This week’s odonate of the week is Coenagrion puella. This is a European species that is very close to my heart. I worked on it during my PhD at the University of Liverpool and it has treated me well by producing some nice publications over the years.
In the most prominent (and recent) of these publications was a fascinating study that was masterminded by my supervisor, Prof David Thompson (Thompson et al., 2011). People have been watching damselfly and dragonfly behaviour for many decades (the first scientific study of their movement was in the 1930s) and a lot of this work has focused on their mating behaviour. These observations were taken as evidence of “success” on the part of the male and female, since both had achieved breeding. However, it is clear that mating and breeding are two different concepts. Mating is the coming together of potential parents while breeding is the successful production of offspring. While mating had been confirmed, very few of these observational studies had followed-up to ensure that the behavioural measures of breeding success were accurate representations of the actual number of offspring produced.
As well as monitoring mating behaviour, as had been done many times before, Dave decided to take legs from the damselflies in order to record their genetic signature. This isn’t the first time people have genotyped damselflies, but here’s the clever bit: By doing this in two generations, he now had a bunch of genetic signatures of a “parental generation” and a bunch of genetic signatures for their offspring in the next generation. Using “microsatellites” (variable regions of the genetic code that do not actually produce proteins, effectively like fingerprints), it is possible to infer which pair of individuals from the first year produced which offspring from the second. We can then calculate the difference between the number of matings each individual achieved and the number of offspring that it actually managed to produce.
The key finding was the there really wasn’t a very strong relationship between the two measures of success. This highlights a gaping hole in our knowledge about odonate biology: while we have spent a lot of time running around with butterfly nets to catch the adults, once the eggs are laid we very rarely follow the larvae. This is despite the fact that more than 99% of individuals do not even survive to adulthood. Furthermore, it was difficult to predict which individuals would produce more or fewer offspring. Parasites seemed to reduce the number of offspring produced by females, but only slightly. The strongest predictor was simply the number of days spent trying to mate. It is likely that this results in more eggs laid, each of which represents a “ticket in the lottery” of larval development.
Thompson, D.J., Hassall, C., Lowe, C.D. & Watts, P.C. (in press) Field estimates of reproductive success in a model insect: behavioural surrogates are poor predictors of fitness, Ecology Letters.