Abstract
Group-living behavior is taxonomically widespread but rare in spiders. The conventional view is that the main pathways to group-living in spiders are either sub-social, where extended maternal care leads to prolonged sibling association; or communal living, where individuals aggregate to exploit a common resource. Female egg-sac guarding behavior occurs throughout kleptoparasitic spiders in the subfamily Argyrodinae (Theridiidae), while individuals in group-living species cohabit in the resource rich webs of their host spiders. These attributes fit both sub-social and communal routes to group-living, which offers new insights to study the early stages of social evolution. We investigated whether members of kleptoparasitic groups in natural populations comprise related individuals by comparing the population structure of two group-living species, Argyrodes miniaceus and A. cf. fissifrons, and two solitary species, A. fasciatus and Neospintharus trigonum. We found that: (1) genetic-spatial autocorrelation in group-living species was highest among spiders sharing the same host web and declined steeply with increasing distance, but no significant autocorrelation at any scale for solitary species; (2) there was high relatedness among group members in two cases of group-living species, which indicated relatedness was not an adhesive agent in most of the groups, but no high relatedness in solitary species; and (3) the host web boundary was not the sole predictor of genetic structures in group-living species. These results suggest that population genetic structure in the group-living species is caused by limited dispersal of group members that is favored by ecological conditions, including the nature and size of resources. In contrast, the absence of genetic structuring in populations of solitary species indicates a high level of dispersal with individual interactions unlikely to have fitness benefits.
Highlights
Group-living has evolved in diverse animal taxa in response to a variety of environmental factors, including spatial distribution of resources [1], mating opportunities [2], risk of predation [3], parent-offspring aggregation [4], and group foraging [5]
We examined the genetic structure of populations of two group-living species, Argyrodes miniaceus and A. cf. fissifrons, and two solitary species, A. fasciatus and N. trigonum, using DNA
Nonmetric multidimensional scaling (NMDS) analysis reached a solution at run 401 with a stress value of 0.186 for the group-living A. miniaceus, and at run 20 with a stress value of 0.105 for the group-living A. cf. fissifrons
Summary
Group-living has evolved in diverse animal taxa in response to a variety of environmental factors, including spatial distribution of resources [1], mating opportunities [2], risk of predation [3], parent-offspring aggregation [4], and group foraging [5]. The nature of the interactions among group members functions as the agent that increases the fitness of group members. These interactions are typically cooperative behaviors, ranging from reciprocal mutualism among non-related individuals to highly caste-differentiated eusocial groups [6, 7]. The conventional view is that the initial formation of groups may arise through sub-sociality, where sociality derives from extended maternal care and temporarily non-dispersed siblings, or through communal aggregations (typically comprising non-related individuals), where individuals aggregate to exploit a common resource [8,9,10]. Most empirical studies of the early stages of social evolution involve species that have attributes that favor either the sub-social route, e.g., woodroaches [18] and Belding’s ground squirrels [9], or communal route, e.g., vampire bats [10]
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