Genetic analysis of two distinct reproductive strategies in sexual and asexual field populations of an endoparasitic wasp, Venturia canescens

Abstract

Asexual (thelytokous) females of the parasitoid Venturia canescens, which develop inside another insect, exhibit evolutionarily stable mixtures of life-history strategies, allowing two genetically distinct wasp lines to coexist sympatrically on the same host resources. Since the two asexual lines differ in a virus-like particle protein-coding gene (VLP1), the question is whether the VLP1 gene is genetically associated with the phenotype. The recent isolation of facultative sexual (arrhenotokous) and asexual V. canescens strains from the same location in Southern France has enabled an investigation of the genetic basis for the observed phenotypic differences, by comparing the two asexual lines with the corresponding homozygous VLP1 genotypes in arrhenotokous strains. This analysis showed similar patterns of morphological and functional differences exist in the ovaries of the two asexual VLP1 lines and in the two homozygous VLP1 genotypes from the field, suggesting that the VLP1 gene alteration either causes the ovarian phenotype or is genetically closely linked to the putative gene. However, the VLP1-gene may not be the only gene contributing to the phenotypic effects observed in the asexual lines. Although the two VLP1-alleles segregate with the relative differences in the ovary distribution of eggs, the absolute egg numbers differ in the corresponding asexual and sexual genotypes. This suggests that an additional unlinked gene may be involved in the transfer of eggs from the ovarioles into the oviduct.

The influence of temperature and host availability on the host exploitation strategies of sexual and asexual parasitic wasps of the same species

“…Previous knowledge on the life history of the thelytokous and arrhenotokous V. canescens is also consistent with this hypothesis. For instance, the larger egg complement and number of ovarioles in thelytokous females than in arrhenotokous females (Li et al 2003; suggest that thelytokous females would benefit to a greater extent from high host availabilities, such as those in granaries and mills (Papaj 2000). Other differences in patch exploitation behaviour between arrhenotokous and thelytokous females were found by Thiel et al (in press).…”

“…The sampling procedure does not allow one to estimate the original number of females that attacked the hosts in the pieces of cardboard, but the number of sampling points and their distance apart ensure an adequate number of foundress females. As Beck et al (1999Beck et al ( , 2001 and Li et al (2003) suggested that a deletion in the sequence encoding a virus-like particle protein has pleiotropic effects on the reproductive biology of V. canescens, only wasps carrying the wild-type allele (called RP by Hellers et al 1996) were used. However, it has subsequently been shown that the strain used in this experiment displays no such pleiotropic effects on reproductive biology (Amat et al 2003).…”

A single locus determines thelytokous parthenogenesis of laying honeybee workers (Apis mellifera capensis)

“…Schneider et al (2003) detected gene flow between arrhenotokous and thelytokous populations in the laboratory. It could be shown that there is a genetic basis for the thelytoky in V. canescens (Li et al, 2003).…”

An empirical model of the sympatric coexistence of two strains of the endoparasitoid wasp Venturia canescens

“…Furthermore, investigations of natural populations from several locations have revealed that wasps displaying similar clusters of phenotypic traits to both laboratory lines occur in the field and can be collected from the same locations (Li et al, 2003;Amat et al, 2003).…”

“…France, using the VLP1 gene as a marker, found that wasps displaying phenotypic clusters qualitatively similar to the laboratory RM-and RP-lines co-occur in natural populations (Li et al, 2003).…”