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: 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: Parasites and the individuals that they attack (called “hosts”) often have a long evolutionary history of interaction. This history often plays-out as an “arms race” where the parasite finds a new way of attacking the host and the host then evolves a defence against that attack, followed by subsequent evolution by the parasite. Not only this, but species of parasites (such as the aquatic mites and protozoa that I work on) that exploit many host species can differentially affect those different hosts. In this study, we were interested in how parasitic protozoa affect closely related damselfly species that differed in their distributions.
What we did: Julia Mlynarek, a PhD student at Carleton University, collected a large number of damselflies from a number of sites around eastern Ontario. The species were grouped into pairs so that we could compare between species from the same genus. She dissected these to find the number of protozoa (like the one shown above) in guts of each animal. We found that species with smaller geographical distributions tended to have more protozoan parasites than closely related species with larger distributions.
Importance: Explaining how parasites affect their hosts is a big question spanning ecology and evolutionary biology. These results suggest that there might be a combined effect of (i) shared parasites due to evolutionary history, and (ii) varying resistance due to different exposure across geographical ranges.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Higher gregarine parasitism often in sibling species of host damselflies with smaller geographical distributions”, was published in the journal Ecological Entomology in 2012. You can find this paper online at the publisher, or on Figshare.
Image credit: Christophe Laumer, CC BY 2.0, http://bit.ly/1rrvyzt
Background: A variety of responses to climate change have been detected in a variety of taxa. Among these is a change in phenology – the timing of the life cycle (like the emergence of an adult dragonfly from its larval case as shown on the right). Since some species use temperature as a cue for when to develop, as the environment warms there is a signal of earlier development in these species.
What we did: I analysed an extensive dataset of sightings of dragonflies and damselflies (Odonata) over a 50-year period in the UK. These 450,000 sightings were of around 40 species and provided a detailed record of dates on which different Odonata species were emerging from their aquatic habitats. I found that there was a significant shift towards earlier emergence which was consistent with that observed in terrestrial species. I further demonstrated that there was a difference between two groups of species that varied in what stage they over-wintered. Those species that sat in the water over winter as eggs did not show a response to climate change while those that were larvae over winter did show a response. I infer from this that the response to climate change is caused by a decline in mortality associated with cooler temperatures in the more vulnerable larval stages.
Importance: As I mention above, a number of studies have demonstrated an effect of climate change on the phenology of animals and plants. This study showed that the signal was present even for animals that occupy aquatic habitats, suggesting that temperature changes influences aquatic and terrestrial ecosystems in much the same way.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Historical changes in the phenology of British Odonata are related to climate”, was published in the journal Global Change Biology in 2007 (my first paper!). You can find this paper online at the publisher, or on Figshare.
Image credit: Sally Crossthwaite, CC BY-NC-ND 2.0, http://bit.ly/1q6HYtH
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Study design and mark recapture estimates of dispersal: A case study with the endangered damselfly Coenagrion mercuriale”, was published in the Journal of Insect Conservation in 2012. You can find this paper online at the publisher, or on Figshare.
Background: I have long been interested by movement of animals in the landscape and whether or not this can be accurately quantified in the field. One of the major issues associated with these field studies (such as mark-release-recapture studies, in which animals are marked with a unique tag then recaptured at a later time) is that you cannot detect dispersal distances that are greater than the size of the study area that you are using. For example, people have been marking damselflies for decades to try to measure how far they fly. However, if you only look for them 500m from where you first found them, you won’t find them flying any further than that.
What we did: This study used a large mark-release-recapture dataset and investigated the effect that expanding a study area has on the maximum dispersal distance detected. We found that the original study (on the endangered southern damselfly, Coenagrion mercuriale) was at a scale sufficient to estimate the maximum distance that the insect is able to fly, around 2km.
Importance: This endangered species has very specific habitat requirements (water meadows and shallow ditch systems) which mean that it has a long distance to move between these rare areas.
Image credit: Paul Ritchie, CC BY-NC-ND 2.0, http://bit.ly/1sZpjCC
Inspired by this xkcd comic, and facilitated by this online tool, people have been summarising all kinds of ideas using the 1,000 most common words. Naturally PhD students have latched onto this as a source of procrastination and, in a show of solidarity, I decided to join them (this was during my lunch break – honest!). Here’s my PhD thesis:
My work looks at how animals change as the world gets warmer. My animal is like a fly but it has four flying bits, eats other animals, and has big eyes. By looking at where people saw these animals in the past, I figured out how the place and time at which they appear changes with how hot it is. I found that they appear earlier when it is hot, which is interesting because these animals spend most of their lives in water. Animals in water had not been shown to change when they appear in this way before. I also looked at the ways in which we look at changes in where animals appear and showed the best way to look at this problem. Last, I looked at how the form of these animals changes as they move when it gets hotter. I found that the animals that had moved a long way had a form that made it easy for them to move (like big flying bits). In short, the changes shown by the animals that I looked at can be used to build a case for a warming world.
“We should be extremely cautious in concluding that an organ could not have been formed by transitional gradations of some kind. Numerous cases could be given amongst the lower animals of the same organ performing at the same time wholly distinct functions; thus in the larva of the dragonfly… the alimentary canal respires, digests and excretes.”
– Charles Darwin, Origin of the Species, Chapter 6Read More »