Adaptations for Group-Living in Social Huntsman Spiders:
The primary research in my laboratory is on the social behavior, mother-offspring dynamics, in the endemic Australian huntsman spider, Delena cancerides (Sparassidae). Delena were the spider stars of the ‘Arachnophobia’!
Complex and long-lasting social interactions among family or communal groups of arachnids (spiders, scorpions, amblypygids, harvestmen, pseudoscorpions, etc.) is extremely rare (Rayor & Taylor 2006), although transient maternal defense of eggs and newly emerged young occurs sporadically throughout the arachnids. Social behavior beyond transient maternal care is only found in 55 spider species (Whitehouse & Lubin 2005) and 17 non-spider arachnids (Rayor & Taylor 2006), or something less than 0.01% of all known arachnid species. Other than the Acarines (mites and ticks), all arachnids are obligate predators which apparently results in steep barriers to group-living. Although rare, sociality is found in 13 diverse, taxonomically unrelated spider families (Aviles 1997, Uetz & Heiber 1997, Lubin & Bilde 2007). Yet across the taxonomic spectrum, all but the social huntsman species share key behavioral traits. All live in web-based societies, even when other members of the family do not build prey capture webs (Aviles 1997). The unequivocal advantage of group-living in social spiders is enhanced prey capture success through shared use of webs and cooperative prey capture (Whitehouse & Lubin 2005). Sociality in spiders is extremely rare.
Delena canerides is considered to be the most unusual of the known social spiders with important characteristics that differ from those of all other social spiders. Unlike all other social spiders, they do not live in webs, are extremely aggressive to non-colony mates, have a 1:1 sex ratio, and are highly outbred with unusual chromosomal races (Rowell & Aviles 1995). Delena simply do not fit any current understanding of spider sociality. Delena are large non-web building spiders that live under the bark of dead trees in year-round colonies of up to 300 individuals. The narrow bark-covered retreats are relatively rare and can readily be defended from intruders, unlike the relatively open web-based colonies of other social spider species. The social demographics of Delena vary along a continuum from a single breeding female with multiple clutches of offspring to the substantially more complex dynamics of multiple adult social groups. Although they lack communal webs that facilitate cooperative prey capture and communication, Delena share prey and interact frequently with a diverse behavioral repertoire. Delena exhibit important components of conflict and cooperation more typical of eusocial insects than social spiders, including aggression toward non colony-mates and competition between reproductive females. Even courtship and mating is unusual in these spiders, as these huntsmen spiders mate for hours, with many partners, and males may simultaneously attempt to copulate with females! Because of the confluence of unusual behavioral and genetic traits, Delenacancerides are a wonderful system to test theories of social evolution and group living.
Projects on Delena cancerides in my laboratory include:
- A comparison of courtship, mother-offspring interactions, prey sharing, and growth rates in Delenawith those seen in solitary huntsmen spider species.
- Studying the social dynamics in colonies with different social demographics.
- Examining the role of prey availability and retreat size on social dynamics.
- Consequences of sociality on courtship and mating patterns in Delena
- Experiments and simulation models to determine which factors affect individuals’ decisions to remain with the social group or depart from the natal colony.
- A determination of genetic relationships within Delena colonies, in collaboration with Dr. David Rowell, Australian National University.
- Investigate factors involved in kin recognition and aggression between non-colony mates.