ArticleBMC genomics2026
Lineage-specific expansion and positive selection of NPC2 genes in the crab spider Ebrechtella tricuspidata and other arachnids.
Article in BMC genomics, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
backgroundNiemann-Pick type C2 (NPC2) proteins have been proposed as soluble carriers for semiochemicals in arthropods, serving as putative functional substitutes for the canonical odorant-binding proteins (OBPs) largely absent in arachnids. However, the evolutionary mechanisms driving NPC2 diversification in spiders—particularly in ambush predators relying heavily on chemical cues—remain unclear.
resultsWe identified a minimum expressed repertoire of 13 high-confidence NPC2 genes in the crab spider Ebrechtella tricuspidata via comprehensive transcriptomic profiling. Comparative phylogenomics across 21 arthropod species revealed that while the generalist herbivore mite Tetranychus urticae underwent a significant repertoire expansion (+ 9 genes, P < 0.001), the E. tricuspidata lineage exhibited a modest numerical gain (+ 3 genes). Despite this, transcriptomic data revealed a striking functional dichotomy within the spider repertoire. The basal singleton EtriNPC2-2 was highly enriched in the abdomen, suggesting a conserved role in visceral lipid transport. In contrast, the derived Etri-B subclade (EtriNPC2-1, -3) and the singleton EtriNPC2-4 were predominantly expressed in chemosensory appendages (palps and legs). This spatial expression shift coincided with strong signatures of episodic positive selection acting on the Etri-B lineage. Structural modeling identified a key adaptive substitution (L33→Q31) at the pocket entrance of EtriNPC2-3, serving as a prime candidate for future functional validation regarding ligand access in the sensillar lymph.
conclusionsOur findings suggest a clear pattern of neofunctionalization, where gene duplication enabled spider NPC2s to diverge from an ancestral visceral function toward a specialized sensory role. This linkage between spatial expression shifts and adaptive sequence evolution provides essential molecular evidence for how ambush spiders evolved a complex chemosensory system in the absence of insect-type OBPs.
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