Advances in Marine Research, Sustainable Oceans and Coastal Systems
From Small Beginnings to Giants: An Integrative Review of Cetacean Gigantism and its Ecological Implications for Aquatic Biology and Fisheries
Abstract
Swomik Saha Arko
Blue whales (Balaenoptera musculus) are not only the most massive animals on earth, but their ancestors were small fry. How and why did some lineages of cetaceans cross the physiological, ecological, and evolutionary barriers necessary for achieving such extreme body size? In this synthesis I combine evidence from physiology, biomechanics, behaviour, paleo biology, genomics and macroecology with that of palaeo-oceanography to explore the processes which have facilitated gigantism in cetaceans and specifically in rorqual whales. What we find is no single cause, but a succession of “gatekeepers” (new innovations that make larger size possible) and “ratchets” (either ecological or genetic situations that favor the retention and amplification of large size). Key gates include: (i) transitions in feeding mode and head/neck specializations that scale prey intake faster than costs (ii) dive and locomotor physiology that support high throughput foraging while maintaining oxygen balance and (iii) genome architectures that ameliorate cancer risk and metabolic stress in long lived monstrous bodies [1-34]. Drivers are Plio–Pleistocene movements of ocean productivity and variance movement strategies that follow ephemeral prey and demographic genomic processes of shipping successful eco physiological packages [35-51]. Comparative information from other aquatic megafauna (ichthyosaurs, sharks) and non marine systems will help resolve broader rules and peculiarities of cetaceans [52-58]. Together, these bodies of evidence shed light on how the biggest animal on Earth “started small”, and why extreme size is not only a rare evolutionary outcome but also a fragile ecological accomplishment.