| dc.description.abstract | In the wild, menopause and a prolonged postreproductive female lifespan are
extremely rare. Besides humans, it has only been found in five toothed whale
species, including killer whales. Thus, toothed whales, with their high degree of
variation in habitat specialisation and social structure, provide an exciting scope
for investigating links between ecology, social behaviour, and life history. In this
thesis, I address some of the questions about menopause in toothed whales, using the mammal-eating Bigg’s killer whale populations as the study system.
In the first chapter, I present an overview of the current knowledge of menopause
with a focus on toothed whales and briefly outline diversity among killer whale
ecotypes. In Chapter 2, I address the question of whether menopause is a unique
trait of the Resident killer whale ecotype, using long-term demographic data to
show that there is a similar postreproductive female lifespan in the fish-eating
Resident killer whales and the mammal-eating Bigg’s killer whales.
In Chapter 3, using more than four decades of association and demographic data,
I demonstrate that Bigg’s killer whale females maintain strong and long-lasting relationships with their adult sons, while daughters disperse, a pattern that indicates
that postreproductive females can support their adult sons, potentially boosting
their reproductive success, and thereby gain inclusive fitness benefits.
In Chapter 4, using multi-generational records of Bigg’s killer whales, I show that
mothers increase the survival of their offspring. This indicates that mothers gain
inclusive fitness benefits from helping their offspring, supporting theoretical predictions for the evolution of menopause.
In Chapter 5, I use unoccupied aerial systems methods to examine leadership
and prey sharing within Bigg’s killer whale family groups. From this, I find that
females lead their group regardless of age and postreproductive females favour
sharing with adult daughters. In contrast, reproductive females avoid sharing with
adult males, indicating selection behind these behaviours is different compared
to the Resident killer whale populations.
In the final chapter, I present a general discussion of my results and suggest
directions and focus for future research questions on menopause generally and
within the Bigg’s killer whale population specifically. | en_GB |
