DOI: 10.5061/dryad.2280gb5xn
title: Condition dependence of (un)predictability in escape behavior of a grasshopper species

description: (Un)predictability has only recently been recognized as an important
 dimension of animal behavior. Currently, we neither know if
 (un)predictability encompasses one or multiple traits nor how
 (un)predictability is dependent on individual conditions. Knowledge about
 condition dependence, in particular, could inform us about whether
 predictability or unpredictability is costly in a specific context. Here,
 we study the condition dependence of (un)predictability in the escape
 behavior of the steppe grasshopper Chorthippus dorsatus. Predator–prey
 interactions represent a behavioral context in which we expect
 unpredictability to be particularly beneficial. By exposing grasshoppers
 to an immune challenge, we explore if individuals in poor condition become
 more or less predictable. We quantified three aspects of escape behavior
 (flight initiation distance, jump distance, and jump angle) in a
 standardized setup and analyzed the data using a multivariate
 double-hierarchical generalized linear model. The immune challenge did not
 affect (un)predictability in flight initiation distance and jump angle,
 but decreased unpredictability in jump distances, suggesting that
 unpredictability can be costly. Variance decomposition shows that 3–7% of
 the total phenotypic variance was explained by individual differences in
 (un)predictability. Covariation between traits was found both among
 averages and among unpredictabilities for one of the three trait pairs.
 The latter might suggest an (un)predictability syndrome, but the lack of
 (un)predictability correlation in the third trait suggests modularity. Our
 results indicated condition dependence of (un)predictability in
 grasshopper escape behavior in one of the traits, and illustrate the value
 of mean and residual variance decomposition for analyzing animal behavior.
description: In order to test the condition-dependence of (un)predictability,
 we exposed steppe grasshoppers <em>Chorthippus dorsatus</em>
 to an immune challenge (n = 66) and recorded the effect of the treatment
 on three escape behavior traits, in comparison to untreated individuals (n
 = 66). Individuals were sampled as nymphs in June/July 2021 from Jena,
 Germany. Subjects were transferred to the laboratory, separated by sex,
 and maintained in groups of up to about 60 individuals in large mesh cages
 of dimensions 47.5 x 47.5 x 93 cm<sup>3</sup>. After their
 final molt, individuals were transferred in pairs of the same sex and the
 same final molt date to smaller mesh cages of dimensions 22 x 16 x 16
 cm<sup>3</sup>. Individuals were maintained with ad libitum
 access to freshly cut grass provided in small vials with water and a water
 tube for moisture. Dead individuals and individuals that lost legs were
 replaced, if possible, with other individuals that matched the cage mate.
 When a replacement was impossible, the remaining cage mate was not used in
 the experiment. Around 15 days after the final molt, a behavioral assay
 was performed as described below. To achieve standardized conditions
 across the behavioral essay, individuals were placed in refrigerators at
 8ᵒC on the evening prior to phenotyping. During overnight cooling,
 individuals were kept individually in cylindrical vials of dimensions 8 cm
 height and 5 cm diameter, with 2-3 leaves of grass. For each pair of same
 sex and final molt date, one individual was randomly selected for an
 immune challenge, while the other was used as control.
 To cause an impairment in the condition of individuals, we
 performed an immune challenge. Treated individuals were anesthetized by
 exposing them for 3 minutes to temperatures of -20ᵒC. They were then
 injected with a solution containing 1.6x108 cells of heat-killed
 <em>Escherichia coli</em> per microliter diluted in Ringer’s
 grasshopper solution. The cell concentration was determined after the
 efficacy of 5 different solutions (with 1.6x108, 1.6x107, 1.6x106,
 1.6x105, and 1.6x104 cells/μL) was tested in 20 individuals each (10 males
 and 10 females). The chosen concentration caused the death of 25% of the
 individuals after 48h and thus seemed sufficiently strong without being
 immediately fatal. Males received 1 µL of the solution, and females, 2 µL
 (females weigh around twice as much as males). In order to maximize the
 differences between control and treated groups (and because we were not
 interested in the effect of heat-killed E. coli as such), control
 individuals did not receive any injection nor were they anesthetized.
 After injections, all individuals (treatment and control) were
 color-marked dorsally with yellow paint (for automated analysis, see
 below). In order to keep track of individual identity, one of the
 individuals was marked with a stripe from the wings to the pronotum, and
 the other with a stripe on the wings and a dot on the pronotum. The type
 of marking was randomly assigned and thus not associated with the
 treatment groups. After being marked, individuals were left for 1 hour
 under a heat lamp in mesh cages of dimensions 22 × 16 × 16
 cm<sup>3</sup>, with fresh grass available, as preparation for
 the behavioral assay. Each pair of treated and control
 individuals was phenotyped simultaneously, with the observer being blind
 to the treatment. The two individuals were placed into a 5.3 x 3.3
 m<sup>2</sup> arena, where they could acclimatize for 5
 minutes. The arena floor was coated with foam rubber to provide a
 non-slippery surface for the grasshoppers to jump. The room temperature
 was maintained constant at 27ᵒC. Individuals were approached with a
 moveable device, which was placed on the ground about 50 cm behind the
 grasshopper and moved smoothly and at a constant speed toward it
 (approximately 130 cm/s2), mimicking an approaching predator. Each
 individual had ten escape jumps recorded on video, with 2 minutes time gap
 between chases. To streamline phenotyping, we alternately simulated
 attacks on the two individuals in the arena. On average, 14 individuals
 were phenotyped per phenotyping date. The software Ethovision XT (Noldus,
 Netherlands), with the Social Interaction Module, was used to track the
 movements of the chaser and the grasshopper. Flight initiation distance
 (FID), jump distance, and jump angle measurements were extracted from the
 tracks.
description: Recommended to save the .txt file in .csv format to align column
 data The dataset consists of a total of 1163
 observations.<br>TrialID refers to each observation.<br>IndID
 refers to the identification number of each individual.<br>FID is
 the flight initiation distance in centimeters, defined as the minimum
 distance between the chaser and the grasshopper before the grasshopper
 jumped.<br>JumpDistance is the jump's length in centimeters,
 defined as the distance between the point where the jump started and where
 the grasshopper landed<br>JumpAngle is the angle of the jump
 direction in degrees in relation to the initial grasshopper body position.
 Straight jumps scored 0ᵒ, while negative values marked jumps to the left,
 and positive values jumps to the right.<br>JumpOrder refers to the
 sequential number of jumps within the 10 trials of an
 individual.<br>JumpYN indicates if the grasshopper jumped or not
 during that trial (Y = jumped, N = didn't jump). <br>Sex is
 coded as M for males and F for females.<br>Treatment refers whether
 an individual was from the control group (C) or if it received the immune
 challenge injection described previously (T)<br>PhenotypingDate is
 the date when the experiment occurred (DD_MM_YYYY)<br>DayTime is
 coded as 24h, with the minutes converted to decimals (for example: 1:30 pm
 = 13.5)<br>PairID is the identification number of a pair of
 grasshoppers of same age and sex, kept in the same cage and phenotyped
 together, one assigned to the treatment group and the other to the control
 group.