Mating behavior in the black hamlet — gamete trading or egg trading?
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The black hamlet (Hypoplectrus nigricans, Serranidae) is a simultaneous hermaphrodite, like many other serranines. It has external fertilization and planktonic eggs and engages in a kind of reciprocal spawning consisting of three components: (1) The clutch is divided into sequentially spawned parcels. (2) Partners regularly alternate release of parcels in a spawning bout. (3) Courtship is associated with the female spawning role. Two hypotheses have been proposed to account for this pattern. The egg trading hypothesis states that the pattern results from competition for fertilizations and assumes that reproductive success (RS) as a male is limited by access to eggs and that female RS is not limited by access to sperm. The gamete trading hypothesis states that the pattern results from eggs being at substantial risk of not being fertilized — i.e. female RS is limited by access to sperm. An analysis was performed of data from the black hamlet and three other serranines to determine whether significant sperm limitation occurs. The evidence fails to support the hypothesis that access to sperm limits female RS. Unspawned eggs were not found in fish collected outside the spawning period, but fish without eggs always had milt (sperm). The percentage of eggs fertilized did not decrease over the course of a spawning bout. There was also a slight positive correlation between the number of eggs released in a spawning and the percentage that were fertilized, and serranines that divide the clutch into parcels do not tend to have higher fecundities than those that do not. The gamete trading hypothesis can therefore be rejected for H. nigricans.
KeywordsCoral reef fishes Courtship Hermaphroditism Mating systems Reciprocity Reproduction Sex allocation Serranidae Spawning Sperm limitation
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