6th INTERNATIONAL SEMINAR ON APTERYGOTA, SIENA, ITALY, 2002Recent advances in Collembola systematics
Introduction
The numerically dominant Hexapoda in most terrestrial ecosystems are Collembola. But they are only moderately diverse compared to many other insect groups, with about 7000 species known on earth to be compared with 350,000 Coleoptera or 125,000 Diptera (Parker, 1982). Why are there so few species of Collembola? Is this moderate diversity a characteristic of the group? I will address this question in exploring how the number of Collembola species increased from the time of Linné to present day in relation to the number of active taxonomists. I will present new approaches and new tools, which have fostered and redirected Collembola systematics during the last three decades, as well as new problems and new gaps that arose as a result of this activity. Finally, I will summarise what have been the main achievements during this period in terms of taxonomical novelties, classification of Collembola and evolutionary issues.
The present work complements previous overviews on Collembola systematics by Fjellberg (1985), Rusek, 1986a, Rusek, 2002, Betsch et al. (1990). I do not approach here the taxonomical problems linked to the phenological plasticity of Collembola species, which has been extensively analysed in the works of Cassagnau, 1985, Cassagnau, 1986. Instead, I focused on recent advances in Collembola systematics with emphasis on issues not or briefly considered in the cited papers, including the statistics of Collembola diversity, new systematical approaches, new morphological tools, significant taxonomical discoveries and revisions.
Section snippets
The statistics of Collembola diversity
The first descriptions of Collembola were published in the 18th century (Linné, 1758). I will trace the development of our knowledge of Collembola diversity by analysing in a historical perspective a species list distributed by Christiansen and Bellinger (1998), with slight modifications. This list includes 6688 species, i.e. the number of species known at this date. Synonymised species as well as varieties or subspecies are not considered. Contrary to more recent web lists, species
New approaches and new tools
Like in most other Arthropod groups, Collembola taxonomy relies on external morphology, and there is no indication that this might change in near future. In synergy with the exploration of unsurveyed habitats and areas it is the discovery and the use of new morphological characters that fostered Collembola taxonomy for the last 30 years. It accounts for the fast pace of species descriptions illustrated in the previous section. These taxonomical advances result for a large part of increasingly
New taxonomical characters
Collembola have no wings and no sclerotised genitalia, which are widely used in the taxonomy of other groups of Hexapoda. However, they have a large set of powerful multistate morphological characters. These features may be grouped in five formal categories: segmentation, chaetotaxic characters, non-chaetotaxic integumentary characters, mouthparts and claw complex.
Some of these characters have not experienced recent improvement in their use in a taxonomical perspective, but are as useful as
Significant taxonomical discoveries
Eight oligo- or monospecific families or subfamilies, and about 250 new genera have been described since 1975. Most were discovered during field collection in new or poorly known areas and habitats, but significant part results also of the splitting of old taxa.
Sand and littoral fauna brought the most unexpected harvest of new taxa (Thibaud and Christian, 1997), including a number of genera and two very strange families: Coenaletidae, created by Bellinger (1985) for the genus Actaletes Giard
Disseminating taxonomic information
The development of Collembola taxonomy is linked to the quality of taxonomical work, but also to the production and dissemination of synthetic information for end-users, in the form of keys, large-scale revisions and reference lists.
The classical “Collembolenfauna Europas” of Gisin (1960), long used by taxonomists and ecologists, was largely outdated at the end of the 1980s. It is only in 1981 that another large-scope book was published, i.e. the first complete revision of the Nearctic species
Conclusions
The taxonomy of Collembola has experienced significant progress during the last three decades. Powerful morphological characters have been discovered. They opened the way for detailed analyses of variability and polytypism and revealed an unexpected diversity in several of the most common Collembola species. Compelling evidence that first instar is the key instar to many classification and phylogeny problems is accumulating. Molecular tools are shaking traditional approaches of Collembola
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2021, Arthropod Structure and DevelopmentCitation Excerpt :In the present contribution, we follow the classification of Deharveng (2004) who divided the Symphypleona into nine families and four subfamilies. In other classifications, especially in the older literature (e.g. Hopkin, 1997), the Symplypleona consists of only one family, the Sminthuridae, that includes all the other symphypleonan families of Deharveng (2004) (then as subfamilies). Consequently general statements about the “Sminthuridae” or the “Symphypleona” should be treated with caution.