Inhibition of optimal behavior by social transmission in the guppy depends on shoaling

Previous research has suggested social learning of foragingbehavior can inhibit learning of the optimal behavior pattern.Based on their transmission chain design, we used small groupsof guppies (Poecilia reticulata) to determine the degree towhich the optimal behavior pattern was inhibited by sociallylearned information. A founder group was trained to take a long, energetically costly route to a food source. The members ofthis group were gradually replaced with naive conspecifics.Replicating the findings of the earlier researchers, it wasclear that the behavior of the founders strongly influencedthe behavior of the naive fish, probably through a process oflocal enhancement. When tested as a group, the naive fish chosethe long route to the food source significantly more oftenthan chance. Each naive fish was also tested in isolation.When tested alone, there was a significant tendency to choosethe short route despite following the long route when testedas a group. These results suggest social learning does notinhibit learning of optimal behavior patterns but that a trade-offoccurs when tested in the group condition. It is possible thatthe advantages for an individual fish of swimming with theshoal, and thus following the socially learned route, may haveoutweighed the potential energetic costs of taking this longerroute.     

Prey synchronize their vigilant behaviour with other group members

It is generally assumed that an individual of a prey species can benefit from an increase in the number of its group''s members by reducing its own investment in vigilance. But what behaviour should group members adopt in relation to both the risk of being preyed upon and the individual investment in vigilance? Most models assume that individuals scan independently of one another. It is generally argued that it is more profitable for each group member owing to the cost that coordination of individual scans in non-overlapping bouts of vigilance would require. We studied the relationships between both individual and collective vigilance and group size in Defassa waterbuck, Kobus ellipsiprymnus defassa, in a population living under a predation risk. Our results confirmed that the proportion of time an individual spent in vigilance decreased with group size. However, the time during which at least one individual in the group scanned the environment (collective vigilance) increased. Analyses showed that individuals neither coordinated their scanning in an asynchronous way nor scanned independently of one another. On the contrary, scanning and non-scanning bouts were synchronized between group members, producing waves of collective vigilance. We claim that these waves are triggered by allelomimetic effects i.e. they are a phenomenon produced by an individual copying its neighbour''s behaviour.