TY - JOUR

T1 - Ontogenetic allometry underlies trophic diversity in sea turtles (Chelonioidea)

AU - Chatterji, Ray M.

AU - Hipsley, Christy A.

AU - Sherratt, Emma

AU - Hutchinson, Mark N.

AU - Jones, Marc E. H.

N1 - Funding Information: Open Access funding enabled and organized by CAUL and its Member Institutions. MEHJ received support from a Discovery Early Career Researcher Award DE130101567 (Australian Research Council) and CAH received support from a Discovery Early Career Researcher Award DE180100629 (Australian Research Council). Funding Information: We are grateful to all the people and institutions who helped make this study possible. We would first like thank all the Andrew Amey, Serjoscha Evers, Darlene Ketten, Michael Fagan, Rob deville, Rod Penrose, Susan E. Evans, Alana Sharp, and Roger Benson who made specimens and CT data available to us and were key in building our sample set. In particular, we would also like thank Carolyn Kovach for assistance and access to specimens at the South Australian Museum. We also thank The Cetacean Strandings Investigation Programme (CSIP), Institute of Zoology, Zoological Society of London, funded by Defra and the Devolved Administrations in Scotland and Wales. We also thank Ruth Williams (Adelaide Microscopy), Jay Black (TrACCES and University of Melbourne), Michelle Korlaet (Dr. Jones and Partners), Sue Taft (University of Hull), and Ben Wigmore (Sound Radiology) for assistance in CT imaging. We would like to thank all the reviewers for their thoughtful and helpful comments which greatly improved our study. Publisher Copyright: © 2022, The Author(s).

PY - 2022

Y1 - 2022

N2 - Despite only comprising seven species, extant sea turtles (Cheloniidae and Dermochelyidae) display great ecological diversity, with most species inhabiting a unique dietary niche as adults. This adult diversity is remarkable given that all species share the same dietary niche as juveniles. These ontogenetic shifts in diet, as well as a dramatic increase in body size, make sea turtles an excellent group to examine how morphological diversity arises by allometric processes and life habit specialisation. Using three-dimensional geometric morphometrics, we characterise ontogenetic allometry in the skulls of all seven species and evaluate variation in the context of phylogenetic history and diet. Among the sample, the olive ridley (Lepidochelys olivacea) has a seemingly average sea turtle skull shape and generalised diet, whereas the green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) show different extremes of snout shape associated with their modes of food gathering (grazing vs. grasping, respectively). Our ontogenetic findings corroborate previous suggestions that the skull of the leatherback (Dermochelys coriacea) is paedomorphic, having similar skull proportions to hatchlings of other sea turtle species and retaining a hatchling-like diet of relatively soft bodied organisms. The flatback sea turtle (Natator depressus) shows a similar but less extreme pattern. By contrast, the loggerhead sea turtle (Caretta caretta) shows a peramorphic signal associated with increased jaw muscle volumes that allow predation on hard shelled prey. The Kemp’s ridley (Lepidochelys kempii) has a peramorphic skull shape compared to its sister species the olive ridley, and a diet that includes harder prey items such as crabs. We suggest that diet may be a significant factor in driving skull shape differences among species. Although the small number of species limits statistical power, differences among skull shape, size, and diet are consistent with the hypothesis that shifts in allometric trajectory facilitated diversification in skull shape as observed in an increasing number of vertebrate groups.

AB - Despite only comprising seven species, extant sea turtles (Cheloniidae and Dermochelyidae) display great ecological diversity, with most species inhabiting a unique dietary niche as adults. This adult diversity is remarkable given that all species share the same dietary niche as juveniles. These ontogenetic shifts in diet, as well as a dramatic increase in body size, make sea turtles an excellent group to examine how morphological diversity arises by allometric processes and life habit specialisation. Using three-dimensional geometric morphometrics, we characterise ontogenetic allometry in the skulls of all seven species and evaluate variation in the context of phylogenetic history and diet. Among the sample, the olive ridley (Lepidochelys olivacea) has a seemingly average sea turtle skull shape and generalised diet, whereas the green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) show different extremes of snout shape associated with their modes of food gathering (grazing vs. grasping, respectively). Our ontogenetic findings corroborate previous suggestions that the skull of the leatherback (Dermochelys coriacea) is paedomorphic, having similar skull proportions to hatchlings of other sea turtle species and retaining a hatchling-like diet of relatively soft bodied organisms. The flatback sea turtle (Natator depressus) shows a similar but less extreme pattern. By contrast, the loggerhead sea turtle (Caretta caretta) shows a peramorphic signal associated with increased jaw muscle volumes that allow predation on hard shelled prey. The Kemp’s ridley (Lepidochelys kempii) has a peramorphic skull shape compared to its sister species the olive ridley, and a diet that includes harder prey items such as crabs. We suggest that diet may be a significant factor in driving skull shape differences among species. Although the small number of species limits statistical power, differences among skull shape, size, and diet are consistent with the hypothesis that shifts in allometric trajectory facilitated diversification in skull shape as observed in an increasing number of vertebrate groups.

KW - Allometry

KW - Chelonioidea

KW - Diet

KW - Ontogeny

KW - Skull

KW - Testudines

U2 - 10.1007/s10682-022-10162-z

DO - 10.1007/s10682-022-10162-z

M3 - Journal article

AN - SCOPUS:85125640959

VL - 36

SP - 511

EP - 540

JO - Evolutionary Ecology

JF - Evolutionary Ecology

SN - 0269-7653

IS - 4

ER -