Abstract
BackgroundFacultative parthenogenesis, seen in many animal phyla, is a reproductive strategy in which females are able to generate offspring when mating partners are unavailable. In some subsocial and eusocial insects, parthenogenesis is often more prevalent than sexual reproduction. However, little is known about how social cooperation is linked to the promotion of parthenogenesis. The domiciliary cockroach Periplaneta americana is well-suited to addressing this issue as this species belongs to the superfamily Blattoidea, which diverged into eusocial termites and shows facultative parthenogenesis.ResultsWe studied environmental factors that influence asexual production of ootheca using behavioral assays in P. americana. When more than three virgin females immediately after the imaginal molt were kept together in a small sealed container, they tended to produce egg cases (oothecae) via parthenogenesis earlier than did isolated females, resulting in apparent synchronization of ootheca production, even among females housed in different containers. In contrast, virgin females housed with genitalia-ablated males or group-housed females with antennae ablated did not significantly promote ootheca production compared to isolated females. Daily addition of the primary sex pheromone component to the container did not promote ootheca production in isolated females. Another line of study showed that grouped females make parthenogenesis more sustainable than previously known; a founder colony of 15 virgin females was sufficient to produce female progeny for a period of more than three years.ConclusionsGroup-housed females promote and stabilize asexual ootheca production compared to isolated females, and that this promotion is triggered by female-specific chemosensory signals (other than sex pheromone) primarily detected by antennae. Promotion of ootheca production between females is likely to be an early stage of social cooperation, reminiscent of the foundation and maintenance of a colony by female pairs in the eusocial termite Reticulitermes speratus.
Highlights
Facultative parthenogenesis, seen in many animal phyla, is a reproductive strategy in which females are able to generate offspring when mating partners are unavailable
Our results show that grouping of females promotes ootheca production, suggesting that this is an early stage of social cooperation, preadaptive to more prevalent parthenogenesis
Ootheca production in isolated females and paired female-male The virgin females isolated immediately after the imaginal molt produced the first ootheca via parthenogenesis at 13.2 ± 4.7 days (Figs. 1c and 2a, Table 1), which was not significantly different from that in mated females (10.5 ± 2.5 days, Figs. 1b and 2a, Table 1)
Summary
Facultative parthenogenesis, seen in many animal phyla, is a reproductive strategy in which females are able to generate offspring when mating partners are unavailable. Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male This occurs in many animal phyla, from rotifiers, nematodes and arthropods. Since most animals that show obligatory parthenogenesis occupy the terminal nodes of phylogenetic trees, the evolutional origin of parthenogenesis could be attributed to the acquisition of a switching mechanism from sexual reproduction to facultative parthenogenesis in more basal taxa [1]. In this context, Blattodea (cockroaches and termites) represent an intriguing phylogenetic group from which sexual reproduction, facultative parthenogenesis and more obligatory parthenogenesis have diversely emerged [4, 6]. Queen succession in the presence of a king is maintained by automictic parthenogenesis with terminal fusion [15]
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