Past volcanic activity predisposes an endemic threatened seabird to negative anthropogenic impacts

Humans are regularly cited as the main driver of current biodiversity extinction, but the impact of historic volcanic activity is often overlooked. Pre-human evidence of wildlife abundance and diversity are essential for disentangling anthropogenic impacts from natural events. Réunion Island, with its intense and well-documented volcanic activity, endemic biodiversity, long history of isolation and recent human colonization, provides an opportunity to disentangle these processes. We track past demographic changes of a critically endangered seabird, the Mascarene petrel Pseudobulweria aterrima, using genome-wide SNPs. Coalescent modeling suggested that a large ancestral population underwent a substantial population decline in two distinct phases, ca. 125,000 and 37,000 years ago, coinciding with periods of major eruptions of Piton des Neiges. Subsequently, the ancestral population was fragmented into the two known colonies, ca. 1500 years ago, following eruptions of Piton de la Fournaise. In the last century, both colonies declined significantly due to anthropogenic activities, and although the species was initially considered extinct, it was rediscovered in the 1970s. Our findings suggest that the current conservation status of wildlife on volcanic islands should be firstly assessed as a legacy of historic volcanic activity, and thereafter by the increasing anthropogenic impacts, which may ultimately drive species towards extinction.

Co-evolution assists geographic dispersal: the case of Madagascar

Interspecific associations may limit the dispersal of individual species, but may also facilitate it when entire co-evolved systems expand their geographic ranges. We tested the recent proposal that episodic land bridges linked Africa and Madagascar at three stages during the Cenozoic by comparing divergence estimates of Madagascar’s angiosperm taxa with their dispersal mechanisms. Plants that rely on gravity for seed dispersal indicate at least two episodes of land connection between Africa and Madagascar, in the Early Palaeocene and Early Oligocene. Seed dispersal by strepsirrhine primates possibly evolved in the Palaeocene, with the divergence of at least one endemic Malagasy angiosperm genus, Burasaia (Menispermaceae). This genus may have facilitated the lemur colonization of Madagascar. Frugivory, nectarivory and gummivory probably generalized in the Oligocene, with the co-evolution of modern lemurs and at least 10 new Malagasy angiosperm families. In the Late Miocene, more angiosperms were probably brought from Africa by birds via a discontinuous land connection, and radiated on Madagascar in diffuse association with birds (asities) and dwarf nocturnal lemurs (cheirogaleids). During the same connective episode, Madagascar was probably colonized by hippopotamuses, which both followed and re-seeded a variety of plants, forming the grassy Uapaca ‘tapia’ forest and ericoid ‘savoka’ thicket.