Clarke, J. T. | bioRxiv Science

bioRxiv2024

Variable patterns of phenotypic evolution among canonical 'living fossil' lineages

Coelacanths, lungfishes, and holosteans represent three emblematic living fossil lineages, thought to be united by similar patterns of phenotypic change through time. While past studies suggest that diverse evolutionary patterns occur within these groups, it is unclear whether these reflect biological differences or arise from contrasting analytical approaches. Here, we examine these lineages under a common framework to assess variation in the evolution of discrete characters, and morphometric shape data, to test whether living fossils show comparable patterns of phenotypic evolution. Our results suggest different evolutionary modes occur, both among and within lineages, as a function of data type. For lungfishes, rates in discrete characters are highest in the Devonian and monotonically decline over time. Coelacanth rates show multiple early peaks followed by a decline toward the recent. Holostean rates show modest peaks but are broadly comparable over time. Patterns of body shape evolution also differ among clades, with strong support for declining rates over time for coelacanths but mixed evidence for similar dynamics in the other groups. Our results imply idiosyncratic processes of evolutionary change among traditional examples of living fossils and indicate a need to explicitly quantify patterns of change rather than apply informal, often qualitative, macroevolutionary classifications.

evolutionary biology↗

bioRxiv2023

Salinity plays a limited role in determining rates of size evolution in fishes globally across multiple scales

Substantial progress has been made to map biodiversity and its drivers across the planet at multiple scales, yet studies that quantify the evolutionary processes that underpin this biodiversity, and test their drivers at multiple scales, are comparatively rare. Studying most fish species, we quantify rates of body size evolution to test the role of fundamental salinity habitats in shaping rates of evolution at multiple scales. We also determine how four additional factors shape evolutionary rates. In up to 1710 comparisons studying over 27,000 ray-finned fish species, we compare rates of body size evolution between five salinity habits using 12 metrics. The comparisons span a molecular tree, supertrees, and ten scales of observation to test for robust patterns and reveal how patterns change with scale. Then, three approaches assess the role of three non-salinity factors on rates, and an alternative habitat scheme tests if lakes influence evolutionary rates. Rates of size evolution rarely differ consistently between salinity habitats; rate patterns are highly clade- and scale-dependent. One exception is freshwater-brackish fishes, which possess among the highest size rates of any salinity, and show higher rates than euryhaline fishes in most groupings studied at most scales, and verses marine, freshwater, and marine-brackish habitats at specific scales. Additionally, species richness had the greatest potential to predict phenotypic rates, followed by branch duration and absolute values of body size. Lacustrine environments were consistently associated with high rates of size evolution. We reveal the rate patterns that underpin global body size diversity for fishes, identifying factors that play a limited role in shaping rates of size evolution, such as salinity, and those such as species richness, age, and lake environments that consistently shape evolutionary rates across half of vertebrate diversity.

evolutionary biology↗