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Examples of Evolution: One Skink, Five Skink, Egg Skink, Live Skink
Episode 11723rd November 2021 • My AP Biology Thoughts • Hopewell Valley Student Publications Network
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My AP Biology Thoughts  

Unit 7 Natural Selection 

EPISODE TITLE: One Skink, Five Skink, Egg Skink, Live Skink

Welcome to My AP Biology Thoughts podcast, my name is Diana along with Sofia and Saahith and we are your hosts for Unit 7: Examples of Evolution-The Three Toed Skink- and I know what you’re thinking…. nope this is not derogatory or a slur. In episode 117, we will be discussing the species the Three Toed Skink and how it relates to the AP Biology Curriculum. We want to thank our sources for the information presented in this podcast episode today which include Reptiles Magazine, National Geographic, Eurekalert.org, syfi.com, phys.org, and sciencedaily.com. You can find the citations and links to these sources in the show notes.

Segment 1: Overview of The Three Toed Skink (Diana)

The three toed skink, aka Saiphos equalis, is found in eastern Australia, primarily in New South Wales and Queensland. The three-toed skink is sometimes mistaken for a snake, eats crawling insects and worms, and is active at night. The three toed skink is a “bimodally reproductive species” WHATS THAT this means that some lay eggs and some give birth. Dr. Whittington, from the School of Life and Environmental Sciences and Sydney School of Veterinary Science at the University of Sydney in the article “Biologists observe a three-toed skink lay eggs and give birth to a baby,” says, “Put in the context of evolutionary biology, being able to switch between laying eggs and giving live birth could allow animals to hedge their bets according to environmental conditions." There are at least 150 evolutionary transitions from egg-laying to live-bearing in vertebrates. To elaborate on this, Sofia will share the interesting evidence of evolution of the Three Toed Skink.

Segment 2: Evidence that supports The Three Toed Skink (Sofia)

Thank you, Diana, for that beautiful introduction to our beloved skinks. In the article, “Which Came First, the Lizard or the Egg”, Dr. Camilla Whittington from the University of Sydney skink research team describes how the earliest vertebrates were egg-layers, but that over thousands of years, embryos remained inside their mother’s for longer, until some began live births. WHAAAAATTTT?? The Three-toed skinks are an example of a species that have evolved to perform both reproduction methods of egg-laying and live births. Get yourself a skink who does both. Direct observation studies have revealed that the skink species located on the warm weathered coasts of New South Wales lay eggs rather than performing live birth. On the contrary, the skinks located in the cold weathered mountains of South Wales give live births. Scientists suggest that mothers in warm climates lay eggs to conserve their own bodies’ resources, while mothers in cold climates protect their young by keeping them inside the oven for longer. Additionally, evolutionary records show that nearly 100 reptile lineages have independently made the transition from egg-laying to live birth in the past, which supports that these skinks transition to adapt to their environment. On to Saahith my HANDSOME best buddy, who has some very wonderful connections between the three-toed sinks and our lovely evolution principles. 

Segment 3: Connection to the Course (Saahith)

These skinks relate to topic 7.2,natural selection , 7.6 evidence of evolution, and 7.7 common ancestry in the AP Biology Curriculum. In the course, it is taught that evolution is supported by scientific evidence from many disciplines (geographical, geological, physical, biochemical, and mathematical data) the Three toed skink is an example of geographical evidence as skinks in warmer areas lay eggs and skinks in colder areas give birth to live younger. The warmer areas lay eggs in order to conserve body resources and live longer and produce more offspring. The colder areas give birth to live young because they want them to stay inside the adult in order to grow more and stay in a warm environment before being out in the cold. This is an example of natural selection as the baby skinks are kept in the parent skink in order to become more developed since they will be in a cold environment which makes it harder for them to live and maintain homeostasis of their body temperature. The skinks in these cold areas that laid eggs have eventually died off since they are not well suited for the environment and provide inadequate young that are unable to survive in the cold. WEAKKKKK !! Also it is believed skinks and snakes common vertebrates at first laid eggs but overtime with that vertebrate evolving at least 115 times, giving birth to live young became more and more common. The skinks in different areas most likely arrived from a common ancestor. To prove it we would need a comparison of DNA nucleotide sequences or amino acid sequences that would provide evidence of evolution and common ancestry.

Thank you for listening to this episode of My AP Biology Thoughts. For more student-ran podcasts and digital content, make sure that you visit www.hvspn.com. (Remember… one skink, five skink, egg skink, live skink)! Ay and for my people out there, remember, always keep it a hundo. Get that 5. Goodbye. 

Music Credits:

  • "Ice Flow" Kevin MacLeod (incompetech.com)
  • Licensed under Creative Commons: By Attribution 4.0 License
  • http://creativecommons.org/licenses/by/4.0/

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Notes on topic: 

https://phys.org/news/2010-09-scientists-evolution-action.html

  • One of 3 reptiles to have diff methods of reproduction in diff places
  • Lay eggs in Sydney, australia and coastal areas of New South Wales
  • Give birth to live young in Northern Highlands of New South Wales
  • Resembles small snake with mini legs, nocturnal
  • Intermediate skinks that retain eggs internally for longer. Live young birthers evolved from these
  • Giving birth to live young is advantage in cold areas

https://www.syfy.com/syfywire/bizarre-lizard-is-evolving-right-nowhttps://www.syfy.com/syfywire/bizarre-lizard-is-evolving-right-now

  • Earliest vertebrates laid eggs
  • Lizards and snakes evolved at least 115 times
  • Egg laying population in sydney is a transitional form from egg laying to live birth

https://reptilesmagazine.com/three-toed-skinks-ability-to-give-birth-and-lay-eggs-may-signal-evolutionary-shift/ 

  • Skinks may be in the midst of evolutionary shift between being an egg-later and a livebearer
  • “Bimodally reproductive” : species can lay eggs or give live births
  • Is the first known vertebrate to perform both in a single litter (clutch)
  • May be intermediate form between animals that lay eggs and those that give birth
  • Camilla Whittington: direction of skink evolution is not known yet
  • Egg-laying is more advantageous in certain areas
  • Oviparous S. equalis is an intermediate form between true oviparity and viviparity

https://www.nationalgeographic.com/animals/article/100901-science-animals-evolution-australia-lizard-skink-live-birth-eggs 

  • Mystery of how young get nourishment before birth during live baby reproduction
  • In egg-laying species the embryo gets nourishment from the yolk, but calcium absorbed from the shell is also important for nutrients
  • The shells of the eggs thin, so the embryos can breathe until the live babies are born covered with only thin membranes
  • But thinner shell has less calcium… can cause deficiencies for young reptiles
  • Uterus secretes calcium that becomes incorporated into the embryo
  • Eggs are more vulnerable to external threats (weather and predators)
  • Internal fetuses are more taxing on the mother
  • Mothers in warm climates lay eggs to conserve their own bodies’ resources
  • Mothers in cold climates protect their young by keeping them inside for longer

https://www.nationalgeographic.com/animals/article/100901-science-animals-evolution-australia-lizard-skink-live-birth-eggs   

  • Skink species lays eggs on the coast but births babies in the mountains
  • Yellow-bellied three-toed skinks along warm coastal lowlands of New South Wales lay eggs
  • Three-toed skinks living in New South Wales higher, colder mountains give birth to live young
  • Evolutionary records show nearly a hundred reptile lineages have independently made the transition from egg-laying to live birth in the past
  • About 20% of all living snakes and lizards give birth to live young only
  • Mothers in warm climates lay eggs to conserve their own bodies’ resources
  • Mothers in cold climates protect their young by keeping them inside for longer

https://www.eurekalert.org/news-releases/737125 

  • Researchers at University of Sydney observed a female skink who gives birth to live babies, give birth to three eggs, then give a live birth from the same pregnancy only weeks later
  • Dr Whittington: "The earliest vertebrates were egg-layers, but over thousands of years, developing embryos in some species were held inside the body for longer, until some animals began to give live birth. People mostly think about humans and other mammals giving birth. But there are many species of reptile that give birth, too." 

https://www.sciencedaily.com/releases/2019/04/190402215619.htm 

Works Cited

Rayne, E. (2020, April 10). Thought evolution was ancient? this lizard is evolving, like, right now. SYFY WIRE. Retrieved October 14, 2021, from https://www.syfy.com/syfywire/bizarre-lizard-is-evolving-right-now. 

Edwards, L. (2010, September 6). Scientists watch evolution in action. Phys.org. Retrieved October 14, 2021, from https://phys.org/news/2010-09-scientists-evolution-action.html. 

Staff, S., & Staff, A. U. T. H. O. R. S. (2020, May 1). Three-toed skink's ability to give birth and lay eggs may signal evolutionary shift. Reptiles Magazine. Retrieved October 14, 2021, from https://reptilesmagazine.com/three-toed-skinks-ability-to-give-birth-and-lay-eggs-may-signal-evolutionary-shift/. 

Handwerk, B. (2021, May 4). Evolution in action: Lizard moving from eggs to live birth. Animals. Retrieved October 14, 2021, from https://www.nationalgeographic.com/animals/article/100901-science-animals-evolution-australia-lizard-skink-live-birth-eggs. 

Handwerk, B. (2021, May 4). Evolution in action: Lizard moving from eggs to live birth. Animals. Retrieved October 14, 2021, from https://www.nationalgeographic.com/animals/article/100901-science-animals-evolution-australia-lizard-skink-live-birth-eggs. 

SydneyUni_Media. (n.d.). Which came first, the lizard or the egg? EurekAlert! Retrieved October 14, 2021, from https://www.eurekalert.org/news-releases/737125. 

Biologists observe a three-toed skink lay eggs and give birth to a live baby. (2019, April 02). Retrieved October 14, 2021, from https://www.sciencedaily.com/releases/2019/04/190402215619.htm

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