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Seasonal abundance and spatio-temporal distribution of the troglophylic harvestman Ischyropsalis ravasinii (Arachnida, Opiliones, Ischyropsalididae) in the Buso del Valon ice cave, Eastern Italian Prealps

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We explore the population of the troglophilic harvestman Ischyropsalis ravasinii inhabiting the Buso del Valon ice cave located in the Italian Prealps. Spatial and temporal distributions of the specimens are investigated in relation to the variation of environmental abiotic conditions in the cave, such as the seasonal temperature and substrate surface typology. Our results show that I. ravasinii is distributed unevenly in the cave, most of individuals being present in the scree-covered section of the cave with superficial activities limited to the warm seasons only. In addition, our data suggests that the presence of a thick layer of rocky debris, together with high humidity and cold temperatures, are important limiting factors for the species. Seven additional species of harvestman are recorded in the cave, including the congeneric troglophilic species Ischyropsalis strandi. This is the first known record of these two troglophilic Ischyropsalis species coexisting within the same cave. An updated map of the distribution of I. ravasinii and I. strandi in the Italian Prealps is provided.
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Seasonal abundance and spatio-temporal
distribution of the troglophylic harvestman
Ischyropsalis ravasinii (Arachnida, Opiliones,
Ischyropsalididae) in the Buso del Valon
ice cave, Eastern Italian Prealps
Ivan Petri1, Francesco Ballarin1,2, Leonardo Latella1
1Department of Zoology, Museo di Storia Naturale of Verona, Lungadige Porta Vittoria 9, 37129, Verona,
Italy 2Systematic Zoology Laboratory, Department of Biological Sciences, Tokyo Metropolitan University 1-1,
Minami-Osawa, Hachioji-shi, 192-0397, Tokyo, Japan
Corresponding author: Francesco Ballarin (ballarin.francesco@gmail.com)
Academic editor: Stefano Mammola|Received 31 January 2022|Accepted 22 March 2022|Published 8 April 2022
http://zoobank.org/8EE93DB7-D70F-4094-A32C-32B7347D6DB6
Citation: Petri I, Ballarin F, Latella L (2022) Seasonal abundance and spatio-temporal distribution of the troglophylic
harvestman Ischyropsalis ravasinii (Arachnida, Opiliones: Ischyropsalididae) in the Buso del Valon ice cave, Eastern
Italian Prealps. Subterranean Biology 42: 151–164. https://doi.org/10.3897/subtbiol.42.81486
Abstract
We explore the population of the troglophilic harvestman Ischyropsalis ravasinii inhabiting the Buso del
Valon ice cave located in the Italian Prealps. Spatial and temporal distributions of the specimens are
investigated in relation to the variation of environmental abiotic conditions in the cave, such as the
seasonal temperature and substrate surface typology. Our results show that I. ravasinii is distributed
unevenly in the cave, most of individuals being present in the scree-covered section of the cave with
supercial activities limited to the warm seasons only. In addition, our data suggests that the presence of
a thick layer of rocky debris, together with high humidity and cold temperatures, are important limiting
factors for the species. Seven additional species of harvestman are recorded in the cave, including the
congeneric troglophilic species Ischyropsalis strandi. is is the rst known record of these two troglophilic
Ischyropsalis species coexisting within the same cave. An updated map of the distribution of I. ravasinii and
I. strandi in the Italian Prealps is provided.
Keywords
Age classes, global warming, Lessinia Mountains, Northern Italy, seasonality, subterranean environment
Subterranean Biology 42: 151–164 (2022)
doi: 10.3897/subtbiol.42.81486
https://subtbiol.pensoft.net
Copyright Ivan Petri 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.
RESEARCH ARTICLE
Subterranean
Biology Published by
The International Society
for Subterranean Biology
A peer-reviewed open-access journal
Ivan Petri et al. / Subterranean Biology 42: 151–164 (2022)
152
Introduction
Harvestmen (Arachnida: Opiliones) are one of the largest orders within the class
Arachnida, numbering 65 families and 6637 species (Blick and Harvey 2011; Kury et
al. 2020). Harvestmen show highly diverse morphology and biology, allowing them to
successfully colonize a large number of habitats including terrestrial and subterranean
habitats. e genus Ischyropsalis C.L. Koch, 1839 (Family Ischyropsalididae Simon,
1879) contains some of most iconic European harvestmen, which are easily
recognizable by their relatively large body size, massive, prominent chelicerae and dark
coloration. Numbering 22 species, all geographically limited to Europe, Ischyropsalis
species are characterized by a high level of endemism. ey are often restricted to a
single mountain chain (Schönhofer 2013; Schönhofer et al. 2015). ey frequently
show frigophilic and hygrophilic habits, having marked preferences for microhabitats
with low temperature and constantly high humidity (Martens 1969; Schönhofer et al.
2015). Recent studies also suggest a direct relationship between the current distribution
of Alpine Ischyropsalis species and the Pleistocene glaciations (Mammola et al. 2019).
Although in high mountains these arachnids can be found in open or shallow humid
habitats, such as scree and mossy landscapes, at lower altitudes they inhabit caves
and other subterranean habitats. us, several Ischyropsalis species display an anity
for hypogean habitats and dierent degrees of adaptations to the subterranean life,
including numerous obligate cave-dwellers (Marcellino 1982; Schönhofer et al. 2015).
Despite their relevance as part of the European cave-dwelling fauna, the ecology
of this genus has been scarcely explored (Martens 1969). To date, only six species
have been partially analyzed in terms of ecology and life cycle, and most of the data
rely on old studies carried out over 50 years ago (e.g. I. luteipes Simon, 1872 and
I.pyrenaea Simon, 1872 see Juberthie 1961; I. strandi Kratochvil, 1936 see Juberthie
1963; I.kollari C.L. Koch, 1839 see Martens 1969; I. dentipalpis Canestrini, 1872 and
I.lithoclasica Schönhofer & Martens, 2010 see Schönhofer and Martens 2010). For
most known cave-dwelling Ischyropsalis no updated information concerning their life
cycle, seasonality, micro-habitat preference or even area of distribution are available.
In caves, where the environmental conditions remain rather constant along the
year (Badino 2010), abiotic factors represent a critical element to dene the structure
and composition of the subterranean communities (Howarth 1980). Local variations
may deeply aect the spatial and temporal distribution of the cave-dwelling arthropods
(Latella et al. 2008). In particular, frigophilic cave species have adapted to living in
cold subterranean habitats characterized by low temperature and the presence of an ice
or snow layer throughout the year, albeit with some seasonal variation (Iepure 2018).
Located in the Italian Prealps (Fig. 1B) at relatively low altitude, the Buso del
Valon ice cave (cadaster number: 438 V/VR) has a permanent internal ice body
and supercial snow (Zorzin et al. 2015). e cave hosts a well-dened assemblage
of arthropods adapted to cold environments including three species of the wingless
limoniid crane ies of the genus Chionea Dalman, 1816 (Avesani and Latella 2016;
Latella et al. 2019). It also shelters a large population of the harvestman I. ravasinii
Abundance and spatio-temporal distribution of a cave harvestman in Italy 153
Hadži, 1942 (Fig. 1D), a troglophilic species endemic to the Venetian Prealps in North-
East Italy. Due to its unique features, the Buso del Valon ice cave represents an ideal
natural laboratory to explore the phenology and microhabitat preference of frigophilic
subterranean species (Avesani and Latella 2016). With this study, we aim to complete
our knowledge of the life cycle and spatio-temporal distribution of I. ravasinii living in
cold subterranean environments in relation to the cave substratus and seasonal changes.
We further plan to use data herein collected as a starting point for long-lasting studies
aiming to monitor the eects of climate change on the frigophilic cave fauna and its
resilience to changes in micro-habitat conditions (see e.g. Howarth, 2021).
Materials and methods
Area of study
e Buso del Valon ice cave (Fig. 1A) is located at ~1700 m a.s.l. in the Lessini Moun-
tains of the Venetian Pre-Alps in Northern Italy (Veneto Region, Province of Verona,
45°41'32.26"N, 11°0.6"11.10"E) (Fig. 1B). e mountain chain forms a trapezium-
shaped massif dominated by Mesozoic and Cenozoic limestones. ese sedimentary rocks
are interspersed by Cenozoic volcanic rocks and Eocenic limestone outcrops (Sauro 1973).
e cave opens with a large shaft approximately 30 m in diameter and 50 m deep. It shows
a vertical E-W course reaching nearly 70 m of depth at its deepest point (Fig. 1A,C).
e Buso del Valon ice cave is one of the few karstic cavities of the Veneto Region with
permanent cold internal temperatures ranging from -8 °C to 7 °C (Fig. 2A) and hosting a
permanent ice body fed by seasonal snowfalls through the entrance. e ice inside the cave
has been retreating in recent years, probably due to climate change (Latella et al. 2019).
Specimens sampling
Field collections were carried out in the cave for approximately two and half years,
from July 2014 to December 2016 resulting in a consecutive temporal series of 30
months. We selected ve sampling stations inside the cave (ST1–4 and DPS), located
in three ecologically dierent areas of the cave: one at the entrance shaft base (ST1),
two on the scree near the border of the internal ice layer (ST2, DPS), two near the bot-
tom (ST3 and ST4) (Fig. 1C). Each selected area was characterized by specic combi-
nation of abiotic factors (e.g. albedo, typology and thickness of substrate; see Table1).
Four stations (ST1–4) were sampled using standard pitfall traps consisting of a glass
cup with an open diameter of 10 cm lled with propylene glycol. A deep scree trap
(DPS, Fig. 1E) was set approximately one meter deep inside the scree for monitoring
possible seasonal vertical movement of the harvestman specimens among the debris.
e DPS trap consisted of a 90 cm long PVC pipe with an inside diameter of 11 cm
and several small holes (5–7 mm in diameter) drilled along its surface (see López and
Oromí 2010). A 10 cm diameter plastic cup lled with propylene glycol was placed
Ivan Petri et al. / Subterranean Biology 42: 151–164 (2022)
154
at the bottom of the pipe to collect the samples. An additional pitfall trap (ST5) was
installed outside the cave near its external border acting as a control station. A bait con-
sisting of a piece of blue mould cheese in a plastic vial was added in each trap to attract
the cave-dwelling arthropods. e collected specimens were xed in 75% ethanol for
Figure 1. Location and outlines of the study area A entrance of the Buso del Valon ice cave B updated
distribution of Ischyropsalis ravasinii and I. strandi: the position of the cave is highlighted by an arrow
C transversal and horizontal sections of the Buso del Valon ice cave (modied from Zorzin et al. 2015),
with the locations of the selected stations and dataloggers used in the study. e extension of the permanent
ice and snow coverage inside the cave is illustrated in light blue. e external station (ST5) is not shown
Dadult male Ischyropsalis ravasinii E replacement of the deep scree trap inside the scree. Abbreviations:
DPS = sampling station with deep scree trap, ST1–4 = sampling stations 1–4 with pitfall traps.
Abundance and spatio-temporal distribution of a cave harvestman in Italy 155
morphological study. All specimens used in this study are preserved in the collections
of the Museo di Storia Naturale of Verona, Italy.
Due to the varying albedo and temperature along the year, the permanent ice and
snow layer inside the Buso del Valon ice cave shows seasonal variation in spatial cover-
age and thickness. Following this feature, the sampling time and consequent analysis
of the data was divided into two time-frames of six months each: from mid-June to
mid-December and from mid-December to mid-June. us, each trap was set in place
for a period of 6 months before being emptied and refreshed. ese periods roughly
correspond to the warm and cold seasons of the year inside the cave, namely the peri-
ods of minimum and maximum temperature (Fig. 2A) and extension of the snow and
ice coverage inside the cave. Two Tinytag Plus data loggers (-30 °C to +50 °C) were
positioned inside the cave for a period of two years, one at the base of the shaft and one
in the lower part of the cave (Fig. 1C), to record the temperature changes during the
two seasons in dierent parts of the study area.
Stages identification and population demography
Identication of adults at species level was carried out under a stereomicroscope
(Bresser Advance ICD 10-160x) according to Martens (1978). Juveniles of I. ravasinii
were distinguished from juveniles of other species (e.g. I. strandi) based on the presence
of eye pigmentation and length of chelicerae basal article. Previous studies have shown
that the life cycle of Ischyropsalis species is divided into six growing instars before the
adult form (Juberthie 1961; Martens 1969). Based on this information, we classied
each collected specimen into one of the seven putative stages (instars IN 1–6 and adults
AD) based on the length of their cephalothorax, chelicerae and cheliceral spines. ese
characters are considered discriminant among dierent instars and thus indicative of
the growing stages (Martens 1969).
Adults and instar richness within each trap were calculated summing the number
of individuals of I. ravasinii collected. Nevertheless, each trap may show unique
results due to the dierent types of traps used (pitfalls and DPS) and slightly dierent
collecting timeframes in dierent years (see Table 2). To avoid sampling bias and to
make the data more directly comparable, for each trap we also dened a trapping rate
(TR, sensu Vater 2011). erefore, the number of specimens collected was converted
Table 1. Position and abiotic factors of the stations used in this study. For the exact position of each
sampling station see Fig. 1C.
Station Type of trap Position Albedo Surface typology Ice/snow coverage
ST1 Supercial pitfall trap Base of the shaft Low Large stones, clay and moss No
ST2 Supercial pitfall trap Middle cave section Low ick scree Yes-seasonal
DPS Deep scree trap Middle cave section Absent ick scree Yes-seasonal
ST3 Supercial pitfall trap Bottom of the cave Very low Large stones and clay No
ST4 Supercial pitfall trap Bottom of the cave Very low Fissured rock Yes-seasonal
ST5 Supercial pitfall trap Outside of the cave Strong Meadow soil No
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156
using the following formula: TR = n° individuals/n° of days of trap activity. Statistical
analyses were carried out and graphs were plotted using PAST4 and EXCEL software.
e map with the updated distribution of I. ravasinii and I. strandi was constructed
using QGIS version 3.4 including known records from literature and new records
collected by the rst author.
Captive breeding
In order to obtain supplementary information on the life cycle of I. ravasinii,
additional specimens were collected from the articial tunnel Galleria Vittorio
Emanuele III located in the Grappa Massif, Venetian Pre-Alps. ree adults and
one juvenile belonging to the 5th instar were collected in March 2020 and raised in
controlled conditions for approximately 14 months. Specimens were kept in plastic
boxes (size 15 × 8 × 10 cm for adults and late instars and 5 × 5 × 3 cm for the early
instars) with small stones and wood sticks and a layer of peat on the bottom. e boxes
were stored in a fridge with a controlled temperature of 6–8 °C. To maintain constant
moisture the boxes were frequently sprayed with nebulized water. Harvestmen were
fed using collembola, small ies or crickets. Hatchlings were raised until reaching the
4th instar. Adults and the juvenile collected in the eld were raised until the end of
their life cycle.
Figure 2. A temperatures recorded over two years in the Buso del Valon ice cave, for the detailed posi-
tion of the dataloggers see Fig. 1A B seasonal instars and adult abundance collected during each separate
trapping period C number of individuals of dierent growth stages collected during the warm and cold
seasons. Abbreviations: AD = adults, IN 1–6 = instars 1–6.
Abundance and spatio-temporal distribution of a cave harvestman in Italy 157
Table 2. List of harvestman species collected in the Buso del Valon ice cave and related stations, includ-
ing numbers of individuals. Abbreviations: AD = adults, DPS = sampling station with deep scree trap, IN
1–6= instars 1–6, ST1–5 = sampling stations 1–5 with pitfall traps.
Species Collection period Station N° of
specimens
Instar Season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 1 IN 1 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 3 IN 1 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 1 IN 1 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 2 IN 2 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 4 IN 2 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 10 IN 3 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 6 IN 4 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 1 IN 4 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 14 IN 5 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 3 IN 5 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 1 IN 5 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 7 IN 6 Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 6 AD (2, 4) Warm season
Ischyropsalis ravasinii 25.IX.2014–14.XII.2014 ST2 1 AD (1) Warm season
Ischyropsalis ravasinii 14.XII.2014–27.VI.2015 DPS 2 IN 1 Cold season
Ischyropsalis ravasinii 14.XII.2014–27.VI.2015 DPS 6 IN 2 Cold season
Ischyropsalis ravasinii 14.XII.2014–27.VI.2015 DPS 20 IN 3 Cold season
Ischyropsalis ravasinii 14.XII.2014–27.VI.2015 DPS 2 IN 4 Cold season
Ischyropsalis ravasinii 14.XII.2014–27.VI.2015 DPS 2 IN 5 Cold season
Ischyropsalis ravasinii 14.XII.2014–27.VI.2015 DPS 2 IN 6 Cold season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 ST1 1 IN 5 Warm season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 ST2 14 IN 5 Warm season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 ST2 2 IN 6 Warm season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 DPS 11 IN 1 Warm season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 DPS 18 IN 2 Warm season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 DPS 20 IN 3 Warm season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 DPS 5 IN 4 Warm season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 DPS 7 AD (3, 4) Warm season
Ischyropsalis ravasinii 27.VI.2015–6.XII.2015 ST3 1 IN 3 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST1 1 IN 4 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST2 9 IN 2 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST2 13 IN 3 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST2 9 IN 4 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST2 18 IN 5 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST2 8 IN 6 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST2 2 AD (2) Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST3 3 IN 4 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST3 2 IN 5 Warm season
Ischyropsalis ravasinii 27.VI.2016–8.XII.2016 ST3 1 IN 6 Warm season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 ST1 2 IN 3 Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 ST2 1 IN 5 Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 DPS 28 IN 2 Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 DPS 42 IN 3 Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 DPS 8 IN 4 Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 DPS 6 IN 5 Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 DPS 5 IN 6 Cold season
Ivan Petri et al. / Subterranean Biology 42: 151–164 (2022)
158
Species Collection period Station N° of
specimens
Instar Season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 DPS 2 AD (1, 1) Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 ST4 1 IN 3 Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 ST4 1 IN 5 Cold season
Ischyropsalis ravasinii 6.XII.2015–27.VI.2016 ST4 3 IN 6 Cold season
Gyas annulatus 6.XII.2015–27.VI.2016 ST4 1 1 juv. Cold season
Gyas annulatus 25.IX.2014–14.XII.2014 ST2 1 1 juv. Warm season
Gyas annulatus 27.VI.2015–6.XII.2015 ST3 1 1 juv. Warm season
Gyas annulatus 27.VI.2015–6.XII.2015 ST2 1 1 juv. Warm season
Histricostoma dentipalpe 27.VI.2016–8.XII.2016 ST1 1 AD (1 ) Warm season
Histricostoma dentipalpe 27.VI.2016–8.XII.2016 ST3 2 AD (1, 1) Warm season
Ischyropsalis strandi 27.VI.2015–6.XII.2015 ST2 2 AD (2) Warm season
Ischyropsalis strandi 25.IX.2014–14.XII.2014 ST2 1 IN 2 Warm season
Ischyropsalis strandi 27.VI.2015–6.XII.2015 DPS 1 IN 1 Warm season
Lacinius horridus 27.VI.2015–6.XII.2015 ST5
(external)
1 AD (1 ) Warm season
Lophopilio palpinalis 27.VI.2015–6.XII.2015 ST5
(external)
15 AD (7, 8) Warm season
Lophopilio palpinalis 27.VI.2016–8.XII.2016 ST1 1 AD (1 ) Warm season
Lophopilio palpinalis 27.VI.2016–8.XII.2016 ST3 2 AD (1, 1) Warm season
Mitopus morio 27.VI.2015–6.XII.2015 ST5
(external)
2 AD (1, 1) Warm season
Mitostoma sp. 6.XII.2015–27.VI.2016 DPS 1 1 juv. Cold season
Nemastoma sp. 27.VI.2016–8.XII.2016 ST2 1 AD (1 ) Warm season
Rilaena triangularis 6.XII.2015–27.VI.2016 ST2 2 AD (2) Cold season
Results
Stages composition and seasonal abundance
A total of 338 specimens of I. ravasinii were collected inside the cave during the study
period (Table 2). Among them, 18 were adults (6 males, 12 females, 5.3% of the
total) and 320 were juveniles (94.7%). Juveniles belonged to the following instars:
IN 1=18, IN 2=67, IN 3=110, IN 4=35, IN 5=63, IN 6=28 (Fig. 3A). No specimens
of I. ravasinii were found in the trap located outside the cave area. Instars and adults
abundance in warm and cold periods are illustrated in Fig. 2B, C. During the warm
seasons, when the extension of the internal ice layer was at its minimum, a total of 205
specimens were sampled. ey were partitioned into the seven stages as follows: IN
1=16, IN 2=33, IN 3=44, IN 4=25, IN 5=53, IN 6=18, AD=16 (Fig. 3A). Juveniles
represented the majority of the collected specimens (92.1%), in particular the rst
three instars (~40% of the total) and especially the IN 5 which alone included ¼ of all
the samples. Male/female sex ratio in this season was 5:11. During the cold seasons,
in the periods of maximum ice extension,133 specimens were collected: IN 1=2, IN
2=34, IN 3=65, IN 4=10, IN 5=10, IN 6=10, AD=2 (Fig. 3A). Again, the majority
of specimens were juveniles (98.5%), in particular those belonging to the early three
instars (83.2%). e male/female sex ratio was 1:1.
Abundance and spatio-temporal distribution of a cave harvestman in Italy 159
Spatio-temporal distribution
Most specimens (95% of the total samples) were collected in the middle section of
the cave, characterized by a thick layer of rocky debris. Samples were collected both
on the surface (ST2: ~40.2%) and in the deep layers (DPS: 55%). All other stations
collected a much smaller number of specimens, between 1.2% and 2.1% of the total
samples (Fig. 3B).
Similar results were obtained considering the collections occurred only in the
warm or the cold seasons. During the warm seasons (Fig.3C) the stations located in
the scree showed the highest trapping rate both on the surface and in the deep layers
(ST2 TR=0.994, DPS TR=0.449). Few specimens were collected in the other stations,
near the entrance (ST1 TR=0.014) or at the bottom of the cave (ST3 TR=0.051; ST4
TR=0.00). During the cold season, all individuals were gathered in the deep layers of
the scree, the deep scree trap showing the highest trapping rate (DPS TR=0.626). In
contrast, only a few individuals were found on the surface, all the surface pitfall traps
showing low trapping rates including in the scree (ST1 TR=0.010; ST2 TR=0.005;
ST3 TR=0.00; ST4 TR=0.025) (Fig.3C).
Life cycle in captivity
Eggs were laid in captivity between late April and June 2020 always in the most humid
part of the breeding boxes where several condensation drops were present. Each egg
cluster contained between 10 to 20 eggs. Egg development, from deposition to hatching,
required about 100 days until middle-late August. Only approximately 50% of the eggs
hatched. Hatchlings needed about 11 months to reach the 4th instar, each growing stage
lasting between one to three months. e juvenile of the 5th instar reached adulthood
approximately three months later, in June 2020 and survived as adult for nearly one more
year until May 2021. e whole life cycle is estimated to last approximately two years.
Additional notes on the opiliofauna of the Buso del Valon ice cave
In addition to I. ravasinii, the congeneric species I. strandi Kratochvil, 1936 was sam-
pled in the study area. Only four specimens of I. strandi were collected during the two
and half years of sampling: two adult females and two juveniles belonging to the 1st and
2nd instars, respectively (Table 2). All the specimens were found in the scree area (ST2
and DPS) during the warm seasons. e small number of individuals did not allow
statistical evaluation. An updated distribution of these two Ischyropsalis species in the
Italian Prealps is illustrated in Fig. 1B. Six additional species of harvestmen belonging
to two dierent families and six dierent genera were also sampled inside the Buso del
Valon cave: Fam. Nemastomidae: Histricostoma dentipalpe (Ausserer, 1867) (3 spec.);
Mitostoma sp. (1 spec.); Nemastoma sp. (1 spec.); Fam. Phalangiidae: Gyas annulatus
(Olivier, 1791) (4 spec.); Lophopilio palpinalis (Herbst, 1799) (18 spec.); Rilaena trian-
gularis (Herbst, 1799) (2 spec.) (see Table 2).
Ivan Petri et al. / Subterranean Biology 42: 151–164 (2022)
160
Discussion
Among the harvestman fauna inhabiting the Buso del Valon ice cave, two coexisting
species belonging to the genus Ischyropsalis were collected: I. ravasinii and I. strandi.
Both the species belong to the Alpine clade sensu Schönhofer et al. 2015, and show
a reduced distribution along the Venetian Prealps. Ischyropsalis strandi is endemic to
the Lessini and Baldo mountains, while I. ravasinii extends its distribution to the East
toward the Cansiglio plateau. us, the Buso del Valon ice cave represents the south-
ernmost record for I. ravasinii (Fig 1B). e distributions of both species overlap in the
western part of the Venetian Prealps (Schönhofer et al. 2015). Our data are in agree-
ment with this nding (Fig. 1B). Despite being sympatric, to our knowledge this is
the rst known case of coexistence of these two troglophilic Ischyropsalis species within
the same cave.
Ischyropsalis ravasinii appears to prosper inside the Buso del Valon ice cave,
forming a large population and being the most abundant representative of the local
harvestman fauna. Additionally, the lack of specimens collected outside the cave
corroborates the strong anity of I. ravasinii for subterranean habitats. However,
Figure 3. A percentage of instars and adult relative abundances B percentage of sampling relative
abundances by station C comparison of the trapping rate (TR) of each station during the warm and cold
seasons. Abbreviations: AD = adults, DPS = sampling station with deep scree trap, IN 1–6 = instars 1–6,
ST1–4 = sampling stations 1–4 with pitfall traps.
Abundance and spatio-temporal distribution of a cave harvestman in Italy 161
the population of I. ravasinii is not uniformly distributed inside the Buso del Valon
ice cave. is species shows a marked preference for the micro-habitat formed
by the thick scree in the central part of the cave, being most abundant near the
border of the permanent ice during both the warm and cold seasons. Most of the
specimens were sampled from the central part of the cave, including juveniles
belonging to all six instars and all the adults. A similar distribution pattern seems
to be followed by I. strandi although on a smaller scale. Ischyropsalis ravasinii is a
troglophilic-hygrophilic species strictly bound to high humidity to deposit eggs
(Juberthie 1964, 1965; and observations with specimens in captivity). It needs
a cool environment of about 4–6 °C to remain active as observed with captive
specimens. e interstitial spaces within the rocky debris may contribute to retain
the suitable humidity and temperature for the harvestmen survival throughout the
year. e scree likely represents the most stable micro-habitat inside the cave in
both the seasons, consequently serving as an ideal habitat for egg deposition and
juvenile development. Other areas of the cave pose colder or drier conditions, at
least for a part of the year (Fig. 2A), or lack a coverage of debris that can be used as
a refuge, thus being a less suitable habitat for this species.
Our data suggests a conspicuous dierence in the seasonal distribution of I.ravasinii
in the scree-covered area of the Buso del Valon ice cave. During the warm season,
when the slightly warmer temperatures and the reduced extension of the ice coverage
allows surface activity, I. ravasinii seems to be similarly present in both supercial
and deep layers within the scree, with a preference for being close below the surface.
In contrast, very few specimens were sampled on the surface during the cold season,
most collections occurred in the DPS trap only. Lower surface temperatures and the
presence of a larger and thicker layer of ice and snow in comparison to the warm
season, most likely hinder the surface activity of I. ravasinii during the cold season.
Such conditions may force I. ravasinii to move deeper into the scree where the micro-
climatic conditions remain more suitable.
Martens (1969) reports that the reproductive season in Ischyropsalis spp. extends
from spring to early summer, with egg hatching in late summer/autumn. Similar
results were observed by us with I. ravasinii eggs hatched in captivity. Accordingly, the
presence of the highest number of early instars (IN 1–3) collected in the cave during
the cold season, together with the low numbers of adults, supports this hypothesis.
e high percentage of the subadult IN 5 found during the warm season also suggests
that the nal maturation of this species occurs mainly during the warmer period.
erefore, it is likely that juvenile I. ravasinii need at least nine months to reach
adulthood and probably even longer. Such hypotheses are in line with our experimental
observations with specimens raised in captivity. After reaching their maturation, adults
of some Ischyropsalis species may live for several months (e.g. I. kollari, see Martens
1969). e records of adults collected in the Buso del Valon ice cave during both the
warm and cold periods also support this hypothesis. Dead adults of this species have
occasionally been found in caves during the early summer months (July and August,
Petri I. personal observation 2020) and captive adults have survived several months
Ivan Petri et al. / Subterranean Biology 42: 151–164 (2022)
162
before dying. Such ndings imply that the life cycle of I. ravasinii extends for more
than one year, possibly around two or more years, as reported for other Ischyropsalis
species (see Juberthie 1968) and experimentally tested by us hatching and raising
specimens in captivity.
Conclusions
e present study oers new data on the spatio-temporal distribution of the troglophilic
harvestmen I. ravasinii adapted to living in cold subterranean environments. We
investigated for the rst time the ecological and seasonal preferences for microhabitats
in I. ravasinii and we report additional data on its life cycle. Despite being the dominant
harvestman in the cave, this species is absent in nearby cavities, including articial
tunnels, which are instead occupied by I. strandi. Since I. ravasinii seems to strongly
rely on the presence of stable, humid and cool habitat, the Buso del Valon ice cave
may provide refuge for this species similarly to other local frigophilic arthropods. In
addition, the typology of substrate seems to play an important role in its survivability,
the wide majority of individuals being collected in the scree-covered area of the cave.
Due to its strict bond with specic environmental conditions I. ravasinii may be
strongly aected by even limited changes occurring to its habitat. Following the rise
in temperatures related to climate change, and the consequent progressive reduction
of the internal ice body, the conditions of the microhabitats inside the Buso del Valon
ice cave are changing at a fast pace (Latella et al. 2019). Such changes may threat the
species survivability similarly to what is occurring to other arthropods living in ice
caves (Mammola et al. 2019; Howarth 2021). Additional studies on the ecology of
I. ravasinii in the Buso del Valon ice cave may help us to explore how this or other
frigophilic subterranean arthropods face the long-term eects of climate change.
Acknowledgements
e authors would like to thank the speleologists of the Commissione Speleologia
Veronese (CSV) who took part in the eld research and the Parco Naturale Regionale
della Lessinia for the authorization to carry out the eld research. Special thanks to
Giorgio Annichini for helping with the cave surveys and to Roberta Salmaso for the
research in the Museum collections. We are also thankful to Victoria Smith (New
Zealand) to revise the English text of an early draft of this manuscript. Special thanks
to Prof. Dr. Jochen Martens for conrming the identications of the populations
collected by the rst author reported in the map (Fig. 1B). We are particularly grateful
to Stefano Mammola and an anonymous referee for their detailed suggestions and
advices which helped to substantially improve the work. is research was granted by
the Federazione Speleologica Veneta and the Natural History Museum of Verona.
Abundance and spatio-temporal distribution of a cave harvestman in Italy 163
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