Molecular evolution of opsins, a gene responsible for sensing light, in scallops (Bivalvia: Pectinidae)

Genetic diversity can cause drastic effects on phenotypes and is commonly the result of a gene duplication event. Gene duplication and subsequent functional divergence of opsins, a G-protein coupled-receptor (GPCR), have played an important role in expanding photoreceptive capabilities of organisms by altering what wavelengths of light are absorbed by photoreceptors (spectral tuning). Relatively few studies have been devoted to exploring the role of opsin duplication and evolution in non-arthropod invertebrates, and even fewer have integrated all the potential genetic diversity of opsins. In this dissertation, I utilized the photosensory system of the scallop, a marine bivalve, to study the evolution and expansion of the genetically diverse opsins, and demonstrate the complicated nature of Gq-opsin diversification after gene duplication. First, I explored how opsin paralogs diversify in function and evolutionary fate by characterizing four rhabdomeric (Gq-protein coupled) opsins in the scallop, Argopecten irradians. Using a phylogenetic framework, I showed a pattern consistent with two rounds of duplication generating the four paralogous Gq-opsins in scallops. Differential expression of the four Gq-opsins across ocular and extra-ocular photosensitive tissues suggested that the Gq-opsins are used in different biological contexts in scallops, while protein modeling reveals variation in the amino acid composition, suggesting the four Gq-opsin paralogs may absorb different wavelengths of light. Second, I investigated how two Gq-opsin paralogs differentiate after a duplication event across the scallop family, Pectinidae. By comparing the rates of evolution between paralogous clades, I demonstrated both paralogs are under purifying selection, yet maintained at rates that are significantly different. I showed that one amino acid position, which is not considered a putative spectral tuning site, stands out as a strong candidate to explain the source of selection driving the difference in evolutionary rates. Finally, I discussed the current role of allelic variation in sensory systems and described how alleles are often discarded in studies of molecular evolution. I demonstrated the breadth of possible allelic variation within an individual and stressed the potential of cryptic genetic variation in the evolution of organisms by examining the allelic variation in Gq-opsins sampled across 34 bivalve species

Herbivory and nutrients shape grassland soil seed banks

Anthropogenic nutrient enrichment and shifts in herbivory can lead to dramatic changes in the composition and diversity of aboveground plant communities. In turn, this can alter seed banks in the soil, which are cryptic reservoirs of plant diversity. Here, we use data from seven Nutrient Network grassland sites on four continents, encompassing a range of climatic and environmental conditions, to test the joint effects of fertilization and aboveground mammalian herbivory on seed banks and on the similarity between aboveground plant communities and seed banks. We find that fertilization decreases plant species richness and diversity in seed banks, and homogenizes composition between aboveground and seed bank communities. Fertilization increases seed bank abundance especially in the presence of herbivores, while this effect is smaller in the absence of herbivores. Our findings highlight that nutrient enrichment can weaken a diversity maintaining mechanism in grasslands, and that herbivory needs to be considered when assessing nutrient enrichment effects on seed bank abundance.EEA Santa CruzFil: Eskelinen, Anu. German Centre for Integrative Biodiversity Research; AlemaniaFil: Eskelinen, Anu. Helmholtz Centre for Environmental Research. Department of Physiological Diversity; AlemaniaFil: Eskelinen, Anu. University of Oulu. Ecology & Genetics; FinlandiaFil: Jessen, Maria Theresa. Helmholtz Centre for Environmental Research. Department of Physiological Diversity; AlemaniaFil: Jessen, Maria Theresa. German Centre for Integrative Biodiversity Research; AlemaniaFil: Jessen, Maria Theresa. Helmholtz Centre for Environmental Research – UFZ. Department of Community Ecology; AlemaniaFil: Bahamonde, Hector Alejandro. Universidad Nacional de La Plata. Ciencias Agrarias y Forestales; Argentina.Fil: Bakker, Jonathan D. University of Washington. School of Environmental and Forest Sciences; Estados UnidosFil: Borer, Elizabeth T. University of Minnesota. Department of Ecology, Evolution & Behavior; Estados UnidosFil: Caldeira, Maria C. University of Lisbon. Forest Research Centre. Associate Laboratory TERRA. School of Agriculture; Portugal.Fil: Harpole, William Stanley. German Centre for Integrative Biodiversity Research (iDiv); AlemaniaFil: Harpole, William Stanley. Helmholtz Centre for Environmental Research – UFZ. Department of Community Ecology; AlemaniaFil: Harpole, William Stanley. Martin Luther University. Institute of Biology; AlemaniaFil: Jia, Meiyu. University of Washington. School of Environmental and Forest Sciences; Estados UnidosFil: Jia, Meiyu. East China University of Technology. School of Water Resources & Environmental Engineering; China.Fil: Jia, Meiyu. Beijing Normal University. College of Life Sciences; China.Fil: Lannes, Luciola S. São Paulo State University-UNESP. Department of Biology and Animal Sciences; Brasil.Fil: Nogueira, Carla. University of Lisbon. Forest Research Centre. Associate Laboratory TERRA. School of Agriculture; Portugal.Fil: Venterink, Harry Olde. Vrije Universiteit Brussel (VUB). Department of Biology; BélgicaFil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina.Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina.Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Porath-Krause, Anita J. University of Minnesota. Department of Ecology, Evolution & Behavior; Estados UnidosFil: Seabloom, Eric William. University of Minnesota. Department of Ecology, Evolution & Behavior; Estados UnidosFil: Schroeder, Katie. University of Minnesota. Department of Ecology, Evolution & Behavior; Estados UnidosFil: Schroeder, Katie. University of Georgia. Odum School of Ecology; Estados UnidosFil: Tognetti, Pedro M. Universidad de Buenos Aires. Facultad de Agronomía; Argentina.Fil: Tognetti, Pedro M. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA); Argentina.Fil: Tognetti, Pedro M. Swiss Federal Institute for Forest, Snow and Landscape Research WSL; SuizaFil: Yasui, Simone-Louise E. Queensland University of Technology. School of Biological and Environmental Sciences; Australia.Fil: Virtanen, Risto. University of Oulu. Ecology & Genetics; FinlandiaFil: Sullivan, Lauren L. University of Missouri. Division of Biological Sciences; Estados UnidosFil: Sullivan, Lauren L. Michigan State University. Department of Plant Biology; Estados UnidosFil: Sullivan, Lauren L. Michigan State University. W. K. Kellogg Biological Station; Estados UnidosFil: Sullivan, Lauren L. Michigan State University. Ecology, Evolution and Behavior Program; Estados Unido

Globally consistent response of plant microbiome diversity across hosts and continents to soil nutrients and herbivores

All multicellular organisms host a diverse microbiome composed of microbial pathogens, mutualists, and commensals, and changes in microbiome diversity or composition can alter host fitness and function. Nonetheless, we lack a general understanding of the drivers of microbiome diversity, in part because it is regulated by concurrent processes spanning scales from global to local. Global-scale environmental gradients can determine variation in microbiome diversity among sites, however an individual host’s microbiome also may reflect its local micro-environment. We fill this knowledge gap by experimentally manipulating two potential mediators of plant microbiome diversity (soil nutrient supply and herbivore density) at 23 grassland sites spanning global-scale gradients in soil nutrients, climate, and plant biomass. Here we show that leaf-scale microbiome diversity in unmanipulated plots depended on the total microbiome diversity at each site, which was highest at sites with high soil nutrients and plant biomass. We also found that experimentally adding soil nutrients and excluding herbivores produced concordant results across sites, increasing microbiome diversity by increasing plant biomass, which created a shaded microclimate. This demonstration of consistent responses of microbiome diversity across a wide range of host species and environmental conditions suggests the possibility of a general, predictive understanding of microbiome diversity

Herbivory and nutrients shape grassland soil seed banks

Abstract Anthropogenic nutrient enrichment and shifts in herbivory can lead to dramatic changes in the composition and diversity of aboveground plant communities. In turn, this can alter seed banks in the soil, which are cryptic reservoirs of plant diversity. Here, we use data from seven Nutrient Network grassland sites on four continents, encompassing a range of climatic and environmental conditions, to test the joint effects of fertilization and aboveground mammalian herbivory on seed banks and on the similarity between aboveground plant communities and seed banks. We find that fertilization decreases plant species richness and diversity in seed banks, and homogenizes composition between aboveground and seed bank communities. Fertilization increases seed bank abundance especially in the presence of herbivores, while this effect is smaller in the absence of herbivores. Our findings highlight that nutrient enrichment can weaken a diversity maintaining mechanism in grasslands, and that herbivory needs to be considered when assessing nutrient enrichment effects on seed bank abundance

Fertilized graminoids intensify negative drought effects on grassland productivity

Abstract Droughts can strongly affect grassland productivity and biodiversity, but responses differ widely. Nutrient availability may be a critical factor explaining this variation, but is often ignored in analyses of drought responses. Here, we used a standardized nutrient addition experiment covering 10 European grasslands to test if full-factorial nitrogen, phosphorus, and potassium addition affected plant community responses to inter-annual variation in drought stress and to the extreme summer drought of 2018 in Europe. We found that nutrient addition amplified detrimental drought effects on community aboveground biomass production. Drought effects also differed between functional groups, with a negative effect on graminoid but not forb biomass production. Our results imply that eutrophication in grasslands, which promotes dominance of drought-sensitive graminoids over forbs, amplifies detrimental drought effects. In terms of climate change adaptation, agricultural management would benefit from taking into account differential drought impacts on fertilized versus unfertilized grasslands, which differ in ecosystem services they provide to society