Submitted by Scott Bennett on 25 September, 2011 - 17:21
Smaller size gave them first access to the eggs
Male fish evolve "sexual tactics" to compensate for diminutive size
"It's nice to find out something about their behaviour that we didn't expect,”
In findings are published in the journal Ethology, scientists from the University of Sheffield have discovered that during spawning, smaller male zebrafish were able to get between a female that had just laid eggs and larger, rival males. Their smaller size gave them first access to the eggs in order to fertilize them.
The team that carried out the study was interested in one particular aspect of zebrafish "society" - their hierarchy.” You can spot the dominant males," explained Penelope Watt, the biologist who led the study. "You see them patrolling the tank, chasing smaller fish away.” She and her team wanted to discover the significance of this dominance in reproduction, so paternity tests on zebrafish embryos were carried out to see if dominant males fathered more offspring. A single female was placed into a tank with two males, one a dominant male and the other a subordinate. The female was contained in a plastic cylinder covered in fine mesh, enabling her to smell the males but not make contact with them.
After 24 hours, the scientists released the female, allowing the fish to spawn. Males and females then released masses of eggs and sperm together at the base of the tank. When the female was ready to lay eggs, males jostled for position close to her. The closer a male was to a female, the better the chance he had of fertilizing her eggs. When the team DNA-tested the resulting offspring, they found that dominant males had fathered more offspring than subordinate animals. Surprisingly, the subordinates that had the best chance of fathering offspring were the smallest. "It's probable that the smaller males are sneaky males and they're more maneuverable," the scientists said. "They can get in between the female and the larger male."
Such devious mating strategies are seen in a number of other fish species. The study findings support the idea that male fish have evolved "sexual tactics" to compensate for their diminutive size. "It's nice to find out something about their behaviour that we didn't expect,” said Dr Watt. "They're a more complex species than we've given them credit for”, she added. ." Zebrafish are widely studied by scientists, particularly in genetic research.