Joining the dark side: waterfall spiders in subterranean habitats, with the description of a new genus and two new species from Brazil (Araneae: Trechaleidae)

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  Joining the dark side: waterfall spiders in subterranean habitats, with the description of a new genus and two new species from Brazil (Araneae: Trechaleidae) Abstract Trechaleidae is a family of spiders often recognized by its semiaquatic species, but its diversity extends beyond these well-known examples. In this study, we describe Troglotrechalea gen. nov. , a new genus with two novel species, T. faleroae spec. nov. and T. agorai spec. nov. , found exclusively in subterranean habitats within karst formations in central and southeastern Brazil. Both species exhibit pale coloration, but unmodified eyes and legs if compared to other species in the family. The slight degree of troglomorphism, along with their geographic and habitat records, suggests that these species are restricted to hypogean habitats, although they probably move through epigean habitats. Additionally, we report in detail the occurrence of the trechaleid genera Enna O. Pickard-Cambridge, 1897, Heidrunea Brescovi...

Allometry and ecology shape eye size evolution in spiders

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Allometry and ecology shape eye size evolution in spiders

Summary

Eye size affects many aspects of visual function, but eyes are costly to grow and maintain. The allometry of eyes can provide insight into this trade-off, but this has mainly been explored in species that have two eyes of equal size. By contrast, animals possessing larger visual systems can exhibit variable eye sizes within individuals. Spiders have up to four pairs of eyes whose sizes vary dramatically, but their ontogenetic, static, and evolutionary allometry has not yet been studied in a comparative context. We report variable dynamics in eye size across 1,098 individuals in 39 species and 8 families, indicating selective pressures and constraints driving the evolution of different eye pairs and lineages. Supplementing our sampling with a recently published phylogenetically comprehensive dataset, we confirmed these findings across more than 400 species; found that ecological factors such as visual hunting, web building, and circadian activity correlate with eye diameter; and identified significant allometric shifts across spider phylogeny using an unbiased approach, many of which coincide with visual hunting strategies. The modular nature of the spider visual system provides additional degrees of freedom and is apparent in the strong correlations between maximum/minimum investment and interocular variance and three key ecological factors. Our analyses suggest an antagonistic relationship between the anterior and posterior eye pairs. These findings shed light on the relationship between spider visual systems and their diverse ecologies and how spiders exploit their modular visual systems to balance selective pressures and optical and energetic constraints.

Chong, K. L., Grahn, A., Perl, C. D., & Sumner-Rooney, L. (2024). Allometry and ecology shape eye size evolution in spiders. Current Biology. https://doi.org/10.1016/j.cub.2024.06.020