Browsing by Subject "Cichlids."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Evolutionary forces driving population differentiation in Lake Malawi rock-dwelling cichlids (Pisces: Cichlidae)(2014-01-28) Husemann, Martin, 1982-; Danley, Patrick D.; Biology.; Baylor University. Dept. of Biology.The East African cichlids with more than 2000 species represent the most diverse vertebrate radiation known. Lake Malawi harbors the most species rich flock with more than 700 endemic cichlids. In this work I use a population based approach to study the forces driving the divergence of populations and the factors contributing to the maintenance of species diversity. I examine the effect of genetic drift on population divergence through time and space using an analysis of effective population sizes. This study indicates that populations of the widespread Maylandia zebra are over 550 individuals in size and are at an equilibrium state. The microendemic Maylandia benetos has a relatively small population size (~500 individuals) and evidence for drift is found. I also examine the phenotypic divergence in ecological and sexual characters in M. zebra. This study reveals that ecological selection plays an important role in the divergence of body shape and length in M. zebra. Divergence in male color pattern shows weaker evidence for selection. Furthermore, the divergence estimates for body shape and melanophore count are slightly correlated. This correlation between an ecological and a sexual trait may indicate that both phenotypes might be under correlational selection. Correlational selection on ecological and sexual traits is further supported by the correlation of body shape and male coloration in replicated sympatric species pairs of Maylandia. A common garden experiment using the sympatric M. zebra and M. benetos, representing a sympatric species pair with divergent coloration, shows that body shape had a strong genetic component but also exhibited phenotypic plasticity. Hybrid crosses of the two species reveal a complicated mode of inheritance for body shape differences and demonstrated high degrees of transgressive segregation. Overall, selection appears to be the driving force of phenotypic evolution in rock-dwelling cichlids. However, small population sizes of microendemics expose them to the effects of drift. Evidence for correlational selection suggests that specific combinations of reproductive and ecological traits might be favored. Finally, phenotypic plasticity and transgressive segregation are two mechanisms generating new phenotypic diversity contributing to the diversification of cichlids.Item Prolactin Gene Duplication within the Family CichilidaeAlmanza, Elaine; Kidd, Michael R.; Kidd, Michael R.; Ynalvez, Ruby A.; Muñoz, Monica; Quintana, Fernando GuillermoThe prolactin gene has undergone a duplication event within the cichlid lineage, producing two distinct forms of prolactin (PRL188 and PRL177). The hormone prolactin is critical for regulating parental care in many species. Cichlid fishes exhibit a wide variety of parental care strategies, including maternal-only, paternal-only, and biparental care. A recent study found evidence for positive selection acting on the duplicate prolactin gene (PRL177), suggesting that this duplication event was associated with the evolution of alternative mating strategies. Polymerase chain reaction was used to isolate and amplify genes for both prolactin hormones and two prolactin receptors from brain derived cDNAs from species in the Ectodini and Tilapiine lineages. To date, a total of 43 species have been surveyed with PRL 188 having been amplified in 29 species, PRL 177 from 12 species, PRLR I from 15 species and PRLR II from 33 species. I was able to amplify PRL 177 in Ectodini lineage, indicating that it is not Tilapiine specific. I also discovered an unexpected rate of sequence divergence of the PRLR II gene in the Ectodini lineage. In this study, I examine the evolution of prolactin genes within the family Cichlidae which exhibit multiple forms of parental care. I hypothesize that PRL 177 should be present throughout the cichlid family.