This electronic thesis or dissertation has been downloaded from Explore Bristol Research, http://research-information.bristol.ac.uk Author: Phangurha, Josh Title: Construction of the orb web in constant and changing abiotic conditions General rights Access to the thesis is subject to the Creative Commons Attribution - NonCommercial-No Derivatives 4.0 International Public License. A copy of this may be found at https://creativecommons.org/licenses/by-nc-nd/4.0/legalcode This license sets out your rights and the restrictions that apply to your access to the thesis so it is important you read this before proceeding. Take down policy Some pages of this thesis may have been removed for copyright restrictions prior to having it been deposited in Explore Bristol Research. However, if you have discovered material within the thesis that you consider to be unlawful e.g. breaches of copyright (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please contact [email protected] and include the following information in your message: •Your contact details •Bibliographic details for the item, including a URL •An outline nature of the complaint Your claim will be investigated and, where appropriate, the item in question will be removed from public view as soon as possible. Construction of the orb web in constant and changing abiotic conditions Joshua Singh Phangurha A dissertation submitted to the University of Bristol in the accordance with the requirements for award of the degree of MSc by Research in the Faculty of Science. School of Biological Sciences Date of submission: 31/08/2018 Word count: 15,060 Abstract Orb weaving spiders are thought to alter their web-building in different abiotic conditions to maximise prey capture success, while being as silk-efficient as possible. However, there is limited evidence to support this, along with a lack of focus on web variation over time under constant conditions. It is important to better understand web-building in constant and changing abitoic environments to determine if spiders perform adaptive manipulations of their webs. Here, both of these concepts are investigated and the hypothesis that web construction under constant abiotic conditions will not change over time, due to a lack of environmental cues for spiders to respond to, is tested. It is also predicted that Zygiella x- notata will reduce the prey capture aspects in high light intensities, when prey would be more active, and silk can be preserved. The webs of both species were monitored in a constant abiotic environment and Z. x-notata web building behaviour was compared in varying environmental light intensities. These experiments explored patterns of variation in the web characteristics of Argiope bruennichi and Zygiella x-notata over time in a constant abiotic environment and identified significant differences in the web building of Z. x-notata in bright and dark conditions. Results show an overall lack of variation in the webs of A. bruennichi over time apart from radii number in webs of adult females and upper mesh spacing in juvenile webs, and no significant variation in the webs of Z. x-notata over time. No significant differences in the web geometry of Z. x-notata webs occurred in the light intensity treatment, except for lower mesh height becoming reduced in darker conditions. These findings suggest that varying abiotic factors, overall, do not influence the adaptive web building decisions of an orb weaver and could only marginally impact specific web aspects. Dedication and acknowledgments I would like to thank Beth Mortimer and Daniel Robert for supervising this project in the Life Sciences building, Paul Chappell and his colleagues at the chemistry department for building the frame set up and the British Ecological Society and Bristol Alumni foundation for funding my travel to Mexico to share this research at the American Arachnological Society’s annual meeting. All photographs used in this thesis were taken by the author. Image 1.1 (2.2MB), 1.2 (8.69MB), 1.4 (467KB), 2.1 (5.89MB), 2.2 (6.35MB), 2.3 (6.58MB), 2.4 (7.26MB), 4.1 (337KB), 4.2 (1.11MB), 4.3 (306KB) and 4.4 (435KB) were all edited in Picasa®. Image 1.3 (9MB) was downloaded from Leica® microscopy software. Author’s declaration I declare that the work in this dissertation was carried out in accordance with the requirements of the University's Regulations and Code of Practice for Research Degree Programmes and that it has not been submitted for any other academic award. Except where indicated by specific reference in the text, the work is the candidate's own work. Work done in collaboration with, or with the assistance of, others, is indicated as such. Any views expressed in the dissertation are those of the author. SIGNED: ............................................................. DATE:.......................... Table of contents Chapter 1 – Introduction and background ………………………………………………................ 1 1.1 – Background on foraging method variation in the natural world ………………………………… 1 1.2 – Biotic influence on web construction ………………………………………………………………………… 2 1.3 – Spider condition ……………………………………………………………………………………………………….. 3 1.4 – Web building influenced by predators …………………………………………………………………………………… 3 1.5 – Wind ……………………………………………………………………………………………………………………………………... 4 1.6 – Light ………………………………………………………………………………………………………………………………………. 5 1.7 – Temperature …………………………………………………………………………………………………………………………. 6 1.8 – Humidity ……………………………………………………………………………………………………………………………….. 7 1.9 – Intraspecific web variation ……………………………………………………………………………………………………. 8 1.10 – Other factors affecting web building ………………………………………………………………………………….. 10 1.11 – Stabilimenta – a prey attractant? ……………………………………………………………………………………….. 11 1.12 – Web damage prevention function of stabilimenta ……………………………………………………………… 12 1.13 – Stabilimenta for predator avoidance ………………………………………………………………………………….. 13 1.14 – Unexplained stabilimenta variation ……………………………………………………………………………………. 14 1.15 – Aim of study ………………………………………………………………………………………………………………………. 14 1.16 – Study species’ ……………………………………………………………………………………………………………………. 15 Chapter 2 – Methodology …………………………………………………………………………………………………. 18 2.1 – Argiope bruennichi and Zygiella x-notata collection ……………………………………………………………... 18 2.2 – Maintenance ………………………………………………………………………………………………………………………… 18 2.3 – Morphometrics ……………………………………………………………………………………………………………………. 19 2.4 – Environmental conditions …………………………………………………………………………………………………….. 21 2.5 – Light intensity experiment (Zygiella x-notata) ………………………………………………………………………. 22 2.6 – Web measurements …………………………………………………………………………………………………………….. 22 2.7 – Statistical methods ………………………………………………………………………………………………………………. 26 Chapter 3 – Results ……………………………………………………………………………………………………………… 26 3.1 – Web building variation under constant abiotic conditions …………………………………………………… 27 3.2 – Juvenile Argiope bruennichi …………………………………………………………………………………………………. 27 3.3 – Adult Argiope bruennichi …………………………………………………………………………………………………….. 34 3.4 – Stabilimenta building ………………………………………………………………………………………………………….. 40 3.5 – Zygiella x-notata …………………………………………………………………………………………………………………. 40 3.6 – Light intensity experiment ………………………………………………………………………………………………….. 47 Chapter 4 – Discussion ……………………………………………………………………………………………………… 49 4.1 – Juvenile upper mesh variation and overall mesh consistency …………………………………………….. 50 4.2 – Spatial constraints ………………………………………………………………………………………………………………. 52 4.3 – Web building experience ……………………………………………………………………………………………………. 54 4.4 – Size limitation hypothesis …………………………………………………………………………………………………… 54 4.5 – Adult Argiope bruennichi radii variation …………………………………………………………………………….. 55 4.6 – Biotic factors more influential on web construction? …………………………………………………………. 56 4.6.1 – Effect of food intake ……………………………………………………………………………………………….. 56 4.6.2 – Prey type …………………………………………………………………………………………………………………. 57 4.6.3 – Prey size …………………………………………………………………………………………………………………. 58 4.6.4 – Hydration ……………………………………………………………………………………………………………….. 58 4.6.5 – Effect of aging ………………………………………………………………………………………………………… 59 4.6.6 – Pollen consumption ………………………………………………………………………………………………… 59 4.6.7 – Effect of reproduction on web construction …………………………………………………………… 59 4.7 – Light intensity experiment (Zygiella x-notata) …………………………………………………………………… 62 4.8 – Hierarchy of variation ……………………………………………………………………………………………………….. 64 4.9 – Lack of stabilimenta ………………………………………………………………………………………………………….. 65 4.10 – Preliminary observations of stabilimenta ……………………………………………………………………….. 66 4.11 – Conclusion ……………………………………………………………………………………………………………………… 67 Appendix ……………………………………………………………………………………………………………………….. 69 References …………………………………………………………………………………………………………………….. 73 Figures, tables and images: Chapter 1 – Introduction and background Image 1.1 & 1.2 …………………………………………………………………………………………………………………………. 16 Image 1.3 & 1.4 …………………………………………………………………………………………………………………………. 17 Chapter 2 - Methodology Figure 2.1 & 2.2 …………………………………………………………………………………………………………………………. 20 Figure 2.3 ………………………………………………………………………………………………………………………………….. 21 Image 2.1 ………………………………………………………………………………………………………………………………….. 23 Image 2.2 & 2.3 ………………………………………………………………………………………………………………………… 24 Image 2.4 …………………………………………………………………………………………………………………………………. 25 Chapter 3 - Results Table 3.1 & Figure 3.1 ………………………………………………………………………………………………………. 28