Veni, vidi, vici? Future spread and ecological impacts of a rapidly expanding invasive predator population.

Economic and ecological consequences of invasive species make biological invasions an influential driver of global change. Monitoring the spread and impacts of non-native species is essential, but often difficult, especially during the initial stages of invasion. The Joro spider, Trichonephila clavata (L. Koch, 1878, Araneae: Nephilidae), is a large-bodied orb weaver native to Asia, likely introduced to northern Georgia, U.S. around 2010. We investigated the nascent invasion of T. clavata by constructing species distribution models (SDMs) from crowd-sourced data to compare the climate T. clavata experiences in its native range to its introduced range. We found evidence that the climate of T. clavata's native range differs significantly from its introduced range. Species distribution models trained with observations from its native range predict that the most suitable habitats in North America occur north of its current introduced range. Consistent with SDM predictions, T. clavata appears to be spreading faster to the north than to the south. Lastly, we conducted surveys to investigate potential ecological impacts of T. clavata on the diversity of native orb weaving spiders. Importantly, Trichonephila clavata was the most common and abundant species observed in the survey, and was numerically dominant at half of the sites it was present in. Our models also suggest that there is lower native orb weaver species richness and diversity closer to where T. clavata was initially found and where it has been established the longest, though human population density complicates this finding. This early study is the first to forecast how widely this spider may spread in its introduced range and explore its potential ecological impacts. Our results add evidence that T. clavata is an invasive species and deserves much more ecological scrutiny.

Endosymbiotic Rickettsiella causes cytoplasmic incompatibility in a spider host.

Many arthropod hosts are infected with bacterial endosymbionts that manipulate host reproduction, but few bacterial taxa have been shown to cause such manipulations. Here, we show that a bacterial strain in the genus Rickettsiella causes cytoplasmic incompatibility (CI) between infected and uninfected hosts. We first surveyed the bacterial community of the agricultural spider Mermessus fradeorum (Linyphiidae) using high throughput sequencing and found that individual spiders can be infected with up to five different strains of maternally inherited symbiont from the genera Wolbachia, Rickettsia, and Rickettsiella. The Rickettsiella strain was pervasive, found in all 23 tested spider matrilines. We used antibiotic curing to generate uninfected matrilines that we reciprocally crossed with individuals infected only with Rickettsiella. We found that only 13% of eggs hatched when uninfected females were mated with Rickettsiella-infected males; in contrast, at least 83% of eggs hatched in the other cross types. This is the first documentation of Rickettsiella, or any Gammaproteobacteria, causing CI. We speculate that induction of CI may be much more widespread among maternally inherited bacteria than previously appreciated. Further, our results reinforce the importance of thoroughly characterizing and assessing the inherited microbiome before attributing observed host phenotypes to well-characterized symbionts such as Wolbachia.

Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator.

Generalist predators are capable of selective foraging, but are predicted to feed in close proportion to prey availability to maximize energetic intake especially when overall prey availability is low. By extension, they are also expected to feed in a more frequency-dependent manner during winter compared to the more favourable foraging conditions during spring, summer and fall seasons. For 18 months, we observed the foraging patterns of forest-dwelling wolf spiders from the genus Schizocosa (Araneae: Lycosidae) using PCR-based gut-content analysis and simultaneously monitored the activity densities of two common prey: springtails (Collembola) and flies (Diptera). Rates of prey detection within spider guts relative to rates of prey collected in traps were estimated using Roualdes' cst model and compared using various linear contrasts to make inferences pertaining to seasonal prey selectivity. Results indicated spiders foraged selectively over the course of the study, contrary to predictions derived from optimal foraging theory. Even during winter, with overall low prey densities, the relative rates of predation compared to available prey differed significantly over time and by prey group. Moreover, these spiders appeared to diversify their diets; the least abundant prey group was consistently overrepresented in the diet within a given season. We suggest that foraging in generalist predators is not necessarily restricted to frequency dependency during winter. In fact, foraging motives other than energy maximization, such as a more nutrient-focused strategy, may also be optimal for generalist predators during prey-scarce winters.

Functional value of elytra under various stresses in the red flour beetle, Tribolium castaneum.

Coleoptera (beetles) is a massively successful order of insects, distinguished by their evolutionarily modified forewings called elytra. These structures are often presumed to have been a major driving force for the successful radiation of this taxon, by providing beetles with protection against a variety of harsh environmental factors. However, few studies have directly demonstrated the functional significance of the elytra against diverse environmental challenges. Here, we sought to empirically test the function of the elytra using Tribolium castaneum (the red flour beetle) as a model. We tested four categories of stress on the beetles: physical damage to hindwings, predation, desiccation, and cold shock. We found that, in all categories, the presence of elytra conferred a significant advantage compared to those beetles with their elytra experimentally removed. This work provides compelling quantitative evidence supporting the importance of beetle forewings in tolerating a variety of environmental stresses, and gives insight into how the evolution of elytra have facilitated the remarkable success of beetle radiation.

Information from familiar and related conspecifics affects foraging in a solitary wolf spider.

As neighbours become familiar with one another, they can divert attention away from one another and focus on other activities. Since familiarity is a likely mechanism by which animals recognise relatives, both kinship and prior association with conspecifics should allow individuals to increase foraging. We attempted to determine if the interference observed among conspecific foragers could be mitigated by familiarity and/or kinship. Because Pardosa milvina wolf spiders are sensitive to chemotactile cues deposited on substrates by other spiders, we used cues to manipulate the information available to focal spiders. We first verified that animals could use these cues to differentiate relatives and familiar conspecifics. We then documented foraging in the presence of all combinations of related and familiar animal cues. Test spiders were slower foragers, less likely to capture prey, and consumed less of each prey item when on cues from unfamiliar kin, but were faster and more effective foragers on cues from familiar non-kin. Their reactions to familiar kin and unfamiliar non-kin were intermediate. High foraging intensity on familiar cues is consistent with the idea that animals pay less attention to neighbours after some prior association. Lower foraging effort in the presence of cues from relatives may be an attempt to reduce kin competition by shifting attention toward dispersal or to provide increased access to prey for hungry relatives nearby. These findings reveal that information from conspecifics mediates social interactions among individuals and affects foraging in ways that can influence their role in the food web.

Nonconsumptive Predator-Prey Interactions: Sensitivity of the Detritivore Sinella curviseta (Collembola: Entomobryidae) to Cues of Predation Risk From the Spider Pardosa milvina (Araneae: Lycosidae).

Predators can affect prey indirectly when prey respond to cues indicating a risk of predation by altering activity levels. Changes in prey behavior may cascade through the food web to influence ecosystem function. The response of the collembolan Sinella curviseta Brook (Collembola: Entomobryidae) to cues indicating predation risk (necromones and cues from the wolf spider Pardosa milvina (Hentz) (Araneae: Lycosidae)) was tested. Additionally, necromones and predator cues were paired in a conditioning experiment to determine whether the collembolan could form learned associations. Although collembolans did not alter activity levels in response to predator cues, numerous aspects of behavior differed in the presence of necromones. There was no detectable conditioned response to predator cues after pairing with necromones. These results provide insight into how collembolans perceive and respond to predation threats that vary in information content. Previously detected indirect impacts of predator cues on ecosystem function are likely due to changes in prey other than activity level.

Fear of predation alters soil carbon dioxide flux and nitrogen content.

Predators are known to have both consumptive and non-consumptive effects (NCEs) on their prey that can cascade to affect lower trophic levels. Non-consumptive interactions often drive these effects, though the majority of studies have been conducted in aquatic- or herbivory-based systems. Here, we use a laboratory study to examine how linkages between an above-ground predator and a detritivore influence below-ground properties. We demonstrate that predators can depress soil metabolism (i.e. CO2 flux) and soil nutrient content via both consumptive and non-consumptive interactions with detritivores, and that the strength of isolated NCEs is comparable to changes resulting from predation. Changes in detritivore abundance and activity in response to predators and the fear of predation likely mediate interactions with the soil microbe community. Our results underscore the need to explore these mechanisms at large scales, considering the disproportionate extinction risk faced by predators and the importance of soils in the global carbon cycle.