Meeting Abstract
Evolutionary novelty can arise from the emergence of new cell types with new biological functions. How new cell types are constructed molecularly during evolution is poorly understood. Here, we deconstruct the assembly of novel cell types comprising an evolutionary key innovation in animals using single cell sequencing. A chemical defense gland in rove beetles (Staphylinidae) is the putative catalyst behind the global radiation of this clade into >16,000 species. We show how defense gland function was pieced together from ancestral molecular source material to create two, clade-specific secretory cell types, each capable of synthesizing and secreting distinct compound classes. Production of noxious benzoquinones by one cell type evolved from duplication of a tyrosine-oxidizing laccase enzyme, with an ancestral role in cuticle tanning. Production of a short-chain alkane by the second cell type evolved from recruitment of a partially duplicated cuticular hydrocarbon pathway lacking elongase-mediated chain extension. The alkane-producing cells form an epithelial reservoir into which both cell types secrete, the alkane dissolving the benzoquinones to create a bioactive defensive secretion. These results exemplify how cell types with new properties are constructed through molecular evolution, and can synergize to create emergent organ functions.
