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| Reciprocity Between Evolution and the Environment |
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| SciMed - Biology | |||
| TS-Si News Service | |||
| Tuesday, 16 February 2010 22:00 | |||
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Riverside, CA, USA. A team of biologists has presented evidence that ecology and There has been a persistent assumption among social critics that ecology is primary in the shaping of evolution where the environment defines a template, and the process of evolution shapes organisms to fit that template. True, biologists have long known that ecology, the interaction between organisms and their environment, plays a significant role in forming new species and in modifying living ones. However, specialized
London, United Kingdom. New findings argue for the persistence of sex-linked chromosomes, such as the male Y  chromosome, refuting theories that the Y is doomed to extinction.
The results confirm that although these chromosom...London, UK. An animal model has been used to better understand the clinical significance of chronic psychotropic drug treatment on structural remodeling of the brain.
The effects of these structural changes has been unclear ...
Ecologists believe in evolution, but many of them make a general assumption that ecological interactions happen on such a short time scale that evolution can be ignored — the way physicists often safely ignore relativity in the majority of their experiments. Reznick says that: "Our results represent a first significant step in showing that evolution cannot be ignored when studying ecological interactions." Reznick's team compared guppies — small freshwater fish that have been the subject of long-term studies — that had adapted to two different types of stream communities in Trinidad. One stream community had a diverse group of fish species, some of which were serious predators on guppies. The other type of community included guppies and just one or a few non-predatory species. Previously, Reznick and colleagues had established that predators cause a substantial increase in guppy mortality rates, resulting in guppies that are younger at maturity, produce more babies, and display different behavior, escape abilities and body shapes.
In the new experiments reported on here, the researchers collected guppies from the two different types of communities. They then quantified their specific impact on the stream ecosystem by placing them in replicate, artificial streams built alongside a natural stream. The researchers chose this specific location in Trinidad for the artificial streams. They could divert water from a spring that normally flowed into the stream in such a way that it first flowed through the artificial streams, and then emptied later into the natural stream. Next, they seeded the artificial streams with organisms such as insect larvae from the natural stream so that all artificial streams had similar ecosystems at the start of the experiment. They found that guppies from the two types of fish communities had substantially different impacts after only four weeks on the structure and function of their ecosystems.
The researchers observed significant differences in the behavior of their model organisms. "Guppies from the more diverse fish communities ate more insect larvae while the low-predation guppies — guppies from the simple fish communities — ate more algae," said Ronald Bassar, a graduate student in David Reznick's lab and the first author of the current research paper. Bassar reports that "These differences in diet resulted in the artificial streams with guppies from the diverse communities having substantially more algae and fewer invertebrates than streams stocked with guppies from the simple communities." "There were corresponding differences in how and at what rate nutrients, like nitrogen or phosphorus, were recycled. The streams with high-predation guppies — guppies from the more diverse fish communities — had less plant production and oxygen consumption, a slower breakdown of leaves that had fallen into the water and a slower accumulation of detritus, the breakdown product of leaves." The researchers found, too, that their findings from their experiments in the artificial streams mirrored their observations in guppies across natural stream communities in Trinidad. "By doing our experiments in the artificial streams we are able to pin down guppies as a likely cause of what we see in the natural streams," Bassar said. "The experiments show that local adaptation causes the evolution of differences in diet, which, in turn, causes differences in ecosystem structure. Our next step is to characterize how this changed ecosystem, in turn, shapes how the guppies adapt to it." FundingThe National Science Foundation supported this research as part of a five year, multi-investigator grant funded by the Frontiers in Integrative Biological Research initiative.
ParticipantsReznick, a professor of biology, and Bassar were joined in the study by a diverse team of biologists and ecosystems ecologists, including Michael Marshal and Cathy Pringle from the University of Georgia; Eugenia Zandonà of Drexel University, Penn.; Douglas Fraser from Siena College; Joseph Travis from Florida State University; Alexander Flecker from Cornell University, NY; and Steven Thomas from the University of Nebraska. The team also included Sonya Auer and Andrés López-Sepulcre, a graduate student and post-doctoral researcher, respectively, from UC Riverside.
CitationLocal adaptation in Trinidadian guppies alters ecosystem processes. Ronald D. Bassar, Michael C. Marshall, Andrés López-Sepulcre, Eugenia Zandonà , Sonya K. Auer, Joseph Travis, Catherine M. Pringle, Alexander S. Flecker, Steven A. Thomas, Douglas F. Fraser, and David N. Reznick. Proceedings of the National Academy of Sciences (PNAS) 2010; ePub ahead of print. doi:10.1073/pnas.0908023107
Abstract Theory suggests evolutionary change can significantly influence and act in tandem with ecological forces via ecological-evolutionary feedbacks. This theory assumes that significant evolutionary change occurs over ecologically relevant timescales and that phenotypes have differential effects on the environment. Here we test the hypothesis that local adaptation causes ecosystem structure and function to diverge. We demonstrate that populations of Trinidadian guppies (Poecilia reticulata), characterized by differences in phenotypic and population-level traits, differ in their impact on ecosystem properties. We report results from a replicated, common garden mesocosm experiment and show that differences between guppy phenotypes result in the divergence of ecosystem structure (algal, invertebrate, and detrital standing stocks) and function (gross primary productivity, leaf decomposition rates, and nutrient flux). These phenotypic effects are further modified by effects of guppy density. We evaluated the generality of these effects by replicating the experiment using guppies derived from two independent origins of the phenotype. Finally, we tested the ability of multiple guppy traits to explain observed differences in the mesocosms. Our findings demonstrate that evolution can significantly affect both ecosystem structure and function. The ecosystem differences reported here are consistent with patterns observed across natural streams and argue that guppies play a significant role in shaping these ecosystems. Keywords: ecological—evolutionary feedbacks, intraspecific variation, ecosystem function.
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