| Summary: | Cytochrome P450s (<i>CYP</i>s) are xenobiotic detoxification genes found in most eukaryotes, and linked in insects to the tolerance of plant secondary chemicals and insecticide resistance. The number and diversity of <i>CYP</i> clans, families, and subfamilies that an organism produces could correlate with its dietary breadth or specialization. This study examined the <i>CYP</i> diversity expressed in the midguts of six species of folivorous stick insects (Phasmatodea), to identify their <i>CYP</i> complement and see if any <i>CYP</i>s correlate with diet toxicity or specialization, and see what factors influenced their evolution in this insect order. <i>CYP</i> genes were mined from six published Phasmatodea transcriptomes and analyzed phylogenetically. The Phasmatodea <i>CYP</i> complement resembles that of other insects, though with relatively low numbers, and with significant expansions in the <i>CYP</i> clades <i>6J1</i>, <i>6A13/14</i>, <i>4C1</i>, and <i>15A1</i>. The <i>CYP</i>6 group is known to be the dominant <i>CYP</i> family in insects, but most insects have no more than one <i>CYP15</i> gene, so the function of the multiple <i>CYP15A1</i> genes in Phasmatodea is unknown, with neofunctionalization following gene duplication hypothesized. No correlation was found between <i>CYP</i>s and diet specialization or toxicity, with some <i>CYP</i> clades expanding within the Phasmatodea and others likely inherited from a common ancestor.
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