Seasonal variation in sexual behavior and web aggregation in a little-known long-jawed spider (Tetragnatha straminea) (Araneae: Tetragnathidae)

Abstract

General insights in sexual selection can be enhanced by the addition of data from under-studied species. Understanding the natural history of these species is acritical first step. Here, we report detailed field observations of Tetragnatha straminea Emerton, 1884, a long-jawed orb weaver common in riparian meadows. Relatively little is known about this spider, in which the elongate chelicerae of males lock with those of females during copulation. We assessed courtship, mate-guarding, intrasexual competition and predictors of female receptivity to mating. As inter-sexual fang-lock is critical to successful mating, we also examined male and female cheliceral allometry. Finally, we observed patterns of aggregative clustering during peak-mating periods, as this may indicate elevated levels of intra-sexual aggression. Overall, females were polyandrous, and it was not possible to predict female receptivity based on the number of males present or female aggressive behavior towards males. Courtship was not evident prior to mating attempts, although some males remained in close proximity to females for extended periods. Towards the middle-to-end of the mating season, multiple females would aggregate in clusters, where elevated intra-sexual aggression and frequent copulations occurred. Our observations suggested that fang-lock clasping may be important in intra-sexual agonistic interactions as well as mating, particularly during mid-season web aggregations. Consistent with this, morphological data suggest a trend towards larger chelicerae in males rather than females. Tetragnatha straminea may be ideal for testing hypotheses regarding effects of seasonal variation in sexual selection, and the evolution of structures that serve more than one sexually-selected function.