Female Komodo dragons live about half as long as their male counterparts because the physically exhaustive nature of housework, such as building huge nests and guarding eggs from predators, leaves them weak.

The Komodo dragon (Varanus komodoensis) is the world’s largest lizard—sometimes reaching ten feet in length! Their formidable body size enables them to serve as top predators. They are able to kill water buffalo, deer, wild boar, and even humans.

Researchers from Australia, Indonesia, and Italy tracked 400 individual Komodo Dragons living in eastern Indonesia for ten years and produced a model of the dragons’ growth rate, published recently in the journal PLoS ONE.

Males and females grow at the same rate and remain the same size until age seven, when they reach sexual maturity. From then on, females start putting all their energy into the chores of motherhood, which makes them grow more slowly and die younger.

Meanwhile, the males’ energy reserves go into growing their bodies larger and larger to give them an edge in competing with other males for females and territory. The researchers found that male Komodo dragons live an average of 60 years, while females average just 32 years.

Professor Tim Jessop from the Department of Zoology at the University of Melbourne and a co-author on the study says that “these sex-based differences seem to be linked to the enormous amounts of energy females invest in producing eggs, as well as building and guarding their nests, a process that can take up to six months, during which they essentially fast, losing a lot of weight and body condition.”

The results could have dramatic consequences for the survival of this endangered species. Conservationists estimate that up to 5,000 individuals remain in the wild, but just 350 are breeding females. Early mortality of females affects fertility rates, making it more difficult to mate, and may be aggravating competition between males over the remaining females. The study could help conservation efforts.

Zuberoa Marcos is a former biologist and current science writer based in Barcelona. She writes articles regularly for Science Today.

Las “labores del hogar” acortan la vida de las hembras de dragón de Komodo

Por Zuberoa Marcos

Las hembras de dragón de Komodo viven, en promedio, la mitad que los machos debido al esfuerzo físico que requieren labores como construir los nidos enormes y proteger los huevos de los depredadores.

El dragón de Komodo (Varanus komodoensis) es el mayor lagarto del mundo. Su tamaño enorme les permite ser depredadores voraces. Son capaces de matar búfalos, ciervos y jabalíes e incluso atacar a seres humanos.

Investigadores de Australia, Indonesia e Italia han realizado durante 10 años un seguimiento de 400 dragones de Komodo que viven en el este de Indonesia, su único hábitat natural. Con los datos obtenidos, el equipo elaboró un modelo de la tasa de crecimiento del dragón. Los resultados has sido recientemente publicados en la revista PLoS ONE.

Machos y hembras crecen a la misma velocidad y tienen el mismo tamaño hasta que alcanzan la madurez sexual, lo cual ocurre alrededor de los siete años de edad. A partir de entonces las mujeres destinan toda su energía a la maternidad, crecen más lento y mueren más jóvenes.

Mientras tanto, los machos emplean sus reservas de energía en hacerse más grandes para poder competir con otros machos por las hembras y el territorio. Los investigadores han descubierto que los dragones de Komodo macho viven un promedio de 60 años y las mujeres sólo 32.

El profesor Tim Jessop, del Departamento de Zoología de la Universidad de Melbourne y co-autor del estudio, comenta que “estas diferencias entre sexos parecen estar vinculadas a las enormes cantidades de energía que las hembras invierten para producir los huevos, construir y cuidar sus nidos, un proceso que puede durar hasta seis meses, durante los cuales pierden mucho peso y su cuerpo se torna frágil. ”

Los resultados podrían tener consecuencias dramáticas para la supervivencia de esta especie en peligro de extinción. Los conservacionistas estiman que hay unos 5,000 individuos en la naturaleza, pero sólo 350 son hembras en etapa reproductiva. La mortalidad precoz de las hembras está dificultando el apareamiento y puede estar agravando la competencia entre los machos por las pocas hembras. El estudio podría ayudar a los futuros esfuerzos de conservación.

Zuberoa Marcos es bióloga molecular y actualmente trabaja como productora de TV y periodista científica. Escribe de forma regular para Science Today.

Image: Sleeping Komodo dragon, Wikipedia

Newts have the amazing ability to regenerate limbs and more, according to Ed Yong in his Discover blog:

They can regenerate parts of their tails, jaws, ears, hearts, spines, eyes and brains.

Very cool, right? But wait there’s more. A new study, published this week in Nature Communciations finds that the newts can do this at any age and over and over and over again, regenerating the exact same body part.

Researchers from Ohio and Japan removed the eye lenses from six Japanese newts (Cynops pyrrhogaster) a total of 18 times each over a 16-year period. And each time an identical eye lens grew back. In addition, reports New Scientist:

By the end of the study the newts were 30 years old, five years older than their average lifespan in the wild. Even so, the regenerated lenses from the last two excisions were indistinguishable from lenses of 14-year-old adults that had never regenerated a lens.

Could this finding have an impact on human health? Ed Yong is doubtful:

Scientists have studied amphibian regeneration for 200 years, with no discernible impact on medicine yet.

While lizards lack the skills for regeneration, they possess excellent problem–solving abilities, according to a Duke University study published this week.

The researchers used an intelligence test usually reserved for birds. They tested anoles from Puerto Rico (Anolis evermanni) using a wooden block with two wells: one empty and the other holding a worm covered by a cap. Four lizards, two male and two female, passed the test by either biting the cap or bumping it out of the way.

The lizards solved the problem in three fewer attempts than birds need to flip the correct cap and pass the test—birds usually get up to six chances a day, but lizards only get one chance per day because they eat less. In other words, if a lizard makes a mistake, it has to remember how to correct it for a full 24 hours. The results were published online in Biology Letters.

This is not the first study demonstrating lizards’ braininess, writes Science News:

[Georgia State’s Walter] Wilczynski’s lab has demonstrated that whiptail lizards can learn and unlearn tasks, and researchers led by Gordon Burghardt of the University of Tennessee at Knoxville have described monitor lizards learning how to get food out of a lab device…

Lizards indeed deserve more respect, says Wilczynski…

Indeed they do.

Image: Manuel Leal/Duke University

The 318 million-year-old reptile footprints were found in sea cliffs on the Bay of Fundy, New Brunswick, Canada. They show that reptiles were the first vertebrates to conquer dry continental interiors. These pioneers paved the way for the diverse ecosystems that exist on land today.

The footprints were discovered by Dr. Howard Falcon-Lang of Royal Holloway, University of London. According to New Scientist,

Around five centimeters long, the five-toed prints were made by small gecko-like creatures. “I discovered them by accident when I tripped over [them],” Falcon-Lang says.

Hundreds of stunning footprints belonging to at least three different kinds of reptile have been preserved at the site, all in sediments that, at the time the prints were made, were more than 500 kilometers [over 300 miles] inland within the supercontinent Pangaea.

The results of this study are published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

New Scientist also reports that “amphibians were the first creatures to make it onto land, hopping up the beach somewhere between 400 and 360 million years ago.” But, it has long been suspected that reptiles were the first to colonize continental interiors since they don’t need aquatic habitats to breed, unlike their amphibian cousins. The new footprint discovery bolsters this theory.

It may have been one small step for reptile-kind, but it was one giant leap for vertebrate diversity.

Image: University of Bristol

Three large, extinct swimming reptiles, the ichthyosaurs, plesiosaurs and mosasaurs, were the top ocean predators during the Mesozoic era, about 251 to 65 million years ago.

Most reptiles today are cold-blooded, meaning their body temperature is determined by how warm or cold their surroundings are. But, some of the modern ocean’s top predators, tuna and swordfish, are “homeothermic” (aka warm-blooded), or able to keep their body temperatures at a constant temperature despite changing environmental conditions.

To see whether the three lineages of Mesozoic marine reptiles were also homeothermic, Aurélien Bernard and colleagues analyzed various types of oxygen in the teeth of these reptiles. They compared the oxygen in the reptile teeth with the oxygen in the teeth of fish from the same environments.

This tooth oxygen is a clue to an animal’s body temperature, because it reflects the composition of oxygen in the blood.

The researchers knew that the fish whose teeth they were studying were cold-blooded. So, when they found reptile teeth with different oxygen signatures, it probably meant that those reptiles had warmer body temperatures than the fish did.

The results suggested that ichthyosaurs and plesiosaurs, which chased their prey, probably controlled their own temperatures. The data for mesosaurs, which are thought to have hunted by ambush, were less clear, but it’s possible that these reptiles could control their body temperature to some degree.

In the Nature blog The Great Beyond, Robert Eagle, PhD, of the California Institute of Technology, challenges the methods used in the study:

Isotope ratios in teeth are dependent not only on body temperature, but on the levels of the oxygen isotopes in the animals’ bloodstreams when their teeth were growing—something that might vary among species due to dietary and physiological differences. In a study published last month in the Proceedings of the National Academy of Sciences (see our previous article on this study), Eagle and colleagues presented an alternative analysis, based on a combination of oxygen and carbon isotopes, which they believe to be less affected by factors other than temperature. “It would be interesting to see if we get the same answer,” he says.

Stay tuned to find out…

A new study, published in the Journal of Animal Ecology, found that the estuarine crocodile, a noted poor swimmer, surfs its way around islands in the South Pacific.

For years researchers were puzzled.  How could this creature, the largest living reptile in the world, occupy islands so isolated from each other?  And why, despite occupying regions as far apart as East India and Fiji or southern China and North Australia, has the species never diversified?

To investigate these questions, an Australian research team (which included the late Steve “The Crocodile Hunter” Irwin) tagged 27 adult estuarine crocodiles with sonar transmitters and used underwater receivers to track their every move over 12 months.

According to an article in today’s Nature:

They found that eight crocodiles undertook a total of 42 long-distance journeys of more than 10 km per day. In 96% of these trips, the reptiles travelled with the current flow. In contrast, the crocodiles were equally likely to travel with and against the current flow when making short journeys.

Surfing the ocean’s surface currents, the crocodiles could voyage from one oceanic island to another. “This not only helps to explain how estuarine crocodiles move between oceanic islands, but also contributes to the theory that crocodilians have crossed major marine barriers during their evolutionary past,” says Hamish Campbell, PhD, one of the authors of the study.

And how do they know how to read the tides? Perhaps they use magnetic cues to know when “surf’s up,” says author Craig Franklin, PhD, in Nature:

It is not clear whether this behavior is learned or inherited, says Franklin. He says that correlations can be drawn between the migratory behavior and cognitive abilities of crocodiles and birds, because the former are more closely related to the latter than to other reptiles. Previous studies have shown that both animals use magnetic cues to navigate.

So if birds and crocs share such tremendous navigational capacity, maybe it’s not such an insult to be called a “bird brain”?  Well, not if you’re the largest living reptile surfing your way to the nearest island…

Image courtesy of Tourism NT