A research team led by Takumi Kato, a second-year doctoral student at the Faculty of Life Sciences, Hokkaido University, found that when multiple female cockroaches are bred, they are parthenogenetic (even if there are no males, only females give birth to genetically similar children). The fact that female-only colonies can be maintained for a long period of time, and that behind that, there is a mechanism that promotes and synchronizes the formation of egg sheaths (capsules containing multiple eggs) when females are bred in a narrow space. Revealed.
Some animals perform "conditional parthenogenesis", which is sexual reproduction when there are males and switches to parthenogenesis when there are only females.It has been introduced in old literature that cockroaches, which are representative of house pests that are widely distributed all over the world, have parthenogenetic ability, but their recognition is low and research on the mechanism has not progressed.Therefore, the research group sought to clarify a part of the prosperity of insect groups such as termites, which are also distributed around the world, by investigating the factors that promote parthenogenesis of cockroaches.
In the experiment, one or more adult female American cockroaches immediately after molting were placed in a small plastic container that could contact each other, and sufficient food and water were given to determine when the parthenogenetic egg sheath was formed for 1 months. Observed over the above.As a result, it was found that when the females were bred alone, there was a tendency for them to vary among the individuals, but when three females were put together, the egg sheath was formed earlier.On the other hand, when combined with a male who cannot mate, when multiple females with amputated antennae are bred, egg sheath formation is slower than in normal individuals, and even when the sex pheromone produced by the female is placed in a container, the egg sheath is formed. There was no promoting effect on formation.From the above results, it was found that it is important to receive chemical substances such as odors emitted by other individuals and mechanical contact with sensory organs such as antennae in order to promote egg sheath formation.
It is speculated that promotion and synchronization of egg sheath formation when multiple females are reared in a small space contributes to increasing the number of offspring by parthenogenesis and improving survival rate, which means that multiple females alone. It explains well the fact that colonies can be maintained for a long period of time in a much more stable manner than females, and can be regarded as the germination of cooperative behavior that leads to the acquisition of true sociality.
