Author Archives: sbphoto2013

Science Drinks – 25.2.14

Attendees: Luc Bussiere, Elizabeth Herridge, Toby Hector, Claudia Santori, Gregor Hogg

To start with, Luc discussed ongoing struggles he is having in presenting some statistical concepts to first year students. It turns out that lecturers often have just as much trouble writing lecture material as we do understanding it! We debated the issue of making the material engaging enough to keep everyone interested in a difficult subject, and considered the contrasting pressure of getting all the information across when the lecture is a pivotal point in the course. Luc will report back on how his lectures went later on….

Next onto science as Toby presented a paper that has found a novel method of looking at depth perception using jumping spiders (Depth perception from image defocus in a jumping spider, 2012). The authors report evidence for the first known example of an animal (the jumping spider) that uses defocused images as a primary mechanism for depth perception.

Claudia then shared an interesting paper on the convergent evolution between Cane Toads and the Madagascan plant Mother of Millions (Interacting Impacts of Invasive Plants and Invasive Toads on Native Lizards, 2012). In a case study on the blue tongue lizard (Tiliqua scinoides) it was observed that while these omnivorous lizards are threatened by the invasion of toads in north western Australia, conspecifics from other areas of Australia are less affected by the poison of the toads, including where the toads have yet to invade. Researchers noticed that this pattern was consistent with the geographic occurrence of an ornamental plant from Madagascar – Mother of Millions (Bryophyllum spp.), introduced in the continent around the same time as the cane toads.

This seems to be a remarkable case of convergent evolution, where the toxins produced by the Mother of Millions are chemically extremely similar to the bufotoxins produced by the toads. The lizards that were found to have evolved resistance to the plant toxins also turned out to be tolerant to the poison of the cane toad.  Different individuals from various geographical areas were collected and injected with a sublethal dose of toxin, and changes in their locomotor performance were then observed. Lizards located in areas where neither Mother of Millions nor Cane Toads were present were found to have to lowest tolerance to the toxins.  This supports the idea that both the Mother of Millions and the Cane Toads impose selection on bufadienolide resistance.

Finally Lilly discussed some of her ongoing work on sexual selection in dance flies!

Bateman 1948: Intra-sexual selection in Drosophila

This is the first of a number of posts on “classic papers” in our new series called Journal Pub .

Our first topic is mating systems, and I have the pleasure of summarizing and commenting on Angus Bateman’s study of sexual selection in Drosophila. In 1948, although ¾ of a century had passed since Darwin published Sexual selection and the descent of man, Bateman (1948) remarked that the evidence that sexual selection explained sexual differences remained circumstantial, and that there was considerable debate concerning the importance of mate competition in producing secondary sex characters. For example, Huxley (1938) argued that monogamous birds with striking secondary sexual differences seemed to display mostly after pair formation (and therefore presumably not in the context of contests at all).

What we now know about the many possible episodes for sexual selection (including for example, the potential for postcopulatory sperm competition and female choice) colours our impression of Huxley’s objections, but at the time Bateman’s empirical approach was probably the only sensible response: could he demonstrate that males and females differ in the potential to gain fitness through mating?

He conducted a classic experiment in which he housed an equal number (either 3 or 5 of each sex) of virgin male and female Drosophila melanogaster together for three or four days, and collected the offspring produced within the fly vials during this time. Because each of his flies carried a unique dominant marker, he was able to unambiguously assign all offspring to their parents, and therefore to retroactively work out the reproductive successes of males and females in his experiment. He first noted that males had much higher variation in fitness than females did: there were more males who had no fitness at all, and a few males had dramatically high fitness. (Note that he did a lot of technical work to make sure that his observations of differences in variance across the sexes were real, and not due to errors in experimental execution or measurement.)

Furthermore, he showed that the relationship between mate number and fitness was much stronger in males than it was in females. The figure below (stolen from his paper) has been reproduced many times to illustrate this key result.

Screen Shot 2013-11-29 at 18.48.09

It’s worth noting that the differences between sexes was much stronger in his last pair of experimental blocks (Series 5 and 6, on the right) than in his first four blocks. The reasons for this discrepancy are not clear, but Bateman speculated that his first four blocks suffered from poor vigour; if weak males could not transfer enough sperm to fertilize all of a female’s eggs, several inseminations would be needed.

The key difference between the sexes therefore was that males can gain a lot from remating, but females usually much less so. If this difference in selection on mating was representative of the general situation in animals, that would explain (as Darwin had suggested) why males so often are the showier, more heavily armed sex: they have more to gain from contests over sex than females do.

In discussing this paper on Tuesday, several people mentioned the very recent (and controversial) publication of work that reanalysed (Snyder & Gowaty 2007) or replicated (Gowaty et al., 2012) Bateman’s classic experiments, criticizing many of the conclusions Bateman had drawn. None of us felt sufficiently well prepared to discuss these in any depth, but perhaps they will be interesting for further reading and discussion another day.

Research Group Meeting: 29th of October 2013

Present:

Dr Luc Bussière, Dr Timothy Paine, Elizabeth Herridge, Thomas Houslay, Toby Hector, Sam Paterson, Claudia Santori, Hazel Smith, Gregor Hogg

Our bi-weekly research meetings continued last night at the William Wallace with a number of interesting topics and surprising revelations such as: ‘I got Hep B in Croy’ from Dr Paine, ‘Twitchers are crazy’ from Lilly and ‘We build houses’ from Luc as a rebuttal on the subject of behavioural response to poor environments.

DISCLAIMER: Some of the above may have been taken wildly out of context.

‘From egg to dead’

The centre of discussion was of Hazel’s summer research project looking at the effect of different life history traits on phenology in dance flies. This impressive undertaking involved her designing a model to test a range of life history parameters (with regards to longevity, mating frequency and physiology) with the hope of making some predictions that could be tested experimentally.

So far her work has focused on getting the model up and running with the aim now to test the rest of the life history parameters. As is often the case, the current model design is very complex but Dr Paine made some helpful suggestions on model simplification such as eliminating aspects of functions that include random variation (for example, in nuptial gift size) and on running sensitivity analysis.

‘Plasticity’

We followed Hazel’s coherent presentation with a fuzzy discussion on plasticity. It got deep. It got so deep in fact that your humble scribe does not feel entirely comfortable leading you down the contorted and abstract path that followed. If you’re really keen though have a look at this paper by Samuel Scheiner on the genetics of phenotypic plasticity that Tom recommended. If that wasn’t enough, have a look at this paper by Emilie Snell-Rood on the costs and benefits of phenotypic plasticity, or there is always ol’ trusty!

‘Yes, surprisingly I am still married…’

Next Tom showing us some cool results from ‘his’ (Tom’s words not mine Mrs Houslay) work on the effect of diet on the chemical composition of male decorated crickets. An arduous undertaking but with some promising implications for his research.

‘Tessellation, a cool word to use when neatly packing your fridge’

We finished up with a discussion on the physics of eyes as Toby presented some problems on the size of facets in some male dance flies.

Any other business:

There was a quick tactical discussion on how to peer pressure Lilly’s sister into presenting her work to the group during her visit. She’s doing some interesting work on dwarf elephants in the Mediterranean, she must be so jealous she’s not studying flies in Scotland! I would also suggest having a look at a short video from the Quirks & Quarks podcast.

Finally Luc proposed a research group Movember team effort extravaganza with a clean shave group photo scheduled for Friday. Movember for those who don’t know is a charity that is based around the noble art of growing a moustache. Lilly, Hazel and Claudia clearly felt left out of this discussion but not to worry as ‘Mosistas’ are considered an integral part of the event!