Could mammals re-evolve oviparity?
Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
As previous answers have indicated, the prevailing belief in evolutionary biology was that once a species transitioned from oviparity (egg-laying) to viviparity (live birth), it was an irreversible step. However, recent research challenges this notion and provides evidence of multiple instances where viviparity evolved from oviparity and then reverted back. In a study conducted by R. Alexander Pyron and Frank T. Burbrink (Early origin of viviparity and multiple reversions to oviparity in squamate reptiles, 2013; Ecology Letters), a comprehensive taxonomic tree of squamate reptiles (both modern and ancestral species) revealed intriguing findings. Firstly, it became apparent that the ancestors of all squamates were viviparous, suggesting that viviparity was present in the lineage and lay dormant in certain species. Secondly, closely related lineages, like iguanids, exhibited frequent transitions between the two reproductive modes. This phenomenon is exemplified by the genus Phrynosoma, where some species display oviparity while others exhibit viviparity. The ability to crossbreed species within a genus and produce viable offspring has further supported the close relationship among species within a genus, as observed by pet hobbyists.
In squamate reptiles, the factors triggering these reproductive switches are a combination of temperature, temperature stability, and predation. It has been noted that in species expanding their territories into colder, northern regions, the newer species on the colder margins tend to be viviparous, while the ancestral species originating from warmer areas remain oviparous. This suggests that temperature and predation pressures play influential roles in determining the reproductive strategy of these reptiles.
This emerging understanding challenges the notion that transitions from oviparity to viviparity are strictly unidirectional. Instead, the evidence indicates a more complex evolutionary pattern involving multiple transitions between the two reproductive modes in different lineages of squamate reptiles.