Biomedical subjects
Publications and source records attributed to Ken Kraaijeveld.
Five neighbouring populations of a cichlid fish from Lake Malawi differ in male courtship colour. Females show strong mate preferences for male coloration from their own populations. This suggests that sexual selection is an important factor contributing to speciation in cichlids.
Mating-induced reductions in female receptivity are common in insects. These responses are of interest because of their utility in insect pest control. In addition, the control of receptivity is likely to be the subject of sexual conflict over remating frequency. We investigated the specific effect of male sterility on female receptivity in an important pest species, the Mediterranean fruitfly (medfly), in which sterile males are often used for population suppression. Sterile males performed less courtship, obtained significantly fewer first and second matings than fertile males, and reduced female receptivity significantly less effectively than did fertile males. We modelled the likelihood of fertile matings and show that the low mating success of sterile males represents a significant problem for medfly sterile insect technique (SIT) programmes.
In some members of the marsupial families Didelphidae and Dasyuridae, males are semelparous, that is, they live for only one mating season. Semelparity is proposed to be the result of the high energy demands of competing for matings with many females during a short breeding season. We argue that high adult female mortality rates between mating and weaning of the offspring selects for a 'bethedging' mating strategy in males. We tested this hypothesis in a well-studied field population of Antechinus agilis by estimating the number of females a male needs to mate with in order to have a high chance of siring at least one offspring that survives to the next breeding season. Our hypothesis predicts that species in which males are semelparous should have higher female mortality rates than species in which males are iteroparous. The limited available data for dasyurid marsupials support this prediction.
Many bird species have ornaments that are expressed equally in both sexes. I use comparative analysis to investigate why some monomorphic birds are highly ornamented, whereas others are drab. The results show a significant positive association between the degree of mutual ornamentation and divorce rate. This result is robust to the removal of the effects of phylogeny, site fidelity, residency, coloniality, nest type, mortality, body size and body-size dimorphism. The level of extra-pair paternity was not related to the degree of mutual ornamentation. I argue that these results are compatible with a process of mutual sexual selection, in which both sexes compete for access to mates. The coupled evolution of ornamentation and divorce rate, from the probable ancestral state of a high degree of ornamentation and a low divorce rate, appears to result mainly from a loss of ornamentation under mate fidelity.
Winter residency is characteristic of the majority of cooperatively breeding birds, but the composition and dynamics of winter groups have been examined in relatively few. In 1996-1998, we examined winter territoriality in the western bluebird, a year-round resident that shows a limited degree of helping behaviour in central coastal California, U.S.A. In spring, most western bluebirds breed as socially monogamous pairs, but a small proportion of pairs (3-16%) have additional breeding-age males helping at the nest, usually assisting parents or brothers. We found that year-round residents commonly wintered in family groups that defended territories similar to those used in spring. Winter groups had an even sex ratio and formed early in the autumn, when hatch-year birds dispersed. More females than males left their natal groups to be replaced by an influx of immigrant hatch-year birds. Winter groups typically consisted of breeders and one or two sons from the prior breeding season along with one or more immigrant females. A second period of dispersal occurred in spring when winter groups broke up and most birds other than the breeding pair left the winter territory. When they bred, yearling males and females often bred with unrelated individuals from their winter groups. Sons were more likely to remain on the study area as yearlings when they wintered with both parents than when they wintered with just one parent. We suggest that young males stay the winter due to benefits of remaining in family groups on mistletoe-based winter territories. Subsequent localized dispersal of sons then leads to opportunistic kin-based interactions later in life. Copyright 2001 The Association for the Study of Animal Behaviour.