20th International Congress of Arachnology

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DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
Oral presentation
Crowding leads to fitness benefits and
reduced dispersal in a colonial spider
Lior Ventura, Yael Lubin
Blaustein Institute for Desert Research, Ben-Gurion
University, Sede Boqer Campus, Israel
Density-dependent dispersal is a mechanism of escaping
decreased fitness associated with intra-specific competi-
tion. In group living species, however, high density is
expected to be beneficial for the individual, at least up to a
certain threshold. A possible mechanism for maintaining
optimal density is negative density-dependent dispersal.
To examine this hypothesis we studied the effect of colony
density on fitness, dispersal and prey capture under dif-
ferent diets in Cyrtophora citricola, a colonial spider
undergoing range expansion. Results support a negative
density-dependent dispersal strategy: dispersal propensity
of spiders decreased with colony density, especially when
prey abundance was high, and spiderling site tenacity
increased with colony density. Spider body mass increased
with density, indicating positive density-dependent fitness
(Allee effect). However, variance in body mass was higher
in dense colonies than among solitary spiders, suggesting
that spiders in the colony differed in their prey capture
success. This interplay between Allee effect and dispersal
strategy may have an important role in the life history
and colonization success of colonial spiders.
Keywords: Allee effect, colonial spider, density-dependence,
dispersal
Oral presentation
Effect of seasonal photoperiod on molting
in Loxosceles reclusaand Loxosceles laeta
Richard S. Vetter
Department of Entomology, Univ. Calif. Riverside,
Riverside, CA 92521, USA
In the winter of 2014–15, I attempted to push immature
brown recluse spiders, Loxosceles reclusa, to maturity
for a pest control experiment. Despite food offerings, they
stopped molting after October although their abdomens
were well-nourished and were maintained at 25° C. It was
surmised that decreased filtered daylight coming through
a paper-covered window might be suppressing molting.
Feeding was halted in January and 88 recluse spiderlings
were checked weekly for molts. Molting resumed at the
beginning of April and continued through May despite
not being fed. To more thoroughly elucidate photoperiod
effects on molting, during the week of the September
2015 equinox, immature brown and Chilean recluses
were set up in three light regimes: 14:10 L:D, natural,
10:14 L:D. Through the winter, brown recluse molting
was suppressed with no molting in the 10:14 regime from
November to late March, minor molting in the natural
exposure and moderate in the 14:10 regime. Chilean
recluses showed no differences in molting across the
three photoperiod regimes. This species difference may
be explained in that brown recluses are temperate zone
creatures where winter is typically accompanied by cold
temperatures and reduced prey availability that would
be detrimental to survival; Chilean recluses are tropical
where winter light cycles may have little significance. The
experiment was still underway when this abstract was
submitted so additional information may develop.
Keywords: behavior, photoperiod, molting, Loxosceles
Student - oral presentation
Odor alters color preference in foraging
jumping spiders
*Michael Vickers, Lisa Taylor
Entomology and Nematology Department 1881
Natural Area Drive University of Florida - Steinmetz
Hall Gainesville, FL 32611, USA
In many prey taxa with aposematic coloration, prey
defenses also involve signals in other modalities (odors,
sounds, etc.). Yet the selective forces that have driven
multimodality in warning displays are not well under-
stood. One potential hypothesis that has recently received
support in the avian literature, is that different signal
components may interact synergistically, such that one
component of the signal (odor) may trigger predator’s
20th International Congress of Arachnology