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.
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."
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!
Discovery of a Key Regulatory Gene in Cardiac Valve Formation
24.05.2017 | Universität Basel
Carcinogenic soot particles from GDI engines
24.05.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.
In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
24.05.2017 | Physics and Astronomy
24.05.2017 | Physics and Astronomy
24.05.2017 | Event News