Gene expression and structural differences underpinning black and white colouration in spiders

This is a Preprint and has not been peer reviewed. This is version 1 of this Preprint. You must log in to post a comment. There are no comments or no comments have been made public for this article. This is a Preprint and has not been peer reviewed. This is version 1 of this Preprint. Add a Comment You must log in to post a comment. Comments There are no comments or no comments have been made public for this article. The presence of multiple colour variants within a single population, known as colour polymorphism, is a striking example of intraspecific phenotypic variation and a model for studying evolutionary processes. These processes depend on the underlying mechanisms such as the genes and pigments involved; but we currently lack such information for non-model groups such as arachnids. We examined the genes associated with colour polymorphism in the Australian Christmas spider, Austracantha minax, a widespread species with two female-restricted colour morphs: one that is completely black and the other presenting a black-and-white pattern on its dorsum. We sequenced the mRNA of individuals of both morphs at different developmental stages and assessed differences in gene expression between colour morphs based on a de novo transcriptome assembly for the species, and integrated this with high resolution electron microscopy observations. We found that gene expression patterns are primarily influenced by the stage of development, and within each stage we found differentially expressed genes between the black and black-and-white morphs, especially in the adult stage. Contrary to expectations, these genes were not associated with melanin or guanine crystal deposition (detected in the microscopy), but were associated with chitin and cuticle metabolic processes. By exploring arachnid coloration at the transcriptomic level, our work reveals for the first time genetic mechanisms underpinning the evolution of colour polymorphism in spiders. https://doi.org/10.32942/X2VS9Q Ecology and Evolutionary Biology, Entomology, Life Sciences colour polymorphism, chitin metabolism, melanin, arachnids Published: 2025-12-05 12:37 CC-BY Attribution-NonCommercial-ShareAlike 4.0 International Conflict of interest statement: None Language: English