The influence of oceanographic fronts and early-life-history traits on connectivity among littoral fish species

Abstract

The spatial distribution of neutral genetic diversity is mainly influenced by barriers to dispersal. The nature of such barriers varies according to the dispersal means and capabilities of the organisms concerned. Although these barriers are often obvious on land, in the ocean they can be more difficult to identify. Determining the relative influence of physical and biotic factors on genetic connectivity remains a major challenge for marine ecologists. Here, we compare gene flow patterns of 7 littoral fish species from 6 families with a range of early-life-history traits sampled at the same geographic locations across common environmental discontinuities in the form of oceanic fronts in the Western Mediterranean. We show that these fronts represent major barriers to gene flow and have a strong influence on the population genetic structure of some fish species. We also found no significant relation between the early-life-history traits most commonly investigated (egg type, pelagic larval duration, and inshore-offshore spawning) and gene flow patterns, suggesting that other life-history factors should deserve attention. The fronts analyzed and the underlying physical mechanisms are not site-specific but common among the oceans, suggesting the generality of our findings.

Fig. 1.

Sampling locations for the 7 species. (A) HE, Herradura; CG, Cabo de Gata; MA, Mallorca; BL, Blanes; and the locations of the fronts (dotted lines). (B) BF. (C) AOF.

Fig. 2.

Standardized F_ST (genetic divergence per geographic unit) among pairwise adjacent sampling locations of D. vulgaris, M. surmuletus, S. cabrilla, T. delaisi, O. melanura, A. imberbis, and S. tinca species.

Fig. 3.

Map of posterior probabilities of population membership and spatial location of genetic discontinuities for populations of D. vulgaris (A), M. surmuletus (B), S. cabrilla (C), O. melanura (D), T. delais (E), A. imberbis (F), and S. tinca (G) species. Contour lines indicate the spatial position of genetic discontinuities between populations. Lighter colours indicate higher probabilities of population membership.