Identifying genetic lineages through shape: An example in a cosmopolitan marine turtle species using geometric morphometrics.

Rocío Álvarez-Varas,Daniel A Godoy,Patricia Zárate,Gabriela M Vélez-Rubio,Hugo A Benítez,Maike Heidemeyer,David Véliz,Alejandro Fallabrino,Sergio N Stampar

doi:10.1371/journal.pone.0223587

Abstract

The green turtle (Chelonia mydas) is a globally distributed marine species whose evolutionary history has been molded by geological events and oceanographic and climate changes. Divergence between Atlantic and Pacific clades has been associated with the uplift of the Panama Isthmus, and inside the Pacific region, a biogeographic barrier located west of Hawaii has restricted the gene flow between Central/Eastern and Western Pacific populations. We investigated the carapace shape of C. mydas from individuals of Atlantic, Eastern Pacific, and Western Pacific genetic lineages using geometric morphometrics to evaluate congruence between external morphology and species’ phylogeography. Furthermore, we assessed the variation of carapace shape according to foraging grounds. Three morphologically distinctive groups were observed which aligned with predictions based on the species’ lineages, suggesting a substantial genetic influence on carapace shape. Based on the relationship between this trait and genetic lineages, we propose the existence of at least three distinct morphotypes of C. mydas. Well-defined groups in some foraging grounds (Galapagos, Costa Rica and New Zealand) may suggest that ecological or environmental conditions in these sites could also be influencing carapace shape in C. mydas. Geometric morphometrics is a suitable tool to differentiate genetic lineages in this cosmopolitan marine species. Consequently, this study opens new possibilities to explore and test ecological and evolutionary hypotheses in species with wide morphological variation and broad geographic distribution range.

Highlights

Marine turtles are migratory species with a complex life history
A correction for allometry was performed and all the shape analyses (PCA and canonical variate analysis (CVA)) were carried out using the covariance matrix of the data corrected by size
The uplift of the Panama Isthmus precedes the divergence in C. mydas described by Dutton et al (2014) [6] in the Pacific Ocean (Eastern and Western Pacific lineages), and this is congruent with the degree of morphological differentiation observed in this study, where differences were more evident between basins (Atlantic-Pacific) than within the Pacific basin

Summary

Introduction

Marine turtles are migratory species with a complex life history Their life cycle includes adult migrations from foraging grounds to generally distant breeding areas, and ontogenetic changes that affect the distribution of juveniles throughout a variety of marine habitats [1]. In the Pacific Ocean, Dutton et al (2014) [6] suggested a complex population genetic structure in C. mydas, with a distinct phylogeographic break between Western and Central/Eastern Pacific populations. Dutton et al (2014) [6] demonstrated that populations of the Central and Eastern Pacific are reproductively isolated from those of the Western Pacific region, evidence from foraging areas in these regions suggests that both juveniles and adults disperse occasionally throughout the Pacific to feed [7,8,9,10]. Individuals with Western Pacific natal origin (Western Pacific genetic lineage) have been observed feeding in Eastern Pacific sites and vice versa

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Discussion

Conclusion