A paper by Jess, Cock, Ryan and Jo used data from nearly 5,000 guppies from natural populations in Trinidad to look at how predation pressure, through its effects on guppy traits, might affect the parasites infecting the guppies. Because the guppy is so well studied, we know that those in the lower courses of rivers experience higher levels of predation pressure than those in the upper courses. This difference in predation pressure has led to a divergence in a number of guppy traits between these populations, including shoaling. Guppies, particularly females, shoal a lot in the lower courses, whereas those in the upper courses don’t. As a rule, males are more likely to be hunting for mates than shoaling. Because the parasite we work on, Gyrodactylus spp., is transmitted from fish to fish during contact, such as happens during shoaling, we predicted, and our data confirmed, that lower course females would have the highest rates of infection, followed by lower course males, followed by the upper course guppies. Seems like avoiding parasites is an unexpected advantage of the male guppy’s insatiable sexual appetite!
Access the paper here:
Stephenson J.F.,van Oosterhout C., Mohammed R.S., Cable J. (2015). Parasites of Trinidadian guppies: evidence for sex- and age-specific trait-mediated indirect effects of predators. Ecology 96: 489-498. http://dx.doi.org/10.1890/14-0495.1