Three-toed skink. Image: Doug Beckers The three-toed skink ( Saiphos equalis ), a small lizard native to eastern Australia, managed to deliver members of the same litter both in eggs and through live birth. This means that the species may be an “intermediate form” between egg-laying animals and species that give birth to live offspring, according to a recent study in _Molecular Ecolog_y. While it’s possible that the skink is transitioning between oviparity, the ability to lay eggs, and viviparity, or the ability to give birth, the ultimate evolutionary trajectory of the animal remains unpredictable. “We don’t know which ‘direction’ evolution is taking,” said corresponding author Camilla Whittington, an evolutionary biologist at the University of Sydney, in an email. “In some environments, egg-laying might be more advantageous than live-bearing. In that situation, we would predict that egg-laying would persist.” Three-toed skinks are one of a handful of species capable of bimodal reproduction, meaning that some populations are oviparous while others are viviparous. However, it is the only species that has ever been seen employing both modes during the same pregnancy, which demonstrates an unprecedented example of reproductive versatility. In addition to the Molecular Ecology study, Whittington and her colleagues […]

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