Promiscuity in Trinidad
Female Trinidadian guppies often mate with multiple males, because the resultant offspring show substantially increased fitness.
Males of a species are keen to spread their sperm as far and as wide as possible. But why would a female wish to mate with multiple males? For the Trinidadian guppy, promiscuity brings with it the risk of nasty diseases and being eaten during the act, all for the sake of a male who doesn't lift a finger to protect or provide. In the August 29 Proceedings of the National Academy of Sciences Evans and Magurran report that it's all worth it because the resultant offspring show substantially increased fitness (Proc Nat. Acad Sci USA 2000, 97:10074-10076). The benefits in characteristics such as antipredator skills may come from sperm competition, in which fit males produce more plentiful and more active sperm. Meanwhile the longer gestation time (and thus lower fecundity) in singly mated guppies may arise because the females are delaying the process of fertilization, just in case a bigger, brawnier guppy happens along.