Abstract
The colonisation of new suitable habitats is crucial for species survival at evolutionary scale under changing environmental conditions. However, colonisation potential may be limited by philopatry that facilitates exploiting successful habitats across generations. We examine the mechanisms of long distance dispersal of the philopatric loggerhead sea turtle (Caretta caretta) by analysing 40 sporadic nesting events in the western Mediterranean. The analysis of a fragment of the mitochondrial DNA and 7 microsatellites of 121 samples from 18 of these nesting events revealed that these nests were colonising events associated with juveniles from distant populations feeding in nearby foraging grounds. Considering the temperature-dependent sex determination of the species, we simulated the effect of the incubation temperature and propagule pressure on a potential colonisation scenario. Our results indicated that colonisation will succeed if warm temperature conditions, already existing in some of the beaches in the area, extend to the whole western Mediterranean. We hypothesize that the sporadic nesting events in developmental foraging grounds may be a mechanism to overcome philopatry limitations thus increasing the dispersal capabilities of the species and the adaptability to changing environments. Sporadic nesting in the western Mediterranean can be viewed as potential new populations in a scenario of rising temperatures.
Highlights
The colonisation of new suitable habitats is crucial for species survival at evolutionary scale under changing environmental conditions
It was not possible to obtain samples from all the clutches, considering that some were laid before starting the present study, while in other cases no samples for genetic studies were collected by the discoverers or were preserved in formalin
A total of six mitochondrial DNA haplotypes were found among the samples, all of them described in previous studies and found in the GenBank (Table 2)
Summary
The colonisation of new suitable habitats is crucial for species survival at evolutionary scale under changing environmental conditions. The circumtropical distribution of most marine turtle species suggests the existence of mechanisms for long distance dispersal[30] It has been proposed for marine turtles that ‘non-philopatric exploratory behaviours are needed to colonize new nesting environments on evolutionary time scales’31, ‘strays and wandering must occur, and are no doubt adaptively advantageous aberrations, necessary for colony proliferation’[16] as ‘absolute natal homing, over the 100-million-year history of this group, would be a strategy for extinction’ 20. The females nesting in the north-western Atlantic have a remigration rate close to 70%35, meaning that a significant portion of the nesting females are not strictly philopatric and lay their clutches in other nesting beaches These deviations are of tens to hundreds of kilometres from the original nesting beach and could explain the lateral spread of the nesting areas along continuous or semi-continuous nesting habitats and the existence of Regional Management Units (RMU)[36]. Colonisation through long distance dispersal across oceans or seas is the only likely explanation for the current circumtropical distribution of most marine turtle species but these transoceanic dispersal strays have not yet been described in detail
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