Fitness trade-offs select for semelparous reproduction in an extreme environment

Semelparity (suicidal or one-time reproduction) is generally thought to evo lve when selection favours individuals that allocate so much energy towards reproduction that death is inevitable. Among mammals, only males of a few marsupial species are known to exhibit this unusual life-history strategy. Here we report evidence that suggests adaptations to an increasingly harsh environment during the early Holocene favoured a switch from iteroparity (r epeated reproduction) to semelparity for a small rodent, Neotoma lepida. Ou r analysis, based on spatial, temporal and physiological relationships betw een body size and temperature and on calculations using life tables and bod y size production allometries, highlights a unique way that mammals may ada pt to changing environmental conditions.