DOI: 10.5061/dryad.zs7h44jmm
title: Can sexual selection promote within-species divergence of male genitalia? A study case with a male-dimorphic arachnid

description: Sexual selection can drive divergence in male genital morphology between
 species, but its role in within-species divergence remains underexplored.
 Male-dimorphic species offer an opportunity to investigate this, as
 different morphs often employ distinct reproductive tactics and face
 different challenges in sperm competition and female stimulation during
 copulation. We tested the hypothesis that sexual selection promotes
 within-species genital divergence using the harvestman Poecilaemula
 lavarrei as a model. This arachnid has two male morphs: larger,
 territory-holding majors, and smaller, sneaker minors. We first described
 copulatory interactions, finding no differences in female acceptance or
 copulation duration between morphs. Morphological comparisons showed that
 major males have longer pars basalis and ventral plate area,
 although no differences in ventral plate width, shape, or relative area of
 the mat of microsetae were detected. Allometric analyses revealed similar
 hypoallometric patterns for pars basalis length and ventral plate width in
 both morphs. However, ventral plate length was isometric in minors and
 hypoallometric in majors, which is the first report of allometric
 differences in genital traits between male morphs of a species. Our
 results suggest that despite differing reproductive tactics, the form and
 intensity of sexual selection on genital morphology is similar between
 morphs, potentially constrained by stabilizing selection.
description: # Can sexual selection promote within-species divergence of male
 genitalia? A study case with a male-dimorphic arachnid Dataset DOI:
 [10.5061/dryad.zs7h44jmm](10.5061/dryad.zs7h44jmm) ## Description of the
 data and file structure Data collected to investigate genital divergence
 between two male morphs of the harvestman *Poecilaemula lavarrei*: larger,
 territory-holding Majors and smaller, sneaker Minors. It includes
 behavioral data such as female acceptance and copulation duration, as well
 as morphological data comprising linear, area, and shape measurements of
 genital structures. ### Files and variables #### File: Angle.csv
 **Description:** This dataset contains angular measurements taken between
 males and females during copulation. Each row represents a measurement
 from a specimen identified by a unique code (Codigo) and categorized by
 male morph type (Morfo, either major - MA - or minor - MI). The dataset
 includes multiple repeated measurements per individual mate (ensuring
 measurement repeatability) under the column Medidas, with the
 corresponding measured angle recorded in Angulo. #### File: copulasU.csv
 **Description:** This dataset records copulation behavior in males of
 different morphs (Major vs. Minor). Each row represents a trial involving
 a male-female pair, identified by a female ID (id_f). The dataset includes
 the male morph type (Morfo), whether copulation occurred (copula, coded as
 Y/N), trial number (trial), and copulation duration (tempo) in MM:SS
 format. The data are used to model copulation probability and copulation
 duration across morphs and trials. This file has some cells intentionally
 left blank. We opted not to fill these cells with "NA" or other
 placeholder values to preserve the compatibility of the dataset with the R
 scripts provided, which expect purely numeric inputs in some columns.
 Modifying these would cause the scripts to return errors or invalid
 results. The empty cells are mainly due to cases where time variable do
 not apply — for instance, copulation duration is missing for mating trials
 in which no copulation occurred. #### File: Genital_M1.csv
 **Description:** The dataset contains linear measurements of genital
 structures from males of the harvestman *Poecilaemula lavarrei*,
 categorized into two male morphs: Major and Minor. The variables include:
 id (Male identifier), morfo (Male morph, either Major or Minor), trunk_len
 (Trunk length), glans_wid1 (Width of the pars basalis), glans_len (Length
 of the pars basalis), dorso (Dorsum width), placa_a_total (Area of the
 pars basalis), tapete_a_total (Area of the mat of microsetae). This file
 has some cells intentionally left blank. We opted not to fill these cells
 with "NA" or other placeholder values to preserve the
 compatibility of the dataset with the R scripts provided, which expect
 purely numeric inputs in some columns. Modifying these would cause the
 scripts to return errors or invalid results. The empty cells are mainly
 from cases of data that could not be collected due to technical
 limitations — for example, when genital structures were damaged (e.g.,
 trunk broken) during specimen preparation, or when it was not possible to
 obtain usable images for measurements. #### File: landmarks_drsl3.tps
 **Description:** The dataset consists of 2D landmark configurations
 digitized from dorsal images of male specimens, formatted in a .tps file.
 Each specimen is identified using the specID = "ID" parameter.
 #### File: landmarksVentral.tps **Description:** The dataset consists of
 2D landmark configurations digitized from ventral images of male
 specimens, formatted in a .tps file. Each specimen is identified using the
 specID = "ID" parameter. The landmarks include both fixed points
 and semi-landmarks, with their classification provided in a separate CSV
 file (curveslide.csv) used to define curve sliding during Generalized
 Procrustes Analysis (GPA). #### File: curveslide.csv **Description:** This
 file defines the sliding structure for landmarks used in geometric
 morphometric analyses. It specifies how individual landmarks should be
 allowed to "slide" during GPA. Each row corresponds to one
 sliding landmark and provides information on its neighboring landmarks.
 The column 'slide' is the ID of the landmark that will be
 allowed to slide, 'before' is the ID of the landmark immediately
 preceding the sliding landmark along the curve, and 'after', the
 ID of the landmark immediately following the sliding landmark along the
 curve. ## Code/software #### R Codes **linear_mesures.R** - Performs
 allometric analysis on genital morphological traits across male morphs
 (Major and Minor) using SMA regression, descriptive statistics, and
 t-tests. Visualizations include log-log regression plots and boxplots for
 trunk length, glans width, and glans length relative to dorsum width.
 **area_measures.R** - Performs statistical comparison of microsetae mat
 and ventral plate areas between male morphs (Major and Minor) using
 t-tests and descriptive statistics. Generates boxplots and log-log
 regression plots for absolute, proportional, and scaled area measures.
 **copula.R** – Processes copulation data to analyze the effects of male
 morph (Major/Minor) and trial number on copulation occurrence and
 duration. Includes data cleaning, variable transformation, and fitting of
 mixed-effects models. **angle.R** – Computes and compares mean angular
 measurements across male morphs (Major and Minor). Includes data cleaning,
 descriptive statistics (mean, SD, min, max, N), and a t-test to assess
 morph differences. **ventral_shape.R** – Performs geometric morphometric
 analysis on ventral landmark data using Generalized Procrustes Analysis
 (GPA) with semi-landmarks. Includes Procrustes ANOVA to assess effects of
 centroid size and male morph type (Major vs. Minor) on shape variation.
 **dorsal_shape.R** – Performs geometric morphometric analysis on dorsal
 landmark data using Generalized Procrustes Analysis (GPA). Includes
 Procrustes ANOVA to evaluate the effect of male morph type (Major vs.
 Minor) on shape, with and without centroid size (Csize) as a covariate.