Research Article |
Corresponding author: Stylianos Chatzimanolis ( stylianos-chatzimanolis@utc.edu ) Academic editor: Zi-Wei Yin
© 2021 Stylianos Chatzimanolis.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Chatzimanolis S (2021) Out of Xanthopygus (Coleoptera: Staphylinidae): escape from polyphyly. ZooKeys 1071: 83-107. https://doi.org/10.3897/zookeys.1071.75947
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Xanthopygus as currently defined is the largest genus in the subtribe Xanthopygina (Coleoptera: Staphylinidae: Staphylininae) with 40 described species. However, the genus is poorly defined, morphologically heterogeneous and previous studies have questioned whether it is a natural group. A morphological (51 characters) Bayesian phylogenetic analysis was performed to test whether Xanthopygus is a monophyletic group. The analysis indicated that Xanthopygus was polyphyletic, and therefore species were split into four different genera. Xanthopygus nigricornis Scheerpeltz was transferred to Oligotergus as Oligotergus nigricornis comb. nov. and Xanthopygus skalitzkyi (Bernhauer) was transferred to Styngetus as Styngetus skalitzkyi comb. nov. A new genus, Photinopygus gen. nov. was erected to accommodate the majority of the species previously in Xanthopygus and Xanthopygus sensu novo is used in a new restricted sense to accommodate the remaining species. Diagnostic features are provided to distinguish species in the genera Photinopygus and Xanthopygus from each other and all other Xanthopygina genera.
New genus, phylogeny, Staphylininae, Staphylinini, Xanthopygina
Recently,
Phanolinus is perhaps one of the most charismatic taxa within Xanthopygina, and even Staphylinidae, with bright metallic coloration covering the whole body. However, many species were described solely based on the differences in coloration and many of them are potential synonyms (Chatzimanolis unpublished data). Elecatopselaphus was recovered as the sister group of Phanolinus (
Xanthopygus (Fig.
Xanthopygus was described by
While it is rather obvious from the taxonomic history above that Xanthopygus is not homogeneous, the goal of this paper is to use a phylogenetic framework to show that Xanthopygus sensu Herman can be confidently split into two or more taxa. Additionally, I seek to define diagnostic characters that can easily separate the various groups within Xanthopygus.
The focus of this paper was to determine whether the species currently in Xanthopygus sensu Herman form a monophyletic group. Thus, the analysis conducted focused on this goal rather than attempting to decipher the exact placement of all the different Xanthopygus species groups within Xanthopygina. For the ingroup, I included 21 species from Xanthopygus, comprising all the different species groups in that genus (Chatzimanolis unpublished data). Xanthopygus borealis Hatch was listed as a valid species of Xanthopygus by
Specimens were examined using an Olympus ZX10 stereomicroscope either as dry mounts or disarticulated in glycerin. Photographs of species were taken using a Canon 40D camera equipped with a MP-E 65 mm macro lens on a Cognisys StackShot 3X macro rail and controller (https://cognisys-inc.com/stackshot-macro-rail-package.html). Images were automontaged using Helicon Focus Pro v.7.7.4 (http://www.heliconsoft.com/heliconsoft-products/helicon-focus/) and post-processed in Adobe Photoshop v.22.3. Tree diagrams were first processed using FigTree v.1.4.4 (http://tree.bio.ed.ac.uk/software/figtree/) and then edited in Adobe Illustrator v.25.2.
In total, 51 morphological characters were scored in Mesquite v.3.61 (
1*. Antennae, antennomere 1 in comparison to antennomere 2: (0) less than twice as long; (1) twice as long or longer.
2. Antennae, antennomere 4, tomentose pubescence: (0) absent (Fig.
3. Antennae, antennomere 4: (0) elongate (Fig.
4. Antennae, antennomere 5: (0) elongate (Fig.
5. Antennae, antennomere 6: (0) elongate (Fig.
6. Antennae, antennomere 7: (0) elongate (Fig.
7. Head, length in comparison to pronotum: (0) shorter (Fig.
8. Head, width in comparison to pronotum: (0) narrower (Fig. CC1–2); (1) subequal (Fig.
9*. Head, shape, posterior margin: (0) slightly extended posteriad on each side of the neck (Fig.
10. Head, eye size relative to length of head (length of head measured from anterior margin of clypaeus to posterior margin of head): (0) small (less than 2/5 length of head) (Fig.
11. Labrum, emargination, shape: (0) V-shaped, lobes moderately separated; (1) broadly U-shaped, lobes strongly separated (Fig.
12. Head, deep punctures demarcating raised postmandibular ridge dorsolaterally: (0) absent (Fig. CT3); (1) present (Fig. S81).
13. Hypostomal cavity (hc): (0) hc moderately delimited (i.e., cavity surface without microsculpture or punctation different from rest of nearby head surface) (Figs S8, S10); (1) hc slightly delimited (cavity distinct only laterally, its surface with same microsculpture or punctuation as rest of nearby head surface).
14. Mandible, curvature: (0) more or less straight, except tip of mandible (Fig.
15. Mandible, left, teeth structure (excludes tip of mandible): (0) one tooth (Fig. CA14); (1) two teeth, separated by deep emargination (Fig.
16. Neck, disc (i.e., dorsal surface of neck not including dorsolateral areas): (0) punctures absent or rather sparse (Fig.
17*. Pronotum, microsculpture: (0) polygon shaped; (1) with transverse lines (seen easily at 70× magnification); (2) with dense micropunctures (Figs CA30, 32,38); (3) with sparse micropunctures (but no transverse lines visible at 70× magnification).
18. Prothorax, disc of pronotum, distribution of punctures: (0) median part of pronotum with punctation beyond midlength (Fig.
19. Prothorax, disc of pronotum, distribution of punctures if punctures continue beyond midlength: (0) more or less homogeneous (i.e., punctures are separated by same distance; Fig.
20. Prothorax, hypomeron, inferior marginal line (iml), development: (0) iml not continued as a separate entity beyond anterior pronotal angles (Fig. S42–44); (1) iml continued as a separate entity beyond anterior pronotal angles and curving around them (Fig. S53).
21. Prothorax, hypomeron, superior marginal line: (0) continuous to anterior margin (Fig.
22*. Prothorax, hypomeron, angles of superior and inferior marginal lines: (0) superior and inferior line produce anterolateral angles parallel to one other (Fig.
23. Prothorax, postcoxal process: (0) absent; (1) present (Fig. S53).
24. Prothorax, basisternum (bs), length relative to length of furcasternum (fs) (bs/fs, measured laterally): (0) bs slightly to moderately longer than fs (bs/fs ratio up to 1.5); (1) bs distinctly longer than fs (bs/fs ratio >> 1.5) (Fig. CP8A).
25. Prothorax, basisternum, position of pair of macrosetae (ms, if present) in relation to anterior margin of prosternum (amp) and the sternacostal suture (ss): (0) ms situated close to amp (i.e., not farther than one fourth the distance between amp and the ss along midline) (Fig. S86); (1) ms situated far from amp (i.e., farther than one fourth the distance between amp and the ss along midline) (Fig. L11A, B, E, F).
26. Mesothorax, elytra, with contiguous polygon-shaped meshed microsculpture (elytra appearing matt): (0) absent; (1) present (Fig. SB2: Gastrisus).
27. Mesothorax, mesocoxae: (0) Mesocoxae contiguous, intercoxal area distinctly recessed compared to mesoventrital and metaventrital processes (Fig. S158); (1) Mesocoxae moderately separated, intercoxal area distinctly recessed compared to mesoventrital process only (Fig. S87); (2) Mesocoxae strongly separated, intercoxal area on approximately same plane as both meso and metaventrital processes (Fig. S117).
28. Mesothorax, mesoscutellum, dense micropunctures: (0) absent (Fig.
29. Mesoventrite, intercoxal process, apex: (0) narrow and pointed (Fig. S60); (1) broad and rounded; (2) narrow and rounded (Fig.
30*. Metathorax, metepisternum, punctures: (0) dorsal 1/3 of metepisternum without punctures throughout its length (Fig.
31*. Metathorax, relative width of metepimeron in comparison to metepisternum near posterior border: (0) metepimeron subequal or slightly wider than metepisternum (Fig.
32*. Metathorax, metacoxae, spines on the posterior surface: (0) 4 or less (Fig.
33*. Metathorax, metafemora, upper posterior margin: (0) crenulate (Fig.
34. Metathorax, metatarsi, tarsomere 3, dorsal surface, chaetotaxy: (0) developed only at margins, dorsal surface of tarsomeres glabrous (or with 1–2 setae) along midline (Fig.
35. Abdomen, tergites 3 and 4, anterior basal transverse carina (ABTC), pair of accessory ridges: (0) absent (Fig.
36. Abdomen, tergite 3, curved carina (arch-like) on disc: (0) absent; (1) present (Fig.
37. Abdomen, tergite 3, punctation medially: (0) absent; (1) present (Fig.
38. Abdomen, tergite 5, curved carina (arch-like) on disc (if curved carina present on tergite 3): (0) absent; (1) present (Fig.
39. Abdomen, sternite 3, basal transverse carina, medial area: (0) straight to arcuate (Fig. L18C); (1) acutely pointed medially (Fig. L18A, D).
40. Abdomen, sternite 5, dense, meshed microsculpture anterolaterally, appearing different in texture to posterior portion (microsculpture more obvious than normal punctures): (0) absent; (1) present (Fig. CH23–34).
41*. Abdomen, sternite 6, two anterior transverse lines: (0) absent; (1) present (Fig.
42. Abdomen, sternite 7, punctation laterally (excluding micropunctures): (0) sparse (each row of punctures separated by more than two puncture width from other rows) (Fig.
43. Male, abdomen, sternite 7, emargination of posterior margin (in comparison to female sternite 7): (0) absent; (1) present (Fig.
44. Male, abdomen, sternite 7, degree of emargination of posterior margin if present: (0) broad and shallow (Fig.
45. Male, abdomen, sternite 7, porose structure: (0) absent (Fig.
46. Male, abdomen, sternite 7, shape of porose structure (if present): (0) circular and pit-like, typically with few modified setae (Fig. CA19); (1) broad and brush-like, with many modified setae (Fig.
47. Male, abdomen, sternite 8, emargination: (0) shallow (just a notch) (Fig.
48. Male, aedeagus, median lobe, apical tooth: (0) absent; (1) present (Fig. CT5).
49. Male, aedeagus, tip of median lobe in dorsal view: (0) pointed (Fig. CA53); (1) rounded (Fig. CA112); (2) broadly expanded (Fig. CA71).
50*. Male, aedeagus, median lobe, serrated apical carina: (0) absent; (1) present (Fig.
51*. Male, aedeagus, median lobe, hook-like carina: (0) absent; (1) present (Fig.
Bayesian analysis were conducted in MrBayes v.3.2.7 (
The Bayesian analysis (Fig.
List of Xanthopygus species sensu Herman and their current name based on this paper. Bold type font on the first column indicates taxa included in the phylogenetic analysis. Taxa not included in this analysis but transferred to Photinopygus have all the diagnostic features of Photinopygus. Similarly, taxa that remained in Xanthopygus but were not included in the analysis have all the diagnostic features of Xanthopygus sensu novo.
Name sensu |
Current status |
---|---|
Xanthopygus alienus Bernhauer, 1905 | Photinopygus alienus (Bernhauer, 1905); comb. nov. |
Xanthopygus apicalis Sharp, 1876 | Photinopygus apicalis (Sharp, 1876); comb. nov. |
Xanthopygus borealis Hatch, 1957 | junior synonym of Tympanophorus puncticollis (Erichson, 1840); (Moore & Legner 1975) |
Xanthopygus cacti Horn, 1968 | junior synonym of Xanthopygus xanthopygus (Nordmann, 1837); (Newton et al. 2000) |
Xanthopygus calidus (Erichson, 1839) | Photinopygus calidus (Erichson, 1839); comb. nov. |
Xanthopygus chapareanus Scheerpeltz, 1969 | Photinopygus chapareanus (Scheerpeltz, 1969); comb. nov. |
Xanthopygus chrysopygus (Nordmann, 1837) | Photinopygus chrysopygus (Nordmann, 1837); comb. nov. |
Xanthopygus chrysurus (Nordmann, 1837) | Photinopygus chrysurus (Nordmann, 1837); comb. nov. |
Xanthopygus cognatus Sharp, 1876 | Xanthopygus cognatus Sharp, 1876 |
Xanthopygus collaris Bernhauer, 1925 | Photinopygus collaris (Bernhauer, 1925); comb. nov. |
Xanthopygus corcovadoensis Scheerpeltz, 1969 | Photinopygus corcovadoensis (Scheerpeltz, 1969); comb. nov. |
Xanthopygus cyanelytrius (Perty, 1830) | Photinopygus cyanelytrius (Perty, 1830); comb. nov. |
Xanthopygus cyanipennis Sharp, 1876 | Photinopygus cyanipennis (Sharp, 1876); comb. nov. |
Xanthopygus depressus Sharp, 1876 | Photinopygus depressus (Sharp, 1876); comb. nov. |
Xanthopygus dimidiatus Bernhauer, 1917 | Photinopygus dimidiatus (Bernhauer, 1917); comb. nov. |
Xanthopygus elegans Bernhauer, 1905 | Photinopygus elegans (Bernhauer, 1905); comb. nov. |
Xanthopygus faustus (Erichson, 1839) | Photinopygus faustus (Erichson, 1839); comb. nov. |
Xanthopygus flohri Sharp, 1884 | Photinopygus flohri (Sharp, 1884); comb. nov. |
Xanthopygus giganteus (Bernhauer, 1906) | Xanthopygus giganteus (Bernhauer, 1906) |
Xanthopygus grimmeri a Duvivier, 1883 |
nomen dubium; ( |
Xanthopygus haemorrhoidalis (Germar, 1824) | Photinopygus haemorrhoidalis (German, 1823); comb. nov. |
Xanthopygus hilaris (Erichson, 1839) | Photinopygus hilaris (Erichson, 1839); comb. nov. |
Xanthopygus iopterus (Erichson, 1939) | Photinopygus iopterus (Erichson, 1939); comb. nov. |
Xanthopygus janthinipennis (Blanchard, 1842) | Photinopygus janthinipennis (Blanchard, 1842); comb. nov. |
Xanthopygus luctuosus (Blanchard, 1842) | Xanthopygus luctuosus (Blanchard, 1842) |
Xanthopygus major (Bernhauer, 1917) | Xanthopygus major (Bernhauer, 1917) |
Xanthopygus max Blackwelder, 1944 | Xanthopygus max Blackwelder, 1944 |
Xanthopygus mirabilis (Erichson, 1840) | Photinopygus mirabilis (Erichson, 1840); comb. nov. |
Xanthopygus morosus Sharp, 1884 | Photinopygus morosus (Sharp, 1884); comb. nov. |
Xanthopygus nigricornis Scheerpeltz, 1969 | Oligotergus nigricornis (Scheerpeltz, 1969); comb. nov. |
Xanthopygus nigripes Sharp, 1876 | Photinopygus nigripes (Sharp, 1876); comb. nov. |
Xanthopygus oliveirae Lynch, 1884 | Xanthopygus oliveirae Lynch, 1884 |
Xanthopygus pexus (Motschulsky, 1858) | Xanthopygus pexus (Motschulsky, 1858) |
Xanthopygus punctatus Bernhauer, 1905 | Photinopygus punctatus (Bernhauer, 1905); comb. nov. |
Xanthopygus puncticollis Sharp, 1884 | Photinopygus puncticollis (Sharp, 1884); comb. nov. |
Xanthopygus rufipennis Sharp, 1884 | Photinopygus rufipennis (Sharp, 1884); comb. nov. |
Xanthopygus sapphirinus (Erichson, 1839) | Photinopygus sapphirinus (Erichson, 1839); comb. nov. |
Xanthopygus skalitzkyi (Bernhauer, 1906) | Styngetus skalitzkyi (Bernhauer, 1906); comb. nov. |
Xanthopygus tepidus (Erichson, 1839) | Photinopygus tepidus (Erichson, 1839); comb. nov. |
Xanthopygus violaceipennis Bernhauer, 1927 | Photinopygus violaceipennis (Bernhauer, 1927); comb. nov. |
Xanthopygus violaceus Sharp, 1876 | Photinopygus violaceus (Sharp, 1876); comb. nov. |
Xanthopygus viridipennis Sharp, 1876 | Photinopygus viridipennis (Sharp, 1876); comb. nov. |
Xanthopygus xanthopygus (Nordmann, 1837) | Xanthopygus xanthopygus (Nordmann, 1837) |
In a tree rooted by Philothalpus, all other taxa were placed in four different clades in a polytomy. The first clade contained Phanolinus colombinus, and the second clade is composed of the sister groups Gastrisus sp. and Gastrisus mimetes (PP = 1). The third clade was unsupported (called here the Xanthopygus clade); it contained several species (Gastrisus nitidus, Triacrus dilatus, Genus 1 and the fours species of Xenopygus) and a large portion of the Xanthopygus species. The species of Xanthopygus in this clade formed a monophyletic group that was strongly supported (PP = 0.92) and will be treated as the Xanthopygus sensu nov. (for details see below on the Taxonomy section). Taxa included here were the ones placed in the genus Lampropygus by early taxonomists. Xanthopygus giganteus was the sister group of Xa. oliveirae (PP = 0.99) and together were the sister group of Xa. major but without support. This clade was placed in a polytomy with Xa. xanthopygus, Xa. cognatus, Xa. pexus and Xa. max. For a list of characters that support Xanthopygus sensu nov. see the Taxonomy section below and Table
List of taxonomic characters that distinguish species of Xanthopygus from Photinopygus. Numbers next to characters refers to the numbers in the data matrix. For a full list of characters and character states see Material and Methods, and for the mapping of the characters on the phylogenetic tree see Suppl. material
Characters | Photinopygus | Xanthopygus |
---|---|---|
4. Antennae, antennomere 5 | (0) elongate (Figs |
(1) subquadrate (Figs |
8. Head, width in comparison to pronotum | (1) subequal (Figs |
(2) wider1 (Figs |
9. Head, shape, posterior margin | (0) slightly extended posteriad on each side of the neck2 (Figs |
(1) more or less at same level with neck border (Figs |
10. Head, eye size relative to length of head | (1) medium (between 2/5 and 2/3 length of head) (Fig. |
(0) small (less than 2/5 length of head) (Fig. |
15. Mandible, left, teeth structure | (2) one bicuspid tooth (Fig. |
(1) two teeth, separated by deep emargination (Fig. |
17. Pronotum, microsculpture | (3) with sparse micropunctures (but no transverse lines visible at 70× magnification) (apomorphy). | (1) with transverse lines (seen easily at 70× magnification)3. |
22. Prothorax, hypomeron, angles of superior and inferior marginal lines | (0) superior and inferior line produce anterolateral angles parallel to one other (Fig. |
(1) superior and inferior line produce anterolateral angles not parallel to one other (Fig. |
28. Mesothorax, mesoscutellum, dense micropunctures | (0) absent (Fig. |
(1) present (Fig. |
29. Mesoventrite, intercoxal process, apex | (2) narrow and rounded (Fig. |
(1) broad and rounded; or (3) broad and pointed (Fig. |
30. Metathorax, metepisternum, punctures | (1) metepisternum covered with punctures or impunctate area less than 1/34 (Fig. |
(0) dorsal 1/3 of metepisterstum without punctures throughout its length (Fig. |
32. Metathorax, metacoxae, spines on the posterior surface | (0) 4 or less (Fig. |
(1) more than 45 (Fig. |
34. Metathorax, metatarsi, tarsomere 3, dorsal surface, chaetotaxy | (1) tarsomeres dorsally setose (setae not restricted to marginal series) (Fig. |
(0) developed only at margins, dorsal surface of tarsomeres glabrous (or with 1–2 setae) along midline (Fig. |
The fourth clade (called here the Photinopygus clade) included Xanthopygus taxa in three different subclades. Xanthopygus skalitzkyi was placed as the sister group of Styngetus deyrollei (Solsky) with weak support (PP = 0.80) and supported by a unique synapomorphy present in all Styngetus species: (character 33:0 and matrices in Suppl. material
The remaining taxa in the fourth clade all belonged in Xanthopygus sensu Herman and were strongly supported as a monophyletic group (PP = 0.99). Xanthopygus punctatus was recovered as the sister group of Xa. flohri but without support (PP = 0.74) and together as the sister group of Xa. sapphirinus (PP = 0.65). That clade was placed in a polytomy with Xa. mirabilis, Xa. cyanelytrius, Xa. puncticollis, Xa. calidus, and a strongly supported clade (PP = 0.90) of Xa. chapareanus + Xa. faustus (PP = 0.95) as the sister group of Xa. rufipennis + Xa. dimidiatus (PP = 0.93). All these taxa previously in Xanthopygus are transferred to a new genus, Photinopygus gen. nov. and the apomorphies supporting this new genus are given below in the Taxonomy section and in Table
Philothalpus (Oligotergus) oculatus, fixed by monotypy (
The genus includes 20 species listed in
The genus is not revised so the following characters (in combination) should be considered only as a partial list: left mandible with single tooth; antennomere 1 less than twice as long as antennomere 2; eyes large; pronotum with dense micropunctures (not in all species).
The type species was not available for the phylogenetic analysis. A formal revision of the genus is forthcoming (Chatzimanolis in preparation) where all species belonging to this genus will be treated and illustrated.
Philonthus viduus Erichson, fixed by subsequent designation by
The genus includes 16 species listed in
The genus is not revised so the following characters (in combination) should be considered only as a partial list: left mandible with bicuspid tooth; protarsi without ventral pale macrosetae (not present in all taxa); metafemur with upper posterior margin crenulate; sternites 3–5 with arch-like carina.
The type species was not available for the phylogenetic analysis. A formal revision of the genus is forthcoming (Chatzimanolis in preparation) where all species belonging to this genus will be treated and illustrated.
Habitus photographs of species of Xanthopygus sensu
Diagnostic characters for Xanthopygus A pronotal hypomeron of Xanthopygus skalitzkyi (Bernhauer) B pronotal hypomeron of Xanthopygus xanthopygus (Nordmann) C mesoscutellum of Xanthopygus cognatus Sharp D mesoscutellum of Xanthopygus mirabilis (Erichson) E mesoventrite of Xanthopygus mirabilis (Erichson), arrow points to intercoxal process F mesoventrite of Xanthopygus xanthopygus (Nordmann), arrow points to intercoxal process. Not to scale.
Diagnostic characters for Xanthopygus A metepimeron (mep) and metepisternum (mes) of Xanthopygus mirabilis (Erichson) B metepimeron (mep) and metepisternum (mes) of Xenopygus analis (Erichson) C metacoxae of Xanthopygus mirabilis (Erichson), arrow points to spines D metacoxae of Triacrus dilatus Nordmann, arrow points to spines E Metatarsus of Xanthopygus xanthopygus (Nordmann) F metatarsus of Xanthopygus flohri Sharp G metafemur of Xanthopygus skalitzkyi (Bernhauer), showing crenulate surface. Not to scale.
Staphylinus calidus Erichson, here designated.
alienus, apicalis, calidus, chapareanus, chrysopygus, chrysurus, corcovadoensis, cyanelytrius, cyanipennis, depressus, dimidiatus, elegans, faustus, flohri, haemorrhoidalis, hilaris, iopterus, janthinipennis, mirabilis, morosus, nigripes, punctatus, puncticollis, sapphirinus, tepidus, violaceipennis, violaceus and viridipennis (see Table
This genus can be distinguished from all other genera in Xanthopygina based on the combination of the following characteristics: head shape rectangular; posterior margin of head slightly extended posteriad on each side of the neck (apomorphy; except in Ph. corcovadoensis and Ph. mirabilis); antennomeres 1–5 elongate; labial palpomere 3 not securiform; medium size eyes; superior marginal line of pronotal hypomeron not continuing to anterior margin; postcoxal process present; pronotum with sparse micropunctures but no transverse lines visible at 70× magnification (apomorphy); mesoscutellum without dense micropunctures (apomorphy); mesoventral process narrow and rounded (apomorphy); metatarsi with setose dorsal surface (apomorphy); tergite 3 (at minimum, some species 3–4 or 3–5) with arch-like carina; and sternite 7 in males with emargination at posterior margin. For a list of characters that distinguish Photinopygus from Xanthopygus, see Table
The name is a combination of the Greek words φωτεινός (shining, bright) and πυγή (rump), and refers to the bright coloration of abdominal segments 7 and 8. The name is masculine.
A formal revision of the genus is forthcoming (Chatzimanolis in preparation) where all species belonging to this genus will be treated and illustrated. Even though some of the species transferred to Photinopygus were not included in the phylogenetic analysis, they can be confidently placed in this genus since they have all the diagnostic features of Photinopygus (see Tables
Staphylinus xanthopygus Nordmann, 1837, fixed by absolute tautonymy (
cognatus, giganteus, luctuosus, major, max, oliveirae, pexus and xanthopygus. (see Table
This genus can be distinguished from all other genera in Xanthopygina based on the combination of the following characteristics: head shape rectangular; head wider than pronotum (apomorphy; however, head size can be variable among specimens of the same species but wider than pronotum); antennomeres 7–10 transverse; left mandible with two teeth separated by deep emargination (apomorphy); labial palpomere 3 not securiform; small size eyes (apomorphy); superior marginal line of pronotal hypomeron not continuing to anterior margin; superior and inferior marginal line of hypomeron produce anterolateral angles not parallel to one other (apomorphy); postcoxal process present; elytra coloration black (except with blue metallic overtones in Xa. xanthopygus); dorsal 1/3 of metepisterstum without punctures (apomorphy; state also present in Ph. mirabilis); with more than four spines on the posterior surface of metacoxae (apomorphy; less than four in Xa. xanthopygus); tergites 3–5 with arch-like carina; and sternite 7 in males with emargination at posterior margin. For a list of characters that distinguish Xanthopygus from Photinopygus, see Table
Diagnostic characters for Xanthopygus A abdominal sternites 7–8 of Xanthopygus skalitzkyi (Bernhauer) B abdominal sternites 7–8 of Xanthopygus viridipennis Sharp, arrow points to the porose structure C abdominal sternites 5–7 of Xanthopygus giganeus (Bernhauer), arrow points to the anterior transverse lines D abdominal tergites 3–8 of Xanthopygus cognatus Sharp, arrow points to arch-like carina on tergite 3 E lateral view of the aedeagus of Xanthopygus faustus (Erichson), arrow points to the serrated apical carina F lateral view of the aedeagus of Xanthopygus dimidiatus Bernhauer, arrow points to the hook-like carina. Not to scale.
A formal revision of the genus is forthcoming (Chatzimanolis in preparation) where all species belonging to this genus will be treated and illustrated.
The phylogenetic analysis presented here strongly rejected the hypothesis that Xanthopygus sensu Herman is a monophyletic group. As was previously defined, Xanthopygus included species that belonged in four distinct (and, as far as it is known, they are not sister to each other) clades, the genera Oligotergus, Photinopygus, Styngetus and Xanthopygus. The classification changes implemented in this paper resolve this issue by defining Xanthopygus in a new sense that includes some species that were described in Lampropygus (a synonym of Xanthopygus), although of the four species originally included in Lampropygus (
Styngetus skalitzkyi and Oligotergus nigricornis were clearly placed in Xanthopygus sensu Herman by mistake by
One of the major issues with Xanthopygus sensu Herman was that the characters used to define the genus (superior marginal line of pronotal hypomeron not continuing to anterior margin, postcoxal process present, and tergites 3–5 with arch-like carina) are not unique to Xanthopygus and the genus was not easily recognizable. Even if somebody were to argue that the phylogeny presented here is not properly resolved, meaning that perhaps Xanthopygus sensu novo and Photinopygus might be sister groups and therefore do not have to be in separate genera, the reality is that Xanthopygus sensu Herman was impossible to diagnose with just the characters presented above. Perhaps more importantly, Photinopygus and Xanthopygus sensu novo do not share any apomorphies that could be used to diagnose Xanthopygus sensu
One of the characters used to define Xanthopygus sensu Herman was the superior marginal line of pronotal hypomeron not continuing to anterior margin. Until recently, it was not clear how widespread this character state is among Xanthopygina. Triacrus dilatus has the same character state and this feature along with the position of Triacrus on the phylogeny of Xanthopygina (
A caveat in this paper is that the backbone relationships presented are unsupported. This is certainly not uncommon in morphology-only analyses using Bayesian statistics, and previous morphology-only Bayesian analyses of Staphylinini had low support values (e.g.,
The phylogenetic position of Xenopygus within the Xanthopygus lineage of genera remains unresolved.
Likewise, the position of Triacrus remains unresolved. In
It is perhaps unfortunate that most of the species that used to belong in Xanthopygus sensu Herman required a new name and were transferred to Photinopygus. However, this action corrected existing taxonomic problems and was necessary. Unfortunately, changing the meaning of an existing genus name is not uncommon; for example,
The Bayesian phylogenetic analysis performed in this paper showed that Xanthopygus sensu Herman is polyphyletic. To solve this problem, one species was transferred to Oligotergus, another to Styngetus, a new genus Photinopygus was erected for many taxa previously in Xanthopygus and Xanthopygus sensu novo was restricted to the remaining species. The new diagnostic characters provided in this paper can be easily used to define Photinopygus or Xanthopygus. Even though this paper helped to untangle the relationships within Xanthopygus sensu Herman, the exact relationships of the genera within the Xanthopygus lineage are still uncertain and would probably require comprehensive molecular phylogenetic analyses to decipher.
I thank Al Newton for important comments on the nomenclature of Xanthopygus and Adam Brunke for comments on the phylogenetic analysis. I thank Adam Brunke, Mariana Chani-Posse, Herald Schillhammer and Alexey Solodovnikov for comments on a previous version of this manuscript. I also thank the collection personnel for the loan of specimens that made this study possible. Partial financial support was provided by the College of Arts and Sciences, University of Tennessee at Chattanooga.
DarwinCore
Data type: Occurences.
Explanation note: DarwinCore format with all types and additional materials examined for the phylogenetic analysis.
Matrix
Data type: Data matrix.
Explanation note: The data matrix in .nex format.
Trace over trees
Data type: Analysis.
Explanation note: The analysis of “trace all characters” in Mesquite presented in .nex format.