When they live in zoos, Mugger crocodiles happily mate and lay eggs. Maybe a little too happily: when they produce two clutches of 25 to 30 eggs each year, a zoo is quickly going be swamped by little croc babies. And rampant habitat loss means that there are fewer places to return them to the wild. What zoos need is reliable crocodile birth control.
One good reason? Keeping males and females in separate enclosures–the current method of population control–makes the crocs more aggressive than normal. If we were talking about a mammal, giving the males a simple vasectomy might be an option. But crocodilians keep their testes and their associated ducts deep inside their abdomen, and getting at them requires major surgery.
William Justin and his colleagues at the Madras Veterinary College came up with a less invasive option: blocking part of the crocodile’s phallus. Crocodiles move sperm into the female through a groove running the length of their phallus called the sulcus spermaticus. It’s in the same location as the mammalian urethra, but crocodiles don’t use the sulcus to urinate: their urine is released directly into a central waste chamber called the cloaca and gets dumped with the animal’s feces.
Blocking the urethra would be fatal to a mammal. But since a male crocodile only uses the sulcus for sex, surgically blocking it turns out to have the same effect as a vasectomy. Males and females can still mate, which seems to make the animals happier, but the eggs she lays stay unfertilized.
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