Testing for signatures of convergent evolution
Northern and southern populations of each species were analysed for
genetic patterns driven by adaptation to some unmeasured factor related
to latitude, by searching for genes with abnormally high patterns of
FST. Using the top candidate approach (Yeaman et
al. , 2016) 73 genes had extreme values of FST in
threespines compared with 65 genes in tubesnouts (Table S4; Fig. 3A).
None of the top candidates were directly shared between these species,
but a pair of candidate genes encoding proteins in the forkhead box
family were detected (Ts: foxo3b ; Tu: foxb2 ; Table S4). No
signatures of high FST could be detected in ninespines
because too many scores were close to FST = 1 to
identify meaningful outliers. Additionally, comparing all species, only
three \({\overset{\overline{}}{H}}_{E}\) scores overlapped in the upper
95% of the distribution (Fig. 3A). The Null-W test identified five
possible signatures of convergent evolution between threespines and
tubesnouts (Fig. 4B), but after adjusting for false discoveries these
signatures lost significance (Table S5). The Null-W test did not
identify any forkhead box genes as candidates.