Optimal mate choice patterns in pelagic copepods

Abstract

The importance of sexual selection for the evolution, dynamics and adaptation of organisms is well known for many species. However, the topic is rarely studied in marine plankton, the basis of the marine food web. Copepods show behaviors that suggest the existence of sexually selected traits, and recent laboratory experiments identified some selected morphological traits. Here, we use a 'life history-based' model of sex roles to determine the optimal choosiness behavior of male and female copepods for important copepod traits. Copepod females are predicted to be choosy at population densities typically occurring during the main breeding season, whereas males are not. The main drivers of this pattern are population density and the difference in non-receptive periods between males and females. This suggests that male reproductive traits have evolved mainly due to mate competition. The model can easily be parameterized for other planktonic organisms, and be used to plan experiments about sexual selection.

Resource and mate availability, and previous social experience modulate mate choice in the copepods Acartia tonsa and Acartia hudsonica

“…Contrary to what was predicted by a mate-selectivity model for copepods (Heuschele et al, 2013), mate choice was stronger in males than in females for recently matured individuals of both species, and also more affected by encounter time. Males of both species are restricted by the number of times they can mate, since they produce a limited number of spermatophores over their lifetime (Burris, unpublished data) at a low rate (only about 1 spermatophore day −1 ) (Ceballos and Kiørboe, 2010).…”

“…In A. hudsonica, day-3 males and females were the least selective (most willing to mate) (Fig. 1B), which is what is predicted by mate choice models (Hubbell and Johnson, 1987;Crowley et al, 1991;Kokko and Monaghan, 2001;Härdling and Kaitala, 2005;Kokko and Mappes, 2005;Heuschele et al, 2013). Compared with the malechoice frequencies for A. hudsonica, however, two of the three interaction treatments were significantly higher for females.…”

“…Here, the benefits of being selective may no longer exist, as copepods run the risk of not finding a mate, or experience increased costs as they search for another mate (Real, 1990). This inference is supported by numerous models (Hubbell and Johnson, 1987;Crowley et al, 1991;Kokko and Monaghan, 2001;Härdling and Kaitala, 2005;Kokko and Mappes, 2005;Heuschele et al, 2013).…”

“…Since males can only mate about once a day and females remain fertilized for up to ten days (Ceballos and Kiørboe, 2010;Burris and Dam, 2014;Burris, unpublished data), these high densities exceed the mating needs of both sexes and likely allow individuals to be selective when choosing a mate. In contrast, at the beginning and end of the growing season for these populations, densities can be low enough that theoretically a potential mate is encountered only every few days (Heuschele et al, 2013). Here, the benefits of being selective may no longer exist, as copepods run the risk of not finding a mate, or experience increased costs as they search for another mate (Real, 1990).…”

Female-biased sex ratios in marine pelagic copepods: Response to Hirst et al. (2013)

“…Consequently, Hirst et al (2010) has been cited as evidence that predation is the main control of sex ratios in pelagic copepods (e.g. Heuschele & Kiør-boe 2012, Lasley-Rasher & Yen 2012, Heuschele et al 2013. Moreover, the statement in Hirst et al (2013, p. 297) that 'predation being important does not infer a bias towards one sex or the other' is at odds with the conclusions in Hirst et al (2010Hirst et al ( , p. 2193) and the hypothesis advanced previously (Kiørboe 2006 Hirst et al (2010;Limnol Oceanogr 55:2193−2206.…”