An antimicrobial Staphylococcus sciuri with broad temperature and salt spectrum isolated from the surface of the African social spider, Stegodyphus dumicola

Some social arthropods engage in mutualistic symbiosis with antimicrobial compound-producing microorganisms that provide protection against pathogens. Social spiders live in communal nests and contain specific endosymbionts with unknown function. Bacteria are also found on the spiders' surface, including prevalent staphylococci, which may have protective potential. Here we present the genomic and phenotypic characterization of strain i1, isolated from the surface of the social spider Stegodyphus dumicola. Phylogenomic analysis identified i1 as novel strain of Staphylococcus sciuri within subgroup 2 of three newly defined genomic subgroups. Further phenotypic investigations showed that S. sciuri i1 is an extremophile that can grow at a broad range of temperatures (4°C-45°C), high salt concentrations (up to 27%), and has antimicrobial activity against closely related species. We identified a lactococcin 972-like bacteriocin gene cluster, likely responsible for the antimicrobial activity, and found it conserved in two of the three subgroups of S. sciuri. These features indicate that S. sciuri i1, though not a specific symbiont, is well-adapted to survive on the surface of social spiders and may gain a competitive advantage by inhibiting closely related species.

When and why do sit-and-wait social spiders disperse?

Dispersal is inherent to all living organisms. Sit-and-wait predators such as social spiders, with their sedentary lifestyles, present an intriguing and underexplored case to examine the proximate and ultimate reasons for dispersal. Though a reduction in dispersal tendencies must accompany the evolution of sociality in spiders, a fraction of the colony may disperse in groups or individually in many species. Such group or solitary dispersal by female social spiders in specific life stages, can lead to colony fission or colony foundation. Males move between colonies, however, there are no direct estimations of male dispersal distances for any species. The structured populations and high inbreeding within colonies suggest that dispersal events occur over limited spatial scales and may be mediated by extrinsic and intrinsic factors. Future studies exploring complex relationships between environmental variables, phenotypes of individuals, colony state and dispersal are advocated. Another area of interest is probing the dispersal process itself to understand the mechanisms of information transfer between individuals at the onset of dispersal. This involves designing studies to examine how break-away groups reach a consensus on when to disperse and where to go.

Spatial proximity and prey vibratory cues influence collective hunting in social spiders

Social spiders are thought to predominantly receive information about their environment through vibrational cues. Thus, group living introduces the challenge of distinguishing useful vibrational information from the background noise of nestmates. Here we investigate whether spatial proximity between colony-mates may allow social spiders (Stegodyphus dumicola) to reduce background noise that might obstruct vibrational information from prey. To do so, we constructed experimental colonies and measured whether the number of spiders in proximity to one another whilst resting could predict the number of spiders that participated in prey capture. Additionally, we exposed spider colonies to five different simulated vibrational cues mimicking prey to determine which cue types spiders were most responsive to. We found that the number of spiders huddled together prior to foraging trials was positively correlated with the number of spiders participating in collective foraging. Furthermore, colonies responded more quickly to pulsed vibrational cues over other types of vibrational patterns. Together these data reveal that both social interactions and prey cues shape how social sit-and-wait predators experience and respond to their environment.