Both oceanic dispersal barriers were congruent with regions of low abundance reported for a similar basin‐scale transect that was sampled 2 years later. A secondary dispersal barrier supported only by 28S pairwise ΦST comparisons was identified in the equatorial upwelling region (between 15°N and 4°S), which is concordant with barriers observed in other zooplankton species.
This barrier is maintained despite the presence of expatriates, a gyral current system, and in the absence of any distinct oceanographic gradients in this region, suggesting that reproductive isolation between these populations must be strong. Based on the congruence of mitochondrial and nuclear differentiation, as well as differences in shell shape, we identified a primary dispersal barrier in the southern Atlantic subtropical gyre (15–18°S). We observed high levels of genetic variability (COI π = 0.034, 28S π = 0.0021) and strong spatial structuring (COI ΦST = 0.230, 28S ΦST = 0.255) across this transect. We examined the spatial distribution of genetic diversity in the mitochondrial cytochrome c oxidase I (COI) and nuclear 28S gene fragments, as well as shell shape variation, across a latitudinal transect in the Atlantic Ocean (35°N–36°S) for the pteropod Limacina bulimoides. However, little is known about the levels of genetic variation and large‐scale population structuring of pteropods, key characteristics enabling local adaptation. While there have been recent efforts to address their capacity for physiological acclimation, it is also important to gain predictive understanding of their ability to adapt to future ocean conditions.
Pteropods, a group of holoplanktonic gastropods, are regarded as bioindicators of the effects of ocean acidification on open ocean ecosystems, because their thin aragonitic shells are susceptible to dissolution.
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