Sister species diverge in modality-specific courtship signal form and function

Understanding the relative importance of different sources of selection (e.g., the environment, social/sexual selection) on the divergence or convergence of reproductive communication can shed light on the origin, maintenance, or even disappearance of species boundaries. Using a multistep approach, we tested the hypothesis that two presumed sister species of wolf spider with overlapping ranges and microhabitat use, yet differing degrees of sexual dimorphism, have diverged in their reliance on modality- specific courtship signaling. We predicted that male Schizocosa crassipalpata (no ornamentation) rely predominantly on diet-dependent vibratory signaling for mating success. In contrast, we predicted that male S. bilineata (black foreleg brushes) rely on diet-dependent visual signaling. We first tested and corroborated the sister-species relationship between S. crassipalpata and S. bilineata using phylogenomic scale data. Next, we tested for species-specific, diet-dependent vibratory and visual signaling by manipulating subadult diet and subsequently quantifying adult morphology and mature male courtship signals. As predicted, vibratory signal form was diet-dependent in S. crassipalpata, while visual ornamentation (brush area) was diet-dependent in S. bilineata. We then compared the species-specific reliance on vibratory and visual signaling by recording mating across artificially manipulated signaling environments (presence/absence of each modality in a 2 × 2 full factorial design). In accordance with our diet dependence results for S. crassipalpata, the presence of vibratory signaling was important for mating success. In contrast, the light and vibratory environment interacted to influence mating success in S. bilineata, with vibratory signaling being important only in the absence of light. We found no differences in overall activity patterns. Given that these species overlap in much of their range and microhabitat use, we suggest that competition for signaling space may have led to the divergence and differential use of sensory modalities between these sister species

Incidence of parasitoids and predators on eggs of seven species of Therididae (Araneae)

Although many characteristics of the egg sacs of spiders likely evolved to reduce the effect of parasites and predators that attack their eggs, many parasite and predator insects have become specialized on spider eggs. Eggs of six of the seven species of Theridiidae included in this study were attacked by wasp parasites (Baeus achaearaneus, Idris sp., and Comastichus zopheros), and two by the specialized spider egg predator (Neuroptera: Zeugomantispa minuta). The incidence of parasites in the egg sacs varied across species. Parasites attacked more than 60% of the egg sacs of Tidarren sisyphoides and Parasteatoda tepidariorum, but none of the sacs of Latrodectus geometricus. The incidence of parasites in the egg sacs was higher during the dry season for T. sisyphoides, and during the rainy season for P. tepidariorum. The proportion of the eggs parasitized per egg sac varied from 0.09 (± 0.19) in Nesticodes rufipes to 0.50 (± 0.46) in T. sisyphoides. Differences in the biology of parasites, as well as in the structure of spider webs and hábitat preference of spiders, may influence the incidence of parasitism and proportion of eggs parasitized in each egg sac.Vicerrectoría de InvestigaciónUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Behavior of rigid macromolecules in self‐assembly at an interface

Self‐assembly (SA) on gold substrates of α‐helical poly(γ‐benzyl‐L‐glutamate) [(PBLG); molecular weight ∼20 000 kd] with a disulfide moiety attached at its N‐terminus (PBLGSS) was investigated. The SA films were compared with control experiments using unlabeled physisorbed (PS) PBLG and Langmuir–Blodgett (LB) deposited PBLG monolayers. Characterization of the films included angle‐dependent x‐ray photoelectron spectroscopy, reflection–absorption Fourier transform infrared spectroscopy, ellipsometry, and contact angle measurements. For PBLGSS, a SA monolayer was formed wherein the α‐helical conformation was retained and the polypeptides were preferentially bound to gold through the disulfide moiety. This terminal bond to the substrate results in a nonplanar distribution of helix axes (i.e., on average tilted up from the gold surface). This is different from the unlabeled PBLG controls, PS film and LB monolayers, wherein, respectively, less polymer was adsorbed and the helices lie in the plane of the gold substrate. Furthermore, polypeptide aggregation in the solution (e.g., in dichloromethane or 1,4‐dioxane) appears to have an influence on the self‐assembling behavior of these macromolecules relative to known nonaggregating solvents (N,N‐dimethylformamide)