MALE GAMETIC STRATEGIES - SPERM SIZE, TESTES SIZE, AND THE ALLOCATIONOF EJACULATE AMONG SUCCESSIVE MATES BY THE SPERM-LIMITED FLY DROSOPHILA-PACHEA AND ITS RELATIVES

The gametic strategy of males comprises the amount of energy invested per sperm, the total amount invested in sperm production, and the patt ern of sperm allocation among successive reproductive bouts. All of th ese variables were measured for each of the four species constituting the nannoptera species group of the Drosophilidae. Extreme interspecif ic variation was identified for all variables and enigmatic male repro ductive strategies, including submaximal insemination of females, part itioning of ejaculate among successive mates, and production of few la rge sperm, were observed. Variation among species in female remating b ehavior was found to occur concomitantly with male remating behavior, probably because of female fertility demands. Relationships among test es size, sperm size, sperm numbers, and mating systems in these fruit flies are examined. These relationships are not consistent with patter ns identified in studies of vertebrate taxa and suggest fundamental di fferences between vertebrates and invertebrates with respect to these traits. Hypotheses to explain the maintenance of male ejaculate delive ry patterns that are consistent with sperm competition and bet-hedging theory are examined, as are potential selection pressures responsible for sperm-size evolution.