Species of infraorder Gryllidea, or crickets, are useful invertebrate models for studying developmental biology and neuroscience. They have also attracted attention as alternative protein sources for human food and animal feed. Mitochondrial genomic information on related invertebrates, such as katydids, and locusts, has recently become available in attempt to clarify the controversial classification schemes, although robust phylogenetic relationships with emphasis on crickets remain elusive. Here, we report newly sequenced complete mitochondrial genomes of crickets to study their phylogeny, genomic rearrangements, and adaptive evolution. First, we conducted de novo assembly of mitochondrial genomes from eight cricket species and annotated protein-coding genes (PCGs) and transfer and ribosomal RNAs using automatic annotations and manual curation. Next, by combining newly described PCGs with public data of the complete Gryllidea genomes and gene annotations, we performed phylogenetic analysis and found gene order rearrangements in several branches. We further analyzed genetic signatures of selection in ant-loving crickets (Myrmecophilidae), which are small wingless crickets that inhabit ant nests. Three distinct approaches revealed two positively selected sites in the cox1 gene in these crickets. Protein 3D structural analyses suggested that these selected sites could influence the interaction of respiratory complex proteins, conferring benefits to ant-loving crickets with a unique ecological niche and morphology. These findings enhance our understanding of the genetic basis of cricket evolution without relying on estimates based on a limited number of molecular markers.

Endocannabinoid system activity contributes to the homeostatic defense against aging and thus may counteract the progression of brain aging. The cannabinoid type 1 (CB1) receptor activity declines with aging in the brain, which impairs neuronal network integrity and cognitive functions. However, the underlying mechanisms that link CB1 activity and memory decline remain unknown. Mitochondrial activity profoundly influences neuronal function, and age-dependent mitochondrial activity change is one of the known hallmarks of brain aging. As CB1 receptor is expressed on mitochondria and may regulate neuronal energy metabolism in hippocampus, we hypothesized that CB1 receptors might influence mitochondria in hippocampal neurons. Here, we found that CB1 receptor significantly affected mitochondrial autophagy (mitophagy) and morphology in an age-dependent manner. Serine 65-phosphorylated ubiquitin, a key marker for mitophagy, was reduced in adult CB1-deficient mice (CB1-KO) compared to those in wild type controls, particularly in CA1 pyramidal cell layer. Transmission electron microscopy (TEM) analysis showed reduced mitophagy-like events in hippocampus of adult CB1-KO. TEM analysis also showed that mitochondrial morphology in adult CB1-KO mice was altered shown by an increase in thin and elongated mitochondria in hippocampal neurons. 3D reconstruction of mitochondrial morphology after scanning electron microscopy additionally revealed an enhanced density of interconnected mitochondria. Altogether, these findings suggest that reduced CB1 signaling in CB1-KO mice leads to reduced mitophagy and abnormal mitochondrial morphology in hippocampal neurons during aging. These mitochondrial changes might be due to the impairments in mitochondrial quality control system, which links age-related decline in CB1 activity and impaired memory.