Samantha Vibert, visiting PhD student (SFU)

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My undergraduate studies took place in Lyon, France and Geneva, Switzerland and I obtained a MSc in Geneva, studying spatial orientation under the supervision of Dr. Ariane Etienne.

My current research interests are animal behaviour and communication. I am in the process of completing my PhD thesis at Simon Fraser University in Vancouver, in the lab of Dr. Gerhard Gries, where I am studying the courtship behaviour and signalling of two fascinating spider species: the western black widow spider Latrodectus hesperus  and the hobo spider Eratigena agrestis. As is well known, spiders use their webs to detect and capture prey. However, the web is also a dance floor on which males sing and dance to females. Female spiders are very good at detecting prey vibrations and will immediately and aggressively respond to them. Male spiders are therefore at risk of being eaten when they court females. I started this project by observing and describing the complex and multi-modal courtship behaviour of my two study species. This initial work led me to ask several research questions.

First, spiders are one of the few animals to create the medium through which signalling takes place. But is there a good match between the transmission properties of the medium (the web) and the signals being propagated through it (prey or male vibrations)? So far this issue has been investigated only in orb weavers. My two research species spin tangle webs (black widow) and sheet webs (hobo spider). Using a laser Doppler vibrometer, I studied the transmission properties of these webs. Surprisingly, my main finding is that the transmission properties of these webs are extremely variable,

producing frequency transmission profiles that vary substantially even within webs. This suggests  spiders likely use other signal variables such as overall amplitude, amplitude changes over time, or duration of a vibration to identify the source of vibrations.

Second,  how do male spiders signal to females that they are not a prey item? Even though female spiders are often aggressive during courtship, they react very differently to the introduction of a male or of a prey onto their web, only immediately attacking the latter. I first recorded the courtship dance of male spiders and then the vibrations produced by two types of prey (crickets and house flies). Male vibrations were on average longer and quieter. In a follow-up experiment I asked whether amplitude alone accounted for females’s different response to males and prey. Indeed, during play-back trials, females attacked loud vibrations but ignored low amplitude ones.

Finally, though vibrations play such an important role for spiders, chemical signalling is an important and often overlooked aspect of spider communication. Courting males continuously deposit silk on the web and on the body of females. My observations indicate that male silk carries a chemical signal. The courtship is therefore multi-modal, involving vibratory and chemical modalities. Are these two modalities redundant, one serving as back-up for the other, or is each serving a distinct function? I conducted an experiment to answer this question, and found that vibrations correlated well with mating success and courtship duration, while presence of silk was correlated with female aggression.