Home‎ > ‎研究内容‎ > ‎大学院セミナー‎ > ‎

Effect of environmental factors on male reproductive investment D-1, Aye Thanda Win

2012/10/25 20:16 に Takashi Matsuo が投稿
2012/10/26

Males of a variety of insect species provide their mates with a nuptial gift during copulation [1]. The size and quality of gift are often dependent on male body size and physiological status [2]. Male body size and status can be affected by environmental factors such as temperature, diet and parasitism. In this seminar, I reviewed the papers related to the effect of environmental factors on male gift size and the consequences of gift size for male and female fitness.

The two important environmental variables, temperature and host species, affected male body size and ejaculate investment. In seed-feeding beetle, Callosobruchus maculates, males reared at lower temperature (20 °C) had larger body size and produced larger ejaculates than males reared at higher temperature (25, 30, 35 °C). Despite producing large ejaculates, males invested less of their body mass in ejaculate at 20 °C but ejaculate size remained constant proportion of their mate’s body mass across temperatures _ the effect of temperature on ejaculate size mirrored the effect of temperature on female body size. Host species also affected male ejaculate size but their effect on ejaculate size relative to male body size was fairly small. The effect of large ejaculate on female fecundity was not found. Because female remate potential is high in this species, the large male gift size is likely to influence his fitness through the reduction of female remating behaviors [3].

Nutritional condition and infection by parasitism can also influence males’ nuptial gift quality and their remate ability [4, 5 & 6]. In Katydids, Gampsocleis gratiosa, nutritionally stressed (low protein and food-deprived) males not only produced smaller gift size but also were less likely to remate than males held on the high-protein diet. Males were unable to maintain their remate frequency by reducing the quality of gift under food stress condition. Thus, decreasing number of sexually active males may result in a sex-role reversal in which females compete for choosy males [5]. In bushcrickets, Poecilimon mariannae, allocation of male investment into the different parts of spermatophore (spermatophylax, ampulla and sperm number) varied with parasitism (tachinid flies). In parasitized males, spermatophylax weight decreased with the level of parasitism in their rematings. Contrary to spermatophylax, sperm number and ampulla weight were reduced in remating not only in parasitized males but also in all males. Physiological costs of males reduce a male’s investment capacity into the spermatophylax but sperm number was unaffected. In this species, an optimal allocation of males into the different parts of the spermatophore was not found [6].

Diapause may cost to males in their investments. In bruchid beetles, Acanthoscelides pallidipennis, females mated to diapause males had longer pre-oviposition period and lower fecundity than females mated to non-diapause males. The depletion of male metabolic reserves during diapause (i.e. physiological constraint) decreased the qualitative or quantitative male investment to females [7].

In conclusion, male physiological status affected by environmental factors caused extra cost to males in their investment, which in turn affects on male and female fitness.



References:

1.    Thornhill R., Alcock J. (1983). The evolution of insect mating systems. Harvard University Press, Cambridge, Mass.
2.    Simmons L.W., Beesley W. J., Lindhjem P., Newbound D., Norris J., Wayne A. (1999). Nuptial feeding by male bushcrickets: an indicator of male quality? Behavioral Ecology10:263-269.
3.    Fox C.W., Stillwell R.C., Wallin W.G., Hitchcock L.J. (2006). Temperature and host species affect nuptial gift size in a seed-feeding beetle. Functional Ecology 20:1003-1011.
4.    Wedell N. (1994).Variation in nuptial gift quality in bush crickets (Orthoptera: Tettigoniidae). Behavioral Ecology 5:418?425.
5.    Jia Z.Y., Jiang Z.G., Sakaluk S.K. (2000). Nutritional condition influences investment by male katydids in nuptial food gifts. Ecological Entomology 25:115?118.
6.    Lehmann G.U.C., Lehmann A.W. (2000). Spermatophore characteristics in bushcrickets vary with parasitism and remating interval. Behavioral Ecology and Sociobiology 47:393?399.
7.    Sadakiyo S., Ishihara M. (2012). Cost of male diapause indirectly affects female reproductive performance. Entomologia Experimentalis et Applicata 143:42-46.

Comments