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.




Read more:
Ancient fossil fills a 75 million-year gap and rewrites lizard and snake history


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.




Read more:
A hidden toll: Australia’s cats kill almost 650 million reptiles a year


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.




Read more:
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.




Read more:
Curious Kids: why do hens still lay eggs when they don’t have a mate?


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.

Advertisements

Leonardo da Vinci revisited: was he an environmentalist ahead of his time?



File 20190315 28505 1vohzad.jpg?ixlib=rb 1.1
Leonardo da Vinci, Landscape drawing for Santa Maria della Neve on 5th August 1473.
Wikimedia commons

Susan Broomhall, University of Western Australia and Andrea Gaynor, University of Western Australia

On the 500th anniversary of his death, this series brings together scholars from different disciplines to re-examine the work, legacy and myth of Leonardo da Vinci.

Leonardo’s notebooks are filled with illustrations of nature, both plants and animals, their interactions with humans and in local ecosystems. Did his deep engagement with the natural world make him an environmentalist ahead of his time?

Leonardo was a child of the Tuscan countryside, raised in the tiny village of Anchiano, although he spent most of his adult life at the courts of dukes, kings and princes.

Some of his work for these patrons involved planning interventions into nature, most often managing waterways, but his sketches suggest his attention roamed further than the projects he was commissioned to undertake.

He spent time with friends in a villa outside of Milan observing the country nearby and sketching plans for gardens there, and ended his life on a little country estate that was then on the outskirts of Amboise in France.

One of his first biographers, Giorgio Vasari, tells us that Leonardo

delighted much in horses and also in all other animals, and often when passing by the places where they sold birds he would take them out of their cages, and paying the price that was asked for them, would let them fly away into the air, restoring to them their lost liberty.

Leonardo da Vinci, Study sheet with cats, dragon and other animals, c. 1513.
Wikiart.org

Leonardo was also reportedly a vegetarian. This supposition comes from the explorer Andrea Corsali’s description of the non-meat-eating Gujarati people (from modern India) as like “our Leonardo da Vinci”.

The many notebooks and loose sheets Leonardo filled with jottings and illustrations across his lifetime reveal his close observation of nature — from cats and crabs to flowers and copses of trees – and the spirit of enquiry from which he drew many lessons.

One jotting simply states: “Ask the wife of Biagio Crivelli how the capon nurtures and hatches the eggs of the hen”.

His understandings of the habits of animals informed a series of fables and proverbs bearing witness to various emotional traits he attributed to them: gratitude, rage, cruelty and generosity among them. He suggested, for instance, that “we see the most striking example of humility” in the lamb.

Star of Bethlehem, Ornithogalum umbellatum
Wikiart.org

The random cruelty of nature

But Leonardo was also struck by the violence of natural processes. Nature appears to have been “rather a cruel stepmother”, he wrote. “Why did nature not ordain that one animal should not live by the death of another?”

He reflected on the random cruelty of nature in a series of riddles, created across his notebooks. For instance, in the entry on walnut trees, he writes in emotional terms of the violence wrought upon these trees as humans enjoyed their seeds: “beaten, and their offspring taken and flayed or peeled, and their bones broken or crushed.”

Leonardo da Vinci, Studies of crabs, c. late 15th century.
Wikiart.org

Still, Leonardo does not seem to have been particularly concerned about the role of humans in enacting violence against other species. His own quest for knowledge and artistic creativity demanded it.

Vasari tells a story of the young Leonardo seeking to depict a frightening creature on a shield he had “brought for this purpose to his room, which no one entered but himself, lizards, grasshoppers, serpents, butterflies, locusts, bats, and other strange animals of the kind …” “The smell in the room of these dead animals was very bad, though Leonardo did not feel it from the love he bore to art.”

Vasari talks of how Leonardo “suffered much in doing it” – but not as much as the other species whose lives were sacrificed for his art.

In other tales, Vasari tells us how Leonardo, while he was working for Giuliano de’ Medici in Rome, discovered an unusual lizard and promptly

made some wings of the scales of other lizards and fastened them on its back with a mixture of quicksilver, so that they trembled when it walked; and having made for it eyes, horns, and a beard, he tamed it and kept it in a box.

For Vasari, these stories show Leonardo’s “marvelous and divine” mind, but they could also be interpreted as showing the instrumental way in which Leonardo thought about nature, as a resource to expand human knowledge and control the environment.

Leonardo da Vinci, Birch copse, c. 1500.
Wikiart.org

Leonardo’s nature

His contemporaries clearly thought there was something different about Leonardo and his interest in nature. Does this make him a kind of pre-modern environmentalist?

Western environmentalism (and before it, preservationism) is often understood to have become possible when nature had been subdued by technology. With urbanisation and development of a middle class, more people could feel sentimental about nature.

Although he was raised in the countryside, Leonardo spent most of his everyday adult life in major European towns in the company of princes and kings. He was no longer concerned directly with the need to cut down wood for warmth or kill animals for food. We could say, then, that he could afford to be more sentimental about nature.

Leonardo da Vinci, Natural disaster, c. 1517.
Wikiart.org

Certainly his exquisite drawings suggest a particular depth of feeling, attunement and sensitivity to the natural world. And yet it seems that preservation of nature was not on Leonardo’s mind.

He had not witnessed the speed and scale of devastation of the natural world wrought by humanity with the onset of industrialisation. Instead, he understood destruction as part of the cycle of nature. If, as he wrote, nature “seeks to lose its life, desiring only continual reproduction”, there was nothing to be protected, for annihilation and creation went hand in hand.The Conversation

Susan Broomhall, Professor of History, University of Western Australia and Andrea Gaynor, Associate Professor of History, University of Western Australia

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

Shorten’s climate policy would hit more big polluters harder and set electric car target


Michelle Grattan, University of Canberra

A Shorten government would add about 100 high polluters to those subject to an emissions cap, and drastically slash the present cap’s level, under the opposition’s climate policy released on Monday.

Labor would aim for a new threshold under a revamp of the existing safeguards mechanism of 25,000 tonnes of direct carbon dioxide pollution annually, which would be phased in after consultation with industry.

This would be a major reduction from the current cap of 100,000 tonnes. About 140 to 160 polluters come under the existing cap.

The safeguards mechanism was established by the Coalition government to cap pollution for the biggest polluters by setting limits or “baselines” for facilities covered. But Labor says it has been ineffective.

On transport, the policy sets an ambitious target of having electric vehicles form 50% of new car sales by 2030. The government fleet would have an electric vehicle target of 50% of new purchases and leases of passenger vehicles by 2025.

The climate change policy covers industry, transport and agriculture, with the proposed measures for the electricity sector, including an in-principle commitment to a national energy guarantee (NEG) and subsidies for batteries, already announced.

The agriculture sector would not be covered by the expanded safeguards policy.

The government’s emissions reduction fund – recently allocated a further A$2 billion over a decade and renamed – would be scrapped if Labor wins the May election.

The climate policy is the third of three key policy announcements the opposition wanted to make before the election is called, likely next weekend. The others were the wages policy and the announcement of the start date – January 1 – for the proposed crackdown on negative gearing.

The opposition has committed itself to a 45% economy-wide reduction in emissions relative to 2005 levels by 2030, compared with the government’s commitment to a reduction of 26-28%.

Labor’s policy confirms that it would not use Australia’s credits from the expiring Kyoto Protocol to help meet its Paris target, saying this course is “fake action on climate change”. Bill Shorten said on Sunday: “It’s only the Australian Liberal Party and the Ukraine proposing to use these carryover credits that I am aware of.”

Labor says it would “work in partnership with business to help bring down pollution.”

“Labor’s approach isn’t about punishing polluters. It’s about partnering with industry to find real, practical solutions to cut pollution, in a way that protects and grows industry and jobs.”

“There will be no carbon tax, carbon pricing mechanism, or government revenue,” Labor says.

“Rather, Labor will reduce pollution from the biggest industrial polluters by extending the existing pollution cap implemented by Malcolm Turnbull.”

“Pollution caps will be reduced over time and Labor will make it easier for businesses to meet these caps by allowing for industrial and international offsets.”

The expanded scheme’s new threshold would capture an estimated 250 of the biggest industrial polluters – 0.01% of all businesses.

Businesses would be able to earn credits for “overachievement” – reducing pollution below their baselines. They could sell these credits or use them to meet their future cap.

“Tailored” treatment would be provided to emissions-intensive trade-exposed industries (EITEs) such as steel, aluminium and cement. There would be a A$300 million Strategic Industries Reserve Fund “to support these industries in finding solutions to cut pollution and remain competitive”.

A Shorten government would consult with industry and experts on baselines for individual entities and the timing of reduction.

It would also put in place “a well-functioning offset market and reinvigorate the land offset market”.

“Currently, a facility that emits more than its baseline must offset excess emissions by purchasing offsets, primarily from the land sector. But currently businesses cannot access international offsets, or offsets from the electricity sector.

“Labor will make it easier for covered businesses to meet any offset obligations, not only by allowing for the creation and sale of offsets if emissions fall below baselines, but also through the purchase of international offsets and potentially offsets from the electricity sector.

“We will also boost offset supply through revitalising the Carbon Farming Initiative (CFI) – including reforms to strengthen the integrity of the CFI, and increasing land and other sector abatement opportunities.

“This will include exploring the establishment of ‘premium’ land sector credits to provide substantial environmental, biodiversity and other co-benefits, establishing a Carbon Assessment Standard to boost the bankability of offset projects, and re-vitalising offset methodology research and development with an additional A$40 million in funding over four years.

“Labor’s plan will help industry reduce pollution at least cost, and give traditional owners, farmers, the forestry industry and traditional owners new opportunities to earn income.”

On transport – which accounts for nearly 20% of Australia’s emissions – Labor says Australia is now last among western countries for electric vehicle uptake.

“Setting a national target will deliver more affordable electric vehicles into the Australian market and drive the switch to electric vehicles, reducing their cost, creating thousands of jobs and cutting pollution.”

Businesses would get an upfront tax deduction to buy electric vehicles, as part of the ALP’s announced Australian Investment Guarantee.

One aspect of moving quickly to government electric vehicle fleets would be that it would develop a secondhand market, Labor says.

“Labor will also work with industry to introduce vehicle emissions standards, to save Australian motorists hundreds of dollars each year at the bowser while driving down pollution on our roads.

“Australia is now one of the only developed nations without vehicle emissions standards in place. As a result, motorists will pay as much as A$500 each year more at the bowser than they should be, as well as seeing pollution on our roads skyrocket.

“Labor will consult on the timeline and coverage of vehicle emission standards to ensure consumers are made significantly better off, and aim to phase-in standards of 105g CO₂/km for light vehicles, which is consistent with Climate Change Authority advice.”

These standards would be in line with those in the United States but less stringent than those in the European Union.

“These standards will be applied to car retailers to meet average emissions standards, rather than imposing blanket mandatory standards on manufacturers.

“This will allow retailers to meet the standards by offsetting high emissions car sales with low or zero emissions car sales – such as electric vehicles.”



Emily Nunell/Michael Hopkin/The Conversation, CC BY-ND

UPDATE: Reaction

The government has reacted predictably to the Labor climate plan, branding it a “new tax”, ahead of what will be a major Coalition scare campaign in the election.

Scott Morrison said the opposition leader “does not have a plan, he just has another tax.

“What we’ve got here is a ‘re-Rudd’ of a failed policy that costs jobs, that costs businesses, that will cost Australians at least $9,000 a year, with the reckless targets that Bill Shorten will make law.”

On electric cars, Morrison said Shorten needed to explain how in 10 years he would take them from 0.2% of the market to 50% – because if he didn’t achieve his “reckless target […] he has to come back and get that money off you”.

Energy Minister Angus Taylor said the Shorten policy “would be a wrecking ball in the economy.

“It would raise the price of electricity and the price of gas and the price of food and the price of cars. Labor needs to come clean on the detail – not just the mechanism, which we know is the carbon tax.”

The Business Council of Australia welcomed the further details Labor had provided but said there were unanswered questions including “what mechanism will drive and manage the transition to lower-emissions generation in the electricity sector?”

“It remains unclear how abatement will be delivered in the electricity sector and how the various announcements made today will contribute to an economy-wide emissions reduction target,” the BCA said.

It said it had strongly supported the National Energy Guarantee (NEG) and called on the ALP, if elected, “to commit to working with the states and territories to implement the scheme as a credible, market-based mechanism to drive abatement and investment in the electricity sector.”

The Labor party has supported in principle a NEG – the plan the Coalition dumped because of an internal split over it.

The Australian Conservation Foundation gave Labor’s policy a qualified tick, describing it as “a serious policy response to the existential threat of global warming that recognises pollution must be cut across all industry sectors.”

“Labor’s climate change plan does address many of the important challenges Australia has in transforming into a zero-pollution economy,” the ACF said.

But “unfortunately, sections of Labor’s policy platform contain significant wriggle room that big polluters may seek to exploit.

“If it wins government Labor must quickly harden the detail around its policies and resist attempts of industry lobby groups like the Minerals Council of Australia, the Business Council of Australia and the Australian Automobile Association to weaken climate action.”The Conversation

Michelle Grattan, Professorial Fellow, University of Canberra

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