Intra-specific variation in skull morphology of juvenile Chelonia mydas in the southwestern Atlantic Ocean

Abstract

The genetic diversity and skull morphology of juvenile Chelonia mydas recruited to the southwestern Atlantic were evaluated to quantify intraspecific variation in the skull shape and size related to (1) broad geographic origin and (2) age (within the most abundant haplotype). 155 C. mydas stranded at 25o S in Brazil were sampled, with 108 assessed for haplotypes (mtDNA) and 102 aged. The hypothesis of no effects of intrinsic variables on the morphology of three skull views was evaluated via 2D geometric morphometrics. Mixed stock analyses identified ten haplotypes among 12 nesting sites, with Ascension Island dominant (65%), then Suriname (10%) and Sao Tome (9%). Compared to CM-A8 (southern Atlantic and west African haplotype) individuals, those assessed as CM-A5 (northern Atlantic and southern Caribbean haplotype) consistently had different skull shapes, which might affect physiology and behaviour. Within CM-A8, there was a positive relationship between centroid size and age (3–5 years), and differences in ventral shape, possibly attributed to ontogenetic diet shifts. The clear morphological differences between haplotypes could imply evolutionary consequences for genetic diversity and trophic polymorphism if there is increased future bias towards CM-A8 (owing to fewer anthropogenic impacts during/post hatching). Conserving priority Caribbean nesting grounds during regional management initiatives might protect phenotypic variability and ultimately population diversity and resilience.