DOI: 10.5061/dryad.7wm37pvr5
title: Eavesdropping micropredators as dynamic limiters of sexual signal elaboration and intrasexual competition

description: To thoroughly understand the drivers of dynamic signal elaboration
 requires assessing the direct and indirect effects of naturally
 interacting factors. Here, we use structural equation modeling (SEM) to
 test multivariate data from in situ observations of sexual signal
 production against a model of causal processes hypothesized to drive
 signal elaboration. We assess direct and indirect effects, and relative
 impacts, of male-male competition and attacks by eavesdropping frog-biting
 midges (Diptera: Corethrellidae) on call elaboration of male túngara frogs
 (Engystomops pustulosus). We find that the intensity of attacks by these
 micropredator flies drives the extent to which frogs elaborate their
 calls, likely due to a temporal trade-off between signaling and
 anti-micropredator defense. Micropredator attacks appear to dynamically
 limit a male’s call rate and complexity and consequently dampen the
 effects of intrasexual competition. In accounting for naturally
 interacting drivers of signal elaboration, this study presents a
 counterpoint to the mechanisms traditionally thought to drive sexual
 selection in this system. Moreover, the results shed light on the
 relatively unexamined and potentially influential role of eavesdropping
 micropredators in the evolution of sexual communication systems.
description: In Gamboa, Panamá, during the summers of 2010 and 2012, we
 observed calling male túngara frogs (<i>Engystomops
 pustulosus</i>) <i>in situ</i>. For each observation,
 which took place between 1900 and 2300 h, we illuminated a calling male
 (hereafter, ‘focal frog’) with infrared LED arrays (Sima SL-201R) and
 recorded audio and video using a Sony DCR-SR220D 120GB Handycam
 Camcorder. Following an observation, the focal frog was toe-clipped to
 prevent pseudoreplication and released at point of capture in adherence to
 protocols established by the American Society of Ichthyologists and
 Herpetologists (https://asih.org/animal-care-guidelines). We conducted all
 research in compliance with Panamanian legal and ethical regulations
 (MiAmbiente collection permits: SE/A-67-10, SC/A-20-12) and following
 IACUC protocols (Texas Tech University: 11056-08; Smithsonian Tropical
 Research Institute: 2011-0616-2014-11). See "Methods" in
 manuscript for more details. To analyze calling
 behaviors, we selected a sequence of the first 50 clean, consecutive
 calls, per focal frog. We used the duration of the sequence, which varied
 per frog, to derive the call rate—i.e. the total number of calls, minus
 one, divided by the time from the beginning of the first call to the
 beginning of the last call. The total number of chucks produced was
 counted over the same time. To assess the threat of frog-biting midge
 (Diptera: Corethrellidae) attacks, the total number of instances in which
 midges landed on the focal frog were counted from video playback during
 the 50-call sequence. We also counted the total number of times the focal
 frog swatted during the same sequence. Out of a total of 100 focal frogs
 that were recorded, we omitted data from fifteen individuals due to high
 background noise levels or poor video quality that precluded behavioral
 analysis. The observed dataset thus includes data from a total of 85
 males.
description: Part of the analysis uses code from: Zuur AF,
 Ieno EN, Walker N, et al (2009) Mixed effects models and extensions in
 ecology with R. Springer New York, New York, NY  It is
 available online at:
 https://highstat.com/Books/BGS/GAMM/RCodeP2/HighstatLibV6.R