Interactions between soil heterogeneity and freezing: Implications for grassland plant diversity and relative species abundances

Plant stress resulting from soil freezing is expected to increase in northern temperate regions over the next century due to reductions in snow cover caused by climate change. Within plant communities, soil spatial heterogeneity can potentially buffer the effects of plant freezing stress by increasing the availability of soil microsites that function as microrefugia. Moreover, increased species richness resulting from soil heterogeneity can increase the likelihood of stress‐tolerant species being present in a community. We used a field experiment to examine interactions between soil heterogeneity and increased freezing intensity (achieved via snow removal) on plant abundance and diversity in a grassland. Patches of topsoil were mixed with either sand or woodchips to create heterogeneous and homogeneous treatments, and plant community responses to snow removal were assessed over three growing seasons. Soil heterogeneity interacted significantly with snow removal, but it either buffered or exacerbated the snow removal response depending on the specific substrate (sand vs. woodchips) and plant functional group. In turn, snow removal influenced plant responses to soil heterogeneity; for example, adventive forb cover responded to increased heterogeneity under ambient snow cover, but this effect diminished with snow removal. Our results reveal that soil heterogeneity can play an important role in determining plant responses to changes in soil freezing stress resulting from global climate change. While the deliberate creation of soil microsites in ecological restoration projects as a land management practice could increase the frequency of microrefugia that mitigate plant community responses to increased freezing stress, the design of these microsites must be optimized, given that soil heterogeneity also has the potential to exacerbate freezing stress responses.     

Photoreceptors for biosynthesis, energy storage and vision

Abstract Living organisms use light as a source of energy and as a means of obtaining information about their environment. Photoreactivating enzyme, provitamins D, retinal (rhodopsins and bacteriorhodopsin), porphyrins (chlorophyll, protochlorophyll and heme), photosynthetic accessory pigments (carotenoids and bilins), phytochrome and riboflavin: these are the molecules which life has settled upon to play the role of light receptor. For some of these photoreceptor molecules a great deal is now known about the chemistry which they perform upon absorbing light; for others virtually nothing is known. Riboflavin, the molecule believed to be functioning in a variety of organisms as the receptor for physiological responses to blue light, is an especially interesting case. Its widespread occurrence in cellular roles other than photoreception make it difficult to separate out the particular flavin which functions as the photoreceptor. It represents a case of a photoreceptor which is at once ubiquitous and elusive.     

The effect of lectins on Cryptosporidium parvum oocyst in vitro attachment to host cells

The influence of lectins on Cryptosporidium parvum oocyst agglutination and on attachment to both fixed Madin Darby Canine Kidney (MDCK) cells and fixed HCT-8 (human colorectal epithelial) cells was examined. Oocyst cell wall characteristics were examined by transmission electron microscopy. Lectin-free oocysts were shown to adhere equally to both MDCK cells and HCT-8 cells. In MDCK cells, the addition of 1-25 microg/ml Codium fragile lectin, 10 microg/ml Maclura pomifera lectin, 10 microg/ml Helix pomatia lectin, and 10-200 microg/ml Artocarpus integrifolia lectin significantly increased attachment to at least 1 of the cell cultures as compared to oocysts incubated without any lectin. The lectin-enhanced attachment was reversed by co-incubation of lectin treated-oocysts with 250 mM of each specific sugar (for a given lectin). In agglutination assays, concentrations as low as 0.5 microg/ml of C. fragile, M. pomifera, and A. integrifolia lectin agglutinated oocysts within 60 min. Finally, in TEM samples, colloidal gold conjugated-lectins from A. integrifolia, C. fragile, H. pomatia, and M. pomifera attached to oocysts, and this could be competitively inhibited by a lectin-specific sugar. This suggests that C. parvum oocysts are highly reactive to N-acetyl galactosamine-binding lectins and that the presence of N-acetyl-galactosamine containing molecules on oocysts can potentially help in oocyst attachment to host cells.     

Characteristics and transferability of new apple EST-derived SSRs to other Rosaceae species

Genic microsatellites or simple sequence repeat markers derived from expressed sequence tags (ESTs), referred to as EST–SSRs, are inexpensive to develop, represent transcribed genes, and often have assigned putative function. The large apple (Malus × domestica) EST database (over 300,000 sequences) provides a valuable resource for developing well-characterized DNA molecular markers. In this study, we have investigated the level of transferability of 68 apple EST–SSRs in 50 individual members of the Rosaceae family, representing three genera and 14 species. These representatives included pear (Pyrus communis), apricot (Prunus armeniaca), European plum (P. domestica), Japanese plum (P. salicina), almond (P. dulcis), peach (P. persica), sour cherry (P. cerasus), sweet cherry (P. avium), strawberry (Fragaria vesca, F. moschata, F. virginiana, F. nipponica, and F. pentaphylla), and rose (Rosa hybrida). All 68 primer pairs gave an amplification product when tested on eight apple cultivars, and for most, the genomic DNA-derived amplification product matched the expected size based on EST (in silico) data. When tested across members of the Rosaceae, 75% of these primer pairs produced amplification products. Transferability of apple EST–SSRs across the Rosaceae ranged from 25% in apricot to 59% in the closely related pear. Besides pear, the highest transferability of these apple EST–SSRs, at the genus level, was observed for strawberry and peach/almond, 49 and 38%, respectively. Three markers amplified in at least one genotype within all tested species, while eight additional markers amplified in all species, except for cherry. These 11 markers are deemed good candidates for a widely transferable Rosaceae marker set provided their level of polymorphism is adequate. Overall, these findings suggest that transferability of apple EST–SSRs across Rosaceae is varied, yet valuable, thereby providing additional markers for comparative mapping and for carrying out evolutionary studies.     

GUS expression driven by constitutive and phloem-specific promoters in citrus hybrid US-802

Transgenic solutions are being widely explored to develop huanglongbing (HLB) resistance in citrus. A critical component of a transgenic construct is the promoter, which determines tissue specificity and level of target gene expression. This study compares the characteristics of five promoters regulating the beta-glucuronidase (GUS) reporter gene in the trifoliate hybrid rootstock US-802. Two of the selected promoters direct high levels of constitutive transgene expression in other dicotyledonous plants: 2X35S, the tandem-repeat promoter of the cauliflower mosaic virus 35S gene and bul409S, a truncation of the potato polyubiquitin promoter. Because Candidatus Liberibacter, the Gram-negative bacterium associated with HLB, infects only the phloem tissue, it may be advantageous to limit transgene expression to the vascular tissue and reduce expression in the fruit. Thus, we also tested three promoters that demonstrate phloem specificity when transformed and expressed in other plants: WDV, from wheat dwarf geminivirus; AtSUC2, the sucrose-H+ symporter gene promoter from Arabidopsis; and CsSUS, the sucrose synthase promoter from citrus. Histochemical staining for GUS activity was observed throughout leaf and stem tissues for the constitutive promoters, while the three phloem-specific promoters largely showed the expected tissue-specific staining. Expression of GUS in some individual transformants with promoters CsSUS and WDV appeared leaky, with some laminar tissue staining. Relative quantification of qRT-PCR data revealed a wide range of mRNA abundance from transgenics with each of the five promoters. Fluorometry also revealed that GUS activity differed depending on the promoter used, but mRNA levels and enzyme activity were not highly correlated.     

Diversification across an altitudinal gradient in the Tiny Greenbul (Phyllastrephus debilis) from the Eastern Arc Mountains of Africa

Background  

The Eastern Arc Mountains of Africa have become one of the focal systems with which to explore the patterns and mechanisms of diversification among montane species and populations. One unresolved question is the extent to which populations inhabiting montane forest interact with those of adjacent lowland forest abutting the coast of eastern Africa. The Tiny Greenbul (Phyllastephus debilis) represents the only described bird species within the Eastern Arc/coastal forest mosaic, which is polytypic across an altitudinal gradient: the subspecies albigula (green head) is distributed in the montane Usambara and Nguru Mountains whereas the subspecies rabai (grey head) is found in Tanzanian lowland and foothill forest. Using a combination of morphological and genetic data, we aim to establish if the pattern of morphological differentiation in the Tiny Greenbul (Phyllastrephus debilis) is the result of disruptive selection along an altitudinal gradient or a consequence of secondary contact following population expansion of two differentiated lineages.     

Homology of the genital sclerites of Megaloptera (Insecta: Neuropterida) and their phylogenetic relevance

The genitalia of Megaloptera are crucial for taxonomic identification and represent a significant component of characters for phylogenetic interpretation of this order. However, several complex genital structures, especially those related to segments 9 and 11 in Megaloptera, have yet to be subjected to a comprehensive survey of homology. The terminology for genital sclerites has been variously and even incorrectly used by different authors, a fact which could lead to much confusion about character evolution. In this paper, we first present a comprehensive morphological comparison of the sclerites of male and female genital segments in 23 megalopteran genera representing all major lineages of Corydalinae, Chauliodinae and Sialidae. Accordingly, we then provide new interpretations on the homology of the genital sclerites which often appear to be considerably different among Megaloptera. Based on our new and revised homology assessments, we conclude that: (i) the small to medium‐sized sclerite beneath the ectoprocts in males of Sialidae represents the fused gonocoxites 11; (ii) the male gonocoxites 11 in Corydalidae are largely reduced and are sometimes retained as a small sclerite beneath the anus; (iii) the predominant sternite‐like sclerite of the female abdominal segment 8 represents the fused gonocoxites 8; and (iv) a pair of sclerites amalgamated with the lateral arms of male gonocoxites 10 in Chauliodinae is the gonocoxites 9. Furthermore, based on our genital homology assessments, we reconstruct an intergeneric phylogeny including all genera of Megaloptera using genital characters in a parsimonious analysis to test their phylogenetic relevance. The phylogeny herein recovered is largely congruent with the results from several previous studies, thus underlying the significant phylogenetic relevance of the megalopteran genital sclerites. The present work provides new insights into the evolution of insect genitalia.