Faux frogs, foam nests, and females: Mate choice as an evolutionary driver of conspicuous mating signals

Abstract

Chapter 1 - Across many taxa, males gather in leks to perform multisensory courtship displays for females. Changes in the sensory scene over the course of mate evaluation are inevitable during a lek. This dynamic nature makes a female’s ability to recall the location of individual signalers an important component of female mate choice. It is hypothesized that complex (especially multimodal) signals may improve a female’s ability to remember, and thus discriminate among potential mates. To test this hypothesis, we employed robotic frogs and a blinding system in playbacks with female túngara frogs (Physalaemus (=Engystomops) pustulosus). Specifically, we asked if the visual component of a multimodal signal improves a female’s ability to remember the location of a signaler. Females’ memory for a multimodal signal was examined after an initial presentation period followed by a holding period and/or silent period. Females were only able to remember a signaler’s location after the introduction of a silent period. They were still able to remember even after a combined 25 s after the obstruction of the visual stimulus (robotic frog). Silence is common in choruses and our data suggest that memory instantiation for multisensory stimuli occurs as a result of this silence.

Chapter 2 - Vision can play a vital role in a receiver’s response to a signal. Often used in tandem with other sensory stimuli, vision is commonly used as a modality for signaling to potential mates. In nocturnal species, however, the neural processing of an image with a limited light source may degrade the resolution and/or details of that scene and the signalers within it. Túngara frogs (Physalaemus (=Engystomops) pustulosus) are a Neotropical species that perform nocturnal multimodal courtship displays (visual, acoustic, and seismic) to attract females. Females have been shown to have a consistent preference for a multimodal display in laboratory settings at a fixed distance. Here, we tested how the distance between a female and a displaying “male” (robotic frog and speaker) influenced the decisions of female túngara frogs. We compared the response of females to a robotic frog at three distances (80 cm, 90 cm, and 110 cm) from the release point of females. At the established 80 cm distance, females significantly chose the multimodal speaker over the unimodal, but this preference vanished at 90 and 110 cm. These data suggest that female túngara frogs are unable to recognize the visual stimulus of a male’s multimodal display as it becomes more distant. This is consistent with observations of natural pairings wherein females sample and choose males at close distances. We suggest that female túngara frogs efficiently integrate visual stimuli in nocturnal conditions, but their distance to a stimulus limits this ability.

Chapter 3 - Anurans exhibit extreme diversity in their reproductive strategies. During fertilization, species from several lineages produce foam nests that buffer developing embryos to their external environment. There have been many proposed functions for the production of these nests, but one function that has received little attention is how foam nests may act as an environmental cue to influence female mating decisions. In the túngara frog (Physalaemus (=Engystomops) pustulosus), males commonly call near foam nests when they are displaying for females. Previously, it was demonstrated that females of this species prefer a male call when it is associated with a real, field-collected nest (Martin et al. 2011). Amplexed pairs also often form communal nests, and it has been hypothesized that foam nests may act as a cue for an ideal oviposition site to amplectant females. Here, we tested the preferences of females using both real and faux, 3D printed foam nests in various treatment conditions. We were unable to find any evidence that females respond to the visual stimulus of foam nests during mate evaluation or that foam nests act as a possible cue for an oviposition site. We did, however, show that females had identical responses to the faux and real foam nests. Our results demonstrate that even in a well-studied organism like túngara frogs, we still have much to learn about their fundamental ecology.

Chapter 4 - In this natural history note, we describe the first observation of a terrestrial vertebrate predator for the foam nests of túngara frogs (Physalaemus (=Engystomops) pustulosus) in the rainforest of Soberanía National Park, Panamá. The snake species we observed feeding on the eggs within the nest was documented as a juvenile Erythrolamprus (=Liophis) epinephelus and this is also the first account of oophagy for this species.