Hodge, Jennifer R., and Bellwood, David R. (2016) The geography of speciation in coral reef fishes: the relative importance of biogeographical barriers in separating sister-species. Journal of Biogeography, 43 (7). pp. 1324-1335.

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Abstract

Aim: To understand how geography has influenced the generation and maintenance of biodiversity. We examined the relative importance of biogeographical barriers in the divergence of extant coral reef fish species.

Location: Pan-tropical coral reefs.

Methods: Sister-species were identified from a recent phylogeny encompassing four fish families (Chaetodontidae, Epinephelidae, Labridae and Pomacanthidae) and classified as allopatric or overlapping based on data compiled from IUCN maps. Nearest linear distances were mapped as indicators of vicariance and compared with previously identified biogeographical barriers. Congruent vicariance versus regional richness determined the relative influence of barriers. Patterns of overlap among non-allopatric sister-species were mapped and assessed.

Results: Congruent vicariance was detected across six previously described biogeographical barriers: the Amazon and Orinoco rivers, Isthmus of Panama, Hawaiian Archipelago, Indo-Pacific, and a previously understudied barrier separating the Western Indian Ocean from the Central Indo-Pacific (CIP) termed the Mid-Indian Ocean Barrier (MIOB). The MIOB showed the strongest vicariant signal. None of the barriers had significantly more or less relative influence. The majority of sister-species were non-allopatric. Overlap was concentrated in an area concordant with the biodiversity hotspot in the CIP, where sister-pairs had significantly low overlap.

Main conclusions: Biogeographical barriers may have influenced vicariance of extant species during the past 5Myr. Older barriers influenced divergence between clades. Turbidity currents produced by outflow from the Ganges and Indus river systems likely explain the strength of the MIOB. Despite the array of described barriers within the CIP, the Sunda Margin Barrier (SMB) was the only vicariant signal detected in the region. Low relative influence of the SMB and significantly low overlap among non-allopatric sister-pairs in the CIP highlights its importance as an area of evolutionary dynamism, where the separation of Indian and Pacific Ocean faunas and their subsequent range expansion has led to increased species overlap and higher regional biodiversity.

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