Prey to predator body size ratio in the evolution of cooperative hunting—a social spider test case
One of the benefits of cooperative hunting may be that predators can subdue larger prey. In spiders, cooperative, social species can capture prey many times larger than an individual predator. However, we propose that cooperative prey capture does not have to be associated with larger caught prey per se, but with an increase in the ratio of prey to predator body size. This can be achieved either by catching larger prey while keeping predator body size constant, or by evolving a smaller predator body size while maintaining capture of large prey. We show that within a genus of relatively large spiders, Stegodyphus, subsocial spiders representing the ancestral state of social species are capable of catching the largest prey available in the environment. Hence, within this genus, the evolution of cooperation would not provide access to otherwise inaccessible, large prey. Instead, we show that social Stegodyphus spiders are smaller than their subsocial counterparts, while catching similar sized prey, leading to the predicted increase in prey-predator size ratio with sociality. We further show that in a genus of small spiders, Anelosimus, the level of sociality is associated with an increased size of prey caught while predator size is unaffected by sociality, leading to a similar, predicted increase in prey-predator size ratio. In summary, we find support for our proposed ‘prey to predator size ratio hypothesis’ and discuss how relaxed selection on large body size in the evolution of social, cooperative living may provide adaptive benefits for ancestrally relatively large predators.
KeywordsSocial evolution Group living Phenotypic plasticity Predator-prey interactions Dietary niche
We would like to thank Y. Lubin, C. Tuni, M. Majer, I. Musli, I. Hoffman, L. L. Chobolo and G. M. Dintwe for help collecting field data. We thank the Schoeman family in Namibia, the Agastya International Foundation and R. Balakrishnan in India, and Y. Lubin in Israel for additional help and hosting. We also thank I. Agnarsson and J. Bechsgaard for providing us with phylogenies.
L.G. was supported by The Leverhulme Trust (Early Career Fellowship: ECF-2016-080). C.H. was supported by the European Research Council (ERC StG-2011-282163 awarded to T.B.). Field work was carried out with financing from Drylands Research SSA grant awarded to C.H. (EC contract number: 026064).
- Aviles L, Guevara J (2017) Sociality in spiders. In: Rubenstein DR, Abbot P (eds) Comparative Social Evolution. Cambridge Cambridge University Press, pp 188–223Google Scholar
- Aviles L, Agnarsson I, Salazar PA, Purcell J, Iturralde G, Yip EC et al (2007) Natural history miscellany - altitudinal patterns of spider sociality and the biology of a new midelevation social Anelosimus species in Ecuador. Am Nat 170(5):783–792. https://doi.org/10.1086/521965 CrossRefPubMedGoogle Scholar
- Crouch TE, Lubin Y (2000) Effects of climate and prey availability on foraging in a social spider, Stegodyphus mimosarum (Araneae, Eresidae). J Arachnol 28(2):158–168. https://doi.org/10.1636/0161-8202(2000)028[0158:Eocapa]2.0.Co;2 CrossRefGoogle Scholar
- Kraus O, Kraus M (1988) The genus Stegodyphus (Arachnida, Araneae). Sibling species, species groups, and parallel origin of social living. In: Kraus O (ed) Verhandlungen des Naturwissenschaftlichen Vereins in Hamburg (NF) 30. Verlag Paul Parey, Hamburg and Berlin, pp 151–254Google Scholar
- Majer M, Svenning J-C, Bilde T (2015) Habitat productivity predicts the global distribution of social spiders. [Original Research]. Front Ecol Evol 3(101). https://doi.org/10.3389/fevo.2015.00101
- Pinheiro J, Bates D, DebRoy S, Sarkar D (2019) nlme: linear and nonlinear mixed effects models, R package version 3.1-138, from https://CRAN.R-project.org/package=nlme
- R Core Team (2019) R: a language and environment for statistical computing, from https://www.R-project.org/
- Schneider JM (1997) Timing of maturation and the mating system of the spider, Stegodyphus lineatus (Eresidae): How important is body size? Biol J Linn Soc 60(4):517–525Google Scholar
- Seibt U, Wickler W (1988) Why Do Family Spiders, Stegodyphus (Eresidae), Live in Colonies. J Arachnol 16(2):193–198Google Scholar
- Villemereuil P, Gimenez O, Doligez B (2013) Comparing parent-offspring regression with frequentist and Bayesian animal models to estimate heritability in wild populations: a simulation study for Gaussian and binary traits. Methods Ecol Evol 4(3):260–275. https://doi.org/10.1111/2041-210x.12011 CrossRefGoogle Scholar
- World Spider Catalog. (2019). World Spider Catalog. Version 20.0 Retrieved 14.05.19, from http://wsc.nmbe.ch