PhD Defense Seminar cum Oral Examination
“Chemical Defence in Web-building Spiders“
Dept. of Biological Sciences, NUS
Friday, 22 Nov 2013: 3.00pm
@ DBS Seminar Room 2, S2 Level 4
Supervisor: Assoc Prof Li Daiqin
All are welcome
“Chemical defence, a major defensive means used by a wide range of organisms, is rarely reported in spiders. In this study, I investigated chemical defence and its evolution in web-building spiders. By discovering a novel property of the web silk produced by the golden web spider, Nephila antipodiana (Nephilidae), I first explained the paradox that ants are rarely reported foraging on the webs of orb-weaving spiders, despite the powerful capacity of ants to subdue prey and repel enemies, the diversity and abundance of orb-web spiders, and the nutritional value of the web and resident spider. This species of spider deposits on the silk a pyrrolidine alkaloid (2-pyrrolidinone) that provides protection from ant invasion. I then studied how spiders obtain this compound, and found that it was biosynthesized de novo. I further explored other potential defensive chemicals on the egg-sacs of spiders with and without parental care, but no defensive compounds were found in any spider eggs, suggesting that spiders may not rely on defensive chemicals for egg protection.
To investigate when the ant-deterrent occurred in the first place and how it has evolved in web-building spiders, I surveyed the presence and absence of 2-pyrrolidinone in 65 genera of typical web-building spiders that belong to 11 families and then map the results onto the phylogenetic tree of web-building spiders. My results showed that ant-deterrent has evolved only once, and lost up to seven times in the orb weavers. Finally, I studied the function and its mechanism of a novel animal behaviour, mate-binding in N. pilipes, in which the male deposits fine silk onto the female body in-between copulation bouts. I demonstrated that chemical defence can be even used by males to defend against a conspecific female’s cannibalism during mating. This study revealed that chemical defence is indeed an important defence mechanism in orb-weaving spiders, thus providing a new perspective to our understanding of chemical ecology in animal world.