How will global warming affect egg-laying and live-bearing species? We asked one of the most extraordinary lizards in the world

By Iván Beltrán

Environmental temperature determines many important aspects of an animal’s life. In ectotherms, commonly known as ‘cold-blooded’ animals, the temperature experienced during embryonic development significantly impacts a hatchling’s physiology and behaviour. For instance, nest temperatures determine offspring sex in turtles and crocodilians and affect body size in squamates, a group comprised of lizards and snakes. Although most squamates are egg-layers (oviparity), live-bearing (viviparity) has evolved independently many times within this group. In viviparous species, the temperatures experienced by the embryo depend on female thermoregulation and not on her choice for the location and depth of the nest as occurs in oviparous species. Hence, the repeated convergent evolution of viviparity is considered to be the result of a response from females to protect the embryos from cold/unsuitable temperatures.

Rising environmental temperatures due to global warming have already caused changes in geographic distribution and local extinctions in many squamate populations around the world. However, we still have a poor understanding of whether global warming will affect viviparous and oviparous species differently.

In a couple of studies published recently, we examined the effect of current and predicted end-of-century developmental temperatures on the phenotype of the Australian lizard Saiphos equalis. This lizard is one of only three reptile species known to exhibit geographic variation in reproductive mode, representing a unique opportunity to study the interaction between global warming and reproductive mode while controlling for relatedness.

The populations of S. equalis along the Northern Tablelands of New South Wales (NSW) give birth to fully-developed hatchlings inside a membrane from which they emerge within a couple of days (Fig. 1a). The populations from the eastern coast of NSW lay shelled eggs in which embryos continue developing outside the female’s body for approximately 7–10 days (Fig. 1b).

We evaluated the effect of different thermal environments during development on the body size, growth rate, thermal preference, foraging ability, locomotor performance and spatial learning of hatchling lizards from oviparous and viviparous populations of Saiphos equalis.

Figure 1. Egg and hatchlings of viviparous (left) and oviparous (right) Saiphos equalis, one of only three lizard species known to exhibit geographic variation in reproductive mode. Photo credit: Théotime Colin and Iván Beltrán.

We found that, regardless of the reproductive mode, elevated temperatures shortened the gestation period of Saiphos equalis. However, only in oviparous lizards, elevated temperatures produced small hatchlings that grew more slowly compared to viviparous lizards from the same treatment. Similarly, elevated temperatures reduced the foraging efficiency of oviparous, but not viviparous, hatchling S. equalis. Future-gestated oviparous hatchlings were more likely to choose the correct refuge and made fewer mistakes in a spatial learning task; however, we found only weak evidence of spatial learning in S. equalis. Finally, elevated temperatures did not affect the thermal preferences and locomotor performance of hatchlings Saiphos equalis (Fig. 2).

Our study shows that both viviparous and oviparous populations of S. equalis were affected by elevated developmental temperatures; however, we found that high developmental temperatures had a stronger effect on oviparous S. equalis. Of the 23 oviparous lizards that hatched successfully under high temperatures, six (26 %) of them died within the six months that the experiment lasted, while all viviparous lizards survived until the end of the experiment.

Figure 2. Negative (–), positive (+) or no (~) effect of elevated developmental temperatures on several phenotypic traits of viviparous and oviparous Saiphos equalis.*Results are inconclusive because we found only weak evidence of spatial learning in the species.

These results suggest that viviparous females are somehow buffering the negative effects of high temperatures on their offspring. One possibility is that females are modifying their thermoregulatory behaviour to mitigate the effect of external temperatures on their offspring. However, it is also possible that our results are due to physiological differences during pregnancy between viviparous and oviparous populations. Although these populations are closely related, recent research has shown that, during pregnancy, viviparous and oviparous females differ in the expression of genes important for uterine remodelling, embryo respiration, and immune regulation.

Our results suggest that, like in other reptiles, global warming will affect multiple phenotypic traits in S. equalis. However, some of these effects may be ameliorated by maternal behaviour and/or physiological responses during pregnancy, particularly in viviparous populations.

Please contact us if you would like a PDF of these papers or access them here:

Beltrán I, Durand V, Loiseleur R & Whiting M.J. 2020. Effects of early thermal environment on the morphology and performance of a lizard species with bimodal reproduction. Journal of Comparative Physiology B 190, 795–809. Link to paper.

Beltrán I, Loiseleur R, Durand V & Whiting M.J. 2020. Effects of early thermal environment on the behavior and learning of a lizard with bimodal reproduction. Behavioural Ecology and Sociobiology 74: 73. Link to paper.

Do I, or don’t I? Are lizards capable of inhibitory control?

Blog post by Sebastian Hoefer

We often think of reptiles as somewhat simple – entirely driven by instinct and the basic need for survival. That is where the expression “Reptilian Brain” comes from. It is certainly true that the anatomy of the . . . → Read More: Do I, or don’t I? Are lizards capable of inhibitory control?

Competing through eating: lessons from a lizard

Post by Isabel Damas

One way invasive species can have a major impact on ecosystems, is by threatening native species, particularly through competition for resources. Animals typically use two strategies to out-compete their opponents: they can be directly aggressive (termed interference competition), or they can indirectly out-compete rivals by consuming more resources (exploitative . . . → Read More: Competing through eating: lessons from a lizard

Dispatches from the field: following the Sulawesi Forest Turtle

Note, this field work formed the basis for Angela’s Masters thesis.

By Angela Simms

I wasn’t sure what to expect on the first night searching for the Sulawesi Forest Turtle. As little as 30 minutes into the stream walk, our local guide spots a large male perched on the edge of the clear shallow . . . → Read More: Dispatches from the field: following the Sulawesi Forest Turtle

Dr. Birgit Szabo talks lizard smarts!

Birgit recently gave a public lecture about her research on lizard cognition at a mini-conference “The Future of Herpetology, Inspiring Women and Forgotten Frogs: A conference promoting women’s voices in herpetology”. Watch her talk (below) and find out more about Birgit and her work on her web page.

Dr. Birgit Szabo talking about . . . → Read More: Dr. Birgit Szabo talks lizard smarts!

Blue-tongue lizards are born smart, at least as smart as their parents!

By Birgit Szabo

As children we have much to learn after we are born. We learn to walk, to talk, to develop our social skills, and when we start school we learn how to read, write and do maths.

​Humans, and many other animals, are considered altricial, meaning that juveniles need to be taken . . . → Read More: Blue-tongue lizards are born smart, at least as smart as their parents!

Australian Geographic features frilled lizard work!

The latest edition of Australian Geographic features the iconic Australian Frill-necked Lizard (Chlamydosaurus kingii). A big part of the article, written by John Pickrell, features our own Christian Alessandro Perez-Martinez! And the top of the page features his photo (reproduced at left). Well done Christian! Have a read of the article.

The paper, . . . → Read More: Australian Geographic features frilled lizard work!

Hot off the press! An invasive lizard species can learn from other species

Check out our new paper on social learning in the Italian wall lizard, Podarcis sicula. This work formed part of Isabel Damas’ PhD thesis, and it was a huge effort! The question of what makes an invasive species successful compared to other species, that may fail to gain a foothold in a new location, . . . → Read More: Hot off the press! An invasive lizard species can learn from other species

What tree skinks know about change: A story in colour and shape

Note from Martin Whiting: This blog posts details a chapter of Birgit Szabo’s PhD recently published in Animal Behaviour and represents an enormous amount of work. Birgit did a 9-month cognition experiment, which could be the longest lizard cognition experiment thus far conducted. (Let us know if it isn’t!) The work is in collaboration . . . → Read More: What tree skinks know about change: A story in colour and shape

Come on a tour of The Lizard Lab

This is a behind-the-scenes video tour of the lab. We will show you our research facilities, some of our study animals, and our lizard enclosures. This video was entirely put together by Cooper Van De Wal. Cooper is a student at Macquarie and volunteers in the lab. He also has his own, highly successful . . . → Read More: Come on a tour of The Lizard Lab