The evolution of social inbreeding mating systems in spiders: limited male mating dispersal and lack of pre‐copulatory inbreeding avoidance in a subsocial predecessor

Cooperation and group living are extremely rare in spiders and only few species are known to be permanently social. Inbreeding is a key characteristic of social spiders, resulting in high degrees of within‐colony relatedness that may foster kin‐selected benefits of cooperation. Accordingly, philopatry and regular inbreeding are suggested to play a major role in the repeated independent origins of sociality in spiders. We conducted field observations and laboratory experiments to investigate the mating system of the subsocial spider Stegodyphus tentoriicola. The species is suggested to resemble the ‘missing link’ in the transition from subsociality to permanent sociality in Stegodyphus spiders because its social period is prolonged in comparison to other subsocial species. Individuals in our two study populations were spatially clustered around maternal nests, indicating that clusters consist of family groups as found in the subsocial congener Stegodyphus lineatus. Male mating dispersal was limited and we found no obvious pre‐copulatory inbreeding avoidance, suggesting a high likelihood of mating with close kin. Rates of polygamy were low, a pattern ensuring high relatedness within broods. In combination with ecological constraints, such as high costs of dispersal, our findings are consistent with the hypothesis that the extended social period in S. tentoriicola is accompanied with adaptations that facilitate the transition towards permanent sociality. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 851–859.     

Microscale variation in alpine grasslands: AFLPs reveal a high level of genotypic diversity in Primula minima (Primulaceae)

The microscale variation and spatial genetic structure of the alpine plant species Primula minima L. was analysed using AFLPs. AFLP analysis based on three primer combinations and 123 fragments revealed no identical genotypes among the 86 studied samples from a 300 × 300 cm plot. Variation within the study plot was high: Nei's gene diversity was 0.22, Shannon's information index 0.33 and the percentage of polymorphic bands was 60.9. Cluster analysis revealed four main groups of genetically similar individuals and mapping these individuals resulted in a clear spatial pattern, with samples from the same group often located close together. The observed microscale structure was corroborated using a Mantel test, which revealed significant correlation of genetic and spatial distances, and by the results of a spatial autocorrelation analysis that indicated a high level of similarity between adjacent samples. An analysis of molecular variance revealed clear differentiation (18%) between the spatial groups. Overall gene flow within the plot was 1.11 and ranged from 0.33 between the spatially most distant groups to 2.33 between directly neighbouring groups. The extraordinary level of diversity detected in this study indicates an unexpectedly strong relevance of reproduction by seed for the species P. minima in alpine grasslands. The strong microscale variation suggests, however, that there is limited dispersal of seeds. Clonal reproduction is of subsidiary importance to sexual reproduction and seems to occur only over very small distances.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 549–556.     

A NESTING SITE AND EGG MORPHOLOGY OF A MIOCENE TURTLE FROM URUMACO, VENEZUELA: EVIDENCE OF MARINE ADAPTATIONS IN PELOMEDUSOIDES

Abstract:  Fossil eggshells from the Late Miocene Urumaco Formation of north-western Venezuela are reported. Stereomicroscopy and scanning electron microscopy were used to examine shell gross morphology and ultrastructure, respectively. Diagnostic turtle features in the eggshells include a distinct pattern of crystal aggregations within the shell units. The eggs had an elliptical shape with a maximum diameter of c . 56·5 mm and width of c . 43·5 mm, as measured in a specimen preserving the egg's outline. Scattered clutches of broken eggshells were found embedded in one horizon of a coarse, sandy sediment, with grains not well sorted containing foraminifera and fragments of bivalve shells. The sediments are rich in ichnofossils and the reddish colour of the sandstone indicates an oxidizing environment. These facts suggest that the eggs were deposited in a beach directly facing the sea or brackish waters, perhaps near a river delta or lagoon, as is typical of the Urumaco sequence. In the same stratigraphical layer and next to one of the egg clusters, a carapace assignable to the pelomedusoid Bairdemys venezuelensis was found, suggesting that this species was a colonial nester that laid its eggs in beaches and lived in a marine or nearshore marine environment.