ИСТИНА

Resident killer whales in the North Pacific live in stable family units which consist of maternal relatives. Both males and females stay in their natal matriline for their entire lives. Each matriline has a repertoire of stereotyped calls – a vocal dialect. These dialects pass from mother to offspring by means of social learning and are thought to change in time through the accumulation of random errors. Therefore, the dialects of more closely related matrilines should be more similar, than the dialects of less related matrilines. The relatedness is also thought to influence the frequency of social interactions between matrilines, with more related matrilines associating more frequently. Therefore, the strength of social associations must correlate with dialect similarity. In this study we tested this prediction on resident killer whales from Eastern Kamchatka, Russia. We calculated a social association index for the matrilines based on the observations of their associations in 2002 and 2004-2011. Then we compared this index with the patterns of call sharing and with the similarity of shared call subtypes across matrilines. Association analysis revealed six clusters of matrilines with a social association index ≥ 0.4. Four of them included matrilines with the same call repertoires, but two included matrilines with different repertoires. Only two of the four clusters included all known matrilines with the particular repertoire, while the other two included only some and not the other matrilines with this repertoire. The similarity of call subtypes in many cases also was not correlated with social associations. Therefore, we conclude that either the social associations between matrilines or the similarity of their repertoires, or both, is not always correlated with matriline relatedness.