Size-selective harvesting affects immunocompetence of guppies

Does size-selective harvesting over long time influence susceptibility of fish to parasitic infections? This is the question that we, with Vitalija in the lead, set out to study using our size-selected guppy lines as the platform. After the initial hurdles of establishing a stable population of Gyrodactylus turnbullii, the study progressed smoothly, and the results are now out.

The study suggests that there are two major factors determining the individual gyro loads of guppies. The first is body size: larger guppies offer more habitat area for these ectoparasites and therefore tend to host higher parasite loads than smaller ones. Harvesting large guppies results in smaller guppies and therefore lower parasite loads. But this is not the whole story: even after adjusting for the body size effect, we found significant differences in parasite loads between guppies originating from different treatments. In particular, guppies from populations subject to harvesting small guppies had higher size-corrected parasite loads than guppies from the large- or random-harvested populations. This suggests that investment in immunocompetence competes for the same resources as body growth, such that selection regime favouring fast growth leads to compromised immunocompetence. 

This stydy will be part of Vitalija's PhD thesis. The activity is related to the project "Cost of life-history adaptations in guppies".

Reference:

Bartusevičiūtė, V., B. Díaz Pauli, A. G. V. Salvanes, and M. Heino. 2022. Size-selective harvesting affects the immunocompetence of guppies exposed to the parasite Gyrodactylus. Proceedings of the Royal Society B: Biological Sciences 289:20220534. doi: 10.1098/rspb.2022.0534.