DOI: 10.5061/dryad.dv41ns1zw
title: Data for: Direct evidence for increased disease resistance in polyandrous broods exists only in eusocial

description: Background The ‘genetic diversity’ hypothesis posits that polyandry
 evolved as a mechanism to increase genetic diversity within broods. One
 extension of this hypothesis is the ‘genetic diversity for disease
 resistance’ hypothesis (GDDRH). Originally designed for eusocial
 Hymenoptera, GDDRH states that polyandry will evolve as an effect of lower
 parasite prevalence in genetically variable broods. However, this
 hypothesis has been broadly applied to several other taxa. It is unclear
 how much empirical evidence supports GDDRH specifically, especially
 outside eusocial Hymenoptera. Results This question was addressed by
 conducting a literature review and posteriorly conducting meta-analyses on
 the data available using Hedges’s g. The literature review found 10 direct
 and 32 indirect studies with both having a strong publication bias towards
 Hymenoptera.  Two meta-analyses were conducted and both found
 increased polyandry (direct tests; n = 8, g = 0.2283, p = &lt;0.0001)
 and genetic diversity generated by other mechanisms (indirect tests; n
  = 10, g = 0.21, p = &lt;0.0001) reduced parasite
 load.  A subsequent moderator analysis revealed that there were
 no differences among Orders, indicating there may be applicability outside
 of Hymenoptera.  However, due to publication bias and low sample
 size we must exercise caution with these results.  Conclusion
 Despite the fact that the GDDRH was developed for Hymenoptera, it is
 frequently applied to other taxa.  This study highlights the low
 amount of direct evidence supporting GDDRH, particularly outside of
 eusocial Hymenoptera.  It calls for future research to address
 species that have high dispersal rates and contain mixes of solitary and
 communal nesting.
description: For definition purposes, ‘parasites’ will be used to mean all
 infecting agents, which include microbial pathogens. We used the
 guidelines Preferred Reporting Items for Systematic reviews and
 Meta-Analysis (PRISMA) outlined in Moher et al. (2009) to undergo a
 literature search to glean studies that test the GDDRH both directly and
 indirectly (see Sup. Fig. 1).  To determine how much direct evidence
 supporting the GDDRH exists, a literature search was conducted using both
 Google Scholar and Web of Science. Combinations of the keywords;
 “Polyandry”, ”Genetic Diversity”, “Multiple Mating”, and ”Disease
 Resistance” were used for each database in May 2020. Next, citations were
 removed if replicates were found between searches and databases, as well
 as non-peer reviewed sources (i.e. books, dissertations). This resulted in
 2,106 citations being left. Titles were then evaluated for relevance and
 2,018 papers were removed. Of the articles remaining we assessed the
 following parameters: (1) disease or infection evaluation (2) genetic
 diversity alterations and (3) determination of study type (reviews were
 eliminated). Those studies that assessed infection, and altered genetic
 diversity were further evaluated and parsed into direct and indirect
 studies.  This process resulted in 42 studies that were
 grouped into direct or indirect tests of the GDDRH (Table 1). For the
 purposes of this paper, a direct study testing GDDRH is defined as one
 that i) directly measures parasitic infection of offspring, with infection
 performed either in the field or direct infection in the laboratory, and
 ii) incorporated correlation with high vs. low genetically diverse host
 populations through mating strategy differences, i.e. monandry vs.
 polyandry. Comparing monandrous broods to polyandrous broods are valuable
 treatments when genetic relatedness is not available: monandry should have
 lower levels of genetic diversity providing the best alternative to
 polyandry for comparison. However, one study does not use monandrous
 broods, but rather compares the relationship between parasite load and
 varying levels of promiscuity (i.e., 10 to 28 mated males per queen in
 Neumann & Moritz, 2000, with genetic relatedness reported).
 Another study manipulated male genetic diversity that led to the effective
 mating rate being 1.3 versus 4 males (Baer & Schmid-Hempel, 1999).
 Both studies were classified as direct tests of the GDDRH. Indirect
 studies examine parasitic infection in groups that may have different
 levels of genetic diversity generated through other mechanisms. For
 example, genetic diversity was manipulated through groups founded by one
 (monogyne) or more than one female (polygyne). Although that is a
 mechanism for increasing genetic diversity, it does not address
 polyandrous behavior, and as a result those studies were classified as
 indirect as long as infection was also assessed. We
 then assessed the studies to determine if they could be included in the
 meta-analysis based on the following parameters: (i) a comparison between
 high and low genetic diversity groups and (ii) assess parasite success
 (i.e., mortality).  We excluded studies that used heterogeneity as a
 measure for genetic diversity as we were interested in the benefits of
 polyandry at the population level and not individual level on parasite
 success.  We also excluded studies that were mathematical models and
 meta-analyses.  This left 8 direct studies and 10 indirect studies that we
 gleaned data from to conduct our meta-analysis. We conducted a meta-analysis
 following the methods described in Hedges (1981), using Hedges’s<i>
 g</i> to estimate effect sizes. Standard mean difference was
 calculated using the <i>escalc</i> function in the package
 <i>metafor</i> in R v. 1.3.1056 (R Development Core Team). The
 web-based tool WebPlotDigitizer
 (https://automeris.io/WebPlotDigitizer/userManual.pdf) was used to extract
 data from publication plots when raw data was not available.
 The terms of the GDDRH posit that polyandry is favored when it
 results in increased genetic diversity, gambling in the likelihood that
 half-siblings will vary in resilience to parasites. In the direct studies
 dataset, standard mean difference effect sizes were calculated by
 extracting parasite harm mean measurements and their standard deviations
 in two groups: monandry or low polyandry and high polyandry. In one study
 (Tarpy & Seeley 2006),<i> t</i>-values and degrees of
 freedom were extracted due to the lack of means and standard deviations.
 As most direct studies looked at the effects of GDDRH in Hymenoptera, we
 first performed a nested random mixed effects model using the
 <i>rma.mv</i> function to account for phylogenetic
 non-independence. The same method to obtain standard mean difference was
 applied on studies indirectly testing GDDRH; however, here, groups were
 categorized into low genetic diversity and high genetic
 diversity. Additionally, we tested whether the
 magnitude of the relationship was dependent on eusocial Hymenoptera for
 both datasets by performing a third analysis using “host Order” as a
 moderator variable. Last, we tested for a potential
 publication bias by plotting a funnel plot for both datasets, i.e., direct
 and indirect studies.