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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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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 ASYMMETRY: FA = |L-R| (FLUCTUATING asymmetry: L-R values ’fluctuate’ between individuals in the population – the asymmetry is not fixed)
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
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
FA and fitness FUNCTION - SYMMETRY FA AS SIGNAL FA Fitness FUNCTION – ’OPTIMAL’ PHENOTYPE Developmental stability GENETIC + ENVIRONMENTAL ’QUALITY’ Genes + Environment
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
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
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 Tail 1-2 Tail 2 Tail 1 Prim 1-2 Prim 2-3
Conclusion The resultsdo notsupport the hypothesis that fluctuating asymmetry is negatively correlated with fitness in the investigated population of pied flycatchers
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?