Population Genetic Differentiation on the Hydrothermal Vent Crabs Xenograpsus testudinatus along Depth and Geographical Gradients in the Western Pacific

Peter Kee Lin Ng,Tin-Yam Chan,Benny Kwok Kan Chan,Teng-Wei Wang,Yi-Yang Lin,Chien-Hui Yang

doi:10.3390/d14030162

Abstract

Connectivity in deep-sea organisms must be considered across both depth gradient and horizontal geographical scales. The depth-differentiation hypothesis suggests that strong environmental gradients (e.g., light, temperature, pressure) and habitat heterogeneity in the deep-sea can create selection pressure, and this can result in genetic population divergence. The hydrothermal vent crab Xenograpsus testudinatus (Xenograpsidae) is common in vents at Kueishan Island, Taiwan, ranging from 10 to about 300 m depths. Xenograpsus testudinatus has also been found in shallow water vents (3–20 m) at Kagoshima and the Izu archipelago of Japan. We examine the sequence divergences in the mitochondrial COI, 16S rRNA and D-loop genes, to test the hypothesis that there is significant genetic differentiation among populations of X. testudinatus along the depth gradient at Kueishan Island (30, 200, 209–224 and 250–275 m), and among different geographical regions (Kueishan, Kagoshima and the Izu archipelago) in the West Pacific. There is neither significant population differentiation among shallow or deep-sea vents, nor between geographical locations. Vertical migration of zoea, upwelling on the eastern coast of Taiwan and the strong effect of the Kuroshio Currents has probably resulted in a high level of planktonic larval dispersal of X. testudinatus along the depth and geographical gradients in the Western Pacific.

Highlights

The life cycles of marine invertebrates typically include planktonic larval and sedentary adult phases
Sixty-nine sequences of the D-loop gene were successfully sequenced from the shallow water vents at Taiwan (TS) and Kagoshima (JS2) and one deep-sea vent (TD2, 209–224 m) at Kueishan Island
The present study revealed neither depths nor geographical distances affect the population differentiation of the vent crab Xenograpsus testudinatus in the West Pacific

Summary

Introduction

The life cycles of marine invertebrates typically include planktonic larval and sedentary adult phases. The duration of planktonic larval development (PLD), larval development modes (planktotrophic or lecithrotrophic) and larval behavior can affect the larval dispersal and connectivity from shallow water [1,2,3] to even bathyal and abyssal depths [4,5,6]. Population genetics of intertidal or shallow water species are often focused on connectivity along the horizontal geographical scales [7,8,9,10,11]. Compared to shallow water species, deep-sea (>200 m deep) organisms often inhabit a relatively wider depth gradient [12]. Connectivity of deep-sea populations occurs across two dimensions—depth gradient and horizontal geographical scales [12]. Strong depth (400 m) and geographical scale population differentiation, for example, were reported in the deep-sea coral Callogorgia delta on the Atlantic coast of the USA [13]

Methods

Results

Conclusion