Mating Systems in Atlantic salmon and Atlantic cod: Synopsis
One of the most phenotypically extreme examples of alternative life histories in vertebrates is found in Atlantic salmon. Mature male parr reproduce at sizes 2-3 orders of magnitude smaller (10-150 g relative to >1000g) and at much less than half the age (typically 1-2 yr compared to 4-8 yr) of anadromous males, which breed following a migration to sea. Prior to spawning, parr compete physically with one another for access to a female, fertilizing eggs in competition with one or more anadromous males. As a group, parr fertilisation success per egg nest can vary between 15 and 60%; at the individual level, parr fertilisation success tends to be low and highly variable. Alternative reproductive tactics in salmon are products of both genotype and the environment. Phenotypes whose environment causes them to fall below a genetically-determined threshold adopt one tactic, while those exceeding the threshold adopt the alternative tactic. Alternative mating tactics are also evident in a broadcast-spawning marine fish, Atlantic cod, whose reproductive behavioural repertoire is considerably more complex than previously thought. Recent work suggests the potential importance of mate choice, mate competition, and acoustic communication in the mating system of Atlantic cod.