Coincident evolution and functional adaptation of the taxonomically restricted genes <i>ivph-3</i> and <i>gon-14</i> in <i>Caenorhabditis</i> nematodes

Poorly conserved or taxonomically restricted genes represent a sizable portion of most genomes. Many of these genes participate in essential processes and can contribute to evolutionary innovation in species. Here, we evaluate two of the Caenorhabditis-restricted class of LIN-15B-domain-encoding genes, ivph-3 and gon-14, and compare their in vivo functions in two species, C. elegans and C. briggsae. We show that within the Elegans supergroup, ivph-3 and gon-14 exhibit sequence constraints distinct from other family members, including maintenance of a one-to-one orthology and a higher degree of sequence conservation. Coincidentally, mutants for either of the genes exhibit strong phenotypic defects that are similar within species (C. elegans or C. briggsae), but with notable differences when comparing between species. These findings highlight the genetic and genomic features associated with the evolution of a taxonomically restricted gene family.