20th International Congress of Arachnology

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of Minnesota Insect Collection, and also freshly collected
specimens from the main campus of Macalester College
(Ramsey County) and the college field station (Dakota
County). We report eight previously undocumented
species and two additional genera, identified using exter-
nal and internal morphological characteristics. This work
increases the known Opiliones species richness of Minne-
sota from five species to thirteen, and the known number
of genera in the state from five to seven, including the
first documentation of the widespread genus Leiobunum .
Keywords: Opiliones, Minnesota, harvestmen, species
richness
Student - poster presentation
Familiarity reduces aggression, but also
mating success, for male Leiobunum aldrichi
William Shoenberger, Dowen Jocson, Kasey Fowler-Finn
Saint Louis University, 143B Macelwane Hall,
Department of Biology, 3507 Laclede Ave. Saint
Louis, MO 63103, USA
Animals often adjust behavior in response to interactions
they have with conspecifics. For example, within a mating
context, males may alter how they compete for mates
depending on the level of familiarity they have with their
competitors. We wanted to test if the mating dynamics
of males change depending on whether they had prior
experience with one another. We did this by using the
harvestmen species Leiobunum aldrichi (Opiliones:
Sclerosomatidae). We quantified mating dynamics (aggres-
siveness, likelihood of successful mating, and duration
of copulation) in male-male-female mating trials where
competing males were either familiar or unfamiliar with
each other. We manipulated familiarity by pairing males
overnight in cages in which they were separated by netting
that allowed them to interact and exchange cues except
through physical altercations. The following day we ran
the male-male-female mating trials in which we paired
males with either a familiar male (the male with which he
was housed overnight) or an unfamiliar male (a male that
was housed with a different male). We found that male-
male aggression in familiar trials was considerably lower
than in unfamiliar trials. We also found males were half as
likely to mate in familiar trials, potentially due to higher
rates of rejection by females. These results demonstrate
familiarity from previous social interactions may play an
important role in mating dynamics.
Keywords: social experience, mating dynamics, behavior,
familiarity, harvestmen
Oral presentation
Muscles, hydraulics and springs: perspectives
on joint mechanics in arachnid locomotion
Jeffrey W. Shultz
Department of Entomology, 4112 Plant Sciences Bldg,
University of Maryland, College Park, MD 20742, USA
This presentation reviews current understanding of the
evolution and biomechanics of muscular, hydraulic and
elastic mechanisms used in propulsive joint extension and
explores new avenues of research. Emphasis is placed on
three aspects, the significance of phylogenetic history, body
size, and leg muscles other than extensors in shaping the
taxonomic distribution of extension mechanisms. 1. Deep
phylogenetic relationships among chelicerates indicates
an evolutionary polarity in arachnids from primitive joints
without dedicated extensor mechanisms (e.g., hydraulics,
kinetic chains) to those with dedicated extension mecha-
nisms (e.g., elastic sclerites, novel extensor muscles), but
finer details will depend on a robust phylogeny of arach-
nids, which does not currently exist. 2. Specific mechanical
predictions can be derived from an assumption of
geometric similarity. The approach successfully predicts
that hydraulic pressure used in propulsive leg extension
is invariant with size, an observation that suggests that
hydraulics is more effective for small arachnids than for
large ones. A similar approach can be used to make test-
able predictions about muscular and elastic mechanisms.
3. Extension mechanisms do not operate in isolation, and
most require antagonists to regulate the rate and range
over which they operate. Antagonists can take the form of
dedicated flexor muscles or muscles at adjacent joints that
can affect extension through a kinetic chain consisting of
the intervening podomere or bi-articular muscles. Further
176 DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
Cushing