Sex differences in territorial defense in a shell-breeding cichlid, Neolamprologus multifasciatus

Abstract

Most studies of territorial defense focus on responses of either male or female residents but not both. In a laboratory study of Neolamprologus multifasciatus, a territorial, shell-inhabiting cichlid from Lake Tanganyika, we altered the distribution of shells to manipulate defense costs and examined resident pairs’ behavioral responses to intruders. Given that defense costs are lower when territories are separated by visually distinctive structures, we used the presence/absence of a buffer zone, an area of bare sand, to alter defense costs. With a buffer zone, males and females invested 10.4 and 5.4 % of their time in defense, respectively. Without a buffer zone, males increased time in defense (30.1 %) more than did females (6.6 %). Females rarely performed highly aggressive acts; males performed such acts more frequently against male intruders than against female intruders and when there was no buffer zone. Overall, intrasexual aggression was more frequent, and males interacted with a greater proportion of same-sex intruders (71.6 %) than did females (33.4 %). Without a buffer zone, the proportion of intruders with which the males interacted increased with the number of intrusions. This was not the case for females or for either sex when a buffer zone was present. These findings show that males and females responded differently to changes in shell distribution. We interpret this finding as a sex difference in response to altered defense costs. The stronger tendency of males to intrude when a buffer zone was absent indicates that the shell-free area between territories may have acted as a visual landmark that reduced intrusions by neighboring territory holders.