Ecological determinants of variation in phenotypic selection on quantitative immune defence traits

• Published in: Oikos Vol. 2023; no. 2
• Main Authors: Langeloh, Laura, Jokela, Jukka, Seppälä, Katri, Seppälä, Otto
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.02.2023
• Subjects: Antibacterial activity; antibacterial properties; Antibiotics; Ecological effects; ecological immunology; Environmental factors; Freshwater; Freshwater molluscs; Gastropoda; Genetic diversity; Genetic variation; Haemolymph; Health risks; Hemolymph; Immune response; Immune system; immunocompetence; Infections; Inland water environment; Lymnaea stagnalis; Mollusca; Mollusks; parasite resistance; Phenoloxidase; phenotypic selection; Phenotypic variations; Population differentiation; Population genetics; Populations; Resource allocation; Risk; selection gradient; Snails; Spatial variations; Stabilizing
• ISSN: 0030-1299; 1600-0706
• DOI: 10.1111/oik.09506

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.