Low Levels of Genetic Diversity within Populations of Hosta clausa (Liliaceae)

Abstract Genetic diversity of Korean populations in Hosta clausa was investigated using starch gel electrophoresis. Hosta clausa is widespread, grows only along streamsides, and has both sexual and asexual reproduction. Populations of the species are small and isolated. Thirty-two percent of the loci examined were polymorphic, and mean genetic diversity within populations (He_p=0.082) was lower than mean estimates for species with very similar life history characteristics (0.131), particularly for its congener H. yingeri (0.250). The mean number of multilocus genotypes per population was 8.7, and genotypic diversity index (D_G) was 0.84. Significant differences in allele frequencies among populations were found in all seven polymorphic loci (P < 0.001). About one-fifth of the total allozyme variation was among populations (G_ST=0.192). Indirect estimate of the number of migrants per generation (Nm=0.48, calculated from mean G_ST) and nine private alleles found indicate that gene movement among populations was low. The low levels of genetic diversity within populations and the relatively high levels of genetic diversity among populations suggest that strong moist habitat preferences, clonal reproduction, low level of gene flow among populations, genetic drift, and historical events may have played roles in the genetic structuring of the species.     

Cassava leaf harvesting as vegetables; a cause of vulnerability of cassava plant to cassava mosaic disease and eventual yield reduction: Ernte von cassavablättern als gemüse; eine ursache für die anfälligkeit der cassavapflanze für die cassava-mosaikkrankheit und für spätere ertragseinbußen

The consequence of harvesting young leaves of cassava as vegetable on the vulnerability of the crop to cassava mosaic disease (CMD) and on storage root yield was investigated using 30 cassava genotypes planted in IITA fields located in the humid forest (Port Harcourt?:?Onne), forest-savannah transition (Ibadan), southern guinea savannah (Mokwa) and northern guinea savannah (Zaria) agroecologies in Nigeria. Tender apical leaves and shoots of the cassava genotypes were removed from forty plants per cassava genotype with the same number of plants considered as control. Whitefly infestation, disease incidence (DI) and symptom severity (ISS) of the disease were assessed at monthly interval for six months and also at the ninth month after planting (MAP). Yield reduction due to this treatment was calculated as percentage harvest index (HI). Whitefly population fluctuated throughout the period of observation at all locations with higher population obtained generally for treated plants compared to control plants. Sprouting leaves of some treated genotypes were observed with severe mosaic symptoms, while corresponding control showed no mosaic symptoms. Contrarily, no remarkable difference was observed in Zaria between the mean ISS of treated and control cassava genotypes. There was a highly significant difference (P?<?0.01) in DI and ISS among cassava genotypes across all locations. Also, there was a highly significant interaction (P?<?0.01) in symptom severity between location (loc) and genotype, genotype and treatment (trt), loc and trt. Interaction between loc, genotypes and trt with regard to DI was highly significant at 2, 3 and 4 MAP, while with ISS, the interaction was highly significant all through the counting period. There was a positive relationship between DI and ISS on plants of genotypes 96/1039 and ISU. The percentage HI (27.4) of treated plants of genotype 95/0166 in Ibadan was remarkably lower than the value obtained for corresponding control (41.9) plants. Also, sharp distinction in% HI of treated (39.5) and control (43.8) ISU was observed in Onne with their respective ISS values as 3.7 and 3.2. Therefore, harvesting tender apical leaves and shoots of cassava as vegetables should be discouraged as it increases the severity of CMD infection in the regenerating shoots of cassava with attendant storage root yield reduction.     

Seasonal mortality trends in tree‐feeding insects: a field experiment

Abstract 1. The majority of general life‐history models treat the environment as being invariable through time, even though temporal variation in selective agents could dramatically change the outcomes, e.g. in terms of optimal size and time at maturity. For herbivorous insects, seasonal differences in food quality are reasonably well described, but seasonal dynamics of top‐down selective forces are poorly documented. 2. The present study attempted to quantify seasonal changes in predation risk of folivorous insect larvae in temperate forest habitats. In a series of field experiments, artificial larvae were exposed to predators, and the resulting bird‐inflicted damage was recorded. The trials were repeated regularly throughout the course of two summers. 3. A distinct peak of larval mortality was recorded in mid‐June (the nestling period for most insectivorous passerine birds), after which predation risk declined to a plateau of 20–30% below the peak value. 4. The recorded pattern is interpreted as a consequence of seasonal changes in the number and behaviour of insectivorous birds, and the abundance of alternative food resources for these predators. 5. A quantitative analysis based on field data indicated that considering temporal variation in mortality in life‐history models is crucial for obtaining realistic predictions concerning central life‐history traits, such as final body size in different generations.     

Organic cation permeation through the channel formed by polycystin-2

Polycystin-2 (PC2), a member of the transient receptor potential family of ion channels (TRPP2), forms a calcium-permeable cation channel. Mutations in PC2 lead to polycystic kidney disease. From the primary sequence and by analogy with other channels in this family, PC2 is modeled to have six transmembrane domains. However, most of the structural features of PC2, such as how large the channel is and how many subunits make up the pore of the channel, are unknown. In this study, we estimated the pore size of PC2 from the permeation properties of the channel. Organic cations of increasing size were used as current carriers through the PC2 channel after PC2 was incorporated into lipid bilayers. We found that dimethylamine, triethylamine, tetraethylammonium, tetrabutylammonium, tetrapropylammonium, and tetrapentylammonium were permeable through the PC2 channel. The slope conductance of the PC2 channel decreased as the ionic diameter of the organic cation increased. For each organic cation tested, the currents were inhibited by gadolinium and anti-PC2 antibody. Using the dimensions of the largest permeant cation, the minimum pore diameter of the PC2 channel was estimated to be at least 11 A. The large pore size suggests that the primary state of this channel found in vivo is closed to avoid rundown of cation gradients across the plasma membrane and excessive calcium leak from endoplasmic reticulum stores.     

Calcium-dependent Conformational Changes in Inositol Trisphosphate Receptors

We have used limited trypsin digestion and reactivity with PEG-maleimides (MPEG) to study Ca²⁺-induced conformational changes of IP₃Rs in their native membrane environment. We found that Ca²⁺ decreased the formation of the 95-kDa C-terminal tryptic fragment when detected by an Ab directed at a C-terminal epitope (CT-1) but not with an Ab recognizing a protected intraluminal epitope. This suggests that Ca²⁺ induces a conformational change in the IP₃R that allows trypsin to cleave the C-terminal epitope. Half-maximal effects of Ca²⁺ were observed at ∼0.5 μm and was sensitive to inhibition by IP₃. Ca²⁺ also stimulated the reaction of MPEG-5 with an endogenous thiol in the 95-kDa fragment. This effect was eliminated when six closely spaced cysteine residues proximal to the transmembrane domains were mutated (C2000S, C2008S, C2010S, C2043S, C2047S, and C2053S) or when the N-terminal suppressor domain (amino acids 1–225) was deleted. A cysteine substitution mutant introduced at the C-terminal residue (A2749C) was freely accessible to MPEG-5 or MPEG-20 in the absence of Ca²⁺. However, cysteine substitution mutants in the interior of the tail were poorly reactive with MPEG-5, although reactivity was enhanced by Ca²⁺. We conclude the following: a) that large conformational changes induced by Ca²⁺ can be detected in IP₃Rs in situ; b) these changes may be driven by Ca²⁺ binding to the N-terminal suppressor domain and expose a group of closely spaced endogenous thiols in the channel domain; and c) that the C-terminal cytosol-exposed tail of the IP₃R may be relatively inaccessible to regulatory proteins unless Ca²⁺ is present.     

Changes in sperm stores, ejaculate size, fertilization success, and sexual motivation over repeated matings in the common toad, Bufo bufo (Anura: Bufonidae)

Fertilization is of central importance in the determination of reproductive success for both males and females. In species where males have the chance to mate repeatedly within a short period of time, sperm stocks may become depleted and males may have to carefully economize on their sperm reserves. Also, intensive intrasexual competition for females and repeated matings may lead to exhaustion on the behavioural level. To determine whether the reproductive potential of males is limited and if such a limitation is due to behavioural exhaustion or sperm depletion, we experimentally investigated changes in sperm stores, sperm expenditure, fertilization success, and sexual motivation over three repeated matings in the common toad, Bufo bufo , where the breeding season is short and sequential polygyny occurs. At the end of the breeding season, the number of sperm stored in the testes of males mated repeatedly was close to 50% lower than in testes of unmated males. Ejaculate size, which was estimated by applying a novel method allowing direct quantification, decreased by 88% from first to third matings. We also observed a drop in fertilization success from the first two to third matings by 65%, which was largest in males that had started the reproductive season in bad body condition. Some of these males also showed a decreased interest in females in the third mating round. Our results suggest that sperm depletion and loss of sexual motivation may together set a limit to the reproductive potential of common toad males. The present study draws attention to a limitation in reproductive potential, which may occur more often than currently anticipated and has the potential to strongly influence several aspects of reproductive behaviour.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 361–371.     

Contrasting levels of genetic diversity between the historically rare orchid Cypripedium japonicum and the historically common orchid Cypripedium macranthos in South Korea

Many terrestrial orchids are historically rare and occur in small, spatially isolated populations. Theory predicts that such species will harbour low levels of genetic variation within populations and will exhibit a high degree of population genetic divergence, primarily as a result of genetic drift. If the origin of the present‐day populations is relatively recent from the same genetically depauperate source population, a complete lack of genetic differentiation between conspecific populations is expected. If a terrestrial orchid was historically common with moderate or high levels of genetic diversity, but has experienced more recent anthropogenic disturbance as a result of over‐collection, it would still exhibit initial levels of genetic variation within populations and a low degree of genetic divergence between populations. To test these predictions, we examined the genetic diversity in six populations (N = 131) of the historically and currently rare Cypripedium japonicum and in four populations (N = 94) of the historically common but now rare C. macranthos from South Korea. Fourteen putative allozyme loci resolved from eight enzyme systems revealed no variation either within or among populations of C. japonicum, which supports the first prediction. In contrast, populations of C. macranthos harboured high levels of genetic variation (mean percentage of polymorphic loci %P = 46.7; mean expected heterozygosity H_e = 0.185) and exhibited a low degree of population genetic divergence (G_ST = 0.059), supporting the second prediction. The lack of genetic variation both within and among conspecific populations of C. japonicum may suggest that populations originated from the same genetically depauperate ancestral population. The high levels of genetic diversity maintained in populations of C. macranthos suggest that the collection‐mediated decrease in the number of individuals is still too recent for long‐term effects on genetic variation. Based on current demographic and genetic data, in situ and ex situ conservation strategies should be provided to preserve genetic variation and to ensure the long‐term survival of the two species in the Korean Peninsula. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 119–129.     

Newly developed polymorphic microsatellite markers in Job's tears (Coix lacryma‐jobi L.)

A microsatellite‐enriched library of Job's tears (Coix lacryma‐jobi L. var. Ma‐yuen Stapf) was constructed using a modified biotin–streptavidin capture method. After screening, 17 polymorphic microsatellites were used for diversity analysis among 30 Job's tears accessions. The number of alleles ranged from one to five alleles per locus with an average of 2.8 alleles. Expected heterozygosity (H_E) and polymorphism information content (PIC) ranged from 0 to 0.676 and from 0 to 0.666, respectively. The newly developed microsatellite markers are expected to be very valuable tools for evaluation of genetic diversity among large germplasm collection of Job's tears present in our Korean Gene Bank.     

Methanethiosulfonate ethylammonium block of amine currents through the ryanodine receptor reveals single pore architecture

The homotetrameric structure of the ryanodine-sensitive intracellular calcium (Ca2+) release channel (ryanodine receptor (RyR)) suggests that the four RyR subunits either combine to form a single pore or that each RyR subunit is an independently conducting pathway. Previously we showed that methanethiosulfonate ethylammonium (MTSEA+) covalently modifies the RyR to reduce current amplitudes in a time-dependent and stepwise manner. To ascertain the number of functionally conducting pores in the RyR, two approaches were combined: modification of the receptor by MTSEA+ and the use of different sized current carriers. Previous reports (Tinker, A., and Williams, A. J. (1993) J. Gen. Physiol. 102, 1107-1129) have shown that the organic cations methylamine, dimethylamine, ethylamine, and trimethylamine are permeant through the RyR but with reduced current amplitude depending upon the diameter of the respective amine. Experiments using the thiol reagent MTSEA+ to modify the channel protein showed that the current amplitudes decrease in steps leading to complete block of the channel when cesium (Cs+) is the current carrier. MTSEA+ modification decreased the number of channel substates as the diameter of the current carrier increased. Comparison of the degree of inhibition of MTSEA+-modified currents allows for differentiation between the two models for channel architecture. These results demonstrate that the conduction pathway for the RyR is comprised of a single central pore.