Sexual selection in the great tit, Parus major

• Main Author: Bickle, Angharad
• Published: University of Leicester 2000
• Subjects: 598.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.696771

This thesis investigated whether there was evidence for sexual selection in the great tit Parus major. The sexually dimorphic badge carried by the great tit was negatively associated with survival of both sexes. This badge, the black chin area, has previously been shown to have a role in male-male competition. The potential benefits to a female great tit of mating with large-badged males were assessed to investigate whether this trait also has a role in sexual selection. Large males produced a greater response to territorial intrusion than their smaller counter parts, a behaviour which may be a form of parental investment. Chicks were transferred between nests in a cross-foster experiment to distinguish between direct and indirect consequences of a male's badge size on offspring development. A potential direct benefit that covaried with badge size was identified, male badge-size was positively related to condition and number of (unrelated) chicks raised. An indirect benefit was also suggested: male's chin area was related to the survival of his offspring raised away from his nest. Large-badged males tended to produce more surviving chicks. When chicks were raised by their own father, male chin area explained variation in chick leukocyte count. Large-badged males produced chicks with low leukocyte counts and low leukocyte count improved chick survival. Female great tits, therefore, may experience both direct and indirect benefits according to the badge size of her mate. Females may also adjust their behaviour according to the phenotype of their mate. For example, there was evidence that the sex ratio of the brood may vary according to male size, with larger males producing more sons. These results are discussed with respect to the current theories of sexual selection.