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
release lines as they move in their webs. Some crucial
aspects of tarsal morphology were elegantly documented
long ago by E. Nielsen. Several recent advances on the
behavioral side have been made possible by video recordings
of behavior. The spider’s legs routinely follow each other in
various behavioral contexts, thus economizing on the
exploratory behavior needed by more posterior legs to locate
new lines. The short-distance searching movements made
by a following leg are asymmetrical (prolateral for legs I
and II, retrolateral for legs III and IV), and these orienta-
tions are appropriate to allow their asymmetrically placed
median claws and serrate accessory setae to contact and
grasp the lines that they encounter. And the tarsus itself (or,
less likely its claw) is routinely twisted on its longitudinal
axis to bring the median claw into a position perpendicu-
lar to the line, thus allowing the claw to clamp even those
lines that are parallel to the spider’s longitudinal axis.
Keywords: behavior, functional morphology, web spiders
Student - oral presentation
Control of signal alignment during the
dynamic courtship display of a salticid
*Sebastian A. Echeverri, Nathan I. Morehouse, Daniel B.
Zurek
Department of Biological Sciences, University of Pitts-
burgh, 4249 5th Avenue, Pittsburgh, PA 15260, USA
Signals are often directional, meaning that they are best
perceived from certain angles. Likewise, sensory systems
often have directional biases. Thus, alignment of directional
signals and directional sensors may often be critical for
effective communication. However, we know little about
how animals establish and maintain alignment during
signaling. We analyzed the dynamic courtship dances of the
jumping spider Habronattus pyrrithrix to better under-
stand how often alignment is achieved, and who is primarily
responsible (i.e. male, female, or both). In this species,
courtship consists of distinct long- and short-range phases.
Males produce a forward-facing visual display that includes
color, pattern, and movement. Females view this display
with two types of eyes: color sensitive principal eyes with
narrow fields of view, and colorblind secondary eyes with
wide fields of view. The combined inputs of these eyes create
a visual field where colors and fine patterns of male displays
can only be perceived by a female if the male is in front of
her. We recorded relative positions and orientations of both
actors throughout courtship to evaluate how consistently
male displays are aligned with the female principal field of
view, and who is responsible. Males always oriented their
displays toward the female. When females were free to move,
male displays were only consistently aligned with female
color vision during the short range phase. When female
position was fixed, signal alignment consistently occurred
during both courtship phases, and maximal alignment
during the short range phase occurred for a greater propor-
tion of time. This suggests that normal female movements
may reduce communication efficacy. In addition, when
tethered females were rotated to face away, males rarely
repositioned themselves to re-align their display. Thus,
although signal alignment is a function of both sexes, males
may rely on females for effective communication.
Keywords: communication efficacy, courtship signaling,
signaling behavior, Salticidae
Oral presentation
Revision of Misumessus (Araneae: Thomis-
idae), with observations on crab spider
epigynal hoods
G. B. Edwards
Florida State Collection of Arthropods, 1911 SW 34th
Street Gainesville, FL 32608 USA
The previously monotypic genus Misumessus, type species
M. oblongus (Keyserling, 1880), is found to consist of
at least seven species distributed throughout most of
North America, all of Central America, Bermuda, and the
Greater and Lesser Antilles. Species are distinguished in
the males primarily by the position of the embolus base
and the length of the filamentous end of the embolus,
with the embolus curling around the tegulum more than
360 degrees. In the females, differences are more subtle,
but length and shape of the median epigynal piece, and
differences in face morphology detail, can distinguish
them. In addition, four of the species have other distinctive