Changing The Unchanged: How Gar Shed Light On The Evolution Of Lineages Affected By Evolutionary Stasis

Gars (Family: Lepisosteidae) have long been considered “living fossils” thanks to their relatively unchanged bodyplan from the late Mesozoic to modern times. Yet, it was only recently that their evolutionary stasis was explored on a genomic level, discovering that they experience extremely low rates of molecular evolution of any jawed vertebrate yet examined. Despite this, there is a vast diversity both physiologically and ecologically within the family. In this study, we identify shared genomic regions undergoing rapid evolution by pinpointing genomic heterozygosity hotspots across genomes of all members within the family Lepisosteidae. Our results show multiple regions of shared heterozygosity amongst all and most genomes within the family Lepisosteidae. Many of the regions of heterozygosity analyzed across these genomes code for genes that influence muscle development, supporting the long observed natural history that certain species of gar are better adapted for riverine systems or fast moving aquatic environments, whereas others are better developed for slow moving aquatic environments. This study also displays that even within the slowest evolving lineages, there is still evolutionary change in certain regions of the genome, and thus could help shed light on how lineages that experience evolutionary stasis still maintain diversity and persist across long spans of geologic time. Thus, our study not only provides insight into the evolution of modern Lepisosteids, but also provides a novel mechanism for analyzing slow evolving lineages.