1,720,975 research outputs found
Adaptation in a Changing World: Evolutionary mechanisms of salt tolerance in a coastal amphibian
No full textIn order to predict evolutionary outcomes of environmental change on populations in nature, we need an improved understanding of the biological mechanisms that affect whether organisms will adapt to a changed environment. This dissertation capitalizes on the unlikely discovery of a freshwater treefrog (Hyla cinerea) inhabiting brackish marshes along the coast of North Carolina to better understand adaptive evolution to a changed environment. The goals of this research are to (1.) examine the extent that salt-exposed, coastal frog populations are diverging from salt-naïve, inland populations in response to saltwater exposure across life stages, (2.) determine the molecular and life history mechanisms that permit this species to persist in brackish habitats, and (3.) explore factors that influence likelihoods of evolution (e.g., density dependence, phenotypic plasticity). Chapter 1 used field surveys, meta-analysis, and common garden experiments to show that Hyla cinerea are unique among frog species in their ability to inhabit saline wetlands. Coastal H. cinerea laid more eggs in saltwater compared to inland H. cinerea, more coastal eggs hatched in saltwater compared to inland eggs, and in the highest experimental treatment (12ppt), early-stage coastal tadpoles had higher survival rates than inland tadpoles. Chapter 2 investigated the role of plasticity in generating divergent phenotypes across larval development. Regardless of salinity, coastal tadpoles grew faster and initiated metamorphosis sooner but at a smaller size compared to inland tadpoles, and more coastal tadpoles survived to metamorphosis. Chapter 3 used individual-based modeling to explore how density dependence and selection interact to affect evolution in complex life cycle organisms. Density dependence increased genetic variation across populations by reducing population size, and evolutionary rescue was most likely to occur when selection precedes density dependence. Chapter 4 used transcriptomics to explore the mechanisms that produce differences across inland and coastal populations. We identified 1,924 differentially expressed genes between coastal and inland frog populations. We found that differentially expressed genes encode diverse molecular functions including ionic and osmotic transporters and stress response pathways. This dissertation shows that coastal H. cinerea can become locally adapted to inhabit brackish habitats and explores several mechanisms that affect adaptive evolution to environmental chang
Data for: Responses to saltwater exposure vary across species, populations, and life-stages in anuran amphibians
No full text<p><span>To predict the impacts of environmental change on species, we must first understand the factors that limit the present-day ranges of species. Most anuran amphibians cannot survive at elevated salinities, which may drive their distribution in coastal locations. Previous research showed that coastal <em>Hyla cinerea</em> are locally adapted to brackish habitats in North Carolina (USA). Although <em>Hyla squirella</em> and <em>Hyla chrysoscelis </em>both inhabit coastal wetlands nearby, they have not been observed in saline habitats. We take advantage of naturally occurring microgeographic variation in coastal wetland occupancy exhibited by these congeneric treefrog species to explore how salt exposure affects oviposition site choice, hatching success, early tadpole survival, plasma osmolality, and tadpole body condition across coastal and inland locations. We observed higher survival among coastal</span><span> <em>H. cinerea</em> tadpoles than inland <em>H. cinerea</em>, which corroborates previous findings. But contrary to expectations, coastal <em>H. cinerea</em> had lower survival than <em>H. squirella</em> and <em>H. chrysoscelis</em>, indicating that all three species may be able to persist in saline wetlands. We also observed differences in tadpole plasma osmolality across species, locations, and salinities, but these differences were not associated with survival rates in saltwater. Instead, coastal occupancy may be affected by stage-specific processes like higher probability of total clutch loss as shown by inland <em>H. chrysoscelis</em> or maladaptive egg deposition patterns as shown by inland <em>H. squirella</em>. </span><span>Although we expected saltwater to be the primary filter driving species distributions along a coastal salinity gradient, it is likely that the factors dictating anuran ranges along the coast involve stage-, species-, and location specific processes that are mediated by ecological processes and life history traits.</span></p><p>Funding provided by: National Science Foundation<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001<br>Award Number: 1701690</p><p>Funding provided by: National Science Foundation<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001<br>Award Number: 1556743</p><p>Funding provided by: North Carolina Sea Grant, North Carolina State University<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/100005623<br>Award Number: 2014-R/14-HCE-3</p><p>Funding provided by: Graduate Women in Science<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/100014816<br>Award Number: </p>
Risk Assessment and Behavioral Choices of Larval Anurans (Lithobates Sphenocephalus)
No full textLarval anurans assess risk and make behavioral choices to avoid predation. Since antipredator behaviors may reduce foraging opportunities, prey behavioral decisions can be constrained by a tradeoff between survival and growth. To improve our understanding of prey risk assessment, I asked whether L. sphenocephalus tadpoles make antipredator behavioral choices based on characteristics of predators such as their lethality, microhabitat use, or taxonomic group. To test this question, I ran an experiment in aquaria that included 13 treatments (6 predators x lethal/nonlethal plus a no-predator control), replicated eight times in a temporal block design. Three predators occupy benthic microhabitats (white crayfish, Pachydiplax dragonfly larvae, and pirate perch), and three occupy pelagic microhabitats (bluegill sunfish, broken-striped newt, and fishing spider). I made behavioral observations of each aquarium twice during each trial, and recorded the prey remaining at the end of each 20-hour trial. Prey antipredator behaviors differed when in the presence of predators from different microhabitats or different taxonomic groupings. When confronted with vertebrate predators (e.g., the fish and the newt) fewer proportions of tadpoles were outside of refuges. The predator microhabitat usage impacted activity levels of tadpoles, as significantly fewer tadpoles were active when presented with a pelagic predator. Species-specific reactions appeared to play a role as large numbers of tadpoles avoided the benthos when sharing habitat with the crayfish. The proportions of visible and moving tadpoles were different between observation periods, which indicates that tadpoles are able to progressively gauge whether the presence of a predator is a threat, since tadpoles increased their visibility and movement levels during the second observation period in nonlethal treatments. Predator lethality did not impact which antipredator behavior was chosen by the tadpole, but it did appear to affect the strength of the response. Predator characteristics such as microhabitat use, taxonomic affiliation, and lethality influence tadpoles as they determine the potential threat of predation and the appropriate behavioral response.M.S
Influence of density and salinity on larval development of salt-adapted and salt-naïve frog populations
No full textEnvironmental change and habitat fragmentation will affect population densities for many species. For those species that have locally adapted to persist in changed or stressful habitats, it is uncertain how density dependence will affect adaptive responses. Anurans (frogs and toads) are typically freshwater organisms, but some coastal populations of green treefrogs (Hyla cinerea) have adapted to brackish, coastal wetlands. Tadpoles from coastal populations metamorphose sooner and demonstrate faster growth rates than inland populations when reared solitarily. Although saltwater exposure has adaptively reduced the duration of the larval period for coastal populations, increases in densities during larval development typically increase time to metamorphosis and reduce rates of growth and survival. We test how combined stressors of density and salinity affect larval development between salt-adapted ("coastal") and non-salt adapted ("inland") populations by measuring various developmental and metamorphic phenotypes. We found that increased tadpole density strongly affected coastal and inland tadpole populations similarly. In high-density treatments, both coastal and inland populations had reduced growth rates, greater exponential decay of growth, a smaller size at metamorphosis, took longer to reach metamorphosis, and had lower survivorship at metamorphosis. Salinity only exaggerated the effects of density on the time to reach metamorphosis and exponential decay of growth. Location of origin affected length at metamorphosis, with coastal tadpoles metamorphosing slightly longer than inland tadpoles across densities and salinities. These findings confirm that density has a strong and central influence on larval development even across divergent populations and habitat types and may mitigate the expression (and therefore detection) of locally adapted phenotypes.Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: 1701690Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: 155674
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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