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    Biodiversity engine for fishes: Shifting water depth    
      
     Date:   
         February 13, 2023   
     Source:   
         Yale University   
     Summary:   
         Fish, the most biodiverse vertebrates in the animal kingdom,   
         present evolutionary biologists a conundrum: The greatest species   
         richness is found in the world's tropical waters, yet the fish   
         groups that generate new species most rapidly inhabit colder   
         climates at higher latitudes. A new study helps to explain this   
         paradox. The researchers discovered that the ability of fish in   
         temperate and polar ecosystems to transition back and forth from   
         shallow to deep water triggers species diversification.   
      
         Their findings suggest that as climate change warms the oceans at   
         higher latitudes, it will impede the evolution of fish species.   
      
      
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   FULL STORY   
   ==========================================================================   
   Fish, the most biodiverse vertebrates in the animal kingdom, present   
   evolutionary biologists a conundrum: The greatest species richness is   
   found in the world's tropical waters, yet the fish groups that generate   
   new species most rapidly inhabit colder climates at higher latitudes.   
      
      
   ==========================================================================   
   A new Yale study helps to explain this paradox. The researchers   
   discovered that the ability of fish in temperate and polar ecosystems   
   to transition back and forth from shallow to deep water triggers species   
   diversification.   
      
   Their findings, published Feb. 11 in the journal Nature Communications,   
   suggest that as climate change warms the oceans at higher latitudes,   
   it will impede the evolution of fish species.   
      
   "The fish clades contributing the most fish diversity in today's oceans   
   are leveraging the water column and the ocean depths, in particular,   
   to diversify," said lead author Sarah T. Friedman, who conducted the   
   research while a G.   
      
   Evelyn Hutchinson postdoctoral associate at Yale. "Fishes that make   
   these forays into the deep ocean are almost exclusively located in   
   high latitudes, where it's easier to move along the water column. These   
   regions are experiencing the most drastic warming due to climate change,   
   which threatens to disrupt speciation by making it more difficult for   
   fish to change depths."  Friedman, now a research fish biologist at the   
   National Oceanic and Atmospheric Administration, coauthored the study   
   with Martha Mun~oz, an assistant professor of ecology and evolutionary   
   biology in Yale's Faculty of Arts and Sciences, and an assistant curator   
   of vertebrate zoology at the Yale Peabody Museum.   
      
   For the study, the researchers analyzed existing data on the global   
   species occurrence of 4,067 fish species that included information on   
   species geographic range and speciation rate. In part, their analysis   
   modeled how often fish lineages might be expected to transition   
   across ocean depths. By laying out a distribution of anticipated   
   shifts in depth, the researchers could compare the number of observed   
   transitions in specific lineages. They found that species-rich,   
   high-latitude lineages -- eelpouts, rockfishes, flatfishes, icefishes,   
   and snailfishes -- transitioned up and down the water column more often   
   than expected. Meanwhile, hyper-diverse tropical lineages, such as gobies   
   and wrasses, changed depth less frequently than predicted.   
      
   Fish clades, evolutionary lineages that share a common ancestor, that   
   can freely disperse along the depth gradient may be more likely to   
   capitalize on novel resources or niches at specific depths and become   
   isolated from other members of their group, the researchers said. This   
   can lead to repeated local adaptation and the evolution of new species.   
      
   Many variables can affect a fish's ability to move between depths,   
   including water temperature, pressure, and light penetration. Friedman and   
   Mun~oz suggest that temperature plays an important role in the ability   
   of high-latitude fish clades to transition along the water column. Fish   
   clades that inhabit colder water have an easier time traveling into   
   ocean depths, where water temperature plummets dramatically. By contrast,   
   tropical fish, which spend their lives in warm, shallow waters, face steep   
   thermal barrier to transitioning to the deep ocean, the researchers said.   
      
   The existing high biodiversity in tropical waters could be a remnant of   
   the deep past when warmer regions were hotbeds of species generation,   
   but over time, most diversification began occurring closer to the Earth's   
   poles, they explained.   
      
   But this biodiversity engine at higher latitudes is vulnerable to   
   climate change. Since the water profile is so much more uniform at   
   higher latitudes than in the tropics, the fish that inhabit them are   
   physiologically fine-tuned to those environments, Mun~oz explained. For   
   them, a one-degree shift in temperature will be physiologically more   
   challenging than for an organism that is more of a thermal generalist.   
      
   "As the oceans warm, organisms might face steeper barriers to dispersal   
   across the depth column," Mun~oz said. "Over time, I think we'll see a   
   slowdown of this engine of biodiversification."  The study was funded by   
   the G. Evelyn Hutchinson Environmental Postdoctoral Fellowship, which   
   aims to enable creative research collaborations in the environmental   
   sciences at Yale by developing diverse academic excellence at the   
   postdoctoral level.   
      
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Fish # Marine_Biology # Nature # Fisheries   
             o Earth_&_Climate   
                   # Water # Environmental_Awareness # Ecology #   
                   Environmental_Issues   
       * RELATED_TERMS   
             o Fish o Fishery o Zebrafish o Fish_farming o Cormorant o   
             Deep_sea_fish o Sei_Whale o Fin_Whale   
      
   ==========================================================================   
   Story Source: Materials provided by Yale_University. Original written   
   by Mike Cummings. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Sarah T. Friedman, Martha M. Mun~oz. A latitudinal gradient   
      of deep-sea   
         invasions for marine fishes. Nature Communications, 2023; 14 (1)   
         DOI: 10.1038/s41467-023-36501-4   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230213201026.htm   
      
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