Junior Recital: Alex Sotka

Junior Recital: Alex Sotkahttps://digitalcommons.kennesaw.edu/musicprograms/2440/thumbnail.jp

Non-consumptive predator effects indirectly influence marine plant biomass and palatability

1. Predators can reduce herbivory and increase plant biomass by consuming herbivores, lowering individual herbivore feeding rates, or both. We tested whether the presence of predators increases plant quality by non-consumptively reducing grazing pressure and thereby weakening the strength of the induced response in plant chemical defences. 2. We performed a 42-day outdoor mesocosm experiment in which the herbivorous amphipod Ampithoe longimana was cultured on the brown seaweed Sargassum filipendula in the presence and absence of olfactory cues of its principal fish predator, the pinfish Lagodon rhomboides. The presence of fish cues reduced per capita rates of amphipod grazing by nearly 50%. Over the span of the mesocosm experiment, this per capita reduction in feeding rate yielded at least a 40% lower growth rate of amphipod populations (i.e. r reduced from 1.01 to 0.61). The lower rates of amphipod grazing (overall or per capita) correlated with higher algal biomass. 3. We pursued a series of laboratory-based feeding choice assays with naive amphipods to determine tissue palatability and the plant traits that mediate feeding choices. Tissue from tanks without grazers was more palatable than tissue from tanks with grazers, a pattern of induced plant defences that has been documented previously. Surprisingly, however, plant tissue from tanks with grazers and fish cues was more palatable than tissue from tanks with grazers but without fish cues. All changes in algal palatability were mediated by polar, but not lipophilic metabolites. These results suggest that the non-consumptive effects of fish predators increases the food quality of Sargassum by weakening the strength of its induced chemical defences. 4. Synthesis. The smell of predators has the potential to regulate herbivore populations and affect the ecological dynamics of plant biomass and chemical defences

Can diversifying selection be distinguished from history in geographic clines? A population genomic study of killifish (Fundulus heteroclitus)

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS ONE 7 (2012): e45138, doi:10.1371/journal.pone.0045138.A common geographical pattern of genetic variation is the one-dimensional cline. Clines may be maintained by diversifying selection across a geographical gradient but can also reflect historical processes such as allopatry followed by secondary contact. To identify loci that may be undergoing diversifying selection, we examined the distribution of geographical variation patterns across the range of the killifish (Fundulus heteroclitus) in 310 loci, including microsatellites, allozymes, and single nucleotide polymorphisms. We employed two approaches to detect loci under strong diversifying selection. First, we developed an automated method to identify clinal variation on a per-locus basis and examined the distribution of clines to detect those that exhibited signifcantly steeper slopes. Second, we employed a classic -outlier method as a complementary approach. We also assessed performance of these techniques using simulations. Overall, latitudinal clines were detected in nearly half of all loci genotyped (i.e., all eight microsatellite loci, 12 of 16 allozyme loci and 44% of the 285 SNPs). With the exception of few outlier loci (notably mtDNA and malate dehydrogenase), the positions and slopes of Fundulus clines were statistically indistinguishable. The high frequency of latitudinal clines across the genome indicates that secondary contact plays a central role in the historical demography of this species. Our simulation results indicate that accurately detecting diversifying selection using genome scans is extremely difficult in species with a strong signal of secondary contact; neutral evolution under this history produces clines as steep as those expected under selection. Based on these results, we propose that demographic history can explain all clinal patterns observed in F. heteroclitus without invoking natural selection to either establish or maintain the pattern we observe today.This work was supported by the National Science Foundation (DEB-0919064 and IOS-105226

GEOGRAPHIC VARIATION AMONG HERBIVORE POPULATIONS IN TOLERANCE FOR A CHEMICALLY RICH SEAWEED

Previous investigations have shown that the sedentary amphipod Ampithoe longimana escapes consumers by selectively living on and eating chemically defended seaweeds in the genus Dictyota. However, A. longimana and Dictyota overlap only in the southern portion of the amphipod's range; Dictyota is not available to amphipods from more northerly regions. We used this disjunction in distribution to test the hypothesis that A. longimana populations co-occurring with Dictyota would have greater tolerance for the seaweed's chemical defenses and would display higher feeding preference for, and fitness on, the seaweed than would more northerly populations. We also evaluated the genetic vs. phenotypic basis of these patterns and attempted to detect trade-offs between tolerance for Dictyota and ability to use other plants as foods. Such geographic studies of herbivory have been conducted using terrestrial insects, but few studies have focused on other herbivores, and this is especially true for marine systems. In multiple-choice feeding assays with both field-collected and laboratory-reared adults, a North Carolina population of A. longimana sympatric with Dictyota more readily fed on Dictyota and was more resistant to Dictyota's deterrent chemistry than was a Connecticut population from outside of Dictyota's geographic range. When raised on Dictyota menstrualis and D. ciliolata, A. longimana juveniles from North Carolina grew faster, matured faster, and produced more reproductive females than did Connecticut juveniles. The differential tolerance for Dictyota has a genetic basis, as it was maintained through two generations grown to maturity in a common environment. When several northern and southern populations were assayed, they displayed similar regional differences in feeding preferences. Though southern juveniles had higher fitness on Dictyota than northern juveniles, southern juveniles performed as well as northern juveniles when raised on seven other seaweeds, including seaweeds (e.g., Fucus vesiculosus and Sargassum filipendula) that produce secondary metabolites in a different class from those found in Dictyota. Thus, tolerating Dictyota did not incur detectable performance trade-offs when juveniles were confined to feeding on alternative seaweeds. Our results suggest that the evolution of host preferences may depend more on the host value as a refuge from enemies than on minimizing the costs of tolerating plant secondary metabolites

Nutrition of marine mesograzers: integrating feeding behavior, nutrient intake and performance of an herbivorous amphipod

Consumers can regulate the acquisition and use of nutrients through behavioral and physiological mechanisms. Here, we present an experimental approach that simultaneously integrates multiple nutritional traits, feeding assays, and juvenile performance to assess whether a marine herbivore (the amphipod Ampithoe valida) regulates the intake of elements (carbon and nitrogen), macronutrients (protein and non-protein) or both when offered freeze-dried tissues of seaweeds varying in nutritional content. We assessed behavioral regulation of nutrients in three ways. First, during no-choice assays, we found that amphipods ingested similar amounts of carbon, but not nitrogen, non-protein and protein, across algal diets. Second, herbivore intake rates of carbon, protein and non-protein components across no-choice assays was similar to intake rates when offered a choice of foods. Third, variation in intake rates of carbon and non-protein components among algal diets was significantly greater than was tissue content of these components, while variation in intake rates of nitrogen was significantly lower; differences in protein intake variation was equivocal. While these analytical approaches are not uniformly consistent, carbon and nitrogen seem to emerge as the nutrient components that are more strongly regulated by A. valida. Juveniles reared on single diets shown patterns of survivorship, growth and reproduction that could not be predicted by these feeding preferences, nor nutrient content. We conclude that an integrative approach that considers the intake of multiple nutrients potentially yields insights into feeding behavior and its performance consequences

Development and characterization of microsatellite loci for the haploid–diploid red seaweed Gracilaria vermiculophylla

Microsatellite loci are popular molecular markers due to their resolution in distinguishing individual genotypes. However, they have rarely been used to explore the population dynamics in species with biphasic life cycles in which both haploid and diploid stages develop into independent, functional organisms. We developed microsatellite loci for the haploid–diploid red seaweed Gracilaria vermiculophylla, a widespread non-native species in coastal estuaries of the Northern hemisphere. Forty-two loci were screened for amplification and polymorphism. Nine of these loci were polymorphic across four populations of the extant range with two to eleven alleles observed. Mean observed and expected heterozygosities ranged from 0.265 to 0.527 and 0.317 to 0.387, respectively. Overall, these markers will aid in the study of the invasive history of this seaweed and further studies on the population dynamics of this important haploid–diploid primary producer

Global patterns in the impact of marine herbivores on benthic primary producers

Despite the importance of consumers in structuring communities, and the widespread assumption that consumption is strongest at low latitudes, empirical tests for global scale patterns in the magnitude of consumer impacts are limited. In marine systems, the long tradition of experimentally excluding herbivores in their natural environments allows consumer impacts to be quantified on global scales using consistent methodology. We present a quantitative synthesis of 613 marine herbivore exclusion experiments to test the influence of consumer traits, producer traits and the environment on the strength of herbivore impacts on benthic producers. Across the globe, marine herbivores profoundly reduced producer abundance (by 68% on average), with strongest effects in rocky intertidal habitats and the weakest effects on habitats dominated by vascular plants. Unexpectedly, we found little or no influence of latitude or mean annual water temperature. Instead, herbivore impacts differed most consistently among producer taxonomic and morphological groups. Our results show that grazing impacts on plant abundance are better predicted by producer traits than by large‐scale variation in habitat or mean temperature, and that there is a previously unrecognised degree of phylogenetic conservatism in producer susceptibility to consumption

Prevalence and Clinical Significance of Helicobacter Pylori-negative Chronic Gastritis in Children

OBJECTIVES: The clinical significance of Helicobacter pylori-negative chronic gastritis (HPNCG) in children is unclear. We examined this issue in patients who had undergone esophagogastroduodenoscopy with systematic gastric sampling. METHODS: Data of 1178 consecutive children who underwent diagnostic esophagogastroduodenoscopy were collected. Baseline characteristics and long-term outcomes were compared between children with active and inactive HPNCG and those with normal gastric histology. Follow-up data were available for up to 13 years. RESULTS: Altogether 24 (2.0%) children had active and 235 (19.9%) inactive HPNCG, 27 (2.3%) were Hpylori-positive, 46 (3.9%) had other gastric pathology, and 846 (71.8%) normal histology. Diarrhea (31.3% vs 25.1%, P  = 0.033), poor growth (23.6% vs 14.7%, P  < 0.001), bloody stools (13.9% vs 7.2%, P < 0.001), anemia (46.5% vs 23.4%, P < 0.001), hypersedimentation (39.7% vs 21.4%, P < 0.001), hypoalbuminemia (40.4% vs 16.2%, P < 0.001), and elevated fecal calprotectin (62.4% vs 31.5%, P < 0.001) were more common and heartburn (13.9% vs 22.9%, P = 0.002) less common in the HPNCG group than in the controls. Both active (OR 3.64,95% CI 1.35-9.82) andinactive (2.98, 2.18-4.08) HPNCG predicted a diagnosis in the initial investigations. Crohn disease (41.7%) was the most common diagnosis in active HPNCG and celiac disease (37.4%) in inactive HPNCG. During follow-up, 7 (9.9%) of the 71 initially nondiagnosed HPNCG children received a diagnosis. CONCLUSIONS: HPNCG is a frequent finding in children undergoing EGD, the active form being associated especially with Crohn disease and the inactive with celiac disease. The long-term prognosis of patients with HPNCG who do not receive an initial diagnosis is good.acceptedVersionPeer reviewe

Combining niche-shift and population genetic analyses predicts rapid phenotypic evolution during invasion

Rapid evolution of non-native species can facilitate invasion success, but recent reviews indicate that such microevolution rarely yields expansion of the climatic niche in the introduced habitats. However, because some invasions originate from a geographically restricted portion of the native species range and its climatic niche, it is possible that the frequency, direction and magnitude of phenotypic evolution during invasion has been underestimated. We explored the utility of niche-shift analyses in the red seaweed Gracilaria vermiculophylla, which expanded its range from the northeastern coastline of Japan to North America, Europe and northwestern Africa within the last 100 years. A genetically-informed climatic niche shift analysis indicates that native source populations occur in colder and highly seasonal habitats, while most non-native populations typically occur in warmer, less seasonal habitats. This climatic niche expansion predicts that non-native populations evolved greater tolerance for elevated heat conditions relative to native source populations. We assayed 935 field-collected and 325 common-garden thalli from 40 locations and as predicted, non-native populations had greater tolerance for ecologically-relevant extreme heat (40°C) than did Japanese source populations. Non-native populations also had greater tolerance for cold and low-salinity stresses relative to source populations. The importance of local adaptation to warm temperatures during invasion was reinforced by evolution of parallel clines: populations from warmer, lower-latitude estuaries had greater heat tolerance than did populations from colder, higher-latitude estuaries in both Japan and eastern North America. We conclude that rapid evolution plays an important role in facilitating the invasion success of this and perhaps other non-native marine species. Genetically-informed ecological niche analyses readily generate clear predictions of phenotypic shifts during invasions, and may help to resolve debate over the frequency of niche conservatism versus rapid adaptation during invasion

The role of multixenobiotic transporters in predatory marine molluscs as counter-defense mechanisms against dietary allelochemicals

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology 152 (2010): 288-300, doi:10.1016/j.cbpc.2010.05.003.Multixenobiotic transporters have been extensively studied for their ability to modulate the disposition and toxicity of pharmacological agents, yet their influence in regulating the levels of dietary toxins within marine consumers has only recently been explored. This study presents functional and molecular evidence for multixenobiotic transporter-mediated efflux activity and expression in the generalist gastropod Cyphoma gibbosum, and the specialist nudibranch Tritonia hamnerorum, obligate predators of chemically defended gorgonian corals. Immunochemical analysis revealed that proteins with homology to permeability glycoprotein (P-gp) were highly expressed in T. hamnerorum whole animal homogenates and localized to the apical tips of the gut epithelium, a location consistent with a role in protection against ingested prey toxins. In vivo dye assays with specific inhibitors of efflux transporters demonstrated the activity of P-gp and multidrug resistance-associated protein (MRP) families of ABC transporters in T. hamnerorum. In addition, we identified eight partial cDNA sequences encoding two ABCB and two ABCC proteins from each molluscan species. Digestive gland transcripts of C. gibbosum MRP-1, which have homology to vertebrate glutathione-conjugate transporters, were constitutively expressed regardless of gorgonian diet. This constitutive expression may reflect the ubiquitous presence of high affinity substrates for C. gibbosum glutathione transferases in gorgonian tissues likely necessitating export by MRPs. Our results suggest that differences in multixenobiotic transporter expression patterns and activity in molluscan predators may stem from the divergent foraging strategies of each consumer.Financial support was provided by the Ocean Life Institute Tropical Research Initiative Grant (WHOI) to KEW and MEH; the Robert H. Cole Endowed Ocean Ventures Fund (WHOI) to KEW; the National Undersea Research Center – Program Development Proposal (CMRC-03PRMN0103A) to KEW; and the National Science Foundation (Graduate Research Fellowship to KEW and DEB-0919064 to EES)