The hormone isotocin may be the driving force behind the superb fatherly instincts of clownfish dads.
We can credit Pixar's animated film Finding Nemo with placing one of the animal world's greatest dads on our radars. The clownfish father in the animated film traversed vast seas to find his missing son. It turns out that though the film is of course fictional, it has a strong basis in reality.
Great dads aren't very common in other animals. Usually, the role of nurturing and protecting young falls on the mother. However, clownfish aren't the only species that make great dads. Giant waterbugs, rheas, the giant African bullfrog, and of course the seahorse all have remarkable fatherly instincts.
Clownfish dads are pretty extraordinary even by animal dad standards. For one thing, their fatherly instincts are so strong that even males who haven't mated yet are able to instinctively take care of eggs.
These fatherly instincts manifest in clownfish in particular ways. Fathers egg-sit until the eggs are ready to hatch and the hatchlings float away. A male clownfish fans the eggs to keep fungus from growing on them. He also nips away at any fungus that may have gotten a foothold, and he gets rid of eggs with dead embryos in them. Any male clownfish would apparently do this for any eggs in his care, even those not his own. Scientists say that any other fish would probably eat strange eggs.
According to a new study, a signaling molecule called isotocin is the root of the clownfish's fatherly instincts. Isotocin is extremely similar to oxytocin, the so-called love hormone that also fuels mothering instincts in humans. Researchers found that blocking isotocin in male clownfish makes them lose their fatherly instincts.
The researchers also blocked the hormone arginine vasotocin to see how it influences fatherly behavior. Scientists think that arginine vasotocin regulates courtship behavior, dominance, and aggression. Blocking this hormone led to a surprising result: the clownfish became even more caring and attentive to their eggs. The researchers think that by blocking this hormone and its effects, the clownfish pay more attention to their eggs instead of paying attention to defending their nest.
Are the parental patterns in clownfish dads similar to those in humans? The researchers don't have a definitive answer yet and more research is necessary. However, evidence suggests that oxytocin also influences fatherly behavior in human males. There's also evidence that the mechanisms that influence parental, reproductive, and aggressive behaviors are present and quite similar in all species.
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