Were the first springtails semi-aquatic? A phylogenetic approach by means of 28S rDNA and optimization alignment

Abstract

Emergence from an aquatic environment to the land is one of the major evolutionary transitions within the arthropods. It is often considered that the first hexapods, and in particular the first springtails, were semi-aquatic and this assumption drives evolutionary models towards particular conclusions. To address the question of the ecological origin of the springtails, phylogenetic analyses by optimization alignment were performed on D1 and D2 regions of the 28S rDNA for 55 collembolan exemplars and eight outgroups. Relationships among the orders Symphypleona, Entomobryomorpha and Poduromorpha are inferred. More specifically, a robust hypothesis is provided for the subfamilial relationships within the order Poduromorpha. Contrary to previous statements, the semi-aquatic species Podura aquatica is not basal or 'primitive', but well nested in the Poduromorpha. The analyses performed for the 24 different weighting schemes yielded the same conclusion: semi-aquatic ecology is not ancestral for the springtails. It is a derived condition that evolved independently several times. The adaptation for semi-aquatic life is better interpreted as a step towards independence from land, rather than indication of an aquatic origin.

Homology and morphology in Poduromorpha (Hexapoda, Collembola)

“…If one confronts the observations on the first instars to the phylogeny of Poduromorpha (D'Haese, 2002(D'Haese, , 2003, some interesting conclusions can be drawn. From Onychiurinae to Neanurinae, the chaetotaxy is increasingly complete (compared to the adult) in the first instar.…”

“…Chaetotaxy has been successfully used in lower level phylogenies (species or genera level, e.g., Deharveng & Bedos, 1991;D'Haese, 2000;D'Haese & Weiner, 1998;Luciáñez & Simón, 1993). However, one might argue that it would be difficult to use it for higher-level phylogenies as homologies are more difficult to assess (but not impos sible as it will be shown here and see D'Haese, 2002), and setae can bring a highly homoplastic signal. Springtails possess chaetotaxic assemblages in which setae have defined positions, which are dispatched according to specific patterns (Nayrolles, 1988;Nayrolles, 1991;Nayrolles & Betsch, 1993).…”

Spatial and temporal variability across life's hierarchies in the terrestrial Antarctic

“…Comprehensive phylogenetic assessments of taxa, using modern molecular methods, and incorporating ecological and biogeographic information, are curiously rare in the literature on Antarctic terrestrial biodiversity. Springtail sequences have been used to inform broader systematic questions ( Frati & Dell'Ampio 2000;D'Haese 2002), and only two recent studies have sought to investigate patterns of speciation across the Antarctic (Allegrucci et al 2006;Stevens et al 2006;§2b) (d) Assemblage and ecosystem levels Antarctic and sub-Antarctic assemblages have changed dramatically over the long term as is clear from the fossil record, and from palynological analyses that provide information on change at scales of several thousand years Cromer et al 2006;. In both the maritime Antarctic and sub-Antarctic, clear successional changes associated with glacial retreat, both in the past and in the present, have been documented, and form among the clearest examples of temporal variation in assemblages (Frenot et al 1998;.…”

Structural mouthpart interaction evolved already in the earliest lineages of insects

“…Collembola show a wide variety of mandible and maxilla forms [5], which is the reason for our coverage of all major groups within Collembola (see electronic supplementary material S2 for taxon coverage). However, we restrict our results to the biting-chewing mouthpart type for Collembola, as groups with this mouthpart type were repeatedly recovered as more ancestral with respect to collembolan phylogenetic relationships [17][18][19].…”