Is more better? Polyploidy and parasite resistance

Abstract

Ploidy-level variation is common and can drastically affect organismal fitness. We focus on the potential consequences of this variation for parasite resistance. First, we elucidate connections between ploidy variation and key factors determining resistance, including allelic diversity, gene expression and physiological condition. We then argue that systems featuring both natural and artificially manipulated ploidy variation should be used to evaluate whether ploidy level influences host -parasite interactions.Keywords: polyploidy; host-parasite interactions; allelic diversity; gene expression; host condition 1. INTRODUCTION Polyploidization 1 has generated variation in ploidy level within and across species [1,2], and new examples are continually being discovered, particularly in animals [3]. Intraspecific ploidy-level variation is associated with a suite of connections between polyploidy and biological phenomena [4,5], and has the potential to influence fitness-related traits [6,7]. We discuss whether ploidy variation could mediate resistance to a ubiquitous enemy-parasites (defined here as an organism that harms its host). Although current theory suggests ploidy level can profoundly influence infection dynamics and host-parasite evolution [8,9], data are scarce [10,11]. PLOIDY AND IMMUNE FUNCTIONPolyploidy (i.e. autopolyploidy) could directly influence immune response to a parasite attack in at least two ways. Firstly, the addition of a new genome may increase allelic diversity. Higher allelic diversity at immune genes could help hosts recognize a greater diversity of parasites [12]. Secondly, if the additional genome copies are expressed, then polyploids may generate higher amounts of gene products related to immune function.(a) Allelic diversity and immune function The high allelic diversity of immune genes is partly a consequence of parasite-mediated selection for rare genotypes and/or novel immune functions [13]. Parasitemediated selection may generate such diversity through mechanisms such as heterozygote advantage [14] and negative frequency-dependence [13]. Heterozygote advantage could be influenced by ploidy level because the extra alleles present in polyploids may increase the probability of heterozygosity for an individual at a given locus. The presence of an extra genome could also increase the likelihood that an individual possesses a rare genotype at resistance loci; this would be advantageous if parasite-mediated negative frequency-dependent selection favours rare genotypes.Studies from natural populations have documented connections between parasite-mediated selection and the maintenance of allelic variation at genes associated with immune function [12,15]. Genetic polymorphism can play an important role in generating variation in recognition molecules [16], and diversity is important for disease resistance in host individuals and populations [17,18]. Furthermore, measures of genome-wide genetic variation (e.g. microsatellite heterozygosity [19,20]) are often correlated with individual immune ...

Host-parasite evolution in male-haploid hosts: an individual based network model

“…5). A result similar to those from previous studies (King et al 2012), and in support of the invasion scenarios of M'Gonigle and Otto (2011). The results here being attributable to the proportion of I-S edges, and the general density of edges in the network.…”

Polyploidy in Animals: Effects of Gene Expression on Sex Determination, Evolution and Ecology

“…A particular type of biotic interactions that has been associated with polyploidy is parasitism and parasite resistance [Nuismer and Otto, 2004;Osnas and Lively, 2006;M'Gonigle and Otto, 2011;King et al, 2012]. A role for polyploidy in immunity has been inferred in the context of (1) allelic and genetic diversity and (2) endopolyploidy (next paragraph).…”

Can resource costs of polyploidy provide an advantage to sex?

“…Since ploidy-level variation can affect traits from gene expression to the rate of spread of beneficial mutations to immune function (reviewed in Otto and Whitton, 2000;Comai, 2005;Mable et al, 2011;King et al, 2012), it may be of relevance when considering the outcome of competition between sexual and asexual lineages that differ in ploidy.…”

“…This finding points to the importance of controlling for hybrid ancestry, which is very common in asexual polyploids, when evaluating the ecological consequences of polyploidy. Given the common co-occurrence of hybridization, polyploidy, and asexuality, it is perhaps not surprising that the extent to which polyploidy is likely to explain different distributions of sexual and asexual taxa is controversial and remains unclear (Mable, 2004;Lundmark and Saura, 2006;Vrijenhoek and Parker, 2009;Maniatsi et al, 2011;King et al, 2012).…”