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: 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

Introduction Song characteristics Two functions of male song: 1. Territory advertisement 2. Female attraction Three stages of song: 1. Subsong 2. Plastic song 3. Crystallized song

Introduction Song 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 H 1 : Nestling nutritional stress effects adult song Bird song is reliable indicator -developmental cost H 0 : No relationship between adult song and nestling nutritional stress

Song system development Song system nuclei RA (robust nucleus of the archstriatum) HVc (high vocal center) Area X Telencephalon Majority of song system growth between 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 Nowicki et al., 2002a

Results RA and HVc song system nuclei are significantly smaller in experimental group Nowicki et al., 2002a

Results (continued) Telencephalon volume significantly smaller in experimental group RA/telencepahlon ratio significantly smaller in experimental group Nowicki et al., 2002a

Discussion Nutritional 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: Kodric-Brown, A. and J.H. Brown (1984) Truth in adverstising: the kinds of traits favored by sexual selection. The American Naturalist 124: Marler, P. and S. Peters (1977) Selective vocal learning in a sparrow. Science 198: Mooney R. (1999) Sensitive periods and circuits for learned birdsong. Current Opinion in Neurobiology 9: 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: 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: 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: 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: 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: