Genetic analysis overturns assumptions on largest ever gecko

[Swampy]

Hoplodactylus delcourti, the giant 60cm gecko famous for being known from one specimen found in a French museum with no locality information attached, is most closely related to New Caledonian taxa, according to this new study. A new genus is erected for it, Gigarcanum.

https://www.sciencenews.org/article/dna-origin-giant-mystery-gecko

The paper itself can be found here: Reappraising the evolutionary history of the largest known gecko, the presumably extinct Hoplodactylus delcourti, via high-throughput sequencing of archival DNA | Scientific Reports

This poses more questions than it answers; did the species lay eggs, like those it is now known to be closely related to? What were a 60cm gecko's eggs like? Who collected the specimen from New Caledonia? When and why did it go extinct? And what was the inspiration for the Maori folk legend of the Kawekaweau, previously linked to this species?

 

[Chlidonias]

I was going to post about this, but was beaten to it.

Trevor Worthy, a palaeontologist who has done masses of work in New Zealand and the Pacific, has long considered that the specimen may have come from New Caledonia because there are no known subfossil remains in New Zealand which can be attributed to the species. Although, as pointed out in the recent paper, there are also no remains known from deposits in New Caledonia or the Loyalty Islands. It's also peculiar that the descriptions given of the kawekaweau from the 1800s match so closely with the specimen.

With regards to "did the species lay eggs, like those it is now known to be closely related to? What were a 60cm gecko's eggs like?" - there are at least two extant New Caledonian species which are live-bearers, so this may have been one as well. Just as an aside, I think it is quite interesting that such large geckos as (for example) R. leachianus still survive on mainland New Caledonia whereas in New Zealand the largest reptiles (e.g. the Tuatara and the Duvaucel's Gecko) now survive only in predator-free environments.

 

[Swampy]

True, it could still be livebearing- but the most parsimonious tree suggested by the authors has the new genus forming a sister group to a Mniarogekko & Eurydactylodes clade, all of which are egg layers. Still doesn't necessarily mean it wasn't a live bearer, but perhaps less likely than it's previously assumed sister position to livebearing Hoplodactylus species.

I wonder if adhesive gecko eggs are significantly less accessible, on average, to an invasive rat than either buried tuatara eggs or Hoplodactylus neonates...

 

[TeaLovingDave]

Trevor Worthy, a palaeontologist who has done masses of work in New Zealand and the Pacific, has long considered that the specimen may have come from New Caledonia because there are no known subfossil remains in New Zealand which can be attributed to the species. Although, as pointed out in the recent paper, there are also no remains known from deposits in New Caledonia or the Loyalty Islands. It's also peculiar that the descriptions given of the kawekaweau from the 1800s match so closely with the specimen.

Given the lack of subfossil remains *anywhere* and the aforementioned similarity to reports of the kawekaweau, I don't see a reason to completely rule out the possibility that it was both endemic to New Zealand and nonetheless closer kin to New Caledonian taxa than those found on New Zealand. I suspect we'll never know one way or another.

 

[Swampy]

It would be the only taxon in a very diverse but otherwise endemic New Caledonian lineage if it did do so, however. Again, not really compelling evidence against, but it would be highly unusual. Not that everything else about this specimen/species isn't already highly unusual!

I suspect we'll never know one way or another.

Barring some very fortuitous fossil discovery or museum draw rummaging...

 

[Chlidonias]

Given the lack of subfossil remains *anywhere* and the aforementioned similarity to reports of the kawekaweau, I don't see a reason to completely rule out the possibility that it was both endemic to New Zealand and nonetheless closer kin to New Caledonian taxa than those found on New Zealand.

I'm not averse to this (it is mentioned as a possibility in the paper itself), but it would seem unlikely given how restricted that lineage is to New Caledonia. However, there are probably other examples in biogeography which are far more unlikely and yet still exist.

 

[Chlidonias]

I wonder if adhesive gecko eggs are significantly less accessible, on average, to an invasive rat than either buried tuatara eggs or Hoplodactylus neonates...

In New Zealand larger adult body size seems to be the reason they cannot survive amongst rats, rather than the eggs or size of babies. The smaller species of geckos and weta, for example, can survive (albeit poorly in many cases) on the mainland but the largest species such as Duvaucel's Gecko or the Giant Weta cannot because the adults are simply too large to find holes which also exclude rats.

I read an article a while ago about a particular island on which both Duvaucel's Geckos and Polynesian Rats existed. The geckos were restricted to inaccessible places such as on cliffs to which the rats couldn't gain access. When the rats were eradicated, the geckos almost-immediately recolonised the island - apparently within six months 70% of the adult geckos were living within the forest.

I don't know why the large geckos in New Caledonia can still survive in mainland forests alongside rats while the large species in New Zealand apparently can't.