CORE Metadata, citation and similar papers at core.ac.uk Provided by ScholarBank@NUS PREDATORY BEHAVIOUR AND BIOLOGY OF A MOSQUITO-EATING JUMPING SPIDER, PARACYRBA WANLESSI JEREMY WOON REN WEI B.Sc. (Hons.), NUS A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF SCIENCE DEPARTMENT OF BIOLOGICAL SCIENCES NATIONAL UNIVERSITY OF SINGAPORE 2007 1 ACKNOWLEDGEMENTS First and foremost, I would like to thank Associate Professor Li Daiqin for all the guidance and support throughout these years spent under his supervision and without whom this thesis would never have been possible. My thanks to Prof. Robert Jackson for the invaluable comments when I was first starting out on this project. I would also like to thank our collaborator in the University of Malaya, Dr. Rosli Hashim, for putting me up in the field station. My thanks also go out to Ms. Goh Poh Moi, for always making sure I had a constant supply of mosquitoes for over three long years. To all the labmates I’ve had, both past and present, for all the lunch/tea sessions and all the madness that we do to keep ourselves sane – the lab was more than just an office thanks to you guys. To my fieldtrip companions throughout the years: Reuben, Kathy and especially Norman, who single-handedly drove me back from K.L. with my swollen face, Yin Yin, Aijie, Eunice and Laura. Special thanks to Matthew Lim, for all the advice throughout my project and Andrew Tham for all the exercise and corn. I would most especially like to thank Chin Yujia, for doing much of the preliminary work and bearing the brunt of the “streamlining” process, for the entertainment, and also for the mushrooms. My deepest gratitude goes to my family, for their enthusiasm in searching out for anything “spider” to give me, and supporting me throughout. Lastly, but most importantly, to my future wife, Tingting, for everything you have done to encourage me, helping out in any way possible and for just being there. i TABLE OF CONTENTS Page ACKNOWLEDGEMENTS i TABLE OF CONTENTS ii ABSTRACT iv LIST OF TABLES v LIST OF FIGURES viii CHAPTER 1 GENERAL INTRODUCTION 1 Optimal Foraging Theory 1 Diet and Preference: Specialist vs. Generalist predators 3 Preference vs. OFT 5 Spiders as predators 7 Salticids 10 Prey preference in salticids 12 Myrmecophagic salticids 13 Araneophagic salticids 16 Culicivorous salticids 22 CHAPTER 2 PREY PREFERENCE OF PARACYRBA WANLESSI 26 Introduction 27 Materials and Methods 32 Results 41 Discussion 50 Conclusion 68 ii CHAPTER 3 DIET AND GROWTH OF PARACYRBA WANLESSI 69 Introduction 69 Materials and Methods 71 Results 76 Discussion 91 Conclusion 99 CHAPTER 4 A STUDY ON THE HABITAT OF PARACYRBA 100 WANLESSI Introduction 100 Materials and Methods 108 Results 113 Discussion 115 Conclusion 119 CHAPTER 5 GENERAL DISCUSSION 120 Paracyrba wanlessi as a specialist inhabitant of 120 fallen bamboo internodes Paracyrba wanlessi as a specialist predator 123 Does Paracyrba wanlessi forage optimally? 125 Future research on Paracyrba wanlessi 127 Conclusions 130 REFERENCES 131 iii ABSTRACT Spiders are commonly envisaged as generalist predators, but recent studies have shown that certain species of jumping spiders (Araneae: Salticidae) demonstrate a pronounced prey preference towards particular prey types. Some salticid species have even been shown to mature faster and grow to larger sizes when fed with their preferred prey type. Paracyrba wanlessi, a salticid from the subfamily Spartaeinae, is known to feed on a large proportion of larval and adult mosquitoes in nature. However, it is currently unclear if the observed proportion of mosquito prey taken in nature is indicative of an actual prey preference or if it is merely due to the relative abundance of various prey types in their natural habitat. I performed a series of prey choice tests using adult P. wanlessi to examine if they show a preference for mosquitoes over other insects as prey, and also the effect of hunger levels on their preference. My results demonstrated that P. wanlessi showed a distinct preference for adult female Aedes albopictus mosquitoes over blood fed mosquitoes, fruit flies and cricket nymphs. Surprisingly, even though half their natural diet was reported to consist of aquatic mosquito larvae, prey preference tests in the laboratory revealed that spiders would almost always choose adults over larval mosquitoes. I also conducted growth rate experiments to investigate whether the development of P. wanlessi was influenced if the spiders were fed on strict diets of Drosophila melanogaster, blood fed and non-blood fed female Ae. albopictus, or a mixed diet of all three prey types. Spiders reared on a mixed diet showed best overall growth and lowest mortality, followed closely by those reared on a non-blood fed mosquito diet. Contrary to expectations, spiders reared on blood fed mosquitoes did poorly, with high mortality rates and few spiders reaching maturity in 352 days. Spiders reared on D. melanogaster fared the worst, with 89% mortality prior to maturity. My findings have implications for the current understanding of vision-based prey preference and predatory specialization in salticids, as well as for the ecology of the phytothelm communities of bamboo internodes, the natural habitat of P. wanlessi. iv LIST OF TABLES Table Title Page Table 2-1. Results from prey choice tests with Paracyrba wanlessi when 45 simultaneously presented with two live prey, adult female Ae. albopictus mosquitoes and D. melanogaster in 227 successful trials. Table 2-2. Results from prey choice tests with Paracyrba wanlessi when 46 simultaneously presented with two live prey, adult female Ae. albopictus mosquitoes and cricket A. domesticus nymphs in 167 successful trials. Table 2-3. Results from prey choice tests with Paracyrba wanlessi when 47 simultaneously presented with two live prey, blood fed and non-blood fed female Ae. albopictus mosquitoes in 116 successful trials. Table 2-4. Results from prey choice tests with juvenile Paracyrba wanlessi 48 when simultaneously presented with two live prey, Ae. albopictus and Cx. quinquefasciatus mosquitoes in 62 successful trials. Table 2-5. Results from prey choice tests with Paracyrba wanlessi when 49 simultaneously presented with two live prey, adult female and larval Ae. albopictus mosquitoes in 122 successful trials. v Table 3-1. Number of individuals of each prey type fed to each spider in 73 their respective groups per week. Spiders in the mixed diet (MX) group were fed one prey type each week, cycling through the 3 prey types, e.g. week 1: blood fed mosquitoes, week 2: non-blood fed mosquitoes, week 3: D. melanogaster before repeating the entire cycle. Table 3-2. Weight of prey consumed for each prey type fed to each spider 76 in their respective groups per week. Spiders in the mixed diet (MX) group were fed one prey type each week, cycling through the three prey types, e.g. week 1: blood fed mosquitoes, week 2: non-blood fed mosquitoes, week 3: D. melanogaster before repeating the entire cycle. Table 3-3. One-way ANOVA of the within-group effects of gender on age 79 to maturity of male and female adult P. wanlessi Table 3-4. One-way ANOVA of the effect of diet on age to maturity of 79 male and female adult P. wanlessi Table 3-5. Summary of life history data for P. wanlessi reared on four 81 different diets Table 3-6. One-way ANOVA of the within-group effects of gender on 83-84 weight and seven body dimensions of male and female 6th instar P. wanlessi Table 3-7. One-way ANOVA and Tukey’s HSD post-hoc multiple 86 comparison tests of weight and seven body dimensions of 4th instar P. wanlessi reared on different diets vi Table 3-8. One-way ANOVA and Tukey’s HSD post-hoc multiple 88 comparison tests of weight and seven body dimensions of 6th instar male P. wanlessi reared on different diets Table 3-9. One-way ANOVA and Tukey’s HSD post-hoc multiple 90 comparison tests of weight and seven body dimensions of 6th instar female P. wanlessi reared on different diets vii LIST OF FIGURES Figure Title Page Fig. 1-1. Adult female Paracyrba wanlessi 25 Fig. 1-2. Adult male Paracyrba wanlessi 25 Fig. 2-1. Schematic diagram of test arena (top-down view) used in live prey 39 choice tests for terrestrial prey pairs. A. Testing arena. The two prey types to be tested are introduced into this area first before allowing the spider to enter at a later time. B. Attached chamber with a blocked connection to allow a spider to be detained until the appropriate time. When the spider is allowed to enter, some individuals occasionally prove reluctant to move at all, in which case the plunger is used to push the spider into the arena. Fig. 2-2. Schematic diagram of test arena used to test terrestrial prey against 40 aquatic mosquito larvae. A. Top-down view. Aquatic larvae are placed in a pool filling the 71 mm square depression in the middle of the arena. The pool has sloping sides down to a 20 mm square base. B. Side view of the arena showing the depth of the pool with sloping sides and also the entrance where the spider is allowed to enter the arena and where the connecting chamber is attached. Fig. 3-1. Schematic diagram showing the five carapace dimensions 75 measured on the exuviae of spiders to determine growth. Fig. 3-2. Survivorship values at each instar for P. wanlessi raised on four 80 different diets. Fig. 4-1. General habitat of P. wanlessi is secondary rainforest interspersed 103 with bamboo clumps along a stream, Sungei Gombak viii Fig.