20th International Congress of Arachnology

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DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
of Topographic and Clinical Anatomy, University
of Bern, CH-3012 Bern, Switzerland; 3Institute of
Ecology and Evolution, Division of Community
Ecology, University of Bern, CH-3012 Bern, Switzer-
land; 4Natural History Museum Bern, Department of
Invertebrates, CH-3005 Bern, Switzerland
Males of several scorpion species possess bigger telsons
than females. In some of these species males repeatedly
sting females during mating. This behavior (“sexual
stinging”) is likely correlated with a sexual dimorphism
in telson and venom gland size. As natural selection
theory predicts bigger female venom glands (females
need more nutrients for their offspring), we hypothesise
that this sexual venom gland dimorphism evolved under
sexual selection in relation to the male’s sexual stinging
behaviour. We investigated morphometrics and morphol-
ogy of male and female telsons and venom glands by
means of light and transmission electron microscopy in
the sexually stinging scorpion Euscorpius alpha (Eus-
corpiidae). Male telsons are significantly bigger and more
voluminous than those of females. In the compound light
microscope and transmission electron microscope, five
different secretory cells can be distinguished with their
representation varying considerably between sexes. While
female secretory epithelium consists mainly of cells filled
by granules, males carry mainly cells containing dissolv-
able vesicles. This cell type likely produces transparent
venom that had been identified in other scorpions as
so-called “prevenom”. The function of this secretion is
discussed in relation to sexual stinging behaviour.
Keywords: sexual stinging, sexual dimorphism, venom
gland, scorpion
Student - oral presentation
Developmental genetics of respiratory
structures in Arachnopulmonate and non-
Arachnopulmonate Orders
*Emily V. W. Setton, Holly Cho, Prashant P. Sharma
Department of Zoology, University of Wisconsin-
Madison, 420 Lincoln Drive, Madison, WI 53706, USA
Understanding of the developmental genetics of arthro-
pod respiratory system is currently limited to the fruit fly
Drosophila melanogaster. The tracheal tubule complex
of D. melanogaster is initially formed by the invagination
of segmentally iterated tracheal placodes in the pleural
regions of abdominal segments. Arachnids represent a
separate case of terrestrialization from insects, and the
developmental origins of arachnid book lungs and tra-
cheal tubules have not received comparable attention.
We examined the development of respiratory primordia
in embryos of a scorpion, a harvestman, and a spider. We
used in situ hybridization and confocal microscopy to
examine the relative placement of respiratory placodes
and assay gene expression of candidate genes that are
critical to tracheal fate specification in D. melanogaster.
Here we show that the respiratory primordia of arachnids
are not positionally homologous to those of insects, as
they occur within the posterior region of the embryonic
parasegment, demarcated by the expression boundary of
the segment polarity gene wingless. Furthermore, we show
that orthologs of tracheal inducer gene tracheal-less are
not expressed in cells of arachnid respiratory organs. These
data suggest that mechanisms of respiratory system devel-
opment are not homologous in insects and arachnids.
Keywords: Scorpiones, book lung, tracheal tubule,
Araneae, Opiliones, evo-devo, homology
Student - poster presentation
Variation in total mercury content among
riparian and non-riparian wolf spiders
*Hailey Shannon1, Derek Wilson1, Tara Barbarich1 ,
Brian Mangan2 , Matthew Persons1
1514 University Avenue, Susquehanna University,
Selinsgrove, PA 17870, USA; 2133 North River Street,
King’s College, Wilkes-Barre, PA 18711, USA
Mercury is a persistent environmental contaminant that
primarily originates from coal-fired power plants. Methyl-
mercury biomagnifies as it moves through food chains,
reaching toxic levels in apex predators. Wolf spiders can
concentrate mercury at high levels, sometimes exceeding
levels found in fish. Since these spiders occupy positions
20th International Congress of Arachnology