Turtles (Testudines) form a monophyletic group with a highly distinctive body plan. The taxonomy and phylogeny of turtles are still under discussion, at least for some clades. Whereas in most previous studies, only a few species or genera were considered, we here use an extensive compilation of DNA sequences from nuclear and mitochondrial genes for more than two thirds of the total number of turtle species to infer a large phylogeny for this taxon. Our results enable us to discuss previous hypotheses on species phylogeny or taxonomy. We are thus able to discriminate between competing hypotheses and to suggest taxonomical modifications. Finally, we pinpoint the remaining ambiguities for this phylogeny and the species for which new sequences should be obtained to improve phylogenetic resolution.

In species with temperature-dependent sex determination (TSD), global climate change may result in a strong sex ratio bias that could lead to extinction. The relationship between sex ratio and egg incubation at constant temperature in TSD species is characterized by two parameters: the pivotal temperature (P) and the transitional range of temperature that produces both sexes (TRT). Here, we show that the proportion of nests producing both sexes is positively correlated to the width of the TRT by a correlative approach from sex ratio data collected in the literature and by simulations of TSD using a mechanistic model. From our analyses, we predict that species with a larger TRT should be more likely to evolve in response to new thermal conditions, thus putting them at lower risk to global change.

To assess the impact of nest covering on a leatherback turtle Dermochelys coriacea nesting beach in French Guiana, we used field study data and a modelling approach. Field results showed that the covering of a pre-existing nest by a new one causes the destruction of the older nest under some conditions of time and covering area, and almost always causes the destruction of the new nest. We then used field results to parameterize a theoretical model of the nesting beach. This allowed us to obtain a 'critical carrying capacity for the beach': the number of nests deposited for which the number of successful nests is maximum; when this number increases, the number of successful nests decreases. With these results, we then concluded that density-dependent nest destruction plays a role in the functioning of the nesting beach. These results are essential for our understanding of nest-site selection at the scale of the beach and its consequences.

Background: We use a simulation-based model to study the impact of female philopatry and heterogeneity of habitat quality on the evolution of primary sex ratio.

Background: Marine turtles deposit their eggs on tropical or subtropical beaches during discrete nesting seasons that span several months. The number and distribution of nests laid during a nesting season provide vital information on various aspects of marine turtle ecology and conservation.

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