20th International Congress of Arachnology

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DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
20th International Congress of Arachnology
Keywords: black widow, cellar spider, dragline, major
ampullate silk glands, morphology, silk proteins, spider silk
Oral presentation
Do all spider genital components respond
to sexual selection?
Ren-Chung Cheng1, Matjaž Kuntner1,2
1Institute of Biology, Scientific Research Centre of Slove-
nian Academy of Sciences and Arts, Ljubljana, Slovenia;
2Department of Entomology, National Museum of Natural
History, Smithsonian Institution, Washington, DC, USA
Genital evolution in animals with internal fertilization
is thought to be under sexual selection and correlated
between the sexes. Prior studies on selected spiders,
for example, demonstrated that both male and female
genital sizes exhibit low allometric slopes, which indicates
that their evolution is driven by cryptic female choice.
However, it is unclear whether such pattern also holds at
inter-specific levels. Furthermore, it may be possible that
genital components respond independently to selection.
A recent comparative study in nephilid spiders showed
that different parts of male genitalia, i.e., intromittent
and non-intromittent organ, may be under different
evolutionary pressures. While sexual selection may play
an important role in male intromittent genital size evo-
lution, the size evolution of non-intromittent part may
relate to the selection pressures that act on male body size.
Because our understanding of the independent evolution
of different genital components is very preliminary, more
comparative research on genital evolution is needed. Here,
we report on comparative tests of these hypotheses in a
female-biased sexually size dimorphic spider clade, genus
Argiope. We first examined allometric patterns and evolu-
tionary rates of body and genital sizes, then investigated
size evolution of different genital components. Finally, we
explored the relationship between sexual size and genital
size dimorphism. Our preliminary analyses failed to detect
any negative allometry in either male or female genital
size evolution, discovered that male genital size was only
correlated to female external but not internal genital size,
and found no relationship between sexual size and genital
size dimorphism. These findings reveal a complicated
nature of genital evolution in spiders, and do not unequiv-
ocally point towards sexual selection as its main driver.
Keywords: Argiope, sexual selection, genital size evolution,
sexual size dimorphism, sexual genital size dimorphism
Poster presentation
Global phylogeny and biogeography of
Argiopinae (Araneae: Araneidae)
Ren-Chung Cheng1 , Ingi Agnarsson2,3, I-Min Tso 4,
Matjaž Kuntner1,2
1Institute of Biology, Scientific Research Centre of
Slovenian Academy of Sciences and Arts, Ljubljana,
Slovenia; 2Department of Entomology, National
Museum of Natural History, Smithsonian Institution,
Washington, DC, USA; 3Department of Biology, Uni-
versity of Vermont, Burlington, VT, USA; 4Department
of Life Science, Tunghai University, TaiChung, Taiwan
The araneid subfamily Argiopinae currently includes
three genera: Argiope, Gea and Neogea totaling 100
species. Renowned for pronounced sexual dimorphism,
unusual mating behaviors, and web decorations, among
other traits, argiopines have been subjected to a wealth
evolutionary research. Nevertheless, their systematics
and biogeography remain unresolved. We present an
updated time-calibrated phylogeny using three nuclear
and three mitochondrial genes for 64 out of 100 argiopine
species, and use it to clarify argiopine systematics and to
reconstruct their biogeographical history. Our analyses
support a major subdivision of this 40 million year old
clade into Neogea + A. trifaciata + lobed shaped Argiope
from Africa and Americas on one hand and A. bruennichi
+ A. aurantia + Gea + all other Old World Argiope, on
the other. Phylogenetic evidence refutes the monophyly
of current genera and rather suggests all are best placed
in Argiope. However, a new argiopine genus will accom-
modate an unusual species of Argiope. Estimations of
ancestral areas suggest Indomalaya + America (or alter-
natively, Indomalaya) as argiopine origin, from where
they dispersed to Africa, Australasia and Western Palearctic
around 20 to 30 million years ago. Around 10 to 20 million