Multimodal signals, imperfect information, and identification of sex in red-backed salamanders (Plethodon cinereus)

As discussed in class and in the text, design rules for mate attraction suggest that courtship signals should have a large range, high locatability, and a high duty cycle, among other characteristics. Chemical signals should involve contact chemicals, and locatability can be improved by the addition of a visual signal, while identification is enhanced by sex-specific signals. Additionally, male mating strategies can be expected to vary depending on the defensibility of females and resources.

Page and Jaeger (2004) examined the role that multimodal signals play in sexual discrimination by red-backed salamanders. Previous research has suggested that multimodal signals should be easier to detect, remember, and discriminate than unimodal signals. Red-backed salamanders are believed to maintain territories for courtship, mating, and egg deposition, as well as to defend food resources. Territories are defended via body postures and chemical signals; the information content of chemical signals and the discrimination abilities of the salamanders are incompletely understood.

The authors performed two laboratory experiments. In the first experiment, males were allowed to acclimate to a chamber and were then presented with male or female “intruders” treated with secretions from the opposite sex (i.e., both olfactory and visual signals were present). In the second experiment, males were presented with swabs of male and female secretions (i.e., only olfactory signals were present). Measured behavioral response variables included time spent in threat posture, time spent moving around the periphery of the chamber (as though trying to escape), number of nose taps (a chemoreception behavior), time spent touching the stimulus, and number of bites by the resident to the stimulus.

In experiment 1, residents did not differ significantly in their behavior toward any category of stimulus; however, before a Bonferroni correction, time spent touching the stimulus and time spent in threat posture differed in response to both males and females in comparison with the control. In experiment 2, the only significant difference was time spent in threat posture in response to both male swabs compared to the control and male swabs compared to female swabs. Biting occurred too infrequently across both experiments to allow for a statistical evaluation. In comparing the two experiments, significant differences in time spent touching the stimulus were reported for female versus female secretions, treated female versus a combination of male and female secretions, and treated male versus a combination of male and female secretions. In sum, the authors suggested increased aggressive behavior of territorial males toward consexual stimuli, regardless of sensory modality, and more time spent bimodal than unimodal stimuli; however, their low statistical support and some problems with independence of data left me not completely convinced of the validity of their biological conclusions.

Page RB, Jaeger RG. Multimodal signals, imperfect information, and identification of sex in red-backed salamanders (Plethodon cinereus). Behavioral Ecology and Sociobiology (2004) 56:132-139.