Polynoncus, Burmeister, 1876

Vinícius, Costa-Silva, Strümpher, Werner P., Tyssen, Patricia J. & Vaz-de-Mello, Fernando Z., 2025, Phylogenetic systematics of the keratin-feeding genus Polononcus Burmeister, 1876 (Coleoptera: Scarabaeoidea: Trogidae), Zoological Journal of the Linnean Society 203 (1), pp. 1-25 : 16-23

publication ID	https://doi.org/10.1093/zoolinnean/zlae172
DOI	https://doi.org/10.5281/zenodo.14825800
persistent identifier	https://treatment.plazi.org/id/A8636C62-FFA0-CB1B-8BA0-FAD1A9702902
treatment provided by	Plazi
scientific name	Polynoncus
status

Treatment

Phylogenetic relationships within Polynoncus View in CoL

Under both phylogenetic analyses (EW and IW), Polononcus was recovered as monophyletic, corroborating the hypotheses of previous research on the genus (e.g. Scholtz 1986, Scholtz and Peck 1990, Browne et al. 1993, Strümpher et al. 2014). Nonetheless, only the topology obtained from the IW model will be discussed here, as the resolution and level of support were beter solved than that of the EW model ( Fig. 10 View Figure 10 ). Polononcus monophyly was well supported (RBS = 92; SR = 71), with five synapomorphies (the last one homoplastic): presence of the one single seta in the sixth antennomere (3:0— Fig. 1A View Figure 1 ); clypeus with apical portion downward abruptly (20:0— Fig. 2A View Figure 2 ); aedeagus with a medial lobe and a dorsal portion surrounding the sof parts (83:0— Fig. 9B View Figure 9 ); parameres not fully sclerotized (92:1— Fig. 9F View Figure 9 ); and with apical torsion inward (93:0— Fig. 9C View Figure 9 ).

Te presence of one single seta in the sixth antennomere was first documented by Costa-Silva et al. (2024) and used as differential diagnosis for the Polononcus species. Te apical portion of the clypeus slopes downward abruptly (forming a straight angle with the front— Fig. 2A View Figure 2 ) is historically used to separate Polononcus from Omorgus in identification keys (e.g. Vaurie 1962, Scholtz 1986, 1990, Gómez 2008, Almeida and Mise 2009, Strümpher et al. 2016, Costa-Silva et al. 2024a). d’Hotman and Scholtz (1990) mentioned that parameres with inward apical torsion is a synapomorphy of Omorginae . However, in this study, this characteristic was observed just in Polononcus species, indicating that parameres with apical torsion inward is a derived condition (apomorphic), while the primitive one (apex with straight shape) is found in Omorgus and other genera of Trogidae .

Within the Polononcus clade, three lineages were retrieved and will be hereafer treated as pedestris (A), pilularius (B), brevicollis clades (C), and their respective subclades (e.g. B1, B2, C1, etc.). Te pedestris clade presented a low branch support (RBS = 8) with three synapomorphies (all homoplastic) ( Fig. 11 View Figure 11 ): antero-basal constriction with shallow shape (52:1), basal tubercles and medial edge of pronotum not connected (55:1— Fig. 6C View Figure 6 ), and the presence of a longitudinal sulcus in the inner face of protibial (78:0). Into this clade, Polononcus pedestris is retrieved as a sister-group of P. ecuadorensis + ( P. tenebrosus + P. sallei ). Tis last subclade ( ecuadorensis + ( tenebrosus + sallei )) is supported by three synapomorphies (the last two being homoplastic) with low branch support (RBS = 8): dorsal surface of a median lobe with a blade-like shape (88:1— Fig. 9G, H View Figure 9 ); apex of the median lobe with a spoon-like shape in lateral view (89:1— Fig. 9I View Figure 9 ); and the inner margin of parameres curve near of the base (96:0— Fig. 9D View Figure 9 ). Even with markable external diagnostic characteristic to separate these three species (see diffential diagnostic in: Costa-Silva et al. 2024a), the spoon-like shape of the median lobe of those three species as a synapomorphy, and the shared geographical distribution from the highest regions of the north-west of the Andean Mountains ( Peru and Ecuador) suggest an evolutive relationship between these species.

Te pilularius clade (B) is beter supported than the pedestris clade (A) and includes all species with asymmetrical male genitalia (RBS = 49; SR = 35) ( Fig. 10 View Figure 10 ). Four synapomorphies, two of which were homoplastic (characters 79 and 90), supported this clade ( Fig. 12 View Figure 12 ): a right mandible with a raised swelling parallel with outer margin (17:0— Fig. 3E View Figure 3 ), protibiae without an apical tooth in the dorsal surface (79:1), dorsal portion of median lobe with asymmetrical lateral margins at the middle (85:1— Fig. 9D View Figure 9 ), and phallobase with a quarter of total aedeagus length (90:2— Fig. 9I View Figure 9 ).

Two subclades (B1 + B2— Fig. 10 View Figure 10 ) can be recognized within ‘ pilularius ’ (B) clade. Te subclade B1 include the species Polononcus galapagoensis and P. seomourensis , the only Polononcus species to occur in the Galapagos Islands (Vaurie 1962, Scholtz 1990b, Costa-Silva et al. 2024a). Considering the restricted geographical distribution of both species (both being confined to the Galapagos Islands), Vaurie (1962) and Scholtz (1986, 1990b) hypothesized that both species share a common ancestor. Te highest branch support of our results (RBS = 100; SR = 34) corroborates this hypothesis ( Fig. 10 View Figure 10 ). Furthermore, Polononcus galapagoensis presents reduced membranous wings, suggesting that the fully winged P. seomourensis is more primitive and responsible for the dispersion of these species among islands (Costa-Silva et al. 2024a), while the wingless P. galapagoensis is more derived and has lost its flight capacity due to environmental pressures [i.e. restricted areas (islands, mountains), wind, temperature, etc.; for more details, see: Darlington (1943), Scholtz (1981)]. Probably as a result of loss of flight capacity, P. galapagoensis is found restricted to the small and isolated northern islands of Galapagos (Costa-Silva et al. 2024a).

Te subclade B2 (RBR = 12; SR = 21) ( Fig. 12 View Figure 12 ) is supported in the presence of the apical callus in the inner margin of protibiae (80:0— Fig. 8F View Figure 8 ). Tis characteristic is mentioned here for the first time in the literature and can be used to distinguish this group from the remaining species of Polononcus . Also, two homoplasies with phylogenetic signal were identified here: the length of AA1+2 venation is a quarter of AA3+4 length (29:1— Fig. 5A View Figure 5 ) and the inner margin of the parameres, near to the base, form a curve of ~90° (96:0— Fig. 9D View Figure 9 ). All species that composed the subclade B2 are insular, and most of them occur within tropical regions ( Brazil, Paraguay, Bolivia, Uruguay, and north-east Argentina). Polononcus gemmingeri + P. pilularius clade (RBS = 3; SR = 35) is recognized as a sister-clade of all remaining species, distinguished by an asymmetrical superior lobe of the aedeagus ( Fig. 10 View Figure 10 ). Te subclade B3 (RBS = 79; SR = 58) is a monophyletic and well-supported group with the lateral margin of pronotum bulbous located in front of the central portion (50:1— Fig. 4E View Figure 4 ), and symmetrical lateral margins at the middle of the superior lobe of aedeagus (85:0— Fig. 9E View Figure 9 ). Tese characteristics may also be used to distinguish the species’ group morphologically (Vaurie 1962) and are included in a dichotomous key for species’ identification or differential diagnosis (i.e. Pitino 1987, Scholtz 1990b, Gómez 2008, Costa-Silva and Diéguez 2020, Costa-Silva et al. 2024a). Even without a formal hypothesis of homology, the arrangements of the terminals present in the identification keys presented by Scholtz (1990b) and, more recently, by Costa-Silva et al. (2024a) are similar to the topologies presented here.

Te brevicollis clade (C) ( Fig. 13 View Figure 13 ) is composed of species distributed across Chile, Argentina, and Uruguay ( Fig. 10 View Figure 10 ). Tis clade is supported with two synapomorphies (all homoplastic) (RBS = 26): pronotum with a surface of medial edges glabrous (49:0— Fig. 4A View Figure 4 ) and odd-numbered tubercles of elytra with elongate shape (71:1— Fig. 7G View Figure 7 ). With few exceptions, the species that compose clade C are the same as those cited by Haaf (1953) and Vaurie (1962) as ‘ brevicollis -group’ in their studies of the global and South American Trogidae species, respectively. Even so, the diagnostic characteristics used by those authors to recognize the brevicollis -group [i.e. presence of humeral callus (70:0— Fig. 7G View Figure 7 ); margins of elytra subparallel (74:1— Fig. 7G View Figure 7 ) and metasternum as wide as long (rhomboidal) (42:0— Fig. 4D View Figure 4 )] were not retrieved as a synapomorphy of this group in this study.

Within clade C, the species Polononcus diffluens + P. cropticus are retrieved as a sister-clade of the other species of the group ( Fig. 13 View Figure 13 ). Te dichotomy of P. diffluens + P. cropticus is supported with four synapomorphies, the first three being homoplastic: shape of anterior margin of labrum symmetric (7:1– Fig. 1D View Figure 1 ); basal tubercles of pronotum rudimentary (44:0— Fig. 4B View Figure 4 ); absence of elytral tubercles (64:1); and dorsal portion of median lobe simple, without ornaments and symmetric (87:0— Fig. 9F View Figure 9 ). According to Diéguez (2019), P. diffluens and P. cropticus present a similar morphology that can be easily confused at first glance. Moreover, both species share a morphological characteristic not typical for Polononcus species: male genitalia are compact and simple, and there is an absence of elytral tubercles. As mentioned by Vaurie (1962), the male genitalia of Polononcus species are rather complex, with a dorsal (usually asymmetrical and variable) portion surrounding the sof parts (also see: Pitino 1987). Tis complexity of the aedeagus shape was treated as a synapomorphy of Polononcus by Scholtz (1986). However, the male genitalia of P. diffluens and P. cropticus lack the ornaments and bizarre structures on the dorsal portions, instead assuming a compact and simple shape typical of those found in Omorgus species; a plesiomorphic condition suggested by Scholtz (1986). Te hypothesis of homology of this character showed a great phylogenetic signal that both species evolved from a common ancestor, and the lack of ornaments in the dorsal portion of aedeagus was result of a secondary lost by phylogenetic reversion (or atavism).

Te subclade C1 (RBS = 63) is supported with two synapomorphies (all homoplastic): presence of a longitudinal sulcus in the inner face of the protibiae (78:0); and apical part of median lobe wide in dorsal view (86:1— Fig. 9E View Figure 9 ). Two lineages of C1 are recognized ( Figs 10 View Figure 10 , 13 View Figure 13 ): subclade P. brevicollis + P. gibberosus + (C2 + C3). All species of these subclades are restricted to Argentina and/or Chile (Diéguez 2008; also see: Costa-Silva et al. 2024a). Both P. brevicollis and P. gibberosus are morphological related species as discussed by Scholtz (1990) and Costa-Silva et al. (2024a). Te lineage C2 + C3 (RBS = 8) is supported with three synapomorphies, the last two of which are homoplastic: fourth maxillary palpomere with a sinuosity in the ventral margin near the apex (12:0— Fig. 3A View Figure 3 ); basal tubercles of pronotum rudimentary (44:0— Fig. 4B View Figure 4 ); and absence of punctuation in the surface of tubercles (69:1— Fig. 7I View Figure 7 ).

Te subclade C2 (RBS = 100; SR = 26) is a well-supported clade of Argentinean species (with the exception of P. burmeisteri , which also occurs in Bolivia —see: Costa-Silva et al. 2024a) with three synapomorphies (all homoplastic): AA1+2 venation of wings with a quarter of AA3+4 length (29:1— Fig. 5A View Figure 5 ); posterior margin of pronotum with constriction (notched) near the angles (54:0— Fig. 6A View Figure 6 ); and surface of hypomeron with setae (57:0— Fig. 6F View Figure 6 ). Tis group of species (C2) is also supported by the taxonomic history proposed by several authors, where the similarity of morphological characteristic put all species together in the identification key and/or differential diagnosis (i.e. Vaurie 1962, Scholtz 1990b, Costa-Silva and Diéguez 2020, Costa-Silva et al. 2024a). In both dichotomous keys for Polononcus species, one carried out by Vaurie (1962) and the other by Costa-Silva et al. (2024a), the authors used the presence of a tooth in the apex of the outer margin of the mesotibia to separate this group from other congeneric species. However, even though it is a good taxonomical characteristic for identification purposes, this character was retrieved as homoplastic (also present in P. peruanus ).

Te subclade C3 (RBS = 30) is supported with only one synapomorphy ( Fig. 13 View Figure 13 ): the interocular distance four or five times the length of the eyes ( Fig. 2C View Figure 2 ). According to Vaurie (1962), this characteristic corresponds to the ‘ bullatus group’, where the species are distinguished by the absence of a humeral callus and reduced or absent wings (as those from the subclade C4). However, the related species P. peruanus and P. aricensis , both macropterous, also present small eyes, contradicting the diagnostic characteristic of Vaurie (1962) and Haaf (1953) for the ‘ bullatus group’. Te true ‘ bullatus ’ group (sensu Vaurie 1962) is retrieved here as monophyletic under the subclade C4 (RBS = 99; SR = 100). Tis well-defined subclade is supported with 18 synapomorphies, being the characters 28, 30, 33, 35, 37, 38, 54, 58, 59, and 69, homoplastic ( Fig. 13 View Figure 13 ): vestigial posterior wings (25:2— Fig. 5C View Figure 5 ); the constriction between R3+4, R3, and R4 venation (‘pinch’) absent (27:1); absence of AA1+2 venation (28:1); end of MP venation not fusing with any venations (30:1— Fig. 5B View Figure 5 ); absence of fusion of the R3+4 venation before the ‘pinch’ (32:1); absence of the R3 venation (33:1); absence of the R4 venation (34:1); absence of the RP venation (35:1); absence of the RP2 venation (36:1); absence of the MP4 venation (37:1); absence of the fusion of R3+4 venation (38:1); shape of metadiscrimen area nearly twice as wide as long (42:0— Fig. 4C View Figure 4 ); posterior margin with a constriction (notched) near the angles (54:0— Fig. 6A View Figure 6 ); presence of an emargination in the internal margin of anterior angle of proepisternum (58:0— Fig. 6E View Figure 6 ); absence of a posterior margin projecting backward in obtuse lobe at the middle (59:1— Fig. 6C View Figure 6 ); presence of the punctuation in the surface of tubercles (69:0); absence of a humeral callus (70:1— Fig. 7F View Figure 7 ); and elytral with margins arcuate from apex to base (74:0— Fig. 7F View Figure 7 ).

Te last two characters (70 and 74) were also cited by Vaurie (1962), Scholtz (1990), Gómez (2008), and Costa-Silva et al. (2024a) in their respective identification keys for Polononcus species. However, these characters are not a true synapomorphy of Polononcus when compared with other wingless species of Trogidae (Scholtz 1981, 2000, Browne et al. 1993). Groups of wingless species of the family are reported from different zoogeographical regions [e.g. Omorgus (O.) pastillarius (Blanchard, 1847) from South America; Omorgus (O.) dohrni (Harold, 1872) from Australia; Phoberus natalensis (Haaf, 1954) from the Afrotropical region], suggesting that loss of flight appeared many times during the evolution of the group. According to Scholtz (1981), the reduction of the wings can ofen be correlated with the locality and habit of the species (i.e. mountains, deserts, or islands; for additional details, see: Roff 1990). As these environments are stable and favourable for the group (e.g. there are readily available food sources), the species do not need to disperse to search for new habitats (Aukema 1990). Due to this selective pressure or occupation, some morphological structures of beetles’ wings were lost, termed atrophy (Fiori 1977, Wagner and Liebherr 1992, Browne et al. 1993).

As also discussed by Scholtz (1981), wingless species of Trogidae are ofen reported within desert and arid regions (i.e. North America, Africa, and Australia). Tese reports match with the geographical distribution of the wingless Polononcus in South America, mainly in arid regions of Argentina and Chile (Costa-Silva et al. 2024a). Terefore, as occurs in other Coleoptera species, the wingless species of Polononcus are ofen large (up to 1.5 mm), relative to the macropterous species (0.6–1.5 mm) (Scholtz 1981). In addition, these species also present a short metasternum, reduced scutellum, absence of humeral callus, and small eyes, in accordance with all non-related species that live in similar regions of the world. For a comprehensive study about the flightless species of Trogidae , see Scholtz (1981) and Browne et al. (1993).