Colobopsis imitans, Schifani & Giannetti & Csősz & Castellucci & Luchetti & Castracani & Spotti & Mori & Grasso, 2022

Schifani, Enrico, Giannetti, Daniele, Csősz, Sándor, Castellucci, Filippo, Luchetti, Andrea, Castracani, Cristina, Spotti, Fiorenza A., Mori, Alessandra & Grasso, Donato A., 2022, Is mimicry a diversification-driver in ants? Biogeography, ecology, ethology, genetics and morphology define a second West-Palaearctic Colobopsis species (Hymenoptera: Formicidae), Zoological Journal of the Linnean Society 194, pp. 1424-1450 : 1434-1436

COLOBOPSIS IMITANS SP. NOV.

Zoobank registration: urn:lsid:zoobank.org:act:6B513EC6-6319-406F-97D0-82C0EF67E626

Etymology: imitans is the present participle of the Latin verb imitor, meaning ‘imitating’, and is here used in apposition. It refers to the interpretation that this species resembles Cr. scutellaris .

Type series: One holotype worker ( Fig. 10 ) and 14 paratype workers from Mondello, Sicily ( Italy), 38.1953, 13.3354, 5 m, 14.X.2018, E. Schifani leg. The holotype is stored in the Hungarian Natural History Museum collection .

Worker description: Morphometric indexes are shown in Table 2 . Subrectangular head, rounded on all sides. A straight, central furrow runs from the frontal triangle to the level where the frontal carinae end. Large eyes, extremely reduced ocelli. Antennae of 12 segments, without a distinct antennal club. Pronotum significantly wider than the rest of the mesosoma. In lateral profile, pronotum and mesonotum gently convex, propodeum profile often showing a central concavity, thus having a saddle-like appearance. Petiolar scale profile anteriorly roundly concave and posteriorly straight, its dorsal crest excavated in frontal view. Well-visible promesonotal and mesoepinotal sutures, as well as metathoracic and propodeal spiracles. All legs with well-developed tibial spurs, more so in the anterior legs, which are characterized by strikingly large femurs (identical to Co. truncata , function unknown). Pigmentation as described in the CSL model. Fine alveolate to areolate sculpture covering the whole body and appendages. Few erect hairs near the posterior margin of the vertex, between the frons and on the clypeus, and few others on the gaster tergites. See Figures 1 , 8 , 10 , 13 .

Soldier (= phragmotic major worker) description: Measurements (two specimens from Sicily): CL = 1327, 1419; CW = 1262, 1470; SL = 865, 942; ML = 1752, 1774; MW = 921, 1103; EW = 264, 331; EL = 409, 459; CS = 1294, 1444; CL/CW = 0.96, 1.05; SL/CS = 0.65, 0.67; ML/CS = 1.23, 1.35. Large cylindrical phragmotic head, and a flattened anterior part formed by the mandibles, part of the clypeus and of the genae. Characterized by strong areolaterugose sculpture and dense coverage of short thick erect hairs in the distalmost half. Rest of the shape, sculpture and pigmentation generally similar to the worker but white dots or stripe on the first gastral tergite sometimes evident. See Figure 10 .

Queen description: Measurements (three specimens from Sicily): CL = 1437–1531; CW = 1281–1406; SL = 1156–1218; ML = 2687–3031; MW = 1281–1312; EW = 325–362; EL = 525–537; CS = 1359–1468; CL/ CW = 1.08–1.11; SL/CS = 0.83–0.87; ML/CS = 1.93– 2.22. Large phragmotic head, similar to the soldier in shape and size (despite larger body size), but well-developed ocelli, much larger eyes and much longer scapi. Immediately distinguishable by the larger, dorsally flatter mesosoma, which is largely unsculptured and shiny. Propodeum profile similar to the end of soldiers’ propodeum. Head red, as in the worker, but the mesosoma is brownish and the white dots or stripe on the first gaster tergite are/is evident. See Figure 11 .

Male description: Measurements (three specimens from Sicily): CL = 875–1093; CW = 781–1000; SL = 937–1001; ML = 2281–2437; MW = 1062–1218; EW = 300–387; EL = 462–525; CS = 828–1046; CL/ CW = 1.09–1.17; SL/CS = 0.92–1.20; ML/CS = 2.32– 2.75. Small, subrectangular head with large ocelli and large eyes protruding laterally. Toothless mandibles. Relatively large mesosoma, propodeum more gently rounded than in queens or workers. Low, round petiolar node. Weak sculpture, shiny mesosoma. Hairy mandibles, other hairs on clypeus and gaster. Entire body ferruginous or brownish, gaster blackish. See Figure 11 . Genitalia as in Figure 12 .

Diagnosis: Generally easy to determine on the basis of worker material due to strong chromatic differentiation from Co. truncata and allopatric distribution (although further investigation is required for possible contact regions in southern Iberia and southern Italy). Some small worker specimens may appear almost completely black, therefore lacking the typical chromatic pattern; workers with entirely red mesosoma seldom observed. Tentative identifications of isolated soldier or queen specimens should be much more cautious, although their chromatic appearance may sometimes appear to be explicit. The low number of males and the lack of particularly evident distinctive characters from Co. truncata do not allow a safe species-level identification of this caste based on morphology. As for workers, the morphometric linear discriminant function provided in the Results section should help with dubious cases, including decoloured specimens. Finally, DNA barcoding, which can be used for the same purpose and can also be employed on the other castes, shows relatively low error rate but may present risks due to the polyphyletic pattern that we observed.

Biological, ecological and phenological notes: Relatively thermophilous; occurring in Sicily from a few meters above sea level to at least 1015 m elevation, ascending up to 1290 m a.s.l. in Morocco, and so far known from coastal lowland areas in Spain. Probably common but also heavily under-recorded due to its cryptic arboreal lifestyle, low colony population (most-likely monogynous), effective mimicry and long periods of inactivity during the most arid and coldest times of the year. Workers and soldiers are unlikely to descend to the ground but were observed to do so at least once, following a sparsely populated Cr. scutellaris trail. Soldiers, in general, are difficult to find outside the nest and are usually seen acting as gatekeepers of the nest entrance. Founding queens were observed to do the same. Nests are hidden in minute holes on the dead parts of arboreal trunks, where Co. imitans often seems to act as secondary user of cavities excavated by xylophagous insects. It exploits Andricus quercustozae (Bosc, 1792) oak galls as nests [occupying about 15% of galls collected in Bosco della Ficuzza (Sicily) in a recent survey, authors’ unpublished data], in a similar way to Co. truncata (see: Giannetti et al., 2019, 2021; Fürjes- Mikó et al., 2020). Polydomy appears probable due to repeated findings of groups of workers with no queen within oak-galls. Nesting observed on several diverse plant species, including at least: Citrus reticulata Blanco , Ci. sinensis (L.) Osbeck, Laurus nobilis L., Olea europaea L., Quercus ilex L., Q. pubescens -group, Q. suber L., Pyrus communis L. and Pittosporum tobira (Thunb.) W.T.Aiton. Dense populations appear to have been found in old Citrus orchards, relatively sparse cork oak ( Q. suber ) woods and also in deciduous oak forests. However, Co. imitans occurs in a broad range of habitats, from cities to agricultural lands to natural forest habitats, but information available has so far been insufficient to depict a satisfactory picture of habitat preferences. Despite the earlier claim by Carpintero et al. (2005), there is currently no evidence backing the fascinating hypothesis that C. imitans foundress queens prefer trees hosting Cr. scutellaris to found their colonies. A focused investigation on this topic would be interesting. Nuptial flights for Co. imitans occur approximately in the same period as Co. truncata (alates in Sicily observed from June 30 to July 13, N = 5, see Supporting Information, File S1). Winged queens and males were repeatedly seen to be attracted by artificial light at night.

Figures

Figure 1. The model species and the two detected chromatic model patterns of Colobopsis: A, Crematogaster scutellaris; B, CSL Colobopsis from Sicily; C, Dolichoderus quadripunctatus from Tuscany; D, DQL Colobopsis from Tuscany.

Figure 8. Trail-following behaviour on Crematogaster scutellaris trails by other ants (indicated with arrows). On the left (A, C, E) CSL Colobopsis; on the right (B, D, F) Camponotus lateralis observed in the same locality performing the same behaviour (photos taken in Palermo (Sicily) during field surveys).

Figure 10. Colobopsis imitans. A, B, E, worker (holotypus); C, D, F, G, soldier (specimen from the type locality). Scale bars: 0.5 mm. Pictures also available on AntWeb.org database, specimen codes: ANTWEB1041481 and ANTWEB1041482.

Figure 11. Colobopsis imitans. A, B, E, F, queen; C, D, G, male. Specimens from the type locality. Scale bars: 0.5 mm. Pictures also available on AntWeb.org database, specimen codes: ANTWEB1041483 and ANTWEB1041484.

Figure 12. Male genitalia of Colobopsis imitans in ventral and dorsal view, specimen from the type locality. Scale bars = 0.25 mm.

Figure 13. Above Cr. scutellaris and species showing a similar chromatic pattern that were collected near Cr. scutellaris trails in Sicily (Italy): A, Co. imitans (worker from Mondello); B, Ca. lateralis (worker from Monte Pellegrino); C, Gelis sp. (Hymenoptera: Braconidae) from Monte Petroso; D, Cr. scutellaris from Levanzo island; E, Phrurolithus sp. (Araneae: Phrurolitidae) from Mondello; F, Ca. ruber (worker from Monte Pellegrino); G, Leptorchestes sp. (Araneae: Salticidae) from Monte Petroso. Below, D. quadripunctatus and species with a similar chromatic pattern collected near its trails or in the same trees in mainland Italy: H, Co. truncata (specimen from Bulgaria, AntWeb code CASENT0280000, photographer Michele Esposito); I, D. quadripunctatus (specimen from Czech Republic, AntWeb code CASENT0179916, photographer Michele Esposito); J, Formicomus pedestris (Rossi, 1790) (Coleoptera: Anthicidae) from Parma (Italy).