May 21, 2019
Publications by EEOB Faculty May 1 - May 31
Hybridization speeds adaptive evolution in an eight-year field experiment
Nora Mitchell, Gregory L. Owens, Stephen M. Hovick, Loren H. Rieseberg & Kenneth D. Whitney. 2019.
Abstract
Hybridization is a common phenomenon, yet its evolutionary outcomes remain debated. Here, we ask whether hybridization can speed adaptive evolution using resynthesized hybrids between two species of Texas sunflowers (Helianthus annuus and H. debilis) that form a natural hybrid in the wild (H. annuus ssp. texanus). We established separate control and hybrid populations and allowed them to evolve naturally in a field evolutionary experiment. In a final common-garden, we measured fitness and a suite of key traits for these lineages. We show that hybrid fitness evolved in just seven generations, with fitness of the hybrid lines exceeding that of the controls by 14% and 51% by the end of the experiment, though only the latter represents a significant increase. More traits evolved significantly in hybrids relative to controls, and hybrid evolution was faster for most traits. Some traits in both hybrid and control lineages evolved in an adaptive manner consistent with the direction of phenotypic selection. These findings show a causal pathway from hybridization to rapid adaptation and suggest an explanation for the frequently noted association between hybridization and adaptive radiation, range expansion, and invasion.
Hybridization is a common phenomenon, yet its evolutionary outcomes remain debated. Here, we ask whether hybridization can speed adaptive evolution using resynthesized hybrids between two species of Texas sunflowers (Helianthus annuus and H. debilis) that form a natural hybrid in the wild (H. annuus ssp. texanus). We established separate control and hybrid populations and allowed them to evolve naturally in a field evolutionary experiment. In a final common-garden, we measured fitness and a suite of key traits for these lineages. We show that hybrid fitness evolved in just seven generations, with fitness of the hybrid lines exceeding that of the controls by 14% and 51% by the end of the experiment, though only the latter represents a significant increase. More traits evolved significantly in hybrids relative to controls, and hybrid evolution was faster for most traits. Some traits in both hybrid and control lineages evolved in an adaptive manner consistent with the direction of phenotypic selection. These findings show a causal pathway from hybridization to rapid adaptation and suggest an explanation for the frequently noted association between hybridization and adaptive radiation, range expansion, and invasion.
Origins, Importance and Genetic Stability of the Prototype Strains Gilliam, Karp and Kato of Orientia tsutsugamushi
Daryl J. Kelly, Paul A. Fuerst, and Allen L. Richards. 2019. Tropical Medicine and Infectious Disease.
Abstract
Scrub typhus, a chigger-borne febrile illness, occurs primarily in countries of the Asia-Pacific rim and islands of the Western Pacific. The etiologic agent is the obligate intracellular rickettsial bacterium Orientia tsutsugamushi. Research on O. tsutsugamushi has relied on the availability of several prototype strains, which were isolated from human cases of scrub typhus in the 1940s and 1950s. We review the history of the three original, and most important, prototype strains, Gilliam, Karp and Kato, including information on their isolation, their culture history, their clinical characteristics, their importance within the research literature on scrub typhus, and recent advances in elucidating their molecular genomics. The importance of these strains to the research and development of clinical tools related to scrub typhus is also considered. Finally, we examine whether the strains have been genetically stable since their isolation, and whether prototype strains maintained in separate laboratories are identical, based on pairwise comparisons of several sequences from four genes. By using genetic information archived in international DNA databases, we show that the prototype strains used by different laboratories are essentially identical, and that the strains have retained their genetic integrity at least since the 1950s. The three original prototype strains should remain a standard by which new diagnostic procedures are measured. Given their fundamental position inany comparative studies, they are likely to endure as a critical part of present and future research on scrub typhus and Orientia.
Riparian forest fragments in rice fields under different management: differences on hymenopteran parasitoids diversity
G. S. Silva, S.M. Jahnke, N.F. Johnson. 2019. Brazilian Journal of Biology. http://dx.doi.org/10.1590/1519-6984.194760
Abstract
Hymenopteran parasitoids are important biological control agents in agroecosystems, and their diversity can be increased with habitat heterogeneity. Thus, the purpose of the study is to evaluate the influence of distance of rice-growing areas from natural fragment, type of crop management (organic and conventional) and crop stages (vegetative and reproductive stages) on parasitoids family diversity. The work took place in two irrigated rice crops, one with organic management (O.M.) and another one with conventional management (C.M.), in the municipality of Nova Santa Rita, RS, Brazil, during the 2013/2014 and 2014/2015 seasons. The parasitoids were collected with Malaise trap arranged at different distances in relation to the native vegetation surrounding the rice crop in both places. Specimens were collected twice a month from seeding until the rice harvest. Average abundance between management, distances and rice development were compared. The most abundant families were Platygastridae, Mymaridae, Encyrtidae, Eulophidae and Trichogrammatidae. Parasitoid average abundance was significantly higher on OM only in the second season. There was a negative correlation between distance from native vegetation and parasitoid abundance in C.M. areas. There were differences in the composition of the parasitoid assembly between the phenological stages of rice.
Constitutive innate immunity of tropical House Wrens varies with season and reproductive activity
B Irene Tieleman, Maaike A Versteegh, Kirk C Klasing, Joseph B Williams. 2019. The Auk: Ornithological Advances. https://doi.org/10.1093/auk/ukz029
Abstract
Abstract
In lowland Neotropical regions, where air temperature and day length remain relatively constant year round, seasonality is determined primarily by changes in rainfall. The wet season triggers the start of breeding for many Neotropical birds but also alters the antigenic environment, likely increasing the risk of disease transmission. We explored 2 hypotheses about temporal variation in constitutive innate immunity of a Neotropical bird, the House Wren (Troglodytes aedon). The antigen response hypothesis proposes that Neotropical wrens upregulate their immune function in the wet season either in anticipation of or in response to vectors that become more prevalent. The resource constraint hypothesis proposes that during periods of putative high resource demand, such as when parents are feeding young, immune function should be compromised and downregulated. Controlling for reproductive stage, we found that microbicidal capacity of blood against Escherichia coli was higher in the wet than the dry season, consistent with the antigen response hypothesis. Phagocytosis of E. coli and Staphylococcus aureus did not differ between wet and dry seasons. Microbicidal capacity and H/L ratio of tropical House Wrens did not vary among reproductive stages, and our data offered no support for the idea that immune function is compromised during the period when parents are feeding young.
Complex interplay of ancient vicariance and recent patterns of geographical speciation in north-western North American temperate rainforests explains the phylogeny of jumping slugs (Hemphillia spp.)
Andrew M Rankin, Thomas Wilke, Michael Lucid, William Leonard, Anahí Espíndola, Megan L Smith, Bryan C Carstens, Jack Sullivan. 2019. Biological Journal of the Linnean Society, blz040, https://doi.org/10.1093/biolinnean/blz040
Abstract
Abstract
The history of the currently disjunct temperate rainforests of the Pacific Northwest of North America has shaped the evolution and diversity of endemics. This study focuses on how geological and climatic perturbations have driven speciation in the area by isolating lineages. We investigated the phylogenetic relationships and historical biogeography of the endemic jumping slugs (genus Hemphillia) using a multi-locus phylogeny. We evaluated the spatial distribution and divergence times of major lineages, generated ancestral area probabilities and inferred the biogeographical history of the genus. Our study revealed eight genetic lineages that formed three clades: one clade consisting of two Coast/Cascade lineages, and two reciprocally monophyletic clades that each contain a Coast/Cascade and two Rocky Mountains taxa. The results of the biogeographical analysis suggest that the ancestral range of the genus occupied Coast/Cascade habitats and then spread across into Northern Rocky Mountain interior habitats with subsequent fragmentations isolating coastal and inland lineages. Finally, there have been more recent speciation events among three lineage pairs that have shaped shallow structures of all clades. We add to our knowledge of the biogeographical history of the region in that we discovered diversification and speciation events that have occurred in ways more complex than previously thought.
Models and modeling in evolution
Kathy L. Malone, Anita Schuchardt, Zakee Sabree. 2019. Evolution Education Re-considered. Chapter in Book (peer-reviewed).
Abstract
Abstract
The use of scientific models and modeling in science education has been demonstrated to achieve cognitive gains in several science disciplines, (Jackson, Dukerich & Hestenes, 2008; Malone, Schuchardt & Schunn, 2017; Schuchardt & Schunn, 2016). In the area of evolution, prior researchers have studied how students view models, and how to support student learning through the use of computer-based modeling. Frequently, researchers used case studies with small samples of students describing the impact of modeling on conceptual change. (Passmore & Stewart, 2002; Wagh & Wilensky, 2014). There is a dearth of quasi-experimental studies in secondary classrooms that examine how the use of models and modeling can affect the cognitive gains of learners in biology and evolution in particularly. This chapter will discuss an evolution unit grounded in the use of modeling and its effects on learning in evolution and attitudes towards science in general. The first section will include a discussion of the modeling activities used in the unit, such as hands-on inquiry activities to develop the model as well as deployments of the model in numerous biology contexts. The second section will include details of the mixed method analysis of the effects of this curriculum on student learning in evolution.
Non-hierarchical competition among co-occurring woody seedlings in a resource-limited environment
Natasha N. Woods, Ryan McCarthy, and Maria N. Miriti. 2019. Ecosphere 10(5):e02751. 10.1002/ecs2.2751
Abstract
Long-term species persistence in plant communities is contingent in part on the conditions that favor establishment and early survival. In stressful habitats, facilitated seedling establishment can enhance species richness by providing a safe-site for species unable to establish in open microsites. However, the indirect effects of seedling competition may drive persistence in locations where seedlings occur in high density. This under-examined dynamic can influence community recovery to stress by favoring competitively dominant species, in particular when stress increases local seedling density in favorable microsites. We present the results of a response surface experiment that examines growth responses among seedlings of Ambrosia dumosa, Eriogonum fasciculatum, and Larrea tridentata that were planted at three densities and four relative frequencies. These species co-occur at an extensively monitored reference community located in the Colorado Desert, California, USA, where extensive drought caused unprecedented mortality that will require novel recruitment for the community to reach pre-disturbance composition. Significant, nonhierarchical competitive responses show that seedling survival is contingent on the species identity and density of neighboring seedlings. This result supports non-hierarchical competition among these common species. Ambrosia and Eriogonum had faster growth rates than Larrea, but also experienced larger reductions in growth from competition than Larrea. Although drought may intensify seedling competition in favorable locations, the context dependency of competitive outcomes may permit coexistence.
Conspecific coprophagy stimulates normal development in a germ-free model invertebrate
Jahnes, Benjamin C; Herrmann, Madeline; Sabree, Zakee L. 2019. PeerJ 7:e6914 DOI 10.7717/peerj.6914
Abstract
Microbial assemblages residing within and on animal gastric tissues contribute to various host beneficial processes that include diet accessibility and nutrient provisioning, and we sought to examine the degree to which intergenerational and community-acquired gut bacteria impact development in a tractable germ-free (GF) invertebrate model system. Coprophagy is a common behavior in cockroaches and termites that provides access to both nutrients and the primary means by which juveniles are inoculated with beneficial gut bacteria. This hypothesis was tested in the American cockroach (Periplaneta americana) by interfering with this means of acquiring gut bacteria, which resulted in GF insects that exhibited prolonged growth rates and gut tissue dysmorphias relative to wild-type (WT) P. americana. Conventionalization of GF P. americana via consumption of frass (feces) from conspecifics and siblings reared under non-sterile conditions resulted in colonization of P. americana gut tissues by a diverse microbial community and a significant (p < 0.05) recovery of WT level growth and hindgut tissue development phenotypes. These data suggest that coprophagy is essential for normal gut tissue and organismal development by introducing beneficial gut bacteria to P. americana, and that the GF P. americana model system is a useful system for examining how gut bacteria impact host outcomes.
Preference of Peponapis pruinosa (Hymenoptera: Apoidea) for Tilled Soils Regardless of Soil Management System
Amanda R Skidmore, Clancy A Short, Chasity Dills, Karen Goodell, Ricardo T Bessin. 2019. Environmental Entomology, nvz052, https://doi.org/10.1093/ee/nvz052
Abstract
Concerns about global pollinator declines have placed a growing focus on understanding the impact of agriculture practices on valuable native pollinators in these systems. Cultivation practices such as tillage disturb agroecosystems and can have negative impacts on ground-nesting pollinators. The squash bee, Peponapis pruinosa (Say), is a ground-nesting specialist pollinator of Cucurbita (Cucurbitaceae) crops (i.e., pumpkins and squash) that often nests in agricultural fields and thus may be vulnerable to these practices. We investigated the impact of tillage on nesting behavior of P. pruinosa in plasticulture and strip-tilled squash systems. We used choice experiments to test nesting substrate preference and nesting success of caged P. pruinosa in two soil tillage systems: strip tillage and plasticulture. The strip tillage system comprised two tillage zones (strip-tilled row with no-till edges), and the plasticulture system comprised two tillage zones (plastic bed and conventional tillage edge). The results of our study indicate that P. pruinosa nesting density did not significantly differ between the strip tillage and plasticulture systems. Within each system, P. pruinosa preferred excavating nests in the most disturbed soil zones (strip-tilled row and conventionally tilled edge). In the strip tillage system, the strip-tilled row had significantly more nests than the no-till edge. Results of these studies suggest that soil tillage practices can influence P. pruinosa nesting choice and production practices should be considered when developing a pollinator protection plan.
Propagule pressure and genetic diversity enhance colonization by a ruderal species: a multi-generation field experiment.
Stephen M. Hovick and Kenneth D. Whitney. 2019. Ecological Monographs 00(00):e01368. 10.1002/ecm.1368
Abstract
Colonization is a critical filter, setting the stage for short-term and long-term population success. Increased propagule pressure (e.g., more founding individuals) usually enhances colonization; however, this pattern may be driven by purely numeric effects, population genetic diversity effects, or both. To determine the independent and interactive effects of propagule pressure and genetic diversity, we conducted a seed addition experiment in the field using the ruderal annual Arabidopsis thaliana. Propagule pressure treatments spanned five levels, from 32 to 960 seeds per 0.25-m2 plot. Founder populations were composed of one, four, or eight genotypes and exposed to ambient or reduced levels of interspecific competition. Genotype monocultures were included to quantify additive vs. non-additive effects. Populations were followed for three generations, with abundance, population persistence and genotype retention (the proportion of introduced genotypes persisting over time) as the major response variables. Increased propagule pressure enhanced abundance immediately following introduction, particularly where nutrient availability was high and competition reduced. Greater propagule pressure also increased the likelihood of population persistence and genotype retention through three generations. However, most populations experienced rapid abundance declines over time, yielding no relationship between propagule pressure and third generation abundance across persisting populations. Under reduced competition, increased genetic diversity led to a marginal increase in persistence through the third generation that was more pronounced, and statistically significant, in low nutrient conditions. Genetic diversity didnot affect persistence through the first generation, thus indicating that genetic diversity effects strengthened over time. Nevertheless, genotypic mixture populations fell short of expectations based on performance in monocultures (negative non-additive effects). Increased genetic diversity was also associated with abundance declines, largely due to one particularly high-performing genotype in the lowest diversity treatments (i.e., genotypic identity effects). Overall, our results indicate that increases in both propagule pressure and genetic diversity can enhance colonization success but are highly context dependent. They also highlight novel ways in which both factors can impact the retention of introduced genetic diversity over time. Our findings pinpoint the determinants of a fundamental population process and have key implications for applications where enhanced or suppressed colonization is desired, including ecological restoration and invasive species management.
Evolutionary history of New World ticks of the genus Dermacentor (Ixodida: Ixodidae), and the origin of D. variabilis
Paula Lado and Hans Klompen. 2019. Biological Journal of the Linnean Society, blz063, https://doi.org/10.1093/biolinnean/blz063
Abstract
This study integrates biogeographical and phylogenetic data to determine the evolutionary history of the New World Dermacentor, and the origin of D. variabilis. The phylogenetic reconstructions presented here strongly support the hypothesis of an Afrotropical origin for Dermacentor, with later dispersal to Eurasia and the Nearctic. Phylogenetic and biogeographical data suggest that the genus reached the New World through the Beringia land bridge, from south-east Asia. The monophyly of the genus is supported, and most of the New World Dermacentor species appear as monophyletic. Dermacentor occidentals constitutes the sister lineage of D. variabilis, and the latter is subdivided into two well-supported clades: an eastern and a western clade. The western clade is genetically more variable than the eastern.
The genus Dermacentor probably originated in Africa, and dispersed to the Palearctic and then to the New World through the Beringian route. Dermacentor variabilis appears to have originated in western North America, and then dispersed to eastern North America, probably in a single migration event.
