Evolution and Organismal Biology

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Evolution and Organismal Biology

Ames, IA, United States
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News Article | May 15, 2017
Site: www.sciencedaily.com

A study from Iowa State University researchers casts new light on how biologists understand the likelihood of coextinction among plants and animals that depend on one another for survival. The study, published recently in the peer-reviewed scientific journal Proceedings of the Royal Society B, focuses on mutualist networks, or webs of mutually beneficial interactions between plants and animals. Examples include fruit-eating birds that eat the fruit from trees while simultaneously helping to disperse the trees' seeds. Current models that examine these relationships have emphasized the possibility of co-extinction, or the extinction of one species leading to the demise of other mutualist species. But Haldre Rogers, an assistant professor in the ISU Department of Ecology, Evolution and Organismal Biology, said previous thinking rarely accounted for how dependent individual species are on their mutualist relationships. The study, led by Evan Fricke, a postdoctoral researcher in Rogers' lab, found that species with many mutualist relationships tend to be more dependent on those interactions for survival. On the other hand, species with few mutualists typically depend little on mutualistic interactions. Factoring that pattern into the equation adds a new dimension that upends much of the previous models, Fricke said. Rogers said the study turned up good news in that many mutualist species aren't as vulnerable as once thought. For instance, birds whose diets depend heavily on fruit usually eat fruit from more than one species of plant. That way, if one food source disappears, the bird has other options. "Nature seems to have some backup plans when you need them," Rogers said. Adding this new understanding of mutualistic dependence reduces predictions of coextinction events by 88 percent compared to older predictive models. Fricke said the research could help guide policymakers to make better use of conservation dollars by highlighting relationships in ecosystems that play core functions and support a range of species. "Previously, we thought that if you were a mutualist with one partner or few partners, you were really vulnerable to coextinction," Fricke said. "So if disease or climate change or hunting wipes out that one partner, you're out of luck. In actuality, species that naturally have few partners are less likely to experience coextinction because they depend very little on those interactions." The data utilized in the study came from synthesizing existing global databases on mutualist organisms as well as data gathered directly by the researchers on plant-seed disperser interactions in the Marianas Islands. The research team then simulated co-extinction events while factoring dependence into their models. Fricke said this new understanding of the dependence on mutualistic relationships changes many of the conclusions biologists have drawn using existing network models. "What makes species and networks resilient to coextinction is not how many partners species have or how interactions are arranged, as previously thought," Rogers said. "It's that species have evolved strategies that balance their dependence on their mutualists with the risk of losing those mutualists." "One of the really crucial details has been missing in previous network studies," Fricke said. "And the conclusions of those studies flip when you include this detail."


The study, published recently in the peer-reviewed scientific journal Proceedings of the Royal Society B, focuses on mutualist networks, or webs of mutually beneficial interactions between plants and animals. Examples include fruit-eating birds that eat the fruit from trees while simultaneously helping to disperse the trees' seeds. Current models that examine these relationships have emphasized the possibility of co-extinction, or the extinction of one species leading to the demise of other mutualist species. But Haldre Rogers, an assistant professor in the ISU Department of Ecology, Evolution and Organismal Biology, said previous thinking rarely accounted for how dependent individual species are on their mutualist relationships. The study, led by Evan Fricke, a postdoctoral researcher in Rogers' lab, found that species with many mutualist relationships tend to be more dependent on those interactions for survival. On the other hand, species with few mutualists typically depend little on mutualistic interactions. Factoring that pattern into the equation adds a new dimension that upends much of the previous models, Fricke said. Rogers said the study turned up good news in that many mutualist species aren't as vulnerable as once thought. For instance, birds whose diets depend heavily on fruit usually eat fruit from more than one species of plant. That way, if one food source disappears, the bird has other options. "Nature seems to have some backup plans when you need them," Rogers said. Adding this new understanding of mutualistic dependence reduces predictions of coextinction events by 88 percent compared to older predictive models. Fricke said the research could help guide policymakers to make better use of conservation dollars by highlighting relationships in ecosystems that play core functions and support a range of species. "Previously, we thought that if you were a mutualist with one partner or few partners, you were really vulnerable to coextinction," Fricke said. "So if disease or climate change or hunting wipes out that one partner, you're out of luck. In actuality, species that naturally have few partners are less likely to experience coextinction because they depend very little on those interactions." The data utilized in the study came from synthesizing existing global databases on mutualist organisms as well as data gathered directly by the researchers on plant-seed disperser interactions in the Marianas Islands. The research team then simulated co-extinction events while factoring dependence into their models. Fricke said this new understanding of the dependence on mutualistic relationships changes many of the conclusions biologists have drawn using existing network models. "What makes species and networks resilient to coextinction is not how many partners species have or how interactions are arranged, as previously thought," Rogers said. "It's that species have evolved strategies that balance their dependence on their mutualists with the risk of losing those mutualists." "One of the really crucial details has been missing in previous network studies," Fricke said. "And the conclusions of those studies flip when you include this detail." Explore further: Domino effect—the loss of plant species triggers the extinction of animals More information: Evan C. Fricke et al. Mutualistic strategies minimize coextinction in plant–disperser networks, Proceedings of the Royal Society B: Biological Sciences (2017). DOI: 10.1098/rspb.2016.2302


Perry G.L.W.,University of Auckland | Moloney K.A.,Evolution and Organismal Biology | Etherington T.R.,University of Auckland | Etherington T.R.,University of Oxford
Journal of Applied Ecology | Year: 2017

Habitat connectivity is a crucial determinant of population dynamics in fragmented landscapes. The corollary of the emphasis on maintaining connectivity to enhance the movement of organisms is that disrupting connectivity should minimise it. Here, we evaluate the efficiency of an invasive species control strategy that targets the most connected habitats in a landscape. A network (spatial graph) provides an intuitive representation of a landscape, and the topology of this network can be used to identify the most connected patches. We implemented a simulation model of the spread of an invasive species on a network and used it to evaluate whether targeting the better-connected components of the landscape enhances control effectiveness. Control strategies based on network topology consistently outperformed both a null strategy of random habitat selection and one based on separation distance alone. The advantages of the connectivity-based strategy were strongest in the early phases of the invasion process, when a small number of habitats are occupied at low population density. However, if long-distance dispersal events were common, the advantages of the connectivity approach weakened. The performance of the connectivity-based strategy is robust to habitat-level demographic stochasticity. In fact, connectivity-based targeting outperforms a strategy focussing on source habitats, with the additional benefit that it requires less information to be implemented. Synthesis and applications. Our simulation model outcomes demonstrate that deliberately targeting the best-connected components of a landscape is an efficient control strategy for invasive species when long-distance dispersal is infrequent, and it is likely to be cheaper than other alternatives such as targeting population sources. Network scientists have developed a range of methods designed to identify the minimal set of nodes on a graph that will disrupt the network as a whole; these tools have potential to aid in the design of more effective control strategies. © 2016 The Authors. Journal of Applied Ecology © 2016 British Ecological Society


Wilsey B.J.,Evolution and Organismal Biology | Barber K.,Evolution and Organismal Biology | Martin L.M.,Evolution and Organismal Biology
New Phytologist | Year: 2015

Summary: During community assembly, early arriving exotic species might suppress other species to a greater extent than do native species. Because most exotics were intentionally introduced, we hypothesize there was human selection on regeneration traits during introduction. This could have occurred at the across- or within-species level (e.g. during cultivar development). We tested these predictions by seeding a single species that was either native, exotic 'wild-type' (from their native range), or exotic 'cultivated' using 28 grassland species in a glasshouse experiment. Priority effects were assessed by measuring species' effect on establishment of species from a seed mix added 21 d later. Exotic species had higher germination and earlier emergence dates than native species, and differences were found in both 'wild' and 'cultivated' exotics. Exotic species reduced biomass and species diversity of later arriving species much more than native species, regardless of seed source. Results indicate that in situations in which priority effects are likely to be strong, effects will be greater when an exotic species arrives first than when a native species arrives first; and this difference is not merely a result of exotic species cultivation, but might be a general native-exotic difference that deserves further study. © 2014 New Phytologist Trust.


Sproul J.S.,Oregon State University | Houston D.D.,Evolution and Organismal Biology | Nelson C.R.,Brigham Young University | Evans R.P.,Brigham Young University | And 2 more authors.
BMC Evolutionary Biology | Year: 2015

Background: Phylogeographic studies of aquatic insects provide valuable insights into mechanisms that shape the genetic structure of communities, yet studies that include broad geographic areas are uncommon for this group. We conducted a broad scale phylogeographic analysis of the least salmonfly Pteronarcella badia (Plecoptera) across western North America. We tested hypotheses related to mode of dispersal and the influence of historic climate oscillations on population genetic structure. In order to generate a larger mitochondrial data set, we used 454 sequencing to reconstruct the complete mitochondrial genome in the early stages of the project. Results: Our analysis revealed high levels of population structure with several deeply divergent clades present across the sample area. Evidence from five mitochondrial genes and one nuclear locus identified a potentially cryptic lineage in the Pacific Northwest. Gene flow estimates and geographic clade distributions suggest that overland flight during the winged adult stage is an important dispersal mechanism for this taxon. We found evidence of multiple glacial refugia across the species distribution and signs of secondary contact within and among major clades. Conclusions: This study provides a basis for future studies of aquatic insect phylogeography at the inter-basin scale in western North America. Our findings add to an understanding of the role of historical climate isolations in shaping assemblages of aquatic insects in this region. We identified several geographic areas that may have historical importance for other aquatic organisms with similar distributions and dispersal strategies as P. badia. This work adds to the ever-growing list of studies that highlight the potential of next-generation DNA sequencing in a phylogenetic context to improve molecular data sets from understudied groups. © 2015 Sproul et al.


Adams D.C.,Evolution and Organismal Biology | Adams D.C.,Iowa State University
Systematic Biology | Year: 2014

Many questions in evolutionary biology require the quantification and comparison of rates of phenotypic evolution. Recently, phylogenetic comparative methods have been developed for comparing evolutionary rates on a phylogeny for single, univariate traits (σ2), and evolutionary rate matrices (R) for sets of traits treated simultaneously. However, high-dimensional traits like shape remain under-examined with this framework, because methods suited for such data have not been fully developed. In this article, I describe a method to quantify phylogenetic evolutionary rates for high-dimensional multivariate data, found from the equivalency between statistical methods based on covariance matrices and those based on distance matrices (R-mode and Q-mode methods). I then use simulations to evaluate the statistical performance of hypothesis-testing procedures that compare for two or more groups of species on a phylogeny. Under both isotropic and non-isotropic conditions, and for differing numbers of trait dimensions, the proposed method displays appropriate Type I error and high statistical power for detecting known differences in among groups. In contrast, the Type I error rate of likelihood tests based on the evolutionary rate matrix (R) increases as the number of trait dimensions (p) increases, and becomes unacceptably large when only a few trait dimensions are considered. Further, likelihood tests based on R cannot be computed when the number of trait dimensions equals or exceeds the number of taxa in the phylogeny (i.e., when p ≥ N). These results demonstrate that tests based on provide a useful means of comparing evolutionary rates for high-dimensional data that are otherwise not analytically accessible to methods based on the evolutionary rate matrix. This advance thus expands the phylogenetic comparative toolkit for high-dimensional phenotypic traits like shape. Finally, I illustrate the utility of the new approach by evaluating rates of head shape evolution in a lineage of Plethodon salamanders. © 2013 The Author(s).


Sproul J.S.,Oregon State University | Houston D.D.,Evolution and Organismal Biology | Nelson C.R.,Brigham Young University | Evans R.P.,Brigham Young University | And 2 more authors.
BMC Evolutionary Biology | Year: 2015

Background: Phylogeographic studies of aquatic insects provide valuable insights into mechanisms that shape the genetic structure of communities, yet studies that include broad geographic areas are uncommon for this group. We conducted a broad scale phylogeographic analysis of the least salmonfly Pteronarcella badia (Plecoptera) across western North America. We tested hypotheses related to mode of dispersal and the influence of historic climate oscillations on population genetic structure. In order to generate a larger mitochondrial data set, we used 454 sequencing to reconstruct the complete mitochondrial genome in the early stages of the project. Results: Our analysis revealed high levels of population structure with several deeply divergent clades present across the sample area. Evidence from five mitochondrial genes and one nuclear locus identified a potentially cryptic lineage in the Pacific Northwest. Gene flow estimates and geographic clade distributions suggest that overland flight during the winged adult stage is an important dispersal mechanism for this taxon. We found evidence of multiple glacial refugia across the species distribution and signs of secondary contact within and among major clades. Conclusions: This study provides a basis for future studies of aquatic insect phylogeography at the inter-basin scale in western North America. Our findings add to an understanding of the role of historical climate isolations in shaping assemblages of aquatic insects in this region. We identified several geographic areas that may have historical importance for other aquatic organisms with similar distributions and dispersal strategies as P. badia. This work adds to the ever-growing list of studies that highlight the potential of next-generation DNA sequencing in a phylogenetic context to improve molecular data sets from understudied groups. © 2015 Sproul et al.


PubMed | Evolution and Organismal Biology
Type: Journal Article | Journal: The New phytologist | Year: 2014

During community assembly, early arriving exotic species might suppress other species to a greater extent than do native species. Because most exotics were intentionally introduced, we hypothesize there was human selection on regeneration traits during introduction. This could have occurred at the across- or within-species level (e.g. during cultivar development). We tested these predictions by seeding a single species that was either native, exotic wild-type (from their native range), or exotic cultivated using 28 grassland species in a glasshouse experiment. Priority effects were assessed by measuring species effect on establishment of species from a seed mix added 21 d later. Exotic species had higher germination and earlier emergence dates than native species, and differences were found in both wild and cultivated exotics. Exotic species reduced biomass and species diversity of later arriving species much more than native species, regardless of seed source. Results indicate that in situations in which priority effects are likely to be strong, effects will be greater when an exotic species arrives first than when a native species arrives first; and this difference is not merely a result of exotic species cultivation, but might be a general native-exotic difference that deserves further study.

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