20th International Congress of Arachnology

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DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
from the northern (Pickeliana spp. and Pseudopucrolia
spp.) and southern (Neosadocus spp., Promitobates spp.
and Sodreana spp.) portions of the AF. Richness ranged
from 2 to 57 species (mean 17.8±13.7 species) and was
higher in sites near the coast in the Southeast region,
decreasing towards the interior (with deciduous forest
formation) and the Northeast region (especially northern
of Bahia). Richness was positively related to humidity,
and sites near cores of AoEs showed larger values than
those more distant from them. Changes in beta diversity
were intense and highly related with the AoEs, showing
abrupt changes from one AoE to another and reflecting
the high endemism level of harvestmen. Preliminary
phylogeographic analyses revealed similar patterns for
both Northeast taxa and corroborated the communities’
diversity results, indicating higher genetic diversity near
the core of the Pernambuco AoE and lineages’ divergences
between southern Bahia and other Northeast localities. In
the Southern Atlantic Forest, Promitobates and Neosado-
cus exhibit genetic discontinuities in Ribeira de Iguape
river valley region, which corresponds to the limit between
two AoEs, while Sodreana presents a more complex
pattern. Our results suggest that the predicted harvestmen
AoEs may have acted as forest refugia, maintaining more
species and higher genetic variability than less stable
areas in the transitional regions between AoEs.
Keywords: beta-diversity, biogeography, Opiliones,
phylogeography
Student - oral presentation
Ontogenetic shift towards stronger, tougher
silk of web building Tasmanian cave spider
*Dakota Piorkowski1, Sean Blamires2 , Niall Doran3,
Chen-Pan Liao1, Tso, I-Min1,4
1Department of Life Science, Tunghai University,
Taichung 40704, Taiwan; 2Evolution and Ecology
Research Centre, University of New South Wales,
Sydney, NSW 2052, Australia; 3Bookend Trust and the
School of Biological Sciences, University of Tasmania,
PO Box 310, Sandy Bay, Tasmania 7006, Australia;
4Center for Tropical Ecology and Biodiversity,
Tunghai University, Taichung 40704, Taiwan
The foraging efforts of trap constructing animals, such as
web building spiders, tend to be confined within the limits
of their trap, accordingly ontogenetic shifts in foraging are
restricted to modifying their traps. While some web-build-
ing spiders vary their web’s architecture through ontogeny,
many spiders, such as the large-bodied Tasmanian cave
spider Hickmania troglodytes, produce a nearly homoge-
neous web design throughout life history. We hypothesized
that in order to meet the high-energy demands of its large
body size, H. troglodytes enhances its webs prey-capturing
abilities by adjusting the physical properties of the major
ampullate silk (MAS); the web’s primary prey stopping
component and structural material. We collected samples
of MAS from webs built in caves from 20 individuals of
varying ontogeny and conducted tensile tests to measure
the MAS physical properties. We found impressive strength
and toughness (ability to deform and absorb energy) of
the MAS that both increased significantly with both spider
carapace width and body length. Our results are the first
to show changes in the physical properties of spider silk
through ontogeny, they also indicate that these spiders focus
on building more resilient and structurally robust webs to
catch disproportionately larger and potentially novel prey
or to preserve web architectural integrity and function for
longer periods of time. The gradual shift in silk produc-
tion and use over the spider’s lifetime should inevitably lead
to improved prey capture abilities. Future investigation
into the mechanisms responsible for these shifts in the
physical properties of MAS may provide better insights into
how spiders produce such strong and tough silk.
Keywords: major ampullate silk, ontogeny, spider web,
cave spider, biomechanics
Student - poster presentation
Trophic cascades: the triangle of
decomposition
*Leslie Potts
Department of Entomology, S-332 Ag. Science Center,
N. Lexington KY 40546-0091, USA
Litter decomposition is driven by multiple factors, includ-
ing climate and soil organisms. In detrital food webs,
20th International Congress of Arachnology