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Severe bone resorption of the vertebral body in reared rainbow trout was thought to be a dysfunction in mineral balance induced by increased growth rate in unfavourable rearing conditions. To verify this assumption, we sampled market-sized trout ( c. 250 g) from 20 fish farms with different rearing conditions. Growth rate was also studied by sampling trout reared in three different water temperatures from fry to market-size. Transverse sections of vertebrae were microradiographed, then digitized. Total bone area (Tt-B.Ar.) and bone profiles were obtained using BONE PROFILER 3.23 software and a mathematical model was developed to statistically compare bone profiles using 12 parameters in four vertebra regions. Tt-B.Ar. and bone profiles were found to vary with rearing conditions and growing temperatures, indicating obvious influences of these factors on bone remodelling. However, vertebral resorption was found to be a general phenomenon. In trout from 190 to 235 mm in length, vertebrae underwent important remodelling resulting in large resorption of the middle area, while the transition and peripheral areas showed an increase in bone deposition. Changes in vertebra architecture seem to be a good compromise between the need to mobilize stored minerals during growth while maintaining vertebral biomechanical properties. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

1. In temperature-dependent sex determination (TSD) species, offspring sex-ratio is dependent on the environmental temperature. For oviparous sauropsid species, temperature within the nest influences gonadal sexual differentiation during a small window of embryogenesis called the thermosensitive period (TSP). 2. The absence of sexual dimorphic characteristic in juveniles of TSD species coupled with the lack of a non-invasive method to determine sex is a great obstacle to studies estimating sex-ratios under natural conditions. Some authors have proposed proxies of sex-ratio obtained through correlative approaches. They commonly extrapolate the empirical profile of sex-ratios as a function of constant incubation temperature established for several species in the laboratory to a field context. However, most of these proxies have been refuted by studies realized under field conditions, and consequently they cannot be used to predict sex-ratio under natural conditions. 3. Here, we propose a new thermal model of TSD using a mechanistic approach. We built this model from a collection of published data of physiological processes (i.e. the growth of the embryo, the growth of gonads and the activity of the enzyme aromatase) underlying the TSD mechanism, for the European pond turtle ( Emys orbicularis). This new approach provides integration of incubation temperature fluctuations, as well as the cumulative and differential effect of high and low temperatures on sexual differentiation to embryo sex determination. 4. The significant consistency obtained between observed and predicted sex-ratios both at diverse constant and fluctuating incubation temperatures provides hope to develop an efficient method to predict sex-ratio under natural conditions. The reliable validity of this new model could have wide-ranging implications for the understanding of the TSD mechanism, as well as its evolutionary and ecological consequences in natural populations. [ABSTRACT FROM AUTHOR]

Abstract: Nesting beaches around the Maroni estuary, at the border between French Guiana and Suriname (South America), currently host about 40% of the world’s population of breeding female leatherback turtles. Although the population size has been variable but always large since the 1980s, observations of leatherbacks in the region before 1950 were sporadic or absent and the number of nesting females was extremely low. These observations motivated us to use molecular markers to investigate whether the appearance of leatherbacks in this region was the result of natural long-term population cycles or of immigration. Analysis of 12 microsatellite loci failed to detect the signature of a recent demographic perturbation in the Maroni population of leatherbacks. This result suggests that the marked increase in population size can neither be explained by natural long-term cycles, nor by a founder effect. We conclude that the current population of the Maroni region likely resulted from extensive migrations of animals from elsewhere. Consequently, the Maroni population probably belongs to a metapopulation whose limits remain currently unknown. This metapopulation dynamic suggested by our results is a major feature that should be taken into account in future conservation strategies. We also estimate the effective population size at 90–220 individuals, which is lower than the target effective population size for conservation purposes. This relatively low effective population size indicates vulnerability, despite the large number of nesting turtles currently observed annually. [Copyright &y& Elsevier]