SHORT COMMUNICATION
Notes on the life history traits of Rhopalurus rochai (Scorpiones, Buthidae) under different
feeding regimes
SarahM.N.Sarmento
1
, Adriano M. de Souza
1
, Marcos Vinicius Meiado
2
and Cleide M. R. de Albuquerque
1,3
:
1
Departamento
de Zoologia /Universidade Federal de Pernambuco, Avenida Morais Rego s/n, Recife – PE, CEP 50570-420, Brazil.
E-mail: cleide.ufpe@gmail.com;
2
Departamento de Botaˆnica/Universidade Federal de Pernambuco,
Recife – PE, Brazil
Abstract. Rhopalurus rochai (Borelli 1910) is a very common scorpion species found in the semiarid areas of Pernambuco
State, Brazil. This work describes the life history traits of 1
st
instar R. rochai such as litter size, development time, dispersal,
and survivorship. The development of 2
nd
instar juveniles under different feeding regimens was also investigated to
determine the effect of food and body mass on intermolt period and number of ecdyses. Field-collected females displaying
an enlarged mesosoma were observed daily in the laboratory to obtain newborns that were used to assess events in the 1
st
instar. Females gave birth on average to 35.8 young (range 5 23–55). The duration of the 1
st
instar (from eclosion to
ecdysis) ranged from 7 to 10 days (n 5 179). Dispersal started as early as one day following ecdysis and lasted up to 9 days
post-molt. All starved juveniles died between days 11 and 30 of the 2
nd
instar. Increasing food ingestion did not enhance the
probability of molting, but decreased risk of mortality and increased the time to the second molt. The relationship between
the weight changes during feeding experiments suggests that the threshold weight for molt is 34.3 mg. Together these results
suggest that developmental periods for R. rochai are slightly greater than those recorded for other buthid genera. These
results indicate that there may be inherent physiological costs associated with rapidly increasing mass that may strongly
impact foraging strategy.
Keywords: Development time, dispersal time, scorpion, starvation, molt
The genus Rhopalurus (Thorell 1876) belongs to the family
Buthidae which, along with Liochelidae, Euscorpiidae, Chactidae,
and Bothriuridae, forms the Brazilian scorpiofauna (Soleglad & Fet
2003). Nine species of this genus (Lenarducci et al. 2005) are known in
Brazil and occur in the Central and Northeast regions within the
cerrado (Brazilian savannas) and caatinga (Lourenc¸o 1986). Despite
numerous studies on the taxonomy and biogeography of Rhopalurus
(Mello-Leita˜o 1945; Lourenc¸o 1986; Lourenc¸o & Pinto-da-Rocha
1997; Manzanilla & De Sousa 2003; Lenarducci et al. 2005), there is
little information on its reproduction, postembryonic development,
and nutrition.
The reproductive fitness of females and individual life span are
important factors in establishing the population size of a species. The
number of offspring produced by a female is one measure of
reproductive fitness, and there may be a positive or negative
correlation between litter size and female body mass (Lourenc¸o et
al. 1996). The duration of postembryonic development is a key factor
in determining generation time, with shorter durations lowering the
risk of mortality before reaching reproductive maturity and enhanc-
ing individual fitness. On the one hand, this type of growth is
frequently associated with higher feeding and food assimilation rates
in conjunction with a more efficient conversion of food into biomass
(Danner & Joern 2003; Branson 2004; McPeek 2004; Stoks et al.
2005). On the other hand, longer development cycles are generally
associated with low mass-accumulation rates and higher reproductive
costs, such as delayed sexual maturation (Stearns & Koella 1986;
Higgins & Rankin 1996; Higgins 2000) and a higher risk of mortality
before reaching adulthood (Higgins & Rankin 1996).
Food availability in the field is influenced by seasonal variation,
and food shortage is a constraint that terrestrial invertebrates often
have to contend with. Such a shortage is likely to affect survival (Iida
& Fujisaki 2007) and reproductive output (Bauerfeind & Fischer
2005), particularly in arthropods with long life cycles. Being animals
with an extended life span, range 5 6–83 months (Polis & Sissom
1990), scorpions will suffer the impact of environmental variation in
food availability. These animals are widely distributed throughout the
world, but nutritional bases for scorpion growth and development are
usually under-investigated. Even the baseline data on their nutritional
needs for survival or molting are lacking.
We describe in this paper some observations about the litter size,
dispersal time, and 1
st
instar duration and survival of R. rochai and
compare this information to available data on other genera of
Buthidae. Considering that nutrition is an important aspect in
determining growth and development in an organism, the effects of
body mass and molting for individuals during 2
nd
instar development
are also presented.
METHODS
Females of R. rochai (n 5 5) were collected in Limoeiro
municipality in the Agreste Mesoregion and Medio Capibaribe
Microregion of Pernambuco State, Brazil (area 5 277.54 km
2
;
07u529290 S, 35u279010 W; 138 m elev.), 90.9 km from the state
capital, Recife. The climate is wet tropical with dry summers. The
rainy season starts in January/February and ends in September, but
may last until October. The specimens were collected under
accumulations of rocks from soil preparation for corn and bean
cultivation or from pastures at sites with rock outcrops and low-
height deciduous and semi-deciduous plants typical of the agreste
(Beltra˜o et al. 2005). Pregnant females (displaying a dilated
mesosoma) were kept in individual plastic containers (8.5 cm
diameter 3 7.8 cm high) with an assay tube containing cotton soaked
in water and a cardboard piece for shelter. They were fed adult
Periplaneta americana (Linnaeus 1758) once every 15 days. In the
laboratory, the temperature was maintained at environmental
conditions of 28u 6 3u C with 12L:12D photoperiod. Observations
were made daily to record the period in which the young were born
3
Corresponding author. E-mail: cleide.ufpe@gmail.com
2008. The Journal of Arachnology 36:476–479
476

and to determine litter size, interval between birth and 1
st
ecdysis,
dispersal time and number of individuals that molted into the 2
nd
instar. Because the offspring clustered on the female dorsum making
an exact count very difficult, litter size was considered as the total
number of individuals recorded after dispersal. Every living and dead
individual was counted except for those that were cannibalized by the
female.
The relation between feeding and molting was studied in a group of
38 juveniles in the 2
nd
instar that were obtained from the litters of two
females. Just after dispersal, scorpions were weighed and divided into
three groups: not fed (n 5 10); fed once/week (n 5 13); fed three times/
week (n 5 15). In each group, scorpions were weighed before and
after feeding, including those that did not feed. One prey item (1
st
instar nymph of P. americana, approximately 5.50 6 0.90 mg) was fed
to each juvenile each time. The difference between final mass and
initial mass was used to determine the influence of feeding on molting
success, survival and intermolt period in these groups. Juveniles from
the unfed group were weighed at the beginning of the experiment and
after death.
The biomass growth of scorpions fed once and three times per week
was compared using a Student’s t test and the mortality of the two
groups was evaluated using a x
2
test. Correlations between initial
biomass and intermolt period, as well as between initial biomass and
life span of the food-deprived individuals, were tested using Spearman
correlation because the data were not normally distributed. The
normality and variance homogeneity of the data were tested using
Shapiro-Wilk and Levene tests, respectively. All tests were conducted
with STATISTICA 7 software with a significance level 0.05. Voucher
specimens are deposited at the Entomological Collection of the
Laboratory of Terrestrial Invertebrates, Universidade Federal de
Pernambuco, Brazil. Most specimens were alive at the time this
manuscript was completed, and they will be deposited at the same
place as soon as they die.
RESULTS
Litter size.—The average number of recorded offspring in R. rochia
was 35.8 6 12.11 individuals (range 5 23–55) (Table 1). Cannibalism
by the female was recorded only at the moment of birth in four out of
the five observations. It was not possible to determine the number of
cannibalized stillborns due to the difficulty of viewing the act once the
offspring were hidden by the pedipalps. However, it was possible to
observe that the cannibalized offspring showed a highly softened,
sometimes wrinkled tegument and small size when compared to those
on the dorsum.
First instar duration and dispersal time.—Litter size, 1
st
instar
duration, survival, and dispersal of R. rochai offspring are shown in
Table 1. The first molt was assessed in 179 individuals from different
litters and occurred on average 9 days after birth (range 5 7–10 days)
and occurred on the same day in all individuals from the same brood.
Dispersal started 1–3 days after the 1
st
molt and was completed 4–
9 days after that. Occasionally, juveniles were observed to climb down
from the mother’s back. No dead scorpions were found during the 1
st
instar period, and all juveniles reached the first molt.
Effects of starvation and feeding on body mass and molting.—Mean
mass variation, intermolt period, and molt frequency of R. rochai
under different feeding treatments and mass variation during
starvation are shown in Table 2. Overall mean body mass just after
juveniles climbed down from their mother’s dorsum was on average
16.43 6 1.28 mg (ranging 5 12.3–18.7 mg). The initial biomass was
not correlated with total life span in food-deprived animals (r 5 0.18,
P 5 0.61) (Fig. 1A). Among these individuals, none (n 5 10) reached
the 2
nd
molt, with mortality occurring between 11 and 30 days after
the 1
st
ecdysis. The biomass lost during food deprivation was on
average 2.8 mg (range 5 2–4 mg) with the lowest mass of 10.5 mg
and highest 14.7 mg. No relationship was observed between initial
biomass and weight loss. Feeding more often did not influence
molting success but did extend the intermolt period (fed once per
week: r 520.34, P 5 0.36, and fed three times per week: r 5 0.59,
P 5 0.04) (Fig. 1B, C). The scorpions fed three times per week
showed a greater biomass increase (53.0 6 13.2 mg) when compared
to those fed only once (45.0 6 4.1 mg), though this difference was not
significant (t 521.73, df 5 16, P 5 0.10) (Fig. 1D). In the group fed
once per week, the minimum weight for molting was 39.6 mg and the
maximum was 51.8 mg, while in the other group the minimum was
34.3 mg and the maximum was 79.9 mg.
Mortality was 30.8% (n 5 4/13) among those fed once per week and
40.0% (n 5 6/15) among those fed three times per week. No
significant difference was found in mortality between groups fed once
or three times per week (x
2
5 0.18; df 51; P 5 0.67). In the former
group, 100% of the deaths occurred during intermolt, while in the
latter 20% were recorded during ecdysis. The mean intermolt period
increased 22.48 days in the group fed more often, varying from 169.77
6 28.97 days in the group fed only once per week to 192.25 6
44.60 days in the group fed three times per week (Table 2).
DISCUSSION
Most reproductive traits, such as litter size, 1
st
instar duration,
dispersal time, and survivorship show a large variation among
scorpion species (Polis & Sissom 1990). Average litter size of R. rochai
recorded in this study (approximately 36 young) is one of the largest
brood sizes yet described for buthid scorpions. Females from most
buthid species give birth to fewer than 27 young (see summary by
Lourenc¸o 2002). A previous study (Matthiesen in Polis & Sissom
1990) has described litter size having range 5 28–49 individuals in R.
rochai. The difference in the number of offspring relative to our
findings (23–55 young) may indicate adaptation to microvariation in
Table 1.—Litter size, first instar duration, survivorship and
dispersal of Rhopalurus rochai offspring from wild-caught pregnant
females maintained in the laboratory.
Number
of individuals/
litter
Interval between
birth and 1
st
molt (days)
Dispersal
time (days)
Survival ratio
of 1
st
and 2
nd
molts (%)
34 9 2–9 100
29 8 3–5 100
55 7 2–8 100
23 10 1–6 100
38 8 2–4 100
Table 2.—Mass variation, intermolt period and molt frequency of Rophalurus rochai during starvation and different feeding patterns. Final
mass for starved juveniles was considered by weighing individuals after death. For other groups, final mass 5 offspring mass before molt or at
death during molt.
Feeding regime
Initial Mass
(mg)
Final Mass
(mg)
Mass lost during
molt (mg)
Molt frequency
(%)
Molt interval
(days)
Starvation (n 5 10) 15.04 6 1.36 12.60 6 1.28 - - -
Feeding once (n 5 13) 17.00 6 1.04 45.01 6 4.14 7.7 6 4.36 69.2 169.77 6 28.97
Feeding three times (n 5 15) 17.03 6 0.99 53.04 6 13.56 3.44 6 3.46 60.0 192.25 6 44.60
SARMENTO ET AL.—R. ROCHAI LIFE HISTORY TRAITS AND NUTRITION 477