Shallow seamounts represent speciation islands for circumglobal yellowtail Seriola lalandi

Sven Kerwath,Rouvay Roodt-Wilding,Henning Winker,Belinda Swart,Aletta Bester-Van Der Merwe,Christopher Wilke,Albrecht Götz,Toufiek Samaai,Wendy West,Stephen Lamberth,Sheroma Surajnarayan

doi:10.1038/s41598-021-82501-z

Abstract

Phenotypic plasticity in life-history traits in response to heterogeneous environments has been observed in a number of fishes. Conversely, genetic structure has recently been detected in even the most wide ranging pelagic teleost fish and shark species with massive dispersal potential, putting into question previous expectations of panmixia. Shallow oceanic seamounts are known aggregation sites for pelagic species, but their role in genetic structuring of widely distributed species remains poorly understood. The yellowtail kingfish (Seriola lalandi), a commercially valuable, circumglobal, epipelagic fish species occurs in two genetically distinct Southern Hemisphere populations (South Pacific and southern Africa) with low levels of gene-flow between the regions. Two shallow oceanic seamounts exist in the ocean basins around southern Africa; Vema and Walters Shoal in the Atlantic and Indian oceans, respectively. We analysed rare samples from these remote locations and from the South African continental shelf to assess genetic structure and population connectivity in S. lalandi and investigated life-history traits by comparing diet, age, growth and maturation among the three sites. The results suggest that yellowtail from South Africa and the two seamounts are genetically and phenotypically distinct. Rather than mere feeding oases, we postulate that these seamounts represent islands of breeding populations with site-specific adaptations.

Highlights

Phenotypic plasticity in life-history traits in response to heterogeneous environments has been observed in a number of fishes
Seamounts have long been known as aggregation sites for large pelagic fishes such as tuna, billfishes and sharks[1]
Two oceanic seamounts that extend into the photic zone are known to exist around southern African waters, Vema (31° 41′ S, 8° 20′ E) in the southern Atlantic Ocean and Walters Shoal (33° 9′ S, 43° 49′ E) in the Southern Indian Ocean (Fig. 1)

Summary

Introduction

Phenotypic plasticity in life-history traits in response to heterogeneous environments has been observed in a number of fishes. Phenotypic plasticity might explain observed differences in growth, maturation and reproduction related traits, depending on natural and fishing mortality, access to resources and environmental variation, as there has been little evidence of genetic isolation of seamount associated pelagic fish populations[2], yet, recent literature has detected genetic structure in wide ranging large pelagic fishes[3], questioning the current understanding of seamounts as mere feeding oases and navigation aids. Two oceanic seamounts that extend into the photic zone are known to exist around southern African waters, Vema (31° 41′ S, 8° 20′ E) in the southern Atlantic Ocean and Walters Shoal (33° 9′ S, 43° 49′ E) in the Southern Indian Ocean (Fig. 1) Both features harbour endemic species[4,5] with a pelagic propagule phase, which suggests the existence of hydrographic mechanisms for larval retention. The larvae and juveniles are often associated with flotsam, which suggests potential for dispersal through ocean currents

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Results

Discussion

Conclusion