DOI: 10.5061/dryad.v15dv422b
title: Adaptive immune response selects for postponed maturation and increased body size

description: The Major Histocompatibility Complex (MHC) genes encode proteins that
 initiate the adaptive immune response by presenting pathogen-derived
 antigenic peptides to T lymphocytes. Host-pathogen coevolution drives MHC
 polymorphism, introducing intraspecific variation in host life expectancy.
 This variation interacts with optimal growth strategy, as growth increases
 reproductive potential. While mortality rate and body size-dependent
 fecundity are major factors shaping life histories, the effect of
 intraspecific variation in MHC-based immunity on the evolution of growth
 strategies and host body size remains unknown. Here, we model how host
 MHC–pathogen coevolution—and its concomitant impact on host mortality—can
 affect the evolution of host life-histories, as represented by age at
 maturation and body size. Life histories were compared in scenarios with
 and without adaptive immune response under equal population-level
 mortality rates. We show that host-pathogen coevolutionary dynamics select
 for postponed maturation and increased body size. Although MHC genes and
 genes that determine body size were physically unlinked, selection imposed
 by the Red Queen process generated linkage disequilibrium between
 immunocompetent MHC alleles and the maturation-postponing alleles that
 prolong growth phase and increase body size. Particularly large body size
 was attained when pathogens mutated slowly, thus allowing the advantage of
 resistant MHC alleles to persist over multiple generations. The emergence
 of adaptive immunity, which is pathogen-specific and enables immunological
 memory, is considered a major evolutionary innovation of vertebrates. Our
 work suggests that the adaptive immune response, mediated by polymorphic
 MHC genes, may drive the evolution of host body size. This form of
 adaptive immunity may have thus predisposed vertebrates to evolve large
 body sizes and exhibit the macroevolutionary patterns of increasing body
 size over time that have been detected in comparative studies. 
description: Data were generated with an individual-based simulation model of
 host-pathogen co-evolution (see details in Ejsmond et al. Adaptive immune
 response selects for postponed maturation and increased body size.
 Functional Ecology). Calculations were performed using resources provided
 by Wroclaw Centre for Networking and Supercomputing (http://wcss.pl), grant no.
 576. We gratefully acknowledge Polish high-performance computing
 infrastructure PLGrid (HPC Centers: WCSS) for providing computer
 facilities and support within computational grant no.
 PLG/2020/013911.
description: The dataset and the code of the program used in the manuscript
 "Adaptive immune response selects for postponed maturation and
 increased body size" published in Functional Biology. The dataset is
 packed in the ZIP archive 'FunctionalEcology__Ejsmond_et_al_
 2023.zip' and contains the results of the simulation model. The data
 and the description of variables are stored in the form of Matlab
 workspace files. The program was implemented and data can be opened with
 Matlab version 9.1. R2016b or higher.