Vertebrate time-tree elucidates the biogeographic pattern of a major biotic change around the K–T boundary in Madagascar

Abstract

The geographic and temporal origins of Madagascar's biota have long been in the center of debate. We reconstructed a time-tree including nearly all native nonflying and nonmarine vertebrate clades present on the island, from DNA sequences of two single-copy protein-coding nuclear genes (BDNF and RAG1) and a set of congruent time constraints. Reconstructions calculated with autocorrelated or independent substitution rates over clades agreed in placing the origins of the 31 included clades in Cretaceous to Cenozoic times. The two clades with sister groups in South America were the oldest, followed by those of a putative Asian ancestry that were significantly older than the prevalent clades of African ancestry. No colonizations from Asia occurred after the Eocene, suggesting that dispersal and vicariance of Asian/Indian groups were favored over a comparatively short period during, and shortly after, the separation of India and Madagascar. Species richness of clades correlates with their age but those clades that have a large proportion of species diversity in rainforests are significantly more species-rich. This finding suggests an underlying pattern of continuous speciation through time in Madagascar's vertebrates, with accelerated episodes of adaptive diversification in those clades that succeeded radiating into the rainforests.Cretaceous-Tertiary | historical biogeography | lineage diversification | rainforest adaptation | overseas dispersal M adagascar's unique biodiversity has attracted the interest of evolutionary biologists and biogeographers for a long time. This island was part of the Gondwana supercontinent. As a part of Indo-Madagascar, it separated from Africa 160-130 Mya.

Diversification rates have declined in the Malagasy herpetofauna

“…On the one hand, studies of vanga birds and day geckos [10][11][12] suggest that species accumulation declines over time, supporting the a model of adaptive radiation, where speciation and adaptation act in concert to produce distinctive new forms until ecological opportunities are exhausted [13][14][15]. On the other hand, a study that included the majority of Malagasy vertebrate clades suggested that diversification rates have been continuous throughout history, possibly indicating the absence of diversification limits on an island as large and diverse as Madagascar, or that Madagascan radiations have not yet reached whatever limits to their diversification may exist [3].…”

“…Madagascar's large size and long period of isolation from neighbouring land masses clearly contributed to this spectacular diversity [2][3][4], but the evolution of this diversity remains poorly understood. To understand the evolution of Madagascar's biodiversity, authors have primarily focused on historical patterns of gene flow and geographical models of speciation, such as riverine barriers or refugial isolation during periods of climate change, but support for these models is mixed [5][6][7][8][9].…”

A necessarily complex model to explain the biogeography of the amphibians and reptiles of Madagascar

“…This megadiverse microcontinent, initially part of Gondwana, has been isolated from other continents since the Mesozoic. Its current vertebrate fauna is a mix of only a few ancient Gondwanan clades and numerous younger radiations, originating from Cenozoic overseas colonizers arriving mainly from Africa [19][20][21] . The extraordinary proportion of family-level endemism in Madagascar, and the long isolation from non-Malagasy sister lineages, provide a unique opportunity to study the mechanisms driving divergence and diversification in situ 22 .…”

Revision of the Afrotropical Mayrellinae (Cynipoidea: Liopteridae), with the first record of Paramblynotus from Madagascar

“…Based on biogeographical dispersal-vicariance analyses in combination with palaeoenvironmental evidence, Liu et al (2007) hypothesized that the African Paramblynotus clade arose as a result of an early dispersal event from the eastern Palaearctic via Arabia during the late Oligocene to early Miocene periods (26-23 mya) with subsequent diversification on the African continent as a result of montane forest fragmentation. Madagascar separated from the African mainland about 160 to 120 mya with India rifting away from Madagascar around 90 mya (Ali et al 2008;Rabinowitz et al 1983) and hence Cenozoic dispersal rather than Gondwanan vicariance is the likely mechanism leading to the presence of Paramblynotus on Madagascar, as shown for other taxa such as vertebrates (Crottini et al 2012). Both the Madagascan faunal and floral elements have strongest affinities with Africa and hence the continent is the likely area of origin for original colonisation of the island (Buerki et al 2013;Crottini et al 2012;Goodman and Benstead 2003;Vences 2004).…”

“…Madagascar separated from the African mainland about 160 to 120 mya with India rifting away from Madagascar around 90 mya (Ali et al 2008;Rabinowitz et al 1983) and hence Cenozoic dispersal rather than Gondwanan vicariance is the likely mechanism leading to the presence of Paramblynotus on Madagascar, as shown for other taxa such as vertebrates (Crottini et al 2012). Both the Madagascan faunal and floral elements have strongest affinities with Africa and hence the continent is the likely area of origin for original colonisation of the island (Buerki et al 2013;Crottini et al 2012;Goodman and Benstead 2003;Vences 2004). There is a high degree of endemism in Madagascar (Goodman and Benstead 2003) across all taxa.…”