Background: Animals and plants have a wide range of colours, and these different colours play different roles in different species. Some species might be signalling to potential predators that they are toxic (like a wasp’s stripes), others might be trying to hide (like a moth’s speckled grey wings), and others might be trying to signal to the opposite sex that they are high quality mates (like a peacock’s train). However, while there are clear functions in principle, the relative importance of different signals might vary depending on the context within which the animal or plant finds itself. For example, male ebony jewelwing damselflies (Calopteryx maculata) have very dark wings and this is thought to allow females of the same species to choose appropriate mates (i.e. to avoid mating with the wrong species). However, the dark pigment can also play a role in temperature regulation. Damselflies cannot generate their own heat and so rely on absorbing heat from the sun, which is helped by the dark pigment. I was interested in how the darkness of the wings varied between locations which experience different temperatures.
What I did: I wanted to collect specimens of this species for analysis from across its entire range in North America, but the range is so large (Florida to Ontario, and New York to Nebraska) that I wouldn’t have been able to travel to sufficient sites within the one season that I have available. Instead, I asked a lot of local dragonfly enthusiasts to catch and send me specimens from their local sites. I am extremely grateful to all of them for helping, as this could not have been done without their kind volunteering of time and energy. I ended up with a substantial dataset of animals from 49 sites across the range. The wings of the animals were clipped from the bodies and scanned using a flatbed scanner, and then the amount of pigment was calculated from the image. I showed that the amount of pigment was pretty constant across the range apart from when the species was found with a similar species: the river jewelwing damselfly (Calopteryx aequabilis). This suggests that there might be an optimal level of pigmentation that is independent of temperature, but that if females start to struggle to identify males of their own species there might be an advantage to changing the levels of pigment.
Importance: There have been a lot of local experiments on the benefits and costs of pigment in animals (including damselflies) but there have been far fewer studies that have looked at large scale patterns in pigmentation. These sorts of studies are essential to describe biological phenomena in the field and to reveal initial patterns in nature that might indicate interesting or novel evolutionary processes.
This is part of a series of short lay summaries that describe the technical publications I have authored. This paper, entitled “Continental variation in wing pigmentation in Calopteryx damselflies is related to the presence of heterospecifics”, was published in the journal PeerJ in 2014. You can find this paper for free at the publisher.
Image credit: That’s one of mine!
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
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