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Measuring Communication Signals in Lizards: How and Why Rich Glor, Losos Lab, WUSTL I. Introduction to communication A. Definition B. Brief history (Marler 1967) C. My approach/outlook II. Communication in lizards A. Anolis carolinensis display description (DeCourcy

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Measuring Communication Signals in Lizards:

How and Why

Rich Glor, Losos Lab, WUSTL


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I. Introduction to communication

A. Definition

B. Brief history (Marler 1967)

C. My approach/outlook

II. Communication in lizards

A. Anolis carolinensis display description (DeCourcy

& Jenssen 1994)

1. Function

2. Ontogeny

3. Causation

4. Evolution


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A. Definition

“Evolution hates definitions;

for every tidy definition a biologist constructs, evolution will have

provided some exception.”

Bradbury & Vehrencamp 1998

Proposed Definition:

Information transfer from sender to receiver


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Wayne Lynch

National Wildlife Federation

e.g., Tuttle & Ryan 1981


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Nature 2004

Nature 2004


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Starring Greg Pryor, University of Florida

(more specifically, his toe), & an unidentified

male Anolis sagrei


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Revised Definition:

Communication is the phenomenon of one organism producing a

signal that, when responded to by another organism, confers some

advantage (or the statistical probability of it) to the signaler

Burghardt 1970

Signal

Sender Receiver

Environment

Decision

&

Response


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Signal

Sender Receiver

Environment

Decision

&

Response

Signals vs. Cues

Receivers vs. Eavesdroppers


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B. Brief history

*Animal communication as a scientific discipline has a recent past

Lorenz Ethologists

1940’s-60’s Tinbergen NATURE/Instinct

Von Frisch Umvelt


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*In contrast to

PavlovBehaviorists

1890’s-1960’sWatson NURTURE/Learning

Skinner Experimental Control


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Definitions of communication:

1950’s-60’s  For the “survival of the species”

*Signaler/receiver cooperation

1960’s-80’s  Individual benefit

*Signaler/receiver competition

1980’s-present  Synthesis

*Honest and dishonest signals

*Context-dependent decision making at the

individual level


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Dugatkin 2004

*Structure/Function relationships between signal mode

and environment



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C. My approach/outlook

Tinbergen’s four questions

(Tinbergen 1963)

*Function

*Ontogeny

*Causation

*Evolution

N. Tinbergen

1907-1988



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Anolis carolinensis range (U.S.)

Modified from Conant & Collins, 1998

  • Huge genus; only species endemic to North America

  • Polygynous social organization

  • Seasonal breeders (~ April-July)

  • Females lay single-egg clutches at ~ weekly intervals

  • No parental care

  • Communication via “headbobbing displays”

  • Excellent field and laboratory model


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Anolis Communication(Jenssen, 1977, 1978)

Headbobbing displays are body movements which raise and

lower the head and dewlap

Headbobbing displays can be divided into core and modifier

components

The core component is the display type; a species-specific

headbobbing pattern that is performed predictably across all

displays of the same type

Display modifiers are postures or movements added to the

display type, but they are neither species-specific nor predictably

associated with any particular display type


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A. Anolis carolinensis display description

(DeCourcy & Jenssen 1994)


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Display Action Pattern (DAP-)Graphing

Charles C. Carpenter

(e.g., Carpenter & Grubitz 1961)


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Anolis carolinensis DAP-graph

A

B

C

1 2 3 4 5 6 7 8 9 10

HEAD AMPLITUDE

1 2 5 6 7 8 9 10

5 6 7 8 9 10

0.0 0.5 1.0 1.5 2.0

DISPLAY DURATION (s)


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The problem of function-labeling

*Longstanding concern; widespread problem

*Similar to problem of anthropomorphism

One behavior  many functions

One function  many behaviors

Anolis carolinensis signaling repertoire good cautionary tale;

 Don’t name the behavior by the context in which it

occurs!


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An overview of subsequent A. carolinensis display

work, via Tinbergen’s four questions:

*Function – examination of sex differences in structure and use

*Ontogeny – display description through development

*Causation – proximate mediators, in this case, steroids (T)

*Evolution – population-level analysis of structure


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1. Function

  • Adult males and females use the same three stereotyped

    display types

Jenssen, Orrell, Lovern 2000


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Sex Differences in Adult Display Use

Nunez, Jenssen, Ersland, 1997 Jenssen, Orrell, Lovern, 2000


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More Sex Differences in Adult Display Use

Males Females

Advertisement Displays YES NO

Territory Patrol Displays YES NO

Ritualized Aggression YES NO

Dewlap in Courtship YES NO

Type C in Courtship YES NO

Display Modifiers YES FEW

Nunez, Jenssen, Ersland 1997, Jenssen, Orrell, Lovern 2000, Orrell & Jenssen 2003


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Also: Jenssen, Greenberg, Hovde 1995

Jenssen & Nunez 1998

Jenssen, Lovern, Congdon 2001



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Juvenile Display Structure

  • Juvenile males and females can display at hatching

  • Juvenile display structure does not differ by sex

  • Juvenile and adult display structure are the same

    • BUT stereotypy differs…

Lovern & Jenssen 2003


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Juvenile Display Use

N=60 juveniles, 515 displays

Size class: H = 15.7, P = 0.001

*

N=30 each sex

Lovern & Jenssen, 2001


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Juvenile Display Use -- Continued

Unlike Adults:

  • Social context has no effect on display type use

  • No advertisement displays, patrolling displays,

    ritualized aggression, courtship

Lovern & Jenssen, 2001, 2003



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Background on Steroids

  • Major class of hormones; highly evolutionarily conserved

  • Primarily synthesized by the gonads and adrenal glands

  • Circulate in bloodstream; affect target tissues throughout

    body via binding to steroid-specific receptors and

    subsequent modification of gene activity

  • Very small (0.5-1.0 pg) quantities can be reliably measured --

    from a variety of tissue types -- by radioimmunoassay (RIA)

  • Sex steroids (androgens and estrogens) play major roles

    in sexual differentiation and adult reproductive function


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Juvenile and Adult T Comparison

*P < 0.001

*

ADULTS

JUVENILES

*

N = 8 50 21 44

Lovern, McNabb, Jenssen, 2001


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Juvenile T-Implant Study

P < 0.001

BLANK IMPLANTS

T IMPLANTS

a

a

b

c

N = 6 6 8 6

Lovern, McNabb, Jenssen, 2001


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T Implant Study: Results

Lovern, McNabb, Jenssen, 2001


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Causation:

Sexual dimorphisms in adult behavior likely arise through

underlying physiological differences between males and

females that mediate the expression of behavior, rather than

through fundamental sex differences in the ability to perform

sexually dimorphic behaviors.


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4. Evolution

Comparisons of Temporal Display Structure across Contexts and Populations in Male Anolis carolinensis:Signal Stability or Lability?

Lovern, Jenssen, Orrell, Tuchak 1999


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Objectives

*To determine if males from three geographically distinct populations possess the same display types

*To determine if males vary the temporal structure of display types (i.e., intra-display structure) across contexts, populations

  • Hypothesis:Due to recent founding of Hawaii population

    (ca. 1950), and dramatic climatic differences found there,

    we expected males in this population to express the highest

    degree of display type variability, potentially due to founder

    effects, genetic drift, and/or unique selective pressures of a

    tropical environment


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Results I:Do Male Anolis carolinensis from Different Populations

Possess the Same Display Types?YES

Nearest Neighbor

Discriminant Analysis

GA: 100% (96%)

FL: 99.5% (92%)

HI: 100% (100%)


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Results II:Do Male Anolis carolinensis Vary Display Type Structure across Populations?MAYBE...

Intra-display structure

Among GA, FL, and HI populations, totaldisplay duration was not significantly different for any display type

However, 18/24 display units were significantly different:

Display Type A: 6/10

Display Type B: 7/8

Display Type C: 5/6




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Conclusions

*Male Anolis carolinensis useall display types (A, B, C) in the field and lab, and in all contexts; display type structure is unaffected by these parameters

*Males from three distinct populations (GA, FL, HI) possess the same three highly stereotyped -- but statistically distinguishable -- display types in their repertoires

*Within relatively small total variance, among- and within-individual differences account for more of the existing variance than does population or context

*Overall, male Anolis carolinensis show display type stability; males from HI show no evidence of increased display lability resulting from potential genetic and/or environmental influences from recent colonization of a novel habitat


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