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Spider webs vary in size to meet the nutritional requirements of the resident spider with the resident's body size strongly informing these requirements. In this way, the effect of body size on web-building behaviour should be apparent across species. To determine whether the size of analogous web structures scales with body size across closely related species, we first measured mainsheet area and adult female body size of 12 sheet-web spider species (Cambridgea). Using these species, we then generated alignments from the cytochrome c oxidase subunit I (COI) and histone 3 (H3) gene regions. These alignments were phylogenetically analysed using Bayesian inference and maximum likelihood methods. While phylogenetic trees for the COI gene suggested that Cambridgea is monophyletic relative to sampled outgroups, H3 did not. Combining our COI phylogenetic tree's branch lengths with data on web-building behaviour, we used phylogenetic least squares to determine whether web size scales with spider size across species. While we found evidence that larger species generally build larger webs, the variation in web size across even similarly sized species suggests that environmental characteristics which influence site selection and prey type may play a role in determining the optimal web size for different species. [ABSTRACT FROM AUTHOR]

In web-building spiders, females are often too widely distributed across the landscape for males to monopolize more than one mate. Consequently, males seek females one at a time and may cohabit with females in their webs. Pre-copulatory cohabitation is most common in araneomorphs, which suggests that the first male to mate with a female will have a greater share of paternity than any subsequent mates (first sperm precedence). However, pairs of adult New Zealand sheet-web spiders (Cambridgea foliata (L. Koch, 1872); Desidae) cohabit for longer than required to achieve copulation. This is counter-intuitive as it suggests that males defend females they have already copulated with, in lieu of seeking additional mating opportunities. To investigate the costs and benefits of extended cohabitation on male and female C. foliata, we conducted surveys of webs of solitary and paired males and females. We found that solitary spiders of both sexes consistently position themselves in the center of their webs but that when in pairs, females are displaced from the webs by males and will frequently leave the web altogether. Males in pairs would respond to vibrations simulating prey, while females would not respond. This strongly suggests that extended cohabitation should be costly for females. By contrast, for males, cohabitation is a valuable foraging strategy which, combined with the advantages of mate-guarding, may compensate for any lost mating opportunities due to foregoing searching for further mates. [ABSTRACT FROM AUTHOR]