Why do males fight for females?

If you think for pleasure, you're not quite right.

In fact, they look for spreading their own genes.

And while the females are sure about their maternity, males cannot be.

When lion males take over a new lioness group, the first thing they do is kill the young, to ensure that the females will grow offspring bearing their genes.

The same thing happens in many species, social (like gorilla) and solitary (like tigers, bears), when a new male takes over the territory of other male and the females in that territory.

But a new research revealed that males can cut off the foreign genes even right after fecundation.

By now, just in one fish species, males were found to eat the fecundated eggs if they're not sure about their paternity.

This happens especially when they have been cuckolded (other lower ranked males ejaculated) during the act of spawning.
The more males are present during spawning, the more likely the male will eat the eggs when they are laid, as it is less likely that he fathered them.

Scientists had long suspected this, but now they could prove it as well.

"The most drastic decision a father can make is to cannibalize his own offspring," explain Suzanne Gray (Ph.D. candidate at Simon Fraser University), Lawrence Dill (Simon Fraser University) and Jeffrey McKinnon (University of Wisconsin - Whitewater).

"These results support and extend previous findings suggesting that confidence of paternity is a key factor in determining a male's behavior toward his offspring, including whether or not to eat them."

The species involved in the study is Telmatherina sarasinorum (photo), a small (6, 8 cm or 2.5 inch long) colorful fish found in Lake Matano, Sulawesi, Indonesia.

The study also pointed that the females, being always sure about the genetics of their offspring, do not cannibalize.

"We want to understand how behaviors evolve," says Gray, "and how behaviors, such as cannibalism, contribute to the diversity we see within and between different species."

As cuckolding is a phenomenon widespread amongst fish species, it means that father cannibalism should be also widespread.