Research Article: Population genetic differentiation of the hydrothermal vent crab Austinograea alayseae (Crustacea: Bythograeidae) in the Southwest Pacific Ocean

Date Published: April 24, 2019

Publisher: Public Library of Science

Author(s): Won-Kyung Lee, Se-Joo Kim, Bo Kyeng Hou, Cindy Lee Van Dover, Se-Jong Ju, Jeffrey A. Eble.


To understand the origin, migration, and distribution of organisms across disjunct deep-sea vent habitats, previous studies have documented the population genetic structures of widely distributed fauna, such as gastropods, bivalves, barnacles, and squat lobsters. However, a limited number of investigations has been conducted in the Southwest Pacific Ocean, and many questions remain. In this study, we determined the population structure of the bythograeid crab Austinograea alayseae from three adjacent vent systems (Manus Basin, North Fiji Basin, and Tonga Arc) in the Southwest Pacific Ocean using the sequences of two mitochondrial genes (COI and 16S rDNA) and one nuclear gene (28S rDNA). Populations were divided into a Manus clade and a North Fiji–Tonga clade, with sequence divergence values in the middle of the barcoding gap for bythograeids. We inferred that hydrographic and/or physical barriers act on the gene flow of A. alayseae between the Manus and North Fiji basins. Austinograea alayseae individuals interact freely between the North Fiji Basin and the Lau Basin (Tonga Arc). Although further studies of genetic differentiation over a geological time scale, life-history attributes, and genome-based population genetics are needed to improve our understanding of the evolutionary history of A. alayseae, our results contribute to elucidating the phylogeny, evolution, and biogeography of bythograeids.

Partial Text

Hydrothermal vent environments are characterized by a lack of light (aside from that generated by high-temperature fluids [1]), lack of photosynthesis, high pressure, steep temperature gradients, and high levels of metals and dissolved gases [2–4]. Since the discovery of hydrothermal vents along the Galapagos Rift in 1977, the description of new species has progressed steadily, and new hydrothermal vent sites have been discovered in deep areas of the seafloor. Seven hundred valid species had been described by 2011, and description of additional species continues [5]. Phylogenetic evidence based on molecular markers generally supports traditional taxonomy, and sometimes reveals the existence of sibling (or cryptic) species [6–8]. However, the origin, migration, and distribution of vent fauna across disjunct vent habitats that may undergo repetitive creation and extinction cycles at a time scale similar to the generation times of vent species are not yet fully understood.

Previous studies have confirmed the monophyly of bythograeid crabs [17], which are distinguished from other Brachyura by reduction of the eyes at the adult stage and complete adaptation to hydrothermal vent environments [56]. Based on phylogenetic analysis, bythograeid crabs have been divided into two main groups, the Bythograea clade and a clade composed of Austinograea, Gandalfus, Allograea, Cyanagraea, and Segonzacia [17]. However, the established phylogenetic trees were constructed using specimens from a single vent area for each species, although some species (A. alayseae, A. hourdezi, A. rodriguezensis, S. mesatlantica, B. laubieri, and B. thermydron) are known to have wide distributions among hydrothermal vent fields. Genetic divergence analysis of bythograeids at the population level has been performed for only one species, A. rodriguezensis, and revealed no genetic differentiation between populations at two vent fields separated by 700 km (Central Indian Ridge) [55, 57].