Personality may be adaptability’s trump card.

A pair of great tits (the bird).
Image via Pixabay.

Researchers at LMU Munich say that differences in personality could be a kind of insurance policy on the part of evolution. Different personalities, they report in a new paper, help maintain the level of biological variation needed to keep whole populations healthy and thriving.

Birds of a feather

The team focused their study on great tits (Parus major). The birds show some level of adaptability to environmental change, most notably through flexibility in choosing when to rear their chicks. High temperatures tend to make them build their nests and lay eggs earlier in the year, while colder temperatures make them put the whole matter off until the weather improves.

Natural selection favors such behavioral adaptability, the team explains, as long as the genetic variation is available — i.e. as long as the right genetic variants encoding reproductive behavior are present in the population, the birds will decide for themselves when is best to lay eggs, since that increases the chances their chicks will survive.

Personality is, at least in part, the source of this behavioral adaptability, the team reports. LMU behavioral biologist Niels Dingemanse and his doctoral student Robin Abbey-Lee have shown that the bolder among these birds lay their eggs earlier, when conditions allow it, while the shy ones wait for safe conditions, the team reports. In essence, their personalities allow them to interact with a threat (in this case, shifting weather) in different ways, which ensure that at least some members successfully rear their chicks.

The level of predation also has an influence on the timing and particularities of nesting behavior. The European sparrowhawk (Accipiter nisus) is a major predator of great tits, the team explains, with fledglings and young tits being the most vulnerable.

Sparrowhawks brood at a time when new generations of tits reach the fledgling stage, to make sure there will be plenty of pickings to feed baby sparrowhawks with. Some great tits, according to the team, react by deferring breeding, to give their offspring a higher chance of survival. They will also become markedly more alert and sing less often as they hear the call of a hunting sparrowhawk.

“In previous studies, however, we found that not all birds display this reaction to the same degree,” says Dingemanse. “Different individuals exhibit different personalities, and some are more explorative, daring and more aggressive than others.”

The team looked into whether these personality differences actually translate into a meaningful variation in the timing of breeding at the population level. During the breeding season – from April to June – the researchers exposed birds in a total of 12 tit populations to either the recorded call of the sparrowhawk or the song of the harmless blackbird.

Under these two conditions, the team explains, character differences did have an impact on the timing of breeding. More daring birds generally tend to explore their local environments more eagerly and thus breed later. The ones spooked by the team, however, began breeding earlier than what’s usual for great tits. Shier birds behaved exactly the opposite way.

It’s interesting to note that in the end, both personality types achieved essentially the same level of breeding success, according to the authors. This suggests that variation in personality does contribute to keeping a population’s genetic variability at healthy levels.

“In this way, populations can also become more resilient in the face of anthropogenic alterations of their environments, such as climate change,” Dingemanse points out.

The paper “Adaptive individual variation in phenological responses to perceived predation levels” has been published in the journal Nature Communications.