There are benefits to both styles, not to mention quirks: One frog species gives birth through holes in its back.
“Are snakes the sole family that evolved multiple organic process options—egg or live birth?” Louis Meluso asked Saturday's Weird Animal Question of the Week.
While snakes area unit pretty distinctive within the kingdom Animalia, on this one they need to share the spotlight.
Many animal teams have some species that lay eggs et al. that birth live young, together with fish, amphibians, and yes, even mammals, says shred Gibbons, biological process life scientist at the University of Georgia’s Savannah Ecology Laboratory. (See "What Comes Before Snake Sex? A Kama Sanskrit literature of appeal Moves.")
Both ways have their edges, he says: birthing permits larger quality for the mother World Health Organization is "not clogged by massive eggs or embryos for a protracted amount," Gibbons says, and a better probability of genetic diversity if there area unit multiple matings and clutches. Live bearing suggests that the mother will higher defend her developing embryo till it's able to turn.
Here's a glance at some animals World Health Organization came to diversify however they multiply.
About fifteen to twenty % of the nine,000 identified species of snakes and lizards area unit live-bearers, Gibbons says. Common garter snakes, for instance, birth live young, whereas pythons lay eggs and guard them. (Related: "Amazing Video: within the World's Largest Gathering of Snakes.")
Some reptiles tailor their fruitful strategy looking on wherever they live.
In Australia, lily-livered three-toed skinks that board higher, colder regions bear live young, whereas those in hotter lowlands lay eggs, that area unit tougher to stay heat underneath cold conditions.
In general, although there area unit fewer reptiles in higher altitudes and in colder temperatures, proportionately a lot of of them area unit live-bearing, he adds. (See "Evolution in Action: Lizard Moving from Eggs to measure Birth.")
Only birds, turtles, and crocodilians bear no live young the least bit.
Live birth is additionally rare in fish, accounting for concerning 2 % of identified species, together with guppies and sharks.
In some sharks that bear live pups, “the mother produces egglets that don't seem to be fertile, and also the babies area unit feeding on them whereas within the ovary,” says David Reznick, associate degree biological process life scientist at the University of CA, Riverside. (See "Pictures: Rare "Cyclops" Shark Found.")