The Intron Evolution Of Entomic Olfactory Receptor Gene, Or83b-like Gene

Nuclear introns are finer molecular markers actually. Introns evolve faster and are less conservative than exons. Intron sequences are better in studying the evolution of closely related species. On the other hand, intron insertion positions are relatively conservative in large-scale evolution, which provide clues in understanding the long-term evolution history. Olfaction is an important sensory input to insects'behavior and host plant recognition using olfactory system by fig-wasps acts as a strict pre-mating isolation mechanism.The atypical olfactory receptor gene Or83b-like which is remarkably conservative among many insects, is crucial to olfactory signal transduction. We investigate its introns and intend to unveil some evolutionary questions. The two non-pollinating fig wasps on Ficus hispida Linn: Philotrypesis pilosa and Philotrypesis sp., may have the latest common ancestor. The PCR's results show that, the identities of nucleotides in coding region and the deduced amino sequences is respectively 98.2% and 99.03% between the two fig wasps, the introns also have 84.5% identity in average. The high identities further confirm their rather close relationship. However, we found inter- and intra-individual length-variant heterozygotes in some introns in P. sp., but P. pilosa has never. So, we speculate P. pilosa is already stable in evolution, but P. sp. is evolutionarily unstable.Genome sequencing datum provides us important materials. Analyzed the 18 species insects'genomic DNA of Or83b which are acquired by genome screening and PCR, we found that intron positions are related to the species'relationship. The more identical intron positions with the relationship closer, maybe the selective constraint changed after speciation and the introns gained or lost. The two other fig wasps on Ficus hispida Linn: Ceratosolen solmsi and Apocrypta bakeri respectively lost one of the old introns, indicate the specific environmental constraint in the syconium. Introns in the conservative amino acid sequence regions can not be easily lost, suggests their unknown function.