Rapid adaptive divergence and FST-QST

Time for another study from the Svensson Lab:

In a recent study published (in early view) in Molecular Ecology, we (Erik Svensson, Anders Hargeby and myself) have quantified phenotypic and quantitative genetic divergence between two ecotypes of our favorite study organism, the aquatic isopod (Asellus aquaticus) in two lakes in southern Sweden. We have tried to assess the relative role of selection and genetic drift during rapid and parallel ecotype divergence events. We demonstrate that for seven quantitative traits, the average QST between ecotypes is significantly greater than the mean FST, which is clearly consistent with a role for divergent selection causing phenotypic and genetic differentiation of these ecotypes. However, some QST-values for traits linked to size-related morphology fall within the distribution of neutral FST-values, whereas it is not the case for pigmentation traits. Our study therefore underscores the need for caution when evolutionary inferences are made from FST-QST analysis.

For instance, many FST-QST studies have investigated large number of populations and traits, without prior ecological and historical knowledge of the system. This aspect is important because if, like it is in our case, you investigate a case of parallel evolution, you may use specific pairwise comparisons as "replicates", and others as “controls”. The hierarchical structure of the populations and their history might therefore be of importance.

Second, neutral markers may sometimes not be so neutral, thus it is important to compare the distributions of FST with the distributions of QST, and not their means, if one wants to infer the role of selection in the divergence process. All these issues have been reviewed in a very nice paper by Whitlock also published in Molecular Ecology in 2008 and that we have discussed in a previous lab-meeting.

A last point I would like to insist on is that of course, this kind of approach will never beat the advantages of directly measuring selection in the wild. However, it might also be tricky to determine is selection is driving divergence between two populations even when estimating selection in the wild, since it is often difficult to encompass all its components at once, for example linked to fecundity, mate choice, intrinsic survival, predation, etc. Thus, by using FST-QST comparisons, one will estimate the role of the “net” selection differential between populations and its role during divergence. And this is also an advantage.

Well, I hope it inspired you to read our paper…

Smells like?

As some of you know I have spent the last 9 months working with Steve Chenoweth at The University of Queensland where we use the model species Drosophila serrata. In this species (and other Drosophila) males court females using a blend of cuticular hyrocarbons (CHCs) that are produced in the oenocytes of both sexes (see pic above), located on the inner surface of the animal’s abdominal cuticle. These CHCs are known to explain around ¼ of male mating success in D.serrata, and are the subject of a lot of work produced by both Mark Blow’s and Steve’s Lab.

With this in mind I wanted to draw your attention to a recent paper in Nature on the important role of the CHC’s produced by another species of Drosophila, D.melanogaster, not only intraspecfic mating interactions, but also species identity and interspecfic matings. In the paper by Billeter et al. (sorry, not open access) they explain how they knocked out the production of the oenocytes of adult male and female D.melanogaster and found some interesting results. Firstly flies missing the oenocytes (oe-) became a hyper-sexual stimulas to other wild caught males. Oe- males and females were courted and mated far more than their wild caught counterparts. By applying different pheromone compounds, singularly, to the oe- individuals they found a slowing in male mating attempts (ie the female pheromones actually put the males off). Another interesting find was that female oe- were actually courted and mated with males from another species (D.simulans), and again by applying one pheromone compound restored the species barrier.

So a few CHC’s in D.melanogaster have been shown to control male-male mating interactions, influence male courting rates and act as a species barrier to other Drosophila males. Think about that next time you try a unisex eau de toilette.

Abstract:

Social interactions depend on individuals recognizing each other, and in this context many organisms use chemical signals to indicate species and sex1. Cuticular hydrocarbon signals are used by insects, including Drosophila melanogaster, to distinguish conspecific indi- viduals from others1–3. These chemicals also contribute to intraspe- cific courtship and mating interactions1–3. However, the possibility that sex and species identification are linked by common chemical signalling mechanisms has not been formally tested. Here we pro- vide direct evidence that a single compound is used to communicate female identity among D. melanogaster, and to define a reproductive isolation barrier between D. melanogaster and sibling species. A transgenic manipulation eliminated cuticular hydrocarbons by ablating the oenocytes, specialized cells required for the expression of these chemical signals. The resulting oenocyte-less (oe2) females elicited the normal repertoire of courtship behaviours from males, but were actually preferred over wild-type females by courting males. In addition, wild-type males attempted to copulate with oe2 males. Thus, flies lacking hydrocarbons are a sexual hypersti- mulus. Treatment of virgin females with the aversive male phero- mone cis-vaccenyl acetate (cVA) significantly delayed mating of oe2 females compared to wild-type females. This difference was elimi- nated when oe2 females were treated with a blend of cVA and the female aphrodisiac (7Z,11Z)-heptacosadiene (7,11-HD), showing that female aphrodisiac compounds can attenuate the effects of male aversive pheromones. 7,11-HD also was shown to have a crucial role in heterospecific encounters. Specifically, the species barrier was lost because males of other Drosophila species courted oe2 D. melano- gaster females, and D. simulans males consistently mated with them. Treatment of oe2 females with 7,11-HD restored the species barrier, showing that a single compound can confer species identity. These results identify a common mechanism for sexual and species recog- nition regulated by cuticular hydrocarbons.

No lab-meeting the coming weeks, but some exciting symposia

This week's Wednesday (28 October), we will not have our usual lab-meeting, and we will probably have a break for a couple of weeks for now, due to (among other things) teaching activities and CAnMove-PI meeting on my part. However, in case somebody wants to utilize "Darwin" on Wednesday, the room is booked between 10 and 12. Feel free to use it!

On Monday and Tuesday, Caroline Isaksson and Tobias Uller from EGI at Oxford University, will visit the department and give two talks (organized by Maria von Post and Andreas Nordén). I would strongly recommend you to go to these seminars, which will take place in the "Red Room" (adjacent to the "Blue Hall"). On Monday there will two regular research seminars on the afternoon, while on Tuesday there will be a "mini-symposium" about applied and societal aspects of ecological research, where I will also contribute with a talk. Here is the schedule for both days:

SEMINAR 26TH OF OCTOBER14.00-15.00 Causes and consequences of oxidative stress in wild animalsCaroline Isaksson

15-15.30 Coffee

15.30-16.30 Why is Sex Determination in Reptiles so Variable? Integrating Development, Ecology & EvolutionTobias Uller


APPLIED ECOLOGICAL SCIENCE - WORKSHOP 27TH OF OCTOBER
Titles and presenters:

1. What can evolutionary ecologists contribute to medicine?
Insights and Inspiration from the World Health Summit
Dr. Tobias Uller, EGI, Oxford University

2. From selfish genes to group selection - implications for society
Prof. Erik Svensson, Lund University

3. Urban ecology
Dr. Caroline Isaksson, EGI, Oxford University

4. Attitudes and biodiversity
Dr. Johan Ahnström, Lund University

Coffee will be served during the afternoon.

Moreover, there will also be another exciting symposium next week, on Friday (30 October), namely a "Darwin-symposium" , organized by the Royal Academy of Sciences and the Royal Physiographic Society (main organizer: Professor Eric Warrant). The speakers include professors Dan-Eric Nilsson from Lund, Siv Andersson from Uppsala and legendary sociobiologist and evolutionary biologist Robert Trivers from the US. Do not miss this! The symposium is a full-day symposium, and you will find more information and directions here. All the talks will take place at "Palaestra" at the main university area (close to "AF-borgen").

Bayesian statistics for next Wednesday meeting

Last lab meeting Erik and Maja told us about a course on the program R and Bayesian statistics in Uppsala they have been attending. Inspired by this we decided to have a meeting where we discuss Bayesian statistics on Wednesday. First we will discuss a review by Beaumont and Rannala which I first read to prepare for a conservation genetic data analysis course last autumn and found really useful as an introduction to the topic. The paper is found here http://www.nature.com/nrg/journal/v5/n4/pdf/nrg1318.pdf

After that Erik and Maja will give a short presentation on what they have learnt in Uppsala.

Labmeeting on hidden genetic variation 14 October 2009

This Wednesday (14/10 2009), I was thinking that we should discuss a recent TREE-article that deals with the fascinating topic of "hidden" genetic variation and its evolutionary implications. You can find this article here. Also, here is another background article, also from TREE, for those of you who wish to learn more.

Hidden genetic variation is genetic variation that is not normally expressed, e. g. genes that is contingent upon environmental conditions before they are expressed, and hence before they can be "seen" by natural or sexual selection and thus contribute to adaptive evolutionary change.
A well-known example of hidden genetic variation are so-called stress proteins or heat shock proteins, that function as molecular "chaperones" to protect cells during extreme environmental conditions, e. g. during high temperature conditions. How important is such hidden genetic variation in evolution? This what we should discuss, among several other topics.

I also hope that our new CAnMove-postdoc Sophia Engel (shared with Anders Hedenströms laboratory) will join in Wednesday, as she has now arrived to Lund. This would be an excellent opportunity to meet the rest of our lab and introduce her to the crowd.

Time and place as usual: "Darwin" at 10.00 on Wednesday (14/10). Any fika-volunteer?

Pictures from the Okavango Delta and Botswana

You might remember that I did an exploratory trip to northern Botswana and the Okavango Delta last winter, with the aim to find some interesting odonate systems for future research. As I have applied for some research grants to work in this fascinating region, I hope that I will be able to return to do some directed and systematic studies in the future.

I have now put up some pictures from this trip on the web, which you can see here. Enjoy!

Hello Svensson Lab!! Here's my travelogue:

Well, I left about 1 month ago and boy has it been a fast month!! I first went to my mom's house and recovered a little bit. I had been in Italy for a meeting and workshop, then I swung through Sweden for a couple days, then flew to Washington State in the northwestern corner of the USA, and by the time I got to my mom's I was pretty worn out. (The photo is of my mom's place, with the Olympic Mountains in the background; the Subaru behind the white car is my new set of wheels.)

After a couple days I bought a car and drove to Oregon to visit some long lost friends. The day after I got there I went and watched one buddy play drums in a surf rock band, and then we walked down the street and I watched another buddy play guitar in a bluegrass band. My job through all of this was to drink strong ales, which I did admirably. Also while in Oregon I went to a shooting range and generally blew stuff up. It was at this moment that I truly felt I'd returned to the US. =-)

After Oregon I went to visit my dad and some other family for a week or so (this involved fishing, lots of motorcycle riding, and deck repair). Then I visited my sister and my nieces, and some other old friends (more beer). Then I returned to my mom's, regrouped, and headed out across the country.

First I went to San Francisco, which was about a 15 hour drive. This is not a productive direction to go when one wants to get to the eastern side of the US, but I had to pick up my desert tortoise, Squiggles. Boy has he grown over the last couple years!!! I quickly realized that she wasn't a she, but a he. I still call him she a lot, though. I also visited several old friends and played on the beach. Yet more beer was drunk. After a couple days in SF, I hit the highway, with Squiggles bravely riding shotgun. Two long days of driving got us to Fort Collins, Colorado. Guess what? Yup: more friends, and more beer. Some hiking and donkey petting. It was wonderful. Then we packed up and drove from Colorado to Hanover, New Hampshire, which took 3 long days of driving (Squiggles, to her, um.. I mean, his... credit didn't complain about the cheap, dirty motels I chose along the way). Dartmouth College is in Hanover, and New Hampshire is in the northeastern side of the state. Total distance from Washington to New Hampshire: 6709 km. Does Lund feel just a bit warmer? It should (sorry). My new postdoc is here at Dartmouth College in the Ryan Calsbeek lab. Ryan works on the evolutionary ecology of lizards, and does creative, first-rate work. I feel very lucky and excited to be here. My job, though, is to fire up some newt science.

Now that I am sort of settled in at Dartmouth, tomorrow I am to do my first day of field work catching newts with someone from the McPeek lab. During my travels I didn't answer almost any emails, and I have hundreds to deal with -- sorry!!!! Be patient and I'll get to you. But right now, as I settle in, every minute is booked and I'm doing my best to catch up.

I'd like to give a warm THANK YOU to everyone at Lund University, and especially the Svennson lab, for an outstanding 2.3 years!!!!! A finer group of people could hardly be found, and I now look forward to visiting you all as my "old friends", and drinking beer, and posting it on a blog. I am a different person as a result of my time with all of you. =-)

Brains, Pain and Autumn Rain

Hej Svensson Lab!

Stockholm is one beautiful city. When I'm not at the Karolinska Institute learning the ropes on human behavioral studies, I am out wandering around the city's busy parks and waterways. It certainly gets dark quick up here.
In the lab, Martin Ingvar has set me under the direction and guidance of two Phd students, Karin Jensen and Fredrick Lindstedt, for a solid introduction to neuroscience. Karin defends her thesis in October while Fred is just beginning his doctoral studies. Erik will be happy to hear that Karin has recently published in PloS ONE, his fav journal.
Fred and I are tasked with designing a study that looks at the interaction between emotion-regulatory genes and pain perception. Over the weeks our colleagues have developed avoidance strategies as we search for 'naïve' subjects to test our methods on. We begin pretrials next week and we'll see if our protocol works. I can't say too much as our future subjects are people and they can google.
I've also become involved with an fMRI brain-imaging study of people who suffer from Fibromyalgia syndrome (FMS). FMS is a disease consisting of lasting chronic pain ( >3 months) that exists without any measurable peripheral tissue damage. Neuro-imaging studies have been essential in establishing how FMS sufferes differ from the general population in how they process pain. I'm learning that FMRI can be a great tool for connecting the dots between the biological, cognitive and psychological systems that determine behavior. Plus, hanging around the scanner means I get a pretty brain scan to take home to Mom (see pic!).
At the moment I am applying for graduate school as well as funding which has me reflecting on my time in Lund. I'm so grateful to have been a part of the Svensson lab- I learned so much!
See you guys in December,
Kram,
Lisa Orr

No lab-meeting this week but another opportunity to broaden your views

This week we will not have a lab-meeting, as I will be in Uppsala, participating in a course about the Open Source-programme "R". As some of you might still want some intellectual input this week anyway, you could always listen to the excellent swedish radio programme "Filosofiska Rummet".

Last Sunday, the theme of this programme were the moralistic and the naturalistic fallacies. I was one of the three participants, together with sociologist Eva Kärfve from Lund University and philosophy professor Per Bauhn from Kalmar. You can listen to the programme here. It is in Swedish, though, but most of you will understand the discussion. Enjoy!