Mixed fish offspring disadvantaged

Fish born to promiscuous females may be at a disadvantage because of their behaviour, according to researchers at the University of Western Australia.

Centre for Evolutionary Biology scientists, Dr Jonathan Evans and Dr Jennifer Kelley, focused on studying the effects of polyandry - where females mate with two or more males within a reproductive cycle. As a result, the female's eggs may be fertilised by more than one male, meaning that the offspring can be either paternal full siblings (same father) or paternal half-siblings (different fathers).

The research, published in the Royal Society science journal Biology Letters, involved artificially inseminating small tropical fish, known as guppies.

It revealed that pairs of full siblings spent more time shoaling and in close proximity than half siblings.

"Shoaling is an important survival skill because it enables guppies to evade predators," Dr Evans said.

"The study confirms that newborn guppies can distinguish their full siblings from what, in effect, are their stepbrothers and stepsisters."

"And more importantly, the fact that they stay closer with their full siblings has implications for group behaviour with respect to avoiding predators, inbreeding and kin selection."

"Related offspring may also show reduced levels of aggression towards one another and have enhanced growth rates."

Dr Evans said "most studies of multiple mating by females had focused on the benefits of this promiscuous behaviour.

"However, we have found that there are potential costs of mating with more than one male because offspring from broods sired by multiple males are less likely to stick together than those from broods fathered by a single male," he said.