20th International Congress of Arachnology

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DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
and other Arachnida.
Keywords: systematics; Mygalomorphae; next-genera-
tion sequencing; biogeography
Oral presentation
Influence of predators and senescence on
male courtship investment in a wolf spider
Andrew J. Roberts1, Diana Saintignon2, Benjamin Nickley2
1Department of Evolution, Ecology, and Organismal
Biology, The Ohio State University at Newark, 1179
University Drive, Newark, Ohio, 43055, USA; 2Depart-
ment of Evolution, Ecology, and Organismal Biology,
The Ohio State University, 300 Aronoff Lab, 318 W.
12th Ave, Columbus, Ohio, 43210, USA.
Active courtship is critical for mate attraction, but benefits
of signal production depend on many influences. Sexual
signaling can be energetically expensive, and has the
potential to attract unwanted attention from predators.
Male brush-legged wolf spiders, Schizocosa ocreata Hentz
(Araneae: Lycosidae), actively signal females in the leaf
litter habitat during their spring breeding season, but face
distinct tradeoffs between current and future reproduction
as the season progresses. Later in the breeding season,
the number of available females, who typically mate only
once, steadily declines, mated females become aggres-
sive and cannibalistic, and leaf litter cover disappears,
increasing male exposure to other predators. Further
complicating reproduction, sexually selected male traits
such as foreleg tufts are subject to wear with increasing
age (senescence), potentially reducing male attractiveness
to females. The terminal investment hypothesis predicts
that with fewer available females, increasing predation
risk, and physiological senescence as the season pro-
gresses, males should take greater risks to secure mating
including courting in the presence of predators. We
exposed males of increasing ages to female cues alone or
female cues combined with predator cues, but found little
evidence to support the terminal investment hypothesis
in this species in that there was no age related increase
in courtship investment in the presence of predator cues.
However, we found evidence of male senescence based on
age-related changes in behavior, which has not previously
been explored in this species. While males maintained
similar levels of active courtship across all age classes,
older males increased their relative investment in mainte-
nance behaviors (grooming) and decreased non-courtship
display behaviors. These findings suggest that studies of
male behavior in this species should be carefully designed
to control for age-related variation in behavioral response.
Keywords: senescence, predation, age effects, chemical
cues, context dependence
Student - oral presentation
What factors affect the relative abun-
dance of dense, three dimensional webs?
*Mark Robertson, Leticia Avilés
Department of Zoology, University of British Colum-
bia, #4200-6270 University Blvd. Vancouver, B.C.
V6T 1Z4, Canada
Using a precipitation-productivity gradient in western
Ecuador, we considered the potential trade-off between
costs of web repair and benefits of predator protection
in influencing the relative abundance of dense, three-
dimensional (3D) spider webs. 3D spider webs require
large amounts of silk and activity to be maintained.
Since heavy rainfall severely damages webs, we pre-
dicted that the relative abundance of 3D webs would
decrease with increasing precipitation. Conversely, as 3D
webs also confer greater protection against predators,
and predators are predicted to be more abundant in
wetter, more productive habitats, the relative abundance
of 3D webs may increase with increasing precipita-
tion. We found that 3D webs significantly increased in
relative abundance with increasing precipitation, which
suggests greater importance of their predator protection
function. We also found, however, that 3D webs may
avoid extensive damage from strong rains by choosing
sites with greater immediate cover, which we found
increased in abundance as precipitation, and thus veg-
etation lushness, increased.
Keywords: web architecture, ecological factors, observa-
tional, environmental gradient
20th International Congress of Arachnology