When Biologists move to the dark side: working hand in hand with physicists to understand the role of color in the evolution of species

PART 1 

 *by Maren Wellenreuther, Anna Runemark and Mikkel Brydegaard

We study a variety of species in our lab, such as ecotypes of isopods and color morphs of lizards and damselflies. In our work on these species, color is one of the main traits that we examine. This is because color affects crypsis (isopods), sexual selection and other life history traits (lizards and damselflies). However, examining color is not a trivial undertaking. For example, biologists often fail to account for differences in animal visual systems when modeling how species are perceived by con- and heterospecifics. Many also fail to realize that most cameras are not sufficiently spectrally resolved (they have 3 bands only) to capture color and that most spectrophotometers are not sufficiently spatially resolved to capture heterogeneity in color patterns (since they give averages rather than spatially resolved measures, consequently, both a donkey and a zebra would appear grey to a high resolution spectrometer). 

Ecotypes of isopods Asellus aquaticus, color morphs of the Skyros Wall Lizard Podarcis gaigeae, and different colors a mating couple of the structurally colored Calopteryx virgo. 

The beginnings…                      

When we first started to measure color, we realized how difficult this task actually is. This is particular true when one wants to conduct color experiments in natural or laboratory settings. What light sources are needed? What color vision does the color-signal-receiver have? Faced with these problems, we quickly recognized that we needed to communicate with people that know how to measure color. The Atomic Physics Section at Lund University has a group (Applied molecular spectroscopy and remote sensing) under the supervion of Sune Svanberg that, among other things, specializes in the measurement of color. First contact with the group was established in 2007 when Fabrice Eroukhmanoff was hoping to quantify the color of isopod ecotypes, of which one ecotype typically inhabits the reed habitat, while the other one prefers chara habitat. Fabrice wanted to quantify the color of different ecotypes. After talking to Mikkel Brydegaard Sørensen, a PhD student in Sune’s group, they realized that in order to compare the photographs, he needed to standardize them posteriori to account for different light environments. The color analyses are presented in, for example, here.  Discussions and exchange of ideas between our group and Sune’s group helped in the years to come to set up carefully planned experiments to examine color traits. 

To illustrate the point…measuring complex color traits in the Skyros Wall lizard

For Anna Runemark, who is studying color morphs of the Skyros Wall lizard but also dorsal coloration, color is one of the core traits of her studies. In her work, she is interested in the strength and direction of sexual selection on different color morphs in island and mainland populations (see here). To measure color differences, Mikkel designed an optically isolated ‘photo-box’ with a standardized light environment (e.g. the only illumination source is the flash) and polarizing filters in front of the flash and the objective to avoid specular reflectance. As the distances from the flash vary with position in the box, the white background is used to interpolate an illumination profile on the lizard, and this was used to correct for illumination differences across the photograph. Lastly, to estimate the entire color probability distribution (includes information about both mean, variance, skewness, kurtosis etc., see e.g. the 2D examples in the figure below), the color of each pixel of the measured colour patch was quantified, spatially accumulated and then divided by the number of pixels to obtain the probability. This method is presented in a paper found here

Figure 4-taken from (Brydegaard, Runemark et al. 2012). Upper row: reflectance distributions for a homogeneously colored yellow-throated lizard. Lower row: corresponding distributions for a orange-yellow patchy specimen. Left column: three 1D distributions for each spectral band. Middle column: 2D chromatic plane distributions color coded with corresponding colors for the two example specimen. Right column: iso-surfaces encapsulating probabilities higher than 1% in the 3D RGB color space of the two sample specimens. Surfaces are coded with corresponding colors.

After these initial dialogs between biologists and physicist, it became clear that we can both learn from each other. We as biologists have an interest in capturing color traits of animals accurately and precisely, while physicist that study natural phenomena have a need to understand the biological underpinnings. As a result of this initial integrative work, the Lund CAnMove group organized a symposium entitled ”The Biology-Physics Interface”. During this day, many of us met and presented our research and discussed ideas. 

Caption: CAnMove symposium ”The Biology-Physics Interface”. Sune Svanberg at the top, and Erik Svensson below.

References

Brydegaard, M., A. Runemark, et al. (2012). "Chemometric approach to chromatic spatial variance. Case study: patchiness of the Skyros wall lizard." Journal of Chemometrics

Eroukhmanoff, F., A. Hargeby, et al. (2009). "Parallelism and historical contingency during rapid ecotype divergence in an isopod." Journal of Evolutionary Biology 22(5): 1098-1110.

Runemark, A. and E. I. Svensson (2012). "Sexual selection as a promoter of population divergence in male phenotypic characters: a study on mainland and islet lizard populations." Biological Journal of the Linnean Society 106(2): 374-389.

Plenary talk by Hanna Kokko on partial migration on Wednesday

Our lab-meeting about the genetics of high-altitude adaptation in humans will start somewhat later than usual on Wednesday, namely at 10.30 on Wednesday September 1, and not the usual time at 10.15. The reason is that there will be an interesting plenary lecture about the evolution of partial migration by Professor Hanna Kokko (University of Helsinkki) that will start at 09.40 in the "Blue Hall".  

Hanna is an excellent speaker, so we might not want to miss this. Her talk will end approximately 10.20, and after that we will start our regular lab-meeting. During the rest of the day and in the afternoon, there will be other interesting talks during the symposium on partial migration, which might be worth attending.

And from 17.00 and onwards, there will be a "CAnMove"-barbecue, organized by postdocs Sophia Engel, Ben Chapman and Miriam Liedvogel. Contact Sophia for more info (sophia.engel@teorekol.lu.se)

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?

Day 2: Genomics of speciation

The second day at Kristineberg has mainly been devoted to the genomic basis of speciation and the genetics of postzygotic isolation. Interesting talks by Michael Nachman, Hopi Hoekstra, Axel Meyer and Dave Presgraves. In general, though, it has been a bit too much about postzygotic isolation, though, to my taste. This, however, reflects that it is a meeting that was organized by Hans Ellegren, whose main interests are in these genomic aspects of speciation and evolution.

Again, my general feeling from yesterday remains: the field of speciation have reached the phase of "normal science", where there are not that many exciting discoveries or new concepts, but rather a lot of "problem solving" and filling in of the gaps. This might not necessarily be a bad thing: when fields are too hot and fast moving, the best science is not necessarily made because people tend to jump on bandwagons and reflect very little once they are on those bandwagons.

I had an interesting lunch discussion with Trevor Price today about the role of learning in evolution, particularly the role of learned mate preferences. This was quite refreshing, since Trevor thinks learning is extremely important and underestimated in the speciation process (as I also believe). When I first brought up the issue of learned mate preferences in on of our lab-meetings about 1 1/2 years ago, I saw mainly a lot of blank faces in the room, but I am more convinced than ever that this is one of the most exciting areas of speciation research in the future (and our coming postdoc Machteld Verzijden would probably agree, I suspect). It is also a natural area where field ecologists and behavioural ecologists could make important contributions and add to a more balanced picture of the speciation process than we would have had if we only relied on genomics data from Drosophila-research.

Another general reflection of this meeting is how large resources many research groups in the US have, compared to us in Sweden. This is particularly evident when it comes to genomic studies, such as large-scale DNA-sequencing efforts, transcriptomics, "454" and microarrays. All these techniques cost a lot of money, more money than we can ever dream of getting in Sweden with the current research financing system. So how then to seriously compete with these groups?

Perhaps the correct answer is not to try to compete at all, but rather try to specialize in areas where these groups are weaker, and not be too frustrated that we do not have access to similar large-scale genomic resources. Our main strength in Lund is our ecological and experimental tradition, not primarily our skills in genomics. This is also where we have to profile and advertise ourselves in the future, as this is an area that separates from other departments. In that sense, we have to push or Linnaeus-programme CAnMOVE in the future and emphasize the strong Lund research tradition of animal movement, dispersal and migration (and the consequences thereof).

Hans Ellegren, the organizer of this meeting, actually suggested that we in Lund should organize a similar meeting about animal movement in the future, and this seems like an excellent idéa. If there is something I think has been missing at this meeting, it is the field experiments and studies on animals in their natural environments, including mate preferences in the wild and dispersal behaviours.

"The Biology-Physics Interface": symposium in Lund Wednesday 25 March

We had some excellent discussions with our visiting Finnish guests, and I was hoping that some of you could soon write some bloggpost(-s), where you summarise your thoughts and impressions about Lamarck, species concepts and/or sympatric speciation. Shawn or Maren perhaps? Also, I think we would be interested in a bloggpost from Tina and Josefin, who had a separate discussion about sexual selection/sexual conflict. Please share with the rest of us some of your thoughts and idéas.

For the next week, I would again like to remind about the workshop on "The Biology-Physics Interface", that I am organizing here in Lund together with limnologist Lars-Anders Hansson. This a so-called CAnMOVE-event - "Centre for Animal Movement" - our new "Linnaeus-programme" about animal movement research. I hope that you all can participate and listen to the talks next Wednesday between 13.00 and 18.30 in the "Red Room" (Ecology Building). Below, I have pasted in the programme for the workshop:


13.00-13.15: Welcome! Introductory words - Erik Svensson

13.15-13.30: Presentation of CAnMove - Susanne Åkesson

13.30-14.15: Remote sensing of animal movement – unconventional laser radar possibilities
Sune Svanberg

14.15-14.45: Dragonflies and damselflies as bioinspirators - Erik Svensson

14.45-15.15: Seeing animal flight through the side-wall of a wind tunnel - Anders Hedenström

15.15-15.45: COFFEE BREAK

15.45-16.15: Nanotechnology in biology - Waldemar Hällström

16.15-16.45: Optical Spectroscopy in Animal Appearance and Perception -
Mikkel Brydegaard

16.45-17.15: Magnetic resonance imaging: Morphology and function - Ronnie Wirestam

17-15-17.45: Individual labeling of small animals (Daphnia) - Bengt Danielsson

17.45-18.30: Plenary Discussion: How can methods from physics be of use in biology?
Moderator: Lars-Anders Hansson