July 26, 2016
Publications by EEOB faculty July 1 - July 31
Quantitative Phosphoproteomics Reveals Signaling Mechanisms Associated with Rapid Cold Hardening in a Chill-Tolerant Fly
Nicholas M. Teets and David L. Denlinger. 2016.
Abstract
Rapid cold hardening (RCH) is a physiological adaptation in which brief chilling (minutes to hours) significantly enhances the cold tolerance of insects. RCH allows insects to cope with sudden cold snaps and diurnal variation in temperature, but the mechanistic basis of this rapid stress response is poorly understood. Here, we used phosphoproteomics to identify phosphorylation-mediated signaling events that are regulated by chilling that induces RCH. Phosphoproteomic changes were measured in both brain and fat bodies, two tissues that are essential for sensing cold and coordinating RCH at the organismal level. Tissues were chilled ex vivo, and changes in phosphoprotein abundance were measured using 2D electrophoresis coupled with Pro-Q diamond labeling of phosphoproteins followed by protein identification via LC−MS/MS. In both tissues, we observed an abundance of protein phosphorylation events in response to chilling. Some of the proteins regulated by RCH-inducing chilling include proteins involved in cytoskeletal reorganization, heat shock proteins, and proteins involved in the degradation of damaged cellular components via the proteasome and autophagosome. Our results suggest that phosphorylation-mediated signaling cascades are major drivers of RCH and enhance our mechanistic understanding of this complex phenotype.
Western Lake Erie Basin: Soft-data-constrained, NHDPlus resolution watershed modeling and exploration of applicable conservation scenarios
Haw Yen, Michael J. White, Jeffrey G. Arnold, S. Conor Keitzer, Mari-Vaughn V. Johnson, Jay D. Atwood, Prasad Daggupati, Matthew E. Herbert, Scott P. Sowa, Stuart A. Ludsin, Dale M. Robertson, Raghavan Srinivasan, Charles A. Rewa. 2016. doi:10.1016/j.scitotenv.2016.06.202
Abstract
Complex watershed simulation models are powerful tools that can help scientists and policy-makers address challenging topics, such as land use management and water security. In the Western Lake Erie Basin (WLEB), complex hydrological models have been applied at various scales to help describe relationships between land use and water, nutrient, and sediment dynamics. This manuscript evaluated the capacity of the current Soil and Water Assessment Tool (SWAT) to predict hydrological and water quality processes within WLEB at the finest resolution watershed boundary unit (NHDPlus) along with the current conditions and conservation scenarios. The process based SWAT model was capable of the fine-scale computation and complex routing used in this project, as indicated by measured data at five gaging stations. The level of detail required for fine-scale spatial simulation made the use of both hard and soft data necessary in model calibration, alongside other model adaptations. Limitations to the model's predictive capacity were due to a paucity of data in the region at the NHDPlus scale rather than due to SWAT functionality. Results of treatment scenarios demonstrate variable effects of structural practices and nutrient management on sediment and nutrient loss dynamics. Targeting treatment to acres with critical outstanding conservation needs provides the largest return on investment in terms of nutrient loss reduction per dollar spent, relative to treating acres with lower inherent nutrient loss vulnerabilities. Importantly, this research raises considerations about use of models to guide land management decisions at very fine spatial scales. Decision makers using these results should be aware of data limitations that hinder fine-scale model interpretation.
Influence of predator cues on terminal investment in courtship by male Schizocosa ocreata (Hentz, 1844) wolf spiders (Araneae: Lycosidae)
Benjamin Nickley, Diana Saintignon, and J. Andrew Roberts.2016. Journal of Arachnology 44(2):176-181. doi: http://dx.doi.org/10.1636/J15-64
Abstract
Sexual signals play a critical role in mate attraction, but fitness benefits of signal production depend on a number of external and internal influences. Sexual signaling can be energetically expensive, and has potential to attract unwanted attention from predators. Male brushlegged wolf spiders, Schizocosa ocreata (Hentz, 1844) (Araneae: Lycosidae), actively signal to females in the leaf litter habitat during their spring breeding season, but face a tradeoff between current and future reproduction as the season progresses. The terminal investment hypothesis predicts that with fewer available females, increasing risk of predation, and stronger influence of senescence as the season progresses, males should take greater risks to secure mating. We explored this idea by exposing males of increasing ages to female cues alone or female cues combined with predator cues. We found little or no direct evidence to support the terminal investment hypothesis in this species, in that males across all ages essentially ceased active courtship in the presence of predator cues, that is, there was no age related increase in courtship investment in the presence of predator cues. However, we found distinct evidence of senescence in males based on age-related changes in behavior, which has not previously been directly explored in this species. While males maintained similar levels of active courtship across all age classes (in the absence of predator cues), older males increased their relative investment in maintenance behaviors (grooming) and decreased non-courtship display behaviors such as tapping and leg raises. These findings suggest that studies of male behavior in this species should be carefully designed to control for age-related variation in behavioral response.
Tissue-Specific Venom Composition and Differential Gene Expression in Sea Anemones.
Jason Macrander, Michael Broe, and Marymegan Daly. 2016. Oxford University Press on behalf of the Society for Molecular Biology and Evolution. doi:10.1093/gbe/evw155
Abstract
Cnidarians represent one of the few groups of venomous animals that lack a centralized venom transmission system. Instead, they are equipped with stinging capsules collectively known as nematocysts. Nematocysts vary in abundance and type across different tissues; however, the venom composition in most species remains unknown. Depending on the tissue type, the venom composition in sea anemones may be vital for predation, defense, or digestion. Using a tissue specific RNA-seq approach, we characterize the venom assemblage in the tentacles, mesenterial filaments, and column for three species of sea anemone (Anemonia sulcata, Heteractis crispa, and Megalactis griffithsi). These taxa vary with regard to inferred venom potency, symbiont abundance, and nematocyst diversity. We show that there is significant variation in abundance of toxin-like genes across tissues and species. Although the cumulative toxin abundance for the column was consistently the lowest, contributions to the overall toxin assemblage varied considerably among tissues for different toxin types. Our gene ontology (GO) analyses also show sharp contrasts between conserved GO groups emerging from whole transcriptome analysis and tissue specific expression among GO groups in our differential expression analysis. This study provides a framework for future characterization of tissue-specific venom and other functionally important genes in this lineage of simple bodied animals.
Phylogeographic model selection leads to insight into the evolutionary history of four-eyed frogs
Maria Tereza C. Thoméa and Bryan C. Carstens. 2016. Proc. Natl. Acad. Sci. USA. 113(29):8010–8017, doi: 10.1073/pnas.1601064113
Abstract
Phylogeographic research investigates biodiversity at the interface between populations and species, in a temporal and geographic context. Phylogeography has benefited from analytical approaches that allow empiricists to estimate parameters of interest from the genetic data (e.g., θ = 4Neμ, population divergence, gene flow), and the widespread availability of genomic data allow such parameters to be estimated with greater precision. However, the actual inferences made by phylogeographers remain dependent on qualitative interpretations derived from these parameters’ values and as such may be subject to overinterpretation and confirmation bias. Here we argue in favor of using an objective approach to phylogeographic inference that proceeds by calculating the probability of multiple demographic models given the data and the subsequent ranking of these models using information theory. We illustrate this approach by investigating the diversification of two sister species of four-eyed frogs of northeastern Brazil using single nucleotide polymorphisms obtained via restriction-associated digest sequencing. We estimate the composite likelihood of the observed data given nine demographic models and then rank these models using Akaike information criterion. We demonstrate that estimating parameters under a model that is a poor fit to the data is likely to produce values that lead to spurious phylogeographic inferences. Our results strongly imply that identifying which parameters to estimate from a given system is a key step in the process of phylogeographic inference and is at least as important as being able to generate precise estimates of these parameters. They also illustrate that the incorporation of model uncertainty should be a component of phylogeographic hypothesis tests.
Macrodinychus mites as parasitoids of invasive ants: an overlooked parasitic association
Jean-Paul Lachaud, Hans Klompen & Gabriela Pérez-Lachaud. 2016. Scientific Reports 6, Article number: 29995. doi:10.1038/srep29995
Abstract
Mites are frequent ant symbionts, yet the exact nature of their interactions with their hosts is poorly known. Generally, myrmecophilous mites show adaptations for dispersal through phoresis, but species that lack such an adaptation may have evolved unusual specialized relationships with their hosts. The immature stages of Macrodinychus multispinosus develop as ectoparasitoids of pupae of the invasive ant Paratrechina longicornis. Feeding stages show regressed locomotor appendages. These mites complete their development on a single host, sucking all of its body content and therefore killing it. Locally high proportions of parasitized host pupae suggest that M. multispinosus could serve as a biological control agent. This is the ninth species of Macrodinychus reported as ant parasite, and the third known as parasitoid of invasive ants, confirming a unique habit in the evolution of mite feeding strategies and suggesting that the entire genus might be parasitic on ants. Several mites’ characteristics, such as their protective morphology, possible viviparity, lack of a specialized stage for phoretic dispersal, and low host specificity, combined with both the general low aggressiveness of invasive P. longicornis towards other ants and its possible susceptibility to generalist ectoparasites would account for the host shift in native macrodinychid mites.
Venom Resistance as a Model for Understanding the Molecular Basis of Complex Coevolutionary Adaptations
Matthew L. Holding, Danielle H. Drabeck, Sharon A. Jansa, and H. Lisle Gibbs. 2016. Integr. Comp. Biol. doi: 10.1093/icb/icw082
Abstract
Venom and venom resistance are molecular phenotypes widely considered to have diversified through coevolution between predators and prey. However, while evolutionary and functional studies on venom have been extensive, little is known about the molecular basis, variation, and complexity of venom resistance. We review known mechanisms of venom resistance and relate these mechanisms to their predicted impact on coevolutionary dynamics with venomous enemies. We then describe two conceptual approaches which can be used to examine venom/resistance systems. At the intraspecific level, tests of local adaptation in venom and resistance phenotypes can identify the functional mechanisms governing the outcomes of coevolution. At deeper evolutionary timescales, the combination of phylogenetically informed analyses of protein evolution coupled with studies of protein function promise to elucidate the mode and tempo of evolutionary change on potentially coevolving genes. We highlight case studies that use each approach to extend our knowledge of these systems as well as address larger questions about coevolutionary dynamics. We argue that resistance and venom are phenotypic traits which hold exceptional promise for investigating the mechanisms, dynamics, and outcomes of coevolution at the molecular level. Furthermore, extending the understanding of single gene-for-gene interactions to the whole resistance and venom phenotypes may provide a model system for examining the molecular and evolutionary dynamics of complex multi-gene interactions.
Comparing range evolution in two western Plethodon salamanders: glacial refugia, competition, ecological niches, and spatial sorting
Tara A. Pelletier, Bryan C. Carstens. 2016. J. Biogeogr. doi:10.1111/jbi.12833
Abstract
Aim
Plethodon dunni and P. vehiculum are sister species with widely overlapping ranges, yet the distribution of P. vehiculum extends almost 400 km farther north than its sister species. We explore Pleistocene refugial structure, competition, physiological tolerances and dispersal ability as contributing factors to the range difference between these two species.
Location
The Pacific Northwest of North America, including Oregon, Washington and British Columbia – the full range of both species.
Methods
We used genetic, environmental and morphological data to test hypotheses that explain this range difference. Genetic data were used to explore range expansion dynamics and population structure. Species distributional models were used to compare current niches to mid-Holocene and Pleistocene distributions. Morphological data were used to assess phenotypic differences between the species and test for evidence of spatial sorting.
Results
Both species underwent rapid range expansions since the Pleistocene and share similar population structure. Species distributional models are different in distribution at all times periods between species. The species are significantly different in all morphological measurements taken. Only P. vehiculum shows evidence of spatial sorting.
Main conclusions
Physiological tolerance and dispersal ability best explain the distributional difference between these species. Spatial sorting most likely plays a key role in the range expansion of P. vehiculum.
