Mortality rate acceleration and post-reproductive lifespan in matrilineal whale species

• Published in: Biology Letters
• Main Author: Foote, Andrew D
• Format: Text
• Language: English
• Published: The Royal Society 2008
• Subjects: Research Article; Killer Whale; Orca; Orcinus orca; Killer whale
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2429943; http://www.ncbi.nlm.nih.gov/pubmed/18252662; https://doi.org/10.1098/rsbl.2008.0006

The strength of selection to increase the span of a life stage is dependent upon individuals at that stage being able to contribute towards individual fitness and the probability of their surviving to that stage. Complete reproductive cessation and a long post-reproductive female lifespan as found in humans are also found in killer whale (Orcinus orca) and short-finned pilot whale (Globicephala macrorhynchus), but not in the long-finned pilot whale (Globicephala melaena). Each species forms kin-based, stable matrilineal groups and exhibits kin-directed behaviours that could increase inclusive fitness. Here, the initial mortality rate and mortality rate-doubling time of females of these three closely related whale species are compared. The initial mortality rate shows little variation among pilot whale species; however mortality rate accelerates almost twice as fast in the long-finned pilot whale as it does in killer whale and short-finned pilot whale. Selection for a long post-reproductive female lifespan in matrilineal whales may therefore be determined by the proportion of females surviving past the point of reproductive cessation.