Come mating time, male longfin squid (Loligo pealeii) get feisty. One touch of a female's egg sac and they go ballistic, grappling any other male within reach. Now scientists have identified the chemical trigger that sets them off. After exposing males to a variety of different egg sac proteins, they isolated one—called Loligo β-microseminoprotein—that drove the squid crazy. Human and mouse seminal fluid contain a similar protein, which is thought to somehow protect sperm, but its true function is unknown. β-microseminoprotein is the first aggression-triggering compound found in marine animals, the researchers reports this week in Current Biology. They suspect it prevents males from wasting their combative energy. After all, why bother fighting another male for a female unless she is fertile?
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