Gouldian finches with distinctive red- and black-faced colour morphs. Nestlings who have a parent of each colour morph tend to have a higher mortality rate than those with parents of the same colour morph, so this has become a key factor in mate selection.
Credit: Sarah Pryke
SYDNEY: Female finches with unattractive partners have stress hormone levels three to four times higher than those with attractive partners and are slower to reproduce, according to a new study.
These findings may shed light on the evolutionary basis for relationship stress in humans, as finches and humans have similar mating systems.
“I would anticipate that we would find very similar things going on in humans,” said lead author Simon Griffith of the Avian Behavioural Ecology Group at Macquarie University in Sydney, of the study published in Proceedings of the Royal Society B.
Like a desperate bar room situation
Both finches and humans are socially monogamous species, and share the responsibility of raising offspring. While over 90% of birds use this mating system, only around 5% of mammals do, and the female is usually solely responsible for raising its young.
Previous work studying socially monogamous animals has assumed that females only pair with males they find attractive.
However, Griffith and his colleagues suspected that when there are only a limited number of males to choose from many females choose to mate with an unattractive male rather than forgo reproduction entirely. Griffith likened the behaviour to “the bar room situation at the end of the night.”
Birds of a feather…
The Gouldian finch, Erythrura gouldiae, is a native Australian bird with three distinct head-colour morphs – red, black and in rare circumstances yellow. Unlike many species, it is clear when a Gouldian finch female is paired with an unattractive partner, as they will ideally choose a male with the same head-colour morph.
Although finches with two different morphs are capable of mating with each other, previous research has shown that the offspring of a red-black mixed-morph pair suffer a higher mortality rate than the offspring of a non-mixed pair.
The genetic incompatibility of the two morphs makes the Gouldian finch an ideal study species for investigating mate choice. “We have a system where the difference is red and black,” said Griffith, making it very easy to tell when a finch is paired with an unattractive partner. The study excluded any finches of the rare yellow morph.
Stress levels linked to mate choice
To test their theory, the researchers created situations where the female finches would have to choose between mating with an unattractive male or not at all, and observed the effects these situations had on reproduction.
Some female finches were kept in large aviaries with males of both the red and black head-colour morph, and were left to choose their own mates. Other females were kept in aviaries with just one male.
The length at which it took the different pairs to mate and lay eggs was measured, as well as the levels of the stress hormone corticosterone that was produced in each of the females. The researchers found that females who chose to mate with an unattractive male (with a different head-colour morph) had corticosterone levels three to four times higher than females who mated with attractive males.
