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Scute pattern variabilities in green sea turtles (Chelonia mydas): Investigation at Chagar Hutang Turtle Sanctuary, Redang Island, Malaysia

par Steenacker, Marion
Président du jury Roisin, Yves
Promoteur Fournier, Denis
Publication Non publié, 2020-06-25

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Résumé :

The carapacial scute pattern of sea turtles is a conserved trait that provides taxonomic information. But non-modal scute patterns (NMSPs), i.e. intraspecific individual variabilities, are observed for almost all species and occur relatively often, particularly in hatchlings. These NMSPs could be associated with a reduced fitness and a lower survival rate of individuals. To better gauge their effects, we surveyed over the eight weeks study duration 156 clutches of 101 nesting females of green sea turtle Chelonia mydas coming lay in Redang Island, Malaysia. For each female, we measured curved carapace length and width and characterized its scute pattern. For each nest, we reported distance from vegetation, sun exposure, if the eggs were handled and relocated just after the oviposition, the incubation duration (a proxy of the incubation temperature), the hatching success (i.e. the proportion of eggs from which hatchlings emerge in the nest chamber) and the proportion of hatchlings with NMSP. For a subsample of 67 nests, we collected 1144 newly emerged hatchlings and compared their scute patterns, size (carapace length, width and carapace size index), mass and their locomotor performances (self-righting ability, running speed and swimming speed). We compared the scute pattern of hatchlings with the one of their mother and found no link suggesting a significant maternal origin effect on scute pattern abnormalities. However, we found that short incubation duration (i.e. high incubation temperatures) and management techniques are the main drivers of scute pattern abnormalities and hatching success. Eggs hatched after a short incubation period and/or eggs that were relocated have a greater propensity to produce non-modal hatchlings. The proportion of hatchlings with NMSP in a nest is negatively correlated to the hatching success. Hatchlings that have been relocated, regardless of their scute patterns, are those with the lowest locomotor performances, i.e. with worst self-righting scores and slowest. Scute pattern negatively impacts self-righting but not displacement speed.Our work highlights the effects of incubation duration and invasive techniques on morphology and fitness of green turtle hatchlings and contribute to better informed management strategies as part of global research efforts to preserve an endangered species. We suggested, for example, to apply relocation exclusively to doomed nests.