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Allacma fusca (Linnaeus, 1758) – Podura fusca Linnaeus, 1758: 608. MAZ: Bakhshi et al. 2014; Bakhshi et al. 2022. Ecology and habitat in Iran: forest soil. General distribution: Holarctic (Fjellberg 2007; Babenko et al. 2019). Genus Caprainea Dallai, 1970, Published as part of Mayvan, Mahmood Mehrafrooz, Greenslade, Penelope & Sadeghi-Namaghi, Hussein, 2023, An annotated checklist of the Collembola (Hexapoda) from Iran, pp. 1-101 in Zootaxa 5275 (1) on pages 58-59, DOI: 10.11646/zootaxa.5275.1.1, http://zenodo.org/record/7898948, {"references":["Linnaeus, C. (1758) Podura (Insecta: Aptera). In: Systema Naturae per Regna tria Naturae, secundum Classes, Ordines, Genera, Species, cum Characteribus, Differentis, Synonymis, Locis. Tomus I. Editio Decima, Reformata. Laurentii Salvii, Holmiae, pp. 608 - 609. https: // doi. org / 10.5962 / bhl. title. 542","Fjellberg, A. (2007) The Collembola of Fennoscandia and Denmark. Part II: Entomobryomorpha and Symphypleona. Fauna Entomologica Scandinavica, 42, 1 - 264. https: // doi. org / 10.1163 / ej. 9789004157705. i- 265","Dallai, R. (1970) Ricerche sui Collemboli. XIV. Le Alpi Apuane. Lavori della Societa Italaliana di Biogeografia, 1, 433 - 482. https: // doi. org / 10.21426 / B 61110531"]}

Paternal genome elimination—a type of reproduction in which males inherit but fail to pass on their father’s genome—evolved independently in 6–8 arthropod clades. Thousands of species, including several important for agriculture, reproduce via this mode of reproduction. While paternal genome elimination is well established in some of the clades, the evidence in globular springtails (Symphypleona) remains elusive, even though they represent the oldest and most species-rich clade putatively reproducing via paternal genome elimination. We sequenced genomic DNA from whole bodies of Allacma fusca males with high fractions (>27.5%) of sperm to conclusively confirm that all the sperm carry 1 parental haplotype only. Although it is suggestive that the single haplotype present in sperm is maternally inherited, definitive genetic proof of the parent of origin is still needed. The genomic approach we developed allows for the detection of genotypic differences between germline and soma in all species with sufficiently high fraction of germline in their bodies. This opens new opportunities for scans of reproductive modes in small organisms.

Symphypleona (sensu stricto) are a group of Collembola (=springtails) that, despite displaying some variation in gene order, have been poorly investigated under the phylomitogenomic perspective. How families and subfamilies of this taxon are evolutionary related is still partially unknown. For this reason we sequenced, and herein described, the complete mitochondrial genome sequence of Allacma fusca (Sminthuridae). This sequence, alongside others from the literature, is here used to study the phylogenetic relationships among Symphypleona.

Allacmafusca (Linnaeus, 1758) * Podura fusca Linnaeus, 1758: 608. Smynthurus fuscus – Latreille 1802: 82. Allacmafusca – Börner 1906: 183. DISTRIBUTION. — Europe. Latreille 1812. France. Bourlet 1841, 1845. — Finot 1890. Ardennes et Côte-d’Or. Denis 1921. Bouches-du-Rhône. Forêtde Cadarache (Rougon & Rougon 1970). — Cadarache (Poinsot-Balaguer 1976d). Calvados. Brébisson 1827 (S. fuscus). Corse. Poinsot-Balaguer 1978. Essonne. Parcdu Laboratoiredu MNHNà Brunoy (Vannier 1972, 1973b, 1979b, 1981; Kilbertus & Vannier 1979; Chauvin & Vannier 1989; Betsch 1991; Chauvat & Ponge 2002). — Parcdu Laboratoire du MNHN à Brunoy et forêt de Sénart (Ponge 1973, 1978, etvar. pustulata, Betsch & Vannier 1977). — Maresde Sénart (Pichard etal. 1989). — Forêtde Sénart (Salmon & Ponge 1999; Ponge etal. 2002). Eure. Lyons-la-Forêt (Carl 1899). Hautes-Pyrénées. Montagned’Arize (Deharveng 1996). Hauts-de-Seine. Maresde Clamart (Pichard etal. 1989). Île-de-France. Environsde Paris (Geoffroy 1762, P. fusca; Boisduval & Lacordaire 1835, Smynthurus fuscus). Landes. Roquefort (Jeannenot 1957, S. stachi). Marne. Environsde Reims? (Lemoine 1883, S. fuscus). Nièvre. Parcrégionaldu Morvan (Ponge etal. 2003). Oise. Labosse (D’Haese 2002). Seine-et-Marne. Forêtde Foljuif (Massoud etal. 1984). Seine-Maritime. Prairiesnaturelles normandes, La Vielle en Paysde Cauxet Saint-Yonprèsde Saint-Étienne-du-Rouvray (Ricou 1959). Sud-Ouest de la France, plaine et moyenne montagne (Cassagnau 1961). Tarn, Aude. Montagne Noire (Cassagnau 1965). TAXONOMIE. — Jeannenot 1957 (redescription). DÉVELOPPEMENT. — Lemoine 1883 (développement embryonnaire). — Betsch & Vannier 1977 (phases juveniles). PHYSIOLOGIE. — Vannier 1972 (surface corporelle d’évaporation); Vannier 1973b (taille, poids sec/poids frais); Vannier 1981 (eau, jeûne); Chauvin & Vannier 1989 (résistance au froid). ÉCOLOGIE. — Cassagnau 1965 (écologie, sol); Rougon & Rougon 1970; Ponge 1973, 1978; Poinsot-Balaguer 1976d (irradiation); Kilbertus & Vannier 1979 (régime alimentaire); Vannier 1979b (régime alimentaire, microfloredu sol); Massoud etal. 1984 (piétinement); Pichard et al. 1989; Betsch 1991 (privation de litière); Deharveng 1996 (déboisement, reboisement); Salmon & Ponge 1999; Chauvat & Ponge 2002 (métaux lourds); Ponge etal. 2002 (toxicité, herbicide); Ponge etal. 2003 (bioindicateur). DONNÉES MOLÉCULAIRES. — D’Haese 2002 (phylogénie)., Published as part of Thibaud, Jean-Marc, 2017, Catalogue des collemboles de France, pp. 297-436 in Zoosystema 39 (3) on pages 406-407, DOI: 10.5252/z2017n3a1, http://zenodo.org/record/5496272, {"references":["LINNAEUS C. 1758. - Systema naturae per regna tria naturae: secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Holmiae, Impensis Direct. Laurentii Salvii: 608 - 609. https: // doi. org / 10.5962 / bhl. title. 542","LATREILLE P. A. 1802 (1801). - Histoire naturelle generale et particuliere des Crustaces et des Insectes 3, Paris, F. Dufart: 69 - 83.","BORNER C. 1906. - Das System der Collembolen nebst Beschreibung neuer Collembolen des Hamburger Naturhistorischen Museums. Mitteilungen aus den Naturhistorischen Museum in Hamburg 23: 147 - 188.","LATREILLE P. A. 1812. - Histoire naturelle des Crustaces et des Insectes. T. 8. Dufart, Paris, 411 p. http: // www. biodiversitylibrary. org / bibliography / 15764","BOURLET L' ABBE 1841. - Memoire sur les Podures et les Sminthurides. Annales de la Societe Entomologique de France in Bulletin Entomologique: XL-XLI et LVII-LVIII.","BOURLET L' ABBE 1845. - Observations sur une pretendue pluie de Podurelles. Nouvelle espece de Podura. Longevite extraordinaire chez un Insecte. Memoires de la Societe d'Agriculture scientifique du departement du Nord: 221 - 226.","FINOT A. 1890. - Faune de la France. Insectes Orthopteres. Thysanoures et Orthopteres proprement dits. Eds Deyrolle, Fontainebleau et Paris: 23 - 42. (reprint: Trans. U. S. Agric. Soc. 22: 186 - 193)","DENIS J. - R. 1921. - Sur les Apterygotes de France. Bulletin de la Societe Zoologique de France: 42: 122 - 134.","ROUGON C. & ROUGON D. 1970. - Premieres donnees sur les Insectes Collemboles et Coleopteres de la foret de Cadarache (B. du Rh.). Annales de la Faculte des Sciences de Marseille 43: 27 - 34.","VANNIER G. 1972. - Estimation de la surface corporelle d'evaporation d'un Insecte apterygote: Allacma fusca (L.), Collembole Symphypleone. Comptes rendus de l'Academie des Sciences 274: 258 - 261.","VANNIER G. 1973 b. - Relation dimensionnellement homogenes entre taille, la surface et le poids des individus de l'espece Allacma fusca (L.), Insecte Collembole. Revue d'Ecologie et de Biologie du Sol 10: 559 - 573.","VANNIER G. 1979 b. - Regime alimentaire entre la microfaune et la microflore du sol; aspects qualitatifs et quantitatifs. Bolletino di zoologia 46: 343 - 361.","KILBERTUS G. & VANNIER G. 1981. - Relations microflore-microfaune dans la grotte de Sainte-Catherine (Pyrenees ariegeoises). II. - Le regime alimentaire de Tomocerus minor (Lubbock) et Tomocerus problematicus Cassagnau (Insectes Collemboles). Revue d'Ecologie et de Biologie du sol 18: 319 - 338.","KILBERTUS G. & VANNIER G. 1979. - Microbial analysis and weight estimation of feces produced by four sympatric Collembola species in forest litter. Revue d'Ecologie et de Biologie du sol 16: 169 - 180.","CHAUVIN G. & VANNIER G. 1989. - Resistance au froid et repletion du tube digestif chez Allacma fusca (Collembola, Symphypleona) et Tinea pellionella (Lepidoptera, Tineidae). Bulletin de la Societe Zoologique de France 114: 111 - 118.","BETSCH J. - M. 1991. - Effets de la privation des apports annuels de litiere sur les Collemboles Symphypleones epiges d'une foret sur rendzine. Revue d'Ecologie et de Biologie du sol 28: 41 - 49.","CHAUVAT M. & PONGE J. - F. 2002. - Colonization of heavy metal-polluted by Collembola: preliminary experiments in compartmented boxes. Applied Soil Ecology 21: 91 - 106. https: // doi. org / 10.1016 / S 0929 - 1393 (02) 00087 - 2","PONGE J. - F. 1973. - Application de l'analyse factorielle des correspondances a l'etude des variations annuelles dans les populations de Microarthropodes. Bulletin d'Ecologie 4: 319 - 327. (det. Poinsot, Massoud, Thibaud, Betsch).","BETSCH J. - M. & VANNIER G. 1977. - Caracterisation des deux phases juveniles d' Allacma fusca (Collembola, Symphypleona) par leur morphologie et leur ecophysiologie. Journal of Zoological Systematics and Evolutionary Research 15: 124 - 141. https: // doi. org / 10.1111 / j. 1439 - 0469. 1977. tb 00534. x","PICHARD S., MASSOUD Z. & ELKAIM B. 1989. - Ecologie des peuplements de Collemboles de quelques mares et de leurs abords en region parisienne. Revue d'Ecologie et de Biologie du sol 26: 451 - 472.","SALMON S. & PONGE J. - F. 1999. - Distribution of Heteromurus nitidus (Hexapoda, Collembola) according to soil acidity: interactions with earthworms and predator pressure. Soil Biology & Biochemistry 31: 1161 - 1170.","PONGE J. - F., BANDYOPADHYAYA I. & MARCHETTI V. 2002. - Intearction between humus form and herbicide toxicity to Collembola (Hexapoda). Applied Soil Ecology 20: 239 - 253. https: // doi. org / 10.1016 / S 0929 - 1393 (02) 00026 - 4","CARL J. 1899. - Note descriptive des Collemboles de la collection de M. Adrien Dollfus recueillis a Lyons-la-Foret (Eure) et dans d'autres localites de France et de Suisse. La Feuille des Jeunes Naturalistes 3: 1 - 8.","DEHARVENG L. 1996. - Soil Collembola diversity, endemism and reforestation: a case study in the Pyrenees (France). Conservation Biology 10: 74 - 84. https: // doi. org / 10.1046 / j. 1523 - 1739. - 1996.10010074. x","GEOFFROY E. L. 1762. - Histoire abregee des insectes qui se trouvent aux environs de Paris. Insectes apteres. Tome 2. Paris, Durand: 581 - 593, 607 - 610. https: // doi. org / 10.5962 / bhl. title. 14710","BOISDUVAL J. A. & LACORDAIRE TH. 1835. - Faune entomologique des environs de Paris. Mequignon-Marvis, Paris 1: 1 - 696.","JEANNENOT F. 1957. - Contribution a l'etude des Collemboles. Sphyrotheca stachi sp. n. Acta Zoologica Cracoviensia 2: 405 - 430.","LEMOINE V. 1883. - Recherches sur le developpement des Podurelles. Association pour l'avancement des Sciences (imp. Chaix): 3 - 40.","PONGE J. - F., GILLET S., DUBS F., FEDOROFF E., HAESE L., SOUSA J. P. & LAVELLE P. 2003. - Collembolan communities as bioindicators of land use intensification. Soil Biology & Biochemistry 35: 813 - 826.","D'HAESE C. A. 2002. - Were the first springtails semi-aquatic? A phylogenetic approach by means of 28 S rDNA and optimization alignement. Proceeding Royal Society London 269: 1143 - 1151.","MASSOUD Z., BETSCH J. - M. & THIBAUD J. - M. 1984. - Experience de pietinement controle du sol d'une foret periurbaine: effet sur le peuplement de Collemboles. Revue d'Ecologie et de Biologie du sol 21: 507 - 518.","RICOU G. 1959. - La faune des prairies naturelles normandes (troisieme note). Revue des Societes savantes de Haute-Normandie 13: 39 - 52. (det Delamare Debouteville).","CASSAGNAU P. 1961. - Ecologie du sol dans les Pyrenees centrales. Hermann, Paris 1 - 235.","CASSAGNAU P. 1965. - Ecologie edaphique de la Montagne Noire basee sur les groupements de Collemboles. Revue d'Ecologie et de Biologie du sol 2: 339 - 375.","VANNIER G. 1981. - Desequilibre de la balance hydrique corporelle chez quatre especes d'Insectes Collemboles apres un jeune de courte duree. Revue d'Ecologie et de Biologie du Sol 18: 29 - 38."]}

Summary Collembola is a group of soil arthropods whose ecophysiological requirements tend to promote inter-population isolation and genetic differentiation. To test this, we analysed the genetic structure of 22 populations of two species of the genus Allacma (A. fusca and A. gallica), using allozyme electrophoresis. Several loci showed distinct differences between the two species, and high levels of genetic divergence (Nei's D=1.144±0.130) were found between them; in addition, the average genetic distance among populations was low in A. fusca (D=0.050±0.034), but considerably higher among those of A. gallica (D=0.435±0.342). The two species were significantly different in average heterozygosity with A. gallica (He=0.062) being more variable than A. fusca (He=0.028). Wright's FST statistics, based on polymorphic loci, indicate that the two species are subdivided into genetically heterogeneous populations, with A. gallica being more differentiated (FST=0.873) than A. fusca (FST=0.533). The observed divergence between and within the two species may result from the absence of gene flow and subsequent allopatric differentiation through genetic drift. In addition, ecological and geological factors may explain the origin of such a differentiation, while the peculiar mode of reproduction may influence the levels of intra-population genetic variability.

Resume Chez le Collembole Symphypleone Allacma fusca, la periode immature preente deux phases: une phase juvenile I qui comprend uniquement la premiere intermue et une phase juvenile II qui regroupe toutes les autres intermues. Ces deux phases se distinguent par d'importantes. modifications qui concernent principalement: - la structure du tegument: a l'eclosion, il est mince et a ornementation composee exclusive-ment de grains primaires alors que des la deuxieme intermue il est epais et profoundement modifie; - le systeme tracheen, rudimentaire a l'eclosion, ramifye apres la premiere mue; - la resistance a la dessiccation: ce n'est qu'a partir de la deuxieme phase juvenile qu'Allacma fusca est capable de reguler ses defenses hydriques en montrant un diagramme de transpiration en plateau. Ces caracteristiques morphologiques, anatomiques et ecophysiologiques de la premiere intermue contraignent l'espece Allacma fusca, dont les stades ulterieurs sont tres resistants a la secheresse, a se maintenir dans le milieu forestier. En considerant l'ensemble de ces reultats, on peut admettre que les Symphypleones representent un groupe entomologique d'un grand inteiet phylogenetique qui permettra d'apporter une reponse plausible au probleme de la conquete des milieux sees, hors du systeme edaphique. La succession de deux phases juveniles distinctes fait apparaitre un clivage, vraisemblablement non homologue de la metamorphose des Insectes epimorphes, dans le cycle vital de ce groupe a developpement protomorphe. Summary Characterisation of two phases of the immature period of Allacma fusca (Collembola, Symphypleona) by their morphology and ecophysiology In the species Allacma fusca (Collembola, Symphypleona), the immature period shows two separate phases: a primary juvenile (phase juvenile I) which corresponds to the single first instar and a secondary juvenile (phase juvenile II) which groups all other stages. These two phases are differenciated by important modifications as follows: - integument structure: after hatching, the cuticule is thin and cuticular ornamentation is formed of primary or single elementary granules; during the second intermoulting, the cuticule becomes thick and its ornamentation is deeply modified by the fusion of the primary granules with their connections. - tracheal system: it is rudimentary after hatching, then becomes ramified after the first! postembryonic moulting. - resistance to dryness: it is only during the secondary juvenile phase that Allacma fusca is able to regulate its rate of water loss, showing a plateau on its typical transpiration curve. All these particular features of the first postembryonic intermoulting (morphology, anatomy and ecophysiology) force this species, in spite of the great resistance to desiccation of its following instars, to remain in the closed forest biotopes. All these results, taken together, suggest that Symphypleona are an entomological group of a great interest which will enable a plausible explanation for the way that terrestrial arthropods can live in dry places, outside the soil layers. The appearance of two juvenile phases in the life-cycle of these primitive insects could be compared with instars' succession (i. e. metamorphosis) in flying-insects, but we still do not seem to be very close to prove that it's the same process. Zusammenfassung Kennzeichnung von zwei Phasen der Jugendentwicklung von Allacma fusca (Collembola, Symphypleona) durch ihre Morphologic und Okophysiologie Der Zeitraum der ontogenetischen Entwicklungsperiode des symphypleonen Collembolen Allacma fusca umfast zwei Entwkklungsphasen: die Jugendphase I, welche ausschlieslich aus der 1. Zwischenhautungszeit besteht, und die Jugendphase II, welche alle ubrigen Zwischen-hautungszeiten umfast. Diese beiden Jugendphasen unterscheiden sich voneinander durch be-deutende Veranderungen, welche insbesondere folgende Strukturen betreffen: - die Integumentstruktur ist nach dem Schlupfen dunn und besitzt ein ausschlieslich aus einer Primarkornung zusammengesetztes Ornament, wahrend sie ab der 2. Zwischenhautungszeit verdickt und eine tiefgreifende Veranderung erfahrt - das Tracheensystem ist beim Schlupfen rudimentar und verzweigt sich nach der 1. Hautung - die Widerstandsfahigkeit gegenuber Austrocknung; Allacma fusca ist erst ab der 2. Jugendphase in der Lage, seinen Wasserhaushalt zu regulieren und zeigt dann ein sich stabilisie-rendes Ausdunstungsdiagramm. Diese besonderen morphologischen, anatomischen und okophysiologischen Merkmale der 1. Zwischenhautungszeit zwingen den Springschwanz Allacma fusca, dessen spatere Stadien gegeniiber der Austrocknung sehr widerstandsfahig sind, wahrend dieser Zeit zum Verbleib in bewaldetem Biotop. Unter Beruksichtigung der in dieser Arbeit aufgezeigten Ergebnisse ist zu erkennen, das die Symphypleona eine entomologische Gruppe von besonderem phylogenetischem Interesse dar-stellen; sie erlauben uns, fur die Besiedlungsmoglichkeit trockener Biotope auserhalb des edaphi-schen Systems eine einleuchtende Antwort zu erbringen. Die Aufeinanderfolge von zwei unter-schiedlichen Jugendphasen last innerhalb des Lebenszyklus dieser Gruppe mit protomorpher' Entwicklungsweise eine Aufspaltung erkennen, die wahrscheinlich nicht als homolog mit der Metamorphose der epimorphen Insekten angesehen werden kann.

The fine structure of the paired sperma- thecae of two Symphypleona Collembola, Sminthurus viridis and Allacma fusca, was studied. The spermathe- cal epithelium is rich in pigment granules, while secre- tory organelles are scarce, consisting of a few mitochon- dria and microtubules, scattered cisterns of endoplasmic reticulum and Golgi systems. Small isolated secretory granules are visible in the apical cell region, where irregular microvilli are present. Beneath the epithelium, large cells rich in endoplasmic reticulum and Golgi sys- tems are present; they are separated from the epithelial cells by a thin basal lamina. The epithelium is lined by a thin cuticle, which forms thin extensions at the begin- ning of the spermathecal duct. At this level, muscle fibers are visible. The spermathecal lumen is filled with many spermatozoa. At molting, the spermathecal epithe- lial cells detach from the cuticle and a large electron- transparent space is evident between the cytoplasm and the cuticle. The cytoplasm has few pigment granules and the spermathecal lumen contains degenerating sper- matozoa. After 3 days, the spermathecal epithelium regains its usual appearance and the spermathecal lumen is empty. The two species of Collembola Symphy- pleona do not have accessory glands. Compared with the Arthropleona Orchesella villosa, which has a single sper- matheca and two accessory glands (Dallai et al. (2008) J Morphol 269:464-478), a great difference has occurred in the organization of the female genital system of these species. The results are discussed in light of the impli- cations for reproductive behavior and egg protec- tion in Symphypleona. J. Morphol. 269:1122-1133, 2008. 2008 Wiley-Liss, Inc.

In the newly hatched larva in Allacma fusca, the midgut epithelium was fully developed and formed by flattened epithelial cells surrounding the yolk mass in the midgut lumen. Immediately after hatching, the first larva began to feed; the migut lumen was filled with the yolk mass and food (mainly algae). Regenerative cells typical of the developing midgut epithelium of many insects were not observed. Initially, midgut cells of the larva were cuboidal but became columnar in shape with distinct regionalization in the distribution of cell organelles. Furthermore, urospherites appeared in the midgut cell cytoplasm, i.e., structures characteristic for the midgut epithelium of insects having no Malpighian tubules. As a result, cells with the capacity for digestion, absorption, and excretion were observed to be completely formed in the first larval stage.

Light and electron microscopy evidence have been obtained to describe the peculiar spermatogenesis in the collembolan species Sminthurus viridis and Allacma fusca (Sminthuridae). In these two species, the two sexes differ for the lack of two chromosomes (the sex chromosomes) in males (males, 2n = 10; females, 2n = 12). While oogenesis seems to proceed normally, spermatogenesis is peculiar because the two daughter cells of the first meiotic division have different chromosome numbers (six and four). The cell receiving four chromosomes degenerates, while the cell receiving six chromosomes completes meiosis and produces identical spermatozoa (n = 6). At fertilization, pronuclei with six chromosomes fuse together to form zygotes with 2n = 12. Male embryos must lose two sex chromosomes during the first zygotic mitosis, as all male cells have 2n = 10 chromosomes. The sex chromosome system of these species can be identified as X1X1X2X2:X1X20. Electron microscopy observations show that the same peculiar spermatogenesis occurs also in two others species of the same family, Caprainea marginata and Lipothrix lubbocki. The peculiar sex determination system described is similar but not identical to what is observed in other insect orders, and it may represent an evolutionary step toward parthenogenesis. It is suggested that this peculiar spermatogenesis is common to all Symphypleona.

The youngest primordial germ cells (PGCs) of Allacma fusca (L.) (Collembola: Sminthuridae) can be identified in embryos at the blastoderm stage as scattered in the yolk mass. They are arranged in pairs connected via intercellular bridges and dispersed among the yolk granules over a relatively small area but they never form multicellular clusters. With progressing development, the mesoderm of the germ band differentiates, the PGCs migrate to the abdominal part of the germ band and enter among mesoderm cells making two clusters of cells in the left and right parts of the abdomen. The mesoderm cells neighbouring the PGC cluster differentiate into a one-layered gonad envelope and produce a thin basal lamina separating the gonad from the rest of the mesoderm. The PGCs are still connected in pairs. At the end of the embryonic development, the gonads have regular spherical shapes and are enclosed within the envelope built up by a layer of flat somatic cells. Now, the PGCs do not occur only in pairs, but chains of cells connected with a sequence of intercellular bridges can also be seen.

In order to analyse the energy providing metabolites fuelling the jump of springtails, jumping experiments have been performed with two groups of springtails, Arthropleona and Symphypleona, which differ in their morphology and behaviour. During rest, the level of adenine nucleotides, especially ATP, in the Arthropleona species, Tomocerus flavescens and Orchesella cincta , is higher than that in the Symphypleona species, Allacma fusca and Dicyrtoma fusca . After a series of jumps a significant decrease of ATP appears in all investigated species while ADP and AMP increase. Phosphoarginine was high during rest in all investigated animals, and depleted after a series of jumps while the concentration of arginine increased simultaneously. Changes in both metabolite types are most pronounced in the Arthropleona. The amount of l -lactate, measured in Orchesella cincta , showed no significant changes. The results suggest that the muscles performing the jump of springtails belong to the type of muscles that are specialized to anaerobic “burst” activity. However, in the Symphypleona species, which are characterized by a more effective oxygen supply, the acquisition of energy may also occur through aerobic metabolism.

Members of the basal hexapod group Collembola perform indirect sperm transfer; males deposit spermatophores on the soil and these are then picked up by females for insemination. Orchesella villosa exhibits a dissociated mating behavior, while Allacma fusca has either associated mating behavior or, more commonly, produces spermatophores without pairing. Sperm ultrastructure in the two species has been studied by TEM and SEM observations to estimate the volume of these cells. The sperm number into each spermatophore has been determined by counting the fluorescent nuclei after Hoechst staining of sperm droplets squash preparations. Sperm droplets at the apex of spermatophores contain numerous spermatozoa of typical appearance, wound up and with a long anterior appendage (peduncle). Sperm droplets of Orchesella villosa are smaller (about 10 times) than in A. fusca, however they contain substantially more sperm cells (about three times). These differences could be explained as follows: (a) sperm of O. villosa are shorter than those of A. fusca (58 and 107 μm, respectively) and thus the volume of a single sperm of O. villosa is about 10 times smaller than in A. fusca; (b) considering the volume of sperm droplets and of sperm cells, the estimated number of sperm cells would be higher in A. fusca than in O. villosa; and (c) the conspicuous reduction of the sperm cells observed in A. fusca is likely linked to the aberrant meiosis present in this species, as well as in all Symphypleona studied so far, that causes a loss of 50% of their sperm.

Apoptotic and necrotic changes in the midgut epithelium cells of Allacma fusca (Collembola, Symphypleona) are described at the ultrastructural level. The morphological sign indicating the beginning of the apoptotic process in these cells is their shrinkage and the transformation of their mitochondria. The nucleus assumes a lobular shape and finally undergoes fragmentation. The intercellular junctions between an apoptotic cell and adjacent epithelial cells gradually disappear. Apoptotic cells are discharged into the midgut lumen just beneath the peritrophic membrane, where they are initially distributed singly but ultimately form a single layer. No phagocytosis was observed, so no apoptotic bodies are formed. Only young midgut epithelium shows apoptosis; as cells age, necrosis accompanies apoptosis, and necrosis finally completely replaces apoptosis.

Summary The fine structure of the male reproductive system of Allacma fusca (L.) is described. The system consists of testes, deferent ducts, seminal vesicles, ejaculatory duct and accessory glands. The nature of each part is established. Secretions from the seminal vesicles are stored in the lumen of these organs, then flow into the ejaculatory duct and are used to produce spermatophores. The epithelium of this tract has secretory activity and osmoregulatory function. Secretions and spermatozoa are stored into two distinct parts of the ejaculatory duct, divided by a transverse cuticular septum.

The internal proprioceptive organs of the distal antennal segments of Allacma fusca (Collembola : Sminthuridae) were examined with light, scanning, and transmission electron microscopy. There are 2 such organs, each belonging to the sensory equipment of a sensory peg. These pegs are part of the sensory organs of the 3rd antennal segment (SO - AIII), and show characteristics of both hair sensilla and chordotonal organs. They have 5 sensory cells of which 4 can be regarded as chemoreceptors, because the walls of the pegs are pierced by pores. The 5th cells are the proprioceptors. Their dendritic outer segments are connected to the base of the SO - AIII peg but show no specializations. Their dendritic inner segments are distally joined to a thecogen cell containing a scolopale. Proximally, they span the hemolymph space within the antenna. The perikaryon of one of the organs is located on a muscle that deflects the 3rd antennal segment (IP - AIII). The perikaryon of the other is attached to the antennal nerve near a point where it is connected to a muscle that deflects the 4th antennal segment (IP - AIV). There is a conspicuous membrane system, associated with microtubules and a prominent ciliary rootlet within the dendritic inner segment of the IP - AIII. The cytological features of the organs are discussed with reference to 2 problems, the phylogeny of chordotonal organs and the process of mechanosensory transduction.

The proprioceptors of the musculature moving the second antennal segment in the collembolan Allacma fusca were examined with the electron microscope. There are five muscles, the most important of which appear to be a levator and a depressor muscle. Only these two muscles are monitored by proprioceptors. These proprioceptors, the scolopidia, are referred to here as the levator (l-) and the depressor (d-) scolopidium. The former contains two, the latter one sensory cell.