Talk by Katie Duryea about sexual selection in Anolis-lizards

 

Posted by Erik Svensson

This Tuesday (October 7 2014, note changed time!) we will listen to our new postdoc Katie Duryea, who will give an informal 1-hour summary of her PhD-thesis research on Anolis-lizards, which was performed at Dartmouth College in the laboratory of Ryan Calsbeek. Feel free to also invite some other folks outside our core lab-group, as Jessica and Tobias are away this Tuesday. Also, note that we will start at 09.00, rather than at 10.30, as we use to.  Here is the title:

"Sexual selection and sexual conflict in Anolis lizards: from molecules to populations."

And here is a short description by Katie about the content of her talk:  

  

"I will cover the  effects of male mating order on sperm precedence, the transcriptomics and molecular evolution of genes expressed during mating in female anoles, and a population study of sexual antagonism on male and female body size in anoles."

When: Tuesday October 7 at 09.00!!!

Where: "Argumentet", 2nd floor, Ecology Building 

Welcome! 

New logo and some words about our visitor statistics and blog impact

Posted by Erik Svensson

Our blog continues to attract many outside readers, since it was first launched some years ago. We have had aobut 93 000 downloads, although all not unique ones, and although some come from automatic web searches and machines, I still think that we can safely conclude that we have had thousands of human visitors. The number of downloads is currently about 1000 per month, which is a decline from about 7000 per month, before we changed the name and adress of the blog in August 2012. However, this cost in terms of lost visitors will probably be worth it in the long term, as we have a steady increase in visitors and the blog name is now more general and less person-centred.

Interestingly, the currently most popular and visited blog post of ours is the one where our new postdoc Lesley Lancaster was introduced to the other lab-members. This blog post has 1007 visits, which makes me wonder if Lesley is more famous and more popular than a post about Richard Dawkins who is number two, with only 845 downloads? Clearly, Lesley is a more up-and-coming scientist though, than Richard Dawkins who has passed his peak a long time ago. 

I have gotten many positive comments from colleagues from outside, as well as putative postdocs and PhD-students who have expressed interest in joining this laboratory. Several have also said that the combination of  laboratory experimental evolution approaches (flatworms and Drosophila) and field experimental work on non-classical model organisms (damselflies, lizards, birds) is a powerful and attractive combination. The new logo above should hopefully capture this synthetic spirit of our research laboratory. Below, you can download the new header of our blog and use as a logo if you wish, or promote us to interested collegues. 

Papers for labmeeting on November 24: genomics and sex ratio evolution

This Wednesday, we will discuss two short papers, one in Nature Genetics and the other one in Nature. They are both very short, but should make interesting reads. The first paper was suggested by Bengt Hansson, and is an example of how the sequencing of entire genomes can shed light over local adaptation, in this case of the plant Arabdopsis lyrata to serpentine soils. You can download that paper here. The second paper is an example of how climatic factors can drive population divergence in sex determination systems, in this case over an altitudinal gradient of an Australian lizard species. You can download that paper here. Abstracts of both papers are provided below.

I hope you enjoy these papers and that we will have a good discussion. Time and place as usual: "Darwin" at 10.15 (Wednesday November 24). Fika volunteers are encouraged to step forward.

Population resequencing reveals local adaptation of Arabidopsis lyrata to serpentine soils  

Thomas L Turner, Elizabeth C Bourne, Eric J Von Wettberg, Tina T Hu & Sergey V Nuzhdin

Nature Genetics 42: 260–263 (2010)

DOI: doi:10.1038/ng.515

A powerful way to map functional genomic variation and reveal the genetic basis of local adaptation is to associate allele frequency across the genome with environmental conditions. Serpentine soils, characterized by high heavy-metal content and low calcium-to-magnesium ratios, are a classic context for studying adaptation of plants to local soil conditions. To investigate whether Arabidopsis lyrata is locally adapted to serpentine soil, and to map the polymorphisms responsible for such adaptation, we pooled DNA from individuals from serpentine and nonserpentine soils and sequenced each 'gene pool' with the Illumina Genome Analyzer. The polymorphisms that are most strongly associated with soil type are enriched at heavy-metal detoxification and calcium and magnesium transport loci, providing numerous candidate mutations for serpentine adaptation. Sequencing of three candidate loci in the European subspecies of A. lyrata indicates parallel differentiation of the same polymorphism at one locus, confirming ecological adaptation, and different polymorphisms at two other loci, which may indicate convergent evolution.

Climate-driven population divergence in sex-determining systems

Ido Pen, Tobias Uller, Barbara Feldmeyer, Anna Harts, Geoffrey M. While & Erik Wapstra

Nature 468: 436–438 (18 November 2010)

DOI: doi:10.1038/nature09512

Sex determination is a fundamental biological process, yet its mechanisms are remarkably diverse. In vertebrates, sex can be determined by inherited genetic factors or by the temperature experienced during embryonic development. However, the evolutionary causes of this diversity remain unknown. Here we show that live-bearing lizards at different climatic extremes of the species’ distribution differ in their sex-determining mechanisms, with temperature-dependent sex determination in lowlands and genotypic sex determination in highlands. A theoretical model parameterized with field data accurately predicts this divergence in sex-determining systems and the consequence thereof for variation in cohort sex ratios among years. Furthermore, we show that divergent natural selection on sex determination across altitudes is caused by climatic effects on lizard life history and variation in the magnitude of between-year temperature fluctuations. Our results establish an adaptive explanation for intra-specific divergence in sex-determining systems driven by phenotypic plasticity and ecological selection, thereby providing a unifying framework for integrating the developmental, ecological and evolutionary basis for variation in vertebrate sex determination.

Island biology and morphological divergence of the Skyros wall lizard Podarcis gaigeae: a combined role for local selection and genetic drift on color morph frequency divergence?

 

















We have recently published a paper on evolutionary processes in isolated islet populations of the Skyros wall lizard, Podarcis gaigeae in BMC Evolutionary Biology. The paper investigates the relationship between neutral genetic divergence and morphological divergence in islet- and mainland populations. The morphological trait we use in the comparisons is throat colour morph, and islet populations show pronounced frequency differences with different morphs being common on different islets. Our data suggests that stochastic forces such as genetic drift and/or founder effects can interact with selection and have an effect even at a morphological level in islet populations with low effective sample sizes. BMC Evolutionary Biology is an open access journal and a link to the paper is found here. The abstract is as follows:

Island biology and morphological divergence of the Skyros wall lizard Podarcis gaigeae: a combined role for local selection and genetic drift on color morph frequency divergence?

Anna Runemark, Bengt Hansson, Panagiotis Pafilis, Efstratios D. Valakos & Erik I. Svensson

Background

Patterns of spatial variation in discrete phenotypic traits can be used to draw inferences about the adaptive significance of traits and evolutionary processes, especially when compared to patterns of neutral genetic variation. Population divergence in adaptive traits such as color morphs can be influenced by both local ecology and stochastic factors such as genetic drift or founder events. Here, we use quantitative color measurements of males and females of Skyros wall lizard, Podarcis gaigeae, to demonstrate that this species is polymorphic with respect to throat color, and the morphs form discrete phenotypic clusters with limited overlap between categories. We use divergence in throat color morph frequencies and compare that to neutral genetic variation to infer the evolutionary processes acting on islet- and mainland populations.

Results

Geographically close islet- and mainland populations of the Skyros wall lizard exhibit strong divergence in throat color morph frequencies. Population variation in throat color morph frequencies between islets was higher than that between mainland populations, and the effective population sizes on the islets were small (N_e:s <>ST) for throat color morph frequencies fell within the neutral F_ST-distribution estimated from microsatellite markers, and genetic drift could thus not be rejected as an explanation for the pattern. Moreover, for both comparisons among mainland-mainland population pairs and between mainland-islet population pairs, morph frequency divergence was significantly correlated with neutral divergence, further pointing to some role for genetic drift in divergence also at the phenotypic level of throat color morphs.

Conclusions

Genetic drift could not be rejected as an explanation for the pattern of population divergence in morph frequencies. In spite of an expected stabilising selection, throat color frequencies diverged in the islet populations. These results suggest that there is an interaction between selection and genetic drift causing divergence even at a phenotypic level in these small, subdivided populations.

Goodbye to 20 % of all lizards by 2080?

An interesting, but depressing study was published in Science this Friday. A research team lead by Barry Sinervo, and also including my colleagues Donald Miles (University of Ohio) and Jean Clobert (CNRS, France) have shown an alarming high rate of local population extinctions in Mexico over the last 35 years. Based on these observed real-time extinctions and biophysical modelling of lizard body temperatures in the field (based on experiments), they conclude that the rate of climate change and increasing temperatures are too high for the lizards to have time to adapt.

Lizards and other ectotherms are constrained in their foraging time in hot climates because they must avoid overheating. In particular, viviparous lizards suffer, since pregnant females are especially sensitive: they carry embryos in their bodies which easily die at high temperatures. It is therefore not surprising that most viviparous lizard populations are found at higher latitudes and altitudes, i. e. in colder climates. As temperatures increase dramatically in these environments, these viviparous lizards face a significantly higher extinction risk compared to oviparous lizards, largely because their foraging time becomes drastically reduced and they have to spend a larger part of the day in the shade, to avoid overheating.

The research team estimate, conservatively, that about 20 % of all lizard species on Earth run a significant and serious risk of becoming extinct before 2080, unless the current global warming trend is reversed. This is rather alarming, as lizards is only one of several organismal groups that are likely to have passed the "extinction" threshold determined by anthroprogenic global warming. Other groups that have been discussed are amphibians.

Perhaps we are now entering the next (the sixth) massextinction, which will also drag humans away from this planet? Keep in mind that one of the most famous massextinctions about 251 milllion years ago (The Perman-Triassic massextinction event) killed between 70 and 96 % of all living species, and happened after a global temperature increase of about 6 degrees. Incidentally, a six-degree temperature increase is one of the scenarios outlined by UN:s intergovernmental panel IPCC in their most pessimistic scenario over the coming 100 years (although some climate scientists consider this a rather realistic scenario). If so, Homo sapiens might not have long time left on this planet.

You can read more about this lizard study here, and do not forget to watch the video, where Jean Clobert and Barry Sinervo discuss their findings.

Lab-meeting on Tuesday 9 March at 13.00 on sexual dimorphism and sex-specific selection

Lab-meeting this coming week will be on Tuesday afternoon (13.00-15.00), not on our usual time on Wednesday mornings. We will discuss a recent paper in Evolution by our Dartmouth colleagues Robert Cox and Ryan Calsbeek on sexual size dimorphism and sex-specific selection in Anolis-lizards:

SEX-SPECIFIC SELECTION AND INTRASPECIFIC VARIATION IN SEXUAL SIZE DIMORPHISM Robert M. Cox and Ryan Calsbeek Sexual size dimorphism (SSD) is thought to evolve due to sex differences in selection on body size, but it is largely unknown whether intraspecific variation in SSD reflects differences in sex-specific selection among populations. We addressed this question by comparing viability selection between two island populations of the brown anole lizard (Anolis sagrei) that differ in the magnitude of male-biased SSD. On both islands, females experienced stabilizing selection favoring intermediate size whereas males experienced directional selection favoring larger size. Thus, sex-specific selection matched the overall pattern of male-biased SSD, but population differences in the magnitude of SSD were not associated with local differences in selection. Rather, population differences in SSD appear to result from underlying differences in the environmental potential for a rapid growth, coupled with sex-specific phenotypic plasticity. Males grew more slowly on the island with low SSD whereas growth of females did not differ between islands. Both sexes had substantially lower mass per unit length on the island with low SSD, suggesting that they were in a relatively poorer energetic condition. We propose that this energetic constraint disproportionately impacts growth of males due to their greater absolute energy requirements, thus driving intraspecific variation in SSD.

This paper should be of interest because of its links to sexual conflict, and incidentally, Bob and Ryan also has a Science-paper that will soon come out on how females manipulate offspring sex depending on the sire's body size in an adaptive fashion, i. e. a resolution of intralocus sexual conflict that you can read more about in this previous blogpost on one of my recent papers on another lizard species (Uta stansburiana).

When to meet? Tuesday March 9, 13.00
Where: "Darwin" room, 2nd floor, Ecology Building

Any fika-volunteer?

Lab-meeting on population divergence in isopods and lizards

This coming Wednesday (30 September), we will discuss one manuscript by Fabrice, Anders Hargeby and me on sexual isolation and migration modification in the aquatic isopod (Asellus aquaticus) and another one by Anna, Bengt and me on colour polymorphism divergence and population genetics in Podarcis-lizards. We would like to have the input from as many as possible on these two interesting manuscripts (at least we think they are interesting, but as authors we are of course highly biased!).

We will start with the lizard manuscript at 10.00, and continue with the isopod manuscript after that. I will send out these manuscripts by e-mail to the whole group today (Monday) provided that Anna and Fabrice send me the updated last versions first. If you do not get it by e-mail, please e-mail Anna (anna.runemark@zooekol.lu.se) and Fabrice (fabrice.eroukhmanoff@zooekol.lu.se) so that they can send you the manuscripts.

Time and place as usual: "Darwin" at 10.00 on September 30 (Wednesday). Any fika volunteer?