Sponge Isopod

Their reproductive strategy is of interest, as both males and females are unusual among animals. Males are polymorphic and exist in 3 forms, α, β, and γ of different sizes. Of the three, α males are the largest and most dominant; they mate with multiple females in a harem. The β males mimic the females and therefore manage to mate with some of the females in an α male's harem. The γ form is much smaller and mimics the juvenile form, also allowing it to escape detection. Relatively speaking, the γ males invest the most energy in their testes, followed by the β males and the α males. Other species in which alternative reproductive strategies caused by a genetic polymorphism occur are the swordtail (Xiphophorus nigrensis), the tree lizard (Urosaurus ornatus), the ruff (Philomachus pugnax) and the side-blotched lizard (Uta stansburiana). The α males guard a spongocoel into which females (as many as 19) enter to mate. Females brood their offspring internally within a brood pouch and use their bodies to provide nutrition to their developing young before they are released. Females only reproduce once, with larger females producing more eggs. Shortly before females become fertile, they can be cannibalistic. They then undergo a sexual moult, losing their mouthparts in the process. …