Project description:Spiders are renowned for their efficient capture of flying insects using intricate aerial webs. How the spider nervous systems evolved to cope with this specialized hunting strategy and various environmental clues in an aerial space remains unknown. Here, we report a brain cell atlas of >30,000 single-cell transcriptomes from a web-building spider (Hylyphantes graminicola). Our analysis revealed the preservation of ancestral neuron types in spiders, including the potential coexistence of noradrenergic and octopaminergic neurons, and many peptidergic neuronal types that are lost in insects. By comparing the genome of two newly sequenced plesiomorphic burrowing spiders with three aerial web-building spiders, we found that the positively selected genes in the ancestral branch of web-building spiders were preferentially expressed (42%) in the brain, especially in the three mushroom body-like neuronal types. By gene enrichment analysis and RNAi experiments, these genes were suggested to be involved in the learning and memory pathway and may influence the spiders’ web-building and hunting behavior. Our results provide key sources for understanding the evolution of behavior in spiders and reveal how molecular evolution drives neuron innovation and the diversification of associated complex behaviors.
Project description:About 430 million years ago spiders and scorpions evolved from a common ancestor that had experienced a whole genome duplication (WGD) The genetic remnants of this WGD event (genes called ohnologs) can still be found in the genome of the approximately 45,000 species of these animals alive today and these ohnologs may have contributed to their adaptation and diversification. Interestingly, the WGD in arachnids like scorpions and spiders was contemporary with independent WGDs in vertebrates. This presents an opportunity to compare these events to determine if there are general principals underlying the outcomes of WGDs and their contribution to animal diversification. Therefore, the aims of this project are to identify arachnid ohnologs, explore how they have contributed to the evolutionary success of these animals, and compare the outcomes of this event to WGD in vertebrates. This includes sequencing new genomes and transcriptomes of species occupying key phylogenetic positions.
Project description:Spiders are a highly diverse group of arthropods that occur in most habitats on land. Notably, spiders have significant ecological impact as predators because of their extraordinary prey capture adaptations, venom and silk. Spider venom is among the most heterogeneous animal venoms and has pharmacological applications, while spider silk is characterized by great toughness with potential for biomaterial application. We describe the genome sequences of two spiders representing two major taxonomic groups, the social velvet spider Stegodyphus mimosarum (Araneomorphae), and the Brazilian white-knee tarantula Acanthoscurria geniculata (Mygalomorphae). We annotate genes using a combination of transcriptomic and in-depth proteomic analyses. The genomes are large (2.6 Gb and 6 Gb, respectively) with short exons and long introns and approximately 50% repeats, reminiscent of typical mammalian genomes. Phylogenetic analyses show that spiders and ticks are sister groups outgrouped by mites, and phylogenetic dating using a molecular clock dates separation of velvet spider and tarantula at 270 my. Based on the genomes and proteomes, we characterize the genetic basis of venom and silk production of both species in detail. Venom protein composition differs markedly between the two spiders, with lipases as the most abundant protein in the velvet spider and present only at low concentration in tarantula. Venom in both spiders contains proteolytic enzymes, and our analyses suggest that these enzymes target and process precursor peptides that subsequently mediate the toxic effects of venom. Complete analysis of silk genes reveal a diverse suite of silk proteins in the velvet spider including novel types of spidroins, and dynamic evolution of major ampullate spidroin genes, whereas silk protein diversity in tarantula is far less complex. The difference in silk proteins between species is consistent with a more complex silk gland morpholgy and use of three-dimentional capture webs consisting of multiple silk types in aranomorph spiders.
Project description:Spiders have distinct capture prey behaviors selected along Araneae´s evolutive history, but mainly based on the use of venom for prey paralysis. Uloboridae spiders lost the venom glands secondarily in evolution. Due to that they extensively wrap prey with silk to paralyze and begin digestion. During the extra-oral digestion, the digestive fluid very efficiently performs the liquefaction of both the prey and the AcSp2 spidroins from the web fibers. Despite the efficiency of this process, the cocktail of enzymes involved in digestion in Uloboridae spiders is unknown. In this study, we evaluated the protein content in the midgut of Uloborus sp. using enzymatic, proteomic, and phylogenetic analysis approaches. Hydrolases as peptidases (endo and exopeptidases: cysteine, serine and metallopeptidases), carbohydrases (alpha-amylase, chitinase, alpha-mannosidase), and lipases were biochemically assayed; 50 proteins, annotated as enzymes, structural proteins, and toxins, were identified. This is the first characterization of the molecules involved in the digestive process and the midgut protein content of a nonvenomous spider.
Project description:Coding and non-coding mutations in DNA contribute significantly to phenotypic variability during evolution. However, less is known about the role of epigenetics in this process. Although previous studies have identified eye development genes associated with the loss of eyes phenotype in the Pachón blind cave morph of the Mexican tetra Astyanax mexicanus1-6, no inactivating mutations have been found in any of these genes2,3,7-10. Here we show that excess DNA methylation-based epigenetic silencing promotes eye degeneration in blind cave Astyanax mexicanus. By performing parallel analyses in Astyanax mexicanus cave and surface morphs and in the zebrafish Danio rerio, we have discovered that DNA methylation mediates eye-specific gene repression and globally regulates early eye development. The most significantly hypermethylated and down-regulated genes in the cave morph are also linked to human eye disorders, suggesting the function of these genes is conserved across the vertebrates. Our results show that changes in DNA methylation-based gene repression can serve as an important molecular mechanism generating phenotypic diversity during development and evolution.