Subterranean Biology 45: |—16 (2023)
doi: 10.3897/subtbiol.45.95850 RESEARCH ARTICLE

https://subtbiol.pensoft.net

of,
Published by
The International Society
for Subterranean Biology

Vertical distribution of spiders (Araneae) in
Central European shallow subterranean habitats

Milan Reza¢', Vlastimil RGZi¢ka’, Jan Dolansky’, Petr Dolejs*

| Crop Research Institute, Drnovskd 507, 161 06 Praha, Czech Republic 2 Biology Centre, Czech Academy
of Sciences, Institute of Entomology, Branisouskd 31, 370 05 Ceské Budéjovice, Czech Republic 3 The East
Bohemian Museum in Pardubice, Zimek 2, 530 02 Pardubice, Czech Republic 4 Department of Zoology,
National Museum — Natural History Museum, Cirkusovd 1740, 193 00 Praha 9 — Horni Pocernice,
Czech Republic

Corresponding author: Milan Rezaé (rezac@vurv.cz)

Academiceditor:StefanoMammola| Received 30September2022| Accepted 16December2022 | Published 1 8January2023
Attps://z00 bank. org/E7888525-734F-4694-A92C-E57DE7D258C2

Citation: Rez4¢ M, Ruzicka V, Dolansky J, Dolejs P (2023) Vertical distribution of spiders (Araneae) in Central
European shallow subterranean habitats. Subterranean Biology 45: 1-16. https://doi.org/10.3897/subtbiol.45.95850

Abstract

Shallow subterranean habitats are among the last habitats in Central Europe to be arachnologically re-
searched. Using stratified pipe traps, we studied the vertical distribution of spiders in soil and interspaces in
bedrock (shallow subterranean habitats). Specifically, we sampled fauna in different substrates, including
limestone, sandy marlstone, sandy marl, claystone, loess, and artificial gravel accumulation. Employing
stratified pipe traps allowed us to identify the depth at which particular species occurred. Across multiple
years and sampling sites, we collected 76 spider species, 21 of which showed an affinity for subterranean
microhabitats. Some of these species occurred in interspaces in soil and bedrock, whereas others have
been previously found in subterranean ant nests and animal burrows. We collected five species (/berina
microphthalma, Centromerus cf. piccolo, Porrhomma cambridgei, P microcavense, and P microps) almost
exclusively at depths over half a meter, suggesting the strong affinity of these species for a subterranean
lifestyle. We provide diagrams of these species’ vertical distribution and photo-document eye reduction.
Our study demonstrates that poorly studied shallow subterranean habitats harbor diverse subterranean

spider fauna, including several previously considered rare species in Central Europe.

Keywords
Araneae, Centromerus, Czechia, edaphomorphism, Jberina, micropthalmic spiders, Palliduphantes, pipe

traps, Porrhomma, soil spiders, troglomorphism

Copyright Milan Rezdé 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.

2 Milan Rezéé et al. / Subterranean Biology 45: 1-16 (2023)

Introduction

Subterranean habitats range from large spaces in caves to tiny spaces such as fissure net-
works in bedrock or soil pores (Culver and Pipan 2014). They are typically characterized
by the absence of light, almost 100% relative air humidity, and small temperature fluc-
tuations over a year (Badino 2010). Animals fully adapted to subterranean habitats, e.g.,
those demonstrating depigmentation, reduced eyes, and other so-called troglomorphic
traits, are sometimes caught by pitfall traps also on the surface but usually as singletons
and only during the humid and cold season (Czech Arachnological Society 2022). Some
subterranean habitats in central Europe are already well-studied from an arachnological
point of view, especially caves or scree slopes (Ruzicka et al. 1995; Ruzicka et al. 2012).
Caves and scree slopes provide relatively large spaces and thus can be inhabited by
troglomorphic spiders like Bathyphantes eumenis buchari Ruzicka, 1988 (Ruzicka 1988)
and Meta menardi (Latreille, 1804) (Mammola and Isaia 2014). In contrast, the arach-
nofauna of shallow subterranean habitats within coarse substrata, which are difficult to
access, is poorly studied (Mammola et al. 2016). Shallow subterranean habitats are areas
of habitable space that are less than 10 m in depth from the surface. These range from
large areas such as shallow caves and lava tubes, to tiny areas such as cracks in ceilings,
or spaces in soil (Culver and Pipan 2014). Different authors have used perforated pipe
traps with one cup on the bottom to sample invertebrates in shallow subterranean habi-
tats and deep soil strata (e.g., Lopez and Oromi 2010; Deltshev et al. 2011; Jiménez-
Valverde et al. 2015; Mammola et al. 2017; Ledesma et al. 2020). Conversely, Schlick-
Steiner and Steiner (2000) constructed a trap consisting of a perforated pipe and a set of
removable plastic cups situated on a central metal axis. The cups collect animals entering
the pipe through holes at different depths, allowing to study the vertical distribution
of arthropods in shallow subterranean habitats. For example, this trap design has been
used to study the vertical distribution of spiders in soil and fissured rock (LaSka et al.
2011; Ruzicka and Dolansky 2016), and springtails (Rendos et al. 2016; Jurekova et al.
2021), and myriapods (Halkova et al. 2020) in forested scree slopes.

In this study, we employed stratified pipe traps to explore spider fauna in soils,
gravel, and loess (up to two meters in depth) on bedrock known to harbor fissure
networks. The study aimed to describe the vertical distribution of spiders in these
unique subterranean ecosystems and to describe species’ preferences for certain types
of substrates (microhabitats).

Materials and methods
Study sites
The research was carried out at ten sites in Czechia (Table 1, Fig. 1). In one site, Su-

chomasty, we documented temperature fluctuations measured by dataloggers Tinytag
Ultra2 every three hours at the maximum sampling depth and on the surface (Fig. 5).

Spiders in shallow subterranean habitats 3

Figure |. Locations of the study sites in Czechia. 1 — Kostelni Biiza, 2 — Rana, 3 — Suchomasty, 4 —

NebusSice, 5 — Ctinéves, 6 — Hostovice, 7 — Mravin, 8 — Pouzdiany, 9 — Dolni Véstonice, 10 — Kurovice.

For details, see Table 1.

Table |. Characteristics of the study sites. n — number of pipe traps.

Site Coordinates Altitude [m a.s.l.]/average
annual temperature

Kostelni Briza 50.1119°N, 570/7 °C
12.6349°E

Rana 50.4067°N, 250/9 °C
13.7450°E

Suchomasty 49.9062°N, 405/8 °C
14.0667°E

Nebu8sice 50.1019°N, 350/9 °C
14.3050°E

Ctinéves 50.3707°N, 265/9°C
14.3180°E

Hostovice 50.0093°N, 230/9°C
15.8509°E

Mravin 49.9445°N, 315/9°C
16.0516°E

Pouzdiany 48.9429°N, 290/10 °C
16.6430°E

Dolni Véstonice 48.8856°N, 205/10 °C
16.6562°E

Kurovice 49.2736°N, 305/9°C

17.5249°E

n/pipe

length
2/110 and

80 cm

1/110 cm
3/200 cm

1/110 cm

2/120 cm

1/130 cm

2/120 cm
2/90 cm
1/90 cm

2/100 cm

Years

2017-
2021

2014—
2016

2015—
2020
2017-
2021

2019-
2021

2015—
2018

2013-
2021
2017-
2021
2019-
2022
2013-
2021

Substrate Vegetation

gravel accumulation sparse Pinus sylvestris and
from a metal mine Betula pendula wood

stony rendzina soil steppe grassland
and fissure network in

sandy marlstone

Stony brown soil on Carpinion forest

limestone bedrock

stony brown soil and Carpinion forest
fissure network in sandy

marlstone (Fig. 2B)
thin ranker soil on planted Robinia wood
sandy gravel
Stony scree soil on deciduous bush
claystone bedrock

(Fig. 2C)

thin rendzina soil on oak forest
sandy marl

Thin rendzina on loess steppe grassland

bare loess deciduous bush

Thin brown soil on Carpinion forest

limestone bedrock

4 Milan Rezéé et al. / Subterranean Biology 45: 1-16 (2023)

Figure 2. A a set of plastic cups taken from the pipe trap in the Carpinus forest on limestone near

Suchomasty (photo M. Safra); the soil profile is inhabited by Porrhomma cambridgei, see Fig. 3A B a
fissure network in sandy marl near Nebusice, which was rich in Porrhomma microcavense, see Fig. 3D
(the pipe trap was ten meters from this quarry wall) (photo M. Rezaé) C, D a scree soil near Hostovice,
which was rich in Porrhomma microps, see Fig. 3E (photo J. Dolansky) E a fissure network in sandy marl
near Mravin (the pipe trap was 200 meters from this profile) (photo J. Dolansky) F a hole for a pipe trap
near Mravin in the soil, which was rich in [berina microphthalma and P. cambridgei, see Fig. 3C (photo
J. Dolansky).

Sampling

The plastic pipes (for lengths see Table 1) had an inner diameter of 7 cm and were per-
forated by oblique, 5 mm wide cuts. Plastic cups were mounted onto a threaded metal
rod at 10 cm distances (for example, a 2-m long pipe contained 20 cups) (Fig. 2A)
and contained a solution of 6% formaldehyde with few drops of detergent (for more
details see Ruzicka and Dolansky 2016). We installed these traps in excavated holes or
boreholes (a drilling machine was used in Suchomasty) and emptied them once a year.
When we installed multiple pipes per site, each pipe was buried in a separate hole. Since
traps were buried for long periods (between 2 and 8 years depending on the site), we ex-
pect the initial mixing of the soil layers to exert a minor role in the distribution of fauna.

Spiders in shallow subterranean habitats 5

Spider identification

Spiders were sorted and examined under an Olympus SZX12 stereomicroscope in
80% ethanol. Spider identification follows Nentwig et al. (2022), and nomenclature is
in accordance with the World Spider Catalog (2022). The individuals were deposited
at the institutions of the authors. Photographs were taken with an Olympus C-5060
wide-zoom digital camera mounted on an Olympus BX40 microscope. The images
were processed using CombineZP image stacking software.

Relation to subterranean habitats

We classified the affinity of particular species to subterranean environments according
to their vertical distribution. Further, we considered (1) morphological adaptations
for subterranean life, (2) habitat, where they were found so far, (3) pattern of their
distribution (common or rare on the surface habitats), (4) what environment they
need for their lifestyle (see column “relation to the subterranean habitat - RSH” in
Table 2). Morphological features, in particular depigmentation and a reduction in
eye size, were recorded during identification, and the carapace size data were taken
from the literature (Merrett et al. 1993; Weiss 1996; Razi¢ka 2018, 2022; Sestdkova
et al. 2018; Nentwig et al. 2022). Data on spider occurrence in Czechia, habitat, and
natural history were taken from a database of records of spiders in Czechia (Czech
Arachnological Society 2022) and Buchar and Ruzicka (2002). The following catego-
ries were distinguished:

1 surface species occur only at the surface, on the ground, or in the vegetation.
Their presence underground is accidental; they possess eyes of normal size and are
normally pigmented.

2 detritus layer species live in detritus on the soil surface. They are rare in deeper
soil layers. They possess eyes of normal size and are normally pigmented. Two special
cases are within this category:

2B species with burrows in soil spend at least part of their lives in shallow bur-
rows in soil; they possess eyes of normal size and are normally pigmented.

2H species requiring high air humidity require habitats with constantly high
air humidity, regardless of whether the habitats are superficial or subterranean; they
possess eyes of normal size and are normally pigmented.

3 soil species are more common deeper in humus soil than in detritus, but they
appear on the soil surface relatively often; they are usually tiny and less pigmented,
and their eyes are relatively smaller than those of their relatives. A special case is within
this category:

3A soil ant nest species spend the majority of their lives in ant nests in the
soil; they are less pigmented, and their eyes are relatively smaller than those of their
surface relatives.

6 Milan Rezéé et al. / Subterranean Biology 45: 1-16 (2023)

4 soil-bedrock species live in the basal mineral layers of soil on eroded bedrock
surfaces (or in other spacious subterranean habitats) and appear on the soil surface very
rarely; they are pale, and their eyes are significantly reduced; they can be larger with
relatively long legs.

Data analyses

We used descriptive statistics [mean, standard error (SEM), and 95% confidence inter-
val] to assess the species’ preference for surface versus subterranean habitats, approxi-
mated via the depth of capture of each individual. In cases where the whole confidence
interval was below a depth of 20 cm (the depth of the two uppermost cups in the trap,
where the surface species can easily enter), we assumed the species to be more common
below 20 cm depth than above it (the species shown in bold in Table 2). Data were
handled in R, version 3.6.2 (R Core Team 2019).

Results

We captured 1179 adult spider specimens belonging to 76 species. In total, 17 spe-
cies were found to be more common under the surface than on the surface (shown in
bold in Table 2); singletons were not evaluated, but they are included in Table 2. Five
species occurred preferentially below 70 cm (more than 15 specimens, Fig. 3). These
were Porrhomma cambridgei, Porrhomma microps, Porrhomma microcavense, Iberina
microphthalma, and Centromerus cf. piccolo. They possessed remarkably reduced eyes
(Fig. 4). We called them “soil-bedrock species”, as they probably occur in the inter-
face between the soil and bedrock. In addition to these five species, we also considered
Pseudomaro aenigmaticus, Nesticus cellulanus, Jacksonella falconeri, Palliduphantes insignis,
Centromerus cf. minutissimus and Theonoe minutissima as belonging to this category. We
further considered eight species to represent soil species (see the chapter Relation to sub-
terranean habitats in MM for definitions of these categories: Mioxena blanda, Porrhomma
microphthalmum, Cicurina cicur, Tapinocyboides pygmaeus, Centromerus cavernarum,
Centromerus serratus, Palliduphantes alutacius, and Palliduphantes pallidus. We also re-
corded two myrmecophilous species occurring in ant nests in the soil, Mastigusa arietina,
and Syedra myrmicarum. The remaining captured species were classified as detritus layer
species (28) or as species with no relation to subterranean habitats (27).

Discussion

At least 21 species collected in our pipe traps exhibited morphological (eye reduction and
depigmentation) and distributional (rare occurrence in surface habitats and regular pres-
ence in subterranean habitats) characteristics typical of subterranean fauna (categories 3
and 4 in Table 2). Of these, twelve species were more frequent below 20 cm than on the
surface (marked bold in Table 2). The numbers of collected individuals in the remain-

Spiders in shallow subterranean habitats 7

Table 2. Vertical distribution of the collected spider species sorted according to the average depth from
the deepest point toward the surface. Depth: mean + SEM (95% confidence interval). The species that
were significantly more common in deep subterranean habitats than close to the surface are shown in
bold. n — number of specimens captured. Sites: Bri — Kostelni Briza, Cti — Ctinéves, Hos — Hostovice,
Kur — Kurovice, Mra — Mravin, Neb — NebuSice, Pou — Pouzdiany, Ran — Rana, Such — Suchomasty, Vés —
Dolni Véstonice. RSH — relation to the subterranean habitat: 1 — surface species; 2 — detritus layer species
(B — with burrows in the soil, H — requiring high air humidity); 3 — soil species (below the detritus layer,
but found relatively often on the soil surface, A — ant nest species); 4 — soil-bedrock species (basal layers of

the soil, very rarely found on the soil surface).

Species Family Depth [cm] n Geology Site RSH
Porrhomma cambridgei Linyphiidae 100 + 5.9 45 sandy marl, limestone Mra, Such 4
Merrett, 1994 (89-112)

Porrhomma microps Linyphiidae 93 + 2.0 (89-97) 156 sandy marl, limestone, Hos, Kur, Mra, 4
(Roewer, 1931) claystone Such
Porrhomma microcavense Linyphiidae 86 + 3.3 (80-93) 24 sandy marlstone Neb 4
Wunderlich, 1990
Mastigusa arietina Dictynidae 80 + 21.2 2 — sandy marl, gravel heap Bit, Mra 3A
(Thorell, 1871) (38-122)
Iberina microphthalma (Snazell Hahniidae 78 + 3.7 (70-85) 25 sandy marl Mra 4
& Duffey, 1980)
Centromerus cf. piccolo Linyphiidae 75 + 3.5 (68-82) 17 loess Pou, Vés 4
Weiss, 1996
Porrhomma campbelli ¥. Linyphiidae 69 + 2.3 (65-74) 12 gravel heap Bif 2
O. Pickard-Cambridge, 1894
Pseudomaro aenigmaticus Denis, Linyphiidae 65 + 31.8 2 gravel heap Bit 4
1966 (3-127)
Walckenaeria capito (Westring, Linyphiidae 63 + 8.0 (47-78) 8 — sandy marlstone, gravel Bri, Ran 2:
1861) heap
Mioxena blanda (Simon, 1884) Linyphiidae 60 + 23.0 3 sandy marl and Cti, Mra, Ran 3
(15-105) marlstone, gravel

Nesticus cellulanus (Clerck, 1757) — Nesticidae 50 + 0 (50) 1 claystone Hos
Robertus neglectus (O. Pickard- _Theridiidae 50 411.5 3 limestone Such e)
Cambridge, 1871) (27-73)
Porrhomma microphthalmum Linyphiidae 43+9.0 (26-61) 3 sandy marl, limestone, | Hos, Mra, Such 3
(O. Pickard-Cambridge, 1871) claystone
Cicurina cicur (Fabricius, 1793) Dictynidae 42 + 1.5 (39-45) 285 loess, sandy marl, Bri, Hos, Kur, Mra, 3

marlstone, limestone, | Neb, Ran, Such,

claystone, gravel heap Vés
Harpactea lepida (C. L. Koch, Dysderidae 4045.4 (29-51) 7 _ limestone, gravel heap Bit, Such 2H
1838)
Centromerus cavernarum Linyphiidae 40 + 14.1 2 gravel heap Bit 3
(L. Koch, 1872) (12-68)
Jacksonella falconeri (Jackson, Linyphiidae 40 + 0 (40) 1 gravel heap Bit 4
1908)
Coelotes terrestris (Wider, 1834) Agelenidae 40 + 0 (40) 1 sandy marl Mra 2B
Micrargus herbigradus Linyphiidae 39 + 3.8 (31-46) 25 sandy marl and Bit, Kur, Mra, Neb 2
(Blackwall, 1854) marlstone, limestone,

gravel heap

Palliduphantes insignis Linyphiidae 35 + 4.0 (27-43) 31 loess Pou, Vés 4
(O. Pickard-Cambridge, 1913)
Syedra myrmicarum Linyphiidae 35 + 3.5 (28-42) 2 sandy marl Mra 3A
(Kulczyriski, 1882)
Palliduphantes alutacius Linyphiidae 34 + 2.2 (30-38) 83 loess, sandy marl, Hos, Kur, Mra, Vés 3
(Simon, 1884) claystone, limestone
Palliduphantes pallidus Linyphiidae 33 + 3.9 (26-41) 35 sandy marlstone, Bri, Neb, Ran 3
(O. Pickard-Cambridge, 1871) gravel heap
Centromerus cf. minutissimus Linyphiidae 30 + 0 (30) 1 gravel heap Bit 4

Merrett & Powel, 1993

8 Milan Rezéé et al. / Subterranean Biology 45: 1-16 (2023)

Depth [cm]

Species

Family

30 + 0 (30)

Geology

Site
Bri

Metopobactrus prominulus

(O. Pickard-Cambridge, 1873)
Walckenaeria dysderoides (Wider,
1834)

Walckenaeria obtusa

Blackwall, 1836

Robertus arundineti (O. Pickard-
Cambridge, 1871)

Piratula uliginosa (Thorell, 1856)
Clubiona terrestris

Westring, 1851

Robertus lividus (Blackwall, 1836)

Agyneta rurestris

(C. L. Koch, 1836)

Histopona torpida

(C. L. Koch, 1837)

Hahnia pusilla C. L. Koch, 1841

Harpactea rubicunda (C. L.
Koch, 1838)

Theonoe minutissima (O. Pickard-
Cambridge, 1879)

Dysdera cechica Rezaé, 2018
Diplostyla concolor (Wider, 1834)

Dysdera erythrina

(Walckenaer, 1802)

Episinus truncatus Latreille, 1809
Mermessus trilobatus

(Emerton, 1882)

Tapinocyba insecta

(L. Koch, 1869)

Tapinocyboides pygmaeus (Menge,
1869)

Amaurobius jugorum

L. Koch, 1868

Trochosa ruricola (De Geer, 1778)
Phrurolithus festivus

(C. L. Koch, 1835)

Centromerus sylvaticus (Blackwall,
1841)

Trachyzelotes pedestris

(C. L. Koch, 1837)
Inermocoelotes inermis

(L. Koch, 1855)

Haplodrassus silvestris (Blackwall,
1833)

Centromerus serratus (O. Pickard-
Cambridge, 1875)

Agroeca cuprea Menge, 1873
Apostenus fuscus Westring, 1851
Tenuiphantes flavipes (Blackwall,
1854)

Euryopis flavomaculata (C. L.
Koch, 1836)

Linyphiidae
Linyphiidae
Linyphiidae
Theridiidae

Lycosidae
Clubionidae

Theridiidae
Linyphiidae

Agelenidae
Hahniidae
Dysderidae
Theridiidae

Dysderidae
Linyphiidae

Dysderidae

Theridiidae
Linyphiidae

Linyphiidae

Linyphiidae

Amaurobiidae

Lycosidae

Phrurolithidae

Linyphiidae
Gnaphosidae
Agelenidae
Gnaphosidae
Linyphiidae
Liocranidae
Liocranidae
Linyphiidae

Theridiidae

30 + 6.2 (18-42)

30 + 0 (30)

30 + 0 (30)

30 + 7.1 (16-44)
30 + 7.1 (16-44)

26 + 3.2 (19-32)
25 + 3.5 (18-32)

25 + 10.6 (446)

24 + 2.1 (20-28)

23 + 2.7 (18-29)

23 + 2.7 (18-29)

23 + 3.7 (16-30)
22 + 1.4 (20-25)

20 + 2.2 (16-24)

20 + 7.7 (5-35)
20 + 0 (20)

20 + 0 (20)

20 + 0 (20)

20 + 0 (20)
20 + 7.7 (5-35)
18 + 1.7 (15-22)
17 + 1.8 (13-20)
17 + 1.2 (1419)
16 + 3.2 (10-22)
15 + 3.5 (8-22)
14 + 2.1 (10-18)
13 + 1.4 (8-32)
13 + 0.7 (11-14)
11 + 0.5 (10-12)

10 + 0 (10)

11

—

Nn

2.

gravel heap
loess, limestone

limestone

limestone

gravel heap

sandy marl, claystone

loess, limestone

limestone, gravel heap

sandy marl

sandy marl, limestone,

gravel heap

sandy marl and

marlstone, limestone

gravel heap

loess, limestone

claystone, sandy
marlstone, limestone

limestone, gravel heap

loess

claystone
gravel
gravel heap

sandy marl

sandy marlstone

loess, sandy marl and
marlstone, limestone,

gravel heap, gravel
loess, limestone, sandy
marlstone, gravel heap
loess, sandy marlstone,

limestone, gravel

limestone, gravel heap

limestone

sandy marl

sandy marlstone, loess

limestone

loess, limestone

limestone

Kur, Such, Vés

Kur

Such

Bri
Hos, Mra

Kur, Pou, Vés
Biri, Such

Mra

Bri, Kur, Mra

Mra, Neb, Such

Bri

Kur, Pou, Vés

Hos, Kur, Neb,
Ran

Bii, Such

Bri

Mra

Ran

Bii, Cti, Mra, Neb,

Ran, Such, Vés
Bii, Neb, Ran,
Such, Vés
Cti, Kur, Ran, Vés
Bri, Kur
Kur
Mra
Pou, Ran
Kur

Kur, Such, Vés

Kur

2H

1

Spiders in shallow subterranean habitats 9

Species Family Depth [cm] n Geology Site RSH
Agyneta saxatilis Linyphiidae 10 + 0 (10) 1 loess Pou 1
(Blackwall, 1844)
Linyphia hortensis Linyphiidae 10 + 0 (10) 1 sandy marl Mra 1
Sundevall, 1830
Micrargus subaequalis (Westring, — Linyphiidae 10 + 0 (10) 1 sandy marlstone Ran 2:
1851)
Oecdothorax retusus Linyphiidae 10 + 0 (10) 1 limestone Kur 2:
(Westring, 1851)
Pelecopsis radicicola Linyphiidae 10 + 0 (10) 1 gravel heap Bit 2
(L. Koch, 1872)
Aulonia albimana Lycosidae 10 + 0 (10) ik limestone Kur 2B
(Walckenaer, 1805)
Pardosa lugubris Lycosidae 10 + 0 (10) 45 sandy marlstone, Kur, Neb 1
(Walckenaer, 1802) limestone
Pardosa riparia Lycosidae 10 + 0 (10) 5 sandy marlstone Ran 1
(C. L. Koch, 1833)
Trochosa terricola Thorell, 1856 Lycosidae 10 = 0 (10) 2 limestone Such 2B
Zora spinimana Miturgidae 10 + 0 (10) 1 limestone Kur 1
(Sundevall, 1833)
Agroeca brunnea (Blackwall, Liocranidae 10 + 0 (10) 1 limestone Kur 1
1833)
Phrurolithus pullatus (C. L. Phrurolithidae 10 + 0 (10) 1 loess Pou 1
Koch, 1835)
Zodarion germanicum (C. L. Zodariidae 10 + 0 (10) 5 limestone Kur 1
Koch, 1837)
Drassyllus praeficus (L. Koch, Gnaphosidae 10 + 0 (10) 1 loess Pou 1
1866)
Drassyllus pumilus Gnaphosidae 10 + 0 (10) 4 loess Pou 1
(C. L. Koch, 1839)
Haplodrassus umbratilis (L. Koch, Gnaphosidae 10 + 0 (10) 3 gravel heap Bit 1
1866)
Zelotes apricorum (L. Koch, Gnaphosidae 10 + 0 (10) 8 limestone Kur 1
1876)
Oxzyptila praticola Thomisidae 10 + 0 (10) 1 limestone Kur 1
(C. L. Koch, 1837)
Oxzyptila trux (Blackwall, 1846) Thomisidae 10 + 0 (10) 1 loess Pou 1
Xysticus luctator L. Koch, 1870 ‘Thomisidae 10 + 0 (10) 1 limestone Kur 1
Euophrys frontalis Salticidae 10 + 0 (10) 2 limestone Kur 1

(Walckenaer, 1802)

ing nine species were too low to demonstrate the same preference. On the other hand,
five other species, Porrhomma campbelli, Walckenaeria capito, Robertus neglectus, Harpactea
lepida, and Micrargus herbigradus, did not exhibit morphological or distributional features
(they are common in surface habitats) characteristic of subterranean fauna but were more
frequent below 20 cm than on the surface (also marked bold in Table 2). However, this
result is based on low specimen numbers. ‘The remaining species did not have any affinity
for the subterranean environment; they usually occur on the soil surface or in detritus.
‘These species probably crawled down the substrate along the pipe where the soil became
loose due to digging. Such vertical migration could have happened during autumn and
winter months when even the surface species search for suitable spots for overwintering.

10 Milan Rezéé et al. / Subterranean Biology 45: 1-16 (2023)

The main subterranean spider groups

The captured subterranean species belonged to the families Linyphiidae, Hahniidae,
Theridiidae, and Nesticidae, with Linyphiidae having the greatest abundance and spe-
cies richness. Three genera dominate in the Central European shallow subterranean
habitats: Centromerus, Palliduphantes, and especially Porrhomma. At two study sites,
Mravin and Suchomasty, Porrhomma cambridgei and Porrhomma microps were found
to occur syntopically. In both cases, the smaller P cambridgei was found deeper than
the larger P microps (Fig. 3A, C). So far, Porrhomma campbelli has been known from
the moss in wet habitats, such as peat bogs, spruce forests, and brook and pond mar-
gins (Ruzicka 2018). Here, we present the first finding of this species from subterra-
nean habitats in Czechia.

The genus Centromerus was represented by four species, two of which, C. cf.
piccolo and C. cf. minutissimus, were new to Czechia. We captured 17 specimens
of Centromerus cf. piccolo at depths of 50-90 cm in loess accumulations in south
Moravia. Previously, Centromerus piccolo had been known only from Germany
(Weiss 1996; Nentwig et al. 2022). As the genitalic morphology of our specimens
slightly differs from the illustrated type specimens of C. piccolo (Weiss 1996), we
can not exclude the possibility that this is a closely related new species. In the arti-
ficial gravel accumulation in western Bohemia, we found two Centromerus females

sueee| ° | A | B see ° | C
ieee | | ie | | el
J.) in eel
a ee 4 ow]
ee | | il eee | |||
‘ 50 50 7 5
ciel i | ean | | | |
oN) IM ie 8) I
°. | ii ROG =.) [TH
ae | CELL mee
tei: fom
see > 1004 “WE © fr005
ym parcial |
fd o =| jinn
rie ||
eee | ||
150— ? 4 O ~~ i)
et D prion stay E
i ol 7) i
woo Ml ay eal mmo | | | tt || |
“+= 50 ‘
aoe | Seti
ay ee Gelte
| 354 ttt =. | TRRRRERREEE
ff Porrhomma microps J ae i Edarteat TTT
oh. ce = 2:00 MTT
trove ae) ||) |}
—_
Pou honiipaimicrocovence =| ERE
§] Centromerus cf. piccolo
!) Iberina microphthalma [| one specimen

Figure 3. Panels show soil profiles and the depth-dependent occurrence of microphthalmic spider spe-
cies (depths in cm) A Suchomasty, soil on limestone B Véstonice, loess C Mravin, stony soil above sandy

marl D Nebusice, stony soil, and fissure network in sandy marl E Hostovice, stony soil above claystone.

Spiders in shallow subterranean habitats 11

Figure 4. Carapaces of female spider species found deep in the Czech shallow subterranean habitats

A Porrhomma microps from Hostovice B P microcavense from Nebusice C P cambridgei from Suchomasty
D lberina microphthalma from Mravin E Centromerus cf. piccolo from Dolni Véstonice. Scale bars: 0.1 mm
(photos V. Ruzicka).

30

20

10 Pee ee Above ground

== Below ground

Temperature (°C)

July 2015 January 2016 July 2016 January 2017 July 2017

Figure 5. Temperature fluctuations in shallow subterranean habitats (below ground) were minor com-
pared to temperature fluctuations on the surface (above ground). Data were collected from the study site
at Suchomasty, between 23 April 2015 to 15 April 2017, taking one measurement every three hours.
Above ground: 2.5 m above the ground, in shade. Below ground: at 2 m depth.

that are not described in the literature. Based on somatic characters (including
small body size, eye reduction, and depigmentation) and the fact that the only
Central European Centromerus species with unknown females was Centromerus
minutissimus, which were known from England, Germany (the site in southern
Saxony-Anhalt is only 200 km northwest of our site), south France and Spain (Mer-
rett et al. 1993; Cardenas and Barrientos 2011; Nentwig et al. 2022, GBIF — www.
gbif.org, INPN — www.inpn.mnhn.fr), we preliminarily determined these individu-
als to be Centromerus cf. minutissimus.

We captured three species of the genus Palliduphantes. Palliduphantes insignis has

been found in Czechia very rarely, only on the steppes on rocks or loess in warm areas

12 Milan Rezéé et al. / Subterranean Biology 45: 1-16 (2023)

(Buchar and Ruzicka 2002). We found 31 specimens at a depth of approximately 30
cm in loess. Thus, its preferred microhabitats are probably micro spaces in soil and fis-
sures in bedrock. Palliduphantes pallidus and Palliduphantes alutacius sensu Miller and
Obrtel (1975) are closely related taxa that are not morphologically clearly separated in
Czechia. Instead, there are mainly typical Palliduphantes pallidus in the western part
of Czechia, while in the eastern part typical Palliduphantes alutacius occurs, and mot-
phologically intermediate forms can be found between. This pattern probably demon-
strates the introgression of these two taxa in this territory. These species are among the
most common subterranean species in Czechia and are also often found at the surface.

Concerning the remaining subterranean linyphiid spiders, we found four species of
the subfamily Erigoninae: Jacksonella falconeri, Mioxena blanda, Pseudomaro aenigmaticus,
and Tapinocyboides pygmaeus. Singletons of these species have rarely been found on the
surface, usually in open xerothermic habitats (Czech Arachnological Society 2022). Our
data show that the main microhabitats of these species are interspaces in various substrata.

The subterranean Hahniidae spiders were represented by three species. European
records of /berina microphthalma were summarized by Ruzicka and Dolansky (2016).
Furthermore, in Czechia, this species was collected in the substratum on claystone, sandy
marlstone, or sandy marl (Ruzicka 2022). We found 17 specimens in the soil on sandy
marl at depths of 40—120 cm (Fig. 3C). Cicurina cicur is common under stones, in leaf
litter, and decaying wood in forests, as well as in shallow subterranean habitats (Buchar
and Ruzicka 2002; Ruzicka and Dolansky 2016). Because of its morphological appear-
ance — depigmentation and small eyes — it is expected for this species to spend most of
its life in the subterranean environment, especially in southern Europe (Mammola et al.
2022). Indeed, we found it to be dominant in the studied shallow subterranean habitats.

Nesticus cellulanus is the only representative of Nesticidae, the spiders mainly oc-
curring in subterranean environments (Mammola et al. 2022). As this species is rela-
tively large, it mainly occurs in caves, scree slopes, or man-made subterranean spaces,
whereas it is rare in interspaces in the substratum.

The family Theridiidae was represented by Theonoe minutissima and some species
of the genus Robertus. Theonoe minutissima regularly occurs in scree slopes, we found
it only inside artificial gravel accumulation. Robertus species recorded during our study
are common in detritus.

Myrmecophilous species

At two sites, Kostelni Briza and Mravin, we captured the relatively large depigmented hah-
niid spider Mastigusa arietina, which is known to live in subterranean ant nests (Nentwig
et al. 2022). At the Mravin site, it was found with another myrmecophilous spider, Syedra
myrmicarum. The dominant co-occurring ant species was Lasius flavus (Fabricius, 1782).

Troglomorphism versus edaphomorphism

The body size and relative length of appendages of subterranean species may depend on
the size of the spaces they inhabit (Pipan and Culver 2017). Predictably, an elongation

Spiders in shallow subterranean habitats 13

of appendages is an adaptation to life in relatively large subterranean spaces, typically
caves (troglomorphism, Zacharda 1979). In contrast, a diminished body size repre-
sents an adaptation to life in relatively small, narrow subterranean spaces, typically
of soils (edaphomorphism, Zacharda 1979). Altogether, the species collected during
this study cover the continuum from troglomorphic to edaphomorphic species. For
example, relatively large, long-legged Porrhomma microps (carapace width 0.84 mm)
and P microcavense (carapace width 0.75 mm) represent typical troglomorphic species.
They are characteristic of the interface between soil and sandy marlstone that harbors
relatively large interspaces (Fig. 2B). Because of harsh climatic conditions during Qua-
ternary glaciations, Central Europe lacks large troglomorphic spiders, known, for ex-
ample, from Mediterranean caves (Culver et al. 2006). The most troglomorphic species
of this region are still small enough to also occur in soil (Ruzicka 1999).

The edaphomorphic species collected during this study were tiny Centromerus
(C. cf. piccolo and C. cf. minutissimus), Porrhomma cambridgei, Iberina microphthalma,
and tiny Erigoninae linyphiids, all of which have carapace widths less than 0.6 mm.
They probably live in narrow interspaces in soil or loess; however, they also occur in
deep caves (Ruzicka and Buchar 2008; Ruzicka 2018, 2022).

Preferences for bedrock and climate

Different shallow subterranean habitats presumably provide microhabitats that are
preferred by different species. Indeed, some subterranean species collected in the soil-
bedrock interface seem to exhibit a preference for specific depths and substrates. For
example, Centromerus cf. piccolo is characteristic of loess, and Porrhomma microcavense
and [berina microphthalma are characteristic of sandy marlstone. The species that oc-
cur in the surface layer of the soil seem not to express such preferences (for example,
Centromerus serratus, C. cavernarum, Mioxena blanda, Palliduphantes spp., Porrhomma
microphthalnum, P microps, Tapinocyboides pygmaeus, Cicurina cicur).

The fauna of shallow subterranean habitats seems to be richer in warm areas than
in cold ones. The species Centromerus cf. piccolo, Mioxena blanda, Palliduphantes in-
signis, Porrhomma cambridgei, and [berina microphthalma are restricted to the warmest
regions of Czechia. Additionally, vegetation can be expected to modify the temperature
regime in the soil. A large number of the soil species found during this study live in
substrates that occur in partly open xerothermic habitats (for example, Centromerus cf.
piccolo, Palliduphantes insignis, Tapinocyboides pygmaeus, and Iberina microphthalma).
On the other hand, some species live in habitats that maintain stable humidity and
temperature, such as scree forests (e.g., Centromerus cavernarum, Porrhomma camp belli,
Theonoe minutissima).

Dispersal

Interestingly, the only artificial habitat that was studied, an almost hundred-year-old
gravel heap from a polymetallic ore mine near Kostelni Briza, harbors relatively rich
subterranean fauna. Several species with relatively small eyes, in particular Jacksonella

14 Milan Rezéé et al. / Subterranean Biology 45: 1-16 (2023)

falconeri, Pseudomaro aenigmaticus, Tapinocyboides pygmaeus, Centromerus cavernarum,

Centromerus cf. minutissimus, Palliduphantes pallidus, Porrhomma campbelli, Theonoe
minutissima, Cicurina cicur, and Mastigusa arietina were found here. Thus, at least
these species are able to colonize new isolated sites, probably by ballooning, and they
cannot be considered relics like the endemic fauna in limestone caves in the Medi-
terranean. For Pseudomaro aenigmaticus, this ability was confirmed by the capture of
specimens in aeroplankton at 12 m height (Blick and Kreuels 2002).

Conclusion

Our study demonstrates that underexplored shallow subterranean habitats in Central
Europe harbor rich subterranean spider fauna. Some of these species were considered
very rare in the past. However, we came to the same conclusion as Polenec (1970):
these species are, in fact, quite abundant in these hardly accessible and largely over-

looked habitats.

Acknowledgements

We thank Stano Pekar for assistance with the statistical analysis, Nela Glorikova for
help with the figures, and Stefano Mammola, Konrad Wisniewski, and Julien Petillon
for revising this manuscript. Milan Reza¢ was supported by the Ministry of Agricul-
ture of the Czech Republic (project MZe RO0418). Vlastimil Ruzicka was supported
by the Institute of Entomology, Biology Centre, Czech Academy of Sciences, project
RVO: 60077344. Research in Suchomasty was allowed and technically and financially
supported by the company Velkolom Certovy schody, a.s. (AP 10/33).

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