Monthly Archives: November 2013

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.

Science Drinks Nov. 19, 2013

Attendees: Claudia Santori, Tim Paine, Moha Abdelaziz Mohamed, Gregor Hogg, Lilly Herridge, Toby Hector, Luc Bussière, Nils Bunnefeld

After an unplanned relocation of the Nov 5 Science Drinks, we found ourselves back at the Wallace, where the smell of new varnish only somewhat made up for the lack of other renovation surprises. Spoiler: the newly renovated pub does not provide free house port on every table after all, at least not yet.

Before the whole crowd had assembled, the keen early arrivals started chatting about spatial autocorrelation, because why not? Both Gregor and Toby face this problem in different respects in their honours work: Gregor finds spatial autocorrelation in his geographic information about species distributions, while Toby faces similar problems when assessing morphological information from different positions on a single animal. As soon as they sat down, we asked Tim and Nils if and how they might have addressed similar issues involving transects (not trans sex) in their ecological work. They respectively pointed to couple of potentially helpful sources. Tim suggested consulting Mark McPeek‘s work on the evolution of dragonfly morphology, while Nils referred us to his better half Lynsey McInnes‘ work on geographic ranges. Very helpful pointers — we’ll expect a status update from Toby and Gregor in a few weeks once they have digested some of these papers.

Lilly’s contribution was recent paper by Dowling and colleagues, recently published in JEB, demonstrating trans-generational effects (not trans sex) of exposure to mates on offspring fitness in Drosophila melanogaster flies. They manipulated female exposure to sexual conflict by both manipulating access to males and by cauterizing the genitals of males in some treatments, so that while there were many males they could not mate and transfer ejaculate accessory gland proteins that are known to impose conflict. Intriguingly, the offspring of the cauterized multiple male treatment did worst of all. It seems like the mechanisms that might cause this are numerous, and worth further study.

Nils then provided a fascinating and long discussion involving both the humanities and sciences, both pure and applied, and which provoked some fairly nuanced philosophy as well as no small amount of depression in the author of this blog. However, because the exact topic is the subject of ongoing work that might just be subject to embargo, I have to write very little here (I know, the readership of this blog is hardly wide enough to pose a risk, but better safe than sorry!) This is a lesson in the benefits of experiencing science drinks in person! Some topics are too hot to summarize later on. Maybe we can link to the paper in due course….

Before anyone could escape for the evening, I asked the crowd for advice on a project proposal concerning cotton plants and Spodoptera caterpillars that a colleague from Bangladesh and I are writing for an upcoming travel grant. Tim and Moha both had some very good insight on the plant biology and herbivory that will be useful in refining our ideas, and suggested some references by Anurag Agrawal and Sharon Strauss that I need to follow up on.

So as you can see (at least for the unexpurgated components of this summary), Science Drinks is usually fun AND productive! Join us for the next session if you can…

Research Group Meeting Nov. 12, 2013

For the second consecutive week, we were forced to relocate from the Wallace Pub on account of renovations. Instead we met at the Meadowpark. After dealing with minor matters related to our own research projects, we discussed the organization of a new initiative for the research group: Journal Pub (aka Beer Review).

As part of an effort to catch up to some of the information age, we’re devoting ourselves to collectively reading some new and classic papers in several corners of evolutionary biology. We’ll organize our efforts using the newest page on our website: Journal Pub. Navigate there to learn about the topics and papers under discussion prior to a particular Journal Pub session, or go there after a session to see the brief written summaries of the papers as well as some annotations of our discussions on each of them. So there’s a bit of wrangling ahead to wrap our heads around a lot of difficult concepts, but it’s exciting to think that we might collectively learn about some very big and important ideas rather productively and quickly.

The first Journal Pub (location TBC) will occur on Nov 26. I have taken the liberty to assign responsibility for chief and adjunct reviewers of each paper, though naturally anyone can read more than the focal assigned papers. Looking forward to the discussions!

Movember

Not science, but maybe still worth noting:

It’s Movember 1st today — the start of a new field season for a rare annual species one finds only at this time of year on the upper lips of folks like me who forego shaving for a good cause. Feel free to donate to the cause of men’s health if you can: find our Institute’s Movember page here, where you’ll see links to the Movember pages for the whole clan. We’ll post updates to the facial hair phenology as it develops….

With