Vesubia jugorum

Vesubia jugorum (Simon, 1881)

Trabea jugorum Simon, 1881: 83.

Vesubia jugorum – Simon 1909: 402.

MATERIAL. –– France • 2 ♀; département des Alpes-Maritimes, Valdeblore, Mont Pepoiri, western slope, in rocky debris; 2360 m a.s.l.; 1.VII.2022; Isaia and Tolve leg., coll. MI • 1 ♀; same data as for preceding; MNHN • 2 ♀; Colmars-les-Alpes, Téte de l’Encombrette, southern slope; steep alpine scree; 2200 m a.s.l.; 3.VII.2021; Isaia and Tolve leg., coll. MI • 5 ♀; Colmars-les-Alpes, Dent de Lièvre, northern slope; flat rocky debris area; 2138 m a.s.l.; 3.VII.2021; Isaia and Tolve leg., coll. MI.

OBSERVATIONS. –– Italy • 1 specimen; Province of Cuneo, Entracque, Lago Bianco dell’Agnello; 2200 m a.s.l.; 8.VIII.2019: Giordana vid. France • 1 ♀; département des Alpes-Maritimes, Entraunes, Lac des Garrets; 2299 m a.s.l.; 22.VIII.2019; Lucas vid. • 1 ♀; Saint-MartinVésubie, Col du Mercantour; 2532 m a.s.l.; 18.VIII.2019; Assmann vid. • 1 ♀; Valdeblore, Vallon des Millefonts, western slope, in rocky debris; 2150 m a.s.l.; 30. VI.2022; Breton vid. • 2 ♀; Mont Pepoiri, western slope, in rocky debris; 2360 m a.s.l.; 1.VII.2022; Isaia and Tolve vid. • 1 ♀; Valdeblore Tête de la Roubine, southern slope, in rocky debris; 2274 m a.s.l.; 3.VII.2022; Isaia and Tolve vid. • 1 ♀; département des Alpes-de-Haute-Provence, Uvernet-Fours, Col de la Petite Cayolle; 2460 m a.s.l.; 5.IX.2019; Lucas vid.

REMARK

These new findings extend the current known distribution range of the species from the previous 2456 km ² to the current 2628 km ². To date, the known occurrences of Vesubia jugorum are 110, i.e., 66 in Italy (Province of Cuneo) and 44 in France (24 in département des Alpes-Maritimes and 20 in département des Alpes-de-Haute-Provence). The new updated distribution of V. jugorum is presented in Fig. 1, and the new records are detailed in Table 2.

MICROCLIMATIC DATA

Temperature data derived from data-loggers positioned under stones showed daily fluctuations in temperature and relative humidity during the warm season until late October, when the temperature quickly drops to 0°C and remains almost constant until the following mid-June. Data from the meteorological station of Rocca dell’Abisso showed strong fluctuations of the air temperatures during the year, ranging from –17 ° in winter to 22 °C in summer (Fig. 3).

OBSERVATIONAL DATA ON LIFE CYCLE, PHENOLOGY AND DIET

Observational data likely confirm for Vesubia jugorum a stenochronus life cycle. Females and juveniles were generally found throughout the summer season, from mid-June to late September (only one record from Mongioie at the beginning of October), whereas adult males were found for a shorter period, from July to mid-September (Fig. 3). No observations were ever carried out in winter due to the high snow coverage in suitable areas. During the summer season, different cohorts were found simultaneously. The highest abundance of adult specimens occurred in July and August, likely corresponding with the mating period. Males were encountered less frequently and their density was generally low, an observation that may be possibly biased by the higher mobility of males and the greatest difficulty in catching them.

Females with cocoons have been found – always in their retreats – from the end of June to the early days of September. Females build circular and silk-lined retreat under stones, with a small opening in the silken walls, occasionally digging an additional small recess into the soil. Females with cocoons did not seem to be territorial, as up to three females have been found in adjoining retreats under the same stone. The cocoons are globular, white and contain on average 200 eggs (89-343, n = 10). According to our observations, females produce more egg sacs in the same season. The production of a second egg sac has been observed in laboratory-reared specimens.

Females of Vesubia jugorum exhibit maternal cares of both cocoons and spiderlings. They carry their cocoon underneath their abdomens attached to the spinnerets. If they lose their egg sac, or if the egg sac is removed, they look for it in the surrounded area until they found it or a surrogate (e.g. a rounded piece of cotton). Under laboratory conditions, females fed while carrying egg sacs or pulli. Female looks after the cocoon for around one month after the laying, until the offspring hatch. The first moult occurs inside the egg sac while the second-instar juveniles emerge from the cocoon through a cleft in the seam, and climb onto their mother opisthosoma, and, occasionally, carapace. Maternal care for spiderlings lasts one week to ten days, after which the spiderlings disperse by falling off from the female body. Shortly after, they moult to the third instar. On average, the duration of the instars is 40 days, with earlier stages moulting every two weeks and later stages being longer up to two months. Given the remarkable size reached by adult specimens, and considering the duration of the growing season, it seems likely that the specimens require an average of 10-12 instars to complete the development, reaching the adult stage over multiple years.

As proved by the specimen collected in earliest time of the growing season, overwintering individuals are generally adult females or immatures at different stages in their development. Unfortunately, we have no data on overwintering behaviour. However, we observed a tendency of the individuals to aggregate during the growing season in areas of high suitability (see, e.g., the high population density observed in July 2019 at Colle della Ciriegia, a highly suitable site where many specimens have been found in a few minutes), and to disaggregate when the temperature drops (no specimens found in samplings carried out in the same locality in mid-October). It seems likely that specimens are very mobile within the rocky areas, showing a higher tendency to aggregate in the snowfree period and to disaggregate as the cold season approaches.

Vesubia jugorum is a cursorial hunter which preys actively. The spider approaches the prey and pounces on it from a close distance, grabbing and surrounding it using the strong, spiny legs. After grabbing it, the prey is bitten with the chelicerae and released with the legs. Vesubia jugorum was observed masticating the prey organisms with the chelicerae, maximizing food assimilation and thus increasing the total energy extracted from each prey item. Laboratory observations showed a generalist predatory habit for V. jugorum. Accepted preys included Orthoptera, Diptera, Lepidoptera, Coleoptera, Isopoda Oniscidea and Araneae. Cannibalism was common, often involving juveniles or smaller individuals, and in general occurring between pairs of specimens with great differences in both mass and size.

Vesubia jugorum shares its habitat with other Alpine spider species such as Alopecosa alpicola (Simon, 1876), Drassodes thaleri Hervé, 2009, Drassodex simoni Hervé, Roberts & Murphy, 2009, Attulus longipes (Canestrini, 1873), Xysticus desidiosus Simon, 1875 and Pardosa nigra (C. L. Koch, 1834) (see Isaia et al. 2015). Tentatively, areas where V. jugorum is locally abundant are generally avoided by Pardosa nigra, which is slightly smaller in comparison, but possibly shares similar ecological requirements.

RESULTS OF THE MONITORING BASELINE PHASE

During the monitoring surveys, 71 females and 29 cocoons were collected. In 12 out of 17 sampling sites, the target of five adult females was achieved, whereas in the remaining five sites the sampling stopped after three searching hours, without reaching the target of five adult females collected. Col de Vars was the only site where no individual was captured. According to the models performed in Mammola et al. (2019), this site has a very low value of habitat suitability. For this reason, Col de Vars was excluded from the monitoring programme.

The results of the measurements of the functional traits collected in each locality with their relative values of habitat suitability (extracted from Mammola et al. 2019) are reported

in Table 3. The femur IV length ranged from 5.590 mm (Col de Mallemort) to 7.510 mm (Serriére de la Lombarde). In the locality with smallest femurs, Mongioie – Bocchin dell’Aseo where the mean femur IV length was 5.778 mm (n = 5), the habitat suitability index was 0.170. The site with the longest femurs IV was Serriére de la Lombarde, with a mean length of 7.288 mm (n = 5). This site had a high habitat suitability index, corresponding to 0.737.

Only in seven sampling sites we were able to collect cocoons, and their finding was generally rare. The cocoon size ranged from 6.915 mm (Passo della Gardetta) to 12.545 mm (Serriére de la Lombarde). The site with the largest average cocoon size was Col du Trem (11.467 mm; n = 2), whereas the locality with the smaller average cocoon size was Passo della Gardetta (8.407 mm; n = 4).

Results of the regression analyses, highlighted relationship very close to statistical significance (P-value = 0.0516) between the length of the femurs IV and the habitat suitability predicted by the model (Fig. 4). No significant relationship was observed between habitat suitability and cocoon size, possibly due to the low sample size.

Specimens collected at Grande Séolane showed an unexpected great length of the femur IV. Accordingly, when excluding this observation, the significance of the regression improves, reaching a P-value of 0.0202.