Fights between males over females are observed in many species that have weapons, but there have been very few cases in which the relationship between the age of the male and the fighting style has been investigated in detail. This is because in order to accurately assess changes in fighting behavior due to age, it is necessary to exclude the influence of factors such as age, body size, and genetic factors as much as possible when observing behavior.

　Therefore, this research group spent about 10 years creating a genetically homogeneous population of the giant horned beetle, a microscopic beetle that uses its developed mandibles to fight each other. From among the bred individuals, we prepared 215 pairs of males with no fighting experience and of uniform size and genetic background. Is there a difference in the intensity of the fight (the time from when the two meet to the time the two fight) and the length of the fight (the time from the start of the fight to the end of the fight)? Examined.

　The results showed that (1) the intensity of fights does not change depending on age, but older males fight longer than younger males, and (2) there is a positive correlation between the intensity and length of fights for young males. However, this relationship disappeared in older males. The reason why fighting patterns change between young and aged males is that, compared to young males, aged males have a limited amount of time for future reproduction, and this increases their obsession with fighting for females. This is thought to be due to the different degrees.

　This research revealed that beetles change their tactics and behavioral patterns depending on their age, and thus answers the questions of why and how organisms fight from the perspective of "surplus investment for the future." It can be said that this gave new suggestions.

Paper information:【Behavioral Ecology and Sociobiology】Experimental quantification of genetic and ontogenetic effects on fighting behavior in the broadhorned flour beetle