Dr. Andrew Roberts -- Ohio State University -- Deptartment of EEOB

Sensory Ecology of an Animal Communication Network

This project (funded by the National Science Foundation) has been a collaborative effort between myself, Dr. George Uetz at the University of Cincinnati, and Dr. David Clark at Alma College. While the proposed work is now in the final stages of analysis, a number of interesting avenues for future research have developed based on these experiments. Students interested in this, or other projects discussed in the links below, should contact me directly (Home).

While most animal communication is evaluated in terms of dyadic sender/receiver interactions, signals are often broadcast widely such that they may become “public” information. Signals can be intercepted not only by potential mates, but also by individuals for whom the signal is not intended such as predators or rivals. In order to understand the potential impact eavesdropping individuals might have in a signaling system, it is necessary to explore properties of the signals being used for communication, how environmental factors may influence signal transmission, and the perceptive abilities of all potential receivers, both intended and unintended, of a given signal.

We have been using an invertebrate model system, the brush-legged wolf spider, Schizocosa ocreata, for empirical testing of hypotheses concerning the efficacy of signal transmission in the environment and costs from natural selection (due to increased predation risk and lost mating opportunities to competitors) associated with signaling traits. In S. ocreata, females elicit male courtship with chemical cues and choose males based on signaling characteristics such as size/symmetry of secondary sexual traits (leg tufts) and rates or duration of courtship behaviors (including leg waving/tapping and vibratory sound production). These spiders live within the complex leaf litter habitat of deciduous forests of eastern North America and are sympatric with a relatively high density of conspecifics (members of the same species) and many vertebrate and invertebrate predators with the potential to intercept signals and impact survival and/or mating success.

The Active Space of Male Courtship Signals:

Pictures of male and female wolf spiders and leaf litter habitat -- More photos can be found in the 'media' section of the site

The efficacy of signal transmission represents a complex interaction between characteristics of the signal itself (e.g. color/size of visual signals, amplitude of vibrations) and signal modifying properties of the environment (e.g. humidity, complexity). In order to evaluate the degree to which receivers might intercept courtship signals, the potential for signal detection must be determined by analyzing environmental and signal characteristics. The first portion of the grant involved ecological and behavioral measurements to determine the potential for signal transmission, perception, and interception. The following were the major objectives: 1) measure environmental complexity and microhabitat – temperature, humidity, leaf litter composition and complexity, and illumination at the forest floor; 2) determine the active space of visual signals – measure visual spectrum of light at the forest floor, variation in background contrast of spiders and surrounding leaf litter, and average distance to obstruction of visual signals; and 3) determine the active space of vibratory signals – attenuation-distance profiles or average distance to total attenuation of seismic signals, detection threshold of spiders, and seismic vibration transmission properties of the environment.

Taylor PW, Roberts JA, & Uetz GW. (2006) Mating in the absence of visual cues by Schizocosa ocreata (Hentz 1844) wolf spiders (Araneae, Lycosidae). Journal of Arachnology, 34(3): 501-505.

Roberts JA, Galbraith E, Milliser J, Taylor PW, & Uetz GW. (2006) Absence of social facilitation of courtship in the wolf spider, Schizocosa ocreata (Hentz) (Araneae: Lycosidae). Acta Ethologica, 9: 71-77.

Unintended Receivers – Consequences of Complex Display:

American toad attacking a virtual spider -- More photos can be found in the 'media' section of the site

Unintended receivers of courtship signals may fall into one of two categories: 1) eavesdroppers (e.g. competitors/rivals) which can potentially exploit the information content of intercepted signals; and 2) cue-readers (e.g. predators) for which the information content of the signal is unimportant but the signal itself reveals the presence of potential prey. We have used digital manipulation and video/seismic playback studies to evaluate the potential impact of vertebrate (American toads) and invertebrate (jumping spiders, other wolf spiders) predation pressure on isolated (and combined) display traits of male S. ocreata. Risk of predation increases with elaboration of a secondary sexual characteristic (leg tufts), and when predators are exposed to multi-modal cues (referring to cues produced in more than one signaling mode simultaneously such as visual and seismic combined). These studies have been expanded to include: 1) video/seismic playback studies of predator response at natural levels of background contrast and signal to noise ratios; and 2) field and laboratory experimentation to determine whether competing males eavesdrop on the courtship behavior of other males to locate and intercept potential mates.

Roberts JA & Uetz GW. (2008) Discrimination of Variation in a Male Signaling Trait Affects Detection Time in Visual Predators. Ethology, 144(6): 557-563.

Roberts JA, Taylor PW, & Uetz GW. (2007) Consequences of complex signaling: Predator detection of multimodal cues. Behavioral Ecology, 18: 236-240

Research Home

The active space of female chemical signals

Impact of El Niño on Group Formation

Cognitive Ecology of Mate Choice