Social environment and masculinization level interact to explain male testosterone levels in a social rodent: Part 1: The male side

Correa, Loreto 1

Published Sep 18, 2023; Updated Nov 20, 2023 on Dryad. https://doi.org/10.5061/dryad.6djh9w16h

Data files

Sep 18, 2023 version files 72.54 KB

Correa_et_al._2023._Male_Testosterone.xlsx

68.05 KB
README.md

4.48 KB

Nov 20, 2023 version files 63.70 KB

Abstract

In vertebrates, male testosterone levels vary across the year being generally higher during the mating relative to the offspring rearing season. However, male testosterone levels may also be influenced by male anogenital distance (AGD) length (a proxy of prenatal androgen exposition), and by the social group environment. In social species, it has been proposed that high levels of testosterone could be incompatible with the development of an amicable social environment. Thus, in these species, it is predicted that males have relatively low levels of testosterone. Our goal was to examine the potential association between male serum testosterone levels, male AGD length, and the social environment in the rodent Octodon degus under natural conditions. We quantified male serum testosterone levels during the mating and offspring-rearing seasons, and we determined the number of females and males in each social group, as well as the composition of groups, in terms of the AGD length of the female and male group mates, from 2009 to 2019. Our results revealed that male testosterone levels covary with the season, being highest during offspring rearing season. Additionally, male testosterone levels vary with male AGD length and female and male social group environments. More importantly, male degus exhibit low levels of testosterone that are indistinguishable from female levels during offspring-rearing season. Similar to other highly social mammals, where males and females live together all year, male amicable behavior could be the best male mating strategy, having as a proximal mechanism, a reduction in circulating testosterone levels.

https://doi.org/10.5061/dryad.6djh9w16h

Summary of dataset contents, contextualized in experimental procedures and results.

Data contained in this file correspond to individual and social group data from a wild population of degus (Octodon degus) and include data from two seasons (mating and offspring rearing) and eleven years (from 2009 to 2019). For model 1, use testosterone data from both sheets (1 and 2). For model 2, use data from sheet 1. For model 3, use data from sheet 2.

Results 3.1.

To test the prediction (i) about focal male serum testosterone levels vary across reproductive season, run model model 1.

Results 3.2.

To test predictions (ii and iii) about that potential effects of male AGD phenotype, number of females, and mean group female AGD, on male testosterone levels during mating season, run model 2.1. To test predictions (ii and iv) about that potential effects of male AGD phenotype, number of males, and mean group male AGD, on male testosterone levels during mating season, run model 2.2.

Results 3.3.

To test predictions (v and vi) about that potential effects of male AGD phenotype, number of females, and mean group female AGD, on male testosterone levels during offspring rearing season, run model 3.1. To test predictions (v and vi) about that potential effects of male AGD phenotype, number of males, and mean group male AGD, on male testosterone levels during offspirng season, run model 3.2.

In all models, log-transformed testosterone is the response variable. Season, focal male AGD, N of males, N of females, mean group female AGD, and mean group male AGD, were fixed factors. Year, Degu ID, were random factors.

Model 1-2-3 included the year of study and degu identity (Degu ID) as random factors.

Model fits were assessed with quantile residual dispersion. Best models were chosen by their AICc values and average model weight.

Description of the data and file structure

The file contains two sheets with data:

Sheet 1: mating season data.

Sheet 2: offspring season period data.

Data from mating period include data from 2010 to 2019. Data from offspring-rearing period include data from 2009 to 2019.
Blank cells corresponds to cells were data do not exists

Variables included:

Year (individual variable).
Degu ID: Ear tag number or degu identity. Some individuals are present several times (2-5 times). For these individuals, each data must be considered as independent data (individual variable).
Sex: F= female/M=male (individual variable).
Group ID: The number of the social group to which the degu belonged. Some males were alone, these males should be included in model 1. Model 2 and 3 that include the analysis of the n of males and females and mean group males and female AGD variables, should be run without data from males that were alone (Social group variable).
N of females: is the total number of females in each social group (Social group variable).
N of males: is the total number of males in each social group (Social group variable).
Focal AGD (mm): is the length of the anogenital distance, expressed in millimeters, of the focal individuals (individual variable).
Mean group female AGD (mm): the mean AGD of female group mates, expressed in millimeters (social group variable).
Mean group male AGD (mm): the mean AGD of male group mates after excluding the focal male AGD. Expressed in millimeters (Social group variable).
Testosterone level (nmol/L): is the measurement of serum testosterone, expressed in (nmol/L). As the testosterone variable does not have a normal distribution, to work with data, the testosterone variable should be transformed by Log (individual variable).

Freeform section for describing any code in your submission and the software used to run it.

Analyses were performed in R 4.1.3 (R Core Team 2022).
Linear mixed models (LMM) were fitted with the package LME4 1.1-31.
DHARMa 0.4.6 and MuMIn 1.46.0 packages were used to perform residual diagnostics and model selection routines, respectively.