Sexual dimorphism in the buccal cavity of paternal mouthbrooding cardinalfishes (Pisces: Apogonidae)

Abstract

The mechanical basis of mouthbrooding in the coral reef cardinalfish (family Apogonidae) has yet to be established. Sexual dimorphism in the anatomy of the oral jaws and buccal cavity of seven species of paternal mouthbrooding apogonids was therefore investigated. A novel silicon injecting technique was used to quantify between sexes differences in size and shape of the buccal cavity. Osteological and morphological measurements were also examined to identify the structural features associated with variation in buccal volumes. Males buccal volumes were proportionally larger by 20–42% in five of the seven species (P<0.01), a change that was largely a result of an increase in the depth of buccal cavity. Absence of distinct osteological differences between sexes suggests that changes in the soft anatomy are primarily responsible for the increased buccal volume in males. The average increase of 31% in buccal volume of males appears to reflect their role in mouthbrooding. This is the first study to demonstrate sexual dimorphism of the buccal cavity of multiple mouthbrooding species.