Mating

In some anglerfish species, males fuse permanently with females during mating; their blood vessels merge and all organs but testes vanish. Research found these species have reduced or lost key immune genes, including MHC, preventing rejection of the joined tissues.

Mosquito males and females beat their wings at different frequencies, but before mating they tune toward a shared harmonic. In *Aedes aegypti*, females (~400 Hz) and males (~600 Hz) converge near 1,200 Hz. A 2009 *Science* study found this synchrony is key to mate choice.

Juvenile male dolphins engage in same-sex sexual play, including inserting the penis into another male's blowhole. This serves as practice for later mating and forges bonds between males. Males who played more as juveniles later had greater reproductive success.