Comparative phylogeography of two seastars and their ectosymbionts within the Coral Triangle (original) (raw)
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Biology letters, 2014
Processes driving and maintaining disjunct genetic populations in marine systems are poorly understood, owing to a lack of evidence of hard barriers that could have shaped patterns of extant population structure. Here, we map two genetically divergent lineages of an obligate rocky shore fish, Clinus cottoides, and model sea-level change during the last 110 000 years to provide the first evidence of a vicariant event along the southern coastline of Africa. Results reveal that lowered sea levels during glacial periods drastically reduced rocky intertidal habitat, which may have isolated populations in two refugia for at least 40 000 years. Contemporary coastal dynamics and oceanography explain secondary contact between lineages. This scenario provides an explanation for the origin of population genetic breaks despite a lack of obvious present-day geographical barriers and highlights the need for including palaeo-oceanography in unravelling extant population patterns.
Comparative phylogeography of the ocean planet
Understanding how geography, oceanography, and climate have ultimately shaped marine biodiversity requires aligning the distributions of genetic diversity across multiple taxa. Here, we examine phylogeographic partitions in the sea against a backdrop of bio-geographic provinces defined by taxonomy, endemism, and species composition. The taxonomic identities used to define biogeographic provinces are routinely accompanied by diagnostic genetic differences between sister species, indicating interspecific concordance between biogeography and phylogeography. In cases where individual species are distributed across two or more biogeographic provinces, shifts in genotype frequencies often align with biogeographic boundaries, providing intraspecific concordance between biogeography and phylogeography. Here, we provide examples of comparative phy-logeography from (i) tropical seas that host the highest marine biodiversity, (ii) temperate seas with high productivity but volatile coastlines, (iii) migratory marine fauna, and (iv) plankton that are the most abundant eukaryotes on earth. Tropical and temperate zones both show impacts of glacial cycles, the former primarily through changing sea levels, and the latter through coastal habitat disruption. The general concordance between biogeography and phylogeography indicates that the population-level genetic divergences observed between provinces are a starting point for macroevolutionary divergences between species. However, isolation between provinces does not account for all marine biodiversity; the remainder arises through alternative pathways, such as ecological speciation and parapatric (semi-isolated) divergences within provinces and biodiversity hotspots.