Fig. 6.

Detecting correlated evolution of extra-pair paternity and syllable repertoire size. We tested for correlated evolution of syllable repertoire size and EPP using the same procedure as in Fig. 5. a When the threshold between smaller and larger syllable repertoires is in the lowest third of observed values (16 unique thresholds ≥1.8 and <10 syllables, red arrows), low rates of EPP with small syllable repertoires are unstable, and we observe elevated transition rates either toward larger repertoires or toward higher rates of EPP. b When the threshold between smaller and larger syllable repertoires is in the middle third of observed values (16 unique thresholds ≥10 and <28.4 syllables, yellow arrows), low rates of EPP are again unstable with small syllable repertoires, and evolutionary transitions toward higher rates of EPP are elevated. c When the threshold between smaller and larger syllable repertoires is in the highest third of observed values (16 unique thresholds ≥28.4 and <241 syllables, blue arrows), the combination of large syllable repertoires and high rates of EPP is unstable, and we observe elevated transition rates either toward smaller repertoires or toward lower rates of EPP. We averaged rate values from all runs, regardless of significance. These results were robust to jackknife resampling across families. In the middle segment, only removing Zosteropidae qualitatively altered the dominant rates of transition such that there was accelerated evolution from low to high EPP regardless of syllable repertoire (Supplementary Figure 31). d For each run of BayesTraits, we performed a likelihood-ratio test to assess whether the model of correlated evolution between EPP and syllable repertoire size was a significantly better fit to the data than the independent evolution model; p-values are plotted against the syllable repertoire size values defining the threshold