Genomic and transcriptomic analyses reveal the adaptation to semi-aquatic and aquatic life in spiders

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  Genomic and transcriptomic analyses reveal the adaptation to semi-aquatic and aquatic life in spiders Abstract Spiders are largely terrestrial, but some lineages have independently adapted to marine and freshwater habitats. Although physiological and behavioral traits supporting these evolutionary transitions have been characterized, the genomic basis of adaptation to aquatic and semi-aquatic habitats in spiders remains unclear. Here, we report a chromosome-level genome assembly for the aquatic spider Argyroneta aquatica. Comparative analysis of 22 spider species supports two independent transitions in semi-aquatic (∼56 Mya) and aquatic (∼44 Mya) lineages. The aquatic spider show distinct respiratory morphology compared with terrestrial spiders, including anterior spiracles and denser tracheoles. Molecular evolution analyses identified lineage-specific shifts in selective constraint or evidence of positive selection linked to trachea development (e.g., Wnt-1, Catenin beta, TMEM23...

Batesian Mimicry Converges Towards Inaccuracy in Myrmecomorphic Spiders

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Batesian Mimicry Converges Towards Inaccuracy in Myrmecomorphic Spiders

Abstract

Batesian mimicry is an impressive example of convergent evolution driven by predation. However, the observation that many mimics only superficially resemble their models despite strong selective pressures is an apparent paradox. Here, we tested the ‘perfecting hypothesis’, that posits that inaccurate mimicry may represent a transitional stage at the macro-evolutionary scale by performing the hereto largest phylogenetic analysis (in terms of the number of taxa and genetic data) of ant-mimicking spiders across two speciose but independent clades, the jumping spider tribe Myrmarachnini (Salticidae) and the sac spider sub-family Castianeirinae (Corinnidae). We found that accurate ant mimicry evolved in a gradual process in both clades, by an integration of compound traits contributing to the ant-like habitus with each trait evolving at different speeds. Accurate states were highly unstable at the macro-evolutionary scale likely because strong expression of some of these traits comes with high fitness costs. Instead, the inferred global optimum of mimicry expression was at an inaccurate state. This result reverses the onus of explanation from inaccurate mimicry to explaining the exceptional evolution and maintenance of accurate mimicry and highlights that the evolution of Batesian mimicry is ruled by multiple conflicting selective pressures.

Kelly, M. B., Derkarabetian, S., McLean, D. J., Shofner, R., Grismado, C. J., Haddad, C. R., Cassis, G., Giribet, G., Herberstein, M. E., & Wolff, J. O. Batesian Mimicry Converges Towards Inaccuracy in Myrmecomorphic Spiders. Systematic Biology. https://doi.org/10.1093/sysbio/syaf037