Thermal selection drives biodiversity origination across the Atlantic/Indian Ocean boundary

Abstract

Intraspecific genetic structure in widely distributed marine species often mirrors the boundaries between temperature-defined bioregions. This suggests that the same thermal gradients that maintain distinct species assemblages also drive the evolution of new biodiversity. Ecological speciation scenarios are often invoked to explain such patterns, but the fact that adaptation is usually only identified when phylogenetic splits are already evident makes it impossible to rule out the alternative scenario of allopatric speciation with subsequent adaptation. We integrated large-scale genomic and environmental datasets along one of the world's best defined marine thermal gradients (the South African coastline) to test the hypothesis that incipient speciation in the sea is due to divergence linked to the thermal environment. We identified temperature-associated gene regions in a coastal fish species that is spatially homogeneous throughout several temperature-defined biogeographical regions on the basis of selectively neutral markers. Based on these gene regions, the species is divided into geographically distinct regional populations. Importantly, the ranges of these populations are delimited by the same ecological boundaries that define distinct infraspecific genetic lineages in co-distributed marine the species, and biogeographical disjunctions in species assemblages. Our results indicate that ecologically-mediated selection represents an early stage of marine speciation in coastal regions that lack physical dispersal barriers.

Sea surface temperature, rather than land mass or geographic distance, may drive genetic differentiation in a species complex of highly dispersive seabirds

“…But gene flow among marine mammals is influenced by SST, driving structuration between ocean basins and among breeding areas (Alexander et al, 2016; Fontaine et al, 2014; Jackson et al, 2014; Richard et al, 2018; Viricel & Rosel, 2014), as do sea turtles (Dutton et al, 1999). Finally, organisms with a pelagic larval phase show globally low structuration (Kelly & Palumbi, 2010), but when detected, structuration is often linked to sea temperature (Benestan et al, 2015; Teske et al, 2005, 2018). Therefore, SST appears as a generic driver of diversification in many marine organisms, not only seabirds, though patterns of structuration are generally weaker (Bowen et al, 2016).…”

Sea surface temperature, rather than land mass or geographical distance, may drive genetic differentiation in a species complex of highly-dispersive seabirds

“…SST plays also a role in the diversification of sea turtles, since only cold-adapted species are able to exchange genes among oceans (Dutton et al 1999). Finally, organisms with a pelagic larval phase show globally low structuration (Kelly & Palumbi 2010) but when detected, structuration is often linked to sea temperature (Benestan et al 2015;Teske et al 2005Teske et al , 2018. Therefore, SST appears as a generic driver of diversification in marine organisms, though their patterns of structuration are generally considerably weaker (see Bowen et al 2016 for a review) than those found here.…”