Life-History Changes That Accompany the Transition From Sexual to Parthenogenetic Reproduction in Drosophila Mercatorum

Abstract

Abstract. In spite of the predicted genetic and ecological costs of sex, most natural populations maintain sexual reproduction, even those capable of facultative parthenogenesis. Unfertilized eggs from natural populations of Drosophila mercatorum occasionally develop into viable adults, but obligately parthenogenetic populations are unknown in this species. To evaluate the microevolutionary forces that both favor and constrain the evolution of parthenogenesis in D. mercatorum, we have measured parthenogenetic rates across a natural, sexually reproducing population and characterized the life-history changes that accompany the transition from sexual to parthenogenetic reproduction in laboratory strains. A highly significant difference in parthenogenetic rate was found between two populations in close geographic proximity, with increased rate found with lower population density. Laboratory strains of parthenogenetic females suffered increased mortality and reduced egg viability relative to their virgin counterparts from a sexual strain. Lifetime egg production was similar across all strains, but a shift in peak egg production to an earlier age also occurred. The combination of these life-history traits resulted in a higher net reproductive value for sexual females, but because they also had a longer generation time, intrinsic rate of increase was not as dramatically different from parthenogenetic females. In environments with high early mortality, there may be no fitness disadvantage to parthenogenesis, but the predicted ecological advantage of a twofold increase in intrinsic rate of increase was not realized. These results support the theory of Stalker (1956) that parthenogenesis is favored in environments in which sexual reproduction is difficult or impossible.

Using Parthenogenetic Lineages to Identify Advantages of Sex

“…In fact, the observation that meiotic parthenogenesis is often associated with low hatching success or juvenile survival (Templeton 1982;Schwander et al 2010) might provide indirect support for the possibility that this type of parthenogenesis facilitates mutational clearance. While these patterns likely stem from homozygosity at recessive deleterious alleles, incompatible epistasis effects, and other mechanisms underlying inbreeding depression (Templeton 1982;Kramer and Templeton 2001;Schwander et al 2010), they also reveal the potential for selection to remove deleterious mutations in these lineages in a manner analogous to the purging of mutational load that can be a consequence of inbreeding depression.…”

Effects of temperature and maternal and grandmaternal age on wing shape in parthenogenetic Drosophila mercatorum

“…We used two different parthenogenetic strains of Drosophila mercatorum: Iv-23-o-Im isolated from a sexually reproducing population in 1990 (Kramer and Templeton, 2001) hereafter referred to as strain 1, and strain 2 which was founded in a Brazilian laboratory (Ezio Mattioli, pers. comm.).…”

Consequences of outbreeding on phenotypic plasticity in Drosophila mercatorum wings

“…The first of the parthenogenetic strains is Iv-23-olm, isolated from a sexual population in Hawaii in 1990 (Kramer and Templeton 2001) and will hereafter be referred to as strain 1. The second is Brazil 1 from Faurby et al (2005) which will be referred to as strain 2.…”