Body size responses to urban temperature variations are driven by life history traits in spiders

Abstract

Abstract Urban ecosystems exhibit altered environmental conditions compared to the rural surroundings, including higher temperatures, the so‐called urban heat island (UHI) effect. Along urbanisation gradients, temperature variations occur at various scales ranging from the landscape to the microhabitat, with possible consequences on living organisms. As ectothermic animals, arthropods are particularly affected by UHIs because warming may directly induce physiological effects on their metabolism. Body size is a commonly used metric to investigate arthropod responses to thermal stress, but the scale‐dependent role of temperature variation as predictor of body size remains unclear. To assess temperature–size relationships across spatial scales and test if a common pattern to several species emerges, we performed morphological measurements on 2283 individuals representing 11 spider species belonging to Hahniidae, Linyphiidae, Lycosidae and Tetragnathidae. Spiders were collected on 36 grasslands distributed along a broad UHI gradient. Intraspecific shifts in body size were related to temperature in the Lycosids Pardosa prativaga and Pardosa pullata at the landscape and local scales, respectively, whereas no clear effects were observed regarding the other examined species. In both species, sex was an important endogenous factor that modulated individual responses; females were more affected than males by temperature. The contrasting amplitudes of the responses observed among Lycodids and the other species indicate that large, low dispersive and univoltine species are under a stronger influence of temperature than small bivotline species that can disperse aerially. Our results on spiders highlight that considering species‐specific life history traits helps to understand contrasting responses among species, and this may be essential for drawing general patterns of phenotypic changes among arthropods under anthropogenic warming. Read the free Plain Language Summary for this article on the Journal blog.