Tuesday, May 21, 2013

Why Did Penguins Stop Flying? The Answer Is Evolutionary

Adelie penguin, Pygoscelis adeliae, flapping wings.
An Adélie penguin flaps its wings, which help the bird to swim.
Photograph by John Eastcott and Yva Momatiuk, National Geographic
Brian Handwerk
for National Geographic
Published May 20, 2013

Penguins lost the ability to fly eons ago, and scientists may have finally figured out why. A new study suggests that getting off the ground eventually just took too much effort for birds that were becoming expert swimmers.

Flight might make some aspects of penguins' Antarctic life much easier. The grueling march of the emperor penguins, for example, might take only a few easy hours rather than many deadly days. Escaping predators like leopard seals at the water's edge would also be easier if penguins could take flight-so scientists have often wondered why and how the birds lost that ability.

A popular theory of biomechanics suggests that the birds' once-flight-adapted wings simply became more and more efficient for swimming and eventually lost their ability to get penguins off the ground.
More efficient diving, on the other hand, increased the opportunities to forage for food at depth. A modern emperor penguin can hold its breath for more than 20 minutes and quickly dive to 1,500 feet (450 meters) to feast.

The new study of energy costs in living birds that both fly and dive provides critical evidence to back up this theory.

"Clearly, form constrains function in wild animals, and movement in one medium creates tradeoffs with movement in a second medium," study co-author Kyle Elliott, of the University of Manitoba, said in a statement.
"Bottom line is that good flippers don't fly very well."

Sit, Swim, and Fly

The thick-billed murre or Br√ľnnich's guillemot (Uria lomvia) uses its wings for diving much like penguins, but it also flies. Scientists theorized that its physiology and energy use may closely resemble those of the last flying penguin ancestors.

Other swimming birds, pelagic cormorants (Phalacrocorax pelagicus), propel themselves through the water with their feet. Elliott and colleagues assert that these birds can be considered biomechanical models for the lifestyle energy use of an ancient penguin ancestor that was the last of its line to take flight.

The thorough technical and isotope analysis of how guillemots burn energy reveals why today's penguins are grounded. Guillemots dive more efficiently than any other flying bird and are bested in diving only by penguins themselves, according to the study.

Flight, however, costs them more energy than any other known bird or vertebrate and has become difficult to maintain.

The team examined thick-billed murres at a colony in Nunavut, Canada, and pelagic cormorants at Middleton Island, Alaska. They injected the birds with stable isotopes of oxygen and hydrogen to serve as tracers to mark the physical costs of their activities. The team also fitted them with time-budget devices that track those activities—recording movements, speeds, and other data much like pedometers do.

"Basically the birds do only three things: sit, swim, and fly. So by measuring lots of birds and combining their time budgets with the total costs of living from the isotope measures, it is possible to calculate how much each component of the budget costs," explained study co-author John Speakman, who leads the Energetics Research Group at the University of Aberdeen, Scotland.

"The assumption is that [penguins] evolved from an auk-like ancestor," Speakman continued.
"This would involve a progressive reduction in wing size, which makes diving more efficient and flying less so. Penguin bones also thickened over the ages, as lighter bones that make it easier for birds to fly gave way to more dense bones, which may have helped make them less buoyant for diving." But Speakman believes the wing changes were the primary adaptation.

Elegant Explanation

"These results make a lot of sense," said University of Texas at Austin's Julia Clarke, who studies bird evolution and how the flight stroke was co-opted for underwater diving.

"There have been different scenarios explored for the origin of penguins but little relevant data. These new findings from other diving birds like murres provide an elegant explanation of a key step in the wing-to-flipper transition."

Katsufumi Sato, a behavioral ecologist at the University of Tokyo's Ocean Research Institute and a National Geographic Society Emerging Explorer, added that the work indicates an important reason why penguins stopped flying and evolved larger body sizes—they needed an edge in the water.

"An interesting example is the little penguin, which is smaller than some Alcidae [a family of penguins]," and weighs only about two pounds (one kilogram), said Sato. "[The] dive cost of the murre is similar to that of the little penguin, which means little penguins cannot survive against the murre, which can dive and fly."

Bigger bodies boost dive efficiency and allow for longer dives, which may be why rapid evolution produced so many bigger-bodied penguins soon after the animals lost the ability to fly.

Penguins Grounded by Taste for Fish?

Comparing multiple species, in the way this study does, points to a compelling pattern, said Chris Thaxter, a seabird ecologist with the British Trust for Ornithology.

"When wings are used both above and below water, there may be an evolutionary tipping point beyond which flight is too costly and unsustainable." Clarke, Sato, and Thaxter were not involved in the study, which was published in the May 20 edition of the journal Proceedings of the National Academy of Sciences.

Scientists don't have fossils of flighted penguin ancestors, and the earliest known penguin dates to just after the Cretaceous-Tertiary boundary (58 to 60 million years ago).

"It is tempting to speculate that the evolution of penguins happened in that explosive radiation [of mammal species] that happened just after the K-T event," when many species went extinct, Speakman said. "However, there is no direct evidence to support this, and it could have happened any time during the late Cretaceous."

In nature such adaptations happen for good reason, typically related to survival and reproduction. So a convincing case might be made for why penguins would have given up flight while taking to the seas.

"What we do know is that in the radiation of the mammals after the K-T event, there suddenly [in geological terms] appear a whole load of mammals that would have been serious competitors for aquatic resources [like] cetaceans and pinnipeds," Speakman said.

"So this new competitive environment may have placed a greater benefit on being more efficient swimmers and divers for aquatic seabirds. That push toward being more efficient in the aquatic environment may have been enough to tip them over the edge into flightlessness."


Thursday, May 16, 2013

Mum and Dad Dinosaurs Shared the Work--Just Like Modern Penguins

Oviraptorid skeleton and eggs in the Senckenberg Museum in Frankfurt am Main. (Credit: EvaK via Wikimedia Commons, Creative Commons license)
May 15, 2013 — A study into the brooding behaviour of birds has revealed their dinosaur ancestors shared the load when it came to incubation of eggs.

Research into the incubation behaviour of birds suggests the type of parental care carried out by their long extinct ancestors.

The study aimed to test the hypothesis that data from extant birds could be used to predict the incubation behaviour of Theropods, the group of carnivorous dinosaurs from which birds descended.
The paper, out today in Biology Letters, was co-authored by Dr Charles Deeming and Dr Marcello Ruta from the University of Lincoln's School of Life Sciences and Dr Geoff Birchard from George Mason University, Virginia.

By taking into account factors known to affect egg and clutch size in living bird species, the authors -- who started their investigation last summer at the University of Lincoln's Riseholme campus -- found that shared incubation was the ancestral incubation behaviour. Previously it had been claimed that only male Theropod dinosaurs incubated the eggs.

Dr Deeming said: "In 2009 a study in the journal Science suggested that it was males of the small carnivorous dinosaurs Troodon and Oviraptor that incubated their eggs. Irrespective of whether you accept the idea of Theropod dinosaurs sitting on eggs like birds or not, the analysis raised some concerns that we wanted to address. We decided to repeat the study with a larger data set and a better understanding of bird biology because other palaeontologists were starting to use the original results in Science in order to predict the incubation behaviour of other dinosaur species. Our analysis of the relationship between female body mass and clutch mass was interesting in its own right but also showed that it was not possible to conclude anything about incubation in extinct distant relatives of the birds."

Palaeobiologist Dr Ruta was involved in mapping the parental behaviour in modern birds on to an evolutionary tree.

Dr Ruta said: "As always in any study involving fossils, knowledge of extant organisms helps us make inferences about fossils. Fossils have a unique role in shaping our knowledge of the Tree of Life and the dynamics of evolutionary processes. However, as is the case with our study, data from living organisms may augment and refine the potential of fossil studies and may shift existing notions of the biology and behaviour of long extinct creatures."

Dr Birchard added: "The previous study was carried out to infer the type of parental care in dinosaurs that are closely related to birds. That study proposed that paternal care was present in these dinosaurs and this form of care was the ancestral condition for birds. Our new analysis based on three times as many species as in the previous study indicates that parental care cannot be inferred from simple analyses of the relationship of body size to shape, anatomy, physiologyand behaviour. Such analyses ought to take into account factors such as shared evolutionary history and maturity at hatching. However, our data does suggest that the dinosaurs used in the previous study were likely to be quite mature at birth."

The project has helped in understanding the factors affecting the evolution of incubation in birds. More importantly it is hoped that the new analysis will assist palaeontologists in their interpretation of future finds of dinosaur reproduction in the fossil record.

Story Source:
The above story is reprinted from materials provided by University of Lincoln.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:
  1. G. F. Birchard, M. Ruta, D. C. Deeming. Evolution of parental incubation behaviour in dinosaurs cannot be inferred from clutch mass in birds. Biology Letters, 2013; 9 (4): 20130036 DOI: 10.1098/rsbl.2013.0036

University of Lincoln (2013, May 15). Mum and dad dinosaurs shared the work. ScienceDaily. Retrieved May 16, 2013, from http://www.sciencedaily.com­ /releases/2013/05/130514213109.htm

How did feathers evolve? - A Video by Carl Zimmer

Wednesday, May 15, 2013

Did Mom or Dad Incubate Dinosaur Eggs?

14 May2013
About 15 feet tall and 40 feet long, Tyrannosaurus rex, whose name means “king of the tyrant lizards,” is one of the largest known land predators to ever roam the Earth.
CREDIT: Photograph © Julius T. Csotonyi (csotonyi.com). Image used with permission.

Male and female dinosaurs may have shared the responsibility of incubating their offspring, but how to determine which parent was involved remains a mystery, according to a new study that re-examines the idea that the brooding behavior of modern birds may predict similar behavior in their dinosaur ancestors.

Modern birds are thought to have evolved from theropods, a group of carnivorous dinosaurs that include such recognizable predators as the Velociraptor and Tyrannosaurus rex.

In research published in the journal Science in 2009, scientists examined the way existing birds incubate their eggs, claiming that only male theropods took part in incubation. But the study, which compared the size of male and female birds with the size and number of eggs that were laid, omits some important factors, said Geoff Birchard, a professor in the department of environmental science and policy at George Mason University in Fairfax, Va., and co-author of the new study. [Image Gallery: Dinosaur Daycare]

"They looked at the number of eggs and how big they were, and said they could figure out whether mommy incubated, daddy incubated, or both did," Birchard told LiveScience. "The problem is, the biology behind it is a little bit off."

Birchard and his colleagues repeated the 2009 study using more data from living bird species. They determined that comparing the size of the birds with the clutch size — which is determined by multiplying the number of eggs laid in a nest by the volume or mass of the eggs — could not effectively determine whether it was the male or female guarding the eggs.

"Our analysis of the relationship between female body mass and clutch mass was interesting in its own right, but also showed that it was not possible to conclude anything about incubation in extinct distant relatives of the birds," study co-author Charles Deeming, a researcher at the University of Lincoln in the United Kingdom, said in a statement.

Part of the problem is that birds do not all exhibit the same brooding behavior.
"There's a huge amount of variation with birds," Birchard said. "With certain bird types, two parents are always involved, but with some bigger birds, only the daddy is incubating the eggs. With dinosaurs, overall, there's a huge amount of variety, too."

And whether the actions of modern birds can be used to predict the behavior of dinosaurs is also a source of debate.

"There are great differences of opinion about it," Birchard said. "There's a long time gap between dinosaurs and the origin of birds, so it's an awful long time for us to say what's being done with birds was also being done with dinosaurs. We use this kind of inference sometimes, but birds are also a very unique group."

The findings of the new study were published online Tuesday (May 14) in the journal Biology Letters.