Biology – Page 79 – David Bradley

Owl pellet dissection

A friend of mine is into nature conservation in a big way and one of the tools of the trade, which to the outsider may seem rather odd, is owl pellet dissection. I had a go at dissecting an owl pellet myself, here you can see the results

Owl pellets are the regurgitated remains (bones, feathers and other indigestibles) that accumulate in this bird of prey’s gizzard after it dines on small rodents and other critters. The dessicated pellets are to be found lying where they are discarded by the owl and can provide important information about what critters are being preyed on in owl territory.

The only way to get at that information, however, is to tease apart the pellet with tweezers and other implements to extract the bones from the tangle of hair and other detritus. It needs a steady hand, a keen eye, and a lot of patience. What you will find within is quite amazing though, tiny jaw bones and skulls, femurs, tibias pelvic bones and more.

Identifying which bone belongs to which creature takes even more patience, but it is possible and provides useful insights into the prevalence or otherwise of particular small mammals in a given area where owls prey.

For more on owl pellet dissection, check out this site http://www.kidwings.com/owlpellets/.

The reason I bring it up (pardon the pun) today, is that owl pellet dissection was the hot new search phrase on the sciencebase site this last month, with dozens of visitors all flapping for information on the subject. It’s not a topic that’s been searched for here before, so I thought I’d provide some background in case we have another flutter of en-raptor-ed activity.

Herring Gulls fighting

These two birds I photographed in my in-law’s garden were anything but lovebirds, although they might look like they were dancing seconds before and seconds after they were tearing each other’s feathers off and spitting blood. This didn’t seem to be a bar-room brawl between chums fighting over fishy scraps, these two were at it for a good half an hour. It has to have been a territorial or mating rights argument of some sort.

Nature really is red in beak and claw.

Erotic brain

What a surprise! Medical researchers have discovered that women’s brains light up when they look at erotic images just as men’s brains do.

Researchers at Washington University School of Medicine in St. Louis measured brainwave activity of 264 women as they viewed a series of 55 colour slides that contained various scenes from water skiers to snarling dogs to partially-clad couples in sensual poses.

What they found may seem like a “no brainer.” When study volunteers viewed erotic pictures, their brains produced electrical responses that were stronger than those elicited by other material that was viewed, no matter how pleasant or disturbing the other material may have been. This difference in brainwave response emerged very quickly, suggesting that different neural circuits may be involved in the processing of erotic images.

“That surprised us,” says WUSTL’s Andrey Anokhin, “We believed both pleasant and disturbing images would evoke a rapid response, but erotic scenes always elicited the strongest response.”

As subjects looked at the slides, electrodes on their scalps measured changes in the brain’s electrical activity called event-related potentials (ERPs). The researchers learned that regardless of a picture’s content, the brain acts very quickly to classify the visual image. The ERPs begin firing in the brain’s cortex long before a person is conscious of whether they are seeing a picture that is pleasant, unpleasant or neutral.

Previous research has suggested that men are more stimulated by erotic images than women. Anokhin says the fact that the women’s brains in this study exhibited such a quick response to erotic pictures suggests that, perhaps for evolutionary reasons, our brains are programmed to preferentially respond to erotic material.

“Usually men subjectively rate erotic material much higher than women,” he says. “So based on those data we would expect lower responses in women, but that was not the case. Women have responses as strong as those seen in men.”

So when one sees statistics on net usage that reveal porn accounts for 80% of traffic, it might not just be males who are using up all that bandwidth? Really? Well, I never!

What’s most intriguing though, is that when one searches for the original news release on this item from WUSTL, the cached page in Google shows the context for the phrase “erotic images elicit” as being:

“Attention grabber Erotic images elicit strong response from brain … When study…”

Well, WUSTL press officer, it certainly grabbed my attention. The news release could have done with a few more pictures though!

Sperm and eggs

Adam Bjork and Scott Pitnick of Syracuse University have found a sexy paradox. But, don’t get too excited, it’s fruit fly sex we’re talking here and specifically sperm and egg production in Drosophila.

Previous work in the Pitnick lab showed that after sex, sperm competition takes place within the females (who mate with several males) can lead to decreased sperm quantities by favouring the production of larger sperm. In other words, never mind the quantity feel the length mode comes into play, because female fruit flies have evolved so that longer sperm have a greater chance of successfully fertilizing eggs. Fertilization failure is obviously important as individuals who fail are essentially an evolutionary dead end.

This leads to the ‘big sperm paradox’ because the idea that postcopulatory sexual selection could favour the evolution of giant sperm clashes with traditional sexual selection theory, which predicts that the most successful sperm competitors will be the males that produce many, tiny sperm. As males evolve to produce larger – and therefore fewer – sperm, eggs become less rare, and sexual selection should weaken, according to theory. The term ‘isogamy’ refers to the state at which males and females have equal investment per gamete (sex cell) when producing sperm and eggs. In a truly isogamous population, each sperm and each egg would have a chance to participate in a successful fertilization. In such a population, sexual selection would be extremely weak, as there would be little or no competition among males to fertilize eggs.

To investigate this apparent paradox between empirical data and traditional theory, Bjork and Pitnick set out to measure the strength of sexual selection in four Drosophila species of varying sperm length, ranging from the anisogamous D. melanogaster (in which a male produces 30 sperm in the time it takes a female to make one egg) to the nearly isogamous D. bifurca (where just six sperm are produced per egg). They found that, contrary to theoretical predictions, the level of competition among males did not decrease; the strength of sexual selection remained high as sperm size increased. Their results show that, once females evolve a preference for longer sperm, intense sperm competition can actually reverse the trajectory of sperm evolution so that the most successful males are those with the most female-like strategy of producing very few, large gametes.’The sperm of Drosophila bifurca is 20 times longer than the male that produces it,’ says Bjork.

‘To put that into perspective, if humans made sperm that long and you took a six-foot man and stood him on the goal line of a football field, his sperm would stretch out to the 40-yard line.’

While it is fascinating, the evolution of giant sperm is puzzling. Says Bjork: ‘Until recently, it was widely believed that selection generated by sperm competition favors males that manufacture the smallest gametes possible in order to maximize sperm number. In essence, sperm competition is attributed with the evolutionary maintenance of anisogamy. I became interested in understanding whether the very act of sexual selection, by definition, can limit its own ability to act.’

The next step is to investigate the details of the effects of sperm length evolution on the intensity of sexual selection.

Details were published in Nature under the banner “Intensity of sexual selection along the anisogamy—isogamy continuum”, which doesn’t give much away unless you’re in the field. The paper’s DOI reference number is 10.1038/nature04683. Use our DOI lookup tool to go straight to it (simply cut and paste the DOI and click DOI lookup in the right-hand toolbox) and don’t forget you can grab the simple script to add this and our other toolboxes to your website.

Chirality – panda thumb

The chirality of life, an issue I’ve discussed on numerous occasions in these and other pages, emerges as yet another source of pseudo-science for the intelligent design lobby. Apparently, the bias in handedness among the molecules of life – amino acids, DNA, etc, could not have arisen spontaneously without a guiding hand…

An interesting discussion on this very subject is underway at The Panda’s Thumb blog, it will be interesting to see where it leads. However, my own interviews with chemists on this subject over the years point to a wide range of natural phenomena that could have led to the emergence of the chiral bias with no need to invoke a supernatural hand.

Human to human bird flu

The World Health Organization has expressed concern that a recent cluster of deaths associated with the H5N1 virus in Indonesia may not have originated with an animal host, suggesting the possibility of human to human transmission of the virus. However, it also cautions that the analytical evidence suggests that the virus has not mutated into a human transmissable form, which means we are not just yet on the verge of a global bird flu pandemic after all.

The news media inevitably picked up on this warning and ran with it, but thankfully the BBC saw the double-edged nature of the WHO announcement points out with some degree of rational response that many people in Indonesia, as in other southeast Asian countries, live in such close proximity to their animals and not necessarily in the most hygienic of circumstances that the likelihood of catching bird flu is much higher in such an environment.

It is the lack of a mutated form of H5N1 among these victims that means we are not yet doomed to see the feathers fly globally.

Sex and Vomeronasal Attraction

The vexing question of whether sex pheromones play a role in human sexual attraction raises its ugly head once again, this time in a posting on The Register. Most scientists would say that there is little evidence that humans rely very much on pheromones for sexual attraction directly. However, others scientists suggest that a tiny organ in the nasal cavity, the so-called vomeronasal organ (VNO), or Jacobson’s organ, can detect chemical attractants that pass between people and are not apparent to us at the thinking level. Moreover, anecdotal evidence would point to smell having a very strong effect in sex whether or not we believe it’s pheromonal or not.

The VNO definitely plays a role in the lives of other animals from cats to snakes and from elephants to mice. In humans the organ seemingly all but disappears even before birth, leaving just a few people with a tiny pit in the septum that might have some vestige of pheromonal responsiveness.

Until, we find specific chemicals that trigger sexual attraction when sniffed, in double-blind controlled tests, it is likely that for the foreseeable future there will be no genuine, working product.

Touch Wood – Short History of Viagra

Just a reminder that the Sciencebase archive of science articles is stuffed full of interesting tid-bits (to use the PC term). Among the most popular pages (attracting the most readers in other words) is the repro of a feature article I wrote some time ago for Tomorrow’s World magazine on the subject of Viagra.

Said item was illustrated with a large banana and two strategically placed apples. I was going to dig out the original paper cutting and scan it for this item, but didn’t fancy getting a search engine rude-filter slapped on the page.

The Viagra article is here.

Zoo Poo

This is one of those lovely science stories that is sure to catch even the tabloid media’s attention as well as give people the opportunity once again to complain about “what scientists do”.

According to CSIRO Livestock Industries scientist Andre-Denis Wright, droppings from rhinos and elephants at Perth Zoo are being put under the microscope to help scientists determine whether or not various strains of protozoa, which help break food down in the guts of “exotic” animals can be introduced into the guts of sheep and cattle to help them thrive in the harsh conditions of the Australian outback.

As part of the Zoo-Poo project scientists have so far sequenced the DNA of protozoa found in a range of faecal samples from rhinos, elephants, orangutans, and red pandas. The study will reveal the origins of various protozoa and identify common protozoal species found in animals from different parts of the world.

Wright is collaborating with rumen microbiologist Burk Dehority of Ohio State University. Dehority has previously found some of the same protozoa in different grazing animals from South America, Africa and Alaska. However, the protozoa from the guts of marsupials in Australia appear to be quite distinct. He has now received poo samples from the zoo animals including a “grab sample of faeces” from a rhino, collected by a zoo handler before it hit the ground. [Nice]

“Very large mammals like the rhino and the elephant eat voluminous amounts of roughage and they are able to take the soluble nutrients out and ferment them in the cecum and then they just pass the roughage out,” explains Dehority, “hey exist on the fact that they just eat volumes.”

He said little was known about how the guts of large animals worked and the research would assist in developing better nutrition for zoo animals as well as livestock.

Phylum Arthropoda

A common search carried out by sciencebase visitors is “Phylum Arthropoda”. Innocent enough, of course, there are bound to be lots of followers of the site interested in insects, arachnids, and crustaceans.

Anyway, the best starting point to get plenty more info on the arthropods is, as usual, Wikipedia. But, if you’re after science lessons on arthropods then check out the K5 science lesson plans page and follow the link to the Columbia Education Center in Portland, Oregon, to get to the specific listings. If you’ve got a particular creature in which you’re interested, please use the sciencebase search box top right, we can’t guarantee that you’ll find what you’re looking for among the sciencebase pages themselves but there are usually other links on the site you can follow to find out more.