FNZ 62 - Trechini (Insecta: Coleoptera: Carabidae: Trechinae) - Origins
Townsend, JI 2010. Trechini (Insecta: Coleoptera: Carabidae: Trechinae). Fauna of New Zealand 62, 101 pages.
(
ISSN 0111-5383 (print),
ISSN 1179-7193 (online)
;
no.
62.
ISBN 978-0-478-34717-9 (print),
ISBN 978-0-478-34716-6 (online)
).
Published 16 Jun 2010
ZooBank: http://zoobank.org/References/0D2B064C-C2E0-41F8-AB9A-BEB2E4B41412
Origins of the Trechini cave fauna
Some geologists take the extreme view that New Zealand or ‘Zealandia’ was totally inundated by sea about 23 million years ago. Campbell & Hutching (2007) discuss this scenario in some detail. From a biological viewpoint I doubt this could have happened. If it were so, then all our fauna, including trechines must have established and/or evolved since Oligocene time. This may well be so for perhaps the majority of our trechine fauna, but I think it is possible that there is also an archaic element in genera associated with older Ordovician marble, i.e., Kupetrechus and Scototrechus. This is not because the formation is so much older, but because the present day distribution of species of the Homaloderine lineage in particular indicates a radiation from this ancient marble. Erebotrechus too, although now also found in caves in Oligocene limestone, may well have survived from this older fauna. Homaloderines have not been found in New Zealand outside the Nelson–Buller area, however they have close epigean relatives in South America, and both epigean and cave-dwelling species in Australia and Tasmania. This relationship is also shown by the subtribe Creobina (Broscini), which is well known in South America and Tasmania, and in New Zealand is at present known by a single species occurring on the remote Bounty Islands. Northwest Nelson is a faunal area of high diversity and endemicity. It should be noted that the relict Kiwitrechus is also endemic to that region which has such a range of relict species (both plant and animal) that it must surely have escaped the Oligocene transgression. Gibbs (2007, p. 90) cites insects such as sandflies and mayflies being totally dependent on cool fresh water, sea water being poisonous to them, and provides a map (p. 193) showing how this fauna could have reached New Zealand 130–35 million years ago. Conran, Bannister & Lee (2009) suggest that “… the presence of a diverse and complex subtropical rainforest with epiphytic orchids surrounding a freshwater lake in Early Miocene Otago supports the assertion that there was land in the New Zealand region throughout the Cenozoic, with theories arguing for post-drowning re-colonization by New Zealand endemic taxa being much less plausible.”
On the other hand, for those like Campbell & Hutching (2007), who believe Zealandia to have been totally submerged, it is possible that dispersal could have occured after separation of Zealandia from Australia. Over time, there would be a high probability of massive floods whereby mini-islets of vegetation complete with decaying logs and fauna would be swept out to sea. Under today’s milder conditions it is known that carabids can be flooded from pastures to be deposited later on nearby beaches (Walker 1904, Townsend 1994). If total submergence of New Zealand occurred in Oligocene Time, there would have been over 20 million years for such storms to provide transport for fauna. Climatically, conditions were probably severe at times, also warmer at other times and this may be why we now have populations of at least 25 species of carabids living in caves and nowhere else. This is a large fauna for a country the size of New Zealand, and to this could be added a host of other invertebrates such as harvestmen (Forster 1965), spiders, millipedes (Johns 1991), centipedes, symphylans, japygids, peripatus (Ruhberg 1985), hydrobiid snails (Haase 2008), and even Homoptera feeding on roots (Fennah 1975).
This does not mean that all these examples are necessarily of ancient stock, perhaps the majority have local surface-dwelling relatives, and it has been shown that cave species can evolve quite rapidly. In Hawaii troglobites seem to have fast-tracked the evolutionary processes. On Maui, the troglobitic carabid Blackburnia howarthi (Samuelson & Liebherr 1992) has evolved in the last 120,000 years (Liebherr & Samuelson 1992). This has been shown by dating the lava tube in which the cave has developed and also the flow below it, which would have ensured the elimination of any pre-existing fauna (Sherrod et al. 2003). There are many examples of lava cave species becoming differentiated in less than 10,000 years (Uéno, pers. comm.). This type of rapid evolution may also explain the presence of Kettlotrechus species in caves at Paturau and Oparara that were inundated by high sealevels during the last interglacial. Ancestors of K. marchanti could have survived in caves above the interglacial sea levels at the highest point of the limestone formation at Kaihoka and then invaded the lower areas as the sea receded, evolving into other species in the process. These and the many species of Duvaliomimus are clearly of the Trechine lineage with bidentate mandibles. Our cave-frequenting Duvaliomimus species and its subgenus Mayotrechus are probably recent invaders of caves, whereas the related genus, Scototrechus, as mentioned earlier, is perhaps much older. It is also feasible that the ancestral form may have been an epigian Duvaliomimus-like species that gave rise to the troglobitic genera.
The origin of the Trechine lineage in New Zealand is puzzling because this lineage appears to be absent in Australia today. Perhaps they were present there when Australia had a wetter climate, and then died out, being unable to survive in the drier conditions. However, parts of Tasmania should have provided suitable habitat, and after all, many trechines of Homaloderine lineage are found there. We have a strange and doubtful connection to China with the striking similarity of our Erebotrechus infernus to the Chinese Sinaphaenops mirabilissimus Uéno & Wang. Both species belong to the Homaloderine lineage, but there the similarity must surely end, the superficial resemblance being explained by convergent evolution. New Zealand has a relatively high number of species of both Trechine and Aepine lineages, yet these appear to be absent from Australia.
Panorama Cave, Sequoia National Park, California, at an altitude of 10,600 feet has freezing conditions, yet it has endemic diplurids and harvestmen. “This area was glaciated only 10,000 years ago, and it is hard to believe anything survived under a mile of ice and meltwater.” (Krajick 2007). There are no troglobitic Carabidae reported from Panorama Cave, although it has been estimated that 250 troglobitic carabids occur in North America (Barr 1981). Krajick also suggests that troglobites in “young” cave systems may have been living previously in old caves, now eroded away. Shatter-zones in hard rocks give ample space for small creatures to migrate. Ian Millar has found that Kupetrechus larsonae can live within screes, and it is generally recognised that the “mesocaverns” (fissures of 0.1–20 cm) have a rich fauna (Howarth 1983). How else could troglobitic carabids establish in old disused Japanese mines (Uéno 1959)? As Uéno (1977b) points out, there is a whole fauna of troglobites living in micro-crevices, only to be discovered by us when we have access via mine shafts, etc. If the cavities are young, the fauna has to be already existing in the surrounding rocks.
So it seems that evolution proceeds at very different rates and at different times for different locations and different creatures. As far as our fauna is concerned, many of the troglobitic Carabidae (and some other groups) may well have origins pre-dating the break-up of Gondwana, while others have evolved more rapidly and recently. Perhaps it is partly due to New Zealand’s turbulent geological history (being on a plate boundary) that caves have become such important refugia. Their future preservation is paramount. It is likely that New Zealand speleologists will find there are many more biological discoveries to be made in the future, as there are still extensive areas of calcareous, potentially caverniferous rock from which no cave inhabiting trechines have been recorded.
If I was asked to speculate where to search, I would suggest Fiordland, near the south coast – maybe caves in Oligocene deposits west of the lower Waiau River where the effects of the glaciations would have been less severe. Entomologists have searched unsuccessfully for trechines in caves like Aurora, Te Anau where the fauna seems to be relatively impoverished, perhaps because of the glaciations (Emberson, pers. comm.).
The roots of our trechine beetles may have been influenced by movements of the alpine fault and the ‘other half’ of the northwest Nelson cave fauna should be looked for further south.There are other examples of flightless carabid beetles that reflect this. Britton (1949) [incorrectly, in my opinion] synonymised Mecodema aeneoniger (Broun) from Wangapeka, Nelson with M. punctatum (Laporte de Castelnau) from Otago because of their close similarity, and the Otago-centred Taenarthrus has more than one undescribed species in northwest Nelson. Movement on the fault may also explain the somewhat anomalous northern distribution of Duvaliomimus (D.) walkeri.