The effects of sexual selection on male extended phenotype polymorphism and potential sleep reductions of Lake Malawi cichlid Nyassachromis microcephalus

Scales, Max

Biological sciences
December 2015

Thesis or dissertation

© 2015 Max Scales. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

Although cichlids are great models for understanding sexual selection their courtship behaviours have not been well documented in regards to any behavioural trade-offs nor has there been researched conducted on their behavioural plasticity in relation to changes in their extended phenotypes. Recent research by Lesku et al. (2012) found that Pectoral sandpipers (Calidris melanotos) reduce their rest periods in order to increase courtship behaviours during breeding season, prompting further enquiries into how widespread this behavioural trade-off is. Negative frequency dependent intrasexual selection could be facilitating the invasion and maintenance of novel bower shapes in cichlid populations, through reductions in conspecific aggression (Magalhaes et al. 2013). We predicted that males would increase nocturnal activity when in the presence of a female and that males would not change their behaviours when their bower sizes were altered, as we would expect behaviours to be related to bower size and shape if negative frequency dependant selection is apparent. We experimentally tested both of these hypotheses on a species of Lake Malawi cichlid (Nyassachromis cf. microcephalus). We separated four dominant males in adjacent tanks, yet still enabled females and subordinate males to freely move between tanks, this was permissible due to their significantly smaller size compared to dominant males. Dominant male bower sizes were changed midway of a two-week observation period and their behaviours towards conspecifics were observed. Cichlids were micro-tagging during our second study with their movements being recorded over a week. Two tanks with a population of only males, and a population of a two males accompanied with a female were used, thus permitting or restricting courtship behaviours. Behaviours of males were found to not significantly differ when given differing sized bowers, suggesting that behaviours are not plastic responses to bower size and negative frequency dependant selection could be acting upon cichlid bowers. No significant changes in nocturnal activity between courting and non-courting males were found, suggesting there is no trade-off between rest and courtship behaviours. However sensor recordings were inaccurate and perhaps didn’t reflect true fish activity along with an uncertainty whether courting males truly displayed courtship behaviours. Overall we have found no evidence suggesting that males trade their rest periods for courtship behaviours. Male behaviours were not plastic responses to bower size and our findings along with Magalhaes et al's. (2013) work suggests that negative frequency dependant selection could be acting upon cichlids to facilitate the invasion of novel bower shapes.

Department of Biological Sciences, The University of Hull
Joyce, Domino A.
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