On cliff effects, male mate preferences and niche use in Calopteryx

#by Maren Wellenreuther

I am following Erik’s recommendation that we should all start to more actively promote our own research, and will present some of my most recent publications.The first work  that I would like to highlight is a paper that was started in 2007, when Shawn Kuchta and I arrived in Sweden to start our postdocs on the two charismatic Calopteryx damselfly species found in Sweden, C. virgo and C. splendens. We both arrived just at the start of the field season in May 2007 and had never worked on odonates before. It was an exciting time: we were both living at the University's field station in the middle of the forest, which was also used as a military training ground, and so we could relax in the evening after a hard day in the field, while watching the military training tanks and troops drive through the forest and fields outside the station. Shawn had worked for many years on salamanders while I had studied marine fish, and the different view points and ideas that came along with having studied such different study systems made our conversations about science and evolution rich and interesting. Shawn's work on  Calopteryx damselflies is seeking to measure the strength of natural selection acting on the two Calopteryx species (see photograph below), by collecting wings from feeding stations and comparing them to the variation present in natural populations. Although Shawn has left Sweden and is now an Assistant Professor at Ohio University, he is still actively involved in Calopteryx research and is currently writing up this data-so stay tuned for more on this soon!

Calopteryx splendens (left) have wing patches that cover roughly 50% of the wings, while C. virgo have almost fully melanised wings.

At that time that Shawn and I started our work on Calopteryx damselflies in Sweden, another member joined the lab group. Her name is Elodie Vercken, and she was a newly finished postdoc from France who had worked with Jean Clobert on colour morphs and alternative strategies in the common lizard Lacerta vivipara. She is now a researcher at INRA (National Institute for Agronomical Research) in Sophia Antipolis in France.

Elodie Vercken in the field in Sweden catching damselflies fort mate choice experiments.

Together with Elodie, I spent my days out in the field to measure male and female mate choice in different populations, and trying to relate this mate preference data to population ecology and phenotypic traits (sympatry versus allopatry and so on). It was a hot summer and we tried to stay cool while tethering males and females of both species to bamboo sticks and painting their wings to perform mate presentation experiments. It was great fun.

Maren Wellenreuther presenting tethered damselflies in the field

Part of the data that we gathered during that summer was recently used in a modeling paper on cliff-edge effects, which tests the counterintuitive idea that the trait value associated with the maximum of an asymmetrical fitness function is not necessarily the value that is selected for when the trait shows variability in its phenotypic expression.
Vercken E, Wellenreuther M, Svensson EI, Mauroy B (2012) Don't Fall Off the Adaptation Cliff: When Asymmetrical Fitness Selects for Suboptimal Traits. PLoS ONE 7(4): e34889.

From that field season, Elodie, Erik and I also published a paper on male mate preferences in C. splendens, to address the question whether males can distinguish between immigrant and resident females, something previously found for females.

Wellenreuther M, Vercken E and Svensson EI (2010) A role for ecology in male mate discrimination of immigrant females in Calopteryx damselflies? Biological Journal of the Linnean Society 100: 506-518

In addition to these two papers, I further delved into an area that I had investigated extensively during my PhD work: Habitat use and divergence in habitat space between species. The idea was to extent the work that was previously done by our lab and other groups on the habitat use of the two Calopteryx species, by expanding the spatial scale so that broader questions can be asked. To do this, a large data set for the whole of Fennoscandia was generated using field data and museum records, and niche modelling was used to estimate the extent of niche divergence versus conservatism and to identify the most important environmental variables that correspond to niche differences.  The large data set in this paper also allowed us to look into the following question: what is the extent of niche divergence in species that are thought to have primarily evolved through sexual selection on secondary sexual traits? Based on our results, we argue that adaptive niche diversification appears to play a relatively minor role in speciation and evolutionary divergence in species groups such as salamaders, East African cichlids, and odonates where sexual selection on secondary sexual traits is pronounced and a key element of diversification. This work was done in collaboration with Keith W Larson who has excellent modelling skills and likes to analyze large data sets.

Wellenreuther M, Larson K W and Svensson E I. (in press) Climatic niche similarity and geographic range limits in ecologically similar co-existing damselflies –Ecology

Maybe Anna Runemark, who is currently finishing her PhD thesis on the Skyros Wall lizard, would like to write the next blog post by telling us about her most recent articles.


Happy Researching!

The abstracts to the papers are posted below. 

Vercken E, Wellenreuther M, Svensson EI, Mauroy B (2012) Don't Fall Off the Adaptation Cliff: WhenAsymmetrical Fitness Selects for Suboptimal Traits. PLoS ONE 7(4): e34889.

Abstract: The cliff-edge hypothesis introduces the counterintuitive idea that the trait value associated with the maximum of an asymmetrical fitness function is not necessarily the value that is selected for if the trait shows variability in its phenotypic expression. We develop a model of population dynamics to show that, in such a system, the evolutionary stable strategy depends on both the shape of the fitness function around its maximum and the amount of phenotypic variance. The model provides quantitative predictions of the expected trait value distribution and provides an alternative quantity that should be maximized (“genotype fitness”) instead of the classical fitness function (“phenotype fitness”). We test the model's predictions on three examples: (1) litter size in guinea pigs, (2) sexual selection in damselflies, and (3) the geometry of the human lung. In all three cases, the model's predictions give a closer match to empirical data than traditional optimization theory models. Our model can be extended to most ecological situations, and the evolutionary conditions for its application are expected to be common in nature.

Wellenreuther M, Vercken E and Svensson EI (2010) A role for ecology in male matediscrimination of immigrant females in Calopteryx damselflies? Biological Journal of the Linnean Society 100: 506-518

Abstract: Sexual selection against immigrants is a mechanism that can regulate premating isolation between populations but, so far, few field studies have examined whether males can discriminate between immigrant and resident females. Males of the damselfly Calopteryx splendens show mate preferences and are able to force pre-copulatory tandems. We related male mate responses to the ecological characteristics of female origin, geographic distances between populations, and morphological traits of females to identify factors influencing male mate discrimination. Significant heterogeneity between populations in male mate responses towards females was found. In some populations, males discriminated strongly against immigrant females, whereas the pattern was reversed or nonsignificant in other populations. Immigrant females were particularly attractive to males when they came from populations with similar predation pressures and densities of conspecifics. By contrast, immigrant females from populations with strongly dissimilar predation pressures and conspecific densities were not attractive to males. Differences in the abiotic environment appeared to affect mating success to a lesser degree. This suggests that male mate discrimination is context-dependent and influenced by ecological differences between populations, a key prediction of ecological speciation theory. The results obtained in the present study suggest that gene-flow is facilitated between ecologically similar populations.

Wellenreuther M, Larson K W and Svensson E I. (in press) Climatic niche similarity and geographic range limits in ecologically similar co-existing damselflies –Ecology
The factors that determine species' range limits are of central interest to biologists. One particularly interesting group are odonates (dragonflies and damselflies), which show large differences in secondary sexual traits and respond quickly to climatic factors, but often have minor interspecific niche differences, challenging models of niche-based species co-existence. We quantified the environmental niches at two geographic scales to understand the ecological causes of northern range limits and the co-existence of two congeneric damselflies (Calopteryx splendens and C. virgo). Using environmental niche modelling, we quantified niche divergence first across the whole geographic range in Fennoscandia and second only in the sympatric part of this range. We found evidence for interspecific divergence along the environmental axes of temperature and precipitation across the northern range in Fennoscandia, suggesting that adaptation to colder and wetter climate might have allowed C. virgo to expand further northwards than C. splendens. However, in the sympatric zone in southern Fennoscandia we found only negligible and non-significant niche differences. Minor niche differences in sympatry lead to frequent encounters and intense interspecific sexual interactions at the local scale of populations. Nevertheless, niche differences across Fennoscandia suggest that species-differences in physiological tolerances limit range expansions northwards, and that current and future climate could have large effects on the distributional ranges of these and ecological similar insects.