Biology subjects

Bechsgaard, J.

Publications and source records attributed to Bechsgaard, J..

5 recordsLinked to original sources

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↗

bioRxiv2025

Convergent Evolution of Sociality Causes Reduction of Mutation Rates in Spiders

Germline mutation rates influence the pace of molecular evolution, yet the roles of selection and life history in shaping their evolution remain to be determined. Comparative systems with replicated evolutionary transitions provide a unique opportunity to determine how changes in life history influence germline mutation rates. In the spider genus Stegodyphus, permanent sociality evolved independently three times within the past million years and is associated with obligate inbreeding, female-biased sex ratios, reduced fecundity, and sharply reduced effective population sizes. We sequenced 202 parent-offspring trios from 34 full-sibling families across three social and four closely related subsocial species and analysed quality-filtered trios in a phylogenetic comparative framework. Each independent transition to sociality was associated with an approximately 2-fold reduction in the de novo mutation rate in the germline. Phylogenetic analyses of synonymous branch lengths suggest that the mutation rates declined in parallel with the transitions to sociality. These rapid reductions in mutation rates in social lineages with small effective population sizes run counter to the drift-barrier hypothesis, which predicts that reduced selection efficacy would lead to higher mutation rates. We find no evidence that reduced mutation rates in the social species was favoured by selection for improving DNA repair efficiency, since there is no upregulation of DNA repair pathway genes in the ovaries of the social species. On the contrary, the mutation rate is reduced across mutational classes and in somatic tissue in social species compared with their subsocial counterparts. These patterns suggest that the reduction in mutation rate in social spiders is a consequence of convergent life history changes, including reduced body size and production of fewer, larger eggs. Our results highlight that the evolution of sociality, which entails major life history changes, can rapidly reshape fundamental evolutionary parameters, such as the germline mutation rate.

evolutionary biology↗

bioRxiv2024

Exploring changes in social spider DNA methylation profiles when succumbing to infection in CpG, CHG, and CHH contexts

Living at high density and with low genetic diversity are factors that should both increase the susceptibility of organisms to disease. Therefore, group living organisms, especially those that are inbred, should be especially vulnerable to infection and therefore have particular strategies to cope with infection. Phenotypic plasticity, underpinned by epigenetic changes, could allow group living organisms to rapidly respond to infection challenges. To explore the potential role of epigenetic modifications in the immune response to a group-living species with low genetic diversity, we compared the genome-wide DNA methylation profiles of five colonies of social spiders (Stegodyphus dumicola) in their natural habitat in Namibia at the point just before they succumbed to infection to a point at least six months previously where they were presumably healthier. We found increases in genome- and chromosome-wide methylation levels in the CpG, CHG, and CHH contexts, although the genome-wide changes were not clearly different from zero. These changes were most prominent in the CHG context, especially at a narrow region of chromosome 13, hinting at an as-of-yet unsuspected role of this DNA methylation context in phenotypic plasticity. However, there were few clear patterns of differential methylation at the base level, and genes with a known immune function in spiders had mean methylation changes close to zero. Our results suggest that DNA methylation may change with infection at large genomic scales, but that this type of epigenetic change is not necessarily integral to the immune response of social spiders.

genomics↗

bioRxiv2024

Sociality in spiders is an evolutionary dead-end

In cooperatively breeding social animals, a few individuals account for all reproduction. In some taxa, sociality is accompanied by a transition from outcrossing to inbreeding, in concert, these traits act to reduce effective population size, potentially rendering transitions to sociality evolutionarily dead-ends. We addressed this hypothesis in a comparative genomic study in spiders, where sociality has evolved independently at least 23 times, but social species are recent and evolutionarily short-lived. We present genomic evidence for the evolutionary dead-end hypothesis in three independent transitions to sociality in the spider genus Stegodyphus. We sequenced, assembled and annotated high-quality, chromosome-level reference genomes from three pairs of closely related social and subsocial Stegodyphus species. Genome sizes range from 2.65 Gb to 3.32 Gb with high synteny, and we identify 10,065 single-copy orthologous genes. We timed the divergence between the social and subsocial species pairs to be from 1.3 to 1.8 million years. Social evolution in spiders involves a shift from outcrossing to inbreeding and from equal to female-biased sex ratio, causing severe reductions in effective population size and decreased efficacy of selection. Based on analyses of purifying selection, we determined whether transitions to sociality co-occurred with divergence. We show that transitions to sociality only had full effect on purifying selection at 119 kya (95CI: 71 kya -169 kya), 260 kya (95CI: 231 ky - 289 kya) and 279 kya (95CI: 230 kya - 332 kya) respectively, and follow remarkably similar convergent trajectories of progressive loss of diversity and shifts to an increasingly female-biased sex ratio. This almost deterministic genomic response to sociality may explain why social spider species do not persist. What causes species extinction is not clear, but could be either selfish meiotic drive that eliminates the production of males, or an inability to retain genome integrity in the face of extremely reduced efficacy of selection.

evolutionary biology↗

bioRxiv2017

The house spider genome reveals an ancient whole-genome duplication during arachnid evolution

The duplication of genes can occur through various mechanisms and is thought to make a major contribution to the evolutionary diversification of organisms. There is increasing evidence for a large-scale duplication of genes in some chelicerate lineages including two rounds of whole genome duplication (WGD) in horseshoe crabs. To investigate this further we sequenced and analyzed the genome of the common house spider Parasteatoda tepidariorum. We found pervasive duplication of both coding and non-coding genes in this spider, including two clusters of Hox genes. Analysis of synteny conservation across the P. tepidariorum genome suggests that there has been an ancient WGD in spiders. Comparison with the genomes of other chelicerates, including that of the newly sequenced bark scorpion Centruroides sculpturatus, suggests that this event occurred in the common ancestor of spiders and scorpions and is probably independent of the WGDs in horseshoe crabs. Furthermore, characterization of the sequence and expression of the Hox paralogs in P. tepidariorum suggests that many have been subject to neofunctionalization and/or subfunctionalization since their duplication, and therefore may have contributed to the diversification of spiders and other pulmonate arachnids.

genomics↗