As few as 7% of male humpback whales in New Caledonia in the south-west Pacific may have fathered offspring, a study has found.
The paternity analysis found that 93% of males had no evidence of genetic offspring throughout the 25-year study period and no male had sired more than two offspring. It was unclear why some males were more successful than others, the authors said.
“It tells us that becoming a father is a very rare outcome for a humpback male and one which they have to compete very strongly for,” said Dr Luke Rendell, a co-author of the study from the University of St Andrews. He said they could compete by fighting off other males or “impressing” females with their song.
“This may in part explain the extreme nature of the song display, one of the most complex songs in the animal kingdom that males spend hours and hours producing during breeding season,” Rendell said.
Writing in the journal Royal Society Open Science, the researchers reported how they had collected photographs and genetic samples of humpback whales for identification during field surveys in the South Pacific between 1995 and 2019.
They then used the genetic data, which encompassed 936 mature males, to determine the paternity of 177 mother–offspring pairs.
The results identified the fathers of up to 79 of the offspring, revealing that 66 of the sampled males were fathers. In other words, 93% had no evidence of having fathered offspring.
The remaining fathers, Rendell said, would have been unsampled males either from the New Caledonian humpback whale population or visitors from other populations. Another genetic analysis suggested there were about 2,000 to 2,600 males that could be fathers to the offspring studied, meaning that just under half were sampled.
Among the identified males that had reproduced, the team found none had sired three or more offspring.
“Male competition might be more about being able to reproduce at all rather than siring a large number of offspring,” the researchers wrote.
However, fathers were at least 3.5 times more likely to sire more than one offspring than expected if mating was random.
While the team noted there were more males on the breeding grounds than females, and females were scattered widely, they said the results suggested some males were more successful at becoming fathers than others.
“Our findings are consistent with similar research in the North Pacific,” Rendell said.
While the researchers said having only a small number of successful males could reduce the genetic diversity of a population, and ultimately affect its ability to adapt to environmental changes, they added that this could be mitigated by mixing with neighbouring populations.
