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Understanding how reproductive timing has evolved to reflect climatic conditions is increasingly important as the climate changes, influencing species persistence and ecosystem dynamics. Among endotherms, seasonal reproduction is often linked to natural selection for reproducing when biotic conditions (e.g. food availability) are most favourable. In contrast, we present evidence that direct effects of an abiotic factor have selected for seasonal reproduction in a tropical mammal. We have shown previously that the African wild dog (Lycaon pictus), a diurnally active coursing predator, has lower reproductive success at high ambient temperatures, when its hunting activity is constrained. We therefore hypothesized that natural selection would favour reproduction during cool weather conditions, in locations where such conditions occur predictably. We show that, as predicted, wild dogs reproduce seasonally at latitudes from 7 to 25 degrees S, such that their pup-rearing periods coincide with the coolest (but not the driest) weeks of the year. Wild dog reproduction is aseasonal at latitudes <= 2 degrees. As the climate warms, some temperate-zone species have tracked optimal conditions through altered phenology. However, in seasonally breeding wild dog populations, any alteration in phenology would require breeding in hotter weather, probably reducing reproductive success. This endangered species may thus have a limited ability to adapt to climate change. Seasonal reproduction might be a trait indicating climate change vulnerability among tropical species.