Today on PLoS - Biology

Interspecific Communicative and Coordinated Hunting between Groupers and Giant Moray Eels in the Red Sea:

The article offers a description and accompanying videos, such as the one showing a grouper and eel swimming side by side as if they are good friends on a stroll. It also offers quantification, which is truly hard to achieve in the field, of the tendencies involved in this mutually beneficial arrangement. The investigators were able to demonstrate that the two predators seek each other's company, spending more time together than expected by chance. They also found that groupers actively recruit moray eels through a curious head shake made close to the moray eel's head to which the eel responds by leaving its crevice and joining the grouper. Groupers showed such recruitment more often when hungry.

Given that cooperative hunting increases capture success for each of the two predators, and that they don't share with each other but swallow the prey whole, their behavior seems a form of "by-product mutualism," defined as a form of cooperation in which both parties achieve rewards without sacrificing anything for the other. They are both out for their own gain, which they attain more easily together than alone.

Divergent Selection on Opsins Drives Incipient Speciation in Lake Victoria Cichlids:

Though Lake Victoria cichlids appear millions of years younger than their counterparts in nearby Lake Malawi, both groups display an enormous range of physical and behavioral traits. This staggering diversity in such young species provides compelling evidence for adaptive radiation, which occurs when divergent selection operates on ecological traits that favor different gene variants, or alleles, in different environments. When divergent selection on an ecological trait also affects mate choice--promoting reproductive isolation of diverging populations--ecological diversity and speciation may proceed in tandem and quickly generate numerous new species.

Despite substantial theoretical and some experimental support for such "by-product speciation," few studies have shown that selection has "fixed" alleles (that is, driven its frequency in a population to 100%) with different effects on an adaptive trait in closely related populations. But now, Yohey Terai, Norihiro Okada, and their colleagues have bridged that gap by demonstrating divergent selection on a visual system gene that influences both ecological adaptation and mate choice in cichlids.