On dispersal, gene flow, population divergence and learning in insects

                                                                            








One consequence of animal movement and dispersal is gene flow between populations. Gene flow is generally thought to limit local adaptation and population divergence, since local selection is opposed by the homogeneising effects of gene flow. In spite of this, we often find that populations differ in morphological, physiological and behavioural traits, and one way why such population divergence can be achieved is through adaptive phenotypic plasticity. In terms of behavioural traits, it is increasingly being recognized that learning can be important, particularly when it comes to population divergence of mate preferences.



We have studied the effects of learning on the development of female mate preferences in a charismatic insect species: the banded demoiselle (Calopteryx splendens). Males of different species in these calopotergid damselflies are well-known for their enigmatic melanized wing patches, which serve multiple ecological functions, including mate recognition and species recognition for females.

Recently, we have showed that female mate preferences are not entirely genetic, but are partly learned, and develops in females as a result of physical pre-mating interactions and/or during mating with males. The result of this learning is that populations that are even close to each other and hence experience a lot of gene flow in between them, can diverge substantially in mate preferences, due to such learning. It is interesting that even these small insects have such advanced cognitive ability so that they can actually learn whom to mate with, and who is the wrong mate! Our paper has recently been published in the journal Evolution, where we also contributed with the cover photo of a male banded demoiselle aggressively defending his valuable territory (a water lilly). Our article was also covered by the popular science site and media outlet Science Daily.

Below is the link to the article and the abstract:


A ROLE FOR LEARNING IN POPULATION DIVERGENCE OF MATE PREFERENCES  


Erik I. Svensson, Fabrice Eroukhmanoff, Kristina Karlsson, Anna Runemark & Anders Brodin

Article first published online: 13 JUL 2010

DOI: 10.1111/j.1558-5646.2010.01085.x

Learning and other forms of phenotypic plasticity have been suggested to enhance population divergence. Mate preferences can develop by learning, and species recognition might not be entirely genetic. We present data on female mate preferences of the banded demoiselle (Calopteryx splendens) that suggest a role for learning in population divergence and species recognition. Populations of this species are either allopatric or sympatric with a phenotypically similar congener (C. virgo). These two species differ mainly in the amount of wing melanization in males, and wing patches thus mediate sexual isolation. In sympatry, sexually experienced females discriminate against large melanin wing patches in heterospecific males. In contrast, in allopatric populations within the same geographic region, females show positive (“open-ended”) preferences for such large wing patches. Virgin C. splendens females do not discriminate against heterospecific males. Moreover, physical exposure experiments of such virgin females to con- or hetero-specific males significantly influences their subsequent mate preferences. Species recognition is thus not entirely genetic and it is partly influenced by interactions with mates. Learning causes pronounced population divergence in mate preferences between these weakly genetically differentiated populations, and results in a highly divergent pattern of species recognition at a small geographic scale.

Damselfly range expansions, field work and media coverage

We soon have the summer of 2009 behind us, and for me and my co-workers it has been an intense field season with damselflies (as usual). In early July, postdoctoral researcher Shawn Kuchta (upper left) made a field and collection trip up to central Sweden and the famous biogeographic limit Limes Norrlandicus, which is traditionally defined by the river Dalälven (which is not completely correct, however).

Many animal and plant species do either not move north of this sharp biogeographic boundary, or they do not move south (in the case of species with northern distributions). This sharp biogeographic barrier is of course extremely interesting in terms of constraints on the evolution of range limits: why do species not simply adapt and evolve traits so that they can expand their current ranges?

According to a much-discussed population genetic model developed by the evolutionary geneticists Mark Kirkpatrick and Nick Barton, range limits of species are constrained by migration and maladaptive gene flow from populations in the centre of a species range, which will "swamp" local adaptation of populations at range limits.

To evaluate this and other explanations for the range limit of the banded demoiselle (Calopteryx splendens, territorial male with wings spread out), Shawn Kuchta and I collected specimens of this species from Central Sweden, with the aim to analyze population genetic parameters (effective population sizes, migration rates etc) of these populations at the range limit, and compare these populations with populations in the centre of the species range. Another postdoc, Maren Wellenreuther, is also involved in this project.

We are also interested in the specific phenotypic traits that might limit range expansion in C. splendens. One such trait, which might be important in terms of thermoregulation, are the size of the dark melanized wing patches which cover c. a. 50 % of the wing area in this species. Compared to its close congeneric relative (C. virgo, lowest figure), C. splendens does not have as much melanin on its wings, and this interspecific difference might explain which C. virgo has a range that extends much further north, up to northernmost Fennoscandia.

The situation might change in the future, though, as studies in the UK on how dragonflies and damselflies respond to ongoing climate change have revealed that both species are expanding their range distributions northwards. Maren Wellenreuther, me and a finnish colleague (K. Tynkkynen) recently investigated the potential future consequences of such range expansions in terms of sexual isolation between these species by experimentally moving C. splendens female in to the allopatric zone of C. virgo. The results? Well, the study has now been accepted for publication and the article will appear in a future issue of the journal Evolution, so keep your eyes open!

During our trip north, Shawn and I also visited CAnMove-leader Professor Susanne Åkesson and her husband Professor Anders Hedenström at their cosy cottage in Östhammar, Uppland. Susanne and Anders took us on a floristic trip, and on the picture in the upper right corner, you see what an enthusiastic plant photographer Susanne is in her spare time! Being a naturalist myself, I think this is very important, to get new idéas for research and teaching.

For those of you who are interested in hearing more about our damselfly research projects, they have been covered quite extensively by Swedish media the last week. I was interviewed by the regional news programme "Sydnytt" about these damselflies and how they might respond to climate change, and you can see this programme here. You can also listen to a 20-minute long radio interview in the programme "Vetandets Värld", and this you can find here. Dragonflies and damselflies thus rock, and they are also excellent research organisms!

New CAnMove postdoc on insect flight: Welcome Sophia Engel!

Together with my co-PI Anders Hedenström, I am pleased to introduce our first CAnMove postdoc Sophia Engel. Sophia will join CAnMove soon on a project dealing with insect flight adaptations and evolutionary ecology, dealing with adaptations for dispersal and predator avoidance. This is an exciting project that will combine field and wind tunnel studies, using moths and calopterygid damselflies as model organisms. Both Anders and I are thus extremely happy to host Sophia as a shared postdoc. Below, I will let Sophia introduce herself in her own words:

"I am interested in the interaction of physiological capabilities, ecology, and evolution in shaping a species’ life-history. My previous research has been at the interface of ecology and physiology: For my doctoral work I focused on avian migration. I combined wind tunnel studies and detailed measurements of water- and energy budgets at various ambient conditions with modeling approaches, and showed that dehydration can be a limiting factor for flight duration under naturalistic ambient conditions for my model species, the Rose-coloured Starling. A more recent project is focused on understanding the effects of climate variability on primary productivity, arthropod consumer performance and ultimately the structure and function of the food web in the Chihuahuan Desert of central New Mexico. I am looking forward to combine these two lines of research, wind tunnel studies and insect ecology, in the project “insect flight and morphological trade-offs” at the CAnMove center in Lund!"