chapter 2 opener: studies of bird song have relied heavily on male white-crowned sparrows

Chapter 2 Opener: Studies of bird song have relied heavily on male white-crowned sparrows

2.1 Song dialects in white-crowned sparrows from Marin, Berkeley, and Sunset Beach, California

Why do different individualsof same species producedifferent dialects of same song?

Development?Brain morphology?Number of offspring?Evolutionary history??

• Proximate Causes

- Are these groups genetically different?

- Environmental/experiences?

Egg removal; hand-reared in lab; isolated; started to sing at 150 days BUT unrecognizable

Critical missing component exists

• Chicks (10 to 50 days old) exposed to tapes of adult white-crowned sparrows singing.

• At 150 days old, started singing, mimicked the exact version of what they had heard on tape by day 200!

• Play the Berkeley dialect - sing Berkeley song

• Play the Marlin dialect - sing Marlin song

• SUPPORTS ENVIRONMENTAL DIFFERENCE HYPOTHESIS

(store info from tutors)

If hand-reared white crowned sparrow is deafened as a young bird and cannot hear itself sing (after listening and before vocalization periods) (after 50 and before 150 days)…

Then bird never produces anything like normal song (see Fig. 2.2)

2.2 Hearing is critically important for song learning in the zebra finch

If they hear songs of another species (10-50 days old)…

Then they develop aberrant songs—similar to “songs” produced by a male that never heard any birdsong…

But if allowed to hear song of same species plus other species at 200 days, it develops a perfect song for its species (see Fig. 2.3)

2.3 Song learning hypothesis based on laboratory experiments with white-crowned sparrows

White-crowned sparrow listens to two songs and after 100 days it sings its song

Social Experience and Song Development

• At early age, immature brain is able to selectively store info about sounds made by white-crowned sparrows and ignore other species’ songs (Fig. 2.3)

• But when exposed to another species (tutor) as well as hearing (only) its own adult live song—after 50 days old—the bird learns the other species’ song (Fig. 2.4)

• Social experience has very powerful developmental effects

2.4 Social experience influences song development

(tutor)

(hidden adult male)

2.6 Sonograms of contact calls of galahs and pink cockatoos reared under different conditions

Unique example:Pink cockatoo steals eggs

Galahs thereforehave foster parents

• Work on the development of singing behavior in male white-crowned sparrows has demonstrated that the birds must learn to sing a particular dialect of the full song of their species. This finding eliminates the genetic differences hypothesis for the song differences between white-crowns in Marin and in Berkeley. Would we be right, therefore, to conclude that the genetic information present in the cells of white-crowned sparrows is irrelevant for the development of the bird’s singing behavior? In this regard, what importance do you attach to the finding that white-crown males apparently can learn their species’ song far more easily than the song of other sparrows?

• To say that the behavioral differences between two individuals are not genetic does not mean that the behavior itself can develop without the genetic information possessed by the two individuals. Both Marin and Berkeley birds have genes, which could be identical in both individuals, and that are vital to the development of their brains. The genes in question influence the structure and capacities of their brains, an essential contribution if their brains are to grow and acquire the ability to learn things. The fact is that all male white-crowns have learning biases that steer them toward the acquisition of a local dialect of their own species. Thus, the gene–environment interactions that take place during development produce a very special kind of brain with limited, but adaptive, properties.

Underlying mechanisms of song development

• Where are white-crowned sparrow memories stored?• What parts of the brain control sound at 5 months of age?• How does young male know to match his song memories

with his initial simpler songs?

Males vs. females• Females do not sing• Do males and females have different brains? • Genetic or environmental?

• Males: 2 Z chromosomes develops testes• Females: Z and W chromosomes develops ovaries

• Male testosterone different brain circuits• Male estrogen in brain different neural pathways

(See Fig. 2.7)

HVC = higher vocal center

2.7 Changes in the song system of young male and female zebra finches

Underlying mechanisms (continued)

• Genetic or environmental (continued)• Estrogen inserted into a female song circuits develop

In zebra finches and most birds that learn songs, numbers of genes are turned on/off in discrete clusters of neurons (nuclei) (Fig. 2.8)

2.11 The song system of a typical songbird

2.8 The timing of gene activity in different components of the avian song control system in males

Underlying mechanisms (continued)

When zebra finches attempt to match a tutor’s song…

…gene called ZENK found in area X is rapidly increased, expressing a specific protein (Fig. 2.9)

2.9 Gene expression in a component of the zebra finch song system

Underlying mechanisms (continued)

Circuits for song-learning

Circuits for production of memorized song patterns

CircuitsHVC and NCM connects to RA connects to nXIIts syrinx (larynx) (Fig. 2.11)

• Ablation experiment of RA or HVC• Ablation of IMAN after 150 days = no effect• Ablation of IMAN before 50 days = song not learned• Stimulation of HVC and RA occurs in response to complex song-

learning (Fig. 2.12)

Blue (production pathway) is the song output pathwayRed (learning pathway)

DLM: Dorso-Lateral division of the Medial thalamus

X: Area X of the paraolfactory lobe

LMAN: Lateral Magnocellular nucleus of the Anterior Neostriatum

MMAN: Medial nucleus Magnocelularis of the Anterior Neostriatum

NIf: interfacial nucleus of the neostriatum

cHV: Hyperstriatum Ventrale

HVc: High Vocal Center (Hyperstriatum Ventralis pars caudalis)

NCM: Neostriatum Caudo-Medial nucleus

NCM

RA: Robust nucleus of the Archistriatum

nXII: nucleus of the 12th cranial nerve

VL medulla: VentroLateral medulla Uva: nucleus Uvaeformis of the thalamusDM: Dorso-Medial subdivision of the intercollicular nucleus

AVT: Area Ventralis of Tsai

Nuclei of the avian song learning and production pathways

Hormone levels mediate sexually related differences in song production nuclei

2.14 Differences in the size of one nucleus of the song system

2.15 Single cells and song learning in the swamp sparrow

Single neuron effects -- record from single cells in HVC -- different songs activate different neurons -- evidence for single neurons storing single

types.

Ultimate causes

Evolution• Look back to when song-learning began in avian order• Of 23 orders, only 3 have song-learning (parrots,

hummingbirds, songbirds) (Figs. 2.14 and 2.15)• Other orders produce complex vocalizations but no

learning involved

• How would you test this?• Ho: Did song-learning evolve independently between

the same orders OR

• HA: Song-learning was ancestral in all birds (see arrow) and then disappeared in most groups

• Which hypothesis is correct? (Fig. 2.16)

2.17 The song of a vocal non-learner, the eastern phoebe

2.16 The phylogeny of song learning in birds

2.17 The song control systems of parrots, hummingbirds, and oscine songbirds (Part 1)

2.18 The song control systems of parrots, hummingbirds, and oscine songbirds (Part 2)

Figure 2.16 and 2.18 The song control systems of parrots, hummingbirds, and oscine songbirds

Reproductive benefits• If song-learning has been selected out in other bird groups,

what advantages (fitness benefits) have resulted in retention of song-learning in parrots, hummingbirds, and songbirds?

• What do these birds gain?• Enhanced competition for territories and mates? (Singing same song

with same dialect may indicate “fit” singers—Fig. 2.19)• Experiment: Removed all males in territories and did playback

experiment

2.19 Does bird song repel territorial intruders?

2.20 White-crowned sparrow females are attracted to the songs of male white-crowned sparrows

Mate attraction hypothesis:Females will respond to taped songs of own species much more strongly than to taped songs of another species

Benefits of learning a dialect• Why do males of the same species sing different dialects?• Any reproductive advantage?• Most bird species do not learn songs, so why use song-

learning? (takes time, energy, and special neural mechanisms—all of which can be directed to other reproductive-enhancing activities)

• Need to ID the reproductive advantage that outweighs the costs