| Popis: |
Research into speciation and t~e processes governing divergence within species has received considerable attel1tion from ecologists and evolutionary biologists in recent years. However, few empirical studies have focused on marine systems, despite the potential evolutionary consequences of the unique conditions in this environment. The coral reef fish genus Hypoplectrus represents an excellent system with which to study marine divergence and comprises 10-14 distinct colour morphotypes. This thesis focuses on the Hypolectrus colour polymorphism and considers how these morphotypes differ genetically, morphometrically and ecologically. Furthermore, the distribution of morphotypes is resolved and the potential implications of these geographical patterns considered. All of these studies include data on multiple colour morphotypes from widely dispersed geographical locations. AFLP molecular marker analysis shows morphotypes to have consistent low level genetic isolation among each other. Some of the markers tested showed significantly higher levels of isolation than expected, suggesting they may be linked to genes under selection. Stable isotope analysis shows little evidence to suggest ecological divergence between morphotypes and they do not appear to possess distinct feeding niches. Morphotypes show quite variable dietary patterns across their range, suggesting against ecological adaptation involving diet. Geometric morphometric results show small but significant differences between morphotypes, which may be due to genetic isolation rather than physical adaptation. The diversity of morphotypes across the Hypoplectrus distribution shows interesting patterns, which suggest morphotypes do not co-occur randomly and that the number of morphotypes present on a reef is positively correlated with general reef fish species richness. Following these results, we now have an improved understanding of the Hypoplectrus colour polymorphism and there are clear directions for future research into the origin of this phenotypic radiation. |
