Daily Archives: 4 October 2012

Bees bumble through their flight plan

Radar tracking of bee flight paths shows that they initially find flowers by trial and error, and refine their route on successive attempts.

Researchers attached tiny transponders to the backs of bumblebees (Bombus terrestris) and set them loose in a field with five artificial flowers, arranged in a pentagon with 50 metre sides. This distance is three times further than bumblebees can see, so they weren’t able to navigate simply by seeing the next target.

Additionally, the amount of sugar available at each ‘flower’ meant that a bee had to visit all five to get its fill. They were each given 7 hours to forage, repeated every day for a month (Lihoreau M, Raine NE, Reynolds AM, Stelzer RJ, Lim KS, Smith AD, Osborne JL & Chittka L 2012, “Radar tracking and motion-sensitive cameras on flowers reveal the development of pollinator multi-destination routes over large spatial scales”, PLoS Biology, doi:10.1371/journal.pbio.1001392).

A bumblebee worker with a transponder attached to its back, visiting an oilseed rape flower
A bumblebee worker with a transponder attached to its back, visiting an oilseed rape flower (Photo by Andrew Martin, via PLoS Biology)

Initially, the flight paths appeared random, but as time went on the bees discarded the longer routes, and so gradually optimised their path. The total distance flown every day dropped dramatically, from 1,953 metres at the start of the month to only 458 metres by the time they finished.

This apparent trial-and-error approach has led the researchers to conclude that the bees learn a route by remembering what direction and how far to fly. This is opposed to previous studies, that have claimed that bees have a sophisticated ‘cognitive map’ of the location of each flower (e.g., Menzel R, Greggers U, Smith A , Berger S, Brandt R, Brunke S, Bundrock G, Hülse S, Plümpe T, Schaupp F, Schüttler E, Stach S, Stindt J, Stollhoff N & Watzl S 2005, “Honey bees navigate according to a map-like spatial memory”, PNAS, vol. 102 no. 8, pp. 3040-3045, doi: 10.1073/pnas.0408550102).

The behaviour observed in the latest study is possible without such detailed spatial data, and so is more in line with the capability you’d expect from bumblebees’ tiny brains.

Even so, it’s remarkable how quickly this new method is able to produce an optimised flight path without a big brain, and all while lugging a hefty radar transponder.

Vitamin D deficiency is a spring thing

New research shows that less exposure to sunlight in the winter months leads to lower levels of vitamin D in spring, with the effects lasting longer and affecting more people than previously thought.

As far as vitamins go, vitamin D is unusual in that we make most of it ourselves (the word vitamin usually refers to nutrients we have to eat because our bodies can’t manufacture them).

A substance in our skin, called 7-dehydrocholesterol, creates vitamin D when exposed to ultraviolet light from the sun – specifically, UVB. The liver then turns the vitamin D into calcidiol, and the kidney turns part of that into calcitriol, which is a hormone that controls levels of calcium and phosphate, and is essential for bone growth.

Iconic photograph Sunbaker, by Max Dupain 1937 (click to embiggen)
Ultraviolet light in sunshine is the main ingredient our bodies need to make Vitamin D (Sunbaker, by Max Dupain 1937)
Vitamin D was first identified because a lack of it can cause rickets, an early childhood disease involving soft or weakened bones. But a deficiency can also lead to osteoporosis and other  bone and muscle pain, and has been linked to multiple sclerosis and cancer, as well as general mortality.

This latest study, by Professor Steven Boyages and PhD student Kellie Bilinski from the Sydney Medical School, looked at vitamin D levels in 24,000 samples taken in 2008-2010 from New South Wales hospital patients (Boyages S & Bilinski K 2012, “Seasonal reduction in vitamin D level persists into spring in NSW Australia: implications for monitoring and replacement therapy”, Clinical Endocrinology, vol. 77, no. 4, pp. 515–523, DOI: 10.1111/j.1365-2265.2012.04398.x).

They found vitamin D deficiencies in up to 58 per cent of the population, and lasting most of the year, but  greatest between autumn and the end of spring. In fact, spring was the worst season despite rising levels of sunshine, due to the time taken to replenish the body’s stores of vitamin D.

In summer, 33 per cent of patients had a deficiency, even though this was when vitamin D levels were highest. Interestingly, women reach their maximum levels in January and men in February.

The comparison of demographic groups revealed a previously unknown risk for females between 20 and 39 years of age – but the cause of this is still unknown.

According to Professor Boyages, the results of this study mean there is a need to review guidelines for vitamin D testing and the use of supplements:

“Ideally testing would occur in spring when vitamin D levels reach their lowest concentration. If an individual is found to be deficient a subsequent test three months afterwards would see if they have been able to replenish their vitamin D.

“Similarly use of vitamin D supplements currently fail to address this factor of seasonal variation. A modified approach would see the use of supplements commence, or increase, at the end of summer and be maintained until the end of spring when they would either be stopped or reduced depending on an individual’s sunlight exposure.”

For more information, see The University of Sydney.

Gender equality vs evolutionary psychology

Don’t believe people when they tell you that differences between men and women are biologically fixed.

This idea, that our brains are wired in a certain way and we can’t do anything about it, is often justified by using evolutionary psychology. This then ends up producing ‘just so’ stories, similar to Rudyard Kipling’s fables, like how the elephant got its trunk because a crocodile pulled on it.

It’s often traditional or conservative attitudes that are explained in this way, like the notion that women are worse at maths because male hunters developed better navigation and visualisation skills. Whereas the alternative view is that any measured differences in aptitude are caused by social factors.

She's a perfectly nice lady from a beautiful city, and there's no reason to be mean just because she thinks a quarterback is a river in Egypt.
Savannah ancestry (xkcd.com)

The thing is, you can actually test whether something like this is cultural or innate by comparing different countries. When you do, you find that the more gender equality there is in a society, the fewer differences there are in male and female performances in things like maths or engineering.

Now, the actual mechanism for that is not clear: research by Gijsbert Stoet and David Geary, from the Universities of Leeds and Missouri respectively, seems to suggest that it’s not due to stereotyping (Stoet G & Geary DC 2012, “Can stereotype threat explain the gender gap in mathematics performance and achievement?”, Review of General Psychology, vol. 16, no. 1, pp. 93-102, doi: 10.1037/a0026617). But whatever the reason, it’s pretty clear that it’s not a fixed biological trait.

Another example is the old idea that men prefer young, fertile partners and women prefer wealthy men, and that our prehistoric ancestors evolved these differences because of their particular lifestyle: where the men were the providers and women stayed at home and raised children.

A recent study looked at this question by surveying people from 31 countries about their choice of mate. That is, they asked them whether criteria like financial prospects or cooking skills are important. They then ranked the countries using the Global Gender Gap Index, developed by the World Economic Forum (Zentner M & Mitura K 2012, “Stepping out of the caveman’s shadow: nations’ gender gap predicts degree of sex differentiation in mate preferences”, Psychological Science, published online 29 August 2012, doi:10.1177/0956797612441004).

They found a clear trend that in countries where there was good gender equality there were also fewer differences in mating preferences (Australia, in case you’re interested, came about the middle of the pack in both the Global Gender Gap Index and the equality of mating choices).

Of course, this doesn’t mean that evolutionary influences are totally irrelevant. As one of the authors, Marcel Zentner, said:

“Indeed, the capacity to change behaviours and attitudes relatively quickly in response to societal changes may itself be driven by an evolutionary program that rewards flexibility over rigidity.”

But really, you’d have to say that it strongly suggests that the evolutionary psychologists are wrong, and that differences between men and women aren’t biologically hard-wired into our brains.