The Genetic System in Parthenogenetic Strains of Drosophila mercatorum

Abstract

Five parthenogenetic laboratory strains of Drosophila mercatorum have been examined for their mode of diploidization in the eggs of females. Diploidization occurs either by pronuclear duplication leading to complete homozygosity or by nuclear fusion. If the latter occurs between pronuclei from different secondary oocytes, heterozygosity can be maintained. Each of the five strains shows some nuclear fusion and three show significantly different amounts, ranging from about 21% to less than 1%. Even in strains with a strong tendency towards homozygosity, it is argued that this dual system of nuclear reconstitution provides for genetic recombination; thus, the strains retain considerable evolutionary potential.

Spontaneous and hybrid origins of parthenogenesis in Campeloma decisum (freshwater prosobranch snail)

“…Although some sexual females seem capable of parthenogenetic reproduction when males are unavail-253 able (Carson, 1967;Templeton et a!., 1976;Templeton, 1982), modification of gametogenesis without depression of fertility and stable development may be difficult obstacles to overcome during initial stages of parthenogenesis (Moritz et al,1 989a). These genetic constraints may account for the rarity of parthenogenesis.…”

Gynogenesis in Drosophila melanogaster.

“…In Drosophila melanogaster as in most other member of this genus, parthenogenetic reproduction has never been reported (Stalker 1954;Murdy and Carson 1959;Carson 1967). Since syngamy, per se, does not seem a prerequisite at least to early embryogenesis (Zaloker et al 1975;Santamaria and Gans 1980;Santamaria 1983), some sperm factor not contained in the nucleus, may be implicated in egg activation of these obligatory bisexual species.…”

“…This appears quite low, but 'it must be noted that this is a rate comparable to that obtained in rthe natural populations . of Dro, sophila mercatorum, the species in which several parthenogenetically reproducing lines have successfully been established (Carson 1967;Templeton et a1.1976) . An attempt to find the impaternate females that can reproduce gynogenetically has brought about one such line, tentatively named gyn-F9,.…”

Preadaptation for parthenogenetic colony foundation in subterranean termites Reticulitermes spp. (Isoptera: Rhinotermitidae)

“…In the route from tychoparthenogenesis, an increase in the opportunity of successful oviposition by unmated females will be an important condition, because it should select for the capacity of parthenogenetic reproduction. For example, some studies using bisexual Drosophila have shown that the ability of thelytokous reproduction can gradually be improved through selection experiments for unfertilized females that reproduce parthenogenetically (Stalker 1954;Carson 1967;Kramer and Templeton 2001). As in those experiments, replicated occurrence of maleless colony initiation might provide the condition for promoting the ability of parthenogenetic reproduction in R. speratus.…”