Photos from the field: Australia is full of lizards so I went bush to find out why



A lace monitor (Varanus varius)
Kristian Bell, Author provided

Kristian Bell, Deakin University

Environmental scientists see flora, fauna and phenomena the rest of us rarely do. In this new series, we’ve invited them to share their unique photos from the field.


Though it may not be as famous a stereotype as shrimps on the barbie, deadly snakes or Vegemite, Australia is renowned in certain scientific circles for being the “land of the lizards”.

Australia has a higher diversity of lizards than anywhere else in the world. The number of different species within a single part of remote, central Australia well exceeds similar desert environments, such as the Kalahari in Africa, or the US.

Over the last 50 years, scientists have tried to understand the cause of this extraordinary and unique diversity.

Some suggest unpredictable resources in the arid outback, such as sporadic rain, favour low-energy animals like lizards over birds and mammals. Others claim a high diversity of termites allows lots of different termite-eating lizards to co-exist.




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Or perhaps the presence of shrubs, sparse trees and grass clumps provide a variety of niches (microhabitats) for tree and litter dwelling species. Despite these many hypotheses, no consensus has ever been reached.

My research explores the role of spinifex, a spiky clumping grass that’s typically found in the arid outback, often in conjunction with lizard diversity hotspots.

With many species found nowhere else on earth, some Australian lizards are threatened with extinction. Understanding how and why lizards use this iconic outback plant can help us conserve them, by predicting how they might respond to disturbances such as habitat loss and climate change.




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Following many trips to the outback, I was surprised to find locals who had never encountered some of the species I was studying. Taking photographs of these often small and overlooked animals helps me to better engage the community and raise the wider public profile of lizards, compared to other, more “charismatic” native animals.

A thriving desert ecosystem

All 60 species of spinifex grasses (members of the Triodia genus) are found only in Australia. Although spinifex habitats cover more than one-fifth of mainland Australia, the plant is little-known and little-loved by non-naturalists.

Spinifex clumps on red dirt
A typical mallee ecosystem where we conduct our research, with plenty of spinifex clumps interspersed with the many-stemmed trunks, characteristic of mallee eucalypts.
Kristian Bell, Author provided

Spinifex typically forms a spiky and impenetrable clump that provides useful, and in some cases essential, resources to lizards, birds, mammals and invertebrates.

But despite the close association of many lizard species to spinifex, we still don’t know exactly why reptiles like it so much.




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Three ideas dominate. First, spinifex may contain lots of food for lizards, such as termites or ants.

Alternatively, the spiky, needle-like leaves of spinifex may offer small lizards a great place to hide from predators. And finally, temperatures deep within a dense spinifex hummock can be very cool compared to the searing desert heat, where temperatures can reach a scorching 50℃.

My research aim is to work out which, if any, of these explanations is true. I do this by measuring variables such as temperature, invertebrate abundance and risk of becoming prey, in spinifex and other plants.

Alongside my supervisors, I have also conducted behaviour trials on a couple of spinifex-loving lizard species: the mallee ctenotus (Ctenotus atlas) and the mallee dragon (Ctenophorus spinodomus).

Setting up behavioural trial enclosures. After more than 100,000 recorded observations, we are only beginning to better understand why lizards like using spinifex.
Kristian Bell, Author provided

We have recorded 230,000 temperatures, caught 16,089 invertebrates, constructed 112 lizard models and classified 143,627 behavioural observations. But such is the complicated nature of the work, we’re only partially closer to understanding the lizard-spinifex relationship. So far, our data suggests temperature is a key component.




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The photos below are generally a result of good fortune and spending inordinate amounts of time in wild places. Pictures of some of the smaller, more skittish animals were taken upon release from pitfall traps.

A close-up of mallee ctenotus, a striped lizard
Mallee ctenotus (Ctenotus atlas)
Kristian Bell, Author provided
A profile of a mallee dragon
Mallee dragon (Ctenophorus spinodomus)
Kristian Bell, Author provided

The above two photos show my study species: the mallee dragon and the mallee ctenotus. Despite one lizard being a skink and the other a dragon, both species are strongly associated with spinifex. The skink tends to forage within spinifex, whereas the dragon emerges into open patches adjacent to spinifex to eat and “signal” to other dragons.

Spinifex with a rainbow in the background

Kristian Bell, Author provided

Spinifex grass, pictured above, with its spiky, needle-like leaves, creates valuable habitat for numerous species of birds, mammals and invertebrates — not just reptiles. Its abundance and influence on many species make it a “foundation species”.

Burton's legless lizard
Burton’s legless lizard (Lialis burtonis)
Kristian Bell, Author provided

This photo above shows a Burton’s legless lizard (Lialis burtonis) — a predator of my study species. These snake-like reptiles are specialist lizard hunters and often use the dense cover of spinifex to their advantage to ambush passing lizards.

Legless lizards might look a bit like snakes, but they have different ancestries and subtle distinguishing features, such as the lizard’s eyelids and external ears, which snakes don’t have.

But many other animals live in or near spinifex, and would happily make a meal of small lizards, including those shown in the following photos. The ability of numerous predators to access the centre of spiky spinifex clumps throws some doubt on the idea spinifex is used as protection from predators.

slender-tailed dunnart
Slender-tailed dunnart (Sminthopsis murina)
Kristian Bell, Author provided
A soaring black shouldered kite
Black shouldered kite (Elanus axillaris)
Kristian Bell, Author provided
Dwyers snake, with a researcher in the background
Dwyers snake.
Kristian Bell, Author provided
Sand monitor
Sand monitor.
Kristian Bell, Author provided

We can’t claim to have cracked the case yet. But we’re a step closer to unravelling the secrets behind one of Australia’s remarkable, and under-appreciated, biodiversity stories.




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Scientists capture rare footage of mother skink fighting a deadly brown snake to protect her babies


The Conversation


Kristian Bell, PhD candidate, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Scientists capture rare footage of mother skink fighting a deadly brown snake to protect her babies



Author provided

Gregory Watson, University of the Sunshine Coast and Jolanta Watson, University of the Sunshine Coast

Unlike many mammals and birds, most reptiles show little sign of being caring parents. But our new research shows one lizard species may be more doting parents than we thought – the adults risking their own safety to protect their babies.

We used cameras in the Snowy Mountains of New South Wales to study the Cunningham’s skink. We were surprised to record evidence of the lizards actively defending their newborn offspring against formidable predators. Our findings are outlined in a paper released today.

Most startlingly, we recorded a mother skink aggressively attacking a large, deadly brown snake while her babies watched on. We also witnessed 12 incidents of skinks chasing magpies away from their young.

We originally set out to record how species such as skinks will cope with climate change. But this evolved into a study of the fascinating and surprising social bonds between lizard offspring and their parents.

Adult and young skinks sun-baking together
Sun-loving skinks live together in social groups.
Authors provided

What is the Cunningham’s skink?

The Cunningham’s skink (Egernia cunninghami) is a large, sun-loving, spiny lizard native to southeast Australia. It’s named after Alan Cunningham, an explorer who collected the first specimen in the Blue Mountains.

The skinks are active during the day. They feed on invertebrates such as insects, snails and slugs, as well as vegetation.

The Cunningham’s skink lives in social groups – a behaviour very rare among lizards and reptiles. In these groups, mothers give birth to live young (rather than eggs) then live alongside their kids, sometimes for several years.

The species has strength in numbers – living in a group makes it easier to spot threats, which helps the group survive.

Adult and young skinks sun-baking together
Thew offspring of Cunningham’s skinks can stay with the parents for several years.

The mother of all discoveries

Using video and thermal imaging, we observed the skinks on 32 days over three years.

Among reptiles, evidence of parental protection in their natural environment has been rare and typically anecdotal. We witnessed four birthing sessions, and then monitored skink encounters in the presence of their offspring.




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Videoing nature can be tricky. Often, the action takes place away from where you’ve directed your camera. So when we saw a snake, it was a scramble to get a free video camera and start recording.

We witnessed two separate encounters with an eastern brown snake. The first involved the snake sneaking up on six-day-old skinks basking in the sun (see footage below). We recorded the mother running towards the predator and biting it for several seconds. The snake writhes around before the mother releases her grip and returns unharmed to her young.

The following year, we encountered two adult skinks attacking another eastern brown snake in bushes. Juvenile skinks were nearby. The skinks bit tight to the snake’s body, and the snake dragged them for more than 15 metres before the skinks released their grip.

Snakes were not the only predator vanquished by the protective skink parents – Cunningham’s skinks regularly chased magpies away from their young. We observed 12 encounters between skinks and magpies. In each case, an adult skink aggressively chased and/or attacked the magpie after the bird came close to the group.

Thermal camera image showing the mother skink attacking the snake while her babies watch on
Thermal camera image showing the mother skink attacking the snake while her babies watch on.

What does this all mean?

Some animals rarely interact with others of the same species, even their offspring. In fact, available data suggests infanticide – where mature animals kill young offspring of the same species – can occur among some skink species.

We saw no such behaviour among the Cunningham’s skink, or aggression towards each other.

While the aggression of the adult skinks towards predators took place in the presence of young, the adults may have been exhibiting self-defence or territorial behaviour. Regardless, the attacks on predators in the presence of newborns does reflect parental care, either directly or indirectly. Our future field excursions will hopefully shed more light on this.

Understanding the factors that bring parents and offspring together, and keep them together, is important in our broader understanding of social evolution – that is, how social interactions of species arise, change and are maintained.

It will also help us understand how animals cooperating with and caring for each other can benefit both the individual, and the whole.




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A few months ago, science gave this rare lizard a name – and it may already be headed for extinction


The Conversation


Gregory Watson, Senior Lecturer, Science, University of the Sunshine Coast and Jolanta Watson, Lecturer in Science, University of the Sunshine Coast

This article is republished from The Conversation under a Creative Commons license. Read the original article.

A few months ago, science gave this rare lizard a name – and it may already be headed for extinction


Australian Museum

Jodi Rowley, Australian Museum

This article is part of Flora, Fauna, Fire, a special project by The Conversation that tracks the recovery of Australia’s native plants and animals after last summer’s bushfire tragedy. Explore the project here and read more articles here.


Bushfires are a threat to most animal species. But for one rare lizard living on a rocky island in the sky, a single blaze could wipe the species off the planet.

The Kaputar rock skink (Egernia roomi) is thought to have have one of the smallest ranges of any reptile in New South Wales – at the summit of a single extinct volcano, Mount Kaputar.

The existence of this mysterious skink was informally known for decades, and in August last year the species was finally scientifically described. But months later, it may already be headed for extinction.

Late last year, bushfires are thought to have ripped through more than half the Kaputar rock skink’s habitat. We don’t yet know what this means for its survival, but the outlook is not good.

The fire in Kaputar National Park that tore through the skink’s habitat.
Narrabri Rural Fire Brigade

A very special skink

The Kaputar rock skink is handsome lizard, typically around 10 centimetres in body length, with dark chocolate brown and grey scales and an orange belly.

It’s found in the Nandewar Ranges near Narrabri. The ranges – weathered remnants of ancient volcanic eruptions between 21 and 17 million years ago – rise out of the surrounding plains in a series of breathtaking rock formations.




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The Kaputar rock skink lives on one of these outcrops, Mount Kaputar. It exists on a narrow band of rock at the summit, more than 1,300 metres above sea level.

This high elevation areas is cooler than the surrounding plains, which suits this cool-adapted species perfectly. But the species’ tiny range means it’s highly vulnerable. When danger strikes, the Kaputar rock skink has nowhere to go.

The skink lives at the highest point of Mount Kaputar.
Jodi Rowley, Author provided

When the fires hit

Bushfires tore through the Nandewar Ranges in October and November last year, reportedly burning more than 17,000 hectares of bush. More than half of Kaputar rock skink habitat is believed to have burned.

The expert panel advising the federal government on bushfire recovery has named the skink as one of 119 severely-affected species needing urgent conservation intervention. But the species’ rugged, remote habitat, combined with COVID-19 restrictions, have delayed efforts to assess the extent of the damage.




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It’s likely that many Kaputar rock skinks died during the fires themselves, although we hope others survived by crawling deep into rock cracks.

But after the fires, threats remain. Vegetation loss may make the skinks easy prey, and in a charred landscape, there may be little for the reptiles to eat.

History tells us fires do affect high-elevation skinks. For example, fire is thought to have driven the rock-dwelling Guthega skink (Liopholis guthega) to become locally extinct at some sites on the Bogong High Plains in northeast Victoria.

A mountain of threats

Species restricted to a small area are vulnerable to any loss of habitat. And fire is not the only threat to the Kaputar rock skink.

Climate change is a big concern. While many species respond to increasing temperatures by migrating uphill to cooler climes, that’s not possible for the skink, which is already precariously perched on a summit.




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Introduced goats may also be taking a toll as they trample through the rocky terrain.

Evidence suggests humans are also a disturbance to the Kaputar rock skink’s habitat. The reptiles live close to the edge of cliff lines that are readily accessible by walking tracks. Trampling of low vegetation has been observed at many sites, as have disturbed rocks – the latter possibly from people wanting to find and photograph the species.

The Kaputar rock skink’s tiny habitat was badly affected by fire.
Mark Eldridge, Author provided

Where to now?

Scientists know relatively little about the Kaputar rock skink. One thing we’re sure of, though, is that the species’ existence is threatened.

Surveys are needed at known skink locations, as well as surrounding areas where it might lie undiscovered. Understanding where the species occurs and how it responds to fires, drought and other disturbances is critical to conservation efforts.




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Of course it’s the middle of winter now, so the skinks may not be very active on their cold mountain top. But my colleagues and I hope to travel to Mount Kaputar soon to survey the skink’s habitat and find out how the species fared.

It’s just months since science officially welcomed the Kaputar rock skink to the world. It’s far too early to say goodbye.

Dane Trembath, an Australian Museum biologist with a focus on reptiles, contributed to this article.

The Conversation

Jodi Rowley, Curator, Amphibian & Reptile Conservation Biology, Australian Museum

This article is republished from The Conversation under a Creative Commons license. Read the original article.

I walked 1,200km in the outback to track huge lizards. Here’s why



Sophie Cross, Author provided

Sophie Cross, Curtin University

In 2017 and 2018 I walked the equivalent of 28 marathons in the scorching Western Australian outback. Why, you ask? To assess how some of Australia’s largest lizard species interact with restored mines.

As part of my PhD research, I hiked in often extreme heat on a mine site in WA’s sparsely populated Mid West region. My fieldwork was both physically and mentally demanding, as I spent many hours each day walking through the bush looking for signs of monitor lizards.

Being in a remote location and mostly alone, I had plenty of time to ponder the wisdom of my career choice, particularly on days when temperatures exceeded 40℃ and not even the lizards ventured from their homes.

Pushing through these mental challenges was difficult at times, but my work has provided me with some of my most rewarding experiences. And what I discovered may be crucial for restoring habitats destroyed by mining.

Restoring abandoned mines

Habitat loss is a leading cause of biodiversity loss worldwide. Although mining typically has a smaller environmental footprint than other major industries such as agriculture or urbanisation, roughly 75% of active mines are on land with high conservation value.




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There are around 60,000 abandoned mines in Australia, but very few of them have been officially closed. How to restore them is a growing public policy problem.

Sophie Cross walked more than 1,200km and tracked a young-adult perentie to find out whether they were using a restored mining area.
Author provided

Recovering biodiversity can be an exceptionally challenging task. Animals are vital to healthy ecosystems, yet little is understood about how animals respond to restored landscapes.

In particular, reptiles are often overlooked in assessments of restoration progress, despite playing key roles in Australian ecosystems.




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Do animals return to restored habitats?

I wanted to know whether restored habitats properly support the return of animals, or whether animals are only using these areas opportunistically or, worse still, avoiding them completely.

To study how reptiles behave in restored mining areas, I hand-caught and tracked a young adult perentie. The perentie is Australia’s largest lizard species, growing to around 2.5m in length, and is an apex predator in arid parts of the country.

I tracked the lizard for three weeks to determine whether it was using the restored area, before the tracker fell off during mating.

The tracking device revealed how the perentie navigated a restored mine, before it fell off during mating.
Author provided

Previous methods of tracking assume the animal used all locations equally. But I used a new method that measures both the frequency with which animals visit particular places, and the amount of time they spend there. This provided a valuable opportunity to assess how effective restoration efforts have been in getting animals to return.

Restoration needs more work

My research, published this week in the Australian Journal of Zoology, shows that while the perentie did visit the restored mine, it was very selective about which areas it visited, and avoided some places entirely. The lizard went on short foraging trips in the restored mine area, but regularly returned to refuge areas such as hollow logs.

The method used GPS and a VHF tracking antenna to follow the perentie.
Author provided

This is because hot, open landscapes with minimal refuges present high risks for reptiles, which rely on an abundance of coverage to regulate their body temperature and to avoid predators. Such costs may make these areas unfavourable to reptiles and limit their return to restored landscapes.

In comparison, undisturbed vegetation supported longer foraging trips and slower movement, without the need to return to a refuge area. Unfortunately, areas undergoing restoration often require exceptionally long time-periods for vegetation to resemble the pre-disturbed landscape.




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How can we help reptiles move back into restored areas?

Restored landscapes often lack key resources necessary for the survival of reptiles. As vegetation can require a long time to reestablish, returning fauna refuges like hollow logs and fauna refuge piles (composed of mounds of sand, logs, and branches) could be crucial to aiding in the return of animal populations.

My research team and I have called for animals to be considered to a greater extent in assessments of restoration success. In the face of increasing rates of habitat destruction, we need to understand how animals respond to habitat change and restoration.

Failing to do so risks leaving a legacy of unsustainable ecosystems and a lack of biodiversity.The Conversation

Sophie Cross, PhD candidate, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Why we’re not giving up the search for mainland Australia’s ‘first extinct lizard’



A grassland earless dragon at Jerrabomberra, NSW, November 1991. The search is now on for this species’ Victorian cousin.
CSIRO/Wikimedia Commons, CC BY

Jane Melville, Museums Victoria

You may have seen news in recent days of the suspected demise of the Victorian grassland earless dragon – now thought to be the first lizard species to be driven to extinction by humans in mainland Australia.

That suspicion arose on the basis of a newly published study in Royal Society Open Science by our research team, in which we discovered that the grassland earless dragons of southeastern Australia are not a single species, but four distinct ones: one that lives around Canberra, two in New South Wales, and one restricted to the Melbourne region.

The most recent confident sighting of the Melbourne species was 50 years ago, in 1969 – hence the fears that the Victorian species has already succumbed.

But despite this worrying news, we’re not leaving this lizard for dead just yet. Conservationists are now combing remaining grassland around Melbourne in a search for survivors.




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Although no lizard species have previously been declared extinct on the Australian mainland, the grassland earless dragons (Tympanocryptis) of southeastern Australia have long been the subject of conservation concern. Even before being split into four separate species, they were already officially listed as endangered.

The Victorian grassland earless dragon (Tympanocryptis pinguicolla) is known only to occur in the native grasslands around Melbourne. A review of historical collections at Museums Victoria show that it was found at several locations including Sunbury, Maribyrnong River (then called “Saltwater River”), and as far west as the Geelong area until the late 1960s.

Although there is little information available about the ecology of this species, it was described by Lucas and Frost in 1894 as:

Inhabiting stony plains and retreating into small holes, like those of the ‘Trap-door Spider,’ in the ground when alarmed […] Often met with under loose basalt boulders.

The last confirmed sighting was near Geelong in July 1969.

First mainland extinction?

Globally, 31 reptiles have been listed as extinct or extinct in the wild, according to the IUCN Red List, the global authority on the status of species. Two skinks and one gecko species have been declared extinct in the wild on Christmas Island, a remote Australian territory in the Indian Ocean. But until now there have been no recorded reptile extinctions on the Australian mainland.

Yet it is too early to give up on the Australian grassland earless dragon. Zoos Victoria researchers have completed a mapping analysis of potential grassland habitats. But this doesn’t give us enough information to say whether or not any grassland earless dragons remain.

There are several factors that leave open the possibility that the Victorian grassland earless dragon is still clinging to survival. There are some remaining habitat areas that have not yet been surveyed, and this species is small, secretive and hard to find. We urgently need more surveys to try and find any remaining populations.




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If these lizards are not yet extinct, their protection will clearly become an urgent conservation priority. But it is hard to develop a conservation program without knowing where the target species actually lives, or indeed whether it is still alive at all.

Zoos Victoria is now leading a campaign, alongside expert ecologists and local communities, to try and confirm the presence or absence of the Victorian grassland earless dragon. This involves various methods, including habitat mapping, camera trapping, and active searching. The team is also working to identify unsurveyed areas that might potentially be home to these elusive lizards.

Last year the team deployed a series of small pitfall traps at two locations in Little River. Unfortunately, no earless dragons were detected during the survey and few lizards of any species were caught, despite the fact that these locations seemed to offer appropriate food and habitat.

The team is not giving up yet and is committed to continuing the search, with Zoos Victoria researchers having identified sites with suitable habitat both within and outside of the historical distribution, which they aim to survey intensively over the coming years. Meanwhile, reptile keepers at Zoos Victoria are developing husbandry techniques to help look after the grassland earless dragon species from Canberra and NSW.

The conservation challenge has got harder, because where previously we were tasked with looking after one species, we now have to safeguard at least three – and hopefully four!


This article is based on a blog post that originally appeared here. It was coauthored by Adam Lee and Deon Gilbert of Zoos Victoria.The Conversation

Jane Melville, Senior Curator, Terrestrial Vertebrates, Museums Victoria

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The first known case of eggs plus live birth from one pregnancy in a tiny lizard


Melanie Laird, University of Otago and Camilla Whittington, University of Sydney

For most animals, reproduction is straightforward: some species lay eggs, while others give birth to live babies.

But our recent research uncovered a fascinating mix between the two modes of reproduction. In an Australian skink, we observed the first example of both egg-laying and live-bearing within a single litter for any backboned animal.

This suggests some lizards can “hedge their bets” reproductively, taking a punt on both eggs and live-born babies to improve overall survival chances for offspring.




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Making reproductive leaps

Most vertebrate species (animals with a backbone) fall neatly into one of two distinctly different reproductive categories.

Oviparous species are egg-layers. These eggs may undergo external fertilisation – such as in spawning fish – or are fertilised and shelled internally, like those of reptiles and birds. Oviparous embryos rely on egg yolk as a source of nutrition to continue development until hatching.

In contrast, viviparous species are live bearers that carry their young to term. Some live-bearing species, including humans, support embryonic development internally via a placenta. Egg-laying is ancestral, meaning that modern live-bearers have descended from egg-laying ancestors.

Physiologically, the evolution of live birth from egg-laying is no mean feat. This transition requires a whole suite of changes, sometimes including the evolution of a placenta – an entirely new specialist organ – as well as loss of the hard outer eggshell, and keeping the embryo inside the body for a longer time.

The placenta is a highly complex organ. One of its jobs is to transfer nutrition to the developing baby.
from www.shutterstock.com

Despite these complex steps, reptiles, particularly snakes and lizards, appear to be unusually predisposed to making the leap to live birth. This capacity has evolved in at least 115 groups of reptiles independently.




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Having it both ways

It’s easy to see why reptiles, as a group, are fascinating models for studying how live birth evolves from egg-laying.

Of particular interest are two Australian skinks that have both live-bearing and egg-laying individuals (known as being bimodally reproductive). These lizards are incredibly valuable to evolutionary biologists as they offer a snapshot into evolutionary processes in action.

The three-toed skink Saiphos equalis is one such species. Reproduction in S. equalis varies geographically: populations around Sydney lay eggs, while those further north give birth to live young.

Whether individuals are live-bearing or egg-laying seems to be genetically determined: when researchers swap their environmental conditions (by moving them from one site to another), the females retain their original reproductive strategy.




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Lizards help us find out which came first: the baby or the egg?


Mothers know best

Our latest research shows this lizard is intriguing in another completely unexpected way.

We observed a live-bearing female that laid three eggs, and then gave birth to a living baby from the same litter weeks later. We incubated two of the eggs, one of which hatched to produce a healthy baby.

A live-bearing female S. equalis in our laboratory colony laid three eggs, one of which hatched to produce a healthy baby.
Camilla Whittington

This finding is remarkable for two reasons. First, as far as we are aware, this is the first example of both egg-laying and live birth within a single litter for any vertebrate.

Second, in some cases, individuals may be capable of “switching” between reproductive modes. In other words, as laying eggs and giving birth each come with their own advantages and disadvantages, individuals may be able to “choose” which option best suits the current situation.

Closer look at eggshells

To better understand this reproductive phenomenon, we investigated the structure of the egg coverings of these unusual embryos in minute detail (using an advanced technology called scanning electron microscopy).

We found that in this litter, the egg-coverings were thinner than those of normal egg-laying skinks and had structural characteristics that overlapped with those of both egg-layers and live-bearers (which have thinner coverings that are greatly reduced).

Egg coverings of S. equalis consist of an outer crust (C) and an inner shell membrane (SM). We compared the structure and thicknesses of these layers of both egg-laying (A) and live-bearing (B) S. equalis to identify similarities with our ‘unusual’ embryos (C).
Melanie Laird

How evolution works

We still don’t know the trigger that caused this female to lay eggs and give birth to a live baby from the same pregnancy.

However, our findings suggest that species “in transition” between egg-laying and live bearing may hedge their bets reproductively before a true transition to live birth evolves.

Being able to switch between reproductive modes may be advantageous, particularly in changing or uncertain environments.

The three-toed skink lives in eastern Australia.
Doug Beckers / flickr, CC BY

For example, extreme cold, drought or the presence of predators can be risky for vulnerable eggs exposed to the environment, meaning that mothers that can carry offspring to term may have the upper hand.

In contrast, lengthy pregnancies can be taxing on the mother, so depositing offspring earlier as an egg may be beneficial in some situations.

We suggest that other species in which live birth has evolved from egg-laying relatively recently may also use flexible reproductive tactics.

Further research into this small Australian lizard, which seems to occupy the grey area between live birth and egg-laying, will help us determine how and why species make major reproductive leaps.




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The Conversation


Melanie Laird, Postdoctoral Fellow, University of Otago and Camilla Whittington, Senior lecturer, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.