[MARMAM] New Publication: Stredulinsky et al. (2021)

Eva Stredulinsky estredulinsky at gmail.com
Thu Feb 18 09:31:13 PST 2021

Dear colleagues,

We are very pleased to announce the recent publication of our paper:
"Family feud: permanent group splitting in a highly philopatric mammal, the
killer whale (*Orcinus orca*)". The article is available here:

Stredulinsky, E.H., C.T. Darimont, L. Barrett-Lennard, G.M. Ellis, and
J.K.B. Ford

For animals that tend to remain with their natal group rather than
individually disperse, group sizes may become too large to benefit
individual fitness. In such cases, group splitting (or fission) allows
philopatric animals to form more optimal group sizes without sacrificing
all familiar social relationships. Although permanent group splitting is
observed in many mammals, it occurs relatively infrequently. Here, we use
combined generalized modeling and machine learning approaches to provide a
comprehensive examination of group splitting in a population of killer
whales (*Orcinus orca*) that occurred over three decades. Fission occurred
both along and across maternal lines, where animals dispersed in parallel
with their closest maternal kin. Group splitting was more common: (1) in
larger natal groups, (2) when the common maternal ancestor was no longer
alive, and (3) among groups with greater substructuring. The death of a
matriarch did not appear to immediately trigger splitting. Our data suggest
intragroup competition for food, leadership experience and kinship are
important factors that influence group splitting in this population. Our
approach provides a foundation for future studies to examine the dynamics
and consequences of matrilineal fission in killer whales and other taxa.

Group living among mammals often involves long-term social affiliation,
strengthened by kinship and cooperative behaviours. As such, changes in
group membership may have significant consequences for individuals' fitness
and a population's genetic structure. Permanent group splitting is a
complex and relatively rare phenomenon that has yet to be examined in
detail in killer whales. In the context of a growing population, in which
offspring of both sexes remain with their mothers for life, we provide the
first in-depth examination of group splitting in killer whales, where
splitting occurs both along and across maternal lines. We also undertake
the first comprehensive assessment of how killer whale intragroup cohesion
is influenced by both external and internal factors, including group
structure, population and group demography, and resource abundance.

Eva Stredulinsky
*Eva Stredulinsky*
*Aquatic biologist*
*Fisheries and Oceans Canada*
*Pacific Biological Station*
*3190 Hammond Bay Road*
*Nanaimo BC  **V9T 6N7*
*Email: eva.stredulinsky at dfo-mpo.gc.ca <eva.stredulinsky at dfo-mpo.gc.ca>*
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