Local adaptation drives thermal tolerance among parasite populations: a common garden experiment

Abstract

Understanding the evolutionary responses of organisms to thermal regimes is of prime importance to better predict their ability to cope with ongoing climate change. Although this question has attracted interest in free-living organisms, whether or not infectious diseases have evolved heterogeneous responses to climate is still an open question. Here, we ran a common garden experiment using the fish ectoparasite Tracheliastes polycolpus, (i) to test whether parasites living in thermally heterogeneous rivers respond differently to an experimental thermal gradient and (ii) to determine the evolutionary processes (natural selection or genetic drift) underlying these responses. We demonstrated that the reaction norms involving the survival rate of the parasite larvae (i.e. the infective stage) across a temperature gradient significantly varied among six parasite populations. Using a Q st /F st approach and phenotype -environment associations, we further showed that the evolution of survival rate partly depended upon temperature regimes experienced in situ, and was mostly underlined by diversifying selection, but also-to some extent-by stabilizing selection and genetic drift. This evolutionary response led to population divergences in thermal tolerance across the landscape, which has implications for predicting the effects of future climate change.

Combining species distribution models and population genomics underlines the determinants of range limitation in an emerging parasite

“…We consistently found a significant effect of water temperature. In particular, cold sites were associated with high prevalence, which matches the biology of this parasite species and also the host habitat preferences (Mazé‐Guilmo et al 2016, Franke et al 2019). However, we also found significant effects of various environmental drivers such as host related factors (host body length and host species), the river topography, the surrounding landscape composition and the anthropogenic fragmentation.…”

Variability of functional traits and their syndromes in a freshwater fish species (Phoxinus phoxinus): The role of adaptive and nonadaptive processes

“…In the case of covariations, among‐ and within‐population variance components were calculated in a similar way but with the addition of a random slope, corresponding to the covariable trait (Supporting Information Appendix ). This allows estimating among‐ and within‐population variance in the covariation between each pair of traits (Mazé‐Guilmo, Blanchet, Rey, Canto, & Loot, ). The generalized linear mixed models were run using the lme4 R‐package (Bates, Maechler, Bolker, & Walker, ).…”

Molecular approaches reveal weak sibship aggregation and a high dispersal propensity in a non‐native fish parasite

“…The free-living infective copepodid (Figure 1) displays modest ability to swim and, not adapted to feeding, can live freely for about 5 days under laboratory conditions (Mazé-Guilmo, Blanchet, Rey, et al, 2016;Piasecki, 1989). Once attached to a host, it transforms into chalimus within 5 hr.…”

“…Based on the ecological information available for T. polycolpus and its host (see section Biological model), we built several nonmutually exclusive predictions. After hatching, the free-living larvae of T. polycolpus released into the water column almost instantaneously develop into an infectious stage (Copepodid instar, see Figure 1) allowing a rapid infection of hosts (within a few days; Mazé-Guilmo, Blanchet, McCoy, et al, 2016;Mazé-Guilmo, Blanchet, Rey, et al, 2016). Moreover, daces are relatively gregarious and often behave in shoals.…”