Understanding how the environment drives the pattern of adaptive radiation may be key to understanding tl1e role of ecology in evolution. The Lake Malawi Haplochomine cichlid fish radiation was seeded by riverine ancestors, yet extant riverine diversity is extremely low. Only Astatotilapia calliptera the putative ancestor of flock currently persists in both the lake and the rivers of the catchment. This presents us with a useful model for assessing tl1e role of environment in driving diversification within a single species. We predict that the contrast in disturbance regime may drive the difference in speciation rate between the two habitats. In tlus thesis, population genetic analysis, functional morphometries, and common garden experiments are used to investigate the level of variation between disturbed river populations and comparatively stable lake populations. The genetic analysis indicates minimal population structuring between Lake Malawi populations compared to within or between river systems. Morphometric data suggests that lake populations are locally diversifying despite this limited isolation. River morphologies are similar despite reduced mixing. Dietary analysis shows that differences in morphology are functional, with the key axis of variation ranging from hard-bodied animals to smaller non-animal resources. Common garden experiments show a clear trade-off between egg-size and number. The majority of sites including all river sites adopt a more conservative strategy focussing on high offspring number. One lake population adopts a high investment strategy. A comparison between lab reared morphology and wild caught morphologies shows that the majority of variation maintained in the wild is through plastic mechanisms. These results suggest that the unpredictability of the riverine environment constrains populations to bet-hedging strategies whilst the highly competitive nature of the lake promotes specialisation. This selection for specialisation could in turn lead to speciation, and may partly explain why speciation within Lake Malawi has been so spectacular
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:685151 |
| Date | January 2015 |
| Creators | Parsons, Paul John |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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