is the questioning of the number of moa species a first cousin to the debate over the number of angels that can dance on the head of a pin? It does matter. The New Zealand avifauna provides unparalleled opportunities for cracking some of the larger general problems of zoogeography and evolution. Because the tertiary and quaternary geological history is known with fair precision, and that knowledge improves each year, before long we should be able to calculate rates of speciation and subspeciation for the birds. Few other countries provide this opportunity. If there is a pattern of distributions common to several species in New Zealand it can be summarised as a zoogeographic model of how this came about in terms of what is known of the geological history. The hallmark of a useful zoogeographic model is its generality, the extent to which it accounts for the distributions of many species, not just one or two. But any attempt to produce such a model runs headlong into 25 species of moas doing something else. Until we know if the moas are, in fact, zoogeographically distinct from the rest of the avifauna, avian zoogeography in New Zealand will hang fire.
I am very grateful to the following people who criticised a previous draft of this note: J. A. Caughley, J. Cracraft,
It is characteristic of an oceanic island that its fauna, in comparison with that of an adjacent continent, is an impoverished one (Falla, 1953). Thus Australia (including Papua/New Guinea) has 66 species of ticks, 52 of which are indigenous whereas the New Zealand sub-region has only 9 named species of ticks. 3 of which are endemic and 6 of which also occur in Australia. One further species, an as yet unnamed argasid from a native bat (Mystacina tuberculata), was collected recently from North Auckland (
The origins of New Zealand's tick fauna and its affinities with those of other countries in the Pacific region have received little attention. The aim of this paper is to investigate the possible origins and means of dispersal of our tick fauna and to place the New Zealand Ixodidae and Argasidae within the framework of current biogeographical knowledge. The data used for this purpose come from a large number of host and locality records, and from publications on bird migration, geology and vertebrate palaeontology.
Ticks are blood-feeding, obligate ectoparasites of vertebrates and are related to spiders and mites. There are two families — the Ixodidae or hard ticks, so called because of the presence of an inflexible dorsal scutum, and the Argasidae, or soft ticks that have a leathery cuticle and no scutum.
Ticks can cause anaemia, paralysis and death of their hosts and, in addition, are among the most successful of those arthropods that transmit viral, protozoan and rickettsial organisms to man and other animals.
Members of both tick families pass through egg, larval, nymphal and adult stages. The Argasidae can have 2 to 7 nymphal instars whereas the Ixodidae have a single nymph stage. Some Ixodidae are 1 or 2-host ticks but most utilise 3 hosts. In other words, each of the 3 feeding stages is punctuated by a free-living phase. During this latter period, the engorged tick moults (if a larva or nymph) or oviposits (if a female) and the ensuing unfed stage later becomes parasitic on another host. Feeding times range from 4 to 21 days (Balashov, 1972) with larvae feeding more rapidly than adults or nymphs.
The Argasidae are mainly multihost ticks and contrast with Ixodidae in that the feeding times of nymphs and adults vary from
The time spent off the host by members of both families depends upon the stage of development reached, the ambient temperature and humidity, and the availability of hosts. The unfed, questing stages of some species of Ixodidae can live without food for at least one year. Some Argasidae have been known to survive for 10 years without a blood meal. Such survival ability would be of considerable value to ticks on isolated, infrequently visited islands or in generally inhospitable areas where hosts only appear sporadically.
The duration of the incubation and premoulting periods can range from days to months, depending upon the temperature and humidity within the immediate environment (Heath, 1974). Generally, low temperatures and low humidities can retard moulting or incubation to the extent that eggs or engorged stages of ticks could be carried over long distances stuck to birds' feathers or feet. Ticks carried on sea-birds face the problem of immersion in sea water but there is evidence (Murray and Vestjens, 1967; Sutherst, 1971) to show that tickets are capable of withstanding prolonged immersion in fresh as well as exceedingly stagnant water, thus periodic immersion in sea water may not disadvantage them.
There are three endemic species of ticks occurring in New Zealand: Aponomma sphenodonti Dumbleton, the tuatara tick, Ixodes anatis Chilton, the kiwi tick, and I. jacksoni Hoogstraal, the cormorant tick.
The genus Aponomma contains about 25 species (Roberts, 1970). Five species are found in Africa, 8 in the Australian-New Guinea-Indonesian region and 4 in the Americas (Hoogstraal, 1956). The genus is unknown in Europe. Most species occur on reptiles and exhibit remarkable host and geographic specificity, factors which could indicate considerable antiquity.
The first rhyncocephalid reptiles, forerunners of the tuatara, appear in the fossil record in the Lower Triassic (Fleming, 1962a). They are known also from East Africa and South America, but probably became extinct, except in New Zealand, in the late Cretaceous or Tertiary (Robb, 1973). This geographical distribution
The tuatara probably dates from the lower Cretaceous (Fleming, 1975) and fossil evidence indicates that it was once widespread on the mainland (Crook, 1975). New Zealand's coastline in the Eocene extended into the Ixodes eudyptidis and the introduced species, Haemaphysalis Iongicornis. Data from various sources (see text).
The reptile and its tick are known to occur together only on Stephens Island (I. G. Crook, pers. comm.). One could speculate that if the tick is found on any of the other offshore islands, it will possibly show a pattern of subspeciation due to the long isolation of these separate tick populations.
When the systematics of the genus Aponomma are finally unravelled, it may be possible to show whether A. sphenodonti has African or South American affinities, especially since its host has at least tenuous links with those continents.
This species was first described from the North Island kiwi, Apteryx mantelli, and occurs in both islands (Fig. 1). It is chiefly regarded as a kiwi tick, the only other recorded hosts being the grey duck, Anas superciliosa, a colonist from Australia, and the Canada goose, Branta canadensis, which was introduced from North America. The earliest known kiwi dates from the Quaternary although Reid and Williams (1975) are inclined to accept Fleming's (1962b) hypothesis that the ancestor or ancestors of the kiwis and moas colonised New Zealand during the Upper Cretaceous.
The affinities of I. anatis are not clear, although Dumbleton (1963) felt that the tick may be contemporaneous with the kiwi and could be included in the subgenus Sternalixodes which occurs on land mammals in Australia. However, I find little agreement between Dumbleton's (1953) description of I. anatis and Roberts's (1970) definition of Sternalixodes.
There still remains the possibility of an Australian origin for the tick, as Reid and Williams (1975) infer that the New Zealand and Australian ratites are more closely related to one another than to those in South America or Africa. Unfortunately, no ticks are known from Australian ratites with which comparisons can be made.
This species was only recently described from New Zealand by Hoogstraal (1967) and its affinities are not yet clear. It is held that I. jacksoni and I. uriae share a relationship within the subgenus Ceratixodes (Dumbleton, 1973), a group which, until now, had had I. uriae as its sole representative. Hoogstraal (1967) does not share Dumbleton's (1973) view but these differences of opinion do not clarify the degree of relationship between the species.
The only known host for I. jacksoni is the spotted shag, Stictocarbo (= Phalacrocorax) punctatus, a sedentary species which occurs only in New Zealand. Further collections, especially from shags in other areas of the southern ocean, are a necessary prerequisite to any further speculation on the origins of I. jacksoni. Shags, together with penguins and petrels, probably constituted the largest component of the early sea-bird fauna of the southern ocean (Oliver, 1955) and I. jacksoni may, in time, be no longer regarded as endemic to New Zealand.
This species occurs commonly on penguins in New Zealand and there are also records of the tick from Australia on a penguin, a gull and a gannet (Roberts, 1970). Because the tick appears to be so common in New Zealand and because there are so few Australian records (Fig. 2) I suggest that we have ‘exported’ I. eudyptidis to Australia. This could have been effected by the little blue penguin (Eudyptula minor) or by gannets (Sula bassana serrator). The latter are known to make east to west Tasman crossings (Stein and Wodzicki, 1955). Although a proportion of New Zealand's plant and animal life appears to have come from Australia, a modest flow of organisms to Australia from New Zealand is a distinct possibility (Fleming, 1976).
Ixodes eudyptidis is very similar to, but distinguishable from I. kohlsi, a tick which is restricted to Australian waters. The latter species is common on the Australian race of the little blue penguin and has also been found on gannets (Roberts, 1970). Dumbleton (1961) felt that because of the absence of significant overlap in the distribution of I. eudyptidis and I. kohlsi, the home range of the hosts did not interdigitate. He was also of the opinion that the
All the species within these complex groups appear to be closely related although they are different in form.
The relationships and localities of the various species as presently accepted, are set out below using data from Zumpt (1952), Arthur (1953), Roberts (1970) and Dumbleton (1973). The question marks serve to emphasise Arthur's (1953) contention that I. percavatus is synonymous with I. auritulus and that I. rothschildi deserves specific ranking instead of its earlier status as a variety of I. percavatus.
In addition to the above species, I. kerguelenensis, Kerguelen Island (Arthur, 1960b), I. kohlsi, Australia, and I. diomedeae, Tristan da Cunha (Murray, 1967), are other sea-bird ticks of the south circumpolar region which may one day be found in the New Zealand subregion.
Ixodes auritulus s. str. occurs almost without exception on land-birds in North America (Cooley and Kohls, 1945). The New Zealand material, being found exclusively on sea-birds, was assigned a sub-specific ranking by Dumbleton (1973). A South American form, I.a. auritulus, was described by Kohls and Clifford (1966) and is almost indistinguishable from I. auritulus material in Australia (Roberts, 1970). Ixodes a. zealandicus has not been recorded north of the equator, although the tick has been taken on the sooty shearwater Puffinus griseus. Dumbleton (1973) feels that carriage of this subspecies to the Northern Hemisphere would be unlikely to be followed by permanent colonisation by the ticks. It is possible, however, that godwits, Limosa spp., may carry the tick north (Dumbleton, 1973) so further examination of these birds is necessary.
Puffinus griseus and distribution of Ixodes uriae. Base map for range and breeding areas of P. griseus from Palmer (1962). Other data from numerous sources (see text).
There is a likelihood that the New Zealand subspecies of I. auritulus has been derived from a North American parent stock but the different host preference tends to contradict t