Revision of the Exechia parva group (Diptera: Mycetophilidae)

Exechia is a diverse genus of small fungus gnats, widespread in the Holarctic Region, while the fauna is largely unknown elsewhere, such as in the Afrotropical and Oriental Region. Members of Exechia can be arranged into several species groups, based on homologies in the male and female terminalia. The Exechia parva group is delimited, based on male terminalia possessing a pair of gonocoxal lobes on the apicoventral gonocoxal margin. Eight previously-described species can be placed in this group, of which six are from the Holarctic Region, while one is recorded each from the Oriental and the Afrotropical Regions.The Exechia parva group was reviewed and found to include 33 species, of which 24 were described as new to science and six were re-described. Identification keys to 32 species for males and nine species for females are provided together with illustrations and photos of male and female terminalia. Species delimitations were based on morphological examination of 94 male and female specimens, as well as DNA barcodes obtained from 124 specimens. Molecular and morphological species delimitations were mostly congruent, except in two cases where two species were delimited within a single Barcode Index Number (BIN). We found that each species is only known from a single zoogeographical region and that several species complexes are largely congruent with zoogeographical divisions, indicating that intercontinental barriers may have a strong impact on the species diversity of the group.

Exechia（小菌蚊属）为小型真菌蚊的一类，广泛分布于北半球温带地区，而其他地区如非洲热带和东方地区的生物群落则鲜为人知。Exechia属的成员可根据雄性和雌性末端结构的同源性划分为数个物种群。其中，Exechia parva物种群以雄性末端在顶腹侧的生殖侧叶上具有一对生殖侧叶瓣为特征。该物种群中包含八个已描述的物种，其中六个源自北半球温带地区，东方和非洲热带地区各有一个。经审查，Exechia parva物种群包含33个物种，其中24个为新发现的物种，六个为重新描述的物种。为32个雄性和九个雌性物种提供了识别关键、插图和末端结构照片。物种界定基于94个雄性和雌性标本的形态学考察，以及从124个标本中获得的DNA条形码。分子和形态学物种界定在大多数情况下具有一致性，但在两个案例中，由于单个条形码索引号（BIN）内界定了两个物种，故存在不一致。研究发现，每个物种仅知存在于单一动物地理区域，且多个物种复合群与动物地理分区大致吻合，这表明洲际屏障可能对物种群多样性产生强烈影响。