High levels of fluctuating asymmetry in isolated stickleback populations.
BACKGROUND
Fluctuating asymmetry (FA), defined as small random deviations from the ideal bilateral symmetry, has been hypothesized to increase in response to both genetic and environmental stress experienced by a population. We compared levels of FA in 12 bilateral meristic traits (viz. lateral-line system neuromasts and lateral plates), and heterozygosity in 23 microsatellite loci, among four marine (high piscine predation risk) and four pond (zero piscine predation risk) populations of nine-spined sticklebacks (Pungitius pungitius).


RESULTS
Pond sticklebacks had on average three times higher levels of FA than marine fish and this difference was highly significant. Heterozygosity in microsatellite markers was on average two times lower in pond (HE ≈ 0.3) than in marine (HE ≈ 0.6) populations, and levels of FA and heterozygosity were negatively correlated across populations. However, after controlling for habitat effect on heterozygosity, levels of FA and heterozygosity were uncorrelated.


CONCLUSIONS
The fact that levels of FA in traits likely to be important in the context of predator evasion were elevated in ponds compared to marine populations suggests that relaxed selection for homeostasis in ponds lacking predatory fish may be responsible for the observed habitat difference in levels of FA. This inference also aligns with the observation that the levels of genetic variability across the populations did not explain population differences in levels of FA after correcting for habitat effect. Hence, while differences in strength of selection, rather than in the degree of genetic stress could be argued to explain habitat differences in levels of FA, the hypothesis that increased FA in ponds is caused by genetic stress cannot be rejected.
Department of Biosciences, Ecological Genetics Research Unit, University of Helsinki, PO Box 65, FI-00014, Helsinki, Finland. juha.merila@helsinki.fi
Nina
N
Trokovic
Gábor
G
Herczeg
Nurul Izza Ab
NI
Ghani
Takahito
T
Shikano
Juha
J
Merilä
D000818:Animals; D017753:Ecosystem; D005260:Female; D014644:Genetic Variation; D005828:Genetics, Population; D008297:Male; D061005:Ponds; D012623:Seawater; D012641:Selection, Genetic; D023701:Smegmamorpha / Q000235:genetics*