Protozoological Studies at Macquarie Island*
[Read before the Wellington Branch, October 25, 1950; received by the Editor, February 19, 1951]
Introduction and Acknowledgments
The primary object of my visit to Macquarie Island, made on December 2, 1949, during the meteorological station cruise of H.M.N.Z.S. Tutira, was to ascertain whether or not the penguins there are parasitized by Plasmodium relictum var. spheniscidae Fantham and Porter, 1944.
Penguins are common hosts for Plasmodium in zoological gardens in temperate countries. Thus Scott (1927), the first investigator to record parasites of this genus from penguins, found the blood of a King Penguin (Aptenodytes patagonica Miller) which died in the Gardens of the Zoological Society of London during 1926 to be heavily infected with Plasmodium. Scott listed the species of parasite concerned as Plasmodium praecox, while at the same time suggesting that it might represent “a new form of Plasdomium”. Rodhain (1937, 1938, 1939) gave accounts of Plasmodium relictum infections in the Blackfoot Penguin, Spheniscus demersus (Linnaeus), in the Antwerp Zoological Gardens. That author confirmed his specific identification by transmitting the parasite to canaries, using as the vector infected Culex pipiens captured in the penguin shelters.
Fantham and Porter (1944) found a Plasmodium to be present in blood smears taken from penguins of four species in their natural habitats, and described it as a new variety (spheniscidae) of Plasmodium relictum. They justified their description of a new variety on the grounds of the large vacuoles of the ring stages, the large size of the schizonts, the high level of intraerythrocytic schizogony together with the low gametocyte level, and the small size of the gametocytes, as compared with the corresponding stages of Plasmodium relictum in other hosts. The hosts and their places of origin were as follows:
Spheniscus demersus (Linnaeus)—Saldanha Bay, South Africa.
(Eudyptes) = Megadyptes antipodes (Hombron and Jacquinot)—Foveaux Strait, New Zealand.
(Eudyptes crestatus) = E. chrysocome (Forster)—south of Gough Island.
Aptenodytes patagonica Miller—South Georgia.
During a survey of avian haematozoa of the New Zealand area (Laird, 1950) a sporozoan, apparently Plasmodium relictum var. spheniscidae, was found in the blood of two species of penguins. Of
[Footnote] * Undertaken during the tenure of a New Zealand University Research Fund Fellowship.
twenty-eight examples of the Drooping-crested Penguin, Eudyptes pachyrhynchus (Gray) from which blood smears were taken on the Snares Islands in December, 1947, three proved to be very lightly infected, while a few plasmodia were found in smears from one of two examples of Megadyptes antipodes (Hombron and Jacquinot) from Campbell Island in January, 1948.
I am indebted to the Royal New Zealand Naval authorities for arranging for me to visit Macquarie Island, also to the Captain and officers of H.M.N.Z.S. Tutira for their kindness and co-operation in the course of the voyage; to Mr. A. Gardner, who gave me invaluable assistance in the field; and to Mr. N. M. Haysom, B.Sc., biologist with the Australian meteorological party on Macquarie Island, who was good enough to take some further smears for me in the early part of 1950.
Peripheral blood smears were secured from penguins by pricking one of the vessels in the flipper, from shags by pricking the metatarsal vein, and from sea elephants by making a small incision in a hind flipper. A range of preparations from juvenile through mature forms was obtained for each species, two thin smears being secured from each example in the majority of cases. All the smears were air dried in the field, and subsequently stained with Giemsa. In addition to the blood preparations, some gut smears were obtained from kelp flies. The material dealt with is summarized in Table 1.
|Systematic position||Common name||Number of specimens|
|Macrorhinus leoninus (Linnaeus)||Sen Elephant||28|
|Aptenodytes patagonica Miller||King Penguin||17|
|Pygoscelis papua (Forster)||Gentoo Penguin||22|
|Eudyptes chrysocome (Forster)||Victoria Penguin||42|
|Eudyptes schlegeli Finsch||Royal Penguin||40|
|Phalacrocorax traversi Rothschild||Macquarie Island Shag||42|
|Coelopa nigrifrons||Lamb Kelp Fly||7|
All the material collected proved negative for haematozoa. This is not surprising as regards the sea elephants, for no seals, or for that matter any other marine mammals, have yet been recorded as hosts for blood parasites. Although this may merely be an index of the scant attention paid to this group of mammals by blood parasitologists, it is possible that the habits of these animals shield them from
the attacks of arthropods able to act as vectors for mammalian haematozoa.
There are no mosquitoes on Macquarie Island. The most unlikely hypothesis that some invertebrate other than a mosquito might be a vector for Plasmodium relictum var. spheniscidae on this and other subantarctic islands free from mosquitoes, would seem to be invalidated by the fact that the 121 penguins of four species (two of them known hosts for this parasite) from which smears were taken during the present investigation, proved negative for haematozoa. If a Plasmodium specific for penguins were indeed transmitted in the sub-antarctic, one would expect to find some at least of such a number of these gregarious birds parasitized.
With regard to the penguins earlier found positive for Plasmodium relictum var. spheniscidae in the New Zealand area, one of the hosts, Eudyptes pachyrhynchus, although centred on the Snares Islands, south of Stewart Island, is also of common occurrence in the southern parts of the South Island of New Zealand. The other host, Megadyptes antipodes, is a sea-going species which breeds on Campbell Island and the Auckland Islands in the subantarctic, also on Stewart Island and on the Otago Peninsula in New Zealand. Plasmodium relictum (Grassi and Feletti) occurs in New Zealand (Laird, 1950). Thus both Eudyptes pachyrhynchus and Megadyptes antipodes could become parasitized after being bitten by coastal mosquitoes infective for P. relictum during visits to this country.
Of the natural infections recorded by Fantham and Porter (1944) for Plasmodium relictum var. spheniscidae, that from Megadyptes antipodes (1 of 10 birds) in Foveaux Strait may be explained on the basis of the suggestion made in the preceding paragraph. Similarly, that from Eudyptes chrysocome (1 of 5 birds) from south of Gough Island is explicable by reason of the fact that this species ranges as far northwards as the southern parts of South America itself, where Culex fatigans, an established vector of Plasmodium relictum, occurs. Spheniscus demersus is indigenous to the southern portions of South Africa, thus the question of possible subantarctic transmission does not arise with regard to this species. Culex fatigans was the only common biting insect in the area where the smears were taken from S. demersus, two of 100 of these mosquitoes proving to have oöcysts on dissection, and one of these two also having small numbers of sporozoites present in its salivary glands (Fantham and Porter, 1944). The smears from the blood of the specimen of Aptenodytes patagonica from South Georgia were obtained after the death of this bird in London, so this infection need not necessarily have been acquired in the southern hemisphere at all.
It is thus concluded that, although penguins are susceptible to infection with Plasmodium relictum, active transmission does not take place in those regions beyond the southern limits of mosquito distribution. Var. spheniscidae is probably merely a morphological variant of the widespread P. relictum, owing its distinctive characters to some environmental factor or factors to which it is exposed in the blood of penguins, as indeed Fantham and Porter themselves suggested. One such factor, which on a purely mechanical basis might help to
explain the large size of the asexual stages of var. spheniscidae, is the large size of the red cells of penguins as compared with those of the more advanced avian stocks to which the great majority of the hosts for P. relictum belong. It is considered that this parasite is adventitiously transmitted to penguins ranging into the northern portions of their area of distribution, by mosquitoes which have become infective after biting either other penguins or birds of other kinds parasitized by P. relictum.
Herpetomonas calliphorae Swingle, 1911. (Pl. 127, figs. 1–13)
Coelopa nigrifrons Lamb, 1909, was found to be extremely abundant in the neighbourhood of stranded kelp, Durvillaea antarctica (Chamisso). Nine examples of this kelp fly were collected at the northern end of the Isthmus on Hasselborough Bay, and smears of their gut contents were made. All proved to be heavily infested with a herpetomonad flagellate. Numerous species of Herpetomonas have been described from muscoid flies, but there are grounds for believing that most, if not all, of these are synonyms of H. muscarum (Leidy), the first described species. H. muscarum occurs in New Zealand (Laird, 1948), and it has thus been possible to compare the Macquarie Island flagellates with material of this species obtained in Wellington as well as with the descriptions in the literature. On the evidence from the available material from C. nigrifrons, the flagellate of this kelp fly appears to differ from H. muscarum in several respects, while it is morphologically indistinguishable from H. calliphorae Swingle, 1911. It is accordingly identified as belonging to the latter species, although at the same time it is recognized that H. calliphorae may eventually prove to be merely a variety of H. muscarum.
It was not possible, under the field conditions prevailing at Macquarie Island, to make separate smears of the various portions of the alimentary tract of C. nigrifrons. All the preparations are smears of the whole gut contents, and in consequence both resting and active stages of the herpetomonad are mingled together in them.
Large flagellate forms predominate, the majority of these being in the biflagellate condition (Figs. 7–9, 11–13). Their dimensions, from the measurement of twenty examples, are as follows:
|Length of body||28.4μ||22.4μ–31.2μ|
|Breadth of body||2.8μ||2.4μ–3.5μ|
|Length of free flagellum||41.8μ||38.0μ–47.8μ|
|Length of axoneme||4.1μ||3.6μ–5.4μ|
Slender post-division uniflagellate parasites (Fig. 6) are of comparable length to the biflagellates, but their breadth is much less (1.1μ–1.4μ). These dimensions correspond closely with those given by Swellengrebel (1911) for the equivalent stages of H. calliphorae. As regards general dimensions, the only significant feature of distinction from H. muscarum is the length of the free portion of the flagellum. This varies within quite narrow limits in H. calliphorae, as is seen from the figures given above, also from those of Swellengrebel (39μ to 40μ), and is about one and a half times the length of the body. In H. muscarum the free portion of the flagellum is about three times as long as the body (Wenyon, 1926; Laird, 1948).
Figures drawn at magnifications of × 2,530 and × 1,700, with the aid of an Abbé camera lucida.
Fig. 1—Non-flagellate, volutin granules in cytoplasm. Fig. 2—Division stage of non-flagellate. Figs. 3–5—Small flagellates, 4 and 5 possibly post-flagellates. Fig. 6—Slender post-division herpetomonad. Figs. 7–9—Herpetomonads in which the basal granule has divided and a second flagellum has been developed, showing stages in nuclear division and the initiation of division of the kinetoplast. In the example seen in Fig. 8 the flagella have not been disturbed during the preparation of the smears, and lie side by side within the achromatic sheath. Fig. 10—Mediuum-sized uniflagellate. Figs. 11–13—Illustrating the completion of division of the kinetoplast, and early (Fig. 12) and late (Fig. 13) stages in cytoplasmic cleavage.
The cytoplasm is alveolar and vacuolated, and stains light blue with occasional darker blue maculation. It may contain from few (Fig. 12) to many (Fig. 11) volutin granules, as was also the case in Swellengrebel's material. The nucleus assumes a deep red stain with Giemsa, and several darker staining chromatin granules are usually apparent. Up to four chromosomes may be visible during the early stages of nuclear division (Figs. 7 and 8). In its resting phase the nucleus is round or ovoid, and is centrally situated. The kinetoplast is very large (0.8μ to 2.2μ by 0.6μ to 1.8μ), as is usual in Giemsa stained preparations of the herpetomonads of flies. This structure is variably located between the anterior end of the body and the nucleus, its usual position (Figs. 6, 10–13) being from 4μ to 6μ from the anterior extremity. It may be round, ovoid or rod-shaped. When over-stained, it is uniformly blackish red (Fig. 6, etc.), but when suitably cleared it presents a distinctly karyosomatic appearance (Figs. 7 and 9). A peripheral chromatic layer staining blackish red invests a central area of pink-staining material which contains one (Fig. 7), two (Fig. 9) or more chromatic granules. This complicated structure of the kinetoplast is a distinctive feature of H. calliphorae, and according to Swellengrebel it is not an artefact due to Giemsa staining, for iron-haematoxylin staining gives results lending themselves to a similar interpretation.
The flagellum originates at a basal granule situated anteriorly to the kinetoplast, and marginal granules are sometimes apparent at the point of exit of the flagellum from the body (Figs. 7–9). Division of the basal granule is followed by the development of a second flagellum. The two flagella are enclosed by a delicate cytoplasmic sheath which stains a very light pink. They remain side by side, converging distally, until quite late in the division process (Figs. 8 and 9), unless the sheath is broken and they are thus disarranged during the smearing process. Following the division of the basal granule the kinetoplast divides (Figs. 9, 11, 12), nuclear division being completed in the meantime. Cytoplasmic cleavage (Figs. 12 and 13) results in the formation of two slender herpetomonads.
Non-flagellate forms (Figs. 1 and 2) compare closely with those of H. calliphorae in their size and morphology, but are significantly larger than the typical equivalent stages of H. muscarum. They are round to avoid in shape, and measure from 5.9μ to 9.7μ by 4.8μ to 7.5μ. (the figures given by Swellengrebel for H. calliphorae are 7μ to 10μ by 6μ to 9μ). Their markedly vacuolated cytoplasm stains deep blue and may contain numerous volutin granules (Fig. 1). The kinetoplast is usually of somewhat reniform shape, and is situated at or towards the proximal end of a non-staining area and in front of or to one side of the round or irregularly shaped nucleus. There is usually no indication of the presence of an axoneme, although some forms of otherwise similar morphology have both an axoneme and a short free flagellum (Fig. 3). Division stages (Fig. 2) are plentiful. A few small flagellates have been seen (Figs. 4 and 5). Owing to the nature of the material, it cannot be stated with certainty whether these are in course of development towards the adult stage or towards the post-flagellate one.
The flagellate under discussion differs from the typical form of H. muscarum in having a relatively shorter flagellum and an apparently more complex kinetoplast, as outlined above. Although in view of the known variability within herpetomonad species these features may prove to be of insufficient value as specific criteria, it is proposed to identify the Macquarie Island parasite as H. calliphorae Swingle, with which it agrees closely in all respects. Because of this latter fact, also the recognized lack of host specificity among the herpetomonads of flies, it is considered that, despite its geographical isolation, there are no valid grounds for describing it as a new species.
One hundred and twenty-one penguins of 4 species, 28 sea elephants, Macrorhinus leoninus (Linnaeus), and 42 shags, Phalacrocorax traversi Rothschild, proved uniformly negative for haematozoa. It is considered that penguins from which Plasmodium has been recorded had become adventitiously infected during visits to the southern extremities of the land masses towards the northern limits of their distribution. The kelp fly, Coelopa nigrifrons Lamb, is given as a new host for Herpetomonas calliphorae Swingle.
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