Known locally as ‘millions fish’ for its beautiful colours, the guppy has been the subject of academic research for many decades, and has given valuable insights into varied scientific questions, ranging from the rate of evolution, to the basis of decision-making.
Recently, attention has turned to the effects that invasive species – those that have spread to areas outside of their native range – might have on ecosystems around the world.
Our research, published this month in the journal Animal Behaviour, investigated how social behaviour might be important in the process of species invasion. Guppies are of special interest here because they have spread from their native range of Trinidad and northeast-South America to every continent except Antarctica.
Our questions were:
When guppies form social groups or shoals, do they shoal with picta?
If they do shoal with picta, do they shoal as closely, or do they keep their distance?
Finally, does this depend on whether guppies and picta have a shared history?
To test this, we observed shoals of six fish. These shoals comprised of either of two sets of three guppies from different sites, or three guppies and three picta.
By focusing on the behaviour of a randomly chosen guppy, we found that guppies were more often found in shoals with picta than in guppy-only shoals.
In these mixed-species shoals, a guppy’s nearest neighbour is more often a guppy.
The distance between a guppy and its nearest neighbour in a shoal was the same regardless of whether the neighbour was a guppy or a picta. Shared history also did not affect this shoaling behaviour.
Without imputing intention or personality, it seems that guppies are quite ‘friendly’ – they will happily shoal with picta, as though they were with other guppies.
Shoaling and other social behaviour may be important in species invasions.
By studying species like the guppy, which have been very successful invaders, we can understand more about how the invasion process works.
For example, when a species arrives in a new environment, it may be a challenge to find food and avoid predators. If, however, it can associate with other similar organisms, it is more likely that it might find suitable food, refugia and important information about predators – as well as enjoying the protection benefits of group-living.
One way of doing this would be to shoal closely with similar species - which the guppy seems happy to do. Perhaps this sociability explains why the guppy has been so successful when introduced to new habitats around the world?
This blog post was written by the lead author of this study, my colleague Jarome Ali.
Read the full paper here: Ali JR, Deacon AE, Mahabir K, Ramnarine IW, Magurran AE, 2018. Heterospecific shoaling in an invasive poeciliid: shared history does not affect shoal cohesion. Animal Behaviour. 138: 1-8.