Stiebens, Victor Alexander (2011) Population genetics and mating strategies of the Loggerhead Sea Turtle (Caretta caretta) in Cape Verde. (Diploma thesis), Christian-Albrechts-Universität, Kiel, Germany, 77 pp.

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Abstract

The maintenance of natural population structure and of genetic diversity are the cornerstones of evolutionary conservation genetics. They represent the adaptive and evolutionary potential of endangered populations to survive. One of the most charismatic endangered marine species is the Loggerhead Sea Turtle (Caretta caretta). Despite being the second largest rookery in the Atlantic, the Cape Verde population has received little scientific attention. During the 2010 nesting season, nesting females were sampled on four different islands (N=111). Using various molecular methods such as sequencing the mtDNA control region and genotyping at 8 microsatellite loci, we determined several elements of the population functioning. First of all, demographic history results suggest the colonization of the archipelago in two distinct waves. High haplotypic and nucleotide diversities reveal that Cape Verde may have served as a stepping stone towards the colonization of Mediterranean Sea. Furthermore, significant genetic differentiation based on mtDNA haplotypes found on one beach indicates the coexistence of two distinct philopatric strategies: one very accurate, where females return to their natal beach (Lazareto beach in S. Vicente) and one more diverse strategy where females seem to spread their clutches over different beaches and islands. Microsatellite data revealed that the same Lazareto beach, also showed genetic differentiation from the rest of the archipelago’s populations. Interestingly, even within an island, beaches only separated by a couple of tens of kilometres showed reproductive isolation. Hence, our study proposes that increasing geographic resolution may reveal complex population functioning and we suggest the consideration of at least two evolutionary significant units in Cape Verde. Because variation at neutral loci cannot provide direct information on selective processes in the interactions between individuals and their environment, nor the possibility of future adaptive changes, genetic diversity at relevant genes should be investigated. To this end, the highly polymorphic genes of the major histocompatibility complex (MHC) class I was chosen and successfully characterized. MHC genes are at the root of the adaptive immune system and have crucial function in specific recognition of parasite-derived antigens. The outstanding polymorphism of those genes has been proposed as important marker of genetic diversity for endangered populations. We found that beside at least one duplication event, three lineages of MHC alleles persist in the population and probably explain the signature of trans-species polymorphism seen among several species of reptiles. Further, we discovered suggestive evidence for female turtles to not mate randomly with regards to MHC, implying MHC-dependent mate choice. With the characterization of this important adaptive marker, both for conservation and evolution, the isolation of the MHC opens many new research directions such as the evolution of mating strategy in large migratory marine species or the role of local adaptation in female philopatric behavior.

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