Proisotoma
Creators: name: Potapov, Mikhail
name: Bogomolov, Maxim
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Entognatha
Collembola
Isotomidae
Proisotoma

description: Dimorphism of Proisotoma
Material (only materials where mobile forms were seen are presented).
P. minima: Russia, Moscow, park, rotten log, 14.x.2014, 7.xi.2015, leg. M.P. and M. Bogomolov; Moscow region, Burtsevo, rotten wood, 24.x.2004, iii.2013, 1.i.2014; Moscow region, Malinki, rotten log in spruce forest, 2.xi.2000, leg. M.P.; Russia, Yaroslavl' region, Borok (Nekouzski district), rotten birch, 26.ix.2013, leg. M.P.; Russia, Komi Republic, Ust'-Vym', mosses at river bank, 21.ix.2001, leg. N. Kuznetsova; Russia, Buryat Republic, nearby Goujekit, rotten wood, 16.viii.2013, 20.viii.2013, leg. M.P.; Russian Far East, Primorsky Krai, Partizansky Region, near Ekaterinovka, rotten wood in deciduous forest, 26.ix.2004; Primorski Krai, Shkotovsky Region, Pidan Mt., rotten wood, 20.ix.2004, leg. M.P.
P. brevidens: Ukraine, Lwivska region, Mikolaevsky District, Kolodruby, under loose bark of oak, 4.x.2002, leg. Ig. Kaprus'.
P. dottrensi: Moscow, park, compost heap, 9.xi.2011, 29.xi.2011, leg. M.P.
The three species listed and P. dualis sp. nov. display dimorphism appearing in normal and mobile forms. Their general appearance in P. m i n i m a and P. dualis sp. nov. is shown in Figs 10–13. The mobile forms show several progressive modifications concerning eyes, furcal apparatus, supporting part of legs, and pigmentation (Table 1). Eyes are presumably more functional (Figs 6 vs. 7; 22 vs. 21, and 26 vs. 25): eye spot is black, ocelli, especially of front group, are larger. Ocelli positioned more medially (G and H in P. dualis sp. nov.) are only slightly enlarged. Each leg of the mobile form with two clavate tibiotarsal hairs (Figs 8 vs. 9 and 19 vs. 20), which were not seen in P. d ot t re ns i. Furca is better developed. Ratio of dens: Ti.3 is 0.8–1.3 in mobile form of P. minima (vs. 0.4–0.8 in norm, Fig. 14); posterior side of dens is tuberculated (Figs 4 vs. 2; 18 vs. 17; and 24 vs. 23); in P. dualis sp. nov. mucro with high lamella at base (Fig. 4), all species has more chitinized skeleton of furcal apparatus, including basal rods and manubrium (Figs 15, 16). Proisotoma dualis sp. nov. shows differences in s - chaetae on body: they are as long as common chaetae of p -row in normal form (Fig. 27) and shorter in mobile form (Fig. 28) but the individual variability is rather high. All the modifications probably indicate more active movement of the modified specimens in more lightened space. These specimens can provisionally be called as "mobile" (the mobile forms). Taxonomically, all other essential specious characters are kept in mobile form (s and ms formulas, number of chaetae on furca, chaetotaxy of antenna, and others). Mobile forms can have fewer anterior chaetae on dens, 5 instead 6, in P. m i n i m a. The maxillary head is not affected by the dimorphism: in both forms of P. minima it is about as figured by Fjellberg (1976a, Fig. 1 C) for P. minuta, particularly, the longest maxillary lamella have two rows of cilias.
For P. minima, only juvenile specimens of middle size can be modified while morphologically normal specimens may belong to any age, from first juvenile instar to adult (Fig. 14). This cannot be confidently assigned to the other three species since the material is not enough. Both young females and males can exhibit mobile forms. Mobile forms occur mostly in autumn and winter in P. minima, but we have several records at the end of summer (see the Material part) that make the cyclomorphosis somewhat doubtful. We have only collected P. dualis sp. nov. in August and September, in both populations mobile forms are mixed with normal ones. One available population of P. brevidens (I.J. Kaprus' leg.) contains normal and mobile forms, of which both were juvenile. Dens of the mobile form is shown in Fig. 29. In the materials from compost in a Moscow park we have recorded the fourth species exhibiting dimorphism. The species was mixed with Proisotoma minuta and P. subminuta Denis, 1931 but 3–5+3–5 ventral chaetae on Th.III and 5 ocelli made it possible to assign it to Proisotoma dottrensi Gisin, 1949. The morphological traits of mobile and normal forms of P. dottrensi are shown in Figs 23–26. Ratio of dens: Ti.3 is 0.85–1.0 in mobile form, although the difference from the normal form using this character can not be confirmed statistically.
No specimens were detected in ecdysis from normal to mobile form or in the opposite way.
In the populations of P. minima we also recorded the normal specimens with strong pigmentation. On the other hand, among the "mobile" specimens some may have no chitininized furcal skeleton. Three key characters, protruding ocelli, clavate tenent hairs of tibiotarsi, and enlarged and tuberculated dens remain the decisive characters for discrimination between two forms (Table 1).
description: Published as part of Potapov, Mikhail & Bogomolov, Maxim, 2016, Taxonomy of the Proisotoma complex. VI. Mobile forms of Proisotoma s. str. with the description of a new species from East Siberia (Collembola: Isotomidae), pp. 257-267 in Zootaxa 4088 (2) on pages 260-262, DOI: 10.11646/zootaxa.4088.2.7, http://zenodo.org/record/257531