Fluctuating asymmetry and fitness in pied flycatchers

Leif Christian Stige – University of Oslo(l.c.stige@bio.uio.no)

Courtship, nest box 248

(he succeded and she laid 7 eggs)

Fluctuating asymmetry (FA)

- small, random departures from perfect symmetry

e.g. ear lengths:

FA = |L-R|

R L

ASYMMETRY:

(FLUCTUATING asymmetry: L-R values ’fluctuate’ between individuals in the population – the asymmetry is not fixed)

Developmental Stability

- the precision of growth of a given genotype in a given environment

- refers to the ability to buffer growth against ’developmental noise’

e.g. growth trajectories of individuals in a clone under exactlyequal environmental conditions:

random’noise’

Siz

e

Age

A. Unstable B. Stable

random’noise’

Siz

eAge

FA and Developmental Stability

- random developmental noise acts on each side, leading tosmall differences between sides

- the size of this difference, FA, reflects the developmental stability

- the two sides of a bilaterally symmetric trait (e.g. ear lengths)can be assumed to have developed in the same environment and with the same genetic basis

EQUAL GENES

EQUAL ENVIRONMENT

RANDOM NOISE

RANDOM NOISE

FA and fitness

Developmental stability

FA FitnessFUNCTION - SYMMETRYFA AS SIGNAL

FUNCTION –’OPTIMAL’ PHENOTYPE

Genes + Environment

GENETIC + ENVIRONMENTAL

’QUALITY’

Empirical evidence of a FA-fitness relation

Møller (1997, Am.Nat. 149:916-932)

- ’vote-counting’ (# studies): FA-growth: 10 yes: 2 noFA-fecundity: 16 yes: 1 noFA-survival: 19 yes: 2 no

Leung and Forbes (1996, Ecoscience 3:400-413)- meta-analysis 61species: mean r (FA – fitness related traits) = -0.26 (SE 0.06) ( i.e. FA explains 6.7% of variation in fitness)- no differences between functional/non-functional, or sexually selected/not sexually selected traits

Møller (1999, Ecology Letters 2:149-156)

- meta-analysis, weighted r [95 % CI]: FA-growth: -0.16 [-0.11, -0,21] n = 10 spp

FA-fecundity: -0.34 [-0.31, -0.37] n = 14 sppFA-survival: -0.24 [-0.22, -0.26] n = 23 spp

Clarke (1998, Am.Nat 152:762-766)- re-evaluated the data cited by Møller (1997): ”a significant proportion of the data (>50%) reported by Møller as supporting a positive relationship between developmental stability and various fitness components fail to do so, ...”

Pied Flycatchers

• Migratory – breeds May-June Norway• Prefer nest boxes• Mainly monogamous - 1/5 of breeding males bigamous• Females build nests and incubate, both parents feed the young

Our study system

• Sørkedalen, Oslo, 2000 and 2001 • Population of 70-75 pairs each year• Totally 108 males and 125 females• Birds caught, measured and observed throughout breeding season

Fitness measures

• Arrival date• Pairing status

(males: bigamous/monogamous/unpaired, females: primary/secondary)

• Time until pairing(from arrival, corrected for arrival date)

• Time until egg laying(from pairing, corrected for pairing date)

• Number of eggs laid(in primary nest, corrected for pairing date)

• Hatching success• Fledging success• Offspring weight• Total number of fledglings• Return rate

FA measures

Prim 1-2

Prim 2-3

Tail 1-2

Tail 2

Tail 1

Spearman Correlation Coeff. with 95% bootstrap conf. limits

FA - FITNESS CORRELATIONS

-1.0 -0.5 0.0 0.5 1.0

ARRIVAL DATE

PAIRING STATUS

TIME UNTIL PAIRING

TIME UNTIL EGG LAYING

NUMBER OF EGGS LAID

HATCHING SUCCESS

FLEDGING SUCCESS

OFFSPRING WEIGHT

TOTAL FLEDGLING PROD.

RETURN RATE

(bigamous/monog./unpaired male, prim./sec. female)

(from arrival, corrected for arrival date)

(from pairing, corr. for pairing date)

(in primary nest, corr. for pairing date)

positive

negative

positive

positive

negative

negative

negative

negative

negative

negative

(n = 99)

(n = 96)

(n = 89)

(n = 90)

(n = 90)

(n = 90)

(n = 81)

(n = 77)

(n = 88)

(n = 99)

(n = 122)

(n = 122)

(n = 122)

(n = 122)

(n = 122)

(n = 108)

(n = 98)

(n = 108)

(n = 122)

Expectedrelation

femalesmales

RESULTS: FA – fitness correlations

Conclusion

The results do not support the hypothesis that fluctuating asymmetry is negatively correlated with fitness in the investigated population of pied flycatchers

Why no correlation?

• The relation between FA and fitness may be indirect, and FA may be a poor indicator of developmental instability - trying to estimate a variance with two data points (high sampling error):

- but averaging across traits (and years) increases precision

Size

Age

FA Developmental instability

• The relation may only be evident in tough conditions

• High measurement error reduces precision (size of error variance 12-71% of inter-individual variation in FA)

• There may be no relation between FA and fitness in pied flycatchers?