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Fluctuating asymmetry and fitness in pied flycatchers

Leif Christian Stige – University of Oslo (l.c.stige@bio.uio.no). Fluctuating asymmetry and fitness in pied flycatchers. Courtship, nest box 248 (he succeded and she laid 7 eggs). Fluctuating asymmetry (FA). small, random departures from perfect symmetry. e.g. ear lengths:. R. L.

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Fluctuating asymmetry and fitness in pied flycatchers

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  1. Leif Christian Stige – University of Oslo (l.c.stige@bio.uio.no) Fluctuating asymmetry and fitness in pied flycatchers Courtship, nest box 248 (he succeded and she laid 7 eggs)

  2. Fluctuating asymmetry (FA) • small, random departures from perfect symmetry e.g. ear lengths: R L ASYMMETRY: FA = |L-R| (FLUCTUATING asymmetry: L-R values ’fluctuate’ between individuals in the population – the asymmetry is not fixed)

  3. Developmental Stability e.g. growth trajectories of individuals in a clone under exactly equal environmental conditions: random ’noise’ random ’noise’ Size Size Age Age A. Unstable B. Stable • refers to the ability to buffer growth against ’developmental noise’ • the precision of growth of a given genotype in a given environment

  4. FA and Developmental Stability EQUAL GENES RANDOMNOISE RANDOMNOISE EQUAL ENVIRONMENT • 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 • random developmental noise acts on each side, leading to • small differences between sides • the size of this difference, FA, reflects the developmental • stability

  5. FA and fitness FUNCTION - SYMMETRY FA AS SIGNAL FA Fitness FUNCTION – ’OPTIMAL’ PHENOTYPE Developmental stability GENETIC + ENVIRONMENTAL ’QUALITY’ Genes + Environment

  6. Empirical evidence of a FA-fitness relation • 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 (1997, Am.Nat. 149:916-932) - ’vote-counting’ (# studies): FA-growth: 10 yes: 2 no FA-fecundity: 16 yes: 1 no FA-survival: 19 yes: 2 no • 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, ...” 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 spp FA-survival: -0.24 [-0.22, -0.26] n = 23 spp

  7. Pied Flycatchers 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 • 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

  8. 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

  9. FA measures Tail 1-2 Tail 2 Tail 1 Prim 1-2 Prim 2-3

  10. RESULTS: FA – fitness correlations

  11. Conclusion The resultsdo notsupport the hypothesis that fluctuating asymmetry is negatively correlated with fitness in the investigated population of pied flycatchers

  12. Why no correlation? FA Developmental instability • 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 • High measurement error reduces precision • (size of error variance 12-71% of inter-individual variation in FA) • The relation may only be evident in tough conditions • There may be no relation between FA and fitness in pied flycatchers?

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