Function of structured signalling in the black widow spider Latrodectus hesperus

Mating behaviour influences the direction and geographic extent of introgression in New Zealand fishing spiders (Dolomedes)

Introgression is a highly influential process in evolution, where genes flow between species that are not fully reproductively isolated. Studies on introgression often focus on describing gene transfer and environmental changes that facilitate the meeting of species. However, the impact of mating systems and behaviour that facilitate gene transfer is less well-known. Dolomedes aquaticus and D. minor are sister species of fishing spiders undergoing one-way, geographically limited mitochondrial introgression, making them an excellent case study for the factors that promote and limit introgression. We used a combination of field observations and crossing experiments to systematically investigate potential prefertilization barriers that could limit introgression and explain the one-way and geographic barriers to introgression in these species. We found that habitat overlap and timing of reproductive maturity were not likely to be important limiting factors to introgression. However, behaviour was an important factor, with male mate choice being implicated in the geographic limitation, and female mate choice being implicated in the one-way limitation. Our results show the importance of using behavioural approaches in the investigation of introgression.

Does female control and male mating system predict courtship investment and mating outcomes? A comparative study in five widow spider species (genus Latrodectus) tested under similar laboratory conditions

BACKGROUND

Male courtship investment may evolve in response to the male's expectation of future mating opportunities or the degree of female control during mating interactions. We used a comparative approach to test this hypotheses by assessing the courtship and mating behaviors of five widow spider species (genus Latrodectus) under common laboratory conditions. We predicted male investment in courtship would be higher in species where males mate only once because of high cannibalism rates (monogyny, L. geometricus, L. hasselti, L. mirabilis), compared to species with rare cannibalism (L. mactans, L. hesperus) in which males should reserve energy for future mating opportunities. Increased male investment, measured as courtship duration, might also evolve with increased female control over mating outcomes if females prefer longer courtships. We tested this by assessing the frequency of copulations, timing of sexual cannibalism, and the degree of female-biased size dimorphism, which is expected to be negatively correlated with the energetic cost of rebuffing male mating attempts.

RESULTS

Copulation frequency was consistently lower in species with extreme female-skewed size dimorphism, and where sexual cannibalism was more prevalent, suggesting the importance of female control for mating outcomes. We confirmed significant interspecific variation in average courtship duration, but contrary to predictions, it was not predicted by male mating system, and there was no consistent link between courtship duration and sexual size dimorphism.

CONCLUSION

We show that the degree of sexual dimorphism is not only correlated with sexual cannibalism, but also with mating success since restriction of male copulation frequency by female Latrodectus affects paternity. However, predictions about male mating system or female control affecting courtship duration were not supported. We propose that the form of female control over mating and cannibalism, and male responses, might be more informative for understanding the evolution of courtship duration. For example, male tactics to avoid female aggression may drive lower courtship duration in species like L. mirabilis. Nonetheless, our results differ from inferences based on published studies of each species in isolation, illuminating the need for standardized data collection for behavioural comparative studies.

Validation of a Novel Stereo Vibrometry Technique for Spiderweb Signal Analysis

From courtship rituals, to prey identification, to displays of rivalry, a spider's web vibrates with a symphony of information. Examining the modality of information being transmitted and how spiders interact with this information could lead to new understanding how spiders perceive the world around them through their webs, and new biological and engineering techniques that leverage this understanding. Spiders interact with their webs through a variety of body motions, including abdominal tremors, bounces, and limb jerks along threads of the web. These signals often create a large enough visual signature that the web vibrations can be analyzed using video vibrometry on high-speed video of the communication exchange. Using video vibrometry to examine these signals has numerous benefits over the conventional method of laser vibrometry, such as the ability to analyze three-dimensional vibrations and the ability to take measurements from anywhere in the web, including directly from the body of the spider itself. In this study, we developed a method of three-dimensional vibration analysis that combines video vibrometry with stereo vision, and verified this method against laser vibrometry on a black widow spiderweb that was experiencing rivalry signals from two female spiders.