Sporadic nesting reveals long distance colonisation in the philopatric loggerhead sea turtle (Caretta caretta)

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.

Population-specific signatures of intra-individual mitochondrial DNA heteroplasmy and their potential evolutionary advantages

“…Furthermore, population sizes are generally low, especially in the Mediterranean 37 and also genetically isolated 30 . Additionally, long distance colonization events have been described for marine turtles 23 and thus new populations are thought to originate from a few individuals 24 . Therefore, these populations are expected to be exposed to different levels of bottlenecks due to founder effects or populations reductions, a phenomenon aggravated by anthropogenic factors such as the extreme population decline suffered by Israeli sea turtle populations during the Second World War 38 .…”

“…They have remarkable biological features that impact on the structuring and connectivity of their populations, like natal homing or long-distance migrations 22 favoring long range colonization. Thus, the founding of new populations of marine turtles have been proposed to be driven by colonizing events of few individuals and thus potentially under strong population bottlenecks due to founder effects 23,24 . The studied mitochondrial DNA fragments exhibit low genetic diversity, possibly due to a combination of low metabolic rate and long generation time 25 , and low mutation rate 26 .…”

How many came home? Evaluating ex situ conservation of green turtles in the Cayman Islands

“…Therefore, the natural recovery of isolated populations on the verge of extinction may be difficult, as little migration would be expected from other populations to increase the number of mating adults. This philopatric behaviour, in both females and males (Clusa et al, ), is the basis for a rapid colonization of new potential nesting areas after the first arrival of marine turtles (Carreras et al, ).…”

Distribution of genetic diversity reveals colonization and philopatry of the loggerhead sea turtles across geographic scales

“…Here, we also reveal another geographic pattern, where gene flow of nesting females has propagated from the centre of the distribution to the edge. This pattern might be the ancient signature of colonization within the Archipelago: after the evolution of site fidelity to the firstly colonized islands, populations were established in all others through sporadic nesting events from the long-distance migrants, as it has recently been described to occur in Mediterranean rookeries (Carreras et al, 2018). Altogether, the observed genetic structure is the likely result of a strong female philopatric behavior as often observed in loggerhead turtles (FitzSimmons et al, 1997; Lee et al, 2007).…”