MALE GAMETIC STRATEGIES - SPERM SIZE, TESTES SIZE, AND THE ALLOCATION OF 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 pattern of sperm allocation among successive reproductive bouts. All of these variables were measured for each of the four species constituting the nannoptera species group of the Drosophilidae. Extreme interspecific variation was identified for all variables and enigmatic male reproductive strategies, including submaximal insemination of females, partitioning of ejaculate among successive mates, and production of few large sperm, were observed. Variation among species in female remating behavior was found to occur concomitantly with male remating behavior, probably because of female fertility demands. Relationships among testes size, sperm size, sperm numbers, and mating systems in these fruit flies are examined. These relationships are not consistent with patterns identified in studies of vertebrate taxa and suggest fundamental differences between vertebrates and invertebrates with respect to these traits. Hypotheses to explain the maintenance of male ejaculate delivery patterns that are consistent with sperm competition and bet-hedging theory are examined, as are potential selection pressures responsible for sperm-size evolution.