Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Big-mouthed babies drove the evolution of giant island snakes

16.05.2012
Some populations of tiger snakes stranded for thousands of years on tiny islands surrounding Australia have evolved to be giants, growing to nearly twice the size of their mainland cousins. Now, new research in The American Naturalist suggests that the enormity of these elapids was driven by the need to have big-mouthed babies.

Mainland tiger snakes, which generally max out at 35 inches (89 cm) long, patrol swampy areas in search of frogs, their dietary staple. When sea levels rose around 10,000 years ago, some tiger snakes found themselves marooned on islands that would become dry and frog-free. With their favorite food gone, the island snakes "are now thriving on an altered diet consisting of skinks, rodents, and nesting oceanic bird chicks," said study author Fabien Aubret of La Station d'Ecologie Experimentale du CNRS à Moulis.


Some tiger snake populations on Australian islands have evolved to be giants, nearly twice the size of their mainland counterparts. New research in the American Naturalist suggests that the need to have big-mouthed babies drove the evolution of these enormous elapids. Credit: Fabien Aubret

Along with the dietary shift came dramatic changes in the snakes' adult body sizes. On some islands, the snakes shrank, becoming significantly smaller than mainland snakes. But other islands have produced giants, measuring 60 inches (1.5 meters) and weighing as much as three times more than mainland snakes.

Aubret hypothesized that the size of available prey on each island was driving the variation in body size. Snakes are gape-limited predators, meaning they swallow their prey whole and can only dine on animals they can wrap their mouths around. This gape limitation would be most pronounced in newborn snakes, when their mouths are at their smallest. Simply put, baby snakes born too small to partake of the local cuisine would have little chance to survive. Where prey animals are larger, selection would favor larger newborn snakes—with larger mouths. That head start in size at birth could be the reason for larger size in adulthood.

To test his idea, Aubret took field expeditions to 12 islands, collecting and measuring 597 adult snakes. He released the males and non-pregnant females, and brought 72 pregnant snakes back to the lab. After the snakes gave birth, he measured each of the 1,084 babies they produced. He then looked for correlations between snake size at birth and the size of prey animals available on each island. He also tested for correlations between birth size and adult size.

"The results were unequivocal: snake body size at birth tightly matches the size of prey available on each island," Aubret said.

As predicted, where prey animals were bigger, newborn snakes were bigger and they grew up to be bigger adults. Where prey animals were smaller, newborn snakes followed suit, leading to smaller adults.

A New Dimension to the Island Rule?

Ecologists have long been interested in the peculiarities of island animals. Observations of pygmy elephants and giant rats led a biologist named J. Bristol Foster to propose what became known as the Island Rule. In general, Foster surmised, big animals on islands tend to get smaller than mainland counterparts because of limited access to food. Small animals tend to get larger because islands tend to have fewer predators. Since it was proposed in the 1960s, numerous exceptions to Foster's rule have been noted, and scientists now agree that the ecological factors that influence island body size are far more complex than Foster had imagined.

Aubret's findings add yet another dimension.

"Mean adult body size has always been used as a traditional measure in the literature," he writes. "On the other hand, patterns of variation for body size at birth in island populations have received, to my knowledge, no attention at all."

Aubret's work shows that selection isn't necessarily acting on adult body size.

"This study confirms that adult size variations on islands may be a nonadaptive consequence of selection acting on birth size," he said. "Animals may become either giant or dwarf adults on islands for the simple fact that they were born either unusually large or small bodied."

Fabien Aubret, "Body-Size Evolution on Islands: Are Adult Size Variations in Tiger Snakes a Nonadaptive Consequence of Selection on Birth Size?" The American Naturalist 179:6 (June 2012).

Since its inception in 1867, The American Naturalist has maintained its position as one of the world's most renowned, peer-reviewed publications in ecology, evolution, and population and integrative biology research. While addressing topics in community and ecosystem dynamics, evolution of sex and mating systems, organismal adaptation, and genetic aspects of evolution, AmNat emphasizes sophisticated methodologies and innovative theoretical syntheses--all in an effort to advance the knowledge of organic evolution and other broad biological principles.

Kevin Stacey | EurekAlert!
Further information:
http://www.uchicago.edu

Further reports about: Snakes big-mouthed babies body size sea level tiger snakes

More articles from Life Sciences:

nachricht A Map of the Cell’s Power Station
18.08.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht On the way to developing a new active ingredient against chronic infections
18.08.2017 | Deutsches Zentrum für Infektionsforschung

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>