OCCURRENCE OF THE BLACK LACE-WEAVER SPIDER, AMAUROBIUS FEROX, IN CAVES POJAVLJANJE PAJKA AMAUROBIUS FEROX V JAMAH Enrico LUNGHI 1,2,* Abstract UDC 595.44:551.435.84 Enrico Lunghi; Occurrence of the Black lace-weaver spider, Amaurobius ferox, in caves Subterranean habitats house a wide range of species which show a number of adaptations to prevailing ecological condi- tions. Spiders are among the most abundant predators in caves; however, most studies on cave spiders focus on species adapted to these habitats. This is the first study related to the occurrence of the Black lace-weaver spider, Amaurobius ferox, in caves. The species lacks adaptations to the subterranean habitats and has been observed within meters from the cave entrance all year round, except in late winter until early spring. Furthermore, its occupancy is positively related to the presence of other three cave-dwelling spiders: Metellina merianae, Meta menardi and Tegenaria sp. Key words: Arachnids, biospeleology, Italy, occupancy, subter- ranean habitat. Izvleček UDK 595.44:551.435.84 Enrico Lunghi: Pojavljanje pajka Amaurobius ferox v jamah V različnih podzemnih habitatih živijo številne živalske vrste, ki so bolj ali manj prilagojene na razmere tamkajšnjega okolja. V jamah so pajki med najštevilčnejšimi plenilci, a večina študij je omejenih na tiste vrste, ki so že izrazito prilagojene na podze- mlje. Pajek Amaurobius ferox ne sodi mednje, v študiji pa je ob- ravnavano njegovo pojavljanje vzdolž jam. Ta površinska vrsta se pojavlja le v vhodih delih jam v vseh letnih časih, z izjemo pozne zime do začetka pomladi. Njeno pojavljanje v teh delih je povezano s prisotnostjo treh v jamah prebivajočih vrst, in sicer pajkov Metellina merianae, Meta menardi in Tegenaria sp. Ključne besede: pajkovci, biospeleologija, Italija, zasedenost, podzemni habitat. 1 Key Laboratory of the Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beichen West Road 1, 100101, Beijing, China, 2 Museo di Storia Naturale dell’Università di Firenze, Sezione di Zoologia “La Specola” , Via Romana 17, 50125 Firenze, Italy, e-mail: enrico.arti@gmail.com * Corresponding author. Received/Prejeto: 01.11.2019 DOI: 10.3986/ac.v49i1.7672 ACTA CARSOLOGICA 49/1, 119-124, POSTOJNA 2020 COBISS: 1.01 INTRODUCTION Subterranean environments (from the deep karst system to the Milieu Souterrain Superficiel) hold par- ticular ecological conditions which frequently promote specific adaptations in the resident species (Culver & Pipan 2015; Ficetola et al. 2019; Mammola 2019). These conditions include the constant darkness, high microcli- matic stability and food paucity (Culver & Pipan 2019). The most studied subterranean habitats are caves (i.e., the large voids suitable for human exploration; Mam- mola 2019); therefore, the majority of studies on subter- ranean species deals with species found in caves. Cave- dwelling species are generally subdivided into three main categories according to their degree of adaptation and the ability to complete their lifecycle in subterranean habitats (Howarth & Moldovan 2018; Mammola 2019). Troglobionts are obligate cave-species which show strong adaptations to subterranean life, such as depigmentation, anophthalmia and elongation of appendages; they can only reproduce successfully in subterranean habitats. Troglophiles are facultative cave-dwelling species which can successfully reproduce in both hypogean and epi- gean environments and may show some specific adap- tations. Trogloxenes are occasional visitors in caves and do not reproduce there; they do not show any specific adaptations. Spiders are among the most abundant predators in caves (Mammola & Isaia 2017). Numerous studies have been performed on cave spiders in recent years (Novak et al. 2010; Carver et al. 2016; Mammola & Isaia 2016; Lipovšek et al. 2018). However, these studies largely fo- cus on species dependant on cave habitats and poorly adapted species are frequently overlooked. Non-obligate cave species can play an important role for the entire eco- system, as they are often major drivers of allochthonous organic matter; e.g., many bats and crickets come back to the caves after foraging outside, and provide valuable or- ganic matter to local communities through their guano, dead bodies or eggs (Ferreira & Martins 1999; Lavoie et al. 2007). More thorough studies on species previously thought to be accidental occurrences have demonstrated that these species actively select subterranean habitats with specific environmental features (Lunghi et al. 2014, 2017, 2018), making them important to the local ecosys- tem. This is the first study related to the occurrence of the Black lace-weaver spider, Amaurobius ferox (Amau- robiidae), in caves (Fig. 1A). This species often occurs within meters from the cave entrance (Mammola et al. 2018) and shows a peculiar behaviour which may work as exaptation to subterranean habitats (Hesselberg et al. 2019a). After the hatching of spiderlings their mother offers herself as food which is an extreme behaviour (known as matriphagy) useful in habitats with limited food availability (Kim & Horel 1998; Kim 2009). This study contributes to improving the scant knowledge on A. ferox ecology. ENRICO LUNGHI Fig. 1: Amaurobious ferox (A) and the other three cave spiders considered in this study: Metell- ina merianae (Tetragnathidae) (B); Meta menardi (Tetragnath- idae) (C); cf. Tegenaria sp. (Age- lenidae) (D) (Photo: E. Lunghi). ACTA CARSOLOGICA 49/1 – 2020 120 OCCURRENCE OF THE BLACK LACE-WEAVER SPIDER, AMAUROBIUS FEROX, IN CAVES METHODS DATA COLLECTION During the 2013, 16 caves located in the North of Tus- cany (Central Italy, between 43 °  52 ′  42 ′′  N, 11 °  07 ′  18 ′′  E and 43 °  59 ′  51 ′′  N, 10 °  13 ′  48 ′′  E; altitudinal range 91–948 m a.s.l.) were surveyed monthly: this included 12 natural caves, 3 semi-natural caves (i.e., artificially enlarged natural caves) and one drainage tunnel. Sur- veyed caves were distributed across the Apennines: Apuan Alps (4), Monti della Calvana (8) and Appen- nino pistoiese (4). Most of the caves were located in forested areas, while two caves and the drainage tunnel were located between forested and urbanized areas. Each cave was surveyed as deep as possible (average explored length around 24 m, range 6–60 m). Starting from the main entrance, the monitored caves were di- vided into 3-meter long sectors to perform fine-scale data collection (Lunghi et al. 2020). Within each cave sector the following abiotic features were recorded: sector width and height (using a tape meter), average wall irregularity (i.e., presence of protuberances on the cave walls), air temperature (°C) and relative humid- ity (%) using a Lafayette TDP92 thermo-hygrometer (accuracy: 0.1 °C and 0.1% RH) and average illumi- nance using a Velleman DVM1300 light meter (mini- mum recordable illuminance: 0.1 lx). Wall irregularity was estimated by flattening a one meter string on the cave walls to trace their shape; then, with a tape me- ter, the linear distance between the two extremities of the string was measured (details in Lunghi et al. 2014). Within each cave sector, the presence and abundance of Amaurobius ferox, on both cave walls and ceil- ing were assessed by Visual Encounter Survey (VES) (Crump & Scott 1994) adopting a standardized survey effort of 7.5 min/sector to control imperfect species detection (Banks-Leite et al. 2014; Lunghi 2018). For additional information on the dataset and sampling methodology refer to Lunghi et al. (2017). STATISTICAL ANALYSES Data was checked for potential outliers and collinearity be- tween microclimatic covariates prior to analysis (Zuur et al. 2010). The presence of outliers was assessed by plotting the data (boxplots). Relative humidity and illuminance had a series of outliers and thus, to improve the linearity of the data, they were angular-transformed and log-transformed, respectively. Correlation between microclimatic variables was low (pairwise Pearson’ s r < 0.48), therefore all variables were included in analysis. Generalized Linear Mixed Mod- els (GLMM) assuming binomial error were used to assess the relationship between the occurrence of A. ferox with the environmental features and the occurrence of the three syntopic spider species Metellina merianae, Meta menardi and Tegenaria sp. (Figs. 1B-D) (R packages lme4, MASS, MuMIn; Venables & Ripley 2002; Douglas et al. 2015; Bartoń 2016; R Development Core T eam 2018). These spe- cies are regularly found on the cave walls and ceiling in the cave entrance and twilight zones (Mammola & Isaia 2017; Hesselberg & Simonsen 2019). The presence/absence of A. ferox was used as a dependent variable, while the sector morphological (height, width and wall heterogeneity) and microclimatic features (temperature, humidity and illumi- nance), along with the presence/absence of the other three syntopic spider species were used as independent vari- ables. As multiple surveys were conducted and the time of survey varied, the month of survey along with the cave and sector identity were used as random factors. Models were built using all possible combinations of the inde- pendent variables. Models were then ranked following the Akaike’s Information Criterion corrected for small sample size (AICc) (Fang 2011). The model with the lowest AICc value was considered the best; nested models and those representing complex versions with higher AICc values than the simpler were not considered as potential candi- dates (Richards et al. 2011). The likelihood ratio test was used to assess the significance of variables included in the best AICc model. RESULTS The presence of Amaurobius ferox within cave sectors was assessed 44 times in 10 caves. Only one individual per cave sector was observed; thus, presence data also cor- responds to observed abundance. Spiders were observed every month, except in February, March and April, and always within the first 6 cave sectors (up to 18 m from the cave entrance). The mean (± SD), min and max val- ues of each feature related to the occupied cave sectors were the following: width, 1.27 ± 1.17 (0.76–8.20) m, height, 2.20 ± 0.83 (0.60–3.25) m, wall irregularity 0.84 ± 0.12 (0.60–0.98), temperature 14.3 ± 4.1 (4–20.2) °C, humidity 86.5 ± 5.8 (68–95.7) %, illuminance 6.5 ± 11.6 (0–51.9) lx. The best AICc model included sector width, tem- perature, illuminance and the presence of all the three syntopic spider species while the second best model ACTA CARSOLOGICA 49/1 – 2020 121 ENRICO LUNGHI (∆AICc = 0.08) included the same variables but not the sector width (Tab. 1).The presence of A. ferox was posi- tively related to illuminance (β = 0.29, χ 2 = 5.62, P = 0.018) and to the presence of the three syntopic spider species (Metellina merianae, β = 1.29, χ 2 = 7.73, P = 0.005; Meta menardi, β = 0.96, χ 2 = 3.86, P = 0.05; Tegenaria sp., β = 1.48, χ 2 = 9.98, P = 0.002); no significant relationship was detected for temperature (β = 0.16, χ 2 = 3.51, P = 0.061) and sector width (β = -0.33, χ 2 = 2.10, P = 0.147). DISCUSSION Amaurobius ferox most likely inhabits caves all year round, selecting specific habitats close to the cave en- trance. The lack of species observations during the first part of the year (February-April) may reflect the period in which this spider overwinters inside cave wall crevices. The best model showed that this species mostly inhabits the cave sectors close to the entrance, characterized by higher illuminance and by the presence of all the three syntopic spider species: Metellina merianae, Meta me- nardi and Tegenaria sp. The difference between the first and the second best model was small (∆AICc = 0.08), and showed similar results. The only difference between these two models was the inclusion of sector width in the former model; however, this variable was not significant. The inhabited cave sectors by A. ferox were those close to the cave entrance, where ecological conditions are most similar to those on the surface (Lunghi et al. 2015), and where prey diversity and abundance is higher (Manenti et al. 2015; Lunghi et al. 2017). Considering the lack of specific adaptations to cope with darkness, A. ferox may need to inhabit more illuminated habitats to success- fully detect and catch prey using visual cues (Uiblein et al. 1992). Furthermore, higher prey abundance may help females to collect sufficient resources for reproduction, which may not be achieved deeper inside caves (Kim & Roland 2000; Kim 2009). Amaurobius ferox tended to occupy cave sectors in which the other syntopic spiders were present. While Metellina merianae and Tegenaria spiders distributions are mostly related to the cave entrance (Lunghi et al. 2017; Hesselberg & Simonsen 2019), M. menardi is of- ten found also throughout the twilight zone (Lunghi et al. 2017; Hesselberg et al. 2019a). The weak correlation between A. ferox and M. menardi might be attributed to different ecological requirements in these two species, as the latter occupies deeper cave sectors (Mammola & Isaia 2014; Lunghi et al. 2017; Hesselberg et al. 2019b). The three syntopic cave spiders are better adapted to subter- ranean habitats and are usually more abundant than A. ferox. Further studies are needed to clarify both coexis- tence and potential competition of these species. Although limited, observations reported here pro- vide the first information on the use of caves by the spi- der A. ferox, a spider that regularly inhabits sectors close to the cave entrance. Future studies will strengthen these results and elucidate the importance of this species for the subterranean habitat. Tab. 1: The best five models based on AICc relating the presence of Amaurobius ferox in caves. Its occurrence was considered as dependent variable. Independent variables were: average wall heterogeneity (Het), humidity (Humid), Height and Width of sectors, means of illumi- nance (Lx), temperature (Temp), and presence/absence of Metellina merianae, Meta menardi and Tegenaria sp. Empty cells indicate that the variable is not included into the relative model. Best model is shown in bold. Independent variables included into the model df AICc ∆AICc Weight Het Humid Height Width Lx Temp M. merianae M. menardi Tegenaria -0.33 0.29 0.16 1.29 0.96 1.48 9 278.6 0 0.082 0.29 0.15 1.30 0.97 1.52 8 278.7 0.08 0.079 3.38 0.32 0.19 1.28 1.01 1.60 9 279.3 0.75 0.056 3.16 -0.32 0.32 0.19 1.27 0.96 1.58 10 279.4 0.84 0.054 0.14 -0.38 0.27 0.16 1.30 0.98 1.49 10 280.1 1.50 0.039 ACTA CARSOLOGICA 49/1 – 2020 122 OCCURRENCE OF THE BLACK LACE-WEAVER SPIDER, AMAUROBIUS FEROX, IN CAVES ACKNOWLEDGEMENTS I am thankful to all Reviewers who contributed in im- proving the first draft of the manuscript. I thank A. C. Hughes for checking the English in the manuscript. The author is supported by the Chinese Academy of Sciences President’s International Fellowship Initiative for post- doctoral researchers (grant number 2019PB0143). RERFERENCES Banks-Leite, C., Pardini, R., Boscolo, D., Righetto Cas- sano, C., Püttker, T., Santos Barros, C. & J. 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