All for one and one for all : The social cooperation in the promotion of parthenogenesis in American cockroaches

Parthenogenesis is a kind of asexual reproduction that does not need the genetic presence of the male.It is a useful reproductive strategy when there has a need for rapidly generating large numbers of female progeny and colonize new habitat.The American cockroach, a worldwide pest which sexual reproduction and parthenogenesis have diversely emerged.In this research, a group of researchers from Hokkaido University was testing how social cooperation is linked to the promotion of parthenogenesis in American cockroaches.

This research was taken by a group of researchers from Hokkaido University.The researchers conducted 11 group during the same period to examine the time difference for the first ootheca production and the second, from August to 2013 to January 2014.Those 11 groups had been separated for 5 purposes.As the control, one female and one male were kept together for sexual reproduction in group 1.In group 2 to group 5, a different number of females had been put in the different containers to evaluate the group effect on asexual reproduction.Then, to assess the effects of the presence of males on asexual reproduction, one female was kept with one or two genitalia-ablated male in group 6 and 7.Also, to evaluate possible sensory organs influencing asexual reproduction, 9 females, in a group of 3, underwent ablation of maxillary/labial palps, pairs of antennae and all antennae/palps in group 8, 9 and 10.Finally, to evaluate the effect of sex pheromones on asexual reproduction, periplanone-B, a primary component of sex pheromones, was added to a container housing one female in group 11.

The results show that when three or more female grouping together, they tend to produce the ootheca earlier than the single female.Secondly, the genitalia-ablated male and periplanone-B does not have a significant effect on promote ootheca production.Thirdly, the ablation of the antennae has delayed the ootheca production.Finally, after the group effect test they keep 15 of virgin female cockroaches together as a colony, after three years more than 300 females with different aged nymphs and adults have survived, some individuals may have reached the fifth generation.

This research shows that the group effect is not only used for the sexual reproduction of females, but also the parthenogenesis of females.Although parthenogenetic eggs show lower fitness than sexually produced eggs, the difference is smaller than that in the results of a previous study.The 15 females colony has shown that 15 virgin females are sufficient to maintain the colony for more than three years only by parthenogenesis.Some types of pest control only kill the male, this result suggests that such methods may have just small effect in controlling the American cockroach.Parthenogenesis results in a low fitness in long-term, but it ensures the reproductive success of the eusocial insects.    

Reference:Ko, K., Masazumi, I., Shouhei, H., Atsushi, Y., Masanori, O., Makoto, M., & Hiroshi, N. (2017). Group-housed females promote production of asexual ootheca in American cockroaches. Zoological Letters, 31-9. doi:10.1186/s40851-017-0063-x