Grieves, L. | Search bioRxiv

bioRxiv2026

Urbanization effects are trait-specific and city-dependent across a widespread spider's global range

Urban environments impose strong selective pressures through biotic and abiotic factors, driving changes in behavior, physiology, and morphology. Yet, responses vary across taxa and cities, and it remains unclear which traits respond consistently and what factors moderate this variation. We addressed these questions using the widespread European garden spider (Araneus diadematus) as a model, measuring size, color, and web-building traits along urban-rural transects in 22 cities across its distribution range. Using a meta-analytic framework, we assessed how city-specific characteristics influenced trait variation. Urbanization consistently reduced relative abdomen surface area, a proxy for body condition. Exploratory meta-regressions suggest that web-building response was predicted by temperature: compared to their non-urban surroundings, urban webs are larger in colder regions and smaller in warmer regions. In contrast, body size and abdomen brightness varied among cities without clear environmental predictors. These findings show that urbanization effects are trait- and context-dependent, likely influenced by local factors such as heat island intensity, microclimate, or prey availability. Linking within- and between-city variation will improve understanding of species phenotypic responses to urban environments.

ecology↗

bioRxiv2024

Multiplex PCR reveals population structure in an inbred communal bird.

We sampled communally breeding p[u]keko (Porphyrio melanotus melanotus, family Rallidae) populations on the North (T[a]wharanui Park) and South (Otokia Reserve) Islands of New Zealand that differ in climate and ecology. North Island populations have year-round territories, philopatry, and form kin groups, resulting in inbreeding. South Island populations have seasonal territories, high dispersal rates, and form non-kin groups, leading to outbreeding. Given behavioural evidence of inbreeding we predicted that the North Island population would exhibit lower heterozygosity and higher inbreeding coefficients than the South Island population. We hypothesized that the South Island population originated via a range expansion from the north and predicted that South Island birds would have lower allelic diversity due to founder effects. To test these predictions, we developed microsatellite primers, optimized multiplex PCRs, and genotyped breeding groups from the North and South Island. Breeding groups from North Island were genetically differentiated, whereas population structure was not detected in the South Island birds. North Island birds had higher inbreeding coefficients and levels of within group kinship, but not allelic diversity, compared to South Island birds. Our results are thus inconclusive about whether the South Island population originated via a range expansion from the north. This pilot study validated microsatellite markers and PCR methods and is the first genetic analysis of population structure and relatedness within communal breeding p[u]keko groups. These genetic tools will be used for larger-scale studies to help resolve the origins of the South Island population and provide further insights into the effects of ecology and behaviour on inbreeding, reproductive success, and population demographics in this species. P[u]keko may provide an excellent model for experimental analyses of inbreeding effects on wild avian populations without the attendant concerns that come with small, endangered populations. This work may thus inform conservation efforts, including translocations of endangered species.

genetics↗