Recent advances in New Caledonian biogeography

Abstract

The biota of New Caledonia is one of the most unusual in the world. It displays high diversity and endemism, many peculiar absences, and far-flung biogeographic affinities. For example, New Caledonia is the only place on Earth with both main clades of flowering plants -the endemic Amborella and 'all the rest', and it also has the highest concentration of diversity in conifers. The discovery of Amborella's phylogenetic position led to a surge of interest in New Caledonian biogeography, and new studies are appearing at a rapid rate. This paper reviews work on the topic (mainly molecular studies) published since 2013. One current debate is focused on whether any biota survived the marine transgressions of the Paleocene and Eocene. Total submersion would imply that the entire fauna was derived by long-distance dispersal from continental areas since the Eocene, but only if no other islands (now submerged) were emergent. A review of the literature suggests there is little actual evidence in geology for complete submersion. An alternative explanation for New Caledonia's diversity is that the archipelago acted as a refugium, and that the biota avoided the extinctions that occurred in Australia. However, this is contradicted by the many groups that are anomalously absent or depauperate in New Caledonia, although represented there by a sister group. The anomalous absences, together with the unusual levels of endemism, can both be explained by vicariance at breaks in and around New Caledonia. New Caledonia has always been situated at or near a plate boundary, and its complex geological history includes the addition of new terranes (by accretion), orogeny, and rifting. New Caledonia comprises 'basement' terranes that were part of Gondwana, as well as island arc and forearc terranes that accreted to the basement after it separated from Gondwana. The regional tectonic history helps explain the regional biogeography, as well as distribution patterns within New Caledonia. These include endemics on the basement terranes (for example, the basal angiosperm, Amborella), disjunctions at the West Caledonian fault zone, and great biotic differences between Grande Terre and the Loyalty Islands.

Vicariance and ecological dispersal in Papilio subgenus Achillides (Papilionidae) and some other butterflies of Asia and the Southwest Pacific

“…This view was accepted by Condamine et al (2013a) to justify the origin of P. montrouzeri by chance dispersal. However, the geological evidence they cited indicates submersion of different parts of New Caledonia at different times -there is no geological evidence for complete submersion at any one time (Heads 2014(Heads , 2019. In addition, chance dispersal does not account for the repetition of similar distributions in large numbers of groups with different ecology and means of dispersal.…”

“…A tectonic explanation for this break is available, as there has been ~2000 km westward movement of the Halmahera arc along the northwestern edge of New Guinea since early or mid Miocene time (Heads 2001). The Pyrrhus clade 1 disjunction between the Greater Sunda Islands and the Solomon Islands corresponds spatially with long-distance terrane translation on major, eastwest strike-slip faults (Heads 2014(Heads , 2019.…”

“…But no matter how many studies have misrepresented fossil-calibrated estimates as actual or maximal ages, it does not change the fact that they cannot represent anything but minimum clade age and they cannot be turned into anything else (Heads 2005(Heads , 2014. Reliance on fossil-calibrated molecular clock ages for clades has resulted in decreased attention being given to the details of distribution and tectonics (Heads 2019). In reality, fossil-calibrated molecular estimates cannot falsify earlier origins of groups, and these may be predicted from other methods of dating, such as Grehan, 2019 Biogeographia 34: 101-117 103 correlation between clade distribution and tectonic events (Heads 2019).…”

“…Reliance on fossil-calibrated molecular clock ages for clades has resulted in decreased attention being given to the details of distribution and tectonics (Heads 2019). In reality, fossil-calibrated molecular estimates cannot falsify earlier origins of groups, and these may be predicted from other methods of dating, such as Grehan, 2019 Biogeographia 34: 101-117 103 correlation between clade distribution and tectonic events (Heads 2019).…”

Two new ant species (Formicidae: Dorylinae, Ponerinae) from New Caledonia

“…The current New Caledonian biota displays a high diversity and endemism resulting from a complex geological and biogeographical history, with Palaeocene and Eocene submersions followed by colonization and radiations of taxa of both Gondwanan and Indo-Malayan origins in the last 37 Ma (Grandcolas et al 2008;Nattier et al 2017). However, there is still a debate on whether the archipelago was entirely or partially submerged, with the survival of archaic groups on ephemeral islands (Heads 2019). Emery's (1883) pioneer work on the ant fauna of New Caledonia resulted in the description of seven species.…”