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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
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