Female cockroaches don't need a mate to lay eggs, but they do like company. New research finds that virgin female cockroaches housed together are quicker to produce offspring than virgin females living alone.
To test the effect of social milieu, the researchers put female cockroaches in different situations. In the control group, a male and a female were housed together and were allowed to mate. In other cases, females were kept with one, two, three or four other females. Other female roaches were kept with castrated males. The researchers also tested the effects of adding pheromones, chemicals that insects use for communication, to all-female cockroach groups.
Then, the researchers counted the number of eggs laid in each condition and how long it took the females to lay eggs. They found that virgin roaches kept alone laid eggs via parthenogenesis after 13.4 days, on average, plus or minus about four days. Virgin roaches kept in groups jumped to parthenogenesis significantly faster. For example, female roaches kept in a trio started laying eggs after an average of 10 days, plus or minus a couple of days.
Even more striking, virgin cockroaches kept in all-female groups laid their second clutch of eggs much sooner than virgin cockroaches kept alone (an average of 18 days versus between 25 and 30 days for the isolated roaches).
This may be a very primitive example of female cooperation, the researchers added. Male roaches housed together tend to fight until they cut each other's antennae off, but females huddle together, and apparently even harmonize, their reproductive schedules. This tracks with overall roach ecology, as males tend to leave roach colonies to avoid inbreeding, while female kin stick together, the researchers wrote.