Central Paper: Nowicki, S. et al. (2002a) Brain development, song learning and mate choice in birds: a review and experimental test of the “nutritional stress hypothesis.” J. Comp. Physiol. A 188: 1003-1014.

Effects of early nutrition and brain development on bird

song and mate choice

By Spring Ligi

Introduction

Signaling system:

1. Signalers: benefit from unreliable signals

2. Receivers: respond only to reliable signals

Sexual Selection: powerful role of females

Direct selection: increase female survival

Indirect selection: increase fitness of female offspring

IntroductionSong characteristics

Two functions of male song:

1. Territory advertisement

2. Female attraction

Three stages of song:

1. Subsong

2. Plastic song

3. Crystallized song

IntroductionSong as a mating signal in birds

Three common song features influencing female choice:

1. Song output

2. Song repertoire

3. Local song structure

How can the ability to produce a more complex song repertoire and/or local song structure be costly?

One possible answer is the nutritional stress hypothesis…

The nutritional stress hypothesis

H1: Nestling nutritional stress effects adult song

Bird song is reliable indicator -developmental cost

H0: No relationship between adult song and nestling nutritional stress

Song system developmentSong system nuclei

RA (robust nucleus of the archstriatum)

HVc (high vocal center)

Area X

Telencephalon

Majority of song system growthbetween 10 and 50 days.

Modified from Bottjer et al., 1985

Support for nutritional stress hypothesis: Ethological approach

Positive relationship between nestling feather length and song repertoire size in great reed warblers

Repertoire size reflects early nutrition

Nowicki et al., 2000

First experimental test of nutritional stress hypothesis: Behavioral approach

Compared brain and song development in two groups of swamp sparrows:

1. Experimental: 7 birds nutritionally stressed from 4 to 14 days of age (70% food volume of control)

2. Control: 9 birds which were fed until satisfied

Nowicki et al., 2002a

Methods

At 20 days of age…

1. Males housed separately

2. Tutored for 12 weeks with

male swamp sparrow songs

At 250 days of age…

1. Song development recorded

in sound isolation chambers

At 1 year of age…

1. Compared accuracy between tutor and adult songs

At 14 months of age…

1. Birds killed and brains removed to determine song system nuclei volume

Male swamp sparrow sonogram

Sonogram of song repertoire of a male swamp sparrow

Trill of repeated syllables

Two or more distinct note types

Nowicki et al., 2002a

Results

Experimental swamp sparrows produced significantly less accurate copies of learned model songs

No significant difference in song repertoire size

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

Control Experimental

Treatment group

Cro

ss-c

orr

elat

ion

sco

re

Nowicki et al., 2002a

Results

RA and HVc song system nuclei are significantly smaller in experimental group

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Control Experimental

Treatment group

HV

C v

olu

me

(mm

3)

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Control Experimental

Treatment group

RA

vo

lum

e (

mm

3)

Nowicki et al., 2002a

Results (continued)Telencephalon volume

significantly smaller in experimental group

RA/telencepahlon ratio significantly smaller in experimental group0

50

100

150

200

250

Control Experimental

Treatment group

Tele

nce

ph

alo

n v

olu

me

(mm

3)

Nowicki et al., 2002a

DiscussionNutritional stress hypothesis supported!

Early nutritional stress effects adult song

Song quantity and quality - reliable indicators

Brain development - link between nutritional stress and song learning

RA nucleus – song quality

HVC and other regions - timing of notes and syllables

Criticisms and Praises Criticisms:

1. Poor choice of subject species

2. Small regression value in Figure 2

3. Small sample size

Praises:

1. Good review of mate choice, brain development, and song learning

2. Good addition of sound experimental data

Future research

1. Test other song system features (neuron and dendrite density)

2. Test behaviors other than song (male cognitive abilities)

3. Investigate effect of other stresses (parasite load, social stress hormones, etc) on song development

4. Test hypothesis on wider variety of birds

Conclusion

Nutritional stress hypothesis supported

Nutritional stress – lasting effect on adult song

Bird song is reliable indicator - developmental costs

References Primary References

Bottjer, S.W., Glaessner, S.L., and A.P. Arnold (1985) Ontogeny of brain nuclei controlling song learning and behavior in zebra finches. The Journal of Neuroscience 5: 1556-1562.

Kodric-Brown, A. and J.H. Brown (1984) Truth in adverstising: the kinds of traits favored by sexual selection. The American Naturalist 124: 309-323.

Marler, P. and S. Peters (1977) Selective vocal learning in a sparrow. Science 198: 519-521.Mooney R. (1999) Sensitive periods and circuits for learned birdsong. Current Opinion in Neurobiology 9: 121-127.Nordeen, K.W., Marler, P. and E.J. Nordeen (1989) Addition of song-related neurons in swamp sparrows coincides

with memorization, not production, of learned songs. Journal of Neurobiology 20: 651-661.Nowicki, S., Searcy, W.A., and S. Peters (2002a) Brain development, song learning and mate choice in birds: a

review and experimental test of the “nutritional stress hypothesis.” J. Comp. Physiol. A 188: 1003-1014.Nowicki, S., Searcy, W.A., and S. Peters (2002b) Quality of song learning affects female response to male bird song.

Proc. R. Soc. Lond. B 269: 1949-1954.Nowicki S., Hasselquist, D., Bensch, S. and S. Peters (2000) Nestling growth and song repertoire size in great reed

warblers: evidence for song learning as an indicator mechanism in mate choice. Proc. R. Soc. Lond. B 267: 2419-2424.

Secondary References

Nowicki, S. and W.A. Searcy (2004) Song function and the evolution of female preferences: why birds sing, why brains matter. NY Acad. Sci. 1016: 704-723.