Animals 'rarely avoid' mating with relatives, new study says

Contrary to what many scientists had assumed, animals — when given a choice — rarely avoid mating with their cousins or siblings, according to a new study published in the journal Nature Ecology & Evolution.

The new study was a meta-analysis, which collected and analyzed information from 139 previous studies on mate choice, conducted over 40 years looking at 88 different species, from fruit flies to chimpanzees. 

Canadian researcher John Fitzpatrick, an associate professor of zoology at Stockholm University, was senior author of the study. He said because previous work on the subject only studied this issue in one species at a time, it took his analysis to reveal the bigger picture. 

He told Quirks & Quarks host Bob McDonald that he was motivated to understand how animals approached the problem of choosing their mates. 

"To our surprise, we found that animals don't really seem to care if they're mating with a relative or not," he said. In fact, they found that animals will breed with kin 73 per cent of the time.

Fitzpatrick's team only included studies conducted in controlled, experimental settings with captive animals, but they included male and female mate choice before, during and after copulation, since some females can influence which sperm fertilize her eggs.

"What was interesting about that is that none of the different experimental conditions mattered," said Fitzpatrick. 

Particularly if there's nobody else around, it might make more sense for them to get some mating, than no mating, even if that's with a relative.- Prof. John Fitzpatrick, Stockholm University

He said evolutionary theorists have  suggested for decades that animals might not care about whether their future mate is a relative.

"It took me a long time to get caught up to what the theorists have been telling us."

This new comprehensive view of the data has potential implications for animals in the wild and in captive breeding programs. 

Lack of selective pressure for mate choice

Inbreeding in animals increases the chance of passing down deleterious genes that can compromise the ability to reproduce, increase susceptibility to certain diseases and decrease lifespan.

"We like to think of [the potential negative effects] as really dramatic costs, but it could be that maybe they're not as high as we think they are," Fitzpatrick added. 

"Particularly if there's nobody else around, it might make more sense for them to get some mating, than no mating, even if that's with a relative." 

In the wild, animals often leave their pack, herd or area where they're born. As a result, Fitzpatrick suggests, many animals might not have evolved to avoid inbreeding.

"In those cases, it's very unlikely that you're going to ever encounter a relative. So there's no sort of selective pressure built in for you to avoid mating with them."

What this means for wild animal conservation

As the mate-choice studies he looked at were all done with captive animals, it's hard to say how much this will apply to animals in the wild. However Fitzpatrick suggests this new insight into animal breeding behaviour should be something taken into account when considering human impact on the environment. 

One of the biggest problems for maintaining animal biodiversity is the destruction and fragmentation of habitat.

This can influence the way animals seek out their mates. Normal dispersal and migration patterns, which would tend to make it less likely that an animal would encounter and mate with a relative, could be constrained. 

"Under those situations, they might be faced with some tough choices when it comes to who to mate with," explained Fitzpatrick. 

"What our results are suggesting is that one of those tough choices — if it comes down to mating with a relative or non-relative — they might not always be choosing the non-relative."

What this means for captive breeding programs

For species at risk, especially endangered animals in conservation breeding programs that might have limited gene pools to begin with, the costs of animal inbreeding becomes even greater.

The goal of most breeding programs is to create self-sustaining populations, making it important to maintain as much genetic diversity as possible to give their offspring the best chance of handling all that life throws at them.

The trouble is, many breeding programs around the world have found they have greater reproductive success when they allow animals to choose their mates, like giant pandas.

Scientists have found that when giant pandas mate with their preferred partners, they mate more often and have more babies, but if they choose to mate with their relatives, that would lead to less genetic diversity. 

Fitzpatrick said in light of this new meta-analysis, conservation scientists will have to figure out how to best balance these two competing demands. 

"What it really does is urges some sort of extra thought into how we're managing animals in captivity to make sure that we're able to maximise and enhance their genetic diversity, but also giving them the choice to pick who they're going to mate with."

Produced and written by Sonya Buyting