PhD: Organism responses to environmental change – testing hypotheses of dietary niche shifts in cichlid fishes over historical and longer timescales

Project Highlights:
Test hypotheses of ecological and evolutionary diversification and displacement linked to environmental change over historical and longer timescales
Conduct the first systematic analysis dental microwear in cichlids
Apply quantitative texture analysis to present day, historical and sub-fossil cichlid teeth to test and constrain hypotheses of diet and dietary responses to environmental change

Cichlids provide textbook examples of speciation driven by dietary specialisation. The link between diversity and trophic niche partitioning should mean that periods of environmental change, colonization events, and introductions of invasive fish species have a significant impact on the dietary ecology of cichlids. Rapid diversification in feeding habits, for example, is predicted by models that link adaptive radiations to relaxed competition and expansion into vacant ecospace. Shifts in dietary niche, potentially associated with character displacement, would be expected to result from introductions of invasive competitor species.

Skeletal remains and teeth of cichlids from African lake sediments are starting to be used to test evolutionary and ecological hypotheses (1, 2) but direct testing requires analysis of dietary preferences in historical and sub-fossil specimens. This is difficult to do based on morphological data, because analysis of functional morphology is hampered by the mismatch between apparent specialization in trophic morphology and actual diet (3, 4), particularly in fishes.

Recently, we developed a new approach to dietary analysis based on the application of quantitative dental microwear texture analysis (DMT; (5)) to cichlids and other fishes (6, 7). DMT analysis of worn surfaces of fish teeth provides a powerful new tool for dietary discrimination and investigation of trophic resource exploitation in fishes. It is particularly useful because the dietary signal accumulates over several days/weeks and therefore avoids the ‘snapshot’ problem inherent in stomach contents analysis. Significantly, DMT analysis can detect subtle dietary differences between individuals and populations in historical, sub-fossil and fossil specimens, and where stomach contents or isotopic data are lacking, but it has yet to be applied to a broad range of cichlids with diverse feeding habits.

This project will develop and apply DMT analysis of cichlids to determine the sensitivity and degree to which DMT can capture the range of diets among cichlids. The outcome of this analysis will allow direct testing of hypotheses of ecological and evolutionary diversification and displacement linked to environmental change over historical and longer timescales.
Dental microwear texture of pharyngeal jaws in the cichlid fish Astatreochromis alluaudi. The specimens illustrate texture from a fish with a diet rich in hard shelled molluscs (right) compared to one that consumed softer food (Modified from (7). Dental microwear texture of pharyngeal jaws in the cichlid fish Astatreochromis alluaudi. The specimens illustrate texture from a fish with a diet rich in hard shelled molluscs (right) compared to one that consumed softer food (Modified from (7).

Methodology
The project will focus on extensive collections of cichlids in the collections of the Natural History Museum (London), Nauralis (Leiden), and research material from collaborator Lauren Chapman (Montreal). Sub-fossil material (e.g. Lake Chala (1)) will also be available for analysis through project collaborators. Further calibration of cichlid DMT through feeding experiments (8), and analysis of character displacement through morphometric analysis is also possible. Dietary analysis will employ quantitative 3D texture analysis of microwear using methods developed at Leicester (7, 9). Our approach will allow robust analysis and hypothesis testing of the role of feeding and diet at different temporal and spatial scales, and has the potential to pick up dietary transitions that predate and potentially drive morphological adaptation of teeth to new functional roles.

Training and Skills
Specialist training will include analytical/experimental design, quantitative tooth microwear texture analysis, and statistics. The emphasis will be on robust quantitative analysis and statistical hypothesis testing. At Leicester, you will join the Centre for Palaeobiology Research – a well-equipped and dynamic group of researchers, PhD and Masters students who meet frequently to discuss their research. This includes other students working on novel analyses of diet and trophic niche in vertebrates.