Interesting new paper for those studying animal physiology:
Penguins are supremely adapted to life in the extreme conditions of the Antarctic, from their thick plumage to huddling behaviour. Using thermal imaging this paper in Biology Letters (http://rsbl.royalsocietypublishing.org/content/9/3/20121192.short?rss=1) demonstrates how Emperor penguins use their well insulated trunk to manage body heat loss in brutally low temperatures. The temperature of the feathered outer surfaces can fall below the surrounding air due to radiative cooling. Heat is lost only through the relatively exposed flipper and head regions – perhaps it is important to maintain some comparatively unfeathered areas in case of overheating?
When considering the evolutionary and physiological significance of adaptations like penguin plumage it is useful to consider how temperature changes affect energy usage in animals. One way of appreciating this is to measure the animal’s ‘thermo-neutral zone’. Since mammals and birds are homeothermic endotherms they maintain a set, relatively high body temperature at which their biochemical processes are optimised. If the ambient temperature falls, animals need to produce heat, increasing their metabolic rate, or rate of energy expenditure. Conversely if it becomes too hot, strategies such as sweating or panting are employed to maintain body temperature, again increasing metabolic rate. In the laboratory we can calculate how much energy is expended by animals in a range of temperatures by measuring how much oxygen they consume. The range of ambient temperatures that does not elicit an increase in metabolic rate to maintain the ideal body temperature is called the thermoneutral zone. This concept is important when we consider the example of adaptation in bird beak size. While heat loss from the exposed beak is undesirable in the cold Antarctic, (reflected in a reduced bill size in penguins), what about birds that live in warmer climes? In the tropics, the toco toucan uses it’s large bill as a heat exchanger, a mechanism analogous to large elephant ears, to maintain it’s optimum body temperature when ambient conditions fall outside the thermoneutral zone. The bird uses countercurrent heat exchange in the blood vessels supplying the bill to modulate heat transfer with the environment. As you can see in the picture below, the bird reduces heat loss in cooler temperatures and increases heat radiation when too warm.
Figure taken from the 2009 paper in Science (http://www.sciencemag.org/content/325/5939/468.full?sid=402de1be-c045-4cb1-8a27-b6d88892d42f)
Just a quick note to let people know that the Palaeontology Journal Club will be starting next Tuesday (23rd Nov.) at 5pm in Jabez Clegg. Each week we’ll be picking a new journal article, and meeting in the pub on the Tuesday to discuss it in a very informal setting. Students from any of the life sciences degrees are welcome to attend.
***as an added incentive, we’re even offering to buy the first round in***
This week’s paper is about ancient DNA. Researchers in New Zealand have tracked the decay rate of DNA in radiocarbon dated fossils of the Moa (an extinct giant ratite). They have found that, even under optimal burial conditions, DNA is unlikely to survive beyond 6-7 million years. Looks like InGen has been lying to us all these years….
BBC Radio 4 has a series called “Great Lives”. The latest episode focused on the man who was probably the greatest evolutionary biologist in the second half of the 20th century, Bill Hamilton. His scientific papers are rather difficult to understand, being largely mathematical. But his ideas, in particular those leading to his theory of kin selection as an explanation of altruism, have been amazingly influential. Richard Dawkins, who popularised Hamilton’s ideas (without the maths) in The Selfish Gene, is on excellent form in this programme, together with Hamilton’s sister, Dr Mary Bliss. 30 minutes of excellent listening.
Click here to listen.
Filed under BBC, Evolution
New ape fossil from around 10 million years ago, a close relative of the last common ancestor of humans, gorillas and chimps. BBC summary.
One of the main theories that explains the existence of large arthropods in previous epochs is the fact that oxygen levels were sometimes much higher, allowing organisms which depend on passive diffusion, like insects, to grow larger. (This was a key aspect of a plot in last year’s TV hit Primeval which featured an unfeasibly large giant centipede from the deep past.) This is a difficult hypothesis to test, but these authors of an open access article in PNAS have done their best, looking at the evolution of trachaea in beetles.
Watch Professor Steve Jones giving his lecture on this subject at the Royal Society. Required viewing. Search for “Steve Jones” in the panel on the right. You can see the slides in the big panel on the left. The video comes up above the search panel.
P Z Myers (University of Minnesota) has a long-standing blog in which he writes – often very amusingly – about evolution, the struggle against creationism and all things scientific. Well worth regular browsing!