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Brood care and family cohesion in the tropical scorpion Pandinus imperator (Koch) (Scorpiones: Scorpionidae)

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Pandinus imperator is a forest dweller of tropical West Africa. In the field, lobserved aggregations of up to 15 individuals. In the laboratory, mixed age groups of related and also unrelated animals lived jointly in terraria rarely showing within-group aggression or cannibalism. Brood-caring behavior of the mother influenced growth rate and survival probabil-ity of the young. With birth, mothers became very aggressive. To study family cohesion in Pandinus, experiments with family groups were con-ducted. Siblings aggregated around their mother. In choice experiments with two fam-ily groups, mothers were placed in enclosures that only the young were able to enter or to leave. Second instars significantly preferred the enclosure containing their own mother. Aggression among unrelated young of the same age was not observed. Feeding experiments studied the possible advantages of long-Iasting group living with regard to enhanced success in prey capture and its effect on growth of the young. Even groups of second instars were unable to subdue large prey on their own. Sibling groups with their mother removed suffered high mortality due to starvation and canni-balism compared to groups with mothers present. Here, young grew significantly faster: they shared the prey that only the mother was able to kill and dismember. Pandinus imperator has to be considered an intermediate subsocial scorpion.
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Acta Zool. Fennic'a 190:267-272
Helsinki
21
December 1990 ISBN 951-9481-35-4 ISSN 0001-7299
© 1990 Finnish Zoological Publishing Board
XI
International Congress
of
Arachnology, Turku, Finland,
7-12
August 1989
Brood care and family cohesion in the tropical
scorpion Pandinus imperator (Koch)
(Scorpiones: Scorpionidae)
Dieter Mahsberg1
ZooloRisches Institut (lll) der Universität, RöntgenrinR 10, D-8700 WürzburR, FRG
Pandinus imperator is a forest dweller
of
tropical West Africa. In the field,
lobserved
aggregations of
up
to
15
individuals.
In
the laboratory, mixed age groups
of
related and
also unrelated animals lived jointly in terraria rarely showing within-group aggression
or cannibalism.
Brood-caring behavior
of
the mother influenced growth rate and survival probabil-
ity
of
the young. With birth, mothers became very aggressive.
To study family cohesion
in
Pandinus, experiments with family groups were con-
ducted. Siblings aggregated around their mother. In choice experiments with two fam-
ily groups, mothers were placed in enclosures that only the young were able to enter or
to leave. Second instars significantly preferred the enclosure containing their own
mother. Aggression among unrelated young
of
the same age was not observed.
Feeding experiments studied the possible advantages
of
long-Iasting group living
with regard to enhanced success in prey capture and its effect on growth
of
the young.
Even groups
of
second instars were unable
to
subdue large prey on their own. Sibling
groups with their mother removed suffered high mortality due to starvation and canni-
balism compared to groups with mothers present. Here, young grew significantly faster:
they shared the prey that only the mother was able to kill and dismember. Pandinus
imperator has to be considered an intermediate subsocial scorpion.
1.
Introduction
Only a few arachnid species exhibit social be-
havior (Buskirk 1981).
In
scorpions, 'social phases'
are normally restricted to interactions during
lFonnerly Dieter Krapf.
mating and the maternal care
of
offspring from
birth to shortly after the first molt. There are,
however, several reports
of
aggregations
in
scor-
pions in the field, consisting partly
of
unrelated
and partly
of
related individuals. These ob-
servations, summarized by Polis &
Louren~o
(1986) suggest that living in a group may be an
important feature
of
some scorpion species. The
268 Mahsberg:
Brood
care in Pandinus
imperator'
ACTA ZOOL. FENNICA Vol. 190
following study describes experiments on group
behavior in Pandinus imperator (Koch) (Scorpi-
onidae), a ground-dwelling scorpion inhabiting
rain and gallery forests
of
tropical Africa. In
Pandinus, group behavior appears to be more
highly evolved than in most other scorpions.
2. Materials and methods
Specimens
of
Pandinus imperator were collected
in a secondary forest in the Ivory Coast/West
Africa. All young used for laboratory experiments
were bred in captivity. The scorpions were indi-
vidually paint-marked. They were kept at a rela-
tive humidity
of
at least 90% and a temperature
of
23°C (night) to 26°C (day). For further details on
breeding conditions, see Krapf (1988).
Aggregation experiments with two (unrelated)
family groups
of
Pandinus (second instars and
their mother) were performed in an arena (I m2)
with four shelters
(l9x10x3
cm), one in each
corner. Before each trial, the soil in the arena was
mixed and shelters were interchanged. Late in the
afternoon, the scorpions were released into the
center
of
the arena. They were active only at night.
By sunrise, at the latest, all were hidden
in
a
shelter. To enclose an adult female, a plastic
container
of
20x20x7
cm
was turned over each
shelter. Small horizontal slits in the container
walls allowed young scorpions to enter such shel-
ters, but prevented the female from leaving them.
The females were randomly distributed into the
enclosures. The scorpions found
undereach
shel-
ter were counted about 24 ho urs after release
(specimens were never found outside a shelter).
The experiments were repeated
12
to
14
times,
and the data pooled thereafter (the experimental
conditions were always the same). Forevaluation
of
data, 'shelter
I'
always referred to the shelter
where the mother was found. The other shelters
(2,3,
and 4) were ranked
in
descending order
of
the total number
of
young which were counted in
each during the entire experiment. The observed
distribution
of
animals was tested against a uni-
form distribution.
For feeding experiments, the second instars
of
a female were randomly allotted to one of the
following groups:
a) mother present; live prey offered,
b) mother absent; live prey, and
c) mother absent; dead prey (which was killed
by
deep freezing).
For evaluation, the data
of
two parallel experi-
ments (two family groups with instars
ofthe
same
age) were pooled. The scorpions were fed adult
females
of
the Argentine cockroach B laptica dubia
(2.35±0.27 g body weight, N=66). The mean body
weight in second in star Pandinus was 0.33±0.05
g (N=34) and 29.96±6.51 g
in
adult, non-gravid
female Pandinus (N=5). Groups were separately
kept in cages (40x30x20 cm) with a water dish
and a hiding place. About once every ten days all
three groups were simultaneously offered one
Blaptica. The cages were checked daily. Cock-
roaches not eaten one day after feeding, as weil as
prey remains, were removed. Before and after
feeding, all scorpions were weighed on a Mettler
laboratory balance. Mean weight ± standard de-
viation are reported.
Table
1.
Behavioral responses of female Pandinus imperator stimulated
by
substrate vi-
brations. Eight adult females without offspring and family groups (four mothers with second
instars) were tested. Statistics: X'=97.08, df=2; P<0.0001 (mxn-contingency table).
Female behavior (% responses)
No response, Orientation Attack,
State of female escape, defense movements stinging n
Non-pregnant (N=8),
no offspring 70.3 28.1 1.6 64
Mother (N=4) with
second instars 7.8 48.4 43.8 153
ACTA ZOOL. FENNICA Vol. 190 Mahsberg: Brood care in Pandinus imperator 269
N refers to the number
of
individuals tested, n
to the numberof observations. For statistics, Mann-
Whitney V-test, Kruskal-Wallis H-test and X2-
tests were used (see Sachs 1984).
3. Results
and
discussion
3.1. Female behavior
Pandinus imperator
is
one
of
the largest extant
scorpion species, and probably the heaviest (Krapf
1988). Normally, these scorpions do not react
aggressively when touched, contrary to buthids
like Androctonus. However, after delivering its
young, the Pandinus female's behavior changes
significantly (Table I); the same was observed in
Heterometrus spp. Both scorpionids, which re-
spond very sensitively to substrate vibrations
(Krapf 1986a), were stimulated by scratching the
ground with a pair
of
pincers. Females without
young tried to escape or showed defensive pos-
tures in most cases.
In
contrast to these non-
aggressive individuals, mothers with offspring
turned quickly towards the stimulus source. In 67
of
all
153
cases, they vigorously grasped the
forceps or even tried to sting, which
is
quite
unusual for Pandinus imperator. In this situation,
intruding conspecifics were sometimes seriously
injured. Potential prey was always captured. Sur-
prisingly, young were never harmed
in
the course
of
such fights, though they often were in close
contact even with their mother' s snapping chelae.
The quick discrimination between intruder, prey,
and offspring was probably mediated by the
numerous chemosensitive hairs on the pedipalps.
Chemoreception
of
prey in scorpions following
contact with the chelae has been demonstrated
earlier (Krapf 1986b). Females
of
Euscorpius
carpathicus (L.) recognize their young through
chemical scents (Vannini et al. 1978). But, as in
most other scorpion species, maternal behavior in
Euscorpius normally ends within a few weeks,
shortly after the first molt
of
the young. In
Pandinus, however, at least under laboratory
conditions, the female tolerates young, which are
now
18
months old. They are still associated with
their mother. Especially for younger stages, the
aggressive behavior
of
the female probably pro-
vides protection from predators, which are nu-
merously reported for scorpions (Polis et al. 1981).
3.2. Family cohesion
About a week after the first molt, the second in-
stars leave their mother's back.
It
was observed
that even
in
large terraria with many hiding places
the young were norrnally found in close contact
with their mother. The aggregation tendencies
of
second instars and their mother were tested in an
arena. In the first experiment, mother and young
were free to choose one
offour
shelters (Table 2).
This experiment was repeated twelve times con-
secutively.
Of
144 young tested, 48.6% aggre-
gated under the female's shelter. The observed
distribution to the four shelters is significantly
different from a uniform distribution (X2=85.72,
dJ=3,
P<O.OOOl).
In the field, offspring probably
leave their mother rarely before finally dispers-
ing. The same is reported in the burrow-inhabiting
Scorpio maurus (L.) (Shachak & Brand 1983) and
in Didymocentrus caboensis (Williams) (Polis &
Louren~o
1986).
Did the Pandinus mother act as an attractant
that promoted aggregations
of
the young? To an-
swer this question, the female was put in an
enclosure. Table 3 shows the distribution
of
the
second instars (N= 12,
14
trials), which could
Table
2.
Aggregation behavior of a family group of
Pandinus imperator (mother with 12 second instars).
All animals were free to choose a shelter. Shelter M
is
the shelter
in
which the mother was found. After each
trial all scorpions were released into the center of the
arena; data from 12 trials are pooled.
Statistics: X'=85.72, df=3; P<0.0001 (x'-test).
Shelter no:
M=1
2 3 4 n
% aggregated 48.6 38.9 10.4
2.1
144
Table
3.
Aggregation behavior of 12 second instars of
Pandinus imperator, which were free to choose one of
four shelters. The mother was enclosed
in
shelter
M.
After each trial all young were released into the center
of the arena. Data from 14 trials are pooled.
Statistics: X'=164.24, df=3; P<0.0001 (x'-test).
Shelter no:
M=1
2 3 4 n
% aggregated 63.7 29.2 6.0 1.2 168
270 Mahsberg:
Brood
care in Pandinus
imperator·
ACTA ZOOL. FENNICA Vol.
190
~
o
""
c
<-
Cl.
Vl
-
-
o
50
~
25
W
->-
-0
§
o
102
[~;;~:·~:]th~
1
1
enclosure
N'green'
=17,
n=204
N'yellow'
=12,
n=144
27
I
empty
Fig.
1.
The distribution
01
second instars
01
two un-
related lamily groups
01
Pandinus
imperator
('green'
and 'yellow')
in
an
arena with lour shelters. The moth-
ers
01
both lamilies were each enclosed under a
shelter; two enclosures were empty. The distributions
01
'green' and 'yellow' offspring are signilicantly differ-
ent (X'=7.84, df=2, P=O.02; mxn contingency table).
freely move around the
arena_
Of
all
168
young
tested, 107 (=63,7%) preferred the mother's en-
closure_ This result differs significantly from the
expected value
(X
2=I64,24, dj=3,
P<O.OOOI).
It
suggests that the hiding place
of
the mother at-
tracts young scorpions, which appear to search for
her.
But
is
it their mother they try to find; can they
discriminate between their own and an alien
mother?
In
a choice experiment, two unreiated
family groups (female and offspring) were tested.
The specifically paint-marked second instars
of
the two families were comparable in age and size
('green':
0.333±0.034
g,
N=I7;
'yellow':
0.349±0,026 g, N=I2; V-test
of
differences in
me an weight:
z=
1.51, n,s.), The two females were
enc10sed under separate shelters. The 29 off-
spring, which never showed any sign
of
interfa-
miliar aggression, were jointly released into the
arena. The young had the opportunity to choose
between the two mothers' places and two empty
shelters, The result (pooled data from
12
trials) is
shown in Fig.
1.
The difference
in
the distribution
of
'green'
and 'yellow' instars is significant
(X
2=7.84, df=2,
P=0.02; mxn-contingency table). The offspring
of
both families aggregated
in
half (' green') and
nearly half
('yellow')
ofpossible cases (n=204
vs
n=
144) undertheir own mother' s shelter. A mother
never harmed alien offspring,
In
the field, P andinus
imperator were found
in
mixed age groups, which
at least partly appeared to be family groups.
It
is
still unc1ear whether different family groups may
occur in c10se vicinity under one log or in one
termite mound, which are the preferred shelters of
P andinus. U nder these circumstances, however, a
family-specific recognition
of
the mother may be
adaptive for the offspring, to avoid intraspecific
predation by males
or
non-gravid females (Van-
nini et al. 1978).
3.3. Feeding experiment
In
the laboratory, I often observed groups
of
older
offspring
of
Pandinus and Heterometrus jointly
killing prey. Second instars tried to attack large
insects also, but normally they did not succeed in
subduing large prey, It was assumed that the
presence
of
the mother is advantageous to the
youngs' access to food. To test this hypothesis,
sibling groups
of
Pandinus imperator, with their
mother present (a) or absent (b, c), were offered
very large prey that were live in two treatments (a,
b) and dead in the other (c), Up until this time, the
offspring had never been fed, The growth
of
the
young from the age
of
86 days to 276 days in
groups
a,
b, and c
is
shown in Fig.
2,
Most strikingly, all offspring in group (b) did
not survive past 157 days; they never succeeded in
killing a cockroach and starved to death.
In
gen-
eral, cannibalism is very low in Pandinus, but in
(b) four young were eaten by siblings (compared
to one case
of
undetermined cause
of
mortality in
group a). From the age
of
94 to
157
days, the
difference
in
the distribution
of
body weights in
groups
a,
b, and
cis
highly significant (H= 14.31 to
16.57, dj=2, P<O.OOl; H-test). There
is
no differ-
ence in me an body
weightof
group
aandc
(z=0,07
to 0,85, V-test, n.s,), Though both groups were
offered the same amount
of
food, one should keep
in mind that in group (a) the mother was present,
and she
is
about a hundred times heavier than
an
ACTA ZOOL.
FENNICA
Vo1.190·
Mahsherg:Broodcare
inPandinus
imperator 271
1.75
1.50
N=10
-12
mother
present,
live
prey
N = 8
-11
[J]
mother
ubsent,
live
prey
1.25
N=9
-11
~
mother
ubsent,
deud
prey
.....
E-
1.00
QJ
3
>-.
"t:l
~
0.75
0.50
0.25
*
*
*
*u
*
.
....
nUll,
86
94
107 119
136
1S7
176
199
231
254
276
uge [duysl
Fig.
2.
Growth and age of second instar Pandinus imperatorduring a feeding experiment. The mean body weights
of three groups are compared. The mother was present in one (black) and absent in two groups (dotted/striped).
About once every ten days all groups were offered one large adult female cockroach (Blaptica dubia), which
was
live
in
two (blackldotted) and dead (striped) in one treatment. Standard deviation of the mean is indicated by line
at top of bar. Statistics: H-test (*
P<O.001).
ear1y second instar. In fact, in the seven months
of
the experiment, the female ate very little.
On
the
other hand, the cockroaches were seized and
crushed exclusively by the mother. An analysis
of
prey remains in the field has shown that the
greatest proportion
of
Pandinus' diet consists
of
diplopods and large beetles. These arthropods are
large prey, difficult and dangerous for individual
young scorpions to subdue even in a group,
but
easily killed by adults. As shown in group c,
scorpions may feed on dead prey, too, which
probably is rarely found in nature by juvenile
scorpions. In the laboratory, groups
of
about 30
young Heterometrus spinijer (Peters) jointly fed
on dead cockroaches and even on a dead young rat
they had dragged into their shelter
(Krapf
1986a).
Dismembering the carcass was rendered possible
only by cooperation. The behavior exhibited
by
Pandinus and Heterometrus resembles the group
feeding
in the
'family
spider'
Stegodyphus
mimosarum Pavesi (Ward & Enders 1985). In this
genus, cooperative brood care is highly developed
(Seibt & Wickler 1988).
Acknnwledf!,ements. I am indebted to K.
E.
Linsenmair and
G.
A.
Polis for valuable comments on the manuscript. I
would also like to thank Petra Eichler and Loretta Rott for
technical help.
References
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R.
E.
1981: Sociality in the arachnida. -In:
Hermann,
H.
R.
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Krapf,
D.
1986a: Verhaltensphysiologische Untersuchun-
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1986b: Contact chemoreception
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imperator'
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... Kin recognition abilities may be present in scorpions. Mahsberg (1990) found in choice experiments that lab-raised juveniles of the subsocial scorpion Pandinus imperator prefer to associate with their own mother rather than with an unrelated female. Yet aggression against non-kin individuals has been reported to be very low (Mahsberg 1990). ...
... Mahsberg (1990) found in choice experiments that lab-raised juveniles of the subsocial scorpion Pandinus imperator prefer to associate with their own mother rather than with an unrelated female. Yet aggression against non-kin individuals has been reported to be very low (Mahsberg 1990). The result of the study of Mahsberg (1990), however, can also be explained by familiarity (cf. ...
... Yet aggression against non-kin individuals has been reported to be very low (Mahsberg 1990). The result of the study of Mahsberg (1990), however, can also be explained by familiarity (cf. categories in Table 7.1) because prior to the experiments the juvenile scorpions stayed with their mother until the second instar. ...
Article
More than 99 % of arachnid species are solitary, aggressive and often cannibalistic predators. A few species are social and cooperative, but they do not reach the level of eusociality found in some insects. Kin recognition is suggested to be a key feature for the evolution of cooperation and sociality and thus found predominantly in those few species. While kin recognition and social interactions are well investigated in spiders, these behaviours are understudied in other arachnid taxa. Nevertheless, social species are also known in the Acari, Pseudoscorpiones, Scorpiones, Opiliones and Amblypygi. Still, we have limited information on the adaptive value of social recognition in arachnids, how it is facilitated and maintained. While this field of research is still young, it has produced some encouraging results. This chapter reviews the knowns and the unknowns of social recognition mechanisms with respect to their importance for the evolution of arachnid sociality. We will particularly focus on kin recognition and kin discrimination. First, we shortly introduce the evolution of sociality in arachnids which provides the background for the understanding of the different recognition and discrimination mechanisms explained subsequently. Further, we illustrate the interspecific discrimination abilities of arachnids, and present the state of the art on intraspecific recognition and kin recognition in spiders and other arachnids. This chapter illustrates that various social recognition abilities and especially kin recognition exist in social but also non-social arachnids. These mechanisms allow different species to distinguish between familiar and foreign, or related and unrelated individuals, to either support or discriminate against them. In contrast to eusocial insects, the necessity of maintaining kin recognition abilities often appears to be obscure and highly context-dependent. Thus, a generalisation of its adaptive value in arachnids is not possible. There is some evidence for the concept of kin recognition facilitating the evolutionary transition from subsocial to permanently social living. However, kin recognition has not yet been demonstrated in permanently social species and is thus subject of ongoing research. It might have been lost during evolution due to the lack of encounters with unrelated individuals in permanent arachnid societies or replaced by direct benefits of cooperation. Finally, we discuss some research gaps and new approaches to improve the knowledge of the adaptive significance of kin recognition in arachnids.
... For example, Scorpio maurus palmatus (Ehrenberg, 1828) reaches densities of 29-54 per 100 m 2 in the Negev Desert of southern Israel Polis and Lourenço 1986). Low levels of dispersal also represent the evolutionary precursor for advanced subsocial behaviour, which has been documented in some species of Heterometrus and Pandinus (Polis and Lourenço 1986;Mahsberg 1990;Kriesch 1994;Shivashankar 1994). ...
... Unlike Opistophthalmus, no described species of Pandinus exhibits psammophilous or lithophilous adaptations.The ecology, behaviour and ecophysiology of P. imperator have been extensively studied (e.g. Toye 1970;Garnier and Stockmann 1972;Casper 1985;Mahsberg 1990). Burrows are preferentially constructed in termite mounds and under stones or logs, and may contain up to 20 individuals, with the largest nearest the entrance (Toye 1970;Polis and Lourenço 1986;Mahsberg 1990). ...
... Toye 1970;Garnier and Stockmann 1972;Casper 1985;Mahsberg 1990). Burrows are preferentially constructed in termite mounds and under stones or logs, and may contain up to 20 individuals, with the largest nearest the entrance (Toye 1970;Polis and Lourenço 1986;Mahsberg 1990). Mixed age groups of related and unrelated individuals cohabit with minimal aggression or cannibalism in laboratory terraria, and group living has been demonstrated to contribute significantly to postembryonic growth rate and survival probability, especially among kin (Mahsberg 1990;Kriesch 1994). ...
Article
A cladistic analysis of relationships among the genera of Scorpionidae Latreille, 1802—Heterometrus Ehrenberg, 1828; Opistophthalmus C. L. Koch, 1837; Pandinus Thorell, 1876; and Scorpio Linnaeus, 1758—based on morphology and DNA sequence data from loci of three genes in the mitochondrial genome (12S ribosomal DNA (rDNA), 16S rDNA and cytochrome oxidase I) and one gene in the nuclear genome (28S rDNA) is presented. The analysis makes use of exemplar species, specifically selected to test the monophyly of the genera, rather than supraspecific terminal taxa. Other methods used in the analysis are justified in the context of a discussion of current methods for phylogenetic reconstruction. Relationships among the scorpionid genera are demonstrated to be as follows: (Opistophthalmus (Scorpio (Heterometrus + Pandinus))). This reconstruction identifies Opistophthalmus as the basal lineage of the Scorpionidae, rather than the sister-group of Scorpio. Revised descriptions, diagnoses and a key to identification of the four scorpionid genera are provided, together with a summary of what is known about their ecology, distribution and conservation status.
... For example, Scorpio maurus palmatus (Ehrenberg, 1828) reaches densities of 29-54 per 100 m 2 in the Negev Desert of southern Israel Polis and Lourenço 1986). Low levels of dispersal also represent the evolutionary precursor for advanced subsocial behaviour, which has been documented in some species of Heterometrus and Pandinus (Polis and Lourenço 1986;Mahsberg 1990;Kriesch 1994;Shivashankar 1994). ...
... Unlike Opistophthalmus, no described species of Pandinus exhibits psammophilous or lithophilous adaptations.The ecology, behaviour and ecophysiology of P. imperator have been extensively studied (e.g. Toye 1970;Garnier and Stockmann 1972;Casper 1985;Mahsberg 1990). Burrows are preferentially constructed in termite mounds and under stones or logs, and may contain up to 20 individuals, with the largest nearest the entrance (Toye 1970;Polis and Lourenço 1986;Mahsberg 1990). ...
... Toye 1970;Garnier and Stockmann 1972;Casper 1985;Mahsberg 1990). Burrows are preferentially constructed in termite mounds and under stones or logs, and may contain up to 20 individuals, with the largest nearest the entrance (Toye 1970;Polis and Lourenço 1986;Mahsberg 1990). Mixed age groups of related and unrelated individuals cohabit with minimal aggression or cannibalism in laboratory terraria, and group living has been demonstrated to contribute significantly to postembryonic growth rate and survival probability, especially among kin (Mahsberg 1990;Kriesch 1994). ...
Article
A cladistic analysis of relationships among the genera of Scorpionidae Latreille, 1802—Heterometrus Ehrenberg, 1828; Opistophthalmus C. L. Koch, 1837; Pandinus Thorell, 1876; and Scorpio Linnaeus, 1758—based on morphology and DNA sequence data from loci of three genes in the mitochondrial genome (12S ribosomal DNA (rDNA), 16S rDNA and cytochrome oxidase I) and one gene in the nuclear genome (28S rDNA) is presented. The analysis makes use of exemplar species, specifically selected to test the monophyly of the genera, rather than supraspecific terminal taxa. Other methods used in the analysis are justified in the context of a discussion of current methods for phylogenetic reconstruction. Relationships among the scorpionid genera are demonstrated to be as follows: (Opistophthalmus (Scorpio (Heterometrus + Pandinus))). This reconstruction identifies Opistophthalmus as the basal lineage of the Scorpionidae, rather than the sister-group of Scorpio. Revised descriptions, diagnoses and a key to identification of the four scorpionid genera are provided, together with a summary of what is known about their ecology, distribution and conservation status.
... ♂ : 6-8 pecten teeth) and are known to often live in groups and exhibit brood care to some extent (Krapf, 1986;Mahsberg, 1990). Although morphological differences between species' pectines may lead to some structural variations in the organization of the pecten neuropil, there appear to be no definitive external pecten features that predict structure and organization of the respective neuropil compartments (Drozd et al., 2020;Melville, 2000;Wolf, 2008). ...
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Scorpions’ sensory abilities are intriguing, especially the rather enigmatic ventral comb‐like chemo‐ and mechanosensory organs, the so‐called pectines. Attached ventrally to the second mesosomal segment just posterior to the coxae of the fourth walking leg pair, the pectines consist of the lamellae, the fulcra, and a variable number of pecten teeth. The latter contain the bimodal peg sensillae, used for probing the substrate with regard to chemo‐ and mechanosensory cues simultaneously. In addition, the lamellae, the fulcra and the pecten teeth are equipped with pecten hair sensillae (PHS) to gather mechanosensory information. Previously, we have analyzed the neuronal pathway associated with the peg sensillae unraveling their somatotopic projection pattern in dedicated pecten neuropils. Little is known, however, regarding the projections of PHS within the scorpion nervous system. Behavioral and electrophysiological assays showed involvement of PHS in reflexive responses but how the information is integrated remains unresolved. Here, we unravel the innervation pattern of the mechanosensory pecten hair afferents in Mesobuthus eupeus and Euscorpius italicus. By using immunofluorescent labeling and injection of Neurobiotin tracer, we identify extensive arborizations of afferents, including (i) ventral neuropils, (ii) somatotopically organized multisegmental sensory tracts, (iii) contralateral branches via commissures, and (iv) direct ipsilateral innervation of walking leg neuromeres 3 and 4. Our results suggest that PHS function as sensors to elicit reflexive adjustment of body height and obstacle avoidance, mediating accurate pecten teeth alignment to guarantee functionality of pectines, which are involved in fundamental capacities like mating or navigation. The comb‐shaped pectines in scorpions are intriguing chemo‐ and mechanosensory organs. By using neuronal tracer and immunohistochemistry, we focused on the projection areas of mechanosensory pecten hair sensillae afferents in two species, Mesobuthus eupeus and Euscorpius italicus. We identified an extensive neuronal pathway, which includes distinct ventral neuropils, multisegmental ascending tracts, contralateral branches, and direct innervation of the third and fourth walking leg neuromeres. These results support the hypothesis that pecten hair sensillae function as sensors to elicit reflexive adjustment of body height and obstacle avoidance.
... In addition, the social structure might be of importance as well. Desert scorpions like M. eupeus are often solitary, probably by necessity when considering low prey densities and relatively high predator pressure [118], while species from tropical forests like H. petersii often live in groups [86,119]. While the numbers of peg sensillae are smaller in H. petersii compared to most desert scorpions, nothing is known about receptor complexity in any scorpion species. ...
Article
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The pectines of scorpions are comb-like structures, located ventrally behind the fourth walking legs and consisting of variable numbers of teeth, or pegs, which contain thousands of bimodal peg sensillae. The associated neuropils are situated ventrally in the synganglion, extending between the second and fourth walking leg neuromeres. While the general morphology is consistent among scorpions, taxon-specific differences in pecten and neuropil structure remain elusive but are crucial for a better understanding of chemosensory processing. We analysed two scorpion species (Mesobuthus eupeus and Heterometrus petersii) regarding their pecten neuropil anatomy and the respective peg afferent innervation with anterograde and lipophilic tracing experiments, combined with immunohistochemistry and confocal laser-scanning microscopy. The pecten neuropils consisted of three subcompart-ments: a posterior pecten neuropil, an anterior pecten neuropil and a hitherto unknown accessory pecten neuropil. These subregions exhibited taxon-specific variations with regard to compartmentalisation and structure. Most notable were structural differences in the anterior pecten neuropils that ranged from ovoid shape and strong fragmentation in Heterome-trus petersii to elongated shape with little compartmentalisation in Mesobuthus eupeus. Labelling the afferents of distinct pegs revealed a topographic organisation of the bimodal projections along a medio-lateral axis. At the same time, all subregions along the posterior-anterior axis were innervated by a single peg's afferents. The somatotopic projection pattern of bimodal sensillae appears to be common among arachnids, including scorpions. This includes the structure and organisation of the respective neuropils and the somatotopic projection patterns of chemosensory afferents. Nonetheless, the scorpion pecten pathway exhibits unique features, e.g. glomerular compartmentalisation superimposed on somato-topy, that are assumed to allow high resolution of substrate-borne chemical gradients.
... Intraspecific and heterospecific coexistence has been observed in several scorpion species, producing different levels of sociability and aggregation (Lira et al 2013). "Social phases" are normally limited to mating and maternal care of offspring from birth to shortly after the first instar (Mahsberg 1990). In some species, unrelated individuals occur together in the field, for mature males and females may share a burrow or the same ground cover during the mating season (Polis and Lourenço 1986). ...
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France Mountain is located within Overton County which is part of the Upper Cumberland region of Middle Tennessee contains only one species of scorpion, also the only species native to the state, Vaejovis carolinianus . This species is poorly researched, and little is known about its life history and ecology. The objectives of this study were to determine if female V. carolinianus prefer to form aggregations under large cover objects or seek out retreat sites where they would be the sole occupant. Based on past research, we hypothesized that females would form aggregations under large cover objects instead of being the sole occupant. A total of 32 scorpions were captured during August and September 2014. During laboratory trials, three scorpions were placed in a plywood tray containing sand substrate and three equally-sized large ceramic tiles. The scorpions were left undisturbed for a 24-hour period, after which the tiles were lifted to check for aggregations. Each group of three scorpions was in the research tray for three consecutive days. Four rounds of aggregation trials were conducted, and t-tests as well as linear regression were used to analyze the data collected. The results of the t-test showed that female V. carolinianus , when given a choice of similarly-sized large cover objects, would select a retreat site where they were the sole occupant; therefore, our initial hypothesis was rejected. Linear regression found relative humidity affected aggregation occurrence, for the largest number of aggregations occurred when the relative humidity was between 67 and 73%.
... Pandinus imperator, Koch 1842 (Scorpionidae), commonly referred to as the emperor scorpion, is among the largest extant species of scorpion reaching up to 20 cm in length and 65 g in mass (Sissom 1990). They are communal animals and can live in groups of up to 15-20 individuals (Mahsberg 1990(Mahsberg , 2001. Pandinus imperator is a nocturnal hunter characterized by a pair of large pedipalps used in prey capture and defense (Casper 1985). ...
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Scorpions have comprised a significant portion of the diversity of predatory arthropods since the Late Paleozoic. Many of these animals are active burrowers today and likely have a substantial, if yet unrecognized, trace fossil record. This project involved the study of the burrowing behavior and biogenic structures of the scorpion Pandinus imperator (Scorpiones: Scorpionidae). Individuals and groups of five animals were placed into sediment-filled terrariums for 30–50 days after which the open burrows were cast and described. Additional experiments were conducted in sediments with two different moisture contents to evaluate the response to this altered environmental condition. Specimens of Pandinus imperator excavated their burrows using the first three pairs of walking legs. The burrow morphologies produced consisted of subvertical ramps, helical burrows, and branching burrows. The burrow elements were elliptical in cross section (12 cm wide × 4 cm high) with concave floors and ceilings. Decreased sediment moisture reduced the complexity of the subsurface structures and reduced the likelihood of their preservation due to gravitational collapse. Burrows of Pandinus imperator were compared to those of the desert scorpion, Hadrurus arizonensis, using nonparametric statistics and found to be distinct. Data collected from these and similar neoichnological studies can be applied directly to interpret trace fossil assemblages found in continental paleoenvironments.
... The first instars do not feed while continuing development on their mother's back; these instars rely entirely on stored maternal nutrients. The first instars from apoikogenic development are commonly weak and inactive (Williams, 1969; Shulov et al., 1960) while first instars of katoikogenic species (e.g., Pandinus imperator) have been used in choice experiments that require considerable mobility as well as chemical sensitivity (Vannini et al., 1978; Vannini & Ugolini, 1980; Mahsberg, 1990 Mahsberg, , 2001). Functioning pectines may be the basis for this sensitivity since embryos and first instars have developing peg sensilla with nerve fibers leading toward the central nervous system (Figs. ...
... It has also been proved that up to the larval moult mother-larva cohesion is maintained through tactile and visual stimuli produced by both the mother and the offspring (Vannini et al., 1978;Vannini & Ugolini, 1980). Chemical stimuli are definitely involved in larvae recognition by mothers (Torres & Heatwole, 1967;Vannini et al, 1978;Vannini & Ugolini, 1980;Mahsberg, 1990) and, probably, in substrate recognition (the mother's back) by the larvae (Ugolini & Vannini, 1983). ...
Article
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Larvae of Euscorpius carpathicus settled on conspecific adults can distinguish between males and females on a chemical basis, with females being preferred to males. The preference for different females depends on their reproductive phase, with mothers being the most preferred. E. carpathicus females offer a better chance of survival against dehydration when mothers than before parturition, and in both cases a better one than males. This proves that the water passage is an effective specialized mechanism which appears periodically and contributes (to what extent is not known) to improving larval survival, especially in dry periods and/or environments.
Article
1. Stegodyphus mimosarum, a social spider, lives in colonies which may contain hundreds of individuals. Feeding behaviour was examined with respect to feeding group size and prey size. 2. Prey were less likely to escape and were subdued more quickly when attacked by more than one spider. 3. During capture small prey were frequently bitten directly on the body whereas large prey were almost always bitten on an appendage. 4. Pulling struggles for subdued prey occurred. They lasted longest over medium sized prey. Small prey were easier to transport to the nest than medium prey and large prey were pulled by more spiders from a single retreat. 5. Spiders which had participated in a capture initially bit preferentially on the prey's head or thorax but others which joined later to feed bit at random. 6. Feeding became less efficient as group size increased and an experiment suggests that individuals injected less poison and digestive enzymes when feeding in groups.
Article
We examine the role of the sit and wait foraging strategy and of the stability and predictability of the biotic environment in shaping population biology and life history traits of the desert scorpion, Scorpio maurus palmatus. The study was carried out in a loessial plain in the Negev desert, Israel. We used a grid system (5x80 m) within the Hammada scoparia plant association. The area was divided into 1,600 squares (50x50 cm) and the presence (within 5 cm) and width of each scorpion burrow was recorded for eight years (1973–1980). It was found that: (1) Dispersal is a common phenomenon for all S. maurus palmatus age groups and takes place only after a heavy rainfall when soil moisture is high. (2) Dispersion patterns change from clumped to random as a function of age. (3) Dispersal is age specific and density dependent. (4) During the dry seasons a high percentage of the population goes into the resting stage.In order to integrate the above findings, a graphical model was constructed with the main assumption that the S. maurus palmatus prey availability relationship is a decreasing function between the scorpion burrow and its food resources. Data and model analysis led to the conclusion that the desert scorpion, S. maurus palmatus, is confronted with a relatively predictable physical environmeent and unpredictable biological environment. Two alternative strategies are available for S. maurus palmatus to overcome prey unpredictability; dispersal during the rainy season and inactivity during the dry seasons.We suggest that many other burrowing desert animals may face the problem of unpredictability of biological resources. Thus it seems that the S. maurus palmatus biological relationship model can be applied, with modifications, to a wide spectrum of desert burrowing animals.
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Verhaltensphysiologische Untersuchungen zum Beutefang von Skorpionen mit besonderer Berücksichtigung derTrichobothrien. -Doctoral thesis
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Angewandte Statistik
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