Invasive damselflies get bigger as they move through the UK

Exif_JPEG_PICTUREBackground: A large number of species are expanding their ranges in response to climate change. This is also true in the damselflies, where the small red-eyed damselfly (Erythromma viridulum) has recently (around 1998) crossed the sea from France to England.  Since then, the species has moved hundreds of kilometres north in an unprecedented range expansion (at least as far as European dragonflies and damselflies are concerned). What is less clear is what impact this expansion has had on the species. Are the newly-founded populations the same as those that are resident in France? Can we trace the arrival and expansion of the species through genetic techniques?

What we did: Simon Keat was a PhD student at the University of Liverpool who was lucky enough to be just beginning his PhD when the small red-eyed damselfly first established in the UK.  Simon surveyed a number of populations around Europe and in the UK, collecting animals to measure them and extract DNA. With the body size measurements we showed that animals tend to show a strong relationship with latitude: populations further north were much larger and this held for both the older populations in France, Belgium and Germany as well as the newer populations in the UK. Looking at the genetics, we had expected to see declining genetic diversity further north, as a small number of individuals led the charge up the country. However, instead of a decline in diversity in the UK we saw an almost complete lack of genetic pattern.  This suggests that the animals were moving in such great numbers that there was not the time for any local patterns to develop.

Importance: Range expansions have important consequences for many aspects of human life: agricultural pests shift and threaten crops, diseases and their vectors shift and threaten human health, and endangered species shift and potentially move out of protected areas. We have shown that during this particular range expansion there has been negligible change in genetic structure but that newly-invaded areas contain relatively large damselflies.  Since damselflies are voracious predators, this could have substantial implications of local ecosystems.

This is part of a series of short lay summaries that describe the technical publications I have authored.  This paper, entitled “Bergmann’s rule is maintained during a rapid range expansion in a damselfly”, was published in the journal Global Change Biology in 2014. You can find this paper at the publisher or archived at figshare.

Image credit: Quartl, http://bit.ly/1uX3BOA, CC BY-SA 3.0.

Advertisements

Rain, not temperature, seems to have driven fossil mammal diversity in North America

skeletons-268954_1280Background: One of the fundamental questions in ecology is “what drives changes in the numbers of species in time and space?” We can look around us today and see that there are generally many more species in the tropics than nearer the poles. However, another way in which we can look around ourselves is to delve into the fossil record to look back in time. Dani Fraser is a PhD student at Carleton University working on large-scale patterns in fossil mammal biodiversity. Dani was interested in looking at spatial patterns and how they changed through time, but rather than just calculating the number of animals living in each area at each time, we looked at the rate at which the communities changed as we moved further north. The idea is that when climates are relatively stable and warm there is little variability in climate and so there is gradual change in species as you move north. However, as the climate becomes more polarised (i.e. colder at the pole relative to the tropics) the rate of change in animal communities becomes more pronounced.

What we did: We looked at extinct mammals in North America during the Cenozoic (36 million years to the present) and showed that there was greater variability in species between regions when mean annual precipitation was lowest. This is consistent with theory, which suggests that when precipitation is (on average) higher communities are more similar to one another as you move north. We then looked at what might be expected from current mammal species under climate change. We used climate models to predict where these species might occur in the future and saw little evidence of the precipitation relationships that we found in the fossil data.

Importance: Much of the work done on biological responses to climate change has focused on temperature, looking at the number of species in each area, and purely ecological responses (i.e. over short time periods). We demonstrate that precipitation can also play an important role in driving responses to global climate. We also show that it isn’t just the number of species that changes in space but the relationship between communities: there is a greater rate of turnover (a greater dissimilarity) in communities as well. Finally, we show that these relationships seem to be present in the evolutionary record but cannot be predicted from the ecological responses of current mammals, suggesting that the patterns we saw in the fossil record are due (at least in part) to evolutionary processes that are not incorporated into climate models.

This is part of a series of short lay summaries that describe the technical publications I have authored.  This paper, entitled “Mean annual precipitation explains spatiotemporal patterns of Cenozoic mammal beta diversity and latitudinal diversity gradients in North America”, was published in the journal PLOS ONE in 2014. You can find this paper for free at the publisher’s website.

Image credit: 134213, http://bit.ly/1C0v0Fy, Public Domain.

Damselfly wings change shape in harsher habitats

Background: Odonata (dragonflies and damselflies) are an ancient order of insects. By this, I mean that they have remained largely unchanged since their ancestors evolved 500 million years ago.  They have a fairly unique flight style which is a product of the configuration and use of their wings. Wing length has been used as a measure of odonate body size for many years, but wing shape has received less attention.

What we did: I was interested in whether wing shape varied with latitude in the UK.  The populations living in habitat in the UK are exposed to a range of temperatures depending on location and it might be that certain wing shapes confer advantages in certain habitats. Based on a survey of seven populations of Coenagrion puella, I compared wing shape using a method called “geometric morphometrics”.  This allowed me to look at shape independently of the size of the wing.  I found that the wing shape in the majority of populations was very similar.  All populations in the south of England were comparable, but the populations in the south of Scotland showed a progressive shift away from this “typical” wing shape until a site near Edinburgh which was significantly (if subtly) different.

Importance: Wing shape has been highly conserved throughout odonate evolution (i.e. ancient odonates are similar in shape to present-day odonates). Because even small variations between species are consistent, wing shape and patterns of wing veins have been used to identify species. My study showed that these wing shapes were not as consistent as people had previously thought and that there might be ecological or evolutionary processes that can cause significant variation.


This is part of a series of short lay summaries that describe the technical publications I have authored.  This paper, entitled “Wings of Coenagrion puella vary in shape at the northern range margin (Odonata: Coenagrionidae)”, was published in the International Journal of Odonatology in 2008. You can find this paper online at the publisher, or on Figshare.

Image credit: Lauri, CC BY-NC-SA 2.0, http://bit.ly/1zicIZC

The impact of environmental warming on Odonata – a review [paper summary]

This is part of a series of short lay summaries that describe the technical publications I have authored.  This paper, entitled “The impact of environmental warming on Odonata – a review”, was published in the International Journal of Odonatology in 2012. You can find this paper online at the publisher, or on Figshare.

Background: Odonata (dragonflies and damselflies) are thought to have evolved in the tropics and possess a number of adaptations that allow them to exist at higher latitudes.  This makes them interesting to investigate in the context of climate change, since these adaptations might facilitate a response to increasing temperatures.

What we did: This paper is a review of the literature looking at the ecology and evolution of Odonata in the context of climate change.  A number of areas are discussed including distributional changes, phenological shifts, evolutionary responses, the effects of drought and the physiological effects of temperature.

Importance: A large amount of work has been carried out on the influence of temperature on the biology of Odonata over the past 50-60 years.  This has come from a variety of loosely-related fields and our review brings this together to provide an overview of the state-of-play concerning our understanding of the topic.


Image credit: Patricia H Schuette, CC BY-NC-ND 2.0, http://bit.ly/1BO5i4r

Damselflies change shape under climate change, only if they are close to their limits

Background: A species’ shape and size can tell you a lot about how the animals are doing in their environment.  For example, species tend to get larger at cooler temperatures, a phenomenon known as “Bergmann’s rule”, and they tend to have greater dispersal traits where they need to move further (such as locations where habitat patches are further apart).

What we did: I was interested in shape and size varied between a species that is not moving north under climate change (Pyrrhosoma nymphula, shown above) and a species that has been expanding its range into Scotland (Coenagrion puella). I collected animals at a series of sites from southern England to Scotland for both species.  The results showed that there was little consistent variation in size or dispersal traits in P. nymphula but that C. puella showed increases in size and the relative investment in the thorax and abdomen (indicative of greater flight ability).  These results, taken together, suggest that there has been selection for dispersal traits in the expanding C. puella.

Importance: The presence of traits that could facilitate response to climate change, such as enhanced dispersal to increase colonisation of new habitats, could make the difference between a species thriving or failing under climate change.  This is particularly important for species that rely on aquatic habitats for their life cycle, because water resources are predicted to be under increasing threat in the future.


This is part of a series of short lay summaries that describe the technical publications I have authored.  This paper, entitled “Latitudinal variation in morphology in two damselfly species with contrasting range dynamics”, was published in the European Journal of Entomology in 2008. You can find this paper for free online at the publisher.

Image credit: Thomas Bresson, CC BY 2.0, http://bit.ly/1p25AAC

Damselflies develop “spotty wings” when it gets cold

Background:  Darwin argued that sexual selection (i.e. the competition between males for females, and the females choosing from among competing males) was as important as natural selection (e.g. predators catching the slowest prey) in driving the evolution of traits. Calopteryx splendens, the banded demoiselle, is a fascinating case of this sexual selection. Males have pigmented bands on their wings which they use to signal to females. Females have been shown to prefer males with bigger bands. Further research demonstrated that the substance that produces these spots is the same substance, melanin, that drives the invertebrate immune response. The male damselflies are, therefore, advertising the strength of their immune system to females in an “honest” display.

Screen Shot 2015-11-01 at 17.25.05What we did: I was interested in the extent to which the wingspot size varied with latitude, since melanin production is strongly tied to temperature.  I had samples of C. splendens from two sites, one in Bedfordshire and another in Northumbria (near to the furthest north site where the banded demoiselle is found).  These two populations showed marked differences in the size of the area of pigment with far more pigment in the south, as would be expected if temperature was a limiting factor. You can see this variation in the picture on the right, which shows a Bedfordshire demoiselle on top and a Northumberland demoiselle on the bottom. The species actually changes from having a discrete band to many animals having only a “spot” in the northern population.

Importance: This was the first demonstration of geographical variation in wingspot size and suggested that ecological (i.e. temperature) processes were influencing wingspot size in addition to evolutionary (i.e. female choice) processes.


This is part of a series of short lay summaries that describe the technical publications I have authored.  This paper, entitled “Variation in the wingspot size and asymmetry of Banded Demoiselle Calopteryx splendens (Harris, 1792)”, was published in the Journal of the British Dragonfly Society in 2009. You can find this paper on Figshare.

Image credit: Paul Ritchie, CC BY-NC-ND 2.0, http://bit.ly/VIQrHD

Damselflies change shape as they move north

Background: It has been proposed that animals and plants of the same species vary in their shape and size depending on where they live. Individuals living close to the cooler, northern range boundary might possess traits that increase their ability to deal with cooler temperatures, for example. However, under climate change the places where animals can live are expected to move as warmer temperatures expand the areas where climate is suitable for different species.

What we did: This study was part of my doctoral research and compared populations of three species between their range core and their range margins.  The three species varied in the degree to which they were expanding their ranges under climate change: Pyrrhosoma nymphula (the large red damselfly) is not expanding in the UK and is found all the way to the northern coast of Scotland, Erythromma najas (the red-eyed damselfly) is found as far north as Cheshire and is not expanding its range margin, and Calopteryx splendens (the banded demoiselle) is found as far north as Northumbria and is expanding rapidly.  The results showed that there was greater variation between the core and range margins in C. splendens, the species which was expanding, less difference in E. najas which is barely expanding, and almost no difference in P. nymphula, which has expanded its range as far as it can.

Importance: In order to respond to climate change, species will likely need to shift their geographical ranges.  This involves being able to colonise new habitats which are currently outside of their range. The detection of variation in morphology such as in this study suggests that there might be traits that would facilitate this colonisation at range margins. If it could be demonstrated that the variation in morphology was evolutionary and not the result of phenotypic plasticity, then this would provide important evidence of adaptation to coping with climate change.


This is part of a series of short lay summaries that describe the technical publications I have authored.  This paper, entitled “Variation in morphology between core and marginal populations of three British damselflies”, was published in the journal Aquatic Insects in 2009. You can find this paper online at the publisher, or on Figshare.

Image credit: Jean-Daniel Echenard, CC BY-ND 2.0, http://bit.ly/1AHimY5