When carapace governs size: variation among age classes and individuals in a free-ranging ectotherm with delayed maturity.

Juvenile growth strongly impacts life-history traits during adulthood. Yet, in juveniles with delayed maturity, elusiveness has hindered age-specific studies of growth, precluding any detailed research on its consequences later in life. Different complex growth patterns have been extracted from captive animals, suggesting species-specific trajectories occur in free-ranging animals. How pronounced are growth and body size variation (VBS) throughout a long-lived ectotherm's life? Is VBS constant among age classes prior to maturity, or do compensatory and/or cumulative effects driven by long-lived-animal-specific strategies create distinct VBS cohorts, to ensure survival? To tackle the issue, we modelled growth data from continuous and dense annual capture-mark-recapture sampling (5096 body measurements of 1134 free-ranging individuals) of both immature and mature, long-lived Hermann's tortoises. We analysed population, cohort, and individual-based growth and VBS. Growth ring inferred ages were cross validated with annual recaptures in 289 juveniles. Analyses unravelled an S-shaped growth curve and identified three age cohorts across which VBS increases in a step-wise manner. Neonate-specific constraints and compensatory effects seem to control VBS until 4 years of age, possibly promoting survival with size. Subsequently, a hardened carapace takes over and cumulative effects fuelled by faster growth progressively increase VBS. Whereas ungulates are in a hurry to attain adult size before growth ceases (minimizing VBS), indeterminately growing tortoises can shape individual asymptotic sizes even after growth decelerates. Tortoise size is clearly shaped by age-specific ecological constraints; interestingly, it is likely the carapace that conducts the strategy, rather than maturity per se.

Genetic variation and population structure in the endangered Hermann's tortoise: the roles of geography and human-mediated processes.

The Hermann's tortoise (Testudo hermanni) is an endangered land tortoise distributed in disjoint populations across Mediterranean Europe. We investigated its genetic variation by typing 1 mitochondrial locus and 9 nuclear microsatellites in approximately 300 individuals from 22 localities. Our goal was to understand the relative impact of natural and human-mediated processes in shaping the genetic structure and to identify the genetic priorities for the conservation of this species. We found that 1) all geographic areas are highly differentiated, mainly as a function of their distance but with a clear genetic discontinuity (F st values larger than 0.4) between the Eastern and the Western subspecies; 2) the contact zone between subspecies is located farthest to the west than previously believed, and it probably coincides with the delta of the largest Italian river; 3) extinction events due to climatic conditions in the Upper Palaeolithic and subsequent human-mediated translocations in the Neolithic possibly explain the unexpected similarity among Spain, Sicily, and Corsica. For conservation purposes, the large majority of genetic pools appears native although hybridization among subspecies, related to extensive 20th century trade of tortoises across Europe, is observed in Spain and some Italian samples. Most populations do not seem at immediate risk of low genetic variation, except the French population, which has very low nuclear genetic diversity (heterozygosity = 0.25) and where 50 out of 51 sampled animals shared the same mitochondrial sequence. In general, restocking and reintroduction plans should carefully consider the genetic background of the individuals.

Is sexual body shape dimorphism consistent in aquatic and terrestrial chelonians?

Comparisons between aquatic and terrestrial species provide an opportunity to examine how sex-specific adaptations interact with the environment to influence body shape. In terrestrial female tortoises, selection for fecundity favors the development of a large internal abdominal cavity to accommodate the clutch; in conspecific males, sexual selection favors mobility with large openings in the shell. To examine to what extent such trends apply in aquatic chelonians we compared the body shape of males and females of two aquatic turtles (Chelodina colliei and Mauremys leprosa). In both species, females were larger than males. When controlled for body size, females exhibited a greater relative internal volume and a higher body condition index than males; both traits potentially correlate positively with fecundity. Males were more streamlined (hydrodynamic), and exhibited larger openings in the shell providing more space to move their longer limbs; such traits probably improve mobility and copulation ability (the males chase and grab the female for copulation). Overall, although the specific constraints imposed by terrestrial and aquatic locomotion shape the morphology of chelonians differently (aquatic turtles were flatter, hence more hydrodynamic than terrestrial tortoises), the direction for sexual shape dimorphism remained unaffected. Our main conclusion is that the direction of sexual shape dimorphism is probably more consistent than sexual size dimorphism in the animal kingdom.