DOI: 10.5061/dryad.nk98sf7tv
title: One for all and all for one: phenotype assortment and reproductive success in masculinized females

description: Homophily by morphological and behavioral traits has been described in
 several species of vertebrates, but its functional consequences remain
 poorly studied. Homophily by plurally breeding females may improve direct
 fitness by enhancing reproductive success. Female mammals may exhibit
 phenotypical masculinization due to exposure to androgens during early
 development, a condition that is associated with maternal performance
 during subsequent breeding. Our goal was to assess whether female
 composition (in terms of masculinization) of plurally breeding groups
 influences female fitness in a natural population of degus (Octodon
 degus). We assessed if plurally breeding female degus assort themselves by
 anogenital distance (AGD), an accurate measure of masculinization level.
 We also quantified if homophily by AGD phenotype affects female
 reproductive success and the reproductive output of the group. Plurally
 breeding groups typically included similarly masculinized (i.e., long AGD)
 females or similarly feminized (short AGD) females, indicating a strong
 degree of homophily. Females weaned more offspring in plurally breeding
 groups with more masculinized females. Additionally, standardized variance
 in the number of offspring weaned decreased in plurally breeding groups
 with mostly masculinized females, indicating greater reproductive equality
 in these groups. We conclude that female degus organize into homophilic
 social groups of similar AGD, and that social groups of masculinized
 females exhibit higher reproductive success.
description: <b>Study
 population: </b>Data come from a long-term study conducted between
 2009 and 2015 (7 generations) on a natural degu population located at
 Estación Experimental Germán Greve Silva (33°23′ S, 70°31′ W, altitude 495
 m), a field station of the Universidad de Chile. <b>Number of females
 examined: </b>Between 2009 and 2015, we recorded AGDs on 190 adult
 females. However, we only include 150 females in the analysis, because
 they were part of 57 multifemale groups.The remaining 40 females were
 excluded from the analysis because they were alone (n=15), were in
 female-male pair (n=16), were in two male-one female trios (n=5), or in a
 three male-one female quartet. Year 2010 was discarded from our analyses
 because there were no social groups with two or more females.
 <b>Individual
 attributes: female AGD and female body weight: </b>Female phenotype
 in terms of masculinization was assessed through anogenital distance
 (AGD), the distance between the ventral anus commissure to the base of the
 genital papilla. We measured the AGD of adult females exhibiting a
 non-perforated vagina with a digital caliper (precision 0.1 mm) at every
 capture event. We calculated the average AGD from 17.8 ± 8.6 measurements
 per female, resulting in a single AGD estimate per female. For all
 statistical analyses, AGD was used as a continuous
 predictor. Repeatability of AGD from the 359 females examined during
 2009-2015 was 0.73 (95% confidence interval: 0.70–0.77, n = 3168
 measurements; 822 measures from autumn, 2346 measures from spring),
 suggesting that AGD is a stable measurement within and between individuals
 and therefore, an efficient trait to estimate the masculinization level of
 females <b>Social group
 attributes: </b>We considered four attributes of social groups.
 These variables were (i) <i>the number of females</i>,
 representing the total number of adult females in the social group; (ii)
 the <i>mean group
 AGD</i>, representing the average AGD of all female group
 members, (iii) <i>the within group coefficient of variation of
 AGD</i>, an estimate of how different the females’ AGD are in a
 group (the degree of heterogeneity in masculinization within the group).
 Additionally, we calculated (iv) <i>the mean AGD of
 groupmates</i> after excluding the AGD value of the focal female
 (<i>mean AGD of group - AGD of focal female)</i>. These
 variables were considered to test the effect of social group composition
 (in terms of female groupmates) on litter size at weaning of each focal
 female. <b>Social group
 determination: </b>The main criterion used to assign individuals to
 social groups was the sharing of burrow systems at night. The sharing of
 burrow systems was determined by (i) burrow trapping during early morning
 activity and (ii) night-time telemetry. <b>Measures of reproductive
 success: </b>For all females, reproductive success was quantified as
 the number of offspring per litter (hereafter LS) at weaning. Variation in
 reproductive success among females in the same plurally breeding groups
 was indexed by the standardized variance in litter size
 (S<sup>2</sup>) at weaning. S<sup>2</sup> was
 calculated as: variance in litter size of adult females in a group/mean in
 litter size of adult female group
 members<sup>2</sup> First model: <i>mean AGD of
 groupmates</i> = <i>AGD of focal female</i> +
 <i>number of females</i> + <i>female body
 weight</i> + (<i>1+ AGD of focal female
 |Year</i>).  Second model: <i>Litter
 size at weaning</i> = <i>AGD<sub> </sub>of focal
 female</i> + <i>mean AGD of groupmates </i>+
 <i>mean AGD<sub> </sub>of group</i> +
 <i>coefficient of variation of<sub> </sub>AGD of group
 </i>+ <i>number of females</i> + <i>female body
 weight </i>+ (<i>1|Year</i>) Third model:
 <i>Standardized reproductive variance </i>= <i>AGD of
 focal female</i> + <i>mean AGD of groupmates</i> +
 <i>mean AGD of group</i> + <i>coefficient of variation
 of AGD of group</i> + number of females +<i> female body
 weight</i> + <i>(1|Year</i>) Marginal and conditional
 R<sup>2</sup> values were reported as measures of
 goodness-fit. Posterior analysis of outlier influence and qq-plots
 revealed no strong departures from model assumptions. All statistical
 analyses were implemented in R 4.0.3. Generalized mixed models were fitted
 using functions in library lme4 1.1–26, and inflation factor values
 were estimated using the library car ver. 3.0-10. Poisson dispersion
 factor was estimated using functions in library blmeco 1.4. All libraries
 were accessed during May 2021.
description: Between 2009 and 2015, we recorded AGDs on 190 adult females.
 However, we only include 150 females in the analysis, because they were
 part of 57 multifemale groups.The remaining 40 females were excluded from
 the analysis because they were alone (n=15), were in female-male pair
 (n=16), were in two male-one female trios (n=5), or in a three male-one
 female quartet. Year 2010 was discarded from our analyses because there
 were no social groups with two or more females. ND:
 undetermined. Female without tissue sampling, then without DNA analyses.
 Litter size, was not determinated.  Correa et al. 2021
 Dataset Readme attached.