For many males, a common strategy is to mate with as many females as possible. Sperm are usually smaller than eggs and cheaper to make. But according to findings published in Nature Communications this month, a female’s reproductive rate – also called fecundity – increases when the male stays to help provide food and care to their offspring. Not only will she have larger litters, she can also breed more often.
Lots of studies have documented the costs of male care: increased predation and parasitism risk, less time for finding food for themselves, and, of course, losing out on mating opportunities. Fathers help mothers out in only 10 percent of mammal species, and this happens more when the male’s prospect of promiscuity is dim. Why care if the female will invest her resources in rearing their offspring?
To see what additional benefits paternal care would provide, Hannah West and Isabella Capellini from the University of Hull compiled the largest, most detailed dataset of male care behavior in mammals: 529 species with and without male care, ranging from bats and cats to deer, dolphins, and dingoes. They collected life history traits including female adult mass, lactation and gestation time, newborn mass, litter size, and maximum lifespan. They also gathered examples of male care behavior, such as provisioning food for the family and huddling with, grooming, and carrying the babies.
The duo found that when males carry the offspring, the females have a shorter lactation period, which means more frequent breeding events. Bringing food for the female also shortens lactation and increases litter size too. Furthermore, in species that have male care, the babies are weaned at a weight that’s about the same as babies in related species without male care. And that’s despite a shorter lactation period, suggesting that offspring enjoying paternal care grow faster.
The father might be giving up mating prospects in the short term, but these findings show that he gains reproductive opportunities in the long term.