Tapinoma erraticum ssp. ambiguum Emery 1925

Seifert, Bernhard, Kaufmann, Bernard & Fraysse, Lorenzo, 2024, A taxonomic revision of the Palaearctic species of the ant genus Tapinoma Mayr 1861 (Hymenoptera: Formicidae), Zootaxa 5435 (1), pp. 1-74 : 57-59

Tapinoma erraticum ssp. ambiguum Emery 1925 [type investigation]

The taxon has been described from Departement Drôme ( France), New Forest ( England) and Prague ( Czechia). All this material was available from MCSN Genova and consisted of three different species. A lectotype has been fixed by SeIfert (2012) In a male, labelled “Drôme France Forel ♂ ”, “ SYNTYPUS TapInoma erratIcum subsp. ambIguum Emery, 1925 ”, “ T. erraticum ambiguum ” and “ Lectotype Tapinoma ambiguum Emery, 1925 design. B.Seifert 2010”. A wild-card run of the lectotype in a LDA using ML and the genital characters SPExc, SPdT, SPWPR, dSPST allocated the lectotype with p= 0.9796 to the T. madeirens e cluster (see below). Among four paralectotype workers from Czechia labelled “ Prag Wasmann”, “ SYNTYPUS Tapinoma erraticum subsp. ambiguum Emery, 1925 ”, one specimen belonged to T. subboreale ( T. madeirense is excluded by geographic indication) whereas the other three specimens belonged to T. erraticum with p> 0.999, using 15 NUMOBAT characters).

Material examined. Considering also samples with very weak separation from the sibling species T. subboreale , numeric phenotypical data were taken in workers in 22 samples with 78 individuals. They originated from Austria (1 sample), France (4), Italy (4), Portugal (8), and Spain (5). For details see supplementary information SI1, SI2. The more safely separable males were investigated in 9 samples with 25 individuals. They originated from France (7 samples) and Portugal (2). For details see supplementary information SI3.

Geographic range. Considering samples with sufficiently safe morphological and/or genetic indication, T. madeirense is by natural distribution a Westmediterranean species found in Madeira (17.0°W, 32,5°N), the whole Iberian Peninsula and S France north to 44.2°N . Nests found in a sealed area with some greenery in the city of Sanremo (43.820°N, 7.787°E) and in a grassland patch in a commercial zone in the city of Parma (44.787°N, 10.381°E) could represent anthropogenous introductions to Italy. The latter is sure for a finding in an apartment house in the city center of Vienna (48.182°N, 16.360°E). T. madeirense goes up to 1280 m in Spain at 37.3 °N .

Diagnosis:—Worker ( Tab. 2, Figs. 30–32 ): All shape ratios given below are, in contrast to those in Tab. 2, primary ratios without RAV and all data are given as arithmetic mean ± standard deviation. Rather small, CS 694 ± 63 µm. Head moderately elongated CL/CW 1.153 ± 0.040. Postocular distance medium-sized, PoOc/CL 0.419 ± 0.009. Anteromedian clypeal excision shallow and wider than deep, ExCly/CS 4.73 ± 0.66 %, ExClyW 6.48 ± 0.90%. The margin of clypeal excision forms a sharp cuticular edge and is at same level as the adjacent clypeal surface. Sum of pubescence hairs and smaller setae protruding at a few micron across margin of clypeal excision low, nExCly 1.87 ± 0.65. Posterior margin of head in full face view not excavated, ExOcc/CS 0.15 ± 0.19 %. Scape moderately elongated, SL/CS 1.022 ± 0.018. Minimum distance of the inner margins of antennal socket rings medium-sized, dAN/CS 0.291 ± 0.007. Eye rather large, EL/CS 0.280 ± 0.007. Metanotal groove rather shallow, MGr/CS 3.08 ± 0.97 %. Mesosoma relatively wide and long, MW/CS 0.661 ± 0.024, ML/CS 1.344 ± 0.028. Second funiculus segment short, Fu2L/CS 12.81 ± 0.47%, IFu2 1.451 ± 0.085. Head, mesosoma and gaster covered by a rather dense pubescence. Anterior margin of clypeus with a few standing setae, the two longest and strongest are based near to the anterolateral margin of clypeal excision. Remaining surface of head capsule and dorsal mesosoma without standing setae, such are present on mandibles, coxae and ventral surface of gaster. Head, mesosoma and gaster dark blackish brown. Antennae, femora and tibia dark brown. Tarsae and metatarsae usually pale yellowish brown.

—Male genital ( Tab. 6, Fig. 33 ): Tips of subgenital plate less distant and depth of excision of subgenital plate much lower than in T. subboreale , SPdT/ML 0.313 ±0.031, SPExc/ML 0.167 ±0.019. Longitudinal distance of the tips of subgenital plate and the tips of the harpago much larger than in T. subboreale , dSPST/ML 0.145 ±0.019.

Taxonomic comments. The taxonomic separation of T. madeirense and subboreale is maintained here despite difficulties to separate the female castes morphologically. The decision is based on successful classification based on male genital characters and support of these classifications by microsatellite data. As overall picture, the nuDNA data indicated an Iberian glacial refuge in madeirense and an Italo-Balkanian refuge in subboreale ( Fig. 51 ) and some introgression in the contact zone in southern France ( Fig. 53 ). Sample means of males could be fully separated by the exploratory data analyses NC-Ward, NC-part.kmeans and NC-NMDS.kmeans using the absolute measurements ML, SPExc, SPdT, SPWPr and dSPST. These classifications were confirmed by a PCA and LDA in any of the 32 nest samples ( Fig. 52 ) and in 98% of 102 Individuals (all raw data are given in supplementary information SI3).

In contrast to these clear results, no exploratory data analysis run with NUMOBAT data of worker samples provided a reasonable species hypothesis. The only approach was here to run a LDA with hypotheses being preestablished in those 50 samples having a credible classification by associated males or by a clear geographic or genetic indication whereas the remaining 17 samples were run as wild-cards. Finally, within a total of 67 samples, only 43% could be classified with posterior probabilities of p> 0.90. This indicates the weak performance of the selected NUMOBAT characters in this case.

The rather clear west-east population separation shown by nuDNA with an Iberian glacial refuge for madeirense and an Italo-Balkanian one for subboreale requires additional comments. T. madeirense arrived in Mediterranean S France probably before subboreale , using the coastal route from Spain alongside other ant species such as Lasius cinereus Seifert 1992 or Cataglyphis piliscapa Forel 1901 . Investigation of nuDNA data in Southern France in localities where anthropogenous introduction was unlikely provided a clear signal for ongoing hybridization between T. madeirense and subboreale ( Fig. 53 ). F1 hybrids or individuals suspected for introgression occurred only in a 50 km long zone along the Rhône river from Nîmes to Montélimar. The establishment of a hybrid zone at the border between Mediterranean and continental bioregions indicates a longstanding equilibrium with T. subboreale , with a probable climatic advantage for the more southern T.madeirense over T. subboreale in the south of this very strong climatic gradient. A recent disturbance of the clear geographic pattern is best explained by anthropogenous introduction. This was obviously the case in findings of subboreale (of Italian origins based on microsatellite data) in several gardening centers and public parks in the Montpellier region or in a finding of madeirense in an apartment house in Vienna / Austria. The classification of the latter finding was based on a posterior probability in a wild-card run of a LDA (p=0.9860) but this is no really sure indication considering the weak performance of the character system. Whatever is true, Tapinoma madeirense has not to be included in the list of Austrian ants as there is no evidence for outdoor nesting and successful colonization.

Biology (according to observations of L. Fraysse from Southern France): Along the French Mediterranean coast and within the Rhône Valley, T. madeirense appears to occupy moderately sun exposed places, dry to moist. Nest were found directly in the ground, under stones, or even under little wood pieces in diverse habitats: clear pine forest both with or without dense grass cover, along shaded grassy paths, in suburban gardens, even in a watered truffle oak grove. Centanni et al (2022)., based on 100 nests, found that the species was as frequent in semi-natural, agricultural or urban landscapes in and around Montpellier ( France). When the nest was directly in the ground, the ants constructed solaria in which the brood is placed just under the surface, using wet soil and the surrounding grasses as it was described for T. subboreale and T. erraticum . Nest density seems to be relatively low compared to the latter, maybe because desirable habitats are more discontinuous in S France. All colonies in S France contained at most a thousand workers, that are not aggressive when disturbed. Polygyny seems occasional, mature colonies contained 1 to 5 queens. Alates seem to be produced continuously during 2–3 weeks in April or May, depending on the annual climate. Nuptial flights occur at most a week after their emergence, a few alates are emitted regularly during hot mornings. Males were observed to practice a particular strategy: they fly near the ground, land and run for 10–50 cm, and then take off again. Moreover, in swimming pools, only males were found during 6 years of nuptial flight. Hence, it seems that flight dispersal of gynes is weak and that gene flow between populations is largely malemediated. Workers forage individually for dead little invertebrates, but are very efficient mass recruiters when a sugar source is found (e.g. hemipteran honeydew, fruit peelings in compost etc.). Nests are often translocated within a season—probably to avoid overheating and desiccation or to be closer to sustainable food sources.

Figures

FIGURE 30. Tapinoma madeirense, head in full face view, Belem / Portugal, 2018.03.25.

FIGURE 31. Tapinoma madeirense, lateral view, Belem / Portugal, 2018.03.25.

FIGURE 32. Tapinoma madeirense, anterior head in dorsofronal view, Belem / Portugal, 2018.03.25.

FIGURE 33. Tapinoma madeirense, male genital in ventral view, Meio da Serra / Madeira, 2002.06.22.

FIGURE 51. Bayesian clustering for K=2 of 15 microsatellite loci of Tapinoma madeirense (orange) and T. subboreale (blue).

FIGURE 52. Separation of nest sample means of males of Tapinoma madeirense (black rhombs) and T. subboreale (white dots) by a principal component analysis considering 5 NUMOBAT characters.

FIGURE 53. Bayesian clustering for K=2 of 15 microsatellite loci of Tapinoma madeirense (orange) and T. subboreale (blue) in southern France with hybridization in a 100 km wide zone along the Rhone river from about Nîmes to Montélimar.