Sexual harassment in a live-bearing fish (Poecilia mexicana): influence of population-specific male mating behaviour

Abstract

We investigated male sexual behaviour and the cost of sexual harassment, as measured by the reduction of female feeding time in the presence of a male, in a cavedwelling population of Poecilia mexicana, in which sexual harassment does not occur naturally. We asked whether the lack of sexual harassment in this population is due to low sexual activity of the males, or low feeding motivation of the females. We experimentally increased the sexual activity of males or the females' feeding motivation, or we used a combination of both treatments. Female feeding time was not lower in the presence of a male than in the presence of a female after sexual deprivation of the males or food deprivation of the females. Only in the combined experiment was female feeding time lower in the presence of a large male than in the presence of a small male, indicating a weak effect of sexual harassment by large males. Virgin females did not suffer a cost of sexual harassment, indicating that sexual experience does not cause the lack of sexual harassment in cave mollies. Males from a surface population, where sexual harassment occurs, significantly reduced the feeding time of cavedwelling females even though these males exhibited surprisingly little sexual behaviour. The sexual activity of cave mollies did not correlate with male body size in any experiment, indicating that even after sexual deprivation, small cave molly males do not switch to the "alternative" mating behaviour known in surface-dwelling P. mexicana, where sexual activity is correlated negatively with male body size.

Influence of male competition on male mating behaviour in the cave molly, Poecilia mexicana

“…A recent study has shown that even cave molly males with increased sexual motivation (after being isolated from females for 7-10 days) do not show the size-dependent pattern of sexual behaviour that is known in surface-dwelling males, although they strongly increase their sexual activity (Plath et al 2004b). This further supports the idea that sizedependent mating behaviour is genetically fixed in the cave molly.…”

Size-dependent male mating behaviour and sexual harassment in a population of Atlantic mollies (Poecilia mexicana) from a sulphur creek

“…At least in the case of nipping behaviour, male body size and the number of sexual behaviours were negatively correlated in this experiment. Such conditional use of size-dependent male mating behaviour was not found in the cave molly, where the genetic basis of this pattern is probably lost (Plath et al 2004b). Apparently, the El Azufre population has an intermediate status between the cave and the nearest clear-water (Río Oxolotan) population.…”

“…We examined whether cave mollies show size-dependent mating behaviour when they increase their sexual activity after sexual deprivation (Plath et al 2004b). However, no correlation between male size and the frequency of male sexual behaviours was found even when cave molly males showed increased sexual behaviour after sexual deprivation (Plath et al 2004b). The genetic basis for typical size-dependent male mating behaviour is probably lacking in the cave population.…”

“…Another question of this study relates to the costs of male sexual harassment for females (Magurran and Seghers 1994;Plath et al 2003Plath et al , 2004b. In a population from a clear-water river, the Río Oxolotan, females suffer a cost of male sexual harassment, which was determined as reduced feeding rates in the presence of a male sexually interacting with the female compared with the feeding time in the presence of another female (Plath et al 2003).…”

“…The experimental design of the behaviour tests followed Schlupp et al (2001) and Plath et al (2003Plath et al ( , 2004b. A food tablet as feeding source was attached to a small Petri dish and placed in the centre of a test aquarium (49×24×24 cm).…”