Despite the wide prevalence of alternative reproductive tactics, little attention has been paid to why reproductively parasitic males are so small. In this study, we tackled this issue in a shell-brooding fish Lamprologus callipterus. Sneaky ‘dwarf males’ of this fish remain much smaller than bourgeois conspecifics throughout their life and employ a unique parasitic tactic, i.e. entering into a gastropod shell where a female is spawning, passing through the space between the female and shell wall and staying behind her to ejaculate throughout the spawning event. Here, we tested the prediction that they remain small to get past her through the shell spaces by interpopulation comparison. We showed, across populations, a negative allometry for sexual size dimorphism, an exponential increase of female size with an increase in shell size and a negative correlation between the magnitude of sexual size dimorphism and shell size. These results suggest that the inner spaces strongly regulate dwarf male size. We conclude that the small bodies of dwarf males arise from adaptation to their unique reproductive behaviour.
Alternative reproductive tactics Shell size availability Sexual size allometry Size limitation
This is a preview of subscription content, log in to check access.
We thank the Japanese Research Team for all their help, and Michael Taborsky, Stefan Walker, Wolf U. Blanckenhorn and two anonymous reviewers for their valuable comments on an earlier draft of the manuscript. This work was supported partly by a Research Fellowship from JSPS for Young Scientists to K.O., an Overseas Scientific Research grant to M.K. and a Global COE program (MEXT).
Svensson O, Kvarnemo C (2007) Parasitic spawning in sand gobies: an experimental assessment of nest-opening size, sneaker male cues, paternity, and filial cannibalism. Behav Ecol 18:410–441. doi:10.1093/beheco/arl098CrossRefGoogle Scholar
Taborsky M (2001) The evolution of bourgeois, parasitic, and cooperative reproductive behaviors in fishes. J Hered 92:100–110CrossRefPubMedGoogle Scholar