1. N I C O L E F I S C H E R , P H . D .
A D V I S O R : A N N A D O R N H A U S , P H . D .
R E S E A R C H A S S I S T A N T : J E N P I M E N T E L , U G
Neural Mechanisms of Behavioral
Variation in Temnothorax Ants

2. Introduction
— Evolutionary success of social
insects can be attributed to their
division of labor.
— The response threshold
model proposes this behavioral
variation as emergent of internal
thresholds for task-associated
stimuli2.
1. Weidenmüller, A (2004) The control of nest climate in bumblebee (Bombus terrestris) colonies: interindividual variability and self
reinforcement in fanning response. Behav Ecol 15(1): 120-8.
2. Wilson, EO (1976) Behavioral discretization and the number of castes in an ant species. Behav Ecol Sociobiol 1:141-54.
Figure taken from cis.arl.arizona.edu, an image
of “Temnothorax rugatulus workers, individually
marked, tending brood”
PC: Alex Wild

3. Background
— Temnothorax rugatulus
— The neural mechanisms under-
lying response thresholds can be
centrally and/or peripherally-
derived.
— Preliminary work on T. rugatulus suggests
significant variation in the number of antennal
sensory hairs, sensilla (Figure 1), which is also
independent of antenna size (n = 25, p = 0.376, R2 =
-0.01)2.
1. Riveros, A, Gronenberg, W (2010) Sensory allometry, foraging task specialization and resource exploitation in honeybees. Behav Ecol
Sociobiol 64: 955-67
2. Fischer, NE, Charbonneau, D, Gronenberg, W, Dornhaus, A (2013) Neural mechanisms of behavioral variation in Temnothorax ants.
University of Arizona. Tucson, AZ.

4. The Problem
— What are the relative
contributions of the CNS
and PNS in creating
response thresholds?
— How do response
thresholds arise from the
peripheral and central
nervous systems to give
rise to intra-specific
variation? Figure taken from Sites.middlebury.edu, a diagram of body
parts included in the CNS and PNS

5. Hypothesis
— Ha: Behavioral variation is dependent on
differences in sensory thresholds.
¡ Ha1: Worker response thresholds emerge
from the PNS.
¡ Ha2: Worker response thresholds are
regulated by the CNS.
— H0: Thresholds are independent of
structural properties.

6. Methods and Approaches
— To test Ha, individual
responses to varying
concentrations of
2-heptanone were
measured.
— Quantified according to
3 seemingly-induced
behaviors:
÷ Walking velocity
÷ Antennal drumming rate
÷ Proportion of time with mandibles
open
Image taken from Phys.org,
a photograph of the Monomorium
destructor’s open mandibles,
PC: Eli Sarnat
Image taken from
Alexanderwild.com,
T. rugatulus ants
painted with patterns
of color to help track
their behaviors

7. Methods and Approaches
— To test Ha1, counted the number
of sensilla on the first segment of
the antenna
— To test Ha2, olfactory input and
processing brain regions are
morphometrically analyzed
¡ Dissection
¡ Histological processing
¡ Confocal microscopy Image taken from Nicole-elise-
fischer.weebly.com, a cross section of a T.
rugatulus brain, emphasizing the mushroom
body (in teal), a region involved in sensory
integration

8. Predictions
— If Ha, workers will react at lower odor
stimulus levels.
¡ If Ha1, workers of similar behavioral
threshold levels will exhibit similarity
in peripheral sensory structures.
¡ If Ha2, workers of similar behavioral
thresholds will exhibit similar
neuroanatomical phenotypes.

9. Directions for this Lab
— Determine whether sensilla number, relative
regional brain volume, both, or neither(H0) are
significant for explaining threshold variation.
¡ Linear stepwise model using sensilla number, regional brain
volume, and their interactions to explain response to 2-
heptanone
— Explore the basis for differential regional brain
volume
¡ Staining and quantifying brain synapses, knowing synaptic
density and cortical thickness makes up the volume of regions
of the brain

10. Directions for Me
— Working with Nicholas
DiRienzo, Ph.D., under the
same advisor
¡ Recent research on individual
differences in web structure
and aggression in black widows
— Testing effects of biogenic
amines and topical solvent types on the behaviors of two
web-building spiders
— Studying the effects of brain hormone levels on behavior
and web structure in Phidippus johnsoni (Red-back spider)
Image taken from Museumvictoria.com.au, a
photograph of a female red-back spider in her web

11. Acknowledgments
— Anna Dornhaus, Ph.D., advisor
— Nicole Fischer, Ph.D., supervisor
— Colin Lynch, B.S.
— Nicholas DiRienzo, Ph.D., future
supervisor
— Arizona Science, Engineering, and
Mathematics Scholars (ASEMS) staff and
faculty