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Author Archives: Peter Tickle
What is this unusual object?
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)
Deep-sea giant squid (Architeuthis) remain one of the ocean’s most charismatic zoological mysteries. While there are plenty of specimens in museums around the world, little is known about their behaviour. Only recently have fleeting glimpses been captured of these creatures in their natural habitat; a 2005 paper (http://rspb.royalsocietypublishing.org/content/272/1581/2583.full) in Proceedings of the Royal Society B described the first ever wild observations of a live giant squid. The author’s photographs showed a huge squid actively hunting at 900m below the surface and they even managed to recover a tentacle that snagged on the bait line (see panels ‘e’ and ‘f’ in the figure).
We also know about the predator-prey interaction between sperm whales and giant squid from the sharp-sucker scars often seen on whale skin and stomach contents (squid beaks are indigestible making them a useful clue to the diet of sperm whales).
Earlier this year, footage taken by a manned submersible was broadcast showing a giant squid 1000m deep in the North Pacific. The footage was captured using near-infrared light (using invisible to humans and squid) since giant squid avoid the bright white light used in conventional filming- perhaps something to do with those enormous eyes? (have a look here: http://www.eeb.yale.edu/ugrad/eeb171pdfs/sa-246-1982.pdf)
See clips from the video at http://www.youtube.com/watch?v=1KN5N1QDaRQ
(picture credit: NHK/NEP/Discovery Channel via Reuters)
As an aside, it’s worth taking a look at this report on the unusual mating behaviour of giant squid – it turns out that male squid giant inject spermatophores directly into wounds that they form on the tentacles of a female:
More recently a somewhat alarming article showed how male squid overcome the challenges of mating at great depths using a ‘super squid sex organ’ – see the long white tubular structure in the picture below.
While I’m sure you’ve all seen the spectacular beaching behaviour of predatory killer whales, Orcinus, and dolphins, Tursiops, here’s a report of similar behaviour from a fish a little closer to home. It seems that catfish, Siluris glanis, have recently learnt to snatch and eat pigeons from the riverbank.
The proof of the matter is shown in this picture:
You can see unsuspecting pigeons resting on the riverbank and predatory catfish lurking nearby. Looking closely at the smaller images reveals a successful bird catch.
Interestingly catfish do not display this behaviour in their natural range and so it may represent a fascinating adaptation to the new environment. Perhaps there are not enough fish to eat in these rivers or maybe catfish have simply developed a taste for pigeon? Either way, behavioural adaptation in this species may have implications for the ecological functioning of this riparian environment.
The paper is available in PLoS ONE: