Effects of fathead minnows and restoration on prairie wetland ecosystems

SUMMARY 1. Research has shown that fish influence the structure and processes of aquatic ecosystems, but replicated studies at the ecosystem level are rare as are those involving wetlands. Some wetlands of the Prairie Pothole Region (PPR) of North America support fish communities dominated by fathead minnows ( Pimephales promelas ) while others are fishless, providing an opportunity to assess the influence of these fish on wetland ecosystems. Additionally, many wetlands have previously been drained and subsequently restored, but the success of these efforts is poorly known and restoration may be impeded by the presence of fish.
2. We assessed the effects of fathead minnows and drainage by studying 20 semipermanent, prairie wetlands in Minnesota from 1996 to 1999. We used a 2 × 2 factorial design to examine the effects of presence and absence of minnows and drainage history (restored/never drained) on the abundance of aquatic invertebrates and amphibians, as well as on the concentrations of chlorophyll a , total phosphorus, total nitrogen and turbidity in the water column.
3. Results showed that fathead minnows are an important determinant of many biotic and abiotic characteristics of wetlands in the eastern PPR. Wetlands with fathead minnows had fewer aquatic insects, large- and small-bodied cladocerans, calanoid copepods, ostracods and larval tiger salamanders, as well as a higher abundance of corixids and greater turbidity and chlorophyll a . A higher concentration of phosphorus in restored basins was the only consistent effect of past management.
4. Fathead minnows usually dominate fish communities in eastern PPR wetlands where fish are present, and can have several strong ecosystem effects. While abiotic variables are important determinants of ecosystem structure in prairie wetlands, they can be strongly influenced by biotic factors.     

Influence of prenatal photoperiod on postnatal prolactin secretion in red deer (Cervus elaphus).

Plasma prolactin concentrations were higher (P < 0.001) in newborn red deer calves whose mothers had been maintained for the last 14 weeks of gestation in long days (18 h light) (group L, n = 9) than in those whose mothers had been kept over the same period in short days (6 h light) (group S, n = 5). After transfer of all hinds and suckled calves on the day of birth to constant intermediate daylength (12 h light), prolactin concentrations decreased exponentially (P < 0.001) in group L calves, but not in group S, during the first 21 days. Thereafter, prolactin fell to a nadir in group L calves and rose to peak values in group S calves at 8-12 weeks post partum (P = 0.003), before converging again by 14 weeks. The pattern of prolactin secretion over the first 14 weeks of life was therefore significantly affected by prenatal photoperiod. Plasma prolactin concentrations in the adult hinds were higher (P < 0.001) in group L than group S at 4-10 weeks before parturition; they were similarly high around parturition and fell thereafter to baseline values after 7 weeks. These results provide evidence that deer fetuses respond to photoperiodic information, thereby acquiring a photoperiodic history in utero that influences postnatal responses to photoperiod.     

Mechanism of photoinhibition in vivo. A reversible light-induced conformational change of reaction center II is related to an irreversible modification of the D1 protein

The light-induced inactivation of the photochemical reaction center II (RCII) of oxygenic chloroplasts (photoinhibition) was investigated in cells and isolated thylakoids of the green alga Chlamydomonas reinhardtii. The process is resolved into a reversible conformational change followed by an irreversible modification of RCII D1 protein. The light-induced changes in vivo persisted in isolated thylakoids. The first step is characterized by (i) destabilization of the secondary acceptor semiquinone anion, Q-B, bound to the D1 protein. This is demonstrated by a reduction in the activation energy of S2,3Q-B charge recombination as measured by the thermoluminescence technique; and (ii) a rise in the intrinsic fluorescence and a decrease of the maximal fluorescence. Unoccupancy of the QB site by plastoquinone partially protected RCII against the light-induced destabilization of Q-B. The extent of charge separation (P+680Q-A) was not affected. However, the slow phase (microsecond) of P+680 dark reduction increased, and the amplitude of signal II was reduced by 20-30%, indicating that in a fraction of RCII, electron donation from Z to P+680 was impaired without losing primary photochemistry. This modification correlates with the irreversible change in D1 protein resulting in the formation of a trypsin-resistant fragment of 16 kDa detected in D1 isolated from light-exposed cells. The change in the Q-B stability could allow charge equilibration with QA and thus explain the rise in the intrinsic fluorescence level and reduction of electron flow to plastoquinone. The change in the lifetime of P+680 can account for further reduction in electron flow (photo-inhibition). The irreversible light-dependent modification of D1 may serve as the signal for its degradation and replacement by a newly synthesized molecule (turnover).     

Development of aleurone and sub-aleurone layers in maize

Electron-microscope studies indicate that the aleurone tissue of maize (Zea mays L.) starts developing approximately 10–15 days after pollination in stocks that take ca. 40 days for the aleurone to mature completely. Development commences when specialized endosperm cells adjacent to the maternal nucellar layer start to differentiate. Differentiation is characterized by the formation of aleurone protein bodies and spherosomes. The protein bodies of the aleurone layer have a vacuolar origin whereas the protein bodies of the immediate underlying endosperm cells appear to develop from protrusions of the rough endoplasmic reticulum. Thus, two morphologically and developmentally distinct types of protein bodies are present in these adjacent tissues. The spherosomes of the aleurone layer form early in the development of this tissue and increase in number as the tissue matures. During the final stages of maturation, these spherosomes become closely apposed to the aleurone grains and the plasma membrane. No further changes are apparent in the structure of the aleurone cells after 40 days from pollination when the caryopsis begins to desiccate.     

Dendrochronological dates confirm a Late Prehistoric population decline in the American Southwest derived from radiocarbon dates

The northern American Southwest provides one of the most well-documented cases of human population growth and decline in the world. The geographic extent of this decline in North America is unknown owing to the lack of high-resolution palaeodemographic data from regions across and beyond the greater Southwest, where archaeological radiocarbon data are often the only available proxy for investigating these palaeodemographic processes. Radiocarbon time series across and beyond the greater Southwest suggest widespread population collapses from AD 1300 to 1600. However, radiocarbon data have potential biases caused by variable radiocarbon sample preservation, sample collection and the nonlinearity of the radiocarbon calibration curve. In order to be confident in the wider trends seen in radiocarbon time series across and beyond the greater Southwest, here we focus on regions that have multiple palaeodemographic proxies and compare those proxies to radiocarbon time series. We develop a new method for time series analysis and comparison between dendrochronological data and radiocarbon data. Results confirm a multiple proxy decline in human populations across the Upland US Southwest, Central Mesa Verde and Northern Rio Grande from AD 1300 to 1600. These results lend confidence to single proxy radiocarbon-based reconstructions of palaeodemography outside the Southwest that suggest post-AD 1300 population declines in many parts of North America.This article is part of the theme issue ‘Cross-disciplinary approaches to prehistoric demography’.     

Glucocorticoid signaling in pancreatic islets modulates gene regulatory programs and genetic risk of type 2 diabetes

Glucocorticoids are key regulators of glucose homeostasis and pancreatic islet function, but the gene regulatory programs driving responses to glucocorticoid signaling in islets and the contribution of these programs to diabetes risk are unknown. In this study we used ATAC-seq and RNA-seq to map chromatin accessibility and gene expression from eleven primary human islet samples cultured in vitro with the glucocorticoid dexamethasone at multiple doses and durations. We identified thousands of accessible chromatin sites and genes with significant changes in activity in response to glucocorticoids. Chromatin sites up-regulated in glucocorticoid signaling were prominently enriched for glucocorticoid receptor binding sites and up-regulated genes were enriched for ion transport and lipid metabolism, whereas down-regulated chromatin sites and genes were enriched for inflammatory, stress response and proliferative processes. Genetic variants associated with glucose levels and T2D risk were enriched in glucocorticoid-responsive chromatin sites, including fine-mapped variants at 51 known signals. Among fine-mapped variants in glucocorticoid-responsive chromatin, a likely casual variant at the 2p21 locus had glucocorticoid-dependent allelic effects on beta cell enhancer activity and affected SIX2 and SIX3 expression. Our results provide a comprehensive map of islet regulatory programs in response to glucocorticoids through which we uncover a role for islet glucocorticoid signaling in mediating genetic risk of T2D.     

Alternative stable states in inherently unstable systems

Alternative stable states are nontransitory states within which communities can exist. However, even highly dynamic communities can be viewed within the framework of stable‐state theory if an appropriate “ecologically relevant” time scale is identified. The ecologically relevant time scale for dynamic systems needs to conform to the amount of time needed for a system's community to complete an entire cycle through its normal range of variation. For some systems, the ecologically relevant period can be relatively short (eg, tidal systems), for others it can be decadal (eg, prairie wetlands). We explore the concept of alternative stable states in unstable systems using the highly dynamic wetland ecosystems of North America's Prairie Pothole Region. The communities in these wetland ecosystems transition through multiple states in response to decadal‐long climate oscillations that cyclically influence ponded‐water depth, permanence, and chemistry. The perspective gained by considering dynamic systems in the context of stable‐state theory allows for an increased understanding of how these systems respond to changing drivers that can push them past tipping points into alternative states. Incorporation of concepts inherent to stable‐state theory has been suggested as a key scientific element upon which to base sustainable environmental management.     

Assessing phylogeographic variation in the Rosyside Dace (Teleostei,Leuciscidae), a widespread morphologically variable taxon

Clinostomus (Leuciscidae) is a wide-ranging freshwater fish genus that occurs throughout eastern North America and southern portions of Canada with two species currently recognized: C. elongatus and C. funduloides. A previous taxonomic study of C. funduloides recognized two subspecies (estor and funduloides) and one diagnosed, but undescribed subspecies based on morphological characteristics and geographic distribution. In this study, we used three molecular markers (cytochrome b, S7 intron 1 and growth hormone intron 4) to test the three lineage hypothesis and evaluate genetic variation of C. funduloides across the range using Bayesian inference. Our results indicate that C. funduloides is not monophyletic, as individuals of C. elongatus nest within C. funduloides in both the mtDNA and nDNA phylogenetic analyses, although the position of C. elongatus varies between data sets. In addition, some of the recovered clades are deeply divergent from one another, further supporting the distinctiveness of many of the populations. Overall, these results suggest that subspecies designations are not warranted and a taxonomic revision is needed as Clinostomus is likely more diverse than is currently recognized.