DOI: 10.5061/dryad.zw3r228j5
title: Within-aggregation roosting location in Prionostemma Opiliones

description: We tested whether the leg condition (missing legs or not) of an arachnid
 species (Prionostemma sp.2) affects roosting location within the group by
 experimentally inducing the formation of aggregations overnight.
 Autotomized individuals roosted more frequently in the aggregation center
 than intact individuals. Additionally, this pattern was observed only for
 aggregations of more than 13 individuals.
description: We studied Opiliones of <em>Prionostemma </em>sp.2 at
 La Selva Research Station, in Puerto Viejo de Sarapiquí, Heredia, Costa
 Rica (10.4311 N, 84.0068 W, elevation: 50 m) in February 2024. We
 collected individuals at night on two the trails (STR and SUR) for lab
 experiments. We conducted this research following research permits of the
 Costa Rican Government (permit # SINAC-ACC-PI-re-003-2024). Additionally,
 we ensure the welfare of Opiliones throughout all stages of this work by
 following suggested guidelines and best practices. To
 test the hypothesis of the location within the group to roost, we placed
 the collected Opiliones in an arena composed of a plastic shoe box (33 ×
 20 × 12 cm) at night (19:00 - 21:00 h) to induce the formation of
 overnight aggregations. We added similar numbers of individuals with both
 leg conditions: The ratio of autotomized to intact individuals across the
 64 groups we studied was 1.19 ± 0.37 (mean ± standard deviation). We
 studied 858 individuals, 46% of whom had eight legs, 38% had seven, 13%
 had six, and 3% had five. We did this in the Environmental Lab at La Selva
 (an open-window room with ambient temperature). A 20 × 10 cm wooden
 surface or bark fragment in each box provided a natural substrate to
 aggregate (Fig. 2A). We kept each box vertical to mimic the tree buttress
 where Opiliones roost. In each trial, we added a total
 of 5 to 22 individuals. We studied 32 small groups (5 - 11 individuals,
 n=308), 17 medium groups (13 - 16 individuals, n=255), and 15 large groups
 (18 - 22 individuals, n=304). We compared the
 proportions of autotomized and intact Opiliones in an aggregation’s center
 and periphery. The following morning, we photographed each group with a
 GoPro Hero 8 placed 50 cm away. To identify individuals as in the “center”
 or the “periphery” of the group from the pictures, we drew circles
 centered on their bodies with a radius equal to approximately 2 body
 widths. Because these circles encompassed each individual, we labeled the
 circles as in the center if they were completely surrounded by other
 circles. Then we labeled circles as in the periphery if they were not
 fully surrounded by others. To test if leg condition
 affects the roosting location choice, we ran a goodness-of-fit
 χ<sup>2 </sup>test with two nominal variables: group position
 (center or periphery) and leg condition (autotomized or intact) using all
 data (858 individuals in 64 aggregations). To explore if the proportion of
 individuals across the group’s locations differed between group size
 classes, we ran three additional goodness-of-fit χ<sup>2
 </sup>tests, one for each group size (small n=308, medium n=255, and
 large n=304). We performed all analyses in R version 4.2.1.
description: # Within-aggregation roosting location in Prionostemma Opiliones **FILE:**
 script_Opiliones_center.R **OVERALL DESCRIPTION:** This file contains the
 R script to run all the analyses performed. The script is fully annotated,
 for easier reproducibility. **FILE:** data_Opiliones_center.csv **OVERALL
 DESCRIPTION:** This file contains the data of the roosting position of
 *Prionostemma* sp.2 Opiliones groups. Each row corresponds to one
 individual. **COLUMN EXPLANATION** * group_ID: A unique identification
 code for each individual recording that matched the date it was recorded *
 group_size: number of Opiliones in each group * number_legs: number of
 legs of that given individual * center_periphery: if the individual was in
 the center of the group (center) or in the periphery (periphery) *
 location: if the individual was in the center of the group (0) or in the
 periphery (1).