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Female mate choice decisions are often based on a variety of male characteristics, some of which may reflect male quality via condition-dependent trait expression. Here, we explore the condition dependence of a male secondary sexual trait in a wolf spider and examine its influence on female mate choice. In the wolf spider Schizocosa uetzi, mature males possess a multimodal courtship display (visual + seismic) in which they slowly raise and lower their dark colored forelegs. Foreleg color is highly variable among S. uetzi males with respect to both total amount and darkness. Using diet manipulations in conjunction with color quantifications, we demonstrate condition-dependent foreleg color. High-nutrient diet males had significantly higher body condition indices and possessed more and darker foreleg color than low-nutrient diet males. However, using multiple mate choice designs, we were unable to demonstrate a female preference for male foreleg color. Using both single and 2-choice mating designs as well as using females from a range of ages, we found that copulation success was consistently independent of male foreleg color. Instead, we found courtship intensity to be the only aspect of male courtship that influenced copulation success-males that copulated displayed more leg raises per second than those that did not copulate.

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Summary Jumping spiders (Salticidae) are famous for their visually driven behaviors [1]. Here, however, we present behavioral and neurophysiological evidence that these animals also perceive and respond to airborne acoustic stimuli, even when the distance between the animal and the sound source is relatively large (~3 m) and with stimulus amplitudes at the position of the spider of ~65 dB SPL. Behavioral experiments with the jumping spider Phidippus audax reveal that these animals respond to low frequency sounds (80 Hz; 65 dB SPL) by freezing—a common anti-predatory behavior characteristic of an acoustic startle response. Neurophysiological recordings from auditory-sensitive neural units in the brains of these jumping spiders showed responses to low-frequency tones (80 Hz at ~65 dB SPL); recordings that also represent the first record of acoustically-responsive neural units in the jumping spider brain. Responses persisted even when the distances between spider and stimulus source exceeded 3 m and under anechoic conditions. Thus, these spiders appear able to detect airborne sound at distances in the acoustic far-field region, beyond the near-field range often thought to bound acoustic perception in arthropods that lack tympanic ears (e.g. spiders) [2]. Further, direct mechanical stimulation of hairs on the patella of the foreleg was sufficient to generate responses in neural units that also responded to airborne acoustic stimuli—evidence that these hairs likely play a role in the detection of acoustic cues. We suggest that these auditory responses enable the detection of predators and facilitate an acoustic startle response.