DOI: 10.5061/dryad.k0p2ngfcx
title: Data for: Juvenile leg autotomy predicts adult male morph in a New Zealand harvestman with weapon polymorphism

description: Intraspecific weapon polymorphisms that arise via conditional thresholds
 may be affected by juvenile experiences such as predator encounters, yet
 this idea has rarely been tested. The New Zealand harvestman
 Forsteropsalis pureora has three male morphs: majors (alphas and betas)
 are large-bodied with large chelicerae used in male-male contests, while
 minors (gammas) are small-bodied with small chelicerae and scramble to
 find mates. Individuals use leg autotomy to escape predators and there is
 no regeneration of the missing leg. Here, we tested whether juvenile
 experience affects adult morph using leg autotomy scars as a proxy of
 predator encounters. Juvenile males that lost at least one leg (with
 either locomotory or sensory function) had a 45 times higher probability
 of becoming a minor morph at adulthood than intact juvenile males. Leg
 loss during development may affect foraging, locomotion, and/or
 physiology, potentially linking a juvenile’s predator encounters to their
 final adult morph and future reproductive tactic.
description: Adult males (N = 86) of
 <em>F. pureora</em> were collected between Waitomo and Te
 Anga, New Zealand, across four sites: Ruakuri Bushwalk, Waitomo
 (38°15'53.7"S 175°04'46.4"E); private land, Te Anga
 (38°15'41.4"S 175°00'53.6"E); Tawarau Forest, Te Anga
 (38°17'24.8"S 174°56'50.2"E); and Marokopa Falls
 Track, Te Anga (38°15'33.6"S 174°50'54.6"E).
 Individuals were hand collected between 21:00 and 02:00 hours in January
 and February 2018.  Sexual maturity was confirmed by the presence of
 a functional genital operculum, which is fused during the juvenile stage
 but can be opened upon the adult moult (Gnaspini 2007). Following Powell
 et al. (2020), we assigned each male to either major morph (alphas and
 betas, <em>N</em> = 63) or minor morph (gamma,
 <em>N</em> = 23). Morph frequency in our sample, with about
 75% of majors and 25% of minors, closely followed that of the larger
 sample in Powell et al. (2020). Males were randomly collected, but it is
 possible that fewer minors were located because they were moving
 cryptically on the forest floor rather than resting on top of vegetation,
 as occurs with majors. We did not consider alphas and betas separately
 because, according to our hypothesis, both morphs probably had access to a
 greater amount of food resources during development. Moreover, Painting et
 al. (2015) hypothesized that trimorphism in New Zealand neopilionids
 arises via both a genetic polymorphism (which promotes the existence of
 two major morphs) and polyphenism (which promotes the existence of majors
 and minors via environmental conditions during development). Therefore,
 because leg loss during development should act exclusively on the
 polyphenic mechanism, our data considers specifically the dichotomy
 between majors and minors. To determine
 the “age” of autotomy, we inspected the remaining trochanter and coxa of
 the specimens that had experienced autotomy. Because harvestmen do not
 regenerate legs, scars remain at the location of legs lost across the
 individual’s life, even if the leg was autotomised early on in
 development. Thus, it is possible to tell if legs were autotomised prior
 to or after the last moult to adulthood (R. Macías-Ordóñez, personal
 communication). Fresh scars representing autotomy <em>during
 adulthood</em> were characterised by a fully intact trochanter. If
 autotomy occurred <em>before adulthood</em>, the trochanter
 was reduced or even absent, with a sclerotised patch of cuticle over the
 location where the trochanter joint used to be. Further, this patch of
 cuticle sometimes had associated setae and in some specimens the coxa
 joint of the missing leg was highly reduced and compressed by the coxa of
 the intact legs, making it clear that legs were autotomized at least one
 moult before adulthood (E. C. Powell, personal observation). For the 50
 individuals that experienced <em>any</em> autotomy, we
 classified scars as <em>recent</em>, if they occurred during
 adulthood, or <em>old</em>, if they occurred during
 development, i.e., as a juvenile at least one moult before
 adulthood. To test whether leg loss (yes or no) during
 development correlates with adult male morph, we generated a generalised
 linear model (GLM) with a binomial response variable (logit link function)
 describing male morph identity: small-bodied minor morph (gamma) and
 large-bodied major morphs (alpha and beta). We did not include the number
 of missing legs in the model because only two males in our sample had more
 than one juvenile autotomy (see ‘Results’). We also tested whether the
 type of leg autotomized during development affects adult male morph
 (response variable) using a GLM with binomial distribution (logit link
 function). We used leg type as a predictor because, as mentioned above,
 legs serve different functions in harvestmen. The predictor variable ‘leg
 type’ was divided into two levels: (a) locomotory legs, which includes
 legs III and IV, and (b) sensory legs, which includes legs II (Willemart
 et al. 2009). Legs I are used both as a locomotory and a sensory appendage
 (Willemart et al. 2009). Thus, to test the sensitivity of our results to
 the classification of legs I, we ran two separate GLMs, first classifying
 them as a locomotory and then as a sensory leg. As mentioned above, only
 two males had more than one juvenile autotomized leg in our sample, and
 thus it was not possible to include male identity as a random factor in
 the analyses. To avoid recording the multiple autotomies of these two
 males as independent points, we removed them from the analyses. All
 statistical analyses were performed in the software R (R Core Team
 2020).
description: The .csv file can be opened with Microsoft Excel, Notepad, OpenOffice Calc, among
 other programs.