Plagiolepis maura Santschi

Espadaler, X., 2007, The ants of El Hierro (Canary Islands)., Advances in ant systematics (Hymenoptera: Formicidae): Homage to E. O. Wilson - 50 years of contributions., Memoirs of the American Entomological Institute, 80, pp. 113-127 : 121-122

21. Plagiolepis maura Santschi cf.

(1, w q m; 18, w; 22, w q; 28, w q; 31, w q; 34, w m; 35, w; 36, w q; 37, w; 38, w; 39, w; 41, w q; 44, w). This is a frequent ant at low altitudes although it was collected also at 600 m and 850 m. Nests are in soil, usually under stones or small wood debris. This identification is provisional. I have not used the name P. barbara canariensis , used by Wellenius (1955) for his samples from El Hierro, because males and females of this species are much larger; in addition, the conspecificity of this last taxon with P. schmitzii is highly probable (unpublished observations). This species has been exceedingly difficult to deal with. The West Mediterranean Plagiolepis sorely need a complete revision, as what follows attest. The key characteristic is aptery in sexuals: in early spring, small males were present in a nest at Arenas Blancas, running very rapidly. Its apterous aspect, suggested at first a social parasite. Thereafter, as all queens from El Hierro showed also to be apterous, their true nature was evident. Sexuals are not ergatoid: but for the lack of wings they have the characteristic male and gyne morphology. At Pie del Risco, one fully winged male was collected. This is the first free-living formicine ant in which wingless males have been noted. After checking material from other islands, it was soon clear that this is best interpreted as a case of wing polymorphism: in queens from the islands of Gran Canaria and La Gomera there is a variable degree of thoracic simplification, from a complete winged thorax to an apterous morphology, lacking tegulae and with a fused scutum and scutellum. An enhanced pilosity in pronotum and scutellum seems to be correlated with thorax simplification.

Aptery in ant males and queens has appeared independently several times under distinct selective pressures and its functional significance is also diverse (Heinze & Ysuji, 1995; Espadaler 1997). Two other species in the genus Plagiolepis are known to have wingless males ( P. xene Staercke and P. ampeloni (Faber) or wingless females ( P. ampeloni ) although this is probably related with the parasitic life of both species. It is legitimate to speculate on wing loss though none of the hypotheses exposed in Wagner & Liebherr (1992) seems to apply in this case. Habitat stability is not applicable because of the recent volcanic eruptions and large-scale landslides at El Hierro (Gee et al., 2001). Habitat isolation neither seems to be appropriate as the numerous sites where this species has been collected attest. The energetic cost of flight is also to be rejected: El Hierro has not a cold climate and, even if the prevailing trade winds, from the Southwest are high, this admittedly ad-hoc explanation is invalidated by the fact that the similarly sized males and females of Solenopsis canariensis have retained full wings. The possibility of winged queens at El Hierro cannot be rejected.