New Insight Into the Evolutionary Arms Race Between Spider Egg Sac Pseudoparasitoids and Active Maternal Care by the Spiders

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  New Insight Into the Evolutionary Arms Race Between Spider Egg Sac Pseudoparasitoids and Active Maternal Care by the Spiders ABSTRACT Pseudoparasitoids can lead to high mortality in spider egg sacs, and in some cases, they reduce the reproductive success of a spider female to zero. On the other hand, a species that develops within the spider's egg sac uses a limited resource derived from a single egg sac for its larval development. Therefore, the most crucial behaviour that increases the fitness of free-living pseudoparasitoid females is choosing the best host for their offspring. We analysed various points of the counter-adaptations of the spider egg sac pseudoparasitoid and spiders exhibiting active maternal care, utilising the ichneumonid  Hidryta fusiventris  (Thomson, 1873) and the wolf spider  Pardosa lugubris  (Walckenaer, 1802). We showed that the oviposition decision of  H. fusiventris  is based on the spider's egg sac size and that the fema...

Extended phenotype affects somatic phenotype in spiders: web builders have lower estimated biting forces than free hunters

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Extended phenotype affects somatic phenotype in spiders: web builders have lower estimated biting forces than free hunters

Abstract

Reciprocal selection between extended and somatic phenotypes is an active area of investigation. Recent research on the influence of web building on somatic evolution in spiders has produced conflicting results, with some finding no effect of web use on somatic evolution and others showing significant effects. These studies differed in focus, with the former surveying general anatomical traits and the latter concentrating on somatic systems with significant functional roles in prey capture. Here we propose and test the hypothesis that prey immobilization by webs is broadly synergistic with cheliceral biting force and that web builders have lower cheliceral forces compared to free hunters. Our analysis focused on the intercheliceral (IC) sclerite and muscles, a newly characterized system that is synapomorphic and ubiquitously distributed in spiders. Using µCT scans, we quantify IC sclerite shape and model IC muscle function. Statistical analyses show that inferred size-corrected isometric muscle force is lower in web-builders than in free-hunters. No such association was found for IC sclerite shape. In the investigation of reciprocal selective effects between extended and somatic phenotypes, our results highlight the importance that these traits be functionally linked and adaptive.

Black, C. R., Shultz, J. W., & Wood, H. M. Extended phenotype affects somatic phenotype in spiders: Web builders have lower estimated biting forces than free hunters. Evolution. https://doi.org/10.1093/evolut/qpae170