Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Mate choice and intrasexual competition in convict cichlids, Cichlasoma nigrofasciatum, was investigated in the laboratory, during courtship, nest building, guarding eggs, and guarding fry. During courtship, females were expected to use male body size to indicate quality and to compete for large males. Females and newly introduced males were tested under two conditions: Treatment1--the males were similar in body length; and Treatment 2--one male was larger than the other two. No significant difference was found between treatments in the frequency of female proximity to males or in the frequency of female-female aggressive behaviour. However, the large male of Treatment 2 was the first male to spawn in each replicate. In both treatments, the females that spawned were significantly more aggressive than the other two females. Females do not necessarily prefer large male body size when initially assessing males. Male and female intrasexual competition was tested at the nest building stage in two habitats differing in the amount of visual cover available. In the habitat offering more cover, neither males nor females behaved more aggressively towards same-sexed fish than in the habitat where the exposure to each other was greater. One male and one female in each replicate dominated the others and these were the ones that spawned. Female choice was tested at the nest-building stage when the female's mate either won or lost a contest with another male. Females spent significantly more time at her mate when he won than when he lost. Likewise, intruder males were favored by females when they won the contest against the mate. Finally, male and female brood defence of the fry against juvenile convict cichlids was tested using large and small parents. Larger body size was not associated with an expected increase in brood defence behaviour. No significant differences between large and small males were found in the eight defence variables. However, small females spent significantly more time near the predators and responded with significantly more bites than the large females. I conclude that mate choice for large body size would not necessarily have a selective advantage in preventing fry predation.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.