Phenotypic variation in divergent mitochondrial haplotypes in migratory three-spined stickleback

Mitochondrial haplotype in migratory three-spined stickleback on North Uist is linked to higher male gonadosomatic index (GSI) in European haplotype fish.

• Why it matters: Mitochondrial genomes can diverge under selection, but it is unclear whether whole-organism phenotypes shift with mitochondrial haplotype differences in natural populations.
• What they did: Stickleback were sampled from six lochs on North Uist and phenotypic traits (organ size, body size, ovule volume/clutch size) plus citrate synthase activity were compared between two divergent mitochondrial haplotypes (trans-Atlantic vs European).
• The result: Male GSI differed by mitochondrial haplotype and citrate synthase activity showed a potential haplotype effect, while other measured traits did not differ; sex and population effects were common.

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