Female fitness is increased by frequent mating in grasshoppers

Abstract

Radiolabeffing experiments with Eyprepocnemis plorans demonstrated that males transfer proteinaceous substances with the ejaculate that are subsequently incorporated into the eggs that the females lay. The amount of male radioactive nutrients detected in the eggs was positively correlated to mating frequency, and the proportion incorporated was almost twice that of egg weight relative to female weight. This might suggest the existence of a specific mechanism selectively incorporating male ejaculate nutrients into the eggs. Another series of experiments with four types of female differing in mating frequency and male availability demonstrated that female production of eggs and embryos is directly proportional to mating frequency. This improvement in female fecundity is from the ejaculate nutrient transfer and both effects are directly dependent on mating frequency. Furthermore, in females crossed sequentially with two different males, there was a significant increase in mating frequency when the female was given the second male. This could be due to an increased mating effort of the second male to displace paternity of the previous male. The low paternity confidence and the polygynandnc mating system that characterize E. plorans suggest that male ejaculate nutrients most likely function as a kind of mating effort rather than paternal investment.

Evidence for B chromosome drive suppression in the grasshopper Eyprepocnemis plorans

“…It is known that males of many insects contribute proteinaceous nutrients with the ejaculate (Markow & Ankney, 1984;Pitnick et al, 1991). We have recently observed transfer of nutrients from ejaculate into eggs of E. plorans using radioactive labelling (Pardo et al, 1995). Interestingly, transfer of nutrients from ejaculate was low in eggs from pods laid promptly after mating but high in subsequent pods, which clearly supports the existence of a minimum time for male effects on female meiotic segregation.…”

Somatic condition determines female mating frequency in a field population of the grasshopper Eyprepocnemis plorans

“…Because females obtain ejaculate nutrients from males, they are prone to mate frequently because this increases their fitness through improving the rate of egg production (Pardo et at., 1995a). It would become advantageous for females to cheat males by simulating the signals that males use for mate choice.…”

“…In the Orthoptera, courtship feeding may be performed by means of external (Tettigonioidea) (Gwynne, 1984) or internal (Acridoidea) (Friedel & Gillot, 1977;Butlin et a!., 1987) spermatophores. In E. plorans, we have shown recently that males transfer proteinaceous substances in the ejaculate, and that these are incorporated into the eggs which the female subsequently lays, which explains why the rates of egg and embryo production are directly dependent of mating frequency (Pardo et al, 1995a).…”

“…As female fitness increases with mating frequency in E. plorans (Pardo et at., 1995a) There are few examples of sexual selection in females, and all of them are related to cases of sex role reversal (Arnold, 1994). Could E. plorans be another species with sex role reversal?…”

“…Males incorporate proteinaceous nutrients into the ejaculate that passes to the female's body and these are incorporated into the eggs she subsequently lays, with a consequent increase in egg and embryo production (Pardo et al, 1995a).…”