MSGID: 1:317/3 6272017e   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    What happens when traits jump between branches of the tree of life   
      
      
     Date:   
         May 3, 2022   
     Source:   
         University of California - Santa Barbara   
     Summary:   
         We all must play the game of life with the cards we're dealt, so   
         the common aphorism goes. In biology, this means organisms must   
         compete through natural selection with the genes and anatomy they   
         were born with.   
      
         But the saying is a lie. Okay, it's not exactly a lie, but modern   
         research suggests that the game of life is far more complicated   
         than we had anticipated. There are opportunities to swap cards   
         and even steal other players' hands.   
      
      
      
   FULL STORY   
   ==========================================================================   
   We all must play the game of life with the cards we're dealt, so the   
   common aphorism goes. In biology, this means organisms must compete   
   through natural selection with the genes and anatomy they were born with.   
      
      
   ==========================================================================   
   But the saying is a lie.   
      
   Okay, it's not exactly a lie, but modern research suggests that the   
   game of life is far more complicated than we had anticipated. There are   
   opportunities to swap cards and even steal other players' hands.   
      
   Researchers at UC Santa Barbara have been investigating the effects   
   of this strategy, particularly the ability to acquire metabolic   
   pathways. The scientists found that adopting another metabolism can   
   have major competitive consequences, with ramifications to a species'   
   evolution and ecology. The results appear in the journal Ecology.   
      
   The term "metabolism" encompasses all the chemical reactions that take   
   place in an organism in order to maintain life. For animals, this includes   
   the nuts and bolts of processes like respiration, digestion, movement,   
   etc. An acquired metabolism is a metabolic pathway that is not encoded   
   in an organism's DNA.   
      
   Examples of acquired metabolisms abound in nature. Some are familiar, like   
   the microbes in a cow's gut that enable it to digest cellulose. Others   
   are more common but less well-known. For instance, consider the symbiotic   
   fungi that help plants source minerals from the soil. And then there are   
   truly unusual acquired metabolisms, like sea slugs that steal chloroplasts   
   from their food so they can photosynthesize.   
      
      
      
   ==========================================================================   
   While acquired metabolisms are well-attested in the literature,   
   previous research mostly considered its interactions with environmental   
   factors. The UC Santa Barbara group investigated their role in growth and   
   community dynamics, focusing on acquired phototrophy, like that of the   
   sea slug. "We really wanted to understand whether or not this acquired   
   phototrophy would give an organism a competitive advantage," said lead   
   author Veronica Hsu, who completed the study as an undergraduate.   
      
   The authors considered two single-celled eukaryotes (organisms whose   
   cells contain a nucleus). The first, a species in the genus Colpidium,   
   subsists on a diet of smaller microbes. The second, Paramecium bursaria,   
   shares its counterpart's diet, but had also acquired the ability to   
   photosynthesize at some point in the past.   
      
   The researchers analyzed the two microbes under four different light   
   conditions. Colpidium got along fine no matter the setting; however, P.   
      
   bursaria fared much better under brighter conditions, where it could   
   take advantage of its unique ability.   
      
   Then the scientists pitted the microbes against each other. They observed   
   a gradient of competitive advantage across different light levels. In   
   the dark, Colpidium outcompeted P. bursaria. Meanwhile, under bright   
   conditions, P.   
      
   bursaria dominated.   
      
   "I think it gets to this idea that you can't be good at everything,"   
   said co- author Holly Moeller, an assistant professor in the Department of   
   Ecology, Evolution and Marine Biology. Adapting to an acquired metabolism   
   might have come at the expense of P. bursaria's hunting prowess. But   
   at high light levels, the boost from photosynthesis more than offsets   
   this handicap.   
      
      
      
   ==========================================================================   
   Remarkably, the two microbes were able to coexist under intermediate light   
   conditions. P. bursaria's acquired phototrophy enabled it to avoid direct   
   competition with Colpidium in what scientists call "niche partitioning."   
   The results demonstrate that symbiosis and acquired metabolism can   
   drastically affect community dynamics. "Expanding on your metabolic   
   repertoire has cascading implications on how you can make a living,   
   and the extent to which you're going to shove other organisms out of   
   the way," Moeller said.   
      
   The researchers then turned to the trusty Lotka-Volterra model to describe   
   what they had witnessed. This model is incredibly simple and versatile,   
   providing biologists a system that can capture all the possible outcomes   
   of competition.   
      
   Developed over 100 years ago, it has become a go-to standard for intro   
   biology classes all the way to peer-reviewed research.   
      
   And yet, this stalwart system couldn't capture the subtlety introduced   
   by P.   
      
   bursaria's acquired phototrophy and the feedback cycle it created. The   
   team had to develop their own system of equations that explicitly   
   accounted for these nuances. "There are a lot of different ways to try   
   to explain competitive outcomes," Hsu said, "and I think this shines a   
   light on how important metabolism can be."  It's important to study how   
   acquired metabolisms influence evolution and ecology because they're   
   a fundamental part of life on Earth. For instance, we generally think   
   of photosynthesis as a characteristic of plants. "But that's an ancient   
   acquisition, too," said Moeller. "They inherited their chloroplasts from a   
   eukaryotic ancestor that domesticated a cyanobacterium."  "Mitochondria   
   are also acquired from bacteria," added Hsu. In fact, both of these   
   organelles have their own DNA, separate from a cell's nuclear genome.   
      
   "This is how eukaryotes have been playing the game for some 2 billion   
   years," Moeller remarked. And our simpler counterparts, prokaryotes,   
   arguably engage in even more biological card-swapping. Many are able to   
   directly share DNA in a process known as "horizontal gene transfer."   
   Moeller's group will continue to study the implications of acquired   
   metabolisms. They're particularly curious about the transition from   
   heterotrophy (obtaining food externally) to autotrophy (producing food   
   oneself), especially photosynthesis. "We're trying to understand what   
   causes these forms of metabolism to jump around the tips of the branches   
   of the tree of life," she said.   
      
   Moeller plans to use mathematic models to investigate these transitions in   
   addition to looking for real-world case studies. And future experiments   
   will involve microbes that are more closely related to each other,   
   enabling the team to control more variables. "The experiments help   
   us build better models," she said, "while the models help us better   
   understand what happened in the experiments."  More research is certainly   
   welcome. Because, in this convoluted corner of biology, at least one   
   thing has become abundantly clear: We'd have a less dynamic, less complex   
   ecology on this planet if organisms could play only with the cards they   
   were dealt.   
      
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_California_-_Santa_Barbara. Original written by Harrison   
   Tasoff. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Veronica Hsu, Ferdinand Pfab, Holly V. Moeller. Niche expansion via   
         acquired metabolism facilitates competitive dominance in planktonic   
         communities. Ecology, 2022; DOI: 10.1002/ecy.3693   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2022/05/220503141321.htm   
      
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