Resume

• 2009

  Doctor of Philosophy (PhD)

  Biology

  Duke University

• 2004

  Bachelor of Science (BS)

  Ecology and Evolutionary Biology

  University of Michigan

• Animal Communication

  Animal Behavior

  College Teaching

  Sensory Ecology

  Physiology

  Biology

  Python

  Eavesdropping on Visual Secrets

  Sonke Johnsen

  Daniel Speiser

  Private communication may benefit signalers by reducing the costs imposed by potential eavesdroppers such as parasites

  predators

  prey

  or rivals. It is likely that private communication channels are influenced by the evolution of signalers

  intended receivers

  and potential eavesdroppers

  but most studies only examine how private communication benefits signalers. Here

  we address this shortcoming by examining visual private communication from a potential eavesdropper’s perspective. Specifically

  we ask if a signaler would face fitness consequences if a potential eavesdropper could detect its signal more clearly. By integrating studies on private communication with those on the evolution of vision

  we suggest that published studies find few taxon-based constraints that could keep potential eavesdroppers from detecting most hypothesized forms of visual private communication. However

  we find that private signals may persist over evolutionary time if the benefits of detecting a particular signal do not outweigh the functional costs a potential eavesdropper would suffer from evolving the ability to detect it. We also suggest that all undetectable signals are not necessarily private signals: potential eavesdroppers may not benefit from detecting a signal if it co-occurs with signals in other more detectable sensory modalities. In future work

  we suggest that researchers consider how the evolution of potential eavesdroppers’ sensory systems influences private communication. Specifically

  we suggest that examining the fitness correlates and evolution of potential eavesdroppers can help (1) determine the likelihood that private communication channels are stable over evolutionary time

  and (2) demonstrate that undetectable signals are private signals by showing that signalers benefit from a reduction in detection by potential eavesdroppers.

  Eavesdropping on Visual Secrets

  The iconic red hourglass of the black widow spiders (genus Latrodectus) is traditionally considered an aposematic signal

  yet experimental evidence is lacking. Here

  we present data that suggest that black widow coloration may have evolved to be an aposematic signal that is more conspicuous to their vertebrate predators than to their insect prey. In choice experiments with wild birds

  we found that the red-and-black coloration deters potential predators: Wild birds were ~3 times less likely to attack a black widow model with an hourglass than one without. Using visual-system appropriate models

  we also found that a black widow’s red-and-black color combo is more apparent to a typical bird than a typical insect. Additionally

  an ancestral reconstruction reveals that red dorsal coloration is ancestral in black widows and that at some point some North American widows lost their red dorsal coloration. Behaviorally

  differences in red dorsal coloration between 2 North American species are accompanied by differences in microhabitat that affects how often a bird will view a black widow’s dorsal region. All observations are consistent with a cost–benefit trade-off of being more conspicuous to predators than to prey. We suggest that limiting detection by prey may help explain why red and black aposematic signals occur frequently in nature.

  Aposematic signals in North American black widows are more conspicuous to predators than to prey

  The information an animal gathers from its environment

  including that associated with signals

  often varies continuously. Animals may respond to this continuous variation in a physical stimulus as lying in discrete categories rather than along a continuum

  a phenomenon known as categorical perception. Categorical perception was first described in the context of speech and thought to be uniquely associated with human language. Subsequent work has since discovered that categorical perception functions in communication and decision-making across animal taxa

  behavioral contexts

  and sensory modalities. We begin with an overview of how categorical perception functions in speech perception and

  then

  describe subsequent work illustrating its role in nonhuman animal communication and decision-making. We synthesize this work to suggest that categorical perception may be favored where there is a benefit to 1) set-ting consistent behavioral response rules in the face of variation and potential overlap in the physical structure of signals

  2) especially rapid decision-making

  or 3) reducing the costs associated with processing and/or comparing signals. We conclude by suggesting other systems in which categorical perception may play a role as a next step toward understanding how this phenomenon may influence our thinking about the function and evolution of animal communication and decision-making.

  Categorical perception in animal communication and decision-making

  We document a previously undescribed vocalisation in the Variegated Fairy-wren (Malurus lamberti)

  the Type II song

  which is given in response to the calls of a specific avian predator. We used playbacks of five species of both predators and non-predators to determine which species most commonly elicit Type II songs. Calls of Grey Butcherbirds (Cracticus torquatus) were the only stimuli to elicit Type II songs. Two other species in the genus Malurus

  the Splendid Fairy-wren (M. splendens) and the Superb Fairy-wren (M. cyaneus)

  are also known to sing Type II songs in response to the calls of specific avian predators. In all these species

  Type II songs may function as displays to conspecifics. This study highlights the possibility that predator-elicited display behaviour may be more widespread in the genus Malurus than was previously recognised.

  A predator-elicited vocalisation in the Variegated Fairy-wren (Malurus lamberti)

  Visual acuity (VA) --- a measurement of the fineness or coarseness of vision --- correlates with the size of an animal

  with larger species often possessing sharper vision. However

  it is unknown whether the same relationship between visual acuity and size holds within a species when individuals differ consistently and substantially in size

  such as through a sexual size dimorphism. Here we examine the visual acuity of three species of sexually dimorphic band-winged grasshoppers

  in which females are the larger sex (Arphia pseudonietana

  Dissosteira carolina

  and Spharagemon equale; total n = 98). Using a radius of curvature estimation method

  we find that females have ∼21% finer vision in the most acute region and axis of the eye than do males. Further explorations of the eyes of the species showing the greatest size dimorphism (D. carolina) suggest that this VA dimorphism is driven by females having larger eyes with more ommatidia. In contrast to many flying insects where males have finer vision to acquire mates

  our study is one of the first to demonstrate a female-biased sexual dimorphism in acuity. Given the number of species in which females are larger than males

  our results suggest that differences in VA between the sexes may be more common than currently appreciated.

  A sexual dimorphism in the spatial vision of band-winged grasshoppers (in review)

  The many dimensions of categorical perception: a response to comments on Green et al.

  The many dimensions of categorical perception: a response to comments on Green et al.

  Acuity

  the fineness with which sensory systems perceive and parse information

  limits the information that organisms can extract from stimuli. Here

  we focus on visual acuity (the ability to perceive static spatial detail) to discuss relationships between acuity and signal form and evolution. Research suggests that acuity varies by orders of magnitude across species

  and that most animals have much lower acuity than humans. Thus

  hypotheses regarding the function of spatial patterns must account for the acuity of relevant viewers. New data quantifying acuity in a range of taxa allow us to examine correlations between acuity and ecology

  elucidate the selective forces that receiver acuity places on signal evolution

  and examine how signals might appear to viewers with different acuities.

  Visual acuity and the evolution of signals

  My research falls within the intersection of ecology

  behavior

  and sensory physiology. Broadly

  I seek to understand how differences in vision influence the behavior and coloration of animals. To accomplish this I investigate both 1) how different behavioral

  ecological

  and morphological factors cause variation in vision between animals and 2) what functional effect these differences have on the animal’s behavior and ecology. My work includes projects in visual acuity (i.e. spatial vision; informally the number of pixels in an animal’s visual scene)

  color vision

  and synthesis papers examining how physiology influences behavior.

  Nicholas

  Elon University

  The College of Wooster

  Duke University

  Duke University

  Colorado College

  NC Governor's School East

  Elon University

  University of Michigan Biological Station

  Human Physiology Lecture (1 section)

  Elon University

  Colorado College

  Colorado Springs

  Colorado Area

  Visiting Assistant Professor

  Raleigh

  NC

  Residential summer school for gifted rising high school seniors.

  Natural Science Instructor

  NC Governor's School East

  Adviser: Dr. Sönke Johnsen\nDepartment of Biology

  Duke University

  Teaching Assistant

  Natural History and Evolution (1 section)

  University of Michigan Biological Station

  Assistant Professor

  The College of Wooster

  Lab Instructor

  Human Physiology (2 sections)

  Elon University

  Summer Term Instructor

  Intensive summer course in animal adaptations.

  Duke University

  The College of Wooster

  Wooster

  OH

  Visiting Assistant Professor