Molecular Divergence Between Two Geographically Overlapping Cryptic Crickets: Loxoblemmus campestris and...

Understanding the minimal genetic changes underlying the earliest stages of speciation remains a central challenge in evolutionary biology. However, most model systems used to study early speciation involve pronounced ecological divergence, making it difficult to isolate the initial genetic changes associated with speciation. Here, we examined genetic differences between the cryptic cricket species Loxoblemmus campestris and L. sylvestris, which inhabit the same geographic region without pronounced ecological or morphological divergence. Despite their morphological similarity, the two species exhibited small but consistent molecular phylogenetic divergence in both mitochondrial and nuclear genomes. To investigate genetic divergence between these species, we conducted population genomic and comparative genomic analyses. We identified amino acid substitutions that were common within each species across orthologous genes and evaluated their evolutionary probabilities (EPs) based on sequence conservation across Orthoptera. Although low EP amino acid substitutions occurred in multiple genes, three genes-Raf, Slit, and Sur-8-contained multiple such substitutions, and all three also showed elevated F _ST values. These genes are functionally connected within the Ras/MAPK signaling pathway. These findings suggest that genetic divergence between L. campestris and L. sylvestris may involve changes concentrated in a limited number of functionally connected genes despite relatively few amino acid substitutions and limited phenotypic differentiation. Cryptic Loxoblemmus species may therefore provide useful systems for investigating early genomic divergence associated with speciation in the absence of pronounced phenotypic divergence.