Entomobrya atrocincta Schӧtt , 1896

Katz, Aron D., Giordano, Rosanna & Soto-Adames, Felipe, 2015, Taxonomic review and phylogenetic analysis of fifteen North American Entomobrya (Collembola, Entomobryidae), including four new species, ZooKeys 525, pp. 1-75 : 15-19

Taxon classification Animalia Collembola Entomobryidae

Entomobrya atrocincta Schӧtt, 1896 Figs 1, 2, 3B, 4, 6, 9, 10, 39

Description.

Body shape and color pattern. Sexually dimorphic in color pattern and body shape. Males and females with variable but characteristically different color patterns (Fig. 9). Male body relatively cylindrical, slender, with bright orange background with black pigment usually forming a thick and complete transverse dorsal band covering posterior margin of Th. 2 and all of Th. 3 and Abd. 1, band sometimes absent. Male light form without dark pigment on Th. 2 through Abd. 6 (except sometimes along anterior margin of Th. 2). Male dark form with band covering Th. 2 through Abd. 2, irregular pigment patterns sometimes forming 1+1 orange spots on Abd. 3, and two narrow longitudinal stripes connected by transverse band on posterior margin of Abd. 4 (Fig. 9 A–D). Females with slightly dorso-ventrally flattened body and slightly larger than males. Female color pattern strikingly different from males, white or light yellow background with black, dark blue or purple pigment forming transverse bands across the posterior margins of Th. 2 through Abd. 4. All females with two longitudinal stripes or triangular extensions connected by two transverse bands on Abd. 4; one incomplete medial band and another complete band on posterior margin of Abd 5 (Fig. 9 E–I). Mesonotum white in both sexes, lacking pigment except for a small irregular band across anterior margin. Medial area of Th. 2 relatively transparent and fat bodies visible through cuticle under a dissecting microscope. Both males and females with purple pigment usually extending from apical end of 2nd antennal segment through apex of 4th antennal segment.

Head. Apical bulb of 4th antennal segment located in deep pit, usually simple, sometimes with up to four distinct lobes. Long differentiated smooth setae on ventral side of 1st antennal segment ≈2.5x short setae. Prelabral setae ciliate. Ornamentation of distal margin of labral papillae with 3-4 small seta or spine-like projections (Fig. 2). Dorsal head chaetotaxy variable (Fig. 10A); macrosetae An’ 0, An3a2, An3a3, S’ 0, S6, Ps3, Pi1, Pa3, and Pm1i always absent; S0 usually present, M3i usually absent, A6 present in roughly half of observed specimens. Eyes G and H small and subequal; eye patch with 5 setae.

Thorax. Chaetotaxy of Th. 2 stable, without variation in number of macrosetae. A row of microsetae occurs along entire posterior margin of Th. 2 (not displayed in figure); a5, m1, m2, m4, m4p, and all posterior macrosetae (series Pi, Pa, Pm, and Pp) present (Fig. 10B). Chaetotaxy of Th. 3 variable: 8 macrosetae always present in zone M, 5 in zone L, and 3 in zone Pl (Fig. 3B); macroseta a5e, m4, a6i, and p1i usually present (Fig. 10C).

Legs. Trochanteral organ with triangular setal pattern and up to 30 setae. Unguis with 4 internal teeth; basal teeth located approximately middle of inner claw length.

Abdomen. Abdominal chaetotaxy variable. Abd. 1, with 4-8 macroseta (Fig. 10D), row of microsetae present along entire posterior margin (not displayed in figure). Abd. 2 with 4-6 macrosetae (Fig. 10E): a2, m3, m3e, and m5 always present; a3 and m3ep polymorphic. Abd. 3 chaetotaxy stable, with 7 macrosetae: a1, a2, a3, m3, am6, pm6, and p6 (Fig. 10F). Abd. 4 inner macrosetae varying from 8-11 (Fig. 10G). Basal mucronal tooth slightly larger.

Remarks.

Entomobrya atrocincta can be distinguished by the male or female color patterns as described above combined with the presence of macrosetae head S4i and Abd. 3 a1 and a2 and the absence of macrosetae head ps3 and Th. 2 m5 (see Table 2 for additional diagnostic characters). The color pattern of female Entomobrya atrocincta is virtually indistinguishable from that of Entomobrya multifasciata and very similar to Entomobrya intermedia , and Entomobrya nivalis . Though these species may exhibit slight differences in color pattern, it is easier to differentiate them with the characters outlined in Table 3. Female Entomobrya multifasciata and Entomobrya atrocincta can be separated by the presence of head macroseta S4i in Entomobrya atrocincta and its absence in Entomobrya multifasciata , and morphology of the labral papillae; Entomobrya multifasciata has 2-3 large seta or spine-like projections per papillae, whereas Entomobrya atrocincta has 3-4 small, seta or spine-like projections per papillae (Fig. 2).

The male form always has a unique orange color, but the distribution of purple pattern is variable. Christian and Bellinger (1998) report four discrete color forms. An additional male color form was collected during this study. The different color forms can commonly be found together within the same population. There are no significant morphological or COI DNA sequence differences between male forms and variation in color pattern (male and female) is attributed to intraspecific variation ( Katz et al. 2015). The most common male form collected in this study (Fig. 9A) is somewhat similar to Entomobrya clitellaria . However, the two forms can be easily separated by chaetotaxy (Table 3).

Sexual dimorphism in this species has caused serious taxonomic confusion due to the similarity of female pattern to Entomobrya multifasciata and Entomobrya nivalis . Ramel et al. (2008) first described the sexual dimorphism of Entomobrya atrocincta from Greece and even noted that records of Entomobrya multifasciata may be misidentified Entomobrya atrocincta females. However, Jordana (2012) separated most European specimens and classified them as Entomobrya nigrocincta Denis based on chaetotaxy, synonymizing Ramel et al.'s (2008) descriptions with Entomobrya nigrocincta . Jordana (2012) attributes the sexual dimorphism (the same displayed by the specimens collected in North America and included in this study) to Entomobrya nigrocincta only, keeping the description by Christiansen (1958b) valid for Entomobrya atrocincta . Molecular data confirm that different color forms represent different sexes of the same species ( Katz et al. 2015), demonstrating the presence of sexual dimorphism in North American Entomobrya atrocincta . However, species diagnosis remains unclear. Chaetotaxy outlined for both Entomobrya atrocincta and Entomobrya nigrocincta by Ramel et al. (2008) and Jordana (2012) do not match the specimens examined in this study (Table 4). The excessive intraspecific variation in chaetotaxy observed in these specimens raises concern about basing species diagnosis strictly on discrete chaetotaxic characters. Further molecular analysis of European populations is needed in order to elucidate the correct taxonomic status and distribution of these two species.

The original description of Entomobrya atrocincta by Schӧtt (1896) was based on the male form collected from California. Christiansen’s (1958b) descriptions and methods for species delimitation placed heavy emphasis on the male genital plate, which may have led to his inadvertent omission of the female form. Given that the combination Entomobrya atrocincta Schӧtt, 1896 has priority over Entomobrya nigrocincta Denis, 1923, and also because the holotype designated for Entomobrya atrocincta was collected in North America, the specimens along with the descriptions outlined in this study have been assigned to Entomobrya atrocincta .

Distribution.

North America, Hawaii and possibly Europe. Records of Entomobrya multifasciata in North America and Hawaii ( Christiansen and Bellinger 1992) are suspect due to their similarity to the female Entomobrya atrocincta color form. A considerable number of collections of Entomobrya atrocincta from Hawaii also include Entomobrya multifasciata , indicating the species is also sexually dimorphic in the Pacific Islands ( Christiansen and Bellinger 1992). Palearctic records of Entomobrya atrocincta may be Entomobrya nigrocincta provided by Jordana (2012). The distribution of Entomobrya atrocincta in North America is shown in Suppl. material 2: B.

Material examined.

USA: 1♂ in vial, Alabama, Clay Co., Talladega National Forest, on CR6000-1 off of Hwy148 (33.19723,-86.06325), in moss on forest floor, 2.i.2012 (A. Katz & M. DuBray), AK12-5; 6♂ & 2♀ in vial, Illinois, Champaign Co., Champaign, Kaufman Lake Park (40.11514,-88.29000), in bird nest, 8.v.2011, AK11-26; 2♂ on slides, 4♂ & 6♀ in vial, Illinois, Champaign Co., Champaign, Kaufman Lake Park (40.11514,-88.29000), squirrel nest, 8.v.2011, AK11-27; 7♂ & 7♀ on slides, 50+♂ & 50+♀ in vial, Illinois, Champaign Co., Urbana, Natural Resource Building (40.10071,-88.22812), in leaf litter under bush by parking lot, 22.iv.2011, AK11-17; 1♂ on slides, Illinois, Champaign Co., Urbana, Meadowbrook Park (40.08063,-88.20828), in leaf litter, 14.iv.2012, AK12-24; 3♀ in vial, Illinois, Champaign Co., Urbana, South side of Natural Resource Building (40.10110,-88.22963), in sweet gum seed pods and leaf litter, 23.iv.2011 (A. Katz & M. DuBray), AK11-15; 3♀ on slides, 20♂ & 10♀ in vial, Illinois, Champaign Co., Urbana, Natural Resource Building (40.10047,-88.22840), in leaf litter under bush along Pennsylvania Ave, 5.v.2011, AK11-25; 1♂ & 1♀ on slides, 50+♂ & 50+♀ in vial, Tennessee, Knox Co., University of Tennessee, Ag. Campus, Morgan Hall (36.01023,-83.93829), on moist fallen bark, April 2010 (E. C. Bernard); 1♂ & 1♀ in vial, Tennessee, Knox Co., Farragut, 12108 Ridgeland Drive (36.01023,-83.93829), in old bald-faced hornet nest, 2.iii.2008 (E. C. Bernard).