Post-copulatory mate guarding in decorated crickets

Abstract

Although post-copulatory mate guarding occurs in a variety of crickets, its adaptive significance remains largely unknown. Mate guarding may function to prevent females from prematurely removing the externally attached sperm ampulla, thereby ensuring maximum insemination. This hypothesis was tested in decorated crickets, Gryllodes supplicans, by comparing ampulla retention times of females guarded by their mates with those of unguarded females. There was no difference in ampulla attachment duration between the two groups, thus falsifying the ‘ampulla-retention assurance’ hypothesis. Two additional hypotheses related to the function of mate guarding were also tested: (1) mate guarding allows a male to remain in close proximity to his mate during the time it takes to produce a new spermatophore and (2) guarding functions to deter rivals from courting the recently mated female. The ‘spermatophore renewal’ hypothesis was rejected because the average inter-copulatory interval of males greatly exceeded the average guarding duration. The ‘courtship reduction’ hypothesis was supported by four lines of evidence: (1) guarded females were less likely to be courted by intruders than were females whose mates had been removed, (2) unguarded females mounted intruders significantly more often than guarded females, (3) the ampullae of unguarded females were more likely to be partially dislodged by the copulatory attempts of intruding males than were those of guarded females, and (4) guarded females were more likely to be maximally inseminated than were unguarded females.