DNA Taxonomy Of Homidia (Collembola:Entomobryidae)

Springtails (Collembola) are small to tiny arthropods and widespread in soil ecosystem. They have an important systematic status in Arthropod and Hexapoda. The genus Homidia, abundant and widespread in China, is an easier identified group in Collembola (Entomobryidae). Morphological characters are often used to delimitate Collembola species at present. However, it may result in the underestimate of diversity because of some limitations of morphological methods. Thus, accurate species delimitation is a challenging task for biologists. A lot of operational methods, mostly based on DNA sequences have been proposed, such as DNA barcoding, which still has many debates. On the contrary, an integrative approach using multiple approaches and multiple molecular markers for defining species is chosen by taxonomists. Markers COI and 28S D1-2 are selected, with many different molecular tools. We studied the 44 morphospecies of Homidia by DNA Taxonomy in the present study. Seventy one species is recognized by 3% of threshold,59 species by 6% of threshold,54 species by 10% of threshold; ABGD, (Automatic barcode gap discovery) which is based on barcoding gap, delimitated 63 species. Seventy species are delimitated by PTP (Poisson tree processes model) which is based on significant substitution difference between intra- and inter-spefcific species. Seventy two species are delimitated by the GMYC (Generalized Mixed Yule Coalescent model). The Bayesian multilocus approach (BPP) is employed to determine the inconsistent or unreliable species based on the GMYC-delimited 72 species. When integrating these results, we adopt the most conservative way, with a final 54 putative species which are slightly greater than number of morphospecies, suggesting cryptic species among partial widespread species. Our results indicate that, both single-locus COI and Bayesian multilocus methods can accurately identify springtail species. The 6% of threshold method and ABGD can preliminary use to delimitate species. Bayesian multilocus approach is the best one to delimitate species when we ignore its computing costs. The standard workflow for DNA taxonomy of Homidia is presented here, using threshold method or ABGD to delimitate species preliminary, then verifying the reliability of candidate species by BPP and other morphological, ecological, geographical information. From another point of view, the number of cryptic species may depends on the level of morphological classification. The traditional classification is reliable in this case. Meanwhile, our study provides data sources for the further phylogenetic study within the genus Homidia.