20th International Congress of Arachnology

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DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
Czech Republic; 5Biology Department, Macalester
College, 1600 Grand Avenue, St. Paul, MN 55105, USA
The taxonomy and systematics of the armored harvest-
men (suborder Laniatores) are based on various sets of
morphological characters pertaining to shape, arma-
ture, pedipalpal setation, and the number of articles at
the termini of the legs. More recently, male copulatory
structures and appendicular secretory organs have been
proffered as a potential source of phylogenetically informa-
tive characters. Few studies have tested the validity of these
character systems in a comprehensive way, with reference
to an independent data class, i.e., molecular sequence data.
We examined as a test case the systematics of Podoctidae,
a family distributed throughout the Indo-Pacific, using a
five-locus molecular phylogeny as a point of reference. We
mapped character data from various structures, includ-
ing shape data, onto the molecular phylogeny, in order to
quantify phylogenetic signal and to characterize evolution-
ary rate and trait correlation of discrete and morphometric
characters. Here, we show that the subfamilies Ibaloniinae
and Podoctinae are paraphyletic, with Erecananinae
nested within Podoctinae. Various genera were recovered
as non-monophyletic. As a first step toward revision of the
systematics of Podoctidae, we once again synonymize
the genus Paralomanius Goodnight & Goodnight, 1948
with Lomanius Roewer, 1923 revalidated. Erecananinae
Roewer, 1912 is synonymized with Podoctinae Roewer, 1912
new synonymy. We pinpoint morphological data classes that
are consistent with phylogenetic signal, and identify those
highly prone to convergence. These results are anticipated
to guide taxonomic practices in Laniatores systematics.
Keywords: Opiliones; Grassatores; morphometrics;
comparative methods; phylogenetic signal
Student - Oral presentation
Interspecific competition, group size and
dispersal in a social spider
*Ruth Sharpe, Leticia Avilés
University of British Columbia, #4200-6270 Univer-
sity Blvd., Vancouver, B.C. V6T 1Z4, Canada
The relative costs and benefits of group living change
with group size. In the social spider Anelosimus eximius,
as colonies grow, the number of insects captured per
capita decreases, but the size of insects increases, causing
biomass captured per capita to peak at intermediate
colony sizes. We show that for small to medium-sized
colonies spiders are larger in larger colonies. We found,
however, that individual condition decreases as colony
size increases, indicating that an individual’s access to
resources may become limited as colonies grow. Using
artificial colonies in the lab we show that individual
spiders are not able to monopolize large prey and that
the variance in individual condition does not increase as
colony size increases, and in fact may even decrease. It
thus appears that scramble competition predominates in
A. eximius colonies, especially at large colony sizes. We
suggest that greater competition in larger colonies may
drive adults to disperse. The fact that dispersing adults
were found to be larger and in better condition compared
to non-dispersers suggests that dispersal may be costly and
that competition in large colonies may result in some indi-
viduals failing to secure sufficient resources to disperse.
Keywords: sociality, competition, dispersal, Anelosimus
eximius, group size, behaviour
Student - poster presentation
New Records of Harvestmen (Arachnida,
Opiliones) from Minnesota, USA
*A. Kenji Shoemaker1, Mercedes M Burns2, Sarah L. Boyer1
1Biology Department, Macalester College, 1600 Grand
Avenue, Saint Paul, MN, 53704, USA; 2Department of
Biology, San Diego State University, San Diego, CA,
92182, USA
Although they are familiar and often abundant in many
of the state’s ecosystems, the Opiliones of Minnesota are
significantly understudied in comparison to surrounding
states and provinces. Minnesota’s current species richness
sits as five species that were last documented over half a
century ago, while some neighboring states and provinces
are known to harbor double or quadruple that number.
We examined unidentified material from the University
20th International Congress of Arachnology