Large amounts of genetic divergence among Italian species of the genus Orchesella (Insecta, Collembola) and the relationships of two new species

The phylogenetic position of two putative new species of the collembolan ge nus Orchesella was investigated by comparison with four other Italian speci es of the genus using a fragment of the mitochondrial gene encoding for sub unit I of cytochrome c oxidase (COI). The gene showed the well-known A + T bias, typical of insect mitochondrial DNA, although A + T content was not a s high as that observed in species belonging to more derived insect orders. The large number of variable sites in 3rd codon positions (85.2% variable) suggested that these sites contain significant homoplasy due to multiple h its. Despite the lack of morphological differentiation, the COI portion exa mined shows remarkable levels of genetic divergence between the putative sp ecies and their closest relatives. Phylogenetic analysis suggests that one of the putative new species is related to O. villosa, whereas the other is included in a clade with O. cincta and O. ranzii. The species O. chiantica appears to be related to O. villosa, agreeing with previous allozyme data. (C) 2000 Academic Press.