A year-round supply of lovely, available mates gives male butterflies on the island of Madeira something extra to live for—something that Swedish males don’t have.
Male Pararge aegeria butterflies live longer on Madeira, off the North African coast, than in Sweden, report Karl Gotthard of the University of Neuchatel in Switzerland and his colleagues. This difference fits predictions that organisms invest resources only where they pay off in reproductive success, the researchers comment in the January Oecologia.
In the balmy climate of Madeira, females of the species mature at any time during the year. The researchers found no difference in the life spans of males and females. In Sweden, however, females emerge from their cocoons and find mates in a synchronized burst. After those glory days, a male’s chance of adding to his reproductive success drops to zero. Sure enough, the Swedish males die well before the females.