Data from: Cline coupling and uncoupling in a stickleback hybrid zone

Strong ecological selection on a genetic locus can maintain allele
frequency differences between populations in different environments, even
in the face of hybridization. When alleles at divergent loci come into
tight linkage disequilibrium, selection acts on them as a unit and can
significantly reduce gene flow. For populations interbreeding across a
hybrid zone, linkage disequilibria between loci can force clines to share
the same slopes and centers. However, strong ecological selection on a
locus can also pull its cline away from the others, reducing linkage
disequilibrium and weakening the barrier to gene flow. We looked for this
‘cline uncoupling’ effect in a hybrid zone between stream resident and
anadromous sticklebacks at two genes known to be under divergent natural
selection (Eda and ATP1a1) and five morphological traits that repeatedly
evolve in freshwater stickleback. These clines were all steep and located
together at the top of the estuary, such that we found no evidence for
cline uncoupling. However, we did not observe the stepped shape normally
associated with steep concordant clines. It thus remains possible that
these clines cluster together because their individual selection regimes
are identical, but this would be very surprising given their diverse roles
in osmoregulation, body armor and swimming performance.