Sibiota Casey, 1906,

Gusarov, Vladimir I., 2002, A revision of Nearctic species of the genus Geostiba Thomson, 1858 (Coleoptera: Staphylinidae: Aleocharinae), Zootaxa 81, pp. 1-88: 18-19

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Sibiota Casey, 1906


Subgenus Sibiota Casey, 1906 

Sibiota Casey, 1906: 350  (Type species: Sibiota impressula Casey, 1906  , by original designation) (as a genus in tribe Bolitocharini  Thomson, 1859).

Sibiota: Fenyes, 1920: 249  (as synonym of Sipalia Mulsant & Rey, 1853  ).

Sibiota: Bernhauer & Scheerpeltz, 1926: 599  (as synonym of Sipalia  ).

Ditroposipalia Scheerpeltz, 1951: 172  (Type species: Leptusa bidens Baudi, 1869  , by original designation) (as subgenus of Sipalia  ), syn. nov.

Sibiota: Seevers, 1978: 128  (as valid genus in subtribe Geostibina Seevers, 1978).

Sibiota: Lohse & Smetana, 1988: 270  (as synonym of Geostiba  ).

Sibiota: Ashe  in Newton, Thayer, Ashe & Chandler, 2000: 371 (as subgenus of Geostiba  ).

(other references for Palaearctic Ditroposipalia  are omitted)

Diagnosis. Sibiota  differs from other subgenera of Geostiba  in having two longitudinal carinae in the middle of male abdominal tergum 7 in front of posterior margin.

Synonyms. Ditroposipalia  is placed in synonymy with Sibiota  because the type species of both have two longitudinal carinae on the male tergum 7.

Discussion. Lohse and Smetana (1988) did not assign any of their four species to subgenera. Pace assigned his three species to subgenera Ditroposipalia  (synonymized here with Sibiota  ) and Lioglutosipalia Scheerpeltz, 1951  . The latter is now considered a synonym of Sipalotricha Scheerpeltz, 1931 ( Assing 1999)  , which lacks modifications on male tergum 7.

The males of both western Nearctic species of Geostiba  have male abdominal tergum with two carinae and are placed in the subgenus Sibiota  (= Ditroposipalia  ). Eight of the twelve Appalachian species have male secondary characters corresponding to Sibiota  and four species are consistent with Sipalotricha  . However there are good reasons to believe that all sixteen native Nearctic species of Geostiba  (that is, excluding G. circellaris  introduced to Newfoundland) form a monophyletic group in relation to Palaearctic species of Sibiota  (= Ditroposipalia  ) or Sipalotricha  .

There are some characters shared by all native Nearctic species of Geostiba  that may be autapomorphies for this group of species. These include: slightly raised elytral suture behind scutellum (except G. impressula  ); the proximal seta on the external side of paramere apex is the longest; internal sac of the aedeagus has two pairs of diverticula ( Figs. 42, 48View FIGURES 38 ­ 50, 198View FIGURES 197 ­ 203, 210View FIGURES 204 ­ 212, 318View FIGURES 316 ­ 320), medial lamellae are short, narrow and bent ventrally ( Figs. 40, 47View FIGURES 38 ­ 50, 201View FIGURES 197 ­ 203, 208View FIGURES 204 ­ 212). This form of the internal sac is very different from the forms found in Palaearctic G. (s. str.) circellaris  ( Figs. 21­22View FIGURES 21 ­ 25), G. (Sipalotricha) infirma  ( Figs. 24­25View FIGURES 21 ­ 25), G. (Sibiota) padana  ( Figs. 26­27View FIGURES 26 ­ 28) and G. (Sibiota) oertzeni  ( Fig. 28View FIGURES 26 ­ 28). The hypothesis of monophyly of the Nearctic group of species can be tested only if representatives from other lineages are included in the analysis, which is outside the scope of the present paper. However, if this hypothesis is accepted and both Sibiota  and Sipalotricha  are monophyletic groups, then all native Nearctic species must be placed in the same subgenus of Geostiba  .

Among the twelve Appalachian species, G. appalachigena  is the least adapted to cryptic habitats such as soil and leaf litter and has the following plesiomorphies: well developed wings, long elytra (longer than pronotum), large eyes (temple length / eye length ratio 2.3­2.7) and large body (pronotal width 0.40­0.47 mm). Geostiba appalachigena  has well developed carinae on the male tergum 7 and could be considered a typical representative of the subgenus Sibiota  . The four species of Geostiba  without carinae can be considered as more adapted to cryptic habitats. In comparison to G. appalachigena  they have the following apomorphies: reduced wings, short elytra (shorter than pronotum), small eyes (temple length / eye length ratio 3.8 ­6.0) and smaller body (pronotal width 0.34­0.44 mm). One can hypothesize that the four species without carinae on male tergum 7 originated from an ancestor or ancestors with carinae. Two arguments confirm that this scenario is possible. Geostiba balsamensis  , one of the smaller species (pronotal width 0.36­ 0.39), has weak enough carinae on tergum 7 that Pace (1997) overlooked them and placed this species in Lioglutosipalia  . The state of the carinae in G. balsamensis  can be considered intermediate between the well developed and the absent states. In many species of Geostiba  the small males are known to lack secondary sexual characters present in the large males ( Assing 2000). The same trend may take place when species evolve to a smaller size.

Taking into account the above arguments, I place all sixteen native Nearctic species of Geostiba  in the subgenus Sibiota  . This subgenus is also represented in the Palaearctic region from Europe to the Caucasus, Central Asia, Siberia and the Far East.












Sibiota Casey, 1906

Gusarov, Vladimir I. 2002


Newton 2000: 371


Casey 1906: 350


Fenyes 1920: 249


Bernhauer 1926: 599


Scheerpeltz 1951: 172


Seevers 1978: 128


Lohse 1988: 270