When males of a species follow different reproductive strategies in different habitats, one might expect the strategy adopted to maximize fitness payoffs under particular ecological conditions. Striped mice (Rhabdomys pumilio) males in the moist grasslands of South Africa follow a roaming mating strategy, visiting several receptive females, and do not participate in parental care. In contrast, males in the arid succulent karoo are permanent members of social groups and help care for young. We predicted that paternal care leads to fitness benefits in striped mice from the succulent karoo but not from the grasslands. Experiments were conducted simultaneously in both locations under captive seminatural conditions to study offspring growth and survival to weaning in two experimental groups: father absent and father present. In the succulent karoo, offspring development was faster when the father was present, but the father's absence did not affect offspring growth in the grasslands. The significantly lower night temperatures in the succulent karoo compared to the grasslands negatively influenced offspring development during the first 3 days after birth, which in turn influenced offspring development until weaning. Exposure to low temperatures is energetically costly to free-living mice, as indicated by a greater loss of body weight during cold spring nights than warmer summer nights. We suggest that paternal care, particularly huddling of pups, improves offspring development in the succulent karoo, whereas the presence or absence of the father does not appear to directly influence offspring growth in the grasslands.