Lasius grandis Forel 1909

Seifert, Bernhard, 2020, A taxonomic revision of the Palaearctic members of the subgenus Lasius s. str. (Hymenoptera, Formicidae), Soil Organisms 92 (1), pp. 15-86 : 67-68

4.4.34 Lasius grandis Forel 1909

Lasius niger var. grandis Forel1909 [typeinvestigation]

Type material: Lectotype (des. E.O. Wilson) plus 4 paralectotype workers on two pins labelled ” L. niger v, grandis Forel type Ronda, Andalousie (C.Voigt)“, ”ANTWEB CASENT 0911047“; depository: MHN Genève.

All material examined. A total of 74 samples with 198 workers were subject to NUMOBAT investigation. These originated from Andorra (2 samples), France (34), Sardinia / Italy (2), Portugal (3) and Spain (33). For details see supplementary information SI1.

Geographic range. Iberia, southernmost France (in Rhone valley north to 44°N), Corsica, Sardinia, introduced to Tenerife. Altitudinal records range from sea level up to 2300 m in the Sierra Nevada at 37°N.

Diagnosis ( Tab. 7 , Figs. 65 –66; key; images in www. AntWeb.org with specimen identifiers CASENT 0906079, CASENT 0911047):

Absolute size rather large (CS 984 µm). Head and scape length indices large (CL/CW 900 1.095, SL/CS 900 1.037); postocular distance low (PoOc/CL 900 0.222); torulo-clypeal distance large (dClAn 900 5.01); eye size medium (EYE/CS 900 0.239); terminal segment of maxillary palp long (MP6/CS 900 0.208). Number of mandibular dents large (MaDe 900 8.62). Pubescence on clypeus moderately dense (sqPDCL 900 4.53); frontal pubescence short (PLF 900 27.2). All body parts with rather numerous standing setae of medium length (PnHL/CS 900 0.145, GuHL/CS 900 0.125, nGu 900 9.8, nSc 900 17.5, nHT 900 19.4). Cuticular surface of dorsal head and mesosoma within the meshes of the microreticulum smooth and shining. There are two color morphs. The dark morph is rather homogenously dark brown with the exception of pale yellowish-brown mandibles, scapes and tibiae. The light morph shows a distinct reddish color component with clypeus, mandibles, mesosoma, petiole and appendages light reddish-brown whereas vertex and gaster are darker reddish-brown. The light morph constitutes 90% of the samples from Corsica and Sardinia and the dark morph 95% of the samples from Iberia and southern France.

Biology. It is the most abundant species of the subgenus in Iberia and inhabits open habitats as well as deciduous and coniferous woodland habitats. It prefers medium to humid moisture conditions and occurs at lower altitudes typically in sheltered conditions (gorges or valleys with running waters). At sites with more precipitations, at altitudes above 2000 m or along the Atlantic coast of Iberia, it occurs in open grassland. Nests are under stones or in soil. Mound construction with mineral soil material, as it is typical for Lasius niger , is occasionally observed. Lasius grandis behaves as aggressively as L. niger after disturbance of the nest. Alates were observed between end of June and end of July.

Comments. Lasius grandis and L. emarginatus can be separated with an error rate of 0% by any variant of NC-clustering and the classification error on the worker individual level by an LDA is only 0.9%. This clear situation offers good conditions for identification of hybrid nests in the vectorial space ( Bagherian et al. 2012; Kulmuni et al. 2010; Seifert 1999, 2006, 2019a, 2019b; Seifert et al. 2010). Occasional hybridization between Iberian L. grandis and L. emarginatus does in fact occur in the contact zone in southern France. A nest sample of five workers from Mount La Rhune (43.3079°N, 1.6318°W, 855 m) is placed exactly intermediate between the clusters of the parental species when run as wild-card in an LDA considering all 16 standard NUMOBAT characters. The posterior probabilities of this sample are p=0.404 for L. emarginatus and p=0.596 for L. grandis whereas the most uncertain samples of L. emarginatus and L. grandis have posterior probabilities of 0.981 and 0.996 respectively. Morphological data exclude the involvement of L. niger and L. platythorax in this case and make involvement of L. cinereus most unlikely.

The Corsican population of Lasius grandis with lighter reddish specimens has been suspected of possibly representing an endemic island species but any attempt to show this by exploratory data analyses failed. Corsican and Iberian populations are not separable by structural characters, both subjectively and by the standard NUMOBAT characters. Furthermore, adding to the NUMOBAT data standardized pigmentation measurements performed in the RGB (Red-Green-Blue) channels did also not provide clusters interpretable as different species. The Corsican and Iberian populations differed significantly in the color-balanced (calibrated) R-values of dorsal pronotum (ANOVA F 1,140 = 7.277, p<0.008) and the geometric mean of the six absolute RGB-values of head and pronotum (ANOVA F 1,140 = 7.612, p<0.007) but the overlap of data is very large.

Figures

Figs. 65 and 66: Lasius grandis; CASENT0906079, photo S. Hartman