DOI: 10.5061/dryad.ns1rn8pxv
title: Data from: Trait-specific indirect effects underlie variation in the response of spiders to cannibalistic social partners

description: Organisms may respond in different ways to the risk posed by conspecifics,
 but the cause of such variation remains elusive. Here, we use a
 half-sib/full-sib design to evaluate the contribution of (indirect)
 genetic or environmental effects to the behavioral response of the
 cannibalistic wolf spider Lycosa fasciiventris (Dufour,
 1835) towards conspecific cues. Spiders showed variation in
 relative occupancy time, activity, and velocity on patches with
 or without conspecific cues, but direct genetic variance was only found
 for occupancy time. These three traits were correlated and could be lumped
 in a principal component: spiders spending more time in patches with
 conspecific cues moved less and at a lower rate in those areas. Genetic
 and/or environmental components of carapace width and weight loss in the
 social partner were significantly correlated with the principal component
 of focal individuals. Individual Variation in these traits may reflect the
 quality and/or quantity of cues produced by social partners, hence focal
 individuals were likely behaving along a continuum of strategies in
 response to the risk posed by social partners. Therefore, environmental
 and genetic trait variation in the social partners may be key to maintain
 trait diversity in focal individuals, even in the absence of direct
 genetic variation.
description: <strong>Spider collection and rearing
 conditions</strong> <em>Lycosa
 fasciiventris</em>
 individuals (adult males and subadult females) were collected between June
 and July 2015 in four different localities within the Almeria province
 (South-East Spain), in dry temporal washes (“ramblas”): near Boca de los
 Frailes (36.8036°N, 2.1386°O), near Carboneras town (36.9667°N, 2.1019°O),
 at Almanzora river (37.3414°N, 2.0078°O) and near Paraje las Palmerillas,
 Estación Experimental Cajamar (36.7917°N, 2.6891°O). They were reared in
 individual tanks (22 cm x 18 cm x 18 cm) with the bottom filled with 2–3
 cm of soil collected from one of the sites. All individuals were fed once
 a week with size-matched crickets (<em>Gryllus
 assimilis </em>Fabricius, 1775) purchased from the pet supply
 virtual store Exofauna (available at: https://exofauna.com). Spiders had
 access to water <em>ad libitum</em> through a 40 ml vial
 filled with water and covered with cotton. Vials were checked and refilled
 every 2-3 days. Holding tanks were placed in a climate chamber that
 simulated outdoor climatic conditions of the preceding weekly average
 conditions in the Almeria province (night:day temperature cycles between
 18.7–34.3 ºC; photoperiod of 17:7 h - 16:8 h light-dark with light bulbs
 of 54W and a relative humidity of 50–65 %). Individuals used in the experiments were removed
 from their mothers’ back 42 ± 8 days after hatching and placed in separate
 cylindrical containers (15 cm height and 6 cm of diameter) inside a growth
 chamber with controlled temperature (25°C ± 1ºC), humidity (70% ± 5%) and
 photoperiod (16:8 hours light:dark). The bottom of each container was
 covered with a filter paper replaced weekly. Water was
 provided <em>ad libitum</em> from a cotton string submerged in
 a reservoir, below each container and providing water by
 capillarity (Moskalik and Uetz 2011). Each week, spiderlings were fed with
 fruit flies (<em>Drosophila melanogaster</em> Meigen, 1830),
 reared in a nitrogen-rich medium supplemented with high-quality dog food
 to ensure survival and growth of spiderlings (Jensen et al. 2011). A
 portion of the offspring within each dam family (3 out of 12) was reared
 in a richer environment by providing them three times the amount of food
 given to the remaining spiders, to examine how this affected both cue
 emission and the response to such cues. For logistic reasons, spiders were
 not reared until maturation and thus their sex was unknown. We assumed
 that sex differences were not very pronounced at the early stages, as is
 the case in a syntopic and co-generic wolf spider (e.g.,
 Fernández‐Montraveta and Moya‐Laraño 2007). <strong>Experiment</strong>
 We aimed at testing the role of genetic and
 indirect genetic effects in shaping the variability in the interaction
 between cue-emitting spiders and spiders that perceive such cues. Our
 experimental design is thus highly asymmetrical, as one individual is only
 present via the cues it emits, whereas behaviour is measured in the other
 individual. Note also that each individual served first as a social
 partner, emitting cues, and was subsequently used to measure its behaviour
 in another arena. All trials were recorded between April
 21<sup>st</sup> and June 8<sup>th</sup> 2016 in a
 total of 50 blocks and 17 recording days. Blocks consisted of 3 rows x 5
 columns = 15 Petri dishes (individuals) recorded under a single camera.
 Usually, three blocks were recorded in a single day with three different
 cameras. More details are provided below.  <strong><em>Cues and traits in social
 partners</em></strong> Behavioral responses to conspecific cues were
 measured in small Petri dishes (5.5 cm diameter) with the bottom covered
 with filter paper divided in two halves: one containing intact filter
 paper (control) and the other impregnated with conspecific cues (e.g.,
 excreta and silk). These cues were produced by juvenile conspecifics
 (hereafter social partners) enclosed in a small Petri dish for 10 days
 with filter paper on the bottom and fed with 10 fruit flies each during
 the first 36 hours. The nature of the cues released included the excreta,
 silk, odour and chemo-tactile cues of dead prey. The spatial position of
 the two filter paper halves was randomized to eliminate any potential side
 bias. As a proxy for the amount of cues produced, we
 used (a) weight loss of spiders confined within a petri dish for 36h and
 (b) carapace width, reflecting body size. In spiders, weight
 loss may be an indication of the quantity or quality of conspecific cues
 released.  Indeed, since a great proportion of the cues likely correspond
 to excreta, animals losing more weight were likely those that also
 released more cues. Alternatively, higher weight loss may be related to
 animals that have higher voracities, as recently found in another wolf
 spider (Rádai et al.
 2017),  which could be associated to their willingness to
 attack conspecifics (Arnqvist and Henriksson 1997). Moreover, carapace
 width is known to be correlated with
 the amount of cues produced in spiders (Persons et al.
 2001). Weight loss was calculated by feeding spiders
 with 10 flies each, then weighting them after 36 hours and after 10 days.
 Proportional weight loss was then estimated as the difference in weight
 between these two measures divided by the initial weight. During this
 period, spiders were provided water <em>ad libitum</em> by
 means of a soaked piece of cotton of about 1 cm in diameter, which was
 re-soaked every two days. Body mass was measured to the nearest 0.1 mg
 using a high-precision scale (Mettler Toledo XP26). Body size was assessed
 by measuring the maximum carapace width (i.e., carapace width at its
 maximum span). Measurements were performed with a stereomicroscope (Leica
 MZ125) with a precision of 0.1 mm. <strong><em>Behavioral
 measurements</em></strong> Spiders in which the behavioral response to
 social cues was measured (hereafter focal individuals) were randomly
 assigned to a Petri dish, but care was taken that they were not
 genetically related to and came from the same feeding treatment as their
 social partner. Note that each individual was used both as social partner
 and focal individual. During the behavioral observations, light was
 made homogeneous by introducing the camera and the Petri dishes inside a
 40x40x30 styrofoam box. Locomotor behavior was measured by monitoring
 spiders, in blocks of 15, through recordings retrieved from a video camera
 (Sony® HDR CX-150) placed overhead. A video-tracking software was
 implemented, allowing estimating movement at 25 frames/second. We obtained
 information for 563 spiders, with a mode recording time of 6 hours for
 each spider (min = 0.38 h, max = 6.04 h, median = 5.5 h). This large
 variation in recording time was due to an ant or fly walking on top of the
 Petri dish, or to a lack of space in the camera hard drive. However, we
 included recording time in the statistical analyses (see below), and it
 did not affect our results. Differences in behavioral patterns between sides
 were estimated using the relative interaction intensity (RII) index
 described in Armas et al. (2004): <em>R<sub>trait </sub>= </em>(<em>trait<sub>cues</sub></em> - <em>trait<sub>control</sub> </em>)<em> /  </em>(<em>trait<sub>cues</sub></em> + <em>trait<sub>control</sub> </em>) where<em> trait<sub>cues</sub></em> is the mean value of the trait in the patch with cues and <em>trait<sub>control</sub> </em>is the mean value of the trait in the patch without cues. Using this general formula, we calculated: (a) the relative activity (RA) index as the time spent moving, (b) the relative mean velocity (RMV) index as the difference in speed and (c) the relative occupancy time (ROT) index as the difference in time spent in patches with or without conspecific cues (fig. S1). In addition to these three traits, we performed a principal component analysis (PCA) to estimate a composite behavioural score based on the three traits, thus accounting for potential correlations among them. This was done in R v.4.0.2 (R Core Team 2020), using the function “principal” in library “psych” without axes rotation (fig. S2). We sought a single PC that explained &gt; 50% of the variance and in which the three traits had substantial loadings (, ≥ |0.7|). In these focal individuals, we also used the measurement of weight loss and carapace width, as described above (cf. Cues and traits in social partners). Moreover, we added a measure of body condition, i.e., the maximum abdomen width (where nutrients and body fats are stored). Body condition has been shown to be negatively associated with movement in these spiders (Moya-Larano 2002), hence we used them as covariates in the statistical models measuring DGE, such as to account for this potential source of variation (see below).