I study the evolution of mating systems, using mainly bushcrickets as model system, focussing on

• Evolution of mate choice

• Functional aspects of nuptial feeding

• Evolution of sexual signals under antagonistic parasitoid pressure

Study organisms

Xederra charactus male marked for experiment (used for Lehmann 2007)

The tiny australian Kawanaphila mirla - a green male (see Lehmann and Lehmann 2007)

Mate choice

Animals of most species do not mate indiscriminately but prefer some partners over others. Mate choice is an important evolutionary process that imposes sexual selection on the opposite sex. The resulting sexual selection can be a strong force in shaping characters and behaviors.

The reproductive behavior of bushcrickets show a diversity of ways in which individuals compete for and select mates. Under high-quality and abundant food, males of the Australian bushcricket Kawanaphila mirla have a much shorter "time-out" from mating than females (Lehmann and Lehmann 2007). This male-biased OSR lead to mating competition in males and choosiness in females.

In Poecilimon zimmeri females exhibit clear choice for the heavier male (Lehmann and Lehmann 2008a), which transfer larger spermatophores (Lehmann and Lehmann 2009).

Mate choice under different population densities showed that sampling and mate choice is altered under environmental influences (Lehmann 2007). Under low density conditions less mates were met and were less likely rejected during copulation attempts than mates under high population conditions.

Nuptial gifts

In bushcrickets, males transfer a nuptial gift during mating. This spermatophore works as sperm protection device and at least sometimes as parental investment. Ingredients in the spermatophore are incorporated into the somatic tissue by females (Voigt et al. 2006) and fuel the female metabolism (Voigt et al. 2008).

Heavier males of Poecilimon zimmeri transfer larger spermatophores (Lehmann and Lehmann 2009) and females exhibit clear choice for heavier males in mating trials (Lehmann and Lehmann 2008a). Such preferences for heavier males reflects a female's preference for a larger spermatophore and therefore for a greater direct benefit.

In line with the hypothesis that spermatophore production is costly, we found that spermatophylax weight was reduced in parasitized bushcricket males (Lehmann and Lehmann 2000a). Parasitized males with a smaller spermatophylax induced a reduced refractory period in females. During this shortened period fewer eggs were deposited, as an effect of the shorter refractory period, whereas the daily egg-laying rate remained the same (Lehmann and Lehmann 2000b).

Parasitoid flies - Ormiini

Tachinid flies of the tribe Ormiini possess a conspicuously inflated prosternal region, enabling them to detect the mating songs of their hosts. The only European Ormiini representative, Therobia leonidei, attacks the singing sex of three different families of bushcrickets (Lehmann 2003, Lehmann 2008). In populations of the Greek phaneropterine bushcricket Poecilimon mariannae males, which produce long calls, were found to be parasitized in large proportions. In contrast, Poecilimon veluchianus produces short calls and is less parasitized (Lehmann and Heller 1998), proving that longer songs are easier to detect. Moreover, male calls that are more attractive to females are also more attractive to parasitoid flies (Lehmann et al. 2001), suggesting a trade-off between sexual and natural selection.

These flies lay their larvae on or near males; the larvae burrow into the cricket’s body, feed on the tissue and kill the animal upon emergence (Lehmann 2006). Developing fly larvae reduce male bushcricket survival and reproductive effort (Lehmann and Lehmann 2000a, 2000b). Parasitized males loose 42% of their potential lifetime reproductive success (PLRS) compared to nonparasitized males. This fitness loss is context dependent; if nonparasitoid related mortality is high, the selection on host males to avoid parasitism is weak (Lehmann and Lehmann 2006).

Parthenogenesis- regression, vestigialization

Unisexual reproduction is a rare but widespread phenomenon in invertebrates and lower vertebrates. This holds true even for bushcrickets, were only few cases of obligate dipoloid parthenogeny are known (Lehmann et al. 2010b). Traits under relaxed selection are expected to become reduced or disappear completely, a process called vestigialization The bushcricket Poecilimon intermedius is one of the few insect species with obligate but diploid parthenogenetic reproduction.