Intersexual Differences in the Gene Expression of Phoneutria depilata (Araneae, Ctenidae) Toxins Revealed by Venom Gland Transcriptome Analyses.

The wandering spider, Phoneutria depilata, is one of Colombia's most active nocturnal arthropod predators of vertebrates and invertebrates. Its venom has been a relevant subject of study in the last two decades. However, the scarcity of transcriptomic data for the species limits our knowledge of the distinct components present in its venom for linking the mainly neurotoxic effects of the spider venom to a particular molecular target. The transcriptome of the P. depilata venom gland was analyzed to understand the effect of different diets or sex and the impact of these variables on the composition of the venom. We sequenced venom glands obtained from ten males and ten females from three diet treatments: (i) invertebrate: Tenebrio molitor, (ii) vertebrate: Hemidactylus frenatus, and (iii) mixed (T. molitor + H. frenatus). Of 17,354 assembled transcripts from all samples, 65 transcripts relating to venom production differed between males and females. Among them, 36 were classified as neurotoxins, 14 as serine endopeptidases, 11 as other proteins related to venom production, three as metalloprotease toxins, and one as a venom potentiator. There were no differences in transcripts across the analyzed diets, but when considering the effect of diets on differences between the sexes, 59 transcripts were differentially expressed. Our findings provide essential information on toxins differentially expressed that can be related to sex and the plasticity of the diet of P. depilata and thus can be used as a reference for venomics of other wandering spider species.

Comparative analysis of codon usage of mitochondrial genomes provides evolutionary insights into reptiles.

Current available information on reptile genomes provides great potential for the study of unique adaptations from a genomic perspective. We compared differences in base composition and codon usage patterns across 400 reptile mitochondrial genomes assessing AT and GC skew, GC frequency, codon usage, effective number of codons, and codon adaptation index. We identified poor GC content in reptile mitochondrial genomes, with a predominant bias toward Adenine. We determined a compositional asymmetry between different taxonomic groups, which are inversely correlated to the rates of rearrangements in the mitogenome. We found that the most common codons in reptile mitochondrion are CTA (L), ATA (M) and ACA (T), which relates with have been found in birds, meaning that these patterns are shared across sauropsid mitogenomes. Codon usage bias clustering and effective codon number analyses revelated compositional asymmetry based on RSCU as well as that reptile mitogenomes are translationally efficient and are under selection pressure. Codon adaptation index revealed highest values in turtles indicating higher translational efficiency of mitochondrial genes among all reptiles, which could be related to metabolic adaptations (i.e., tolerance to anoxic conditions). This was also seen in other groups such as crocodiles (i.e., acclimation to cold) and snakes (phylogenetic origin of toxin-secreting oral glands and the evolutionary redesign of cytochrome c oxidase complex genes). We discuss our findings in the context of potential adaptations and evolutionary implications that these genomic differences provide to reptiles.