M. Chapuisat et al., SEX-RATIO REGULATION - THE ECONOMICS OF FRATRICIDE IN ANTS, Proceedings - Royal Society. Biological Sciences, 264(1385), 1997, pp. 1255-1260
In many insect societies, workers can manipulate the reproductive outp
ut of their colony by killing kin of lesser value to them. For instanc
e, workers of the mound-building For mica exsecta eliminate male brood
in colonies headed by a single-mated queen. By combining an inclusive
fitness model and empirical data, we investigated the selective cause
s underlying these fratricides. Our model examines until which thresho
ld stage in male brood development do the workers benefit from elimina
ting males to rear extra females instead. We then determined the minim
al developmental stage reached by male larvae before elimination in F.
exsecta field colonies. Surprisingly, many male larvae were kept unti
l they were close to pupation, and only then eliminated. According to
our model, part of the eliminated males were so large that workers wou
ld not benefit from replacing them with new females. Moreover, males w
ere eliminated late in the season, so that new females could no longer
be initiated, because matings take place synchronously during a short
period. Together, these results indicate that workers did not replace
male brood with new females, but rather reduced total brood size duri
ng late larval development. Male destruction was probably triggered by
resource limitation, and the timing of brood elimination suggests tha
t males may have been fed to females when these start to grow exponent
ially during the final larval stage. Hence, the evolution of fratricid
es in ants is best explained by a combination of ecological, demograph
ic and genetic parameters.