Category: Odonates

Damselfly sex doesn’t always produce children, and that’s a problem for evolutionary biologists!

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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

Less common species tend to have more parasites

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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

British dragonflies are emerging earlier in the year under climate change

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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

Study design and mark recapture estimates of dispersal [paper summary]

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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.

9303167014_cdbcb32d61_zBackground:  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

I did a map!

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I have been playing with R’s capacity to produce interactive maps and (after much trial-and-error) have finally come up with something that shows an interesting pattern.  The data plotted below are the species richness of dragonflies and damselflies from the British Dragonfly Society‘s database in West Yorkshire over the last 20 years.  The data are summarised to 1km grid squares on the British National Grid.  Below is a screenshot because WordPress doesn’t like iframes, but click it to go to the full map.

Capture

The scale is a bit odd to emphasise the range of the data, and there are many neater ways to do this.  In particular, R gives the option to render in interactive 3D using OpenGL, create actual interactive maps using Shiny, and use the Leaflet jscript packages.  There are more details on the plotGoogleMaps package that I used for this little map here.  The code is below:

Dragonfly.grid <- read.table("Dragonfly data.txt",header=TRUE)
attach(Dragonfly.grid)
Dragonfly.grid[,2]<-Dragonfly.grid[,2]*100
Dragonfly.grid[,3]<-Dragonfly.grid[,3]*100
library(RColorBrewer)
coordinates(Dragonfly.grid)<-c('Easting','Northing')
Dragonfly.grid<-as(Dragonfly.grid,'SpatialPixelsDataFrame')
proj4string(Dragonfly.grid) <- CRS('+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs')
m=plotGoogleMaps(Dragonfly.grid,zcol='Species',at=c(0,2,3,4,6,8,12,21),colPalette= rev(rainbow(7,start=0,end=4/6)))

Created by Pretty R at inside-R.org

PhD opportunities in ecology and evolution

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As part of the new NERC Doctoral Training Program at the University of Leeds, I have two PhD projects to advertise that are now (as of 15th November 2013) open to applicants:

1: DragonFlight: Linking the mechanics and energetics of flight to conservation status and responses to climate change in dragonflies

dragonfly-177338_1280The DragonFlight project builds on my earlier interests in dragonfly dispersal (1), macroecology (2), and flight morphology (3).  There has quite a bit of work done on the flight of dragonflies, but much of this has taken place in the laboratory and has not considered what goes on in the field.  Similarly, there has been quite a lot of landscape-scale work done in the form of mark-recapture studies or analyses of historical records (including my own), but none of this has really tested for the traits that underlie flight ability.  This project will link detailed biomechanical measurements of dragonfly flight to our knowledge of responses to climate change (i.e. range shifts) or conservation status.

2: Teaching old beetles new tricks: applying novel genetic techniques to re-establish a classic ecological model system, Tribolium

I’m really excited about this project.  Andrew Peel, a colleague at Leeds, has been working on the evolution of beetles (and animals in general) for a while and uses Tribolium as a model system.  I have been interested in the ecology of this system for some time and this project represents us banging our brains together. In particular, there are lots of nice ways that we can incorporate Andrew’s contemporary genomic techniques (e.g. RNAi) to test for genetic drivers of ecological phenomena.  The species is also an important pest species of stored grain, making any advances potentially applicable to pest control.

Note that both of these are “competitively funded”, which means that there are more projects than we can fund.  We interview candidates for all projects and then award the best candidates the projects that they applied for.  There are more details on the website, including how to apply.  Deadline is 24th January 2014.

References:
(1) Hassall C, Thompson DJ (2012) Study design and mark recapture estimates of dispersal: a case study with the endangered damselfly Coenagrion mercuriale. Journal of Insect Conservation, 16, 111-120.
(2) Hassall C, Thompson DJ (2010) Accounting for recorder effort in the detection of range shifts from historical data. Methods in Ecology and Evolution, 1, 343-350.
(3) Hassall C, Thompson DJ, Harvey IF (2008) Latitudinal variation in morphology in two sympatric damselfly species with contrasting range dynamics (Odonata: Coenagrionidae). European Journal of Entomology, 105, 939-944.

Communicating camouflage and mimicry: chocolate, hover flies and Teddy Roosevelt

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In September I gave a Cafe Scientifique talk at the Leeds City Museum on the evolution of mimicry and camouflage.  For those of you who aren’t familiar with the concept, Cafe Scientifique offers an opportunity for scientists to give short (or long, depending on how it is run) talks on their research to a general audience and then take questions in an informal setting.  I have always been a fan of this kind of outreach, and when Clare Brown, the curator of Natural History at Leeds Museum asked if I wanted to give a talk I jumped at the opportunity.  I spent a bit of time pulling resources together for the talk and I thought I would post them here in case anybody else could find a use for them.  I have outlined the talk I gave below:Read More »

Dragonfly intestines: nature’s Swiss Army knife

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“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 »