The Persistence of Facultative Parthenogenesis in Drosophila albomicans

Abstract

Parthenogenesis has evolved independently in more than 10 Drosophila species. Most cases are tychoparthenogenesis, which is occasional or accidental parthenogenesis in normally bisexual species with a low hatching rate of eggs produced by virgin females; this form is presumed to be an early stage of parthenogenesis. To address how parthenogenesis and sexual reproduction coexist in Drosophila populations, we investigated several reproductive traits, including the fertility, parthenogenetic capability, diploidization mechanisms, and mating propensity of parthenogenetic D. albomicans. The fertility of mated parthenogenetic females was significantly higher than that of virgin females. The mated females could still produce parthenogenetic offspring but predominantly produced offspring by sexual reproduction. Both mated parthenogenetic females and their parthenogenetic-sexual descendants were capable of parthenogenesis. The alleles responsible for parthenogenesis can be propagated through both parthenogenesis and sexual reproduction. As diploidy is restored predominantly by gamete duplication, heterozygosity would be very low in parthenogenetic individuals. Hence, genetic variation in parthenogenetic genomes would result from sexual reproduction. The mating propensity of females after more than 20 years of isolation from males was decreased. If mutations reducing mating propensities could occur under male-limited conditions in natural populations, decreased mating propensity might accelerate tychoparthenogenesis through a positive feedback mechanism. This process provides an opportunity for the evolution of obligate parthenogenesis. Therefore, the persistence of facultative parthenogenesis may be an adaptive reproductive strategy in Drosophila when a few founders colonize a new niche or when small populations are distributed at the edge of a species' range, consistent with models of geographical parthenogenesis.

The fitness effects of delayed switching to sex in a facultatively asexual insect

“…Our finding that a solely parthenogenetic strategy conferred lower fitness than a solely sexual one is consistent with previous studies on other facultative systems. In many facultatively parthenogenetic insects, parthenogenesis results in lower reproductive performance compared to sex, manifesting as depressed fecundity (Chang et al., ), poor offspring viability (Corley & Moore, ), and/or reduced offspring lifespan (Kramer & Templeton, ). S. larryi appears to be no different in this regard, with parthenogenetically produced offspring performing less successfully than sexually produced offspring.…”

“…Several empirical studies have compared sexual and asexual reproductive performance in internally fertilized facultative systems (e.g., Chang et al., ; Corley & Moore, ; Matsuura & Kobayashi, ). However, explicit assessments of the costs and benefits of switching to sex are scant.…”

Switch from sexual to parthenogenetic reproduction in a zebra shark

“…Sexual reproductive competency of parthenogenetic offspring has not yet been demonstrated in vertebrates though it has been recorded from other organisms (e.g. Drosophila 31). …”

Parthenogenesis and developmental constraints

“…Cycling parthenogenesis, in which several generations of sexually reproduced offspring from fertilized eggs alternate with asexually reproduced offspring from unfertilized eggs is also common and occurs in over 15,000 species (Riparbelli, Gottardo, & Callaini, 2017). It occurs in a wide range of taxa including ostracods, snails, aphids, insects, fishes, amphibians, reptiles, and birds and is generally associated with a vastly lower reproductive success than sexual or obligate parthenogenetic reproduction (e.g., Bell, 1982;Chang, Ting, Chang, Fang, & Chang, 2014;Murdy & Carson, 1959;Olsen, 1974;Seiler & Schaffer, 1960;Sprackling, 1960,). Some taxa are both cycling parthenogens and haplodiploids, for example, monogodont rotifers and gall wasps.…”

“…In chickens and turkeys ploidy restoration in sporadic parthenogenesis is also extremely unsuccessful (Cassar et al, 1998;Olsen, 1974). After long periods of intense selection for parthenogenetic capacity in Drosophila, chickens and turkeys, reproductive success significantly improves, but stays nonetheless dramatically low, for example, 6% of viable offspring from hatched eggs in D. albomicans after 20 years of selection and after 12 years 0.25% of viable male adult turkeys produced parthenogenetically, with some able to sire offspring (Chang et al, 2014;Olsen, 1965). After long periods of intense selection for parthenogenetic capacity in Drosophila, chickens and turkeys, reproductive success significantly improves, but stays nonetheless dramatically low, for example, 6% of viable offspring from hatched eggs in D. albomicans after 20 years of selection and after 12 years 0.25% of viable male adult turkeys produced parthenogenetically, with some able to sire offspring (Chang et al, 2014;Olsen, 1965).…”