It’s not all black and white: investigating colour polymorphism in manta rays across Indo-Pacific populations

Intraspecific colour polymorphisms have been the focus of numerous studies, yet processes affecting melanism in the marine environment remain poorly understood. Arguably the most prominent example of melanism in marine species occurs in manta rays (Mobula birostris and M. alfredi). Here, we use photo identification catalogues to document the frequency variation of melanism across Indo-Pacific manta ray populations and test for evidence of selection by predation acting on colour morph variants. We use mark-recapture modeling to compare colour morph survivorship in three M. alfredi populations and assess the relationship between frequency variation and geographical distance. While large differences in melanism frequencies existed among populations of both species (0-40%), apparent survival estimates revealed no difference in survivorship between morphs. We found a significant association between phenotypic and geographical distance in M. birostris, but not in M. alfredi. Our results sugge...