Home‎ > ‎研究内容‎ > ‎大学院セミナー‎ > ‎

Operational Sex-ratio and Male Reproductive Investment, D-3, Aye Thanda Win

2014/10/19 20:27 に ユーザー不明 が投稿

        The operational sex-ratio (OSR) - the ratio of sexually receptive males and females” has profound effect on male reproductive investment and female fitness through intra- and inter-sexual competition [1].

        The biased OSR may affect some aspects of male pre-copulatory courtship behaviors [2, 3].  For example, in the housefly, Musca domestica, males courted females more at a male-biased OSR (2M: 1F, and 5M: 1F) than in unbiased OSR (1M: 1F), but courtship duration was not significantly different among OSR treatments and male-male interaction was similar between (2M: 1F and 5M: 1F) treatments [2].  In contrast, in the African butterfly, Bicyclus anynana, males courted females less in male-biased OSR (2M: 1F) than in unbiased OSR (1M: 1F) and female-biased OSR (1M: 2F).  Moreover, males flew more than females when in ((1M: 1F) but not in either (1M: 2F) or (2M: 1F).  However, males and females had similar rate of walking and fluttering behaviors [3]. 

        The biased OSR may also influence male post-copulatory reproductive investment (e.g. copulation duration and sperm number) [4, 5, 6].  Males Mediterranean flour moth, Ephestia kuehniella, produced more sperm when in the presence of rivals (RM) than in additional females (AF).  This result suggests that males should save sperm for future copulations when additional females are present and produce more sperm in response to sperm competition when rival males are present [4].  In contrast, males Drosophila pseudoobscura increased copulation duration and the transfer of fertilizing (eusperm) sperm but not non-fertilizing (parasperm) sperm when exposure to rival males.  This finding supports that parasperm in flies was not driven by sperm competition [5].  However, male domestic crickets (Acheta domesticus) did not change transferred sperm number based on sperm competition risk when perceived rival one to two rival males [6]. 

        The ability of males respond to the presence of rival may be influenced by the number of rivals, conspecific or heterospecific rivals, male age, etc. [5, 7].  In D. pseudoobscura, males did not increase their mating duration when males were exposed to a heterospecific male [5].  When increasing the number of rivals above 1, no detectable effect was found in D. melanogaster.  Additionally, age at which males were exposed to rivals did not affect their ability to respond to rivals [7]. 

        The biased OSR may affect reproductive fitness of female through changes in male ejaculate investment [2, 4, 5].  In M. domestica, females laid more eggs at male biased OSR (2M:1F and 5M:1F) treatments than in unbiased OSR (1M:1F) [2].  Similarly, in D. pseudoobscura, males exposed to rivals also achieved higher offspring production [5].  Contrary to above findings, males Mediterranean flour moth in the presence of rivals inseminated fewer females and produced fewer offspring [4].

        When in the presence of sexual competitors, males change their behavior and reproductive investment, suggesting that they can detect the presence of a competitor. The senses (e.g. visual, acoustic, olfactory cues and physical contact) may involve in the assessment of a competitor.




1.)    Weir L.K.,Grant J.W.A., Hutchings J.A. 2011. The influence of operational sex ratio on the intensity of competition for mates. Am. Nat. 177: 167-176.

2.)    Carrillo J., Danielson-Francois A., Siemann E., Meffert L. 2011. Male-biased sex ratio increase female egg laying and fitness in the housefly, Musca domestica. J Ethol doi10.1007/s10164-011-0317-6.

3.)    Westerman E.L., Drucker C. B., Monteiro A. 2014. Male and female mating behavior is dependent on social context in the butterfly Bicyclus anynana. J Insect Behav (27): 478-495.

4.)    Xu J., Wang Q. 2014. Ejaculate economics: an experimental test in a moth. Biol Lett (10): 20131031.

5.)    PriceT. A. R., Lize A., Marcello M., Bretman A. 2012. Experience of mating rivals causes males to modulate sperm transfer in the fly Drosophila pseudoobscura. J Insect Physiol (58): 1669 – 1675.

6.)    Worthington A. M., Gress B. E., Neyer A. A., Kelly C. D 2013. Do male crickets strategically adjust

the number and viability of their sperm under sperm competition? Anim Behav. http://dx.doi.org/10.1016/j.anbehav.2013.04.010.

7.)    Bretman A., Fricke C., Hetherington P., Stone R., Chapman T. 2010. Exposure to rivals and plastic responses to sperm competition in Drosophila melanogaster. Behav Ecol doi: 10.1093/beheco/arp 189.