Effects of Parthenogenesis and Geographic Isolation on Female Sexual Traits in a Parasitoid Wasp

Abstract

Population divergence in sexual traits is affected by different selection pressures, depending on the mode of reproduction. In allopatric sexual populations, aspects of sexual behavior may diverge due to sexual selection. In parthenogenetic populations, loss-of-function mutations in genes involved in sexual functionality may be selectively neutral or favored by selection. We assess to what extent these processes have contributed to divergence in female sexual traits in the parasitoid wasp Leptopilina clavipes in which some populations are infected with parthenogenesis-inducing Wolbachia bacteria. We find evidence consistent with both hypotheses. Both arrhenotokous males and males derived from thelytokous strains preferred to court females from their own population. This suggests that these populations had already evolved population-specific mating preferences when the latter became parthenogenetic. Thelytokous females did not store sperm efficiently and fertilized very few of their eggs. The nonfertility of thelytokous females was due to mutations in the wasp genome, which must be an effect of mutation accumulation under thelytoky. Divergence in female sexual traits of these two allopatric populations has thus been molded by different forces: independent male/female coevolution while both populations were still sexual, followed by female-only evolution after one population switched to parthenogenesis. K E Y W O R D S :Attractiveness, geographic isolation, Leptopilina clavipes, sperm storage, thelytoky, Wolbachia.

Decay of sexual trait genes in an asexual parasitoid wasp

“…Asexual lineages of this species have degenerated spermathecae (Kraaijeveld et al 2009) and reduced male fertility (Pannebakker et al 2005). The spermatheca-specific and testis-specific genes identified as carrying deleterious mutations thus represent candidates underlying these degenerated phenotypes.…”

“…Spermathecae in asexual L. clavipes are heavily degraded and non-functional (Kraaijeveld et al 2009). Males derived by curing asexual mothers from Wolbachia infection are still fertile—albeit to a reduced degree (Pannebakker et al 2005).…”

“…Isofemale lineages of L. clavipes were maintained at Leiden University (The Netherlands) as described previously (Kraaijeveld et al 2009). Three females were used to initiate each subsequent generation for at least 65 generations, thus likely resulting in high inbreeding levels in these isofemale lineages.…”

“…The parasitoid wasp Leptopilina clavipes provides a promising study species in which to address this issue. L. clavipes features both sexual and asexual reproducing lineages and its asexual lineages have decayed female-specific as well as male-specific traits (Pannebakker et al 2005; Kraaijeveld et al 2009). …”

Genetics of decayed sexual traits in a parasitoid wasp with endosymbiont-induced asexuality

“…In particular, many traits are expected to decay following a transition from sexual to asexual reproduction, making this transition of special interest for studies of trait decay and the genetic causes thereof (for example, Carson et al , 1982; Pannebakker et al , 2004a; Jeong and Stouthamer, 2005; Kraaijeveld et al , 2009; Russell and Stouthamer, 2011; Schwander et al , 2013). For example, any trait specific to the male sex is useless under asexual reproduction in all-female species.…”