Frequent misdirected courtship in a natural community of colorful Habronattus jumping spiders

Spatial Overlap and Behavioral Interactions Among Four Habronattus Jumping Spider Species in a Mixed-Species Assemblage

Within mixed-species assemblages, closely related species may face interspecific competition and reproductive interference. Species may evolve adaptations to outcompete or coexist, though most assemblages likely exist in a nonequilibrium state between the two extremes. Understanding the dynamics between potentially syntopic species requires careful studies conducted at a fine spatial resolution, an especially important consideration for small invertebrate animals. We characterized interspecific interactions within a mixed-species assemblage consisting of four species of Habronattus jumping spiders, a genus that can be found in syntopic assemblages where males are known to indiscriminately court conspecific and heterospecific females alike. Through detailed focal observations, we evaluated how species overlap in their spatial occurrence, temporal occurrence, light environment, movement level, and behavioral interactions, including courtship. We assessed whether the observed heterospecific interactions occurred more frequently than random chance by comparing the observed data to network reference models. Our findings revealed interspecific overlaps across all evaluated variables, which may indicate shared environmental requirements amongst the species and potential interspecific competition and interference. However, there was a notable temporal shift between H. calcaratus and H. coecatus. H. decorus showed some divergence in spatial occurrence and light environment that may be a phylogenetic signal or potentially associated with its distinct courtship display. Additionally, we observed sex differences in movement levels across all species that could represent a selection for male "scramble competition" strategy. Lastly, heterospecific behavioral interactions, including courtship, were frequently observed but occurred less often than random chance, as represented by network reference models. Altogether, our findings suggest that individuals in this assemblage are engaged in some level of interspecific competition and reproductive interference, but there may be mechanisms to mitigate these pressures. This study establishes an ecological foundation to investigate possible adaptive responses in this assemblage, such as reproductive character displacement and sensory drive.

Males discriminate between substrate-borne cues of conspecific females based on age and mating status in the jumping spider, Habronattus brunneus

Sexual selection is often studied with a focus on female mate choice, wherein females evaluate male signals to select an optimal mate. However, in some systems, males should also make careful decisions about the females they choose to court, particularly when faced with the risk of precopulatory sexual cannibalism. Here, we explore the idea that male jumping spiders (Habronattus brunneus) may mitigate this risk by responding to female cues probably associated with female aggression and/or receptivity. We tested mature male spiders' ability to discriminate between substrate-borne cues (i.e. silk and excreta) produced by conspecific females of different ages and mating statuses. We found that males spent more time exploring cues produced by mature, non-mated females compared with either immature females or mated females. Heightened interest in cues produced by females that are sexually mature but not yet mated may allow males to reduce cannibalism risk, reduce wasted courtship effort and increase their reproductive success. The use of chemical and/or tactile cues in jumping spider courtship behaviour has been vastly understudied compared with the ways they use vision; this study provides the groundwork for understanding how these sensory modalities interact.

Hybridization despite elaborate courtship behavior and female choice in Neotropical tree frogs

The mechanisms of hybridization can be elucidated by analyzing genotypes as well as phenotypes that could act as premating barriers, as the reproductive interactions among heterospecifics can alter the evolutionary history of species. In frogs, hybrids typically occur among species that reproduce explosively (in dense aggregations) with few opportunities for mate selection but are rare in species with elaborate courtship behaviors that may prevent erroneous mating. Using 21 microsatellite markers, we examined hybridization in the prolonged-breeding tree frogs Bokermannohyla ibitiguara and B. sazimai sampled within a contact zone in the Brazilian savanna (72 tadpoles; 74 adults). We also compared acoustic and morphological data. We confirmed both parental species genetically; STRUCTURE results confirmed 14 hybrids, 11 of which were second-generation according to NEWHYBRIDS, all with intermediate values of genetic dissimilarities compared to the parentals. Morphological and acoustic analyses revealed that hybrids showed variable but not necessarily intermediate phenotypes. Moreover, 2 hybrids exhibited call types different from parentals. The reproduction of B. ibitiguara involves territorial and aggressive males, elaborate courtships with acoustic and tactile stimuli, choosy females, and opportunistic strategies. Our study uncovers a rare case of viable hybridization among closely related frogs with such a combination of complex courtship behaviors and mate choice. We discuss the likely directionality and mechanisms behind this phenomenon, and highlight the importance of investigating hybridization even in species that show elaborate reproduction and female choice to advance our understanding of animal diversification.

Male courtship reduces the risk of female aggression in web-building spiders but varies in structure

Male courtship serves multiple functions in addition to inducing females to accept them as a mate. In predatory species, male courtship can function to reduce the risk of sexual cannibalism. This is particularly important in web-building spiders in which males risk being mistaken for prey when they enter the female’s predatory trap—the web—in order to commence courtship. Male spiders generate vibrations by shuddering in the female’s web. Shudder vibrations can delay female aggression, even toward prey struggling in the web. We predicted that shudder vibrations are highly conserved across species of web-building spider as males all face the same constraint of not being mistaken for prey by females. We examined how conserved shudder vibrations are across web-building spiders by testing whether female Trichonephila plumipes delay aggressive behavior toward real prey struggling in the web during playback of conspecific or heterospecific (Argiope keyserlingi) male shudder vibrations. We found that while conspecific shudder vibrations do indeed delay female predatory behavior, heterospecific male shudder vibrations do not. There is evidence of shudder or shudder-like vibrations in male courtship behavior across web-building spider families, but these vary in structure. This suggests that despite strong constraints on courtship signal design to separate predatory responses from sexual responses, there is additional selection driving the divergence of signals across distantly related spider species.

Sexually dimorphic dorsal coloration in a jumping spider: testing a potential case of sex-specific mimicry

To avoid predation, many animals mimic behaviours and/or coloration of dangerous prey. Here we examine potential sex-specific mimicry in the jumping spider Habronattus pyrrithrix. Previous work proposed that males' conspicuous dorsal coloration paired with characteristic leg-waving (i.e. false antennation) imperfectly mimics hymenopteran insects (e.g. wasps and bees), affording protection to males during mate-searching and courtship. By contrast, less active females are cryptic and display less leg-waving. Here we test the hypothesis that sexually dimorphic dorsal colour patterns in H. pyrrithrix are most effective when paired with sex-specific behaviours. We manipulated spider dorsal coloration with makeup to model the opposite sex and exposed them to a larger salticid predator (Phidippus californicus). We predicted that males painted like females should suffer higher predation rates than sham-control males. Likewise, females painted like males should suffer higher predation rates than sham-control females. Contrary to expectations, spiders with male-like coloration were attacked more than those with female-like coloration, regardless of their actual sex. Moreover, males were more likely to be captured, and were captured sooner, than females (regardless of colour pattern). With these unexpected negative results, we discuss alternative functional hypotheses for H. pyrrithrix colours, as well as the evolution of defensive coloration generally.

Evolutionary impacts of introgressive hybridization in a rapidly evolving group of jumping spiders (F. Salticidae, Habronattus americanus group)

Introgressive hybridization can be a powerful force impacting patterns of evolution at multiple taxonomic levels. We aimed to understand how introgression has affected speciation and diversification within a species complex of jumping spiders. The Habronattus americanus subgroup is a recently radiating group of jumping spiders, with species now in contact after hypothesized periods of isolation during glaciation cycles of the Pleistocene. Effects of introgression on genomes and morphology were investigated using phylogenomic and clustering methods using RADseq, ultraconserved elements (UCEs), and morphological data. We characterized 14 unique species/morphs using non-metric multidimensional scaling of morphological data, a majority of which were not recovered as monophyletic in our phylogenomic analyses. Morphological clusters and genetic lineages are highly incongruent, such that geographic region was a greater predictor of phylogenetic relatedness and genomic similarity than species or morph identity. STRUCTURE analyses support this pattern, revealing clusters corresponding to larger geographic regions. A history of rapid radiation in combination with frequent introgression seems to have mostly homogenized the genomes of species in this system, while selective forces maintain distinct male morphologies. GEMMA analyses support this idea by identifying SNPs correlated with distinct male morphologies. Overall, we have uncovered a system at odds with a typical bifurcating evolutionary model, instead supporting one where closely related species evolve together connected through multiple introgression events, creating a reticulate evolutionary history.

Variation in activity rates may explain sex-specific dorsal color patterns in Habronattus jumping spiders

In many animals, color pattern and behavior interact to deceive predators. For mimics, such deception can range from precise (near-perfect mimicry) to only subtle resemblance (imperfect mimicry) and such strategies often differ by sex because of differing ecological selection pressures. In this field study, we examine variation in behavior and ecology that may be linked with sex differences in dorsal color pattern in three sympatric species of Habronattus jumping spiders (H. clypeatus, H. hallani, H. pyrrithrix). Males of these species have conspicuous dorsal patterning that is subtly reminiscent of the general color patterns of wasps and bees, while females are cryptic. We show that, compared with females, these conspicuous males exhibited increased leg-waving behavior outside of the context of courtship; such behavior is common in jumping spiders that mimic wasps and bees presumably because a mimic’s waving legs resemble antennae. Males of a fourth sympatric species (H. hirsutus) without conspicuous dorsal patterning did not exhibit increased leg-waving. These results are consistent with and offer preliminary support for the idea that male color and behavior may work together to deceive predators. We also examined whether higher movement rates of males (who must wander to find females) and/or different use of the microhabitat by the sexes could explain sexual dichromatism. We found that microhabitat use was similar for males and females, but males of all three conspicuously-colored species spent more time actively moving than females. To our knowledge, this is the first study to speculate that conspicuous male dorsal coloration in Habronattus may have a deceptive function, and to explore why dorsal coloration differs between the sexes.