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Pair bonds, reproductive success, and rise of alternate mating strategies in a social carnivore. Ausband DE. Behavioral Ecology. 2019 Nov
Monogamy is commonly observed across a wide variety of species and taxa and arises when young are altricial, parental investment in young is high, and mate monopolization is generally not possible. In such species, pairs may bond for multiple breeding seasons while successfully rearing young. Individuals, however, may attempt to bypass the dominant mating strategy particularly when breeding opportunities are limited. Currently, we do not know how pair bond duration affects the efficacy of alternative mating strategies in populations with a monogamous mating system. Additionally, inferences about pair bond effects on reproductive success (i.e., both clutch size and recruitment) are largely limited to long-lived birds and little is known about effects on mammalian cooperative breeders. I used genetic sampling and pedigrees to examine the effects of pair bond duration on reproductive success (i.e., litter size, recruitment) and mating strategies in a population of gray wolves (Canis lupus) in Idaho, USA. There was a positive, marginally significant relationship between pair bond duration and apparent survival of offspring. Increased pair bond duration was also associated with a dampening in the prevalence of other alternative mating strategies such as sneaker males and polygamy. The selective advantage of alternative mating strategies is a combination of population, group (for applicable species), individual, and social influences such as pair bonds. The distribution of pair bonds in a monogamous population affects the selective advantage, and hence frequency, of various mating strategies observed.
Photo A male and female wolf, along with their pups, are photographed near Salmon, Idaho in 2017. (Idaho Department of Fish and Game / Courtesy)
By Eli Francovich
In the rugged, sometimes violent world of the wolf, it pays to have mom and dad around.
The longer wolf couples are together, the more likely their offspring are to survive into adulthood, according to new research from the University of Idaho.
According to the study, which will be published in the journal Behavioral Ecology, for each year a wolf pair stays together, the odds of their pups surviving into adulthood increased 20%.
Put another way, “they get 20% better at what they do every year,” study author David Ausband said.
The study used nine years of scat data collected by Ausband and others from wolves throughout Idaho.
A male and female wolf play near Kelly Creek on the Idaho/Montana border in 2017. (Idaho Department of Fish and Gam / Courtesy)
Ausband started collecting the data as a graduate student at the University of Montana.
He then worked for the Idaho Department of Fish and Game before taking a job at the University of Idaho last year. His research examines a relatively understudied area: the impact of monogamy in mammals.
“Remarkably, I could not find a study that measured pair bond duration and its effects on reproduction in a mammalian cooperative breeder,” Ausband writes in the study.
In particular, he wanted to see how legal hunting impacted monogamy in wolves, how monogamy impacted pup rearing and how monogamous relationships changed the overall social structure of a pack.
He expected to find that hunting reduced monogamy, possibly fraying pack dynamics.
“I thought … harvest would reduce pair bonds. And that’s not what I found,” he said. “And it’s because pair bonds are super short. They only last a couple years.”
On average, wolf pairs stayed together for 2.2 years, although there was wide variance. For instance, one wolf couple documented by Ausband stayed together for at least nine years, basically an eternity for an animal that is considered ancient at 13. The average of 2.2 years found in Idaho aligned with rates “measured in a recolonizing wolf population in Sweden that experienced relatively high rates of human-caused mortality.”
“There are some (pairs) that last a long time and those that do (last) stomp,” Ausband said. “They’re super good at what they do.”
Why the pairings are, on average, so short isn’t clear. But Ausband believes it has to do with the vicissitudes of wolf life, whether that’s younger wolves trying to establish themselves as alphas, the inherent danger of trying to kill large, panicked ungulates with your face, or human hunting.
“Wolf packs are dynamic,” he said. “There is more drama in a wolf pack than in a middle school dance. There is always stuff going.”
Overall, wolves were monogamous about 72% of the time, he found.
In addition to increasing pup survival, monogamy also stabilized pack dynamics. Monogamous pairs reduced the occurrence of “sneaker males” and decreased polygamy in the group.
Sneaker males are males who mate and then leave the hard work of rearing offspring to others.
Monogamous wolf pairs were, overall, better at maintaining control of their packs, although pack size played a big role. Possibly, smaller wolf packs (partially caused by hunting) are easier for an alpha male and female to maintain control over, he said.
“If a pair is together, and their group size is large, it’s harder to police sneaker males. If you have 20 wolves to keep track of, it’s really hard to keep sneaker males out,” he said. “It’s a lot like human families. Or a big classroom at an elementary school. If you have a lot of kids, it’s harder to police.”
The study builds on, and adds to, research done in Minnesota’s Voyageurs National Park suggesting that wolves learn, rather than relying solely on instinct.
There, scientists observed wolves lying in wait along known beaver paths, often picking their ambush site far from the water. In fact, according to National Geographic, some wolves appeared to specialize in killing beavers.
In Idaho, Ausband found that when an older wolf mated with a younger wolf, the older appeared to teach the younger how to parent. Pups born to those pairings were more likely to survive than pups born to two first-time parents.
Understanding how wolves live and breed is important information for scientists and managers.
“If we don’t understand the truth about how an animal breeds, we’re not going to be very good at managing and conserving them,” Ausband said.