Convergent evolution of mechanically optimal locomotion in aquatic invertebrates and vertebrates.
Examples of animals evolving similar traits despite the absence of that trait in the last common ancestor, such as the wing and camera-type lens eye in vertebrates and invertebrates, are called cases of convergent evolution. Instances of convergent evolution of locomotory patterns that quantitatively agree with the mechanically optimal solution are very rare. Here, we show that, with respect to a very diverse group of aquatic animals, a mechanically optimal method of swimming with elongated fins has evolved independently at least eight times in both vertebrate and invertebrate swimmers across three different phyla. Specifically, if we take the length of an undulation along an animal's fin during swimming and divide it by the mean amplitude of undulations along the fin length, the result is consistently around twenty. We call this value the optimal specific wavelength (OSW). We show that the OSW maximizes the force generated by the body, which also maximizes swimming speed. We hypothesize a mechanical basis for this optimality and suggest reasons for its repeated emergence through evolution.
Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, United States of America.
Rahul
R
Bale
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois, United States of America.
Izaak D
ID
Neveln
Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, United States of America.
Amneet Pal Singh
AP
Bhalla
Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, United States of America; Department of Biomedical Engineering, Northwestern University, Evanston, Illinois, United States of America; Department of Neurobiology, Northwestern University, Evanston, Illinois, United States of America.
Malcolm A
MA
MacIver
Department of Mechanical Engineering, Northwestern University, Evanston, Illinois, United States of America.
Neelesh A
NA
Patankar
D000818:Animals; D005075:Biological Evolution; D001696:Biomechanical Phenomena; D007448:Invertebrates / Q000502:physiology*; D013550:Swimming; D014714:Vertebrates / Q000502:physiology*; D014867:Water
D014867:Water