Zoological Studies

Vol. 51 No. 5, 2012

Sex Ratio and Mating Behavior in the Calanoid Copepod Pseudodiaptomus annandalei

Gaël Dur1,2,3,4,6, Sami Souissi2,3,4, François G. Schmitt2,3,4, Shin-Hong Cheng5, and Jiang-Shiou Hwang1,*

1Institute of Marine Biology, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung 202, Taiwan
2Université Lille Nord de France, Lille F-59000, France
3Université des Sciences et Technologies de Lille, LOG, Wimereux F-62930, France
4Centre national de la recherche scientifique, UMR 8187, Wimereux F-62930, France
5Tungkang Biotechnology Research Center, Fisheries Research Institute, Council of Agriculture, 67 Fongyu St., Tungkang, Pingtung 928, Taiwan
6Department of Ecosystem Study, School of Environmental Science, University of Shiga Prefecture, 2500 Hassaka-cho, Hikone-city, Shiga Prefecture 522-8533, Japan

Gaël Dur, Sami Souissi, François G. Schmitt, Shin-Hong Cheng, and Jiang-Shiou Hwang (2012) Information on mating is one of the primary requirements for successful population maintenance of copepods.  Several studies on copepod mating were conducted, but none has ever investigated the effect of the sex ratio.  Using optical systems, this study examined the plasticity of encounters, the rejection rate, and the mate guarding duration as a function of the sex ratio in the little known tropical species Pseudodiaptomus annandalei, that lives in aquaculture ponds in southern Taiwan.  Our study results exhibited strong variability that may have obscured the effect of the sex ratio.  Nevertheless some patterns did emerge.  The number of encounters, very low with a highly male-biased sex ratio, increased as the sex ratio became more balanced.  After reaching a maximum with an even sex ratio, it decreased again as the sex ratio became more female-biased.  The male rejection rate exhibited a similar trend, higher for an even sex ratio and decreasing with a more-unbalanced sex ratio, except for a strongly female-biased sex ratio.  The rejection rate was associated with the number of encounters in four of the 5 tested conditions.  Females exhibited stronger choosiness when encounters were higher and relaxation when encounters were low.  However, under female-biased sex ratio conditions, despite a lower encounter rate, females were very selective.  This result is in agreement with theoretical models that predict a possible slackening of mate selection when encounters are mate limited.  Although the sex ratio is supposed to induce a modification in mate guarding, no differences were found here.  This pioneer study should lead to interesting debates and new insights on the effects of the sex ratio on copepod behavior. 

Key words: Pre-copulatory behavior, Mate selection, Calanoid copepod, Pseudodiaptomus annandalei.

*Correspondence: Tel: 886-935289642.  Fax: 886-2-24629464.  E-mail:jshwang@ntou.edu.tw