Behaviour

Pelvicachromis taeniatus is a dwarf cichlid from West Africa that is occasionally kept as an aquarium fish In this species, females seek to impress potential mates as well by fanning out their large, violet pelvic fin.

 

The results, published this month in BMC Evolutionary Biology, also suggest male choice can drive females to evolve exaggerated traits, a finding that disputes the traditional belief that sexual selection is a one-way road, allowing only females to affect male appearance.

 

Small groups of sticklebacks (Gasterosteus aculeatus) reach consensus when choosing which of two replica fish to follow. As group size increases, the fish make more accurate decisions.

"It turned out that stickleback fish preferred to follow larger over smaller leaders," said Ashley Ward of Sydney University

"Not only that, but they also preferred fat over thin, healthy over ill, and so on. The part that really caught our eye was that these preferences grew as the group size increased, through some kind of positive social feedback mechanism."

Richard Connor of the University of Massachusetts Dartmouth tracked 120 males in the Shark Bay, Western Australia and found no evidence that dolphins form the groups to control either territory or sexual partners, suggesting their society is unusually open.

The researchers found no evidence that the large and complex social network in Shark Bay, comprising hundreds of bottlenose dolphins, is a closed group defended by males.

They also found no evidence that males defend smaller ranges or groups of females within this network.

Sharks are known to "dive" frequently through the water column and many functions have been attributed to the behaviour, such as thermoregulation, search and reduction of the COT. Few studies, however, have been able to frame these in conjunction with theoretical optima and test predictions for differing movement structures.