Seismic sexual signal design of two sympatric burrowing tarantula spiders from meadows of uruguay: Eupalaestrus weijenberghi and Acanthoscurria suina (Araneae, Theraphosidae)

Eupalestrus weijenberghi (Thorell 1894) and Acanthoscurria suina Pocock 1903 are two fossorial, sympatric, synchronic, and similar-sized species of tarantulas that inhabit the meadows of Uruguay. Both species use seismic signals for communicating during courtship (body vibrations in males, leg tapping in females), but little is known either about temporal and spectral signal characteristics or effective signal range. Males were elicited to court (body vibrations) by exposing them to sexual pheromones in one end of a terrarium, whereas females were successively placed in burrows at different distances from the courting male. Seismic male signals were registered by using a geophone placed near the females. We found that E. weijenberghi male signals reach at least 135.75 cm, whereas A. suina signals reach at least 110.5 cm. There was no correlation between latency of female response and distances at which the male was courting for either of the spider species. For A. suina, a bout of vibration was characterized by two syllables (tucks), followed by a series of syllables (buzz 1 and buzz 2). Eupalestrus weijenberghi males show several tucks, followed by buzz 1 and buzz 2. Differences in sexual signals (length of syllables and number of tucks) are assumed to maintain the reproductive isolation between these similar sized, sympatric and synchronic species. Similarities are seen in adaptations to the same environment, allowing effective rates of sexual communication at long distances.