Temnothorax apenninicus Csősz, Schifani, Seifert, Alicata & Prebus, 2024

Csősz, Sándor, Schifani, Enrico, Seifert, Bernhard, Alicata, Antonio & Prebus, Matthew M., 2024, A new species of yellow acorn ant discovered in Italy via integrative taxonomy (Temnothorax luteus - complex, Formicidae), Evolutionary Systematics 8 (2), pp. 183-197 : 183-197

Temnothorax apenninicus Csősz, Schifani, Seifert, Alicata & Prebus sp. nov.

Description.

Worker (Fig. 5 A – C , Table 3 ).

Body color yellow; light brown. Body color pattern concolorous except for the posterior margin of the first gastral tergite which is often characterized by a weak transversal band interrupted in its central portion. Appendages yellow, except for the usually infuscate antennal clubs. Absolute cephalic size: 0.604 mm [0.537, 0.699]. Cephalic length vs. Maximum width of head capsule (CL / CW): 1.154 [1.116, 1.202]. Clypeal depression absent. Ground sculpture of submedian area of clypeus conspicuous areolate. Head frontal sculpture: main sculpture forked costate; rugoso-reticulate, ground sculpture conspicuous areolate; punctate. Gena sculpture: main sculpture scabrous; rugoso-reticulate, ground sculpture conspicuous areolate; punctate. Postocular distance vs. cephalic length (PoOC / CL): 0.375 [0.360, 0.389]. Eye length vs. absolute cephalic size ( EL / CS): 0.224 [0.210, 0.236]. Frontal carina distance vs. absolute cephalic size (FR / CS): 0.336 [0.321, 0.358]. Scape length vs. absolute cephalic size (SL / CL): 0.804 [0.755, 0.842]. Dorsal region of mesosoma sculpture: main sculpture forked costate; rugoso-reticulate, ground sculpture conspicuous areolate; punctate. Lateral region of pronotum sculpture: main sculpture forked costate; rugoso-reticulate, ground sculpture conspicuous areolate; punctate. Mesopleuron sculpture: main sculpture forked costate; rugoso-reticulate, ground sculpture conspicuous areolate; punctate. Metapleuron sculpture: main sculpture forked costate; rugoso-reticulate, ground sculpture conspicuous areolate; punctate. Mesosoma length vs. absolute cephalic size ( ML / CS): 1.198 [1.148, 1.248]. Maximum mesosoma width vs. absolute cephalic size ( MW / CS): 0.611 [0.585, 0.634]. Metanotal depression absent, the mesosomal dorsal contour line broadly convex in profile. Propodeal spines present. Propodeal spine shape: moderately long, curving downward.

Spine length vs. absolute cephalic size ( SPST / CS): 0.284 [0.252, 0.320]. Minimum spine distance at its base vs. absolute cephalic size ( SPBA / CS): 0.266 [0.223, 0.311]. Apical spine distance vs. absolute cephalic size ( SPTI / CS): 0.341 [0.300, 0.391]. Petiole width ( PEW / CS): 0.258 [0.242, 0.291]. Postpetiole width ( PPW / CS): 0.349 [0.321, 0.399]. Frontal profile of petiolar node contour line in lateral view concave. Subpetiolar process well developed, tooth-like. Dorsal region of petiole sculpture: ground sculpture conspicuous areolate, main sculpture scabrous. Dorso-caudal petiolar profile contour line in lateral view broadly convex. Dorsal region of postpetiole sculpture: ground sculpture conspicuous areolate, main sculpture scabrous. Surface of the first gastral tergite smooth.

Queen (Fig. 6 A – C ).

Body color yellowish brown, with anterior side of gastral tergites yellow, and appendages yellow except the infuscate antennal clubs. Head subrectangular, clypeal depression absent, clypeus smooth and shiny with vertical costae running parallel on the sides and no central carina. Head frontal sculpture: main sculpture costate in the center to areolate-rugose near the posterior and lateral margin, ground sculpture weakly areolate to smooth. Gena sculpture: main sculpture costate, ground sculpture weakly areolate. Mesosoma dorsum flat in profile view, propodeal spines well-developed, horizontal and with a wide base. Dorsal region of mesosoma sculpture: mesoscutum longitudinally costate, mesoscutellar disk largely smooth and shiny, propodeum scabrous. Lateral region of mesosoma sculpture: mostly covered in weak longitudinal costae, converging towards the spine in the propodeum, except for the katepisternum which is mostly smooth and shiny. Frontal profile of petiolar node contour line in lateral view concave. Subpetiolar process well developed, tooth-like. Petiole and postpetiole sculpture: main sculpture scabrous, ground sculpture areolate. Surface of the first gastral tergite smooth.

Male (Fig. 7 A – C ).

Body color brown, appendages pale yellowish. Head subtriangular, clypeal depression absent, clypeus smooth and shiny with vertical costae running parallel on the sides and no central carina. Head sculpture: ground sculpture conspicuous areolate, main sculpture carinate-rugose near the ocelli. Propodeal spines absent. Dorsal region of mesosoma sculpture: mesoscutum anteriorly smooth and posteriorly finely covered in irregurar longitudinal costae, mesoscutellar disk with fine longitudinal costae, propodeum areolate. Lateral region of mesosoma sculpture: largely areolate, katepisternum mostly smooth and shiny. Frontal profile of petiolar node contour line in lateral view concave. Petiole and postpetiole sculpture: main sculpture areolate, part of the petiolar dorsum and whole postpetiolar dorsum smooth. Surface of the first gastral tergite smooth.

Type material.

Holotype: Italy, Sicily, Piano Battaglia, 37.87411, 14.02068, 1580 mH, leg. E. Schifani, 28. 05. 2020 ( CASENT 4010120 , ASUHIC : Arizona State University Hasbrouck Insect Collection, Tempe, Arizona, U. S. A.).

Paratypes: Altogether 37 workers are designated as paratypes, the complete list of which is also given in Suppl. material 1: Italy, Sicily, Piano Battaglia , 37.87411, 14.02068, 1580 mH, leg. E. Schifani, 28. 05. 2020, 3 workers ; Italy, Sicily, Piano Battaglia , 37.87457, 14.01825, 1570 mH, leg. E. Schifani, 28. 05. 2020, 1 worker ; Italy, Sicily, Monte Carbonara , 37.885949, 14.031195, 1830 mH, leg. E. Schifani, 23. 05. 2021, 3 workers ; Italy, Sicily, Monte Carbonara , 37.886381, 14.032484, 1830 mH, leg. E. Schifani, 23. 05. 2021, 1 worker ; Italy, Sicily, Monte Mufara , 37.874657, 14.015228, 1550 mH, leg. E. Schifani, 15. 09. 2022, 3 workers ; Italy, Sicily, Etna Monte Scavo , 37.7733, 14.9515, 1750 mH, leg. A. Alicata, 24. 07. 1992, 3 workers ; Italy, Sicily, Etna località Galvarina , 37.7733, 14.9513, 1850 mH, leg. A. Alicata, 22. 07. 1992, 3 workers ; Italy, Sicily, Etna Monte Maletto , 37.7733, 14.9513, 1850 mH, leg. A. Alicata, 22. 07. 1992, 3 workers ; Italy, Sicily, Etna Monte Maletto , 1850 mH, leg. A. Alicata, 22. 07. 1992, 3 workers ; Italy, Sicily, Etna Monte Ruvolo , 37.7480, 14.8910, 1400 mH, leg. A. Alicata, 18. 08. 1992, 3 workers ; Italy, Sicily, Etna Monte Sona , 37.66688, 14.9843, 1390 mH, leg. A. Alicata, 16. 05. 1992, 3 workers ; Italy, Sicily, Etna Monte S. Maria , 37.8240, 14.990, 1632 mH, leg. A. Alicata, 05. 09. 1992, 2 workers ; Italy, Sicily, Etna , 2000 mH, leg. A. Alicata, 10. 07. 1993, 3 workers ; Italy, Calabria, Pollino National Park – Pian Grande , 39.833595, 16.053456, 1230 mH, leg. A. Alicata, 27. 08. 2021, 3 workers ; Italy, Latium, Pratone di Monte Gennaro , 42.05880, 12.82697, 1020 mH, leg. V. Dolci, 03. 09. 2017, 2 workers ; Italy, Lombardy, Riserva Naturale Boschi del Giovetto di Palline , 45.955014 10.125193, 1462 mH, leg. E. Schifani, 25. 06. 2019, 2 workers ; The paratypes are deposited in the following institutions: HNHM (Hungarian Natural History Museum, Budapest, Hungary), MHNG (Muséum d’histoire naturelle, Genf, Switzerland), NHMB (Naturhistorisches Museum Basel, Switzerland), NHMW (Naturhistorisches Museum Wien, Austria), SCPC (Private collection of SC), SMNG (Senckenberg Museum für Naturkunde Görlitz, Germany).

Etymology.

The name refers to the Apennines Mountains that span from Sicily to northern Italy, encompassing most of the species’ distribution and likely constituting its glacial refugium.

Morphological diagnosis.

The only qualitative difference between T. apenninicus and T. luteus is represented by the normally infuscate antennal clubs and infuscate first gastral tergite of the first (features that may be subsequently lost depending on the preservation state of the specimens). In the Italian fauna, a chromatic pattern superficially similar to T. apenninicus is known for T. minozzii (Santschi 1922) , which is however characterized by much shorter spines, a different petiole shape and a smooth head sculpture, and only known from a lowland site.

The three species considered in this revision represent otherwise true cryptic species, as no single morphometric ratio allows for separation at the individual level. The nest sample mean values spine length ratio ( SPST / CS) help to tell Temnothorax apenninicus sp. nov. workers apart from its congeners T. luteus and T. racovitzai with an acceptably high success rate (Fig. 8 , Table 4 ). However, a narrow overlap is still present.

The striking morphological similarity does not allow drastic trait reduction in individual workers while maintaining the desired classification success in the three-species scenarios. However, if species pairs are considered, T. apenninicus can be easily separated from T. luteus and T. racovitzai based on a combination of three morphometric traits.

Between T. apenninicus and T. luteus , the combination of three traits D 3 a = 79.6279 * CL - 117.9626 * POO - 94.5116 * SPST - 5.015 yields only five misclassified cases out of the total 145 individuals, with an overall accuracy of 0.966, [95 % CI: (0.921, 0.989)] or permitting 3.4 % error rate (Fig. 9 ).

Discriminant (D 3 a) scores for the species are as follows:

D 3 a apenninicus (n = 40) = + 1.71 [- 0.67, + 3.74]

D 3 a luteus (n = 104) = - 1.71 [- 4.46, + 1.89]

Separating T. apenninicus from T. racovitzai can be safely achieved based on the following traits: D 3 b = 72.92828 * ML - 68.1532 * SL - 95.02586 * SPST - 1.566. This function yields only four misclassified cases out of the total 118 individuals, with an overall accuracy of 0.966, [95 % CI: (0.914, 0.991)] or permitting a 3.4 % error rate (Fig. 10 ).

Discriminant (D 3 b) scores for the species are as follows:

D 3 b apenninicus (n = 40) = + 1.819 [- 0.191, + 4.096]

D 3 b racovitzai (n = 78) = - 1.819 [- 4.764, + 0.787]

Distribution and ecology.

The range extends from Sicily to the Alps (Fig. 11 ). Temnothorax apenninicus appears to be a mountain species that lives preferably in meadows and open habitats. Nests are built opportunistically on the ground, in rock crevices, or under stones. Most of our data come from the southern portion of T. apenninicus distribution range: T. apenninicus is probably the highest elevation Temnothorax species in Sicily (Etna, Mt. Carbonara), ranging from 1400 to 2000 m. At higher latitudes, we expect a downshift of the elevational range, with the single record from central Italy (Latium) at 1020 m, and the one from the southern edge of the Alps at 1460 m. On the Etna, multiple colonies were found to be parasitized by the social parasite T. muellerianus (Finzi, 1922) also referred to as Chalepoxenus muellerianus (see Ward et al. 2015, 2016; Seifert et al. 2016). Buschinger et al. (1988) noted that the local population of this social parasite (previously known as Chalepoxenus siciliensis Kutter, 1973 ) seemed to have specialized in parasitizing a species “ close to Leptothorax tristis ” (i. e., a former name of T. luteus ), which most likely was T. apenninicus .

Figures

Figure 5. Temnothorax apenninicus worker in lateral (A), head (B), and dorsal view (C).

Figure 6. Temnothorax apenninicus queen in lateral (A), head (B), and dorsal view (C).

Figure 7. Temnothorax apenninicus male in lateral (A), head (B), and dorsal view (C).

Figure 8. Quartiles that partition spine length ratio nest sample mean values (SPST / CS). Lower and upper extremes, and 25 %, 50 %, 75 % quantiles are shown.

Figure 9. Discriminant (D 3 a) scores for Temnothorax apenninicus and T. luteus worker individuals.

Figure 10. Discriminant (D 3 b) scores for Temnothorax apenninicus and T. racovitzai worker individuals.

Figure 11. Distribution map of the Temnothorax samples analyzed in this study. Map from Stadia Maps - stadiamaps. com and Stamen Design (stamen. com), plotted using the R package “ ggmap ” (Kahle and Wickham 2013).