Ecological selection against hybrids, the reduction in hybrid fitness attributed solely to environmental factors, was tested by introducing young-of-the-year benthic, limnetic and F1 hybrid sticklebacks Gasterosteus aculeatus to divided experimental ponds and lake enclosures. The frequency of hybrids in samples taken at the end was significantly lower than their frequency at introduction. Hybrid survival was significantly lower in pond-sides in which they were initially the most common cross type than in pond-sides in which they were initially rare, suggesting that hybrid survival may be frequency-dependent. Growth rate of F1 hybrids was marginally lower than benthic growth rates, being significantly lower than in ponds and not different in lake enclosures. The diet of hybrids overlapped with both parent species in ponds and with benthic diets in lake enclosures. The results suggest that ecological selection is acting against young-of-the-year hybrid sticklebacks. 相似文献
For years, the field of drug delivery has focused on (1) controlling the release of a therapeutic and (2) targeting the therapeutic
to a specific cell type. These research endeavors have concentrated mainly on the development of new degradable polymers and
molecule-labeled drug delivery vehicles. Recent interest in biomaterials that respond to their environment have opened new
methods to trigger the release of drugs and localize the therapeutic within a particular site. These novel biomaterials, usually
termed "smart" or "intelligent", are able to deliver a therapeutic agent based on either environmental cues or a remote stimulus.
Stimuli-responsive materials could potentially elicit a therapeutically effective dose without adverse side effects. Polymers
responding to different stimuli, such as pH, light, temperature, ultrasound, magnetism, or biomolecules have been investigated
as potential drug delivery vehicles. This review describes the most recent advances in "smart" drug delivery systems that
respond to one or multiple stimuli. 相似文献
The pink cusk-eel (Genypterus blacodes), a benthic-demersal fish confined to the southern hemisphere, supports an important commercial fishery in Chile where it is exploited over an extensive geographic area. Although the fishery was originally divided into a northern (41º28′–47º00′S) and southern (47º00′–57º00′S) zone for the purposes of fisheries management, recent studies have reported significant differences in life history parameters between these zones. Individuals from the southern zone reached larger asymptotic sizes and possessed higher survival rates compared to the northern zone. We estimate and compare the gonadosomatic index (GSI), shape of the maturity ogive, and length at 50 % maturity (L50%) of female G. blacodes between management zones and across time using biological data collected from the industrial fleet between 1985 and 2009. Females in the northern zone had higher monthly mean GSI than females in the southern zone. Our analyses also revealed L50% to be significantly higher in the southern zone than in the northern zone from 1985 to 2009. The significant differences in life-history traits between fishery management zones agree with the trade-offs predicted by Charnov’s life history theory. Together these results provide additional support for the hypothesis that two separate stocks exist and suggest that females from the northern zone have developed a life-history strategy, which favours early maturation and a proportionally greater investment in reproduction than females from the southern zone. 相似文献
Identification of parasite genes that underlie traits such as drug resistance and host specificity is challenging using classical linkage mapping approaches. Extreme QTL (X-QTL) methods, originally developed by rodent malaria and yeast researchers, promise to increase the power and simplify logistics of linkage mapping in experimental crosses of schistosomes (or other helminth parasites), because many 1000s of progeny can be analysed, phenotyping is not required, and progeny pools rather than individuals are genotyped. We explored the utility of this method for mapping a drug resistance gene in the human parasitic fluke Schistosoma mansoni.
Results
We staged a genetic cross between oxamniquine sensitive and resistant parasites, then between two F1 progeny, to generate multiple F2 progeny. One group of F2s infecting hamsters was treated with oxamniquine, while a second group was left untreated. We used exome capture to reduce the size of the genome (from 363 Mb to 15 Mb) and exomes from pooled F2 progeny (treated males, untreated males, treated females, untreated females) and the two parent parasites were sequenced to high read depth (mean = 95-366×) and allele frequencies at 14,489 variants compared. We observed dramatic enrichment of alleles from the resistant parent in a small region of chromosome 6 in drug-treated male and female pools (combined analysis: = 11.07, p = 8.74 × 10-29). This region contains Smp_089320 a gene encoding a sulfotransferase recently implicated in oxamniquine resistance using classical linkage mapping methods.
Conclusions
These results (a) demonstrate the utility of exome capture for generating reduced representation libraries in Schistosoma mansoni, and (b) provide proof-of-principle that X-QTL methods can be successfully applied to an important human helminth. The combination of these methods will simplify linkage analysis of biomedically or biologically important traits in this parasite.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2164-15-617) contains supplementary material, which is available to authorized users. 相似文献
Currently, association studies are analysed using statistical mixed models, with marker effects estimated by a linear transformation of genomic breeding values. The variances of marker effects are needed when performing the tests of association. However, approaches used to estimate the parameters rely on a prior variance or on a constant estimate of the additive variance. Alternatively, we propose a standardized test of association using the variance of each marker effect, which generally differ among each other. Random breeding values from a mixed model including fixed effects and a genomic covariance matrix are linearly transformed to estimate the marker effects.
Results
The standardized test was neither conservative nor liberal with respect to type I error rate (false-positives), compared to a similar test using Predictor Error Variance, a method that was too conservative. Furthermore, genomic predictions are solved efficiently by the procedure, and the p-values are virtually identical to those calculated from tests for one marker effect at a time. Moreover, the standardized test reduces computing time and memory requirements.The following steps are used to locate genome segments displaying strong association. The marker with the highest − log(p-value) in each chromosome is selected, and the segment is expanded one Mb upstream and one Mb downstream of the marker. A genomic matrix is calculated using the information from those markers only, which is used as the variance-covariance of the segment effects in a model that also includes fixed effects and random genomic breeding values. The likelihood ratio is then calculated to test for the effect in every chromosome against a reduced model with fixed effects and genomic breeding values. In a case study with pigs, a significant segment from chromosome 6 explained 11% of total genetic variance.
Conclusions
The standardized test of marker effects using their own variance helps in detecting specific genomic regions involved in the additive variance, and in reducing false positives. Moreover, genome scanning of candidate segments can be used in meta-analyses of genome-wide association studies, as it enables the detection of specific genome regions that affect an economically relevant trait when using multiple populations.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2105-15-246) contains supplementary material, which is available to authorized users. 相似文献
The complex societies of ants and other social insects rely on sophisticated chemical communication. Two families of small soluble proteins, the odorant binding and chemosensory proteins (OBPs and CSPs), are believed to be important in insect chemosensation. To better understand the role of these proteins in ant olfaction, we examined their evolution and expression across the ants using phylogenetics and sex- and tissue-specific RNA-seq.
Results
We find that subsets of both OBPs and CSPs are expressed in the antennae, contradicting the previous hypothesis that CSPs have replaced OBPs in ant olfaction. Both protein families have several highly conserved clades with a single ortholog in all eusocial hymenopterans, as well as clades with more dynamic evolution and many taxon-specific radiations. The dynamically evolving OBPs and CSPs have been hypothesized to function in chemical communication. Intriguingly, we find that seven members of the conserved clades are expressed specifically in the antennae of the clonal raider ant Cerapachys biroi, whereas only one dynamically evolving CSP is antenna specific. The orthologs of the conserved, antenna-specific C. biroi genes are also expressed in antennae of the ants Camponotus floridanus and Harpegnathos saltator, indicating that antenna-specific expression of these OBPs and CSPs is conserved across ants. Most members of the dynamically evolving clades in both protein families are expressed primarily in non-chemosensory tissues and thus likely do not fulfill chemosensory functions.
Conclusions
Our results identify candidate OBPs and CSPs that are likely involved in conserved aspects of ant olfaction, and suggest that OBPs and CSPs may not rapidly evolve to recognize species-specific signals.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2164-15-718) contains supplementary material, which is available to authorized users. 相似文献
Several classifications of adult asthma patients using cluster analyses based on clinical and demographic information has resulted in clinical phenotypic clusters that do not address molecular mechanisms. Volatile organic compounds (VOC) in exhaled air are released during inflammation in response to oxidative stress as a result of activated leukocytes. VOC profiles in exhaled air could distinguish between asthma patients and healthy subjects. In this study, we aimed to classify new asthma endotypes by combining inflammatory mechanisms investigated by VOC profiles in exhaled air and clinical information of asthma patients.
Methods
Breath samples were analyzed for VOC profiles by gas chromatography–mass spectrometry from asthma patients (n = 195) and healthy controls (n = 40). A total of 945 determined compounds were subjected to discriminant analysis to find those that could discriminate healthy from asthmatic subjects. 2-step cluster analysis based on clinical information and VOCs in exhaled air were used to form asthma endotypes.
Results
We identified 16 VOCs, which could distinguish between healthy and asthma subjects with a sensitivity of 100% and a specificity of 91.1%. Cluster analysis based on VOCs in exhaled air and the clinical parameters FEV1, FEV1 change after 3 weeks of hospitalization, allergic sensitization, Junipers symptoms score and asthma medications resulted in the formation of 7 different asthma endotype clusters. We identified asthma clusters with different VOC profiles but similar clinical characteristics and endotypes with similar VOC profiles, but distinct clinical characteristics.
Conclusion
This study demonstrates that both, clinical presentation of asthma and inflammatory mechanisms in the airways should be considered for classification of asthma subtypes.
Electronic supplementary material
The online version of this article (doi:10.1186/s12931-014-0136-8) contains supplementary material, which is available to authorized users. 相似文献
Understanding the evolution of specialization in host plant use by pollinators is often complicated by variability in the ecological context of specialization. Flowering communities offer their pollinators varying numbers and proportions of floral resources, and the uniformity observed in these floral resources is, to some degree, due to shared ancestry. Here, we find that pollinators visit related plant species more so than expected by chance throughout 29 plant–pollinator networks of varying sizes, with “clade specialization” increasing with community size. As predicted, less versatile pollinators showed more clade specialization overall. We then asked whether this clade specialization varied with the ratio of pollinator species to plant species such that pollinators were changing their behavior when there was increased competition (and presumably a forced narrowing of the realized niche) by examining pollinators that were present in at least three of the networks. Surprisingly, we found little evidence that variation in clade specialization is caused by pollinator species changing their behavior in different community contexts, suggesting that clade specialization is observed when pollinators are either restricted in their floral choices due to morphological constraints or innate preferences. The resulting pollinator sharing between closely related plant species could result in selection for greater pollinator specialization. 相似文献
Identifying the correlates of extinction can help prioritize species for conservation effort, an important step when developing effective conservation policies. Most previous studies on extinction vulnerability have been restricted to a single predictor within a specific region. To understand the mechanism underlying predictors of extinction risk, an examination of the contribution of various factors at different scales is an important step. We investigated the contribution of phylogeny, ploidy level, habitat breadth, and life form on both provincial and national conservation ranks of Alberta’s prairie ecoregion plant species. We collected data on conservation status, chromosome number, habitat breadth, and life form for 1274 species. We used phylogenetic comparative models to assess (1) the relative contribution, significance, and possible interaction of predictor variables in determining extinction vulnerability, and (2) the possible underlying mechanisms governing observed patterns of extinction vulnerability at the provincial and national level. We find that the contribution, significance, and predictive power of variables were often scale-dependent. While the impact of habitat breadth was significant at both provincial and national scales, ploidy and life form was only significant at the national and provincial level, respectively. We also found a significant negative interaction between ploidy and habitat breadth at both geographical scales, such that among widespread species (species with a higher habitat breadth), diploids are less likely to be at risk than polyploids. Our study reveals the importance of the study scale on the accuracy of extinction prediction. We also suggest that discriminating between regionally restricted and non-restricted species could improve the predictability of sub-global extinction patterns.