DOI: 10.5061/dryad.2bvq83c0v
title: Data from: Neighbor density and post-contact immobility duration as antipredator behavior: Antlion larvae do not fit the selfish prey hypothesis

description: Remaining immobile for an unpredictable period after being touched by a
 potential predator (post-contact immobility, PCI) may favor survival.
 However, the factors that determine variation in PCI duration are poorly
 understood. We tested whether PCI duration depends on the surrounding
 conspecific density (the selfish prey hypothesis) in the tropical antlion
 larvae Myrmeleon crudelis. These insects avoid predation by being immobile
 or burying themselves. The selfish prey hypothesis predicts a reduction in
 the PCI duration as conspecific density increases because this high
 density of conspecifics around can stimulate the redirection of the
 predator's interest in other nearby potential prey. In the field, we
 measured PCI and found that its duration was independent of the
 conspecific density. We also measured the PCI of a subset of larvae in a
 density-reduction lab experiment. We found that larvae displayed shorter
 PCI duration when we reduced their number of neighbors to zero. These
 results suggest that antlion larvae did not follow the selfish prey
 hypothesis. We propose two alternative explanations. First, the larvae
 have a limited ability to detect neighbors in the field and keep up with
 the changing number of surrounding active pits. Second, burying may be
 more important than PCI as an antipredator strategy. In our lab
 experiment, larvae had a more accurate idea of the conspecific density
 around their pit because they explored the area. We propose that knowing
 the absence of conspecifics triggered a shorter PCI duration. Under a high
 predation risk (i.e., no other prey to which the predator would redirect
 its attention), the larvae select the unequivocal antipredator behavior of
 burying. This work illustrates the relevance of accurate information in
 deciding how to avoid predation, especially when prey can prioritize
 between alternative behaviors which success varies between contexts.
description: <em>Field observations</em> We
 randomly selected 103 focal antlion pits (1-5 cm in diameter) and placed a
 25 x 25 cm square plot with the selected focal pit at the plot center.
 Next, we counted the number of traps inside the plot and measured the pit
 diameter of all of them with a digital Caliper to the nearest 0.1 mm. We
 calculated the density of conspecifics around the focal pit (i.e., # of
 pits/625 cm<sup>2</sup>) and the total area of the surrounding
 pits (i.e., the sum of the area of all pits inside the plot excluding the
 focal larva’s area). The area of each pit was estimated using the formula
 of π * r<sup>2</sup>. We measured PCI
 duration as the difference (in seconds) between when the antlion landed on
 the substrate and when its body moved for the first time. We extracted the
 focal larva from the ground by gently scooping the soil in the trap ~5 cm
 deep with a spoon. We placed the spoonful on a plastic kitchen sifter to
 locate the larva. Once located, we held it dorsoventrally with
 entomological forceps to simulate a predator attack. We dropped the larva
 inside the plot from which it was taken on a sector of bare soil from ~ 10
 cm from the ground, simulating a predator's involuntary drop. Using a
 chronometer, we measured the time in seconds to the nearest 0.1s between
 the larva’s first contact with the soil and its first movement (i.e.,
 PCI). When the larva began to move, it quickly burrowed into the
 ground.  <em>Laboratory
 experiment</em> In lab conditions, we tested if
 antlion larvae modulate their PCI in response to their number of neighbors
 by experimentally reducing the original neighbor density found in the
 field. We brought to the laboratory a subset of 30 randomly selected
 individuals after measuring their PCI in the field. The larvae experienced
 environmental conditions similar to those in the field since the
 laboratory does not have temperature or photoperiod control. We gently put
 each larva at the center of the container and let it acclimate for three
 days, an adequate lapse for antlions to build their pit traps. All larvae
 moved around the container, searching for a place to build the pit,
 leaving visible paths in the substrate. Larvae did not receive food during
 the experiment. Three days later, we repeated the
 protocol performed at the field to measure the PCI. In the lab, we
 collected the individuals from the pits inside the container using a
 spoon, and we quickly took them with entomological forceps 10 m away from
 the lab building to a field site with the same soil substrate where we had
 conducted the field trials. The behavior of the larvae was similar the
 second time we measured the PCI (after being in the lab) in terms of their
 behavior in the field.
description: # Antlion larvae post-contact immobilization duration
 [https://doi.org/10.5061/dryad.2bvq83c0v](https://doi.org/10.5061/dryad.2bvq83c0v) ## Description of the data and file structure ReadME Antlion data - selfish prey FILE: “antlion data selfish prey.csv” OVERALL DESCRIPTION:  This file contains the data of the post-contact immobilization (PCI) duration in seconds of different antlion larvae measured in the field and a subset measured in the lab. COLUMN EXPLANATION: Phase: Denotes the source of data: Either “Field_observations” or the “Lab_experiment”. A subset of larvae were tested in both conditions. Individual: The individual ID code for each larvae. Pit_diameter_cm: The diameter of each of the antlion larvae in the field was measured to the nearest 0.1cm with calipers. Number_of_neighbors: The total number of other antlion larvae with active pits in a 25x25 cm square plot surrounding the focal larvae pit. Post_contact_immobilization_PCI_s: The difference (in seconds) between when the antlion landed on the substrate and when its body moved for the first time. Larvae were dropped on a substrate from 10cm in height after being held with forceps.  Location: The specific location within the field site (Las Cruces Research Station) were subsets of data points were acquired. The categories reflect different locations throughout the facilities, which are easily identified and located on the station’s maps. Collectors: The specific pair of researchers who conducted the trials. Density: The number of antlion pits inside the 25 x 25 cm square plots (i.e., # of pits/625 cm2). Surrounding_pit_area: The sum of the diameters of all of the antlion larvae inside the 25 x 25 cm square plots (all measured to the nearest 0.1cm with calipers).