20th International Congress of Arachnology

Natural History, Smithsonian Institution, Wash-

ington, DC 20013, USA;

Advanced Light Source,

Lawrence Berkeley National Laboratory, Berkeley,

CA 94720, USA;

Entomology Department, California

Academy of Sciences, San Francisco, CA 94118, USA;

Department of Environmental Science, Policy and

Management, University of California at Berkeley,

Berkeley, CA 94720, USA.

woodh@si.edu

Small animals possess intriguing morphological and

behavioral traits that allow them to capture prey, includ-

ing innovative structural mechanisms that produce

ballistic movements by amplifying power. Power-

amplification occurs when an organism produces a

relatively high power output by releasing slowly stored

energy almost instantaneously, resulting in movements

that surpass the maximal power output of muscles. For

example, trap-jaw power-amplified mechanisms have

been described for several ant genera, which have evolved

some of the fastest known movements in the animal

kingdom. However, power-amplified predatory strikes

were not previously known in one of the largest animal

classes, the arachnids. Mecysmaucheniidae spiders, which

occur only in New Zealand and southern South America,

are tiny, cryptic, ground-dwelling spiders that rely on

hunting rather than web-building to capture prey. Analy-

sis of high-speed video revealed that power-amplified

mechanisms occur in some mecysmaucheniid species,

with the fastest species being two orders of magnitude

faster than the slowest species. Molecular phylogenetic

analysis revealed that power-amplified cheliceral strikes

have evolved four times independently within the family.

Furthermore, we identified morphological innovations

that directly relate to cheliceral function: a highly modi-

fied carapace where the cheliceral muscles are oriented

horizontally; modification of a cheliceral sclerite to have

muscle attachments; and in the power-amplified species,

a thicker clypeus and clypeal apodemes. These structural

innovations may have set the stage for the parallel evolu-

tion of ballistic predatory strikes.

Keywords: ballistic movement, functional morphology,

phylogenetic, evolution

Student - oral presentation

Exploring the relationship between collec-

tive personality and behavioral plasticity

in warring arthropod societies

*Colin M. Wright, Carl N. Keiser, Jonathan N. Pruitt

Department of Biological Sciences, University of

Pittsburgh, 5562 Hobart Street #415 Pittsburgh, PA

15217, USA

cmw132@pitt.edu

Collective personalities of animal societies can sometimes

predict whether they flourish or whether they fail. These

collective personalities often arise from the behavioral

composition of the individuals that comprise the society.

Different behavioral compositions generally perform

differently in orchestrating and shaping complex tasks

such as foraging, prey capture, and colony defense. In

instances where predators and prey share a long evolution-

ary history, prey species sometimes exhibit a specialized,

species-specific, anti-predator response to their presence.

Here we show how different behavioral compositions of

desert social spider (

Stegodyphus dumicola

) societies

survive and modulate their collective foraging and defen-

sive behavior in the presence or perceived presence of a

common voracious predator, the pugnacious ant (

Anoplo-

lepis custodiens

). Our results reveal a subtle interaction

between group composition and group experience in deter-

mining the collective behavior of spider societies, which, in

turn, can impact their survival under siege in situ.

Keywords: sociality, plasticity, personality, predation

Poster presentation

Competition and autotomy affect survival

and development in cellar spiders

Kerri Wrinn

, Todd Levine

University of Wisconsin Rock County, 2909 Kellogg

Ave, Janesville WI, 53546, USA;

Carroll University,

100 N East Ave, Waukesha, WI 53186, USA

kerri.wrinn@uwc.edu

Cellar spiders,

Pholcus phalangioides

, are well-known for

their cosmopolitan distribution, facilitated by their ability

to live indoors in colder areas. Indoor living combined

202

DENVER MUSEUM OF NATURE & SCIENCE

REPORTS

No. 3, July 2, 2016

Cushing