Peretti, A. V. | bioRxiv Science

bioRxiv2024

A novel expression domain of extradenticle underlies the evolutionary developmental origin of the chelicerate patella

Neofunctionalization of duplicated gene copies is thought to be an important process underlying the origin of evolutionary novelty and provides an elegant mechanism for the origin of new phenotypic traits. One putative case where a new gene copy has been linked to a novel morphological trait is the origin of the arachnid patella, a taxonomically restricted leg segment. In spiders, the origin of this segment has been linked to the origin of the paralog dachshund-2, suggesting that a new gene facilitated the expression of a new trait. However, various arachnid groups that possess patellae do not have a copy of dachshund-2, disfavoring the direct link between gene origin and trait origin. We investigated the developmental genetic basis for patellar patterning in the harvestman Phalangium opilio, which lacks dachshund-2. Here, we show that the harvestman patella is established by a novel expression domain of the transcription factor extradenticle. Leveraging this definition of patellar identity, we surveyed targeted groups across chelicerate phylogeny to assess when this trait evolved. We show that a patellar homolog is present in Pycnogonida (sea spiders) and various arachnid orders, suggesting a single origin of the patella in the ancestor of Chelicerata. A potential loss of the patella is observed in Ixodida. Our results suggest that the modification of an ancient gene, rather than the neofunctionalization of a new gene copy, underlies the origin of the patella. Broadly, this work underscores the value of comparative data and broad taxonomic sampling when testing hypotheses in evolutionary developmental biology.

evolutionary biology↗

bioRxiv2018

Immunological female role tested on artificial plugs in three scorpion species

Within arachnids, genital plugs are morphologically diverse, and they can be formed by male, female or be a contribution of both sexes. Although several species of scorpions with genital plugs are known, the physiological effects on the female after being plugged have not been well studied yet. This work compares three scorpion species, two with genital plugs and one without. We first describe the genital plugs morphology of two Urophonius species. Second, through the placement of artificial genital plugs in the female genital atrium, we tested 1) whether there are interspecific differences in the immune encapsulation response on the artificial genital plug, 2) if there are an effect in the hemocyte load in the hemolymph, and 3) if individuals immunological parameters and body weight are correlated. Additionally, we describe and quantify the hemocytes in these species. In both species of Urophonius, genital plugs were found covering the female genital aperture and blocking the genital atrium. The plugs consist of three zones that are distinct in morphology and coloration. We found different patterns of encapsulation and melanization on the artificial plug according to the species, with a greater and more specific response in females of plug producing species. Also, these species showed a decrease in the hemocyte load one month after the placement of the artificial plug, possibly due to the recirculation of the hemocytes into the genital area. In addition, correlations were found between the body weight and the immunological parameters, as well as between different immunological parameters. Our results suggest that females contribute to the formation of genital plugs by adding material and generating the darkening of the genital plugs in certain zones. This comparative study can help to provide a wider framework of different physiological consequences related to a particular postcopulatory mechanism such as the genital plugs.

evolutionary biology↗