Latest article on Wolbachia infecions in Fijian damselflies

I am very excited to announce that our latest paper in Scientific Reports, on the Nesobasis damselflies in Fiji is available online as of today! In this paper we explore the relationship between these endemic island damselflies and a group of alpha-protobacteria called Wolbachia. These bacteria are intracellular (living inside the cells of their hosts), and are fairly common in insects and other arthropods. As these bacteria are intracellular, they are passed on in eggs but not in sperm, and so male hosts represent a reproductive dead-end for the bacteria, as they cannot infect the next generation of hosts.

This has led to a number of strange relationships between the hosts and their Wolbachia parasites, with Wolbachia sometimes killing male hosts, or feminizing them, to improve their own chances at reproduction. Wolbachia can also cause cytoplasmic incopatability (CI) in their hosts, with males and females of a particular host species only being able to successfully mate with other individuals that carry compatible strains of Wolbachia. CI can sometimes drive speciation in host species by limiting mating opportunities within host populations.

We found a large number of Neosbasis species to be infected with Wolbachia, —a total of 25 different Wolbachia strains were detected across these damselfly species, and another genus of Fijian damselfly, Melanesobasis, was also infected. Many of the damselflies carry multiple strains of Wolbachia. We also found different rates of infection across different islands; about half of the species on Viti Levu, the largest island in Fiji, were infected with Wolbachia, while all of the species on Vanua Levu (the second largest island) were infected.

In previous work we had shown that for some species of Nesobasis, males are much less common than females at reproductive sites, causing us to suspect that Wolbachia might be killing males, but Wolbachia were found to be common in these species as well as in species where males are abundant, and so they are not likely to be skewing host sex ratios. The possibility that CI might have something to do with helping to create all of these species of Nesobasis is an intriguing idea, and one that these results suggest would be worthwhile to explore!

Please check out the paper here at Scientific Reports!

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...