Cover February 2023

FEBRUARY's cover portrays great pond snails Lymnaea stagnalis! This species is common in lakes and ponds, where they are hosts for multiple parasites making the snail immune function an important determinant of their evolutionary fitness.

Read more about this study by Langeloh et al. (2022) "Ecological determinants of variation in phenotypic selection on quantitative immune defence traits".

ABSTRACT

Immune defence is an important determinant of organismal fitness. While theoretical models based on tradeoffs in resource allocation predict quantitative immune traits to be subject to stabilizing selection due to associated energetic costs and self-harm, empirical studies report mainly positive directional selection. This discrepancy may arise from multiple ecological factors that vary in nature and could influence selection. We examined if selection on immune activity varies depending on immune challenge/infection risk, between immune traits and among populations in the freshwater snail Lymnaea stagnalis. We assessed selection on the phenoloxidase-like and antibacterial activity of snail haemolymph while manipulating the level of immune challenge imposed by environmental microbes. We did this using snails from multiple populations and also quantified within-population family-level variation (i.e. evolutionary potential) in the snails' immune activity. We found that the strength of immune challenge and the examined immune trait determined selection on the snails' immune function. Thus, variation in infection risk can be an important factor in maintaining genetic variation in defence traits. Additionally, immune traits showed low among-population differentiation but high within-population genetic variation. This pattern could arise if natural snail populations are exposed to higher temporal than spatial variation in infection risk.

PHOTO BY: Otto Seppälä

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