Evolution of different mating system in cichlid fishes

Cichlid fishes (Perciformes: Teleostei) have received considerable attention from scientists not only because they represent the most speciose vertebrate group that underwent repeated explosive radiations, but also because of the high species diversity and the complexity of social behaviors. Complex behaviors include cognitive (spatial) maps, social learning, individual recognition, and reproduction, the genetic and molecular basis of which are still poorly understood. In the cichlid fish model Astatotilapia burtoni, the neuropeptide genes gonadotropin releasing hormone (GnRH) and somatostatin as well as some relevant receptors have been discovered to be involved in socially controlled differences in dominance behavior and phenotype. The neuropeptide arginine vasotocin (AVT), the non- mammalian homolog of arginine vasopressin (AVP), plays an important role in reproductive behaviors, including spawning, courtship-associated communication and attending behavior, and socially mediated sex change in fish. In voles, males of monogamous species were demonstrated to have a greater extent and distribution of oxytocin and vasopressin binding in the brain than males of polygamous species, and species of distinct breeding mode showed differences in hippocampal size and spatial ability. This proposal aims at elaborating two major tasks: (i) the identification of behavioral and neural differences underlying species differences in social organization; and (ii) the identification of genes underlying differences in social organization. One goal of the first project part is to investigate whether AVT is fundamental to pair bond formation in vertebrates. To achieve this aim, a monophyletic group of East African Tanganyikan cichlids, the Ectodini clade, in which several independent transitions from monogamy to polygamy occurred, is used as a model system. Behavioral observations in the field, as well as measurement of AVT receptor distribution by in situ hybridization in the brains of Xenotilapia flavipinnis (monogamous) and Enantiopus melanogenys (polygamous) will provide insight in the importance of AVT in the social organization of cichlids. To achieve the goal of the second project aspect, the cichlid DNA microarray, which was shown to work reliably in all East African cichlids, will be applied to the analysis of brain expression profiles to identify additional genes likely to be involved in pair bonding behavior in different species. This analysis will determine whether and to which extent the same or different groups of genes get recruited in independent evolutionary transitions between monogamy and polygamy. As soon as candidate genes are identified, those brain areas that exhibit differences in gene expression will be determined.