Do males prefer unmated females? Male mate choice in the chameleon grasshopper <em>Kosciuscola tristis</em> — ASN Events

Do males prefer unmated females? Male mate choice in the chameleon grasshopper Kosciuscola tristis (#159)

Giselle Muschett 1 , Marie Herberstein 2 , Kate DL Umbers 3
  1. Macquarie University, Gladesville, NSW, Australia
  2. Macquarie University, North Ryde, NSW
  3. University of Western Sydney, Penrith, NSW

Males of many species choose their mate according to a females’ reproductive status. Mated females can differ in their chemical or behavioural cues and these differences provide males with information her status. Most studies report a preference for unmated females but this is reliant on the particular mating system. Males of the chameleon grasshopper Kosciuscola tristis frequently engage in aggressive combat over access to females, a very rarely reported behaviour in grasshoppers. Females have been observed mating multiple times under laboratory conditions, but it is uncertain whether there is sperm transfer in subsequent matings. Studies suggest that under polyandrous systems there should be selective pressure on males to discern a females’ mating status and mate preferentially with unmated females. To test this hypothesis, we ran mate choice experiments where one male chose between a mated and an unmated female in a semi-natural mating arena. We found that males did not discriminate between mated and unmated females and readily started to copulate with either in equal proportions. However, males mated much longer – up to 10 times longer, with unmated females than with mated females. Our results suggest K. tristis females do not significantly change their behaviour nor produce any specific pheromones post-copula that indicate their mating status. As such, males show no pre-copulatory selection mechanism. We speculate there must be post-copulatory selection mechanism in this species and males may be transferring a spermathecal “plug”, preventing any future spermatophore transfer. While research on spermathecal plugs in grasshoppers is limited (Thomas, 2011), Hartman and Loher, (1999) reported that the empty spermatophore of male gomphocerine grasshoppers acts as a temporary plug in the female’s spermathecal duct. Further research is needed to determine whether a similar mechanism is present in K. tristis.