Male and female shell-brooding cichlids prefer different shell characteristics

In resource defence polygyny, where males defend resources that females use for reproduction, the resource characteristics preferred by the two sexes are expected to match. We tested this expectation by comparing the shell characteristics preferred by males and females in the shell-brooding cichlid fish Lamprologus callipterus. In this species, males attract females by collecting and defending shells within which females breed. We added shells to males' nests and found that females were more likely to occupy large shells but made no distinction between new, smooth shells and old shells coated with mineral deposits. In contrast, when we placed additional shells adjacent to males' nests, males were more likely to retrieve shells covered in mineral deposits but showed no significant preference for large shells over small shells. Furthermore, many shells in males' nests were smaller than the smallest shell that females used for breeding. The discrepancy between male and female preferences suggests that empty shells in L. callipterus nests may have additional functions, beyond serving as breeding substrate. We discuss the possibility that shells may also be extended phenotype signals analogous to the decorations of a bower