PhD Defense Seminar cum Oral Examination
“Sociality of spiders of the Genus Anelosimus (Araneae: Theridiidae), with focus on species in Southeast and East Asia“
Thu 28 Aug 2014: 10.00m
DBS Conference Room (S3 Level 5)
All are welcome
“The genus Anelosimus (Araneae: Theridiidae) consists of 64 nominal species, of which six are social, 14 subsocial and five solitary, while the sociality of the remaining species are unknown. Although intensive work has been conducted on spiders of this genus in North and South America, little is known about Anelosimus in Asia. As a model system, a comprehensive study of spiders of this genus would further the understanding of sociality in spiders. Therefore, the goal of this thesis was to supplement the knowledge of Anelosimus, with concentration on species found in Southeast and East Asia and to explore factors affecting the evolution of sociality in this genus.
The findings of this study includes nine newly described species. Eleven previously described species were also included and supplemented with photographs, updates of missing male/female descriptions and information on natural history. The natural history of ten species of Anelosimus collected from China, Malaysia and Singapore were also examined, with special focus on traits such as habitat and colony structure, maternal care, cooperative behaviour, dispersal and a number of reproductive traits. Seven of these species were determined to be solitary, while the remaining three species are subsocial. Examination of the sensory receptors in subsocial and solitary species also revealed that subsocial species have a lower density of mechanoreceptors, which may result in lowered sensitivity towards conspecifics, promoting aggregation.
An analysis of the worldwide distribution of 35 Anelosimus species revealed that solitary species tend to occur in habitats with high rainfall and temperature, subsocial species occur in areas with low rainfall and temperatures while social species are commonly found in areas with high rainfall and intermediate temperatures. This may be associated with the ability of web structure to withstand rain damage, prey abundance and effects of temperatures on metabolism and growth of spiders.
Finally the prevalence of parasites in nests of eight Anelosimus species and the presence of the endosymbiotic bacteria Wolbachia 37 species of Anelosimus were tested. Results obtained suggest that cooperative web maintenance from juveniles in subsocial species may aid in reducing the number of parasites in the bigger nests of subsocial spiders. Meanwhile due to solitary spiders’ preference in constructing webs on small wildflowers, there are higher numbers of parasitic organisms such as mites, lepidopteran larva and hymenopterans in their nests. Wolbachia infection was also not found to be widespread amongst Anelosimus species tested. However, infection appears to be more prevalent in social species.
Overall, this study has revealed a high concentration of solitary species and an absence of social species in Southeast and East Asia. Factors such as mechanoreceptor densities, rainfall, temperature and Wolbachia infection have also been found to affect the development of sociality in Anelosimus.”