FNZ 15 - Ambositrinae (Insecta: Hymenoptera: Diapriidae) - Biogeography
Naumann, ID 1988. Ambositrinae (Insecta: Hymenoptera: Diapriidae). Fauna of New Zealand 15, 168 pages.
( ISSN 0111-5383 (print), ; no. 15. ISBN 0-477-02535-8 (print), ). Published 30 Dec 1988
As is the case in many other groups of New Zealand insects (see Watt 1975), endemism is very high in the Ambositrinae. All New Zealand ambositrine species and five of the seven genera are endemic; only Pantolytomyia and Diphoropria are shared with other regions. Pantolytomyia is represented in New Zealand by seven species, and elsewhere only by a single, taxonomically isolated species in eastern Australia. Diphoropria is represented in New Zealand by two species which form a species-group morphologically remote from all other species-groups. Diphoropria is the dominant ambositrine genus in Australia, New Guinea, and on the south-west Pacific islands: in all these areas there is a total of about 35 species, some of which are very common. One of the New Zealand species, D. sinuosa, is among the most common of New Zealand's microhymenopterans.
Ambositrinae are known from New Caledonia, Norfolk Island, and Lord Howe Island, but species from these islands are more closely related to Australian and New Guinea ambositrines than to New Zealand species (Naumann 1987 and unpublished).
There are no close affinities between the New Zealand and South American Ambositrinae. Masner (1969) suggested that several micropterous South American ambositrines could be referred to Parabetyla, which is represented by six species in New Zealand. However, these South American micropters are more closely related to Dissoxylabis, their resemblance to species of Parabetyla being the result of convergence (Naumann 1982; see also remarks following redescription of Parabetyla).
The austral disjunct distribution of the world's Ambositrinae and of the Mycetophilidae plus Keroplatidae, which include the only recorded hosts, has been discussed at some length by Naumann (1982). Since the New World ambositrine genera are still poorly understood, and the phylogeny depicted in Text-fig. 1 remains tentative, it is premature to speculate further on the historical biogeography of the subfamily. However, it does seem clear that Pantolytomyia, Archaeopria, Oiphoropria, Maoripria, and the common ancestor of the Parabetyla + Zealaptera + Betyla group were isolated on the New Zealand land mass when this effectively lost contact with Cretaceous Gondwanaland. The Dissoxylabis group of genera (characterised by the presence of a pronotal scrobe) is well represented in both Australia and South America, and if the phylogeny depicted in Text-fig. 1 is correct, should have had the opportunity to enter New Zealand before the latter's biological isolation. It is possible that eventually Betyla will prove to be a New Zealand representative of the Dissoxylabis group (see discussion of pronotal scrobe under 'Phylogeny').
New Zealand is particularly rich in ambositrine species with primitive gastral segmentation and wing venation. The three species of Archaeopria and seven species of Pantolytomyia make up 29% of the New Zealand ambositrine fauna. In Australia, only Pantolytomyia ferruginea Dodd, which represents 2.2% of the ambositrine fauna, preserves the primitive ambositrine segmentation and venation.
New Zealand is also rich in wing-reduced forms: 89% of the species are either exclusively wing-reduced or have wing-reduced morphs. The corresponding figure for the Australian Ambositrinae is about 66%.
The New Zealand ambositrine fauna is large (36 species) considering the rather small land area. Australia, with a much larger land area, has 45 species. However, most of Australia is arid and inhospitable to ambositrines, which are restricted today to the small areas of moist forest in the east and south-west.
Naumann (1982) suggested that the driving force for speciation within the Australian Ambositrinae was the alternation between pluvial periods when ambositrines dispersed widely over the east and south, and arid periods when populations were isolated in forest tracts and small, moist refugia. How are we to account for the almost equally species-rich New Zealand ambositrine fauna?
It must be remembered that the outline of the New Zealand archipelago changed dramatically during the Tertiary (Fleming 1980). In the Cretaceous and Eocene the land was largely continuous, with a few isolated islands in the north. During this period primitive taxa would have been able to disperse widely. The present-day widespread distribution of all species of Archaeopria and of some species of Pantolytomyia may date from this period.
During the Oligocene, northern and southern land masses were widely separated, providing the opportunity for speciation on either side of the water barrier. Intermingling and wide dispersal throughout New Zealand was once again possible during the Miocene. In the Pliocene New Zealand was once again archipelagic. During the Pleistocene succession of glacial and interglacial periods sea levels fluctuated, at times allowing dispersal of land animals across the present-day Cook and Foveaux straits and at other times isolating land animals on islands. During the glacial periods much of the South Island was unsuitable for ambositrines because of widespread ice cover and the spread of tundra at the expense of forest areas. Some coastal areas (along with most of the North Island) escaped the worst effects of glaciation. Here scrubland and perhaps forest survived. Almost certainly there were several such isolated coastal refugia, and these have been used to explain Pleistocene speciation in alpine plants, cicadas, and other terrestrial animals (Fleming 1980). Possibly these also permitted speciation in Ambositrinae.
Reconstructions of the geological history of New Zealand since the Cretaceous provide, then, a picture of a changing archipelago of land areas hospitable to Ambositrinae and isolated from each other by water or glaciation. These hospitable areas periodically were interconnected by forested land. Since Ambositrinae in general favour moist forest habitats and eschew deforested areas or marine barriers, and since many New Zealand ambositrines are flightless, with particularly limited dispersal powers, this changing scenario provides a reasonable explanation for the present-day species diversity.
Milder post-glacial conditions have permitted considerable recent dispersal of Ambositrinae, and earlier distribution patterns have been partially obscured.
Text-fig. 2 gives the number of species recorded in each of the areas defined by Crosby et al. (1976). The Ambositrinae are particularly diverse in the west and north of the South Island and in the Taranaki, Bay of Plenty, Auckland, and Northland areas. This reflects:
- the greater number of suitable, moist forest habitats in these areas today (see fig. 3.9 in Wardle et al. 1983);
- the geological history of New Zealand; and
- considerable specialist collecting effort, particularly on the west coast of the South Island.
Archaeopria. All three species are widespread throughout New Zealand. The spccies are very distinct and retain many character states which are plesiomorphic for the Ambositrinae. It is reasonable to suggest that the species are very old, and that their widcspread distribution may have been attained in the early Tertiary.
Pantolytomyia. Species such as P. flocculosa n.sp. and P. taurangi n.sp. retain striking plesiomorphic character states, and may have attained their present wide distributions very early in the Tertiary also. The takere species-group, comprising four species, all with wing-reduced females, is restricted to the South Island, and each species is more or less limited in its geographical range. It is likely that each survived (or perhaps originated) in an isolated coastal scrub refugium during Pleistocene glaciation, and because of the restricted dispersal powers of the females has since dispersed to only a limited extent. P. insularis n.sp., a member of the takere group, is the only ambositrine endemic to Stewart Island, and may have differentiated since Stewart Island was isolated by a rise in sea level 9500 years ago (Fleming 1975). There are examples of endemic Stewart Island taxa in other land animals, e.g., distinct races of birds (Bull & Whittaker 1975) and an endemic simuliid species (McLellan 1975).
Maoripria. The present-day restricted distributions of some wing-reduced Maoripria similarly may be the result of origin in or confinement to glacial refugia, and subsequent limited dispersal. M. annettae n.sp. and M. earlyi n.sp. are known from the South Island and the south of the North Island, which may reflect a previous distribution on the Pliocene southern island (see Fleming 1980), which included southern portions of the present-day North Island.
Diphoropria. D. kuscheli n.sp., which as far as is known is entirely macropterous, D. sinuosa macropters, and moderately wing-reduced D. sinuosa brachypters (type A brachypters) are widespread through New Zealand. However, most records of the more strongly wing-reduced type B brachypters of D. sinuosa are from the South Island, and brachypterous males are known only from the south-west of the South Island. Probably the extremes of wing reduction are favoured by the extreme moist, cool conditions of the south-west (see Naumann 1982 for a discussion of factors influencing wing reduction in Ambositrinae).
Parabelyla. All females of Parabetyla are micropterous. One species from each of three species-groups has been recorded from both the North and South islands. Within the spinosa group, P. pokorua n.sp., P. ngarara n.sp., and P. spinosa Brues each has limited distribution, perhaps focusing on Pleistocene glacial refugia.
Zealaptera. The single, apterous species Z. chambersi n.sp. is widespread throughout New Zealand.
Betyla. All Betyla females are apterous. B. fulva is widespread throughout New Zealand. The closely related B. prosedera n.sp. is absent from the southern half of the South Island, perhaps as a result of glaciation. B. auriger n.sp. is restricted to the north of the South Island, a distribution probably focusing on a glacial refugium. Presumably B. thegalea n.sp. attained its present distribution straddling Cook Strait before the last Pleistocene appearance of the strait. The distribution of the closely related B. karamea n.sp. and B. rangatira n.sp. appears to reflect unglaciated areas. B. karamea is known from the largely unglaciated North Island and an area focusing on the glacial refugia in the north of the South Island. The disjunct distribution of B. rangatira focuses on several South Island glacial refugia. Within the eupepla group, B. eupepla n.sp. and B. tuatara n.sp. are widespread. The restricted distribution of B. wahine n.sp. and B. paparoa n.sp. may be traceable to South Island glacial refugia. B. midas n.sp. is known from a single specimen from the Hunua Range, south-east of Auckland AK; it is perhaps premature to speculate that it originated on a Pliocene island in this region.
Males have been associated with females for very few species of Betyla. Among the unassociated males there are four wing-reduced species which are of biogeographical interest in that they are restricted to the South Island.
Wing-reduced forms are more numerous on the South Island. Of those species which include wing-reduced female morphs, only one (B. midas) is restricted to the North Island, 15 are known from both the North and South islands, and an additional 14 are known only from the South Island. Males are less commonly wing-reduced, so for them the contrast between the islands is less striking. However, all the wing-reduced Betyla males (representing four species) and brachypterous male morphs of D. sinuosa are known only from the South Island.
There is one further interesting biogeographical observation to be made on wing-reduced forms. In Australia there are nine species of Diphoropria in which females are exclusively micropterous. In New Zealand there are no micropters, despite the abundance and widespread distribution of Diphoropria macropters and brachypters. Presumably, in New Zealand, the niches which could have been occupied by micropterous Diphoropria have been taken up by the many species of Maoripria, Parabetyla, Zealaptera, and Betyla, most or all of which have micropterous or apterous females, and all of which are absent from Australia.