Look out for Loners

This post contributed by Nadine Lymn, ESA Director of Public Affairs

Personality traits that lead an individual to want to avoid crowds could actually be playing a role in biological invasions, says a recent study that appeared in the Proceedings of the Royal Society Biological Sciences.  Julien Cote and colleagues at the University of California at Davis looked at the personality traits of the mosquitofish, Gambusia affinis and found that the less sociable individuals travelled farther than their more amicable counterparts.

Successful invasions happen in multiple stages: introduction of a species (either naturally or intentionally introduced by people), spread, establishment, growth to high density, and finally, high impact on the community the species invaded.  Previous studies that compare characteristics between species suggest that aggressive and ‘fast lifestyle’ personality traits seem to go hand-in-hand with a species’ ability to establish, grow rapidly to a high density, and have high impacts on the surrounding community.  Cote and colleagues were interested in looking at how individual traits within a species might be influencing invasions.

Credit: Roman Slaboch

The researchers released G. affinis in an experimental stream with five pools.  While most fish stayed in the release pool, others swam on, many of them ending up all the way downstream in the fifth pool.  When the study was repeated, most of the individuals who left the first pool to swim farthest away—the most asocial individuals—did so again.

In their paper, the authors say that:

If individuals leaving their pond of introduction have different personality traits than individuals staying, it would have important implications for the invasion process.  Obviously, our measurement of dispersal might not precisely match dispersal distance in the wild.  However, our aim is not to provide quantitative prediction of dispersal distance in the wild but to show that dispersal behavior might depend on personality traits in this invasive species.

The authors acknowledge that different traits needed to complete the various stages of invasion might be in conflict.  For example, an inclination for frequent dispersal would be at odds with reaching a high enough population density for successful establishment.  But interestingly, evidence exists—say the authors—that asocial individuals usually stay in low-density patches, moving on only when a population becomes dense:

Importantly, the increase in population size should then drive asocial individuals out, leading to colonization of additional empty patches.

 Cote, J., Fogarty, S., Weinersmith, K., Brodin, T., & Sih, A. (2010). Personality traits and dispersal tendency in the invasive mosquitofish (Gambusia affinis) Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2009.2128