Whales' extraordinarily long median life spans: A lot of food for evidence-based thoughts
Within this challenging and intriguing scenario, it has been additionally suggested that all balaenid species and, perhaps, also the vast majority of great whales have an unrecognized potential for an extraordinarily long life expectancy that has been masked by the demographic disruptions of industrial whaling as well as by several other anthropogenic noxae (1). And, while this has profound implications both on the basic biology and on the conservation of the increasingly threatened whale populations inhabiting the seas and the oceans of our Planet, I also feel the need to emphasize that the detrimental effects of microbial pathogens strongly impacting the health and conservation status of free-ranging cetaceans should be carefully taken into account. This is very well exemplified by Cetacean Morbillivirus (CeMV), which throughout the last 35 years has been responsible for dramatic epidemics and die-offs among cetaceans living along the Atlantic USA coast as well as in the Mediterranean Sea, in the Black Sea and in other geographical areas (2).
The dynamin-like GTPase genes Myxovirus 1 (Mx1) and Mx2 are known to defend mammals against multiple DNA and RNA viruses, including Measles Virus (MeV) in humans and CeMV in cetaceans as far as Mx1 is specifically concerned. Within this framework, while Mx1 and Mx2 were evolutionarily made non-functional in Odontocetes (toothed whales, including dolphins and orcas), a similar situation did not occur in Mysticetes (baleen whales) when they diverged from Odontocetes, approximately 35 million years ago (3). And, although this could reasonably argue in favour of substantial differences existing in the way dolphins and whales respond to CeMV (as well as to other viral agents), with the former ones being more prone to suffer from, and succumb to, epidemic disease outbreaks (3), it should be duly kept in mind, at the same time, that a number of whale species, such as fin whales (Balaenoptera physalus) living in the Mediterranean Sea basin, have been proven to be susceptible to CeMV infection (4). This might help explain, at least partially, why North Atlantic right whales have a median life span shorter than southern right whales (1), which could be less vulnerable to CeMV infection. This would additionally imply, as a consequence, that we need to deepen our knowledge on the host-related factors driving, along with or alternatively to Mx1 and Mx2, susceptibility/resistance to CeMV as well as to other viral pathogens potentially impacting the health and conservation status of the highly endangered North Atlantic right whale populations.
References
1. Breed GA, Vermeulen E, Corkeron P. (2024). Extreme longevity may be the rule not the exception in Balaenid whales. Sci. Adv. 10(51): eadq3086. doi: 10.1126/sciadv.adq3086.
2. Zinzula L, Mazzariol S, Di Guardo G. (2022). Molecular signatures in cetacean morbillivirus and host species proteomes: Unveiling the evolutionary dynamics of an enigmatic pathogen? Microbiol. Immunol. 66: 52-58. doi: 10.1111/1348-0421.12949.
3. Braun BA, Marcovitz A, Camp JG, Jia R, Bejerano G. (2015). Mx1 and Mx2 key antiviral proteins are surprisingly lost in toothed whales. Proc. Natl. Acad. Sci. USA 112: 8036-8040. doi: 10.1073/pnas.1501844112.
4. Mazzariol S, Centelleghe C, Beffagna G, Povinelli M, Terracciano G, Cocumelli C, Pintore A, Denurra D, Casalone C, Pautasso A, Di Francesco CE, Di Guardo G. (2016). Mediterranean Fin Whales (Balaenoptera physalus) Threatened by Dolphin MorbilliVirus. Emerg. Infect. Dis. 22: 302-305. doi: 10.3201/eid2202.15-0882.
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