New article on Intraspecific Aposematism in damselflies

My latest article, with Jose Andres and Tom Sherratt, has just become available in PLOS ONE:

Conspicuous Coloration in Males of the Damselfly Nehalennia irene (Zygoptera: Coenagrionidae): Do Males Signal Their Unprofitability to Other Males?



In damselflies, sexual colour dimorphism is commonly explained as a consequence of selection on traits that increase male attractiveness to females. However, while many species in the damselfly family Coenagrionidae (Insecta: Odonata) are sexually dimorphic, the males do not engage in displays, and male competition for mates resembles a “scramble”. An alternative explanation for the sexual differences in coloration within these species is that sexual dimorphism has evolved as a sex-related warning signal, with males signalling their uprofitability as mates to other males, thereby avoiding harassment from conspecifics. We evaluated an underlying assumption of the theory that male-male harassment rate is influenced by colour by comparing harassment of males of the species Nehalennia irene that had been painted to make them appear: (i) similar to an unaltered male (blue), (ii) different from a male (orange) and (iii) more similar to a female (black). When caged together we found that blue-painted males experienced significantly lower harassment than black-painted males. When unpainted males were caged with each type of painted male we found that blue-painted males and the unpainted males housed in the same cages experienced lower rates of harassment than males housed in cages where some males were painted black, suggesting that a single, reliable signal of unprofitability may benefit the individuals that carry it. While our results do not in themselves demonstrate that sexual colour dimorphism originally evolved as an intra-specific warning signal, they do show that harassment is influenced by coloration, and that such selection could conceivably maintain male coloration as a warning signal.


Paper on polymorphisms in Polythore damselflies available from PLOS One

Our latest paper on the very colorful Polythore damselflies of Andean South America is now available from PLOS One:

Mixed Signals? Morphological and Molecular Evidence Suggest a Color Polymorphism in Some Neotropical Polythore Damselflies

These damselflies have highly diverse wing colors, with black, orange and white patterns combined in the same wing (see the banner at the top of this page for one example, a male of Polythore ornata).  These are more complex wings patterns than those seen in the majority of damselfly species, and normally we would expect that each of these different patterns is carried by a different species, and serves as a signal of identity during mating.  However, our initial analysis suggests otherwise;  a comparison with genetic sequences among several individuals with different wing color patterns shows that, in some cases, individuals with identical genetic sequences carry very different wing patterns, and that other individuals with more diverse genetics carry the same wing pattern.

There are a few reasons that this could happen: these species could be in the process of forming, with hybridization between individuals with different wingforms being common.  It could also be that selective pressures other than mating are behind the evolution of these colors.  One suggestion is that there might be selection for these damselflies to resemble co-occuring toxic butterflies, gaining protection from predators through resembling defended organisms (a type of mimicry known as Batesian mimicry).  Our current data cannot test these different theories, so more work will be required...



First Polythore manuscript submitted!

Happy to report that our first manuscript on the Polythore damselflies, which presents our analyses of wing patterning and basic phylogenetic relationships in five Peruvian species, is submitted!  This represents a lot of work on the part of many students and colleagues, and I am proud of our team!  I'll offer more details here when the fate of the manuscript is determined...