Entomobrya assuta Folsom, 1924

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 : 13-14

Taxon classification Animalia Collembola Entomobryidae

Entomobrya assuta Folsom, 1924 Figs 2, 3A, 7, 8, 39

Description.

Body shape and color pattern. Body dorso-ventrally flattened. Dorsal color pattern highly variable, and in many cases, without clear discrete forms (Fig. 7). Patterns usually consisting of black or dark blue pigment on a white, yellow, orange, or light purple background. Thorax pigmentation variable. Sometimes Th. 2 and Abd. 3 entirely dark, forming two strong transverse bands. All forms studied have a dark transverse band across the posterior margin of Abd. 2. Abd. 3 entirely dark or with two or three pale spots. Abd. 4 and 5 also with 2-3 pale spots each. Posterior margin of Abd. 4 usually lacking pigment, forming an irregular pale transverse band. Antennae usually entirely purple, but 1st antennal segment at times considerably lighter.

Head. Apical bulb of 4th antennal segment usually bilobed, sometimes simple or, rarely, trilobed. Long differentiated smooth setae on ventral side of 1st antennal segment ≈3x short setae. Prelabral setae finely ciliated, seemingly smooth at low magnification under light microscopy. Distal margin of labral papillae with 2-3 small spine-like projections (Fig. 2). Dorsal head chaetotaxy reduced in comparison with other species (Fig. 8A); macrosetae An’ 0, A6, M3i, S’ 0, S1, Pi1, Pa2, Pa3, Pm2, and Pm1i always absent; An3a3 seen in one individual; M3 present in 1/4 of individuals observed; S0 and Pa1 usually present. Eyes G and H small and subequal. Eye patch with 5 setae.

Thorax. Thoracic chaetotaxy extremely reduced but stable, without macrosetae variation in specimens studied. A row of microsetae present along entire posterior margin of Th. 2 and Th. 3 (not displayed in figures). Th. 2, with a5 and 5 posterior macrosetae (Fig. 8B): p4, p5, p6, p6e, and p6ep. Th. 3, with 7 macrosetae (Fig. 8C): a5, a6, m5, m6, m7, p4, and p6; macrosetae a1, a2, and a3 absent. Chaetotaxy of zone Pm extremely reduced for both thoracic segments, without macrosetae (Figs 3A; 8B,C).

Legs. Trochanteral organ with triangular setal pattern and up to 23 setae. Unguis with 4 inner teeth; basal teeth located approximately middle of inner claw length.

Abdomen. Abdominal chaetotaxy reduced but stable, no macrosetae variation observed. Abd. 1 with 1 macroseta only (Fig. 8D); row of microsetae along entire posterior margin present (not displayed in figure). Abd. 2 with 3 macrosetae: m3, m3e, and m5 (Fig. 8E). Abd. 3 with 4 macrosetae: a2, m3, pm6, and p6. Mesosetae a2a, inserted slightly anterior and exterior to a2, sometimes with relatively large socket resembling socket of macroseta a3, but due to mesoseta a2 a’s close proximity to a2, it is most likely a duplicate of a2 rather than homologous to a3 (Fig. 8F). Abd. 4 with 4 inner macrosetae (Fig. 8G). Mucronal teeth subequal.

Remarks.

Entomobrya assuta is the only species with the color pattern as described above in combination with the absence of all the following macrosetae: head Ps3, Th. 2 m2 and m3, Abd. 2 a2, a3 and m3ep, and Abd. 3 a1 (see Table 2 for additional diagnostic characters). Among all species observed in this study, only Entomobrya assuta and Entomobrya citrensis sp. n. share this unique pattern of substantially reduced dorsal chaetotaxy. Entomobrya assuta and Entomobrya citrensis sp. n. share very similar chaetotaxy and color pattern. In fact, Entomobrya citrensis sp. n. was at first considered to be an undescribed color form of Entomobrya assuta , but molecular data provides evidence for their separation ( Katz et al. 2015).

Subsequent comparative morphological observations between the two forms show that head macroseta Ps3 and Abd. 2 macroseta a3 are both absent in Entomobrya assuta , but present in Entomobrya citrensis sp. n.; additionally, Entomobrya citrensis sp. n. has a complete, dark transverse band located medially across Abd. 4, whereas this band is absent in Entomobrya assuta . Labral morphology also separates these species, Entomobrya assuta has relatively uniform labral papillae, each with two to three seta or spine-like projection, whereas Entomobrya citrensis sp. n. has up to five minute bumps or serrations on the two internal papillae and only two larger spine-like projections on the two external papillae (Fig. 2). It should be pointed out that the last character may be variable and should be used in combination with chaetotaxy and color pattern for diagnosis.

Christiansen and Bellinger (1998) reported seven different color forms of Entomobrya assuta , each occurring in separate localities across North America. Many of these color forms were not sampled for this study, and in view of the discovery of Entomobrya citrensis sp. n. it is possible that some of them may represent distinct species. Future determinations of Entomobrya assuta will have to be based on analysis of chaetotaxy and other morphological characters outlined in the present description and not just color pattern.

Entomobrya assuta appears to be an intrusion of a southern subtropical or tropical Entomobrya lineage into the Nearctic region. Christiansen and Bellinger (1998) noted that the dorsal and genital chaetotaxy of Entomobrya assuta is more similar to tropical rather than Nearctic species. In fact, the reduction in chaetotaxy approaches that seen in Entomobrya longiseta Soto-Adames and Entomobrya linda Soto-Adames from the Caribbean, more than other Nearctic forms.

Distribution.

Endemic to North America (Suppl. material 2: A).

Material examined.

USA: Cotypes (J. W. Folsom), 2 on slide, Vermont, Clarendon, under bark Mar-April 1898 (O. W. Barrett), INHS Cat. No. 528,332; Cotypes (J. W. Folsom), 5 in vial, same information as above; Cotypes (J. W. Folsom), 4 in vial, Geneva, N. Y., June 18, 1917, beneath apple bark (H. Glasgow). Other material examined: 2 in vial, Alabama, Covington Co., Conecuh National Forest, off Co. Rd. 11 (31.07900,-86.61203), under bark, 2.i.2012 (A. Katz & M. DuBray), AK12-6; 3 on slides, 20 in vial, Florida, Taylor Co., Econfina State Park (30.0656,-83.91066), under bark, 9.viii.2011, AK11-116; 2 in vial, Illinois, Champaign Co., Champaign, Kaufman Lake Park (40.11514,-88.29000), in bird nest, 8.v.2011, AK11-26; 3 on slides, 5 in vial, Illinois, Champaign Co., Urbana, Brownfield Woods (40.14462,-88.16543), on low-lying vegetation, 7.vii.2011, AK11-60; 1 on slide, Illinois, Champaign Co., Urbana, bird nest, 28.ix.1957 (R. Hurley); 5 on slides, Illinois, Iroquois Co., Iroquois County Forest Preserve (40.99279,-87.59734), under bark, 19.viii.1989 (F. Soto-Adames); 1 in vial, Illinois, Jasper Co., Sam Parr State Fish and Wildlife Area (39.03293,-88.12516), under bark, 15.vii.2011 (A. Katz & F. Soto-Adames), AK11-73; 2 in vial, Illinois, Jo Davies Co., South Blanding Rd., Stevenson Property (42.29895,-90.36967), under bark, 27.viii.2011, A11-148; 1 on slide, 6 in vial, Illinois, Jo Davies Co., Princess Mine 1 (42.30565,-90.39740), under bark, 26.viii.2011, AK11-142; 1 in vial, Illinois, Jo Davies Co., Princess Mine 1 (42.30565,-90.39740), beating vegetation, 26.viii.2011, AK11-143; 4 in vial, Illinois, Jo Davies Co., South River Rd., Asgard Vent 1 (42.30170,-90.40345), under bark, 27.viii.2011, AK11-153; 1 on slide, 7 in vial, Illinois, Jo Davies Co., South River Rd., Asgard Vent 2 (42.30378,-90.40108), under bark, 27.viii.2011, AK11-157; 1 on slide, Illinois, Kankakee Co., Kankakee River State Park (41.19482,-87.96875), from bird nest, 10.iv.2011, AK11-6; 1 on slide, Illinois, Kankakee Co., Kankakee River State Park (41.19482,-87.96875), from squirrel nest, 10.iv.2011, AK11-8; 1 in vial, Illinois, Mason Co, Revis Hill Nature Prairie Reserve (40.15246,-89.85330), beating vegetation, 18.vii.2011 (A. Katz & F. Soto-Adames), AK11-86; 2 on slides, 4 in vial, Illinois, Mason Co., Sand Ridge State Park (40.40892,-89.87590), beating branches, 18.vii.2011 (A. Katz & F. Soto-Adames), AK11-82; 2 on slides, 8 in vial, Illinois, Piatt Co., Lodge Park (40.06709,-88.56596), under bark, 23.vii.2011, AK11-100; 1 in vial, Illinois, Pike Co., Lincoln’s New Salem State Park (39.96868,-89.83386), beating grasses, 18.vii.2011 (A. Katz & F. Soto-Adames), AK11-90;1 on slide, 3 in vial, Illinois, Pope Co., Lake Glendale (37.41350,-88.65982), under bark, 24.ix.2011, AK11-160; 1 on slide, Illinois, Vermilion Co., University of Illinois Observatory, Nixon Fork, leaf littler, 25.iv.2009 (F. Soto-Adames & L. Deem), FD09-25; 1 in vial, Illinois, Vermilion Co., Kennekuk Cover County Park, Windfall Prairie Nature Preserve (40.20995,-87.74181), aspirated from bushes, 16.vi.2011 (A. Katz & F. Soto-Adames), AK11-59; 3 on slides, Illinois, Will Co., Braidwood (41.25118,-88.19494), soil and leaf litter, 6-8.ix.2011 (F. Soto-Adames); 2 on slides, Michigan, Ingham Co., Michigan State University, Baker Wdlt. (42.66527,-84.36264) under bark of standing dead pine, 24.vii.2008 (E. C. Bernard), BW-11; 1 on slide, Michigan, St. Clair Co., Algonac State Park (42.65447,-82.52430), under bark of recently fallen maple, 25.vii.2008 (E. C. Bernard), ASP-15; 8 in vial, Pennsylvania, Chester Co., Wayne, sweep of Forsythia sp., 29.vi.2012, AK12-50; 7 on slides, 30+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).