The cost of peripheral males in a brook trout mating system

A focus-on the reproductive contributions of males displaying alternative l ife histories has neglected the role of size-dependent peripheral males in salmonine mating systems. We documented mating behaviour of brook trout, Sa lvelinus fontinalis, including observations of spawning, over two breeding seasons to determine the mating costs of peripheral males to dominant males (kleptogamy) and females (egg cannibalism). For males and females, the mat ing costs of peripheral males were substantial because more than half (56%) of all observed brook trout spawnings involved peripheral males. Males tha t paired with large females experienced a greater incidence of kleptogamy d ue to increased numbers of peripheral males present. Large males face a con flict when mating in that they prefer to spawn with large females; however, these same females attract numerous males against which the dominant male cannot defend. From paternity studies, we estimated that males that had per ipheral males participate in spawning may fertilize, on average, equal numb ers of eggs compared to males spawning solely with a smaller female. Female s that paired with relatively smaller males had significantly more eggs eat en by peripheral males than females that paired with relatively larger male s. Latency to spawn by females increased when paired with a relatively smal l male, and resulted in females obtaining a larger spawning partner. The ob served patterns of size-assortative mating, kleptogamy and cannibalism are discussed in relation to mate choice for this population of brook trout. (C ) 1999 The Association for the Study of Animal Behaviour.