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.
What 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
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
Background: Water quality is measured in a number of different ways: measuring levels of chemicals and pollutants, measuring temperature and other physical parameters, and monitoring the animals and plants that are living in the water. The theory is that the animals and plants living in the water have certain requirements of their habitat (particularly a need for clean water) and so you can use the presence of certain “fussy” animal groups as a proxy for water quality. The problem is that, under climate change, species are moving around as environmental conditions – especially temperature – changes. This means that changes in the animal and plant communities at a given site might give the appearance of an increase in water quality while actually the arrival of new species is simply the result of climate change.
What we did: I analysed an extensive dataset of British dragonfly and damselfly (known collectively as the “Odonata”) sightings to look for a pattern of geographical movement since 1960. Dragonflies and damselflies are an important group in biological water quality monitoring, as they are particularly sensitive to pollution. I found that the patterns of water quality that would be detected using Odonata at a generic site would appear to change over time with the changes in Odonata communities, independent of any changes in water quality.
Importance: Biological communities are used extensively in the monitoring of freshwaters and this research emphasises the need to take distributional shifts that occur as a result of climate change into account when using this method. It is likely that water quality is improving, with better treatment of wastewater and better enforcement of environmental regulation, but accurate monitoring is the key to continuing improvement. Secondly, this paper demonstrates once more the fact that Odonata are responding to climate change.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “The impact of climate-induced distributional changes on the validity of biological water quality metrics”, was published in the journal Environmental Monitoring and Assessment in 2010. You can find this paper online at the publisher, or on Figshare.
Image credit: Tambako the Jaguar, CC BY-ND 2.0, http://bit.ly/1v8EGcK
Background: Parasites drain resources from their hosts in order to survive and reproduce. The effects that this has on the host have been shown to be substantial in some species of dragonfly and damselfly. However, in order to assess how serious these effects are, we need to know something about patterns of parasitism: how many parasites does an animal carry and how does that number vary throughout the year?
What we did: We had a two year study looking at a single population of the azure damselfly, Coenagrion puella, at a single site in southern England. All the damselflies (1036 in total) emerging from the pond were caught, marked individually, and the number of parasitic mites that were clinging to them were counted. Technically these mites don’t suck blood, but they do feed on the “haemolymph” of the insects, which is the insect equivalent. We had a number of hypotheses as to what might drive variations in parasitism: higher temperatures might increase the effectiveness of mites at finding and latching-on to hosts, larger animals might have more parasites, or there might be a difference between sexes in parasitism. We found that most of the variation in parasitism was related to the animals emerging in the middle of the season having the most parasites, while animals emerging early or late had fewer parasites.
Importance: The seasonal pattern suggests that variation in parasitism is the result of ecological interactions where parasites have evolved to take advantage of their hosts’ patterns of development. Given that dragonflies and damselflies have been shown to be emerging at different times in response to climate change, it remains to be seen whether mites will be able to track these changes.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Phenology determines seasonal variation in ectoparasite loads in a natural insect population”, was published in the journal Ecological Entomology in 2010. You can find this paper online at the publisher, or on Figshare.
Image credit: Brad Smith, CC BY-NC 2.0, http://bit.ly/1q6YTeA
Background: Ageing is thought to be one of the most widespread biological phenomenon, though it has often been said that insects do not live long enough to experience it. Experiments with insects in laboratories under ideal conditions have shown that ageing does occur, but there are very few studies that have demonstrated this in the wild.
What we did: We used two extensive datasets of sightings of the azure damselfly, Coenagrion puella, to look for an effect of “demographic senescence”. What this means is that the chance of an animal dying on any given day increases as it gets older. Hundreds of animals were marked and followed for their whole lives over two summers. The damselflies live for, on average, 7 days after marking and that follows a period of around 10-12 days of maturation. What we showed was that, even over so short a lifespan, there was a detectable signal of age-related mortality. We also demonstrated that there were a number of other variables, principally weather and parasites, that also influence the chance of a damselfly dying.
Importance: Ours was only the second study that comprehensively demonstrated ageing in a wild insect population.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Empirical evidence of senescence in adult damselflies (Odonata: Zygoptera)”, was published in the Journal of Animal Ecology in 2010. You can find this paper online at the publisher, or on Figshare.
Image credit: Tim, CC BY-NC-SA 2.0, http://bit.ly/1vvSVWl
Background: Climate change is causing a range of effects in plants and animals. One of the most noticeable is the colonisation of new areas as the environment warms to a point where animals are able to persist where once they could not. However, the sources of data used to detect these kinds of patterns tend not to be systematically collected and so present unique challenges during analysis. In particular, a lot of existing data on sightings of animals that are used to detect trends under climate change originate from enthusiastic amateurs who make a note of which species they see and where.
What we did: I analysed a series of different methods that have been used to control for the effects of recorder effort bias in the detection of range shifts. This recorder effort bias occurs when there are far more recorders looking for animals in a later period and so the chance of discovering those extreme populations increases. Thus range shifts could simply be an artefact of increased sampling. I demonstrate that the methods that have been used before vary in the detection of range shifts and that some make more sense than others. I follow this up with a case study on range shifts in British Odonata and make recommendations concerning the most appropriate methods.
Importance: Climate change is an important issue and we need cutting-edge analytical tools if we are to properly assess its impacts on the world. I hope that this paper has contributed to this aim.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Accounting for recorder effort in the detection of range shifts from historical data”, was published in the journal Methods in Ecology and Evolution in 2010. You can find this paper for free online at the publisher.
Image credit: Ken Slade, CC BY-NC 2.0, http://bit.ly/1qAae4a
Background: Species distribution models (SDMs) have been used for a number of different purposes. This approach involves the mapping of species distributions (like the map shown on the right, for the citrine forktail damselfly) onto environmental variables to evaluate the contributions of those variables to determining the species range. This knowledge can then be use to predicted where the species will be in the future under climate change. However, another way in which they can be used is to predict in which areas the species has not been found but could potentially exist.
What we did: My study applied SDMs to this latter problem, predicting where 176 species of North American dragonflies and damselflies occur based on the patchy recording that is currently available. The models fitted reasonably well, which isn’t surprising given the reliance of dragonflies and damselflies on warm, dry weather for their adult stage. This highlighted areas for which the models predicted species presence but where those species had not been recorded. I also demonstrated that the patterns of diversity found in North America were consistent with those found in Europe.
Importance: This kind of study can be used to predict where rare or endangered species may have gone undiscovered as well as directing limited conservation efforts towards areas that are likely to have high diversities of animals or plants but have not been properly explored. We can also look for regions that have been under-surveyed and where resources need to be focused.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Predicting the distributions of under-recorded Odonata using species distribution models”, was published in the journal Insect Conservation and Diversity in 2012. You can find this paper online at the publisher, or on Figshare.
Image credit: L. B. Tettenborn, CC BY-SA 3.0, http://bit.ly/XHiqce
Background: When this paper was published, we had already demonstrated that ageing (an increase in the probability of dying in older individuals) was present in one species of damselfly. This was a surprise, as many biologists speculated that short-lived animals like damselflies did not live long enough in the wild to experience ageing. However, anybody who has worked with insects in the field knows that they exhibit clear signs of ageing like the tattered wings of the dragonfly shown above. Having shown that at least one species of damselfly age, it was still unclear as to whether this was the exception or the rule.
What we did: We expanded our analysis from a single species to consider all the species for which there was published data on age-related mortality which we could use to detect ageing. We found that this phenomenon was present in the vast majority of studies in which we were able to test for it. Furthermore, we were able to show that it was more apparent in territorial species where males face greater stress in having to defend their territories to obtain mates.
Importance: This study conclusively demonstrated that ageing is commonplace in dragonflies and damselflies, where once it had been proposed that no wild insect populations exhibited ageing at all. We also show a hallmark of the evolution of territoriality in the lifespans of dragonflies and damselflies.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “A comparative analysis of senescence in adult damselflies and dragonflies”, was published in the Journal of Evolutionary Biology in 2011. You can find this paper online at the publisher, or on Figshare.
Image credit: steews4, CC BY-ND 2.0, http://bit.ly/1rrAEeW
Background: At the core of ecology and evolutionary biology is the concept of “fitness”, broadly defined as the number of copies of an animal’s genes it manages to leave in subsequent generations. However, biologist rarely measure this genetic fitness. Instead, we use proxies such as the number of times an animal mated or the number of eggs an animal laid. Sometimes, we use proxies that are even further removed, such as body size (under the assumption that larger females lay more eggs).
What we did: This study compared two traditional forms of fitness measurement, daily mating rate and lifetime mating success, with a genetic measure of fitness based on finding the number of offspring each individual produced in the next generation. We monitored a single, isolated pond over two years and individually identified all damselflies of the species Coenagrion puella, the azure damselfly. Each individual also had a genetic sample taken and we used genetic markers called “microsatellites” to identify each individual. When we came back the next year, we did the same thing. This species goes through one generation per year so we knew that all the animals in the second year were the offspring of those in the first. By comparing the genetics of the potential parents with those of the potential offspring we were able to assign offspring to parents to produce a much more accurate picture of this concept of “fitness”. Unfortunately, what we found was that our behavioural measurements did not reflect this more accurate measure of fitness.
Importance: Since the concept of fitness is so important to evolutionary biology, it is important to test the assumptions of the studies that have sought to measure it. We have demonstrated that some of those previous studies were not using particularly reliable proxies for fitness. However, we have provided a case study of a potential method for avoiding these problems: by directly genotyping and assigning parents to offspring in the field we can get a much clearer picture of what “fitness” really means.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Field estimates of reproductive success in a model insect: behavioural surrogates are poor predictors of fitness”, was published in the journal Ecology Letters in 2011. You can find this paper online at the publisher, or on Figshare.
Image credit: One of mine, CC-BY 3.0
Background: Ponds have been identified as a very important habitat in the landscape. They enhance regional biodiversity, help control floodwater, reduce pollution in run-off from agricultural and urban land, and provide greenspace and biodiversity in urban environments. However, because of their small size (typically less than two hectares), they have been neglected by scientists until the last couple of decades.
What we did: This study used a large dataset of 454 ponds that had been surveyed in the north of England to identify all of the invertebrate and plant species that inhabited them. A wide range of physical, chemical and biological variables were also measured and, as the title of the paper suggests, we investigated which of these variables were related to the species richness of different plant and animal taxa. We were able to predict a reasonable amount of the diversity of invertebrates in general, but predictions varied between groups of invertebrates. In general, more shade and a history of drying up reduced the diversity of all groups.
Importance: It has been shown that landowners and managers tend to manage ponds and other natural resources using “received knowledge”. in other words, there is little evidence base for such management. Our study demonstrated a few important relationships which can be used to inform this kind of management.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Environmental correlates of plant and invertebrate species richness in ponds”, was published in the journal Biodiversity and Conservation in 2011. You can find this paper online at the publisher, or on Figshare.
Image credit: That’s one of mine, CC-BY 3.0.