Remembering the summer: field work with damselflies in Skåne

Winter is approaching fast, and what could be better then than to try to remember the past beatiful summer for as long as possible?Varm summers means field work with insects, at least for some of us. This was also the case for myself, CAnMove postdoc Sophia Engel and a number of other students and postdocs working with field studies of calopterygid damselflies. Here is a nice movie about CAnMove-related field work from Lund University's Youtube-channel. This movie contains an interview with Sophia and myself, where we explain what kind of experiments we did, and why. Unfortunately, this movie is in Swedish, not English, but at least you can enjoy the pictures!

Basically, we have quantified flight speeds of individually marked damselflies of two species (Calopteryx virgo and C. splendens), and we relate this performance-trait to wing morphology (shape), longevity in the field and mating success (sexual selection). A key player in this system is an enigmatic avian predator which kills these insects: The white wagtail (Motacilla alba), which also appears in the movie. The ornithologists among you readers will hopefully also realise how fascinating this insect system actually is, since it obviously also involves a bird! A key goal of ours is to link morphology to performance and fitness, and combine flight speed estimates with data on morphology and fitness. Such studies are rarely possible to perform, particularly not in natural populations of insects, so we are quite excited about the results that will hopefully come out from this work.

If the movie above does not work, you could follow this link instead. Enjoy! And go back and watch this movie whenever you miss the summer...

More on climate change and the consequences of range expansions in damselflies

Some of you might remember a recent post about our damselfly field work last summer in Central Sweden, where we studied the range limits of the banded demoiselle (Calopteryx splendens) at the biogeographic limit "Limes Norrlandicus".

Here is a follow-up post on that theme, briefly discussing one of our most recently published articles that is now out in Evolution. The abstract for that article can be found here, but since this journal is not yet open source (unfortunately) you cannot access the entire article. If you are interested in a pre-print or reprint, please contact me or Maren Wellenreuther(maren.wellenreuther@zooekol.lu.se).

This study was a collaborative project together with our colleague Katja Tynkkynen at University of Jyväskylä, and the experiments were performed in the summer of 2008. The basic idéa was to investigate the potential consequences of the future range expansion in the calopterygid damselfly C. splendens ("CS" see picture on map above!), which is soon expected to move north in to the allopatric zone in Northern Scandinavia of its close relative C. virgo ("CV"; see picture above). These two morphologically similar congeneric damselflies are sympatric over the major part of Europe, and it is only in the northern areas that C. virgo occurs alone (i. e., allopatry), and where C. splendens does not yet occur (see map above).

However, things might change in the future: a recent study have revealed that C. splendens and many other damselfly and dragonfly species are currently expanding northwards in response to increasing temperatures and ongoing climate change. Increasing temperatures are particularly affecting ectothermic animals like damselflies and other insects, which respond very rapidly to the ongoing climate change in Europe and elsewhere in the northern Hemisphere. Thus, we would soon expect that dispersing individual C. splendens on the move from the south will encounter the isolated C. virgo populations in the north. As usual, the issue of "animal movement" is the key to many fascinating biological phenomena!

What will happen when the more southern species C. splendens expands in to the zone where "naive" C. virgo populations have been isolated for quite long time? Have these northern allopatric C. virgo populations lost their species recognition ability entirely, i. e. do they not discriminate against heterospecifics anymore? This would be expected, since (per definition) there cannot be any selection for species recognition in the absence of heterospecifics. Alternatively, since these northern C. virgo populations are most likely derived from southern populations that expanded northwards after the last Ice Age, they might still have a genetic evolutionary "memory" and discriminate against heterospecifics, that is based on their past evolutionary interactions with C. splendens when they co-occurred in the south.

We investigated this by experimentally simulating range expansion ourselves: we took C. splendens females from the sympatric zone in southern Finland and transported them to northern Finland where they were presented to the local C. virgo males. We then recorded the local male's reaction to this "novel" female phenotype and compared with the responses of C. virgo males in the sympatric zone. It turned out, rather surprisingly, that northern C. virgo males from the allopatric zone did actually show some discrimination against heterospecific C. splendens females, although the level of mate discrimination was weaker than among C. virgo males from the sympatric zone in the south. Thus, mate recognition against heterospecifics had been lost, although not entirely so. This will have some consequences for what to expect following range expansions in these and other insect species.

One potential risk of range expansions following climate change are changed interspecific interactions, which can lead to local extinctions, e. g. through hybridizations and/or heterospecific matings. This risk might not be as great as one might fear in this damselfly species pair, since obviously some level of mate recognition and ability to discriminate against heterospecifics is still there. The interesting remaining question is of course: how long will a maladaptive (or at least neutral) trait that is no longer maintained by selection persist, and why do these C. virgo males still discriminate against heterospecific females long after they run any risk of meeting them?


SIMULATING RANGE EXPANSION: MALE SPECIES RECOGNITION AND LOSS OF PREMATING ISOLATION IN DAMSELFLIES

Wellenreuther M, Tynkkynen K, Svensson EI.

Prolonged periods of allopatry might result in loss of the ability to discriminate against other formerly sympatric species, and can lead to heterospecific matings and hybridization upon secondary contact. Loss of premating isolation during prolonged allopatry can operate in the opposite direction of reinforcement, but has until now been little explored. We investigated how premating isolation between two closely related damselfly species, Calopteryx splendens and C. virgo, might be affected by the expected future northward range expansion of C. splendens into the allopatric zone of C. virgo in northern Scandinavia. We simulated the expected secondary contact by presenting C. splendens females to C. virgo males in the northern allopatric populations in Finland. Premating isolation towards C. splendens in northern allopatric populations was compared to sympatric populations in southern Finland and southern Sweden. Male courtship responses of C. virgo towards conspecific females showed limited geographic variation, however, courtship attempts towards heterospecific C. splendens females increased significantly from sympatry to allopatry. Our results suggest that allopatric C. virgo males have partly lost their ability to discriminate against heterospecific females. Reduced premating isolation in allopatry might lead to increased heterospecific matings between taxa that are currently expanding and shifting their ranges in response to climate change.

Evolution. 2009 Aug 6. [Epub ahead of print]

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!