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Lycosidae: The grassland spiders

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The hypothesis is formulated that the Lycosidae co-evolved with grassland and dispersed with the expansion of this type of habitat. Arguments that sustain this view are the abundance of Lycosidae in open habitats with low vegetation and their relative rareness in dense forest, the lack of typical hunter adaptations to achieve grip on smooth surfaces and the fact that the family is only known in the fossil record from the Miocene onwards, which is in synchronization with the spreading of grassland.
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EuropEan arachnology 2005 (Deltshev, C. & Stoev, P., eds)
Acta zoologica bulgarica, Suppl. No. 1: pp. 125-130.
1 Invertebrate non-insects section, Royal Museum for Central Africa, B-3080 Tervuren, Belgium. E-mails:
rudy.jocque@africamuseum.be, malderweireldt@hotmail.com
Lycosidae: the grassland spiders
Rudy Jocqué1, Mark Alderweireldt1
Abstract: The hypothesis is formulated that the Lycosidae co-evolved with grassland and dispersed with the
expansion of this type of habitat. Arguments that sustain this view are the abundance of Lycosidae in open
habitats with low vegetation and their relative rareness in dense forest, the lack of typical hunter adaptations
to achieve grip on smooth surfaces and the fact that the family is only known in the fossil record from the
Miocene onwards, which is in synchronization with the spreading of grassland.
Key words: adaptation, grip, Miocene, Araneae, Pisauridae
Introduction
Lycosidae or wolf spiders are a clearly delimited and well dened spider family both on somatic
and behavioural characteristics. They have a unique eye pattern and a typical egg sac and spider-
lings carrying behaviour. However, their systematics are particularly problematic because of the
often faint distinctions between the different taxa, on specic as well as generic level. It has been
suggested (aldErwEirEldt, Jocqué 1992, wundErlich 2004) that Lycosidae are a family of recent
evolutionary origin. Taxonomic revisions have in several cases been problematic as confronted
with particular difculties in species and genus delimitations and diagnoses (e.g. aldErwEirEldt
1996, 1999, aldErwEirEldt, Jocqué 1992, 2005). From these studies ample indications are found
that at least certain groups of Lycosidae apparently demonstrate recent speciation processes.
But apart from these indications resulting from the taxonomic approach, no data have been
put forward to support this opinion. The present paper is the rst one that gathers a series of argu-
ments to defend the recent origin of the family mainly based on the indications that Lycosidae are
particularly well adapted to grassland habitats. It is hypothesised that Lycosidae have co-evolved
with that type of vegetation.
Habitat preferences
The idea of promoting Lycosidae to the “grassland spiders” par excellence comes mainly from our
experience with soil dwelling spiders in tropical as well as temperate habitats. Especially during
eld work in tropical Africa, some striking observations were made that asked for explanation.
An example:
During our sampling campaigns (Jocqué et al. 2005) in the frame of a forest rehabilitation
project in Ivory Coast (West Africa), we were confronted with the fact that Lycosidae, despite
being a very widespread and very speciose spider family in Africa, are particularly scarce to even
absent in dense (primary) forest. We were at rst looking for a representative of the Lycosidae as
indicator species in monitoring for several reasons. Many Lycosidae are diurnal and very active
and therefore easy to spot and observe. As the females carry the egg sacs attached to the spin-
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EuropEan arachnology 2005
nerets, these are easily collected during the reproductive season. The number and the size of the
eggs can be used as good parameters to estimate the tness and general condition of the parents
and their populations (e.g. aldErwEirEldt, MaElfait 1988, BontE, MaElfait 2001, hEndrickx
et al. 2003). However, surprisingly, Lycosidae appeared to be rather rare in the forests of eastern
Ivory Coast in contrast to the nocturnal Ctenidae, which proved to be absolutely ubiquitous. In
areas where the forest canopy was opened, even locally, and were grasses (Poaceae) had formed
a thin herb layer, Lycosidae (mainly Pardosa injucunda o.p-caMBridgE) made their appearance.
In locations devoid of grasses, Lycosidae remained absent. Several pitfall trap studies demonstrate
that Lycosidae have been found to be the dominating spider group in a wide range of habitats.
russEll-sMith et al. (1987, 1999), Van dEr MErwE, dippEnaar-schoEMan (1996), warui et al.
(2005) found them to be the dominating family in African savanna habitats. They are also abun-
dant in other herb dominated vegetations such as swamps, but are particularly scarce in densely
forested habitats.
Similar observations were made in forests in Congo D.R. near Kisangani (Juakaly, pers.
comm.), Gabon (Pauwels, pers. comm.), Malawi, Comoros, Rwanda, Guinea and Equatorial
Guinea (own observations). More or less the opposite seems to be true for Ctenidae. Figs 1 and
2 summarise some pitfall data for Lycosidae in a gradient of different habitat types. In nocturnal
transects, along which spiders with grate-shaped tapeta were caught according to a distance sam-
pling protocol (Jocqué et al. 2005), lycosids were so rare in the dense forest patches, that it was
decided to concentrate on Ctenidae alone. Lycosidae numbers increase with the area covered by
the herb layer which is negatively correlated with the degree of canopy closure. The tendency in
Ctenidae is exactly the opposite. The less degraded the forest, the more abundant they become.
Lycosidae and Ctenidae thus seem to counterbalance each other in a habitat gradient. The propor-
tion of Lycosidae/Ctenidae might therefore be an excellent and easy to use indicator for forest
quality (see Jocqué et al. 2005).
About webs, claws and claw tufts
Lycosidae versus Ctenidae
Jocqué (1995) and dippEnaar-schoEMan, Jocqué (1997) attracted the attention to the fact that
there is a tendency in spiders to abandon the habit of webbing and return to the hunting strategy.
The majority of spider species are indeed hunters. In almost all spider families consisting of
mainly web building spiders, there are taxa that have switched to a hunting way of life (e.g. al-
dErwEirEldt 1994; overview in Jocqué 1995). As far as known, these almost invariably belong to
the more derived taxa. Lycosidae are an excellent example of this tendency. The more ancestral
taxa in the family are purely web-inhabiting. Among these are Hippasa, Aulonia and Amblyo-
thele. But the majority of the wolf spiders have turned into a purely hunting life style. Typical
for web building spiders is the presence of three tarsal claws: one dorsal pair of large claws, and
one smaller, more ventrally inserted, unpaired claw. This is shown on the scanning EM picture
in Fig. 3a. The third tarsal claw appears to be an adaptation for life on a web and is present in
almost all webbing spiders.
Most hunting spiders on the other hand have lost the third claw and many have developed
extensive scopulae and well developed claw tufts, as shown in Fig. 3b. The latter provide the own-
ers with a perfect grip on smooth surfaces (Fig. 3d) thanks to the so called “Van der Waals forces”
(kEsEl et al. 2003). These forces are based on the dipole-dipole attraction between large molecules
provided there is close contact between them. The tips of claw tuft setae are nely divided, resulting
in several hundreds of thousand of contact points between the leg tip and the substrate.
Ctenidae are a perfect example of a family with very well developed claw tufts. This ad-
aptation makes them very well equipped to move over very smooth surfaces such as forest tree
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R. Jocqué & M. Alderweireldt: Lycosidae: the grassland spiders
leaves. For some species, e.g. Petaloctenus (see Jocqué, stEyn 1997), the leaves of forest tree
saplings is their preferred substrate. In these tropical forests, tree leaves are very smooth (Fig. 3d)
and provided with a drip tip to evacuate excess of water in order to prevent algal growth (wolfE
1985, wolfE, upchurch 1986, 1987). Lycosidae on the other hand, are not equipped with such
an adaptation like claw tufts and are as a consequence rarely seen on forest leaves. However,
most grasses and many herb species have either a rough surface (Fig. 3c) or are provided with
an extensive layer of hairs. In many cases this is an adaptation to prevent excessive transpira-
tion. But on such a surface a claw tuft is useless for good grip. In contrast to this, claws provide
a much better adherence and it is therefore easily understood why Lycosidae move remarkably
easy over herbs and grasses.
Fig. 1. Number of Lycosidae captured during a two-year trapping cycle in ve stations with different tree
density in eastern Ivory Coast (Jocqué, unpublished).
Fig. 2. Number of Lycosidae captured during a one-year trapping cycle in ve stations with different tree
density in eastern Congo D.R. (Juakaly, unpublished)
0
100
200
300
400
500
600
700
0
20
40
60
80
100
Canopy closure
Lycosid abundance
100
200
300
400
500
600
700
20
40
60
80
100
Canopy closure
Lycosid abundace
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EuropEan arachnology 2005
This reasoning is conrmed by observing actively hunting, non-web building members of the
Pisauridae (e.g. Charminus, Cispius, Pisaura). They also have retained the third claw and wander
around on herbs, grasses and lower bushes. Pisauridae are indeed spiders of the lower shrub and
upper herb layer par excellence although one clade including Thalassius, Dolomedes, Hygropoda
and Hypsithylla, appears to have developed shing behaviour. However, they also hide in high
shrubby vegetation during periods of inactivity. This explains why Pisauridae are rare or absent
in pitfalls but are frequently caught in pan traps and Malaise-traps. The nursery webs of Pisaura
for instance are most often constructed in high grasses or between branches of low bushes with
rough surfaces. Claw tufts are useless in these conditions, while the third claw proves crucial to
move easily through this kind of vegetation. Just like Lycosidae they are absent in higher strata
and only very exceptionally found in canopy fogging samples (De Bakker, pers. comm.).
The fossil record
Recent studies of the presence of the spider families in the fossil record are particularly instructive.
The fascinating study of pEnnEy (2004) shows that the rst records of Lycosidae are as recent as
the Miocene. As illustrated in his cladogram Lycosidae seem to have evolved far more recently
than most other spider families. The striking observation however is that the Miocene period is
exactly the period in which grassland habitats dominated by Poaceae have become a major habi-
tat occupying by now a large proportion of the surface of continents. crEpEt, fEldMann (1991)
summarise data about the earliest remains of grasses in the fossil record. Although grass pollen
occurs sporadically since the Eocene (salard-chEBaldaEff 1981), evidence of grassland com-
munities in Africa does not appear until the mid-Miocene, about 14 million years ago (JonEs 1997,
Fig. 3. a – tip of tarsus of a three clawed spider; b – claw tufts and scopulae; c – rough surface; d – smooth
surface.
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R. Jocqué & M. Alderweireldt: Lycosidae: the grassland spiders
rEtallack 1992). pickford (1985) provides evidence for co-evolution of some elements in the
fauna with grasses dating back from that period. Similarly, the synchronisation of lycosid radiation
and the expansion of grassland habitats can therefore be regarded as a plausible phenomenon.
The hypothesis
Combining all the observations explained above, we emit the following hypothesis: Lycosidae
originated fairly recently in the evolutionary history of spiders and were exclusive web spiders
until the Miocene. As far as the habitat structure is concerned, they had fairly simple demands as
they were providing their own substrate in the shape of a sheet web. The spreading of grasslands
from the Miocene onwards provided the Lycosidae with an excellent habitat that gave them the
possibility to spread as hunters without particular new adaptations: the combination of acute vi-
sion and their perfect grip on rough surfaces were the perfect requisites to become the grassland
hunters par excellence. Thanks to this, they were able to radiate quickly to become today one of
the most speciose families on the African continent (aldErwEirEldt, Jocqué 1994) and beyond.
It is therefore stated that Lycosidae have co-evolved with the expansion of grassland habitats and
by extension in all kinds of open habitats with short vegetation, since the Miocene.
Received: 12.12.2005
Accepted: 20.03.2006
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Lycosidae – тревните паяци
Р. Жоке, М. Алдервейрелд
(Резюме)
В настоящата статия е изказана хипотезата, че паяците от семейство Lycosidae са произлезли
съвместно с тревните съобщества и са разширили ареала си заедно с експанзията на този
тип хабитат. Аргументите, които подкрепят тази хипотеза са: обилието от представители
на това семейство в открити местообитания с ниска растителност, сравнително рядкото им
присъствие в гъсти гори, липсата на типичните ловни приспособления за улавяне на жертва
на гладка повърхност, както и фактът, че семейството е известно във фосилната летопис едва
от миоцена насам, което е в синхрон с появата и експанзията на тревната растителност.
... Based on the remarkable abundance of wolf spiders in open habitats and in the fossil record (Wunderlich 2004a), the retention of the third tarsal claw, and the conservative morphology, Jocqué and Alderweireldt (2005) proposed that Lycosidae had a relatively recent origin and had co-evolved with grasslands and, by extension, all types of open habitats. Recently, a dated phylogenetic analysis (Piacentini and Ramírez 2019) inferred that the family appeared before the expansion of grasslands and diversified (about 50 Ma) with the reduction of tropical forests and the advance of open habitats. ...
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... The biogeographic histories of Pardosa suggest that the evolution of this genus was strongly affected by grassland expansions resulting from historic climatic and environmental shifts. These findings mirror other studies highlighting the vital role of the evolution of grasslands in lycosid biogeography (Jocqué and Alderweireldt 2005;Piacentini and Ramírez 2019). ...
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... Spiders in the Zodariidae family have been reported to occur in a variety of habitats, such as rocky outcrops, montane grassland, bushveld, woodland and forest (Whitmore et al. 2002;Modiba, Dippenaar, and Dippenaar-Schoeman 2005;Foord et al. 2008;Jansen et al. 2013;Haddad 2022). However, the Lycosidae family is known to be associated with grassland and savanna habitats instead of woodland and densely forested habitats (Dippenaar-Schoeman and Wassenaar 2002;Jocqué and Alderweireldt 2005), but was indeed also found to be dominant in woodland, thicket and sand forest in Maputaland (Haddad 2022; this study), thus being able to persist in a wide range of different habitat types. Physical, vegetation and habitat structure affect the abundance and spider diversity and thus impact the makeup of the spider community structure (Jiménez-Valverde and Lobo 2007;Malumbres-Olarte et al. 2013;Dippenaar-Schoeman et al. 2018). ...
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