Evolution of the relative width of the head and alveolar surfaces in map turtles (Testudines: Emydidae: Graptemys)

Abstract

Replicate adaptive radiations are dichotomous morphological patterns related to resource use and repeated in a series of isolated habitats. Biologists have long noted a dichotomy in relative head width and alveolar width among species of map turtles ( G a p h j s ) , particularly with regard to adult females, which are much larger than adult males in all 12 species. I measured plastron length (PL), head width (HW), and alveolar width (AW) of nearly 2300 specimens representing the 12 recognized species, and used allometric regressions to investigate this genus as an example of both sexual dimorphism in trophic morphology and replicate adaptive radiation. Sexual dimorphism was noted in HW after correction for PL, with females having wider heads than males of simiiar body sizes, but AW as corrected for HW was not dimorphic, thus absolute differences in AW are the simple result of differences in HW. Sexual differences in HW probably relate to the dimorphic niches of G@hys, as females of three species have been reported to occupy deeper water further from shore than conspecific males. Based on predicted HW at maximum PL in adult females, species were categorized as mega-, meso-, or microcephalic. Differences in relative head width are related to differences in degree of molluscivory, with little molluscivory in microcephalic females, moderate to high molluscivory in mesocephalic females, and high molluscivory iri megacephalic females. Distributions of Gr@temys species in sympatry and dopatry reveal patterns consistent with structuring of distributions via competitive interactions. Superimposing data on relative HW on a phylogeny of the genus suggests there may have been one or two episodes of character displacement, with subsequent character assortment, in Gr@-@ys evolution. This conclusion is similar to the current model for the evolution of body size during the radation of Anolis lizards in the northern Lesser Antilles. 2000The h e a n sofiety of London ADDITIONAL KEY WORDS-trophic morphologysexual dimorphismcharacter displacementcharacter assortmentmolluscivory.

New sea turtle from the Miocene of Peru and the iterative evolution of feeding ecomorphologies since the Cretaceous

“…Because all other species of durophagous stem-cheloniids are known only from cranial material, we cannot realistically expect cladistic analyses to tease apart convergent lineages. The fact that a durophagous feeding ecology and correlated skull characters can evolve independently within closely related turtle lineages (Claude, 2004) and can even be plastic within a single species (Dalrymple, 1977;Lindeman, 2000) further emphasizes the pattern of homoplasy recovered by our analysis. Because of this homoplasy, the monophyly of poorly known durophagous stem cheloniids cannot be accepted at face value, and that is why we recommend against lumping them all into the genus Euclastes.…”

Intersexual allometry differences and ontogenetic shifts of coloration patterns in two aquatic turtles, Graptemys oculifera and Graptemys flavimaculata

“…1991 on melanism) and speculated that dietary preferences could cause this phenomenon. Although there is considerable dietary overlap among small individuals and dietary niche partitioning between adult males and females in numerous Graptemys species (see Seigel and Brauman 1994 for G. flavimaculata ; reviewed for the genus Graptemys by Lindeman 2000, 2013), no study has investigated the molecular components of the yellow pigmentation within Graptemys to determine whether the yellow is carotenoid based, which would be obtained via diet (Goodwin 1986). …”

An extinct map turtleGraptemys(Testudines, Emydidae) from the late Pleistocene of Florida

“…Extreme sexual dimorphism and molluscivory in female Graptemys are characteristics of all species within the megacephalic clade (Ernst et al, 1994;Lindeman, 2000;Lindeman and Sharkey, 2001;Lindeman, 2008;Stephens and Wiens, 2009). Males of the same species are significantly smaller and do not show adaptations for strict molluscivory, although they may take small gastropods in their diet (Sanderson, 1974;Lee et al, 1975).…”