Mining a photo library: Eggs and egg sacs in a major spider family

Abstract

This study explores the potential use of photos for extracting basic data on spider eggs and presents a first rough but comprehensive overview of egg sizes, egg numbers per egg sac, and egg sac shapes in 468 species of pholcid spiders representing 73 genera. Egg diameters ranged 0.29–1.73 mm; egg numbers ranged 3–110. Egg sacs were mostly round or oval, but tended to be elongated in species with elongated abdomens, and flattened in very short-legged species. Potential effects of female body size, abdomen shape, and microhabitat on egg size and number were evaluated by phylogenetic generalized linear models across all investigated species. Our analyses showed that both egg size and egg number are strongly determined by female body size. We found a clear trend for small species to have relatively larger eggs. Ecology and body shape also played a role, albeit at a considerably lower level and with complex interactions among variables: Relative to body size, ground-dwelling species had smaller eggs than space and leaf dwellers; species with a long abdomen had larger eggs than species with a short abdomen. The effect of body size on clutch size depended on body shape and microhabitat: It was slightly weaker in space-dwelling than in other species; species with long abdomens had more eggs in ground and leaf microhabitats, whereas space dwellers carried more eggs when having short abdomens.