Molecular analysis of some camel cytochrome P450 enzymes reveals lower evolution and drug-binding properties

Camels bear unique genotypes and phenotypes for adaptation of their harsh environment. They have unique visual systems, sniffing, water metabolism, and heat-control mechanisms that are different from other creatures. The recent announcement for the complete sequence of camel genome will allow for the discovery of many secrets of camel life. In this context, the genetic bases of camel drug-metabolizing enzymes are still unknown. Furthermore, the genomic content of camel that rendered it highly susceptible to some drugs (as monensin and salinomycin) and became easily intoxicated needs to be investigated. The objectives of this work are the annotation of camel genome and retrieval of camel for cytochrome P450 (CYP) 1A1, 2C, and 3A enzymes. This is followed by comprehensive phylogenetic, evolution, molecular modeling, and docking studies. In comparison with the human enzymes, camel CYPs showed lower evolution rate, especially CYP1A1. Furthermore, the binding of monensin, salinomycin, alfa-naphthoflavone, felodepine, and ritonavir was weaker in camel enzymes. Interestingly, rerank score indicated instable binding of monensin and salinomycin with camel CYP1A1 as well as salinomycin with camel CYP2C. The results of this work suggest that camels are more susceptible to toxicity with compounds undergoing metabolic oxidation. This conclusion was based on lower evolution rate and lower binding potency of camels compared with the human enzymes.     

Genetic diversity and population structure of Mongolian domestic Bactrian camels (Camelus bactrianus)

The tradition of animal husbandry in the context of a nomadic lifestyle has been of great significance in the Mongolian society. Both Bactrian camels and horses have been invaluable for the survival and development of human activities in the harsh arid environment of the Mongolian steppe. As camels offer unique and sustainable opportunities for livestock production in marginal agro‐ecological zones, we investigated the current genetic diversity of three local Mongolian camel breeds and compared their levels of variation with common native Mongolian camels distributed throughout the country. Based on mitochondrial and nuclear markers, we found levels of genetic diversity in Mongolian populations similar to that reported for Chinese Bactrian camels and for dromedaries. Little differentiation was detected between single breeds, except for a small group originating from the northwestern Mongolian Altai. We found neither high inbreeding levels in the different breeds nor evidence for a population decline. Although the Mongolian camel census size has severely declined over the past 20 years, our analyses suggest that there still exists a stable population with adequate genetic variation for continued sustainable utilization.     

Genetic diversity and phylogeographic structure of Bactrian camels shown by mitochondrial sequence variations

The Bactrian camel includes various domestic (Camelus bactrianus) and wild (Camelus ferus) breeds that are important for transportation and for their nutritional value. However, there is a lack of extensive information on their genetic diversity and phylogeographic structure. Here, we studied these parameters by examining an 809‐bp mtDNA fragment from 113 individuals, representing 11 domestic breeds, one wild breed and two hybrid individuals. We found 15 different haplotypes, and the phylogenetic analysis suggests that domestic and wild Bactrian camels have two distinct lineages. The analysis of molecular variance placed most of the genetic variance (90.14%, P < 0.01) between wild and domestic camel lineages, suggesting that domestic and wild Bactrian camel do not have the same maternal origin. The analysis of domestic Bactrian camels from different geographical locations found there was no significant genetic divergence in China, Russia and Mongolia. This suggests a strong gene flow due to wide movement of domestic Bactrian camels.     

Microscopic and molecular detection of Deraiophoronema evansi (Lewis, 1882) in domestic Bactrian camels (Camelus bactrianus) of Mongolia

Cameline filarosis is an important parasitic disease having an economic impact on the camel industry around the world. However, there has been no study on filarosis in Bactrian camels of Mongolia. Therefore, the aim of the present study was to detect and identify microfilariae of Deraiophoronema evansi (D. evansi) in Bactrian camels from three provinces, located in southern and southwestern Mongolia. Blood samples were obtained from 400 healthy two-humped camels of different ages and both sexes. All blood samples were analysed using a variety of diagnostic techniques. Microfilariae were detected in 30 Bactrian camels (7.5%) by the Knott technique, while 13 Bactrian camels (3.3%) tested positive in a direct smear test. D. evansi was detected in 18 Bactrian camels (4.5%) by PCR assay. Prevalence was shown to be high among Bactrian camels in the age group up to 5 years, while the lowest positive results were obtained for Bactrian camels in the 5–10-year age group and the over 10-year age group. To confirm the morphological identification, D. evansi–COI gene sequences were subjected to phylogenetic analyses. The D. evansi–COI gene sequences from Mongolian two-humped camels were identical to sequences from Iranian one-humped camels and were clustered together with these sequences in the phylogeny. This is the first report of molecular detection and identification of microfilariae of D. evansi in Bactrian camels of Mongolia.     

Population genetic analysis of the domestic Bactrian camel in China by RAD‐seq

Restriction site‐associated DNA sequencing (RAD‐seq) is one of the most effective high‐throughput sequencing technologies for SNP development and utilization and has been applied to studying the origin and evolution of various species. The domestic Bactrian camels play an important role in economic trade and cultural construction. They are precious species resources and indispensable animals in China's agricultural production. Recently, the rapid development of modern transportation and agriculture, and the deterioration of the environment have led to a sharp decline in the number of camels. Although there have been some reports on the evolution history of the domestic Bactrian camel in China, the origin, evolutionary relationship, and genetic diversity of the camels are unclear due to the limitations of sample size and sequencing technology. Therefore, 47 samples of seven domestic Bactrian camel species from four regions (Inner Mongolia, Gansu, Qinghai, and Xinjiang) were prepared for RAD‐seq analysis to study the evolutionary relationship and genetic diversity. In addition, seven domestic Bactrian camel species are located in different ecological zones, forming different characteristics and having potential development value. A total of 6,487,849 SNPs were genotyped. On the one hand, the filtered SNP information was used to conduct polymorphism mapping construction, LD attenuation analysis, and nucleotide diversity analysis. The results showed that the number of SNPs in Dongjiang camel was the highest, the LD coefficient decayed the fastest, and the nucleotide diversity was the highest. It indicates that Dongjiang camel has the highest genetic diversity. On the other hand, the filtered SNPs information was used to construct the phylogenetic tree, and F_ST analysis, inbreeding coefficient analysis, principal component analysis, and population structure analysis were carried out. The results showed that Nanjiang camel and Beijiang camels grouped together, and the other five Bactrian camel populations gathered into another branch. It may be because the mountains in the northern part of Xinjiang and the desert in the middle isolate the two groups from the other five groups.     

Cloning and Molecular Characterization of HSL and Its Expression Pattern in HPG Axis and Testis during Different Stages in Bactrian Camel

Hormone-sensitive lipase (HSL) is a key enzyme in animal fat metabolism and is involved in the rate-limiting step of catalyzing the decomposition of fat and cholesterol. It also plays an important regulatory role in maintaining seminiferous epithelial structure, androgen synthesis and primordial germ cell differentiation. We previously reported that HSL is involved the synthesis of steroids in Bactrian camels, although it is unclear what role it plays in testicular development. The present study was conducted to characterize the biological function and expression pattern of the HSL gene in the hypothalamic pituitary gonadal (HPG) axis and the development of testis in Bactrian camels. We analyzed cloning of the cDNA sequence of the HSL gene of Bactrian camels by RT-PCR, as well as the structural features of HSL proteins, using bioinformatics software, such as ProtParam, TMHMM, Signal P 4.1, SOPMA and MEGA 7.0. We used qRT-PCR, Western blotting and immunofluorescence staining to clarify the expression pattern of HSL in the HPG axis and testis of two-week-old (2W), two-year-old (2Y), four-year-old (4Y) and six-year-old (6Y) Bactrian camels. According to sequence analysis, the coding sequence (CDS) region of the HSL gene is 648 bp in length and encodes 204 amino acids. According to bioinformatics analysis, the nucleotide and amino acid sequence of Bactrian camel HSL are most similar to those of Camelus pacos and Camelus dromedarius, with the lowest sequence similarity with Mus musculus. In adult Bactrian camel HPG axis tissues, both HSL mRNA and protein expression were significantly higher in the testis than in other tissues (hypothalamus, pituitary and pineal tissues) (p < 0.05). The expression of mRNA in the testis increased with age and was the highest in six-year-old testis (p < 0.01). The protein expression levels of HSL in 2Y and 6Y testis were clearly higher than in 2W and 4Y testis tissues (p < 0.01). Immunofluorescence results indicate that the HSL protein was mainly localized in the germ cells, Sertoli cells and Leydig cells from Bactrian camel testis, and strong positive signals were detected in epididymal epithelial cells, basal cells, spermatocytes and smooth muscle cells, with partially expression in hypothalamic glial cells, pituitary suspensory cells and pineal cells. According to the results of gene ontology (GO) analysis enrichment, HSL indirectly regulates the anabolism of steroid hormones through interactions with various targets. Therefore, we conclude that the HSL gene may be associated with the development and reproduction of Bactrian camels in different stages of maturity, and these results will contribute to further understanding of the regulatory mechanisms of HSL in Bactrian camel reproduction.     

Comparison of virokine from camel pseudocowpoxvirus (PCPV) with Interleukin 10 of the Dromedary camel (Camelus dromedarius)

Cellular interleukin-10 (IL-10) gene from the peripheral blood mononuclear cells of the healthy Dromedary camel (Camelus dromedarius) and viral IL-10 (vIL-10) from the skin scabs of the Dromedary camels infected with contagious ecthyma (a parapoxviral infection in the camels) were amplified by polymerase chain reaction, cloned and characterized. Sequence analysis revealed that the open reading frame (ORF) of dromedarian camel IL-10 is 537 bp in length, encoding 178 amino acid polypeptide while open reading frame of vIL-10 from camel is 561 bp, encoding 187 amino acid polypeptide. The Dromedary camel IL-10 exhibited 62.6% and 68.5% sequence identity at the nucleotide and amino acid level, respectively, with vIL-10 from camel. Sequence analysis also revealed that the Dromedary camel IL-10 shared 99.4% and 98.3% identity at the nucleotide and amino acid level, respectively, with the Bactrian camel (Camelus bactrianus). But vIL-10 from camel shared 84.7% and 83.4% sequence identity at the nucleotide and amino acid level, respectively, with vIL-10 from reindeer (Rangifer tarandus), which is a ruminant species belonging to the order Artiodactyla. The present study was conducted to evaluate the evolutionary origin of the camel parapoxvirus with parapoxviruses of cattle and sheep and the resultant sequence analysis revealed that camel parapoxvirus is closely related to cattle parapoxvirus than sheep parapoxvirus (Orf virus).     

Giant cells in the placenta of the bactrian camel in the fetal period of development]

Polyploid giant cells resulting from differentiation of normal cytotrophoblast cells were found in the composition of the placenta cytotrophoblast of the Bactrian camel. In the placenta of the Bactrian camel the transformation of cytotrophoblast cells into multinuclear giant cells is realized via endomitotic polyploidization and distinctly reflects active synthetic processes occurring in these cells related with the trophic function of the placenta. It may be supposed that giant cells of the placenta of female Bactrian camels also participate in the endocrinous function of the placenta. Their histolitical function is completely excluded.     

High mitochondrial differentiation levels between wild and domestic Bactrian camels: a basis for rapid detection of maternal hybridization

Hybridization between wild species and their domestic congeners often threatens the gene pool of the wild species. The last wild Bactrian camel (Camelus ferus) populations in Mongolia and China are examples of populations facing such a hybridization threat. To address this key issue in the conservation of wild camels, we analysed wild, hybrid and domestic Bactrian camels (Camelus bactrianus) originating from Mongolia, China and Austria. Through screening of an 804‐base‐pair mitochondrial fragment, we identified eight mitochondrial haplotypes and found high sequence divergence (1.9%) between C. ferus and C. bactrianus. On the basis of a mitochondrial DNA sequence fixed difference, we developed a diagnostic PCR restriction fragment length polymorphism (PCR‐RFLP) assay to differentiate between wild and domestic camel samples. We applied the assay to 81 individuals and confirmed the origin of all samples including five hybrids with known maternal ancestry. The PCR‐RFLP system was effective for both traditional (blood, skin) and non‐invasive samples (faeces, hair), as well as for museum specimens. Our results demonstrate high levels of mitochondrial differentiation between wild and domestic Bactrian camels and that maternal hybridization can be detected by a rapid and reliable PCR‐RFLP system.     

双峰驼睾丸和隐睾细胞外基质相关蛋白的组织化学特征及超微结构比较

为探索细胞外基质相关蛋白在隐睾双峰驼的分布情况及其组织化学特征,应用电镜技术和多种组织化学方法比较了隐睾和正常睾丸的超微结构,组织化学特点及层粘连蛋白（LN）、Ⅳ型胶原（Col Ⅳ）和硫酸乙酰肝素糖蛋白（HSPG）的分布特征。结果显示：(1)与正常睾丸间质结构相比,光镜下隐睾生精小管发育不全,间质内胶原纤维稀疏,网状纤维分布明显,间质血管及生精小管固有膜PAS及AB-PAS阳性反应较弱。电镜下,隐睾生精上皮基膜明显增生,外围I型胶原纤维较少,管周肌样细胞不典型;间质毛细血管及Leydig细胞周围纤维细胞多见,而正常睾丸在间质毛细血管及Leydig细胞周围多分布有成纤维细胞。(2) 免疫组织化学染色显示,正常睾丸组织的Col Ⅳ、LN及HSPG在Leydig细胞内均为强阳性表达,Col Ⅳ和LN在毛细血管内皮细胞强阳性表达,后者在Sertoli细胞的表达尤为明显,HSPG在精原细胞无表达;隐睾时Col Ⅳ、LN及HSPG在Leydig细胞内阳性表达均明显减弱,Col Ⅳ、LN在管周肌样细胞及毛细血管内皮细胞阳性表达也减弱明显,HSPG在精原细胞较强阳性表达,且在精子细胞呈强阳性表达。免疫组织化学图像分析结果显示,双峰驼正常睾丸组织中Col Ⅳ和LN的分布显著高于隐睾组织（P<0.05）,HSPG检测结果在正常睾丸与隐睾之间无统计学差异（P>0.01）。该研究表明,双峰驼隐睾生精小管发育异常,间质组织中合成胶原纤维的能力下降,睾丸细胞外基质的重要成分Col Ⅳ,LN与正常组差异显著与生精小管及Leydig细胞异常发育有关,而HSPG在隐睾生精上皮的强阳性表达与精原细胞发育不成熟密切相关。     

Flavin-containing monooxygenase activity in camel tissues: comparison with rat and human liver enzymes

We previously reported the occurrence of multiple forms of drug metabolizing enzymes in camel tissues. In this study, we demonstrated for the first time, flavin-containing monooxygenase (FMO)-dependent metabolism of two model substrates methimazole (MEM) and N,N'-dimethylaniline (DMA) by camel liver, kidney, brain and intestine. FMO-catalyzed metabolism in the microsomes of camel tissues was independent of cytochrome P450 (CYP) activity and exhibited a pH and temperature dependence characteristic of FMO enzymes. Use of inhibitors of CYP activities, SKF525A, octylamine or antibody against NADPH-P450 reductase, did not significantly alter the FMO-dependent substrate metabolism. Using MEM as a model substrate for FMO activity, we show that camel liver has an activity similar to that in rat and human livers. MEM metabolism in extrahepatic tissues in camels was significantly lower (60%-80%) than that in liver. Our results suggest occurrence of FMO in camel tissues, with catalytic properties similar to those in rat and human livers. These results may help in better understanding the effects of pharmacologically and toxicologically active compounds administered to camels.     

New Pliocene remains of Camelus grattardi (Mammalia,Camelidae) from the Shungura Formation,Lower Omo Valley,Ethiopia, and the evolution of African camels

Abstract

Camels are exceptionally rare in the Plio-Pleistocene fossil record of Africa, hindering attempts to understand the evolution of this family on the continent. Here we describe recently collected camel specimens from the Shungura Formation, Lower Omo Valley, Ethiopia, and attribute these remains to Camelus grattardi. The new specimens date to the late Pliocene (~3 to 2.6 Ma) and consist of three upper molars, one upper premolar, and two proximal metatarsals. The dental specimens confirm this species’ small P4 relative to its molars, a trait that differs significantly from all extant and fossil Old World camels. The metatarsals indicate that C. grattardi was similar in size to the living Bactrian camel, C. bactrianus. Phylogenetically, we find no suitable ancestor, sister, or descendant of the eastern African fossil camel, which suggests greater lineage diversity in Plio-Pleistocene Camelus than previously recognised. Microwear analyses suggest that C. grattardi was likely a mixed-feeder preferring browse, which is consistent with carbon isotopes of enamel from the Turkana Basin. A review of the fossil record of African camels suggests no clear paleoenvironmental association, as fossil camels occur in a range of environments from dry savannas with no permanent water bodies to closed woodlands along the paleo-Omo River.     

Redox homeostasis and respiratory metabolism in camels (Camelus dromedaries): comparisons with domestic goats and laboratory rats and mice

We have previously reported the occurrence of multiple forms of drug-metabolizing enzymes in camel tissues. Here, we investigate glutathione (GSH)-dependent redox homeostasis, reactive oxygen species (ROS) production and mitochondrial respiratory functions in camel tissues and compare them with imported domestic goats and laboratory rats and mice. Cytochrome P450 2E1 (CYP 2E1) and GSH-metabolizing enzymes were differentially expressed in the liver and kidney of these animals. Camel liver has significantly lower GSH pool than that in goats, rats and mice. Mitochondria isolated from the tissues of these animals showed a comparable ability to metabolize specific substrates for respiratory enzyme complexes I, II/III and IV. These complexes were metabolically more active in the kidney than in the liver of all the species. Furthermore, the activity of complex IV in camel tissues was significantly lower than in other species. On the other hand, complex II/III activity in camel kidney was higher compared to the other species. In addition, as expected, we observed that inhibitors of these enzyme complexes augment the production of mitochondrial ROS in camel and goat tissues. These results help to better understand the metabolic ability and adaptation in desert camels in comparison with domestic goats and laboratory rats and mice since they are exposed to different environmental and dietary conditions. Our study may also have implications in the pharmacology and toxicology of drugs and pollutants in these species.     

Results of <Emphasis Type="Italic">Camelus dromedarius</Emphasis> and <Emphasis Type="Italic">Camelus bactrianus</Emphasis> Genotyping by Alpha-S<Subscript>1</Subscript>-Casein,Kappa-Casein Loci,and DNA Fingerprinting

Genotyping of Kazakh camels Camelus dromedarius (milk breed) (n = 18) and Camelus bactrianus (meat breed) (n = 18) by alpha-S₁-casein (αs₁-CN) and kappa-casein (κ-CN) loci was conducted using the PCR–RFLP analysis method. A new pair of primers was suggested for the amplification of the CSN3 gene fragment with subsequent cleavage of the reaction products by AluI restriction endonuclease in order to identify the gene genetic variants. DNA polymorphism was detected only for the kappa-casein locus; no genetic polymorphism for alpha-S₁-casein gene was found in the studied populations. Analysis of the results of DNA fingerprinting demonstrated that the band sharing (BS) coefficient between the groups was low enough (0.13), and the genetic distance (D) between Dromedary and Bactrian breeds was 0.305. The results of genotyping of Bactrian and Dromedary Kazakh camel breeds by alpha-S₁-casein, kappa-casein loci, and DNA fingerprinting indicate that the Dromedary breed female camels are more polymorphic as compared with Bactrian.     

Plant P450s as versatile drivers for evolution of species-specific chemical diversity

The irreversible nature of reactions catalysed by P450s makes these enzymes landmarks in the evolution of plant metabolic pathways. Founding members of P450 families are often associated with general (i.e. primary) metabolic pathways, restricted to single copy or very few representatives, indicative of purifying selection. Recruitment of those and subsequent blooms into multi-member gene families generates genetic raw material for functional diversification, which is an inherent characteristic of specialized (i.e. secondary) metabolism. However, a growing number of highly specialized P450s from not only the CYP71 clan indicate substantial contribution of convergent and divergent evolution to the observed general and specialized metabolite diversity. We will discuss examples of how the genetic and functional diversification of plant P450s drives chemical diversity in light of plant evolution. Even though it is difficult to predict the function or substrate of a P450 based on sequence similarity, grouping with a family or subfamily in phylogenetic trees can indicate association with metabolism of particular classes of compounds. Examples will be given that focus on multi-member gene families of P450s involved in the metabolic routes of four classes of specialized metabolites: cyanogenic glucosides, glucosinolates, mono- to triterpenoids and phenylpropanoids.     

Characterization of heavy-chain antibody gene repertoires in Bactrian camels

Camelids are the only mammals that can produce functional heavy-chain antibodies (HCAbs). Although HCAbs were discovered over 30 years ago, the antibody gene repertoire of Bactrian camels remains largely underexplored. To characterize the diversity of variable genes of HCAbs (VHHs), germline and rearranged VHH repertoires are constructed. Phylogenetics analysis shows that all camelid VHH genes are derived from a common ancestor and the nucleotide diversity of VHHs is similar across all camelid species. While species-specific hallmark sites are identified, the non-canonical cysteines specific to VHHs are distinct in Bactrian camels and dromedaries compared with alpacas. Though low divergence at the germline repertoire between wild and domestic Bactrian camels, higher expression of VHHs is observed in some wild Bactrian camels than that of domestic ones. This study not only adds our understanding of VHH repertoire diversity across camelids, but also provides useful resources for HCAb engineering.     

野双峰驼各分布区的生存环境差异及评价

世界上野双峰驼(Camelus bactrianus ferus)目前仅分布于中国新疆境内及中蒙边境,即：中国新疆的塔克拉玛干沙漠、阿尔金山北麓、戛顺戈壁、中蒙边境及蒙古国西部的外阿尔泰戈壁。总数共计730～880头。目前已为极度濒危物种。本文对野驼在不同分布区由于生境及人类活动影响所造成的差异加以对比研究并进行评价,为野骆驼保护提供依据。     

Molecular characterization of ticks and tick-borne piroplasms from cattle and camel in Hofuf,eastern Saudi Arabia

The aims of the present study were to characterize ticks infesting the dromedary camel and cattle in Hofuf, Eastern Saudi Arabia and to determine the piroplasms that they may harbor. DNA was extracted from ticks, collected from camels and cattle, using commercial kits and subjected to polymerase chain reaction using specific primers for the amplification of ticks and piroplasms DNA. The cytochrome oxidase subunit I mitochondrial gene (COI) was used for characterization of ticks whereas partial 18S rRNA gene (18S rRNA) was used for piroplasms characterization. Ticks were genetically identified as Hyalomma dromedarii and Hyalomma anatolicum. Both cattle and camel in Hofuf, were found to be infested with both species. Both ticks identified as H. dromedarii and H. anatolicum from camels and cows showed 100% identity to COI sequences from the same species available in GenBank. Only Theileria annulata DNA was amplified from both H. anatolicum and H. dromedarii infesting cattle. None of the ticks collected from camels revealed DNA of piroplasms. T. annulata DNA was reported for the first time from Hofuf and the role of both H. anatolicum and H. dromedarii as potential vectors for this parasite in cattle in Saudi Arabia has been documented for the first time.     

Irisin/FNDC5: A participant in camel metabolism

The quantification, localization, production, function, and regulation of irisin/FNDC5 in camel species have not been previously studied. The objective of this study was to detect the irisin content in Arabian camel blood and tissues and study the gene expression of FNDC5 and PGC-1α in camel skeletal muscles and white adipose tissue depots under basal conditions. To monitor if exercise influences blood and tissue irisin protein levels as well as FNDC5 and PGC-1α gene expression levels, we analyzed irisin concentrations in the serum, skeletal muscles (soleus and gastrocnemius), and white adipose tissues (hump, subcutaneous, visceral, epididymal, and perirenal) in both control (n = 6) and exercised group (n = 6) using ELISA and determined the cellular localization of irisin/FNDC5 and the mRNA levels of FNDC5 and PGC-1α in skeletal muscles and adipose tissues via immunohistochemistry and real-time PCR, respectively. The possible regulatory roles of exercise on some hormones and metabolites as well as the detection of links between serum irisin and other circulating hormones (insulin, leptin, and cortisol) and metabolites (glucose, free fatty acids, triglycerides, and ATP) were explored for the first time in camels. Our results indicated that exercise induces tissue-specific regulation of the camel irisin, FNDC5, and PGC-1α levels, which subsequently regulates the circulating irisin level. Significant associations were detected between the levels of irisin/FNDC5/PGC-1α in camels and the metabolic and hormonal responses to exercise. Our study suggested that irisin regulates, or is regulated by, glucose, FFA, insulin, leptin, and cortisol in camels. The novel results of the present study will serve as baseline data for camels.     

Cytochrome P450 diversification and hostplant utilization patterns in specialist and generalist moths: Birth,death and adaptation

Across insect genomes, the size of the cytochrome P450 monooxygenase (CYP) gene superfamily varies widely. CYPome size variation has been attributed to reciprocal adaptive radiations in insect detoxification genes in response to plant biosynthetic gene radiations driven by co‐evolution between herbivores and their chemically defended hostplants. Alternatively, variation in CYPome size may be due to random “birth‐and‐death” processes, whereby exponential increase via gene duplications is limited by random decay via gene death or transition via divergence. We examined CYPome diversification in the genomes of seven Lepidoptera species varying in host breadth from monophagous (Bombyx mori) to highly polyphagous (Amyelois transitella). CYPome size largely reflects the size of Clan 3, the clan associated with xenobiotic detoxification, and to some extent phylogenetic age. Consistently across genomes, families CYP6, CYP9 and CYP321 are most diverse and CYP6AB, CYP6AE, CYP6B, CYP9A and CYP9G are most diverse among subfamilies. Higher gene number in subfamilies is due to duplications occurring primarily after speciation and specialization (“P450 blooms”), and the genes are arranged in clusters, indicative of active duplicating loci. In the parsnip webworm, Depressaria pastinacella, gene expression levels in large subfamilies are high relative to smaller subfamilies. Functional and phylogenetic data suggest a correlation between highly dynamic loci (reflective of extensive gene duplication, functionalization and in some cases loss) and the ability of enzymes encoded by these genes to metabolize hostplant defences, consistent with an adaptive, nonrandom process driven by ecological interactions.