Arcanys rostratus Chemyreva, 2024

Chemyreva, Vasilisa G., Legalov, Andrei A. & Perkovsky, Evgeny E., 2024, A new genus of Ambositrinae (Hymenoptera, Diapriidae) from Rovno amber and remarks on the Eocene distribution of the subfamily, Ecologica Montenegrina 79, pp. 104-112 : 107-112

Arcanys rostratus Chemyreva , sp. nov.

https://zoobank.org/ urn:lsid:zoobank.org:act:7483AD0B-6524-4376-9F0D-E533F3ECCE23

Figs 1 , 2

Type material. Holotype: ♂, SIZK K-27639, Klesov, Rovno Oblast, Rovno amber, late Eocene. Amber fragment with holotype is a parallelepiped, sized 4: 3.2: 1.5 mm. Syninclusions: 2 Diapriidae ( Belyta inc. s., Diapriidae inc. s.), Acari (Galumnoidea), stellate hairs.

Etymology. The species name derived from the Latin rostrum (“beak”) and refers to the beak-like mandibles of the new species.

Diagnosis. As for the genus.

Description. Body length about 1.9 mm; fore wing length about 1.7 mm; antennae length about 1.6 mm.

Head as long as high, smooth. Antennal shelf strongly prominent; antennal sockets separated, broadened and sculptured apically in frontal and lateral view. Clypeus convex, 1.35 times as wide as high and 3.9 times as wide as tentorial pit diameter. Face covered with scattered suberect setae. Postantennal excavation small, setose inside. Ventral margin of frons with prominent lateral processes, not touching walls of antennal sockets. Eyes large, bare, wider than high; the largest diameter of eye 0.5 times height of head (measured from top of ocelli to top of mandibles). Ocelli large and strongly projecting, located strictly on top of head.

Antenna filiform, homogeneously pubescent ( Fig. 1B ). Scape the longest segment, tapered before apex; A3 1.7 times as long as A2 and 2.9 times as long as wide; A4 0.95 times as long as A3, broadened in the mid-length and with carina and shallow emargination reaching the middle of the segment ( Fig. 1B ); A5‒A13 elongate, about 2.7 times as long as wide; A14 1.1 times as long as A3 and longer than all other flagellomeres.

Mesosoma. Pronotal collar very short, vertical and almost bare; lateral pronotum smooth and mainly glabrous but anteriorly covered with pubescence and foamy structure. Propleura smooth and pubescent, with foamy structure. Mesoscutum convex, smooth and bare. Scutellar disk weakly convex, its posterior margin with row of punctures, axillar depression smooth, mainly glabrous but with foamy structure at the bottom; axilla smooth, its outer carina quite wide and posteriorly with short axillar process not bent into hook ( Fig. 2A ); lateral rim of scutellum not foveolate. Mesopleuron smooth and glabrous laterally, pubescent ventrally; subalar furrow narrow and bare; epicnemial pit large and densely pubescent inside ( Figs 1B , 2A ). Metanotum relatively long, its maximal length 0,45 times as long as scutellar disc; lateral excavation of metanotum smooth and glabrous; metascutellum sparsely pubescent. Metapleuron mainly sparsely and shortly setose but bare medially with anteroventral metapleural pit densely pubescent inside and ventral side of metapleuron with foamy structure. Nuchal area fused with dorsal area of propodeum, both setose ( Fig. 1E ). Fore wing 2.6 times as long as its maximum width. Legs slender; femora of all legs longitudinally strigose to reticulate ( Fig. 2 )

Metasoma. Petiole covered with scattered setae, longitudinally carinate, ventrally with foamy structure; swollen medially and with constrictions before the anterior and posterior ends. Gaster as long as mesosoma. T3 and T4 short equal in length; T5 bearing spiracles, as long as T3 and T4 measured together; T6 small and hidden under T5 , with one segmented cerci. S2 small and setose; S3 the largest sternite, smooth, more densely setose anteriorly and with few scattered suberect setae posteriorly ( Fig. 2C ); S4‒S6 short and equal to each other; S7 1.55 times as long as S6; S8 sub-triangular. T3 ‒ T5 looked almost bare; S4‒S8 all covered with scattered long suberect setae .

Discussion

According to the existing generic keys and generic diagnoses of Ambositrinae (Nauman 1982, 1987, 1988) and the characters used by Naumann (1988) in his analysis of the phylogeny of this subfamily, the new genus described here is close to the genera Ambositra and Diphoropria Kieffer, 1905 . Arcanys rostratus sp. nov. differs significantly from Ambositra species by venation and from Diphoropria by a complex of features, mentioned above as unique for the new genus (listed in the “Remarks”), since the species of the genus Diphoropria have: notauli, distinct and high median carina on metascutellum and propodeum (both usually higher than lateral carina and plica respectively), excavated base of T2 with two lateral carinae. The new genus differs from other genera of the tribe Betylini by the same complex of characters, with the exception of a single genus − Maoripria Naumann, 1988 . The species of Maoripria have no notauli and their arcuate base of T2 have no notches, longitudinal grooves or lateral carinae. However, in Maoripria all other discussed features are similar to other genera of the tribe Betylini and are different from those of the new species. In addition, the species of Maoripria have several specific characters, such as: antennal sockets with inner wall produced dorsally; parafrontal carina present; male flagellum fusiform; base of T2 usually with blunt median process; marginal vein curved and only barely touching the anterior margin of fore wing. None of the above is typical of the new species.

The Gondwanan origin of Ambositrinae looked problematic even before the discovery of this subfamily in Baltic amber ( Masner 1969, Chemyreva et al. 2024). For example, Naumann (1982) found that “ Pantolytomyia is considered to be the most plesiomorphic ambositrine genus. It occurs in Australia, New Guinea and New Zealand. If the subfamily is of southern origin, the apparent absence of Pantolytomyia from South America (and Africa) is puzzling.” ( Naumann 1982, p. S84). For now, two genera and five species of Ambositrinae are known from the late Eocene of Northern and Eastern Europe (Baltic and Rovno amber), and one extant genus Propsilomma Kieffer is distributed throughout the Nearctic except for northern Canada ( Kieffer 1916; Masner 1964; Naumann 1982; Comério et al. 2016). This distribution is not typical of Gondwanan-derived taxa, but of globally distributed or Laurasian taxa that became totally or partially extinct in the Northern Hemisphere after the transition from the equable greenhouse Eocene climate to the icehouse Oligocene and Neogene climate ( Eskov 1992; Gumovsky et al. 2018; Jenkins Shaw et al. 2024).

Recent Ambositrinae are represented in the tropics, particularly in Melanesia ( Naumann 1987), but are more common and diverse in frost-free temperate climate, e. g. Tasmania and south of New Zealand. The subfamily is represented by 12 species on Tasmania, by 34 species on the South Island and nearby Stewart Island of New Zealand, by 20 species on the North Island and only 13 species known from the Melanesia subregion ( Naumann 1982, 1987, 1988). Thus, the South Island has 1.7 times more species than the North Island (although the area of the South Island and Stewart Island combined is only 1.3 times that of the North Island) and 2.6 times more than Melanesia (although Melanesia is 6.2 times larger than the South Island). Area of Tasmania is 1.7 times less than area of North Island and North Island has 1.7 times more species than Tasmania. So, the climate of the South Island can be considered as the most favorable for the extant Ambositrinae and their hosts. Equable climate (see Prokin et al. 2024 and references therein) of the late Eocene Rovno amber forest had some similarities with southern Australasian climates, e. g., climates of south of Tasmania and south parts of New Zealand. Volhynian Uplift, on which the Rovno amber forest was situated, at least most of the late Eocene was an island ( Popov et al. 2001, 2009; Ivanov et al. 2016), so we have enough grounds for comparison of its fauna with Tasmania and the islands of New Zealand ( MacArthur & Wilson 1967). The area of the South Island is at least 1.5 times larger than the estimated area of Volhynian Uplift (the area of Volhynian Uplift was calculated based on the maps given by Popov et al. (2001) and Ivanov et al. 2016), however, it is important to take into account that Rovno amber was redeposited from the northern part of Volhynian Uplift, while the biota of the southern part of Volhynian Uplift is unknown from fossil resins). So, the number of known species per unit area of the Rovno amber forest and the South Island is at least comparable. Similar results are obtained when comparing lowland fauna. It seems that the plain region of Southland in the extreme south of the South Island is the closest New Zealand analogue to the climate of the Rovno amber forest. Thus, in the Southland region ( Naumann 1988, p. 172: SL), which is one and a half times larger than the two large amber-bearing districts of the Rovno Oblast (Sarny and Varash), 7 species of Ambositrinae are known ( Naumann 1987), while in the amber from the Sarny and Varash districts ‒ 4.

The abundance and diversity of the Rovno amber Ambositrinae testify the Laurasian origin of the subfamily, at least of some of its clades. The humid equable upper microthermal and lower mesothermal climate seems to be the most favorable for the ambositrine hosts (even in Melanesia ( Naumann 1987)). Аmbоsitrinае аrе mоrе divеrsе in upper hill соuntrу and in montane аrеаs: fоur species have been rесоrded at altitudes between 0 to 500 m, nine bеtwееn 500 to 1500 m, and eight аbоvе 1500 m). It is possible that the extinction of Eurasian Ambositrinae and/or their hosts was caused by the transition to a greater annual temperature variation in the mid-latitudes and often much drier climate. The only determined to the genus level host of extant ambositrine is famous glow-worm Arachnocampa luminosa (Skuse, 1890) ( Keroplatidae ). The relict genus Arachnocampa Edwards, 1924 is known from eastern states of Australia (one from wet tropics, three subtropical and four temperate regions’ species, including one from the Tasmanian cool temperate rainforest ecoregion) and New Zealand ( Marshall 1892). Arachnocampa are highly susceptible to desiccation and therefore require high humidity or direct contact with water within their habitat to survive ( Baker 2010), similarly at least New Zealand ambositrines are most common and diverse in the wettest regions of the South Island as well ( Naumann 1988). Arachnocampa flies are bad fliers, mostly with very limited distribution, so if European ambositrine hosts were similar in this aspect to Arachnocampa , their extinction after the serious climate changes could have been fast.

Particularly important are the European connections of the Afrotropical ambositrines, i.e. Ambositra . The extant species is Afrotropical ( Chemyreva et al. 2024a), and stable connections between Africa and Eurasia appear only in the Miocene. Many other European amber taxa migrated to Africa as well as Ambositra (see e.g. Golub et al. 2021; Perkovsky et al. 2024b). An interesting new example is the extant East African mountain subgenus Neomicrambe Otero & Pereira, 2019 ( Cryptophagidae ) with two species in Danish amber ( Lyubarsky et al. 2024a, 2024b). The example of the Ambositra distribution indicates the direction of the migration especially clear. Only Madagascar is at least 6 times larger than the area of Volhynian Uplift ( Ambositra is also known from the continental part of Afrotropics), but we know four species in Rovno amber and only one extant species in Afrotropics ( Chemyreva et al. 2024a).

Acknowledgements

The authors are very grateful to Dr. Dmitry Vorontsov (Koltzov Institute of Developmental Biology, Russian Academy of Sciences , Moscow) for his help in taking the holotype photographs and preparation of the amber with holotype inclusion, to Prof. Alexandr P. Rasnitsyn (Paleontological Institute, Russian Academy of Sciences , Moscow) for the discussion, to Dr. Andranik Manukyan and an anonymous reviewer for their helpful suggestions that significantly improved this article. This study was performed as part of the State Research Project No 122031100272–3 for CVG .

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Figures

Figure 1. Arcanys rostratus sp. nov. A, whole inclusion in lateral view; B, head and antennae in lateral view; С, D, face; E, meso- and metasoma in dorso-lateral view; fs, foamy structures; lcm, lateral carina of metascutellum; mcm, median carina of metascutellum; mcp, median carina of propodeum; pl, plica. Scale bars: A, 1 mm; B, E, 0.5 mm.

Figure 2. Arcanys rostratus sp. nov. A, head and mesosoma in lateral view; B, metasoma in ventral view; С, meso- and metasoma in lateral view; D, fore wing venation; LT, laterotergite; S2 and S3, second and third sternites; mv, marginal vein; sv, stigmal vein. Scale bars 0.5 mm.