Species conservation profile of the stenoendemic cave spider Pimoa delphinica (Araneae, Pimoidae) from the Varaita valley (NW-Italy)

Pimoa delphinica Mammola, Hormiga & Isaia, 2016 is a troglophile araneoid spider endemic of the high Varaita valley (Western Alps, Province of Cuneo, NW Italy). In spite of relatively intense field research and examination of museum collections, the species is restricted to ten localities, thus showing a reduced extent of occurrence (EOO; 26 km) and area of occupancy (AOO; 12 km). Although the habitat and the subpopulations of P. delphinica are not currently threatened, the species is potentially exposed due to its extremely narrow geographic distribution range, subdivision in subpopulations and low dispersal capacity. 2 2 © Mammola S et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Basis of EOO and AOO:
Min Elevation/Depth (m):

Basis (narrative)
During relatively intense speleological research studies in the Western Alps, we collected Pimoa delphinica in a few caves and military bunkers in the municipalities of Casteldelfino, Sampeyre and Sant'Anna di Bellino (Varaita valley, Western Alps, Province of Cuneo, Italy). Specifically, the species occurred in four small wild caves and a few subterranean military bunkers in Casteldelfino and Sant'Anna di Bellino and an abandoned house in the hamlet of Becetto (Sampeyre). Two additional localities reported in Isaia et al. (2011) and Mammola et al. (2016b)-Buco del Nebin 1 [Speleological Cadastre: Pi 1158] and Buco del Nebin 2 [Pi 1159] caves-are in need of verification, since only juvenile specimens were collected. However, even if confirmed, these additional localitites would fall within the known extent of occurrence of the species (cf. Suppl. material 1). Despite our extensive study of Pimoa specimens from Italy and France-including material stored in Museums or private collections and original records-we have not been able to find additional records of Pimoa delphinica outside this small area (detail in Mammola et al. 2016b).
We used the verified occurrence records of the species to calculate the extent of occurrence (EOO) as the minimum convex hull and the area of occupancy (AOO) through a 2x2 km grid, as implemented in the red R package (Cardoso 2016).

Range description
Pimoa delphinica is a stenoendemic species with a restricted Western Alpine distribution. The species is recorded in seven nearby localities, in the high Varaita valley. Its distribution range represents a small enclave (ca. 20 km ) within the range of distribution of the sister species P. graphitica Mammola, Hormiga & Isaia, 2016 Trend:

Justification for trend
The species is troglophile (sensu Sket 2008), showing a preference for dark and moisty habitats. Yet, the species exhibits a moderate plasticity in its ecological requirements, being able to colonize both cave and extra-cave environments, such as forests in high altitude habitats. The distribution range of Pimoa delphinica is enclosed within the range of the more widespread P. graphitica, which is apparently competing with the former thus limiting its expansion (Mammola et al. 2016b). The subterranean habitats colonized by P. delphinica are as yet not threatened by direct human activities. However, biogeographic studies and genetic data suggested that past climate change determined strong contraction in the distribution ranges of the species of alpine Pimoa (Mammola et al. 2016b, Mammola et al. 2015. It is thus plausible that anthropogenic climate change may determine reduction or habitat shift for this species. In order to confirm this hypothesis statistically, a deeper study of the detailed occurrence of this species in its distribution range is required. Habitat specialist:

Population
Unknown. Unknown

Justification for trend
No information about population size are currently available.

Unknown
Unknown Unknown

Population Information (Narrative)
A census of the population has never been attempted. According to our observations, populations are locally abundant. In two caves in which Pimoa delphinica was found in syntopy with the congeneric P. graphitica, mixed nuclear alleles between the two species have been found, indicating the existence of unidirectional introgression of males of P. graphitica into females of P. delphinica (Mammola et al. 2016b).

Justification for trend
Examining the known range of distribution and taking into account habitat connectivity, it is possible to identify two subpopulations within the range. The first subpopulation includes the localitites from Casteldelfino and the Bellino valley, which are more connected through alpine scree and larch woods, acting as potential route of dispersal. The other subpopulation is found on the other slope of the Varaita valley, in the nearby of the hamlet of Becetto (municipality of Sampeyre). The subpopulation are as yet not threatened.

Terrestrial
Yes Species conservation profile of the stenoendemic cave spider Pimoa delphinica ...

Habitat (narrative)
The species primarily lives in the twilight zone of wild caves and other similar sheltered habitats, in high alpine environments (Fig. 3a). Healthy populations were also observed in artificial subterranean habitat (military bunkers and mines), offering suitable cool climatic conditions (Fig. 3b, c, d). Further individuals of P. delphinica were collected in pitfall traps placed within the rocky debris on the floor of the cellar of an abandoned cottage (Becetto, Sampeyre). During summertime, we observed juveniles-tentatively classified as P. delphinica-in an epigean environment, near the locus typicus (Fig. 3c), in a larch (Larix decidua) wood. Accordingly, it is possible that juveniles of P. delphinica may be able to disperse trough epigean habitats under suitable climatic condition. Extra-cave dispersal was also documented for the congeneric alpine species P. graphitica and P. rupicola, as justified by occasional catches of juveniles and males in pitfall traps placed in the leaf litter of broad-leaved woods at mid-altitudes (e.g., , Isaia et al. 2014, Jackson 1929, Mammola et al. 2015, Mammola et al. 2016b).

Ecology and traits (narrative)
Little is known about the ecology of Pimoa delphinica. We report the result of our sporadic observations, which are not supported by specific studies or statistical inference. Like other Pimoa species (cf. Mammola et al. 2016a, Mammola et al. 2015, Hormiga 1994, P. delphinica exhibits a moderate ecological plasticity. In caves, it is found preferentially in the twilight zone. We observed adult males and females during the summertime. Adults display thanatotic behaviour when disturbed, possibly as a protection against predators (cf. Rogers andSimpson 2014, Novak et al. 2016 Research needed:

Justification for threats
See "Extent of occurrence".

Conservation actions
In Place

Justification for conservation actions
A portion of the distribution range of Pimoa delphinica falls within the border of the Natural Park "Parco del Monviso".
The installation of information panels educating the visitors about this peculiar endemic species would positively increase the awareness of the caves as a natural heritage deserving protection.