Schistocephalus infestation improves prey-size selection by three-spined sticklebacks, Gasterosteus aculeatus

Schistocephalus -infected sticklebacks ate slightly less but fed more selectively on larger prey than non-infested fish. It follows that, in the short-term, the net energy gain in foraging is larger for infested fish. This matches the expectation that infested sticklebacks compensate energy losses due to Schistocephalus.     

Evaluation of ovum fixation and storage in three-spined stickleback

Ripe eggs removed from three-spined sticklebacks stored in 50% isopropyl alcohol showed significantly Sower mean masses than those stored in 10% formalin. These results are considered in relationship to preservation techniques for stickleback.     

Genetic relationships among marine and freshwater populations of the European three-spined stickleback (Gasterosteus aculeatus) revealed by microsatellites

To assess the population genetic structure of the three-spined stickleback, Gasterosteus aculeatus, variability at 18 microsatellite loci was examined in 1724 individuals from 74 locations covering most of the species distribution range in Europe. The results revealed high overall degree of differentiation (F(ST) = 0.21) but contrasting level of divergence and genetic variability between habitat types. Marine populations were genetically relatively uniform even across great geographical distances as compared to substantial differentiation among freshwater populations. Analysis of molecular variance indicated low but significant (2.7%) variation in allele frequencies between geographical regions, but a negligible effect of habitat type (0.2%). The phylogenetic pattern was not explained by habitat type, but a weak signal of populations clustering according to geographical or water system origin was found. The results support the view that three-spined stickleback marine ancestors colonized northern European fresh waters during the postglacial marine submergence c. 10,000 years ago, whereas in the Mediterranean region colonization probably dates back to the Pleistocene. The independent origins of river and lake populations indicate that they originate from multiple colonizations rather than sharing common ancestry. In the continuous marine environment, the low degree of differentiation among populations can be explained by gene flow among subpopulations and large effective population size buffering divergence in neutral markers. In contrast, among postglacially established freshwater populations differentiation appears to be driven by genetic drift and isolation. The stepwise mutations appear to have contributed to the population differentiation in the southern part of the three-spined stickleback distribution range.     

Habitat stability and predation pressure affect temperament behaviours in populations of three-spined sticklebacks

1. There is growing interest in the causes and consequences of animal temperaments. Temperament behaviours often have heritable components, but ecological variables can also affect them. Numerous variables are likely to differ between habitats, and these may interact to influence temperament behaviours. 2. Temperament behaviours may be correlated within populations (behavioural syndromes), although the underlying causes of such correlations are currently unclear. 3. We analysed three different temperament behaviours and learning ability in three-spined sticklebacks, Gasterosteus aculeatus, to determine how different ecological variables influence them both within and between populations. We selected populations from four ponds and four rivers that varied naturally in their exposure to predators. 4. High-predation river populations were significantly less bold than a high-predation pond and low-predation river populations, and low-predation pond populations were significantly less bold than a high-predation pond population. Within populations, temperament behaviours were correlated in one high-predation river population only. 5. These results suggest that multiple ecological factors can interact to affect temperament behaviours between populations, and also correlations in those behaviours within populations.     

Polymorphism and signature of selection in the MHC class I genes of the three-spined stickleback Gasterosteus aculeatus

The role and intensity of positive selection maintaining the polymorphism of major histocompatibility complex (MHC) class I genes in the three-spined stickleback Gasterosteus aculeatus was investigated. The highly polymorphic set of MHC class I genes found was organized in a single linkage group. Between 5 and 14 sequence variants per individual were identified by single-stranded conformation polymorphism (SSCP) analysis. Segregation analysis studied in 10 three-spined stickleback families followed the expected pattern of Mendelian inheritance. The gamete fusion in three-spined stickleback thus seems to be random with respect to the MHC class I genes. The DNA sequence analyses showed that the expressed MHC class I loci are under strong selection pressure, possibly mediated by parasites. Codons that were revealed to be under positive selection are potentially important in antigen binding. MHC class I sequences did not form significant supported clusters within a phylogenetic tree. Analogous to MHC class II genes, it was not possible to assign the class I sequences to a specific locus, suggesting that the class I genes may have been generated by recent gene duplication.     

Individual MHC class I and MHC class IIB diversities are associated with male and female reproductive traits in the three-spined stickleback

Genes of the major histocompatibility complex (MHC) are indispensable for pathogen defence in vertebrates. With wild-caught three-spined sticklebacks (Gasterosteus aculeatus) we conducted the first study to relate individual reproductive parameters to both MHC class I and II diversities. An optimal MHC class IIB diversity was found for male nest quality. However, male breeding colouration was most intense at a maximal MHC class I diversity. One MHC class I allele was associated with male redness. Similarly, one MHC class IIB allele was associated with continuous rather than early female reproduction, possibly extending the reproductive period. Both alleles occurred more frequently with increasing individual allele diversity. We suggest that if an allele is currently not part of the optimum, it had not been propagated by choosy females. The parasite against which this allele provides resistance is therefore unlikely to have been predominant the previous year - a step to negative frequency-dependent selection.     

Genetic variation affecting host-parasite interactions: major-effect quantitative trait loci affect the transmission of sigma virus in Drosophila melanogaster

In natural populations, genetic variation affects resistance to disease. Whether that genetic variation comprises lots of small-effect polymorphisms or a small number of large-effect polymorphisms has implications for adaptation, selection and how genetic variation is maintained in populations. Furthermore, how much genetic variation there is, and the genes that underlie this variation, affects models of co-evolution between parasites and their hosts. We are studying the genetic variation that affects the resistance of Drosophila melanogaster to its natural pathogen — the vertically transmitted sigma virus. We have carried out three separate quantitative trait locus mapping analyses to map gene variants on the second chromosome that cause variation in the rate at which males transmit the infection to their offspring. All three crosses identified a locus in a similar chromosomal location that causes a large drop in the rate at which the virus is transmitted. We also found evidence for an additional smaller-effect quantitative trait locus elsewhere on the chromosome. Our data, together with previous experiments on the sigma virus and parasitoid wasps, indicate that the resistance of D. melanogaster to co-evolved pathogens is controlled by a limited number of major-effect polymorphisms.     

Multiple parasites are driving major histocompatibility complex polymorphism in the wild

Parasite mediated selection may result in arms races between host defence and parasite virulence. In particular, simultaneous infections from multiple parasite species should cause diversification (i.e. balancing selection) in resistance genes both at the population and the individual level. Here, we tested these ideas in highly polymorphic major histocompatibility complex (MHC) genes from three-spined sticklebacks (Gasterosteus aculeatus L.). In eight natural populations, parasite diversity (15 different species), and MHC class IIB diversity varied strongly between habitat types (lakes vs. rivers vs. estuaries) with lowest values in rivers. Partial correlation analysis revealed an influence of parasite diversity on MHC class IIB variation whereas general genetic diversity assessed at seven microsatellite loci was not significantly correlated with parasite diversity. Within individual fish, intermediate, rather than maximal allele numbers were associated with minimal parasite load, supporting theoretical models of self-reactive T-cell elimination. The optimal individual diversity matched those values female fish try to achieve in their offspring by mate choice. We thus present correlative evidence supporting the 'allele counting' strategy for optimizing the immunocompetence in stickleback offspring.     

Characterization and evolution of ovine MHC class II DQB sequence polymorphism

The second exons of OLA-DQB genes from 13 merino sheep were sequenced following amplification by the polymerase chain reaction or isolation from a cDNA library. Ten distinct exon 2 sequences, coding for 10 novel amino acid sequences, were characterized in these sheep. The single-strand conformation polymorphism technique was shown to be capable of discriminating between all sequences. This brings the total number of different OLA-DQB exon 2 sequences (nucleotide and amino acid) which have been characterized to 12, and demonstrates that the OLA-DQB region is highly polymorphic with 29% of nucleotide and 46% of amino acid sites showing variation. Evidence is presented that the OLA-DQB sequences belong to at least two lineages of DQB genes. Some ovine DQB sequences are more like bovine DQB counterparts than other ovine DQB sequences suggesting that the artiodactyl DQB gene and allele lineages predate the separation of the ovine and bovine species 20 million years ago.     

Innate versus adaptive immunity in sticklebacks: evidence for trade-offs from a selection experiment

In vertebrates, the immune system consists of two arms of different characteristics: the innate and the acquired immune response. Parasites that are only shortly exposed to the immune system are most efficiently attacked by fast, constitutive innate immune mechanisms. Here, we experimentally selected within four fish families for high innate resistance versus susceptibility of three-spined sticklebacks (Gasterosteus aculeatus) against infection with the eye-fluke (Diplostomum pseudospathacaeum), a parasite whose metacercariae are protected from the immune system within the eye lens. We predicted that in families with high susceptibility, the adaptive immune system would be upregulated when challenged with infection. In accordance, we found that MHC class IIB expression is increased by approximately 50% in those lines selected for higher parasite load (i.e. low innate response). This suggests extensive genetic correlations between innate and adaptive immune system and/or crosstalk between both lines of defense. An efficient, specific innate immune response might reduce overall activation of the immune system and potentially alleviate associated effects of immunopathology.     

Expression of MHC class I, MHC class II, and cancer germline antigens in neuroblastoma

Background: Neuroblastoma is the most common solid extracranial tumor in childhood, still with poor survival rates for metastatic disease. Neuroblastoma cells are of neuroectodermal origin and express a number of cancer germline (CG) antigens. These CG antigens may represent a potential target for immunotherapy such as peptide-based vaccination strategies. Objective: The purpose of this study was to analyze the presence of MAGE-A1, MAGE-A3/A6, and NY-ESO-1 on an mRNA and protein level and to determine the expression of MHC class I and MHC class II antigens within the same tumor specimens. Methods: A total of 68 tumors were available for RT-PCR, and 19/68 tumors were available for immunohistochemical (IHC) analysis of MAGE-A1, MAGE-A3/A6, and NY-ESO-1. In parallel, the same tumors were stained with a panel of antibodies for MHC class I and MHC class II molecules. Results: Screening of 68 tumor specimens by RT-PCR revealed expression of MAGE-A1 in 44%, MAGE-A3/A6 in 21%, and NY-ESO-1 in 28% of cases. Immunohistochemistry for CG antigens of selected tumors showed good agreement between protein and gene expression. However, staining revealed a heterogeneous expression of CG antigens. None of the selected tumors showed MHC class I or MHC class II expression. Conclusions: mRNA expression of MAGE-A1, MAGE-A3/A6, and NY-ESO-1 is congruent with the protein expression as determined by immunohistochemistry. The heterogeneous CG-antigen expression and the lack of MHC class I and II molecules may have implications for T-cell–mediated immunotherapy in neuroblastoma.     

绵羊MHC区段3个预测基因的验证与表达分析

对新疆美利奴细毛羊基因组MHC(Major histocompatibility complex)区段细菌人工染色体(BAC)文库的DNA序列进行测定,经过序列比对分析,首次预测了约130个新基因,其中有8个CDS(Coding sequences)未在其他物种中发现其同源序列,推测可能系绵羊所特有。在此基础上,文章对绵羊MHC区段预测的3个新基因(分别命名为OaN2、OaN5、OaN6)进行了实验验证和表达分析。从绵羊肺组织中克隆到了OaN2的cDNA序列,其长度为270 bp;从肠系淋巴结中扩增得到OaN5和OaN6的cDNA序列,长度分别为309 bp和205 bp。上述3个基因的GenBank登录号分别为JF330782、JF330783和JF330784。利用Northern blotting技术进行转录本水平分析,发现这3个新基因均在免疫器官肠系淋巴结中高表达。通过Western blotting和原位免疫组化技术对OaN2蛋白水平进行了表达谱分析,结果表明OaN2蛋白在绵羊脾脏和肠系淋巴结等免疫器官中高表达,在心、肝及胰脏中不表达。这是首次通过实验验证绵羊MHC区段的3个预测的新基因,为其在绵羊免疫器官中的功能研究奠定了基础。     

MHC class I variation associates with parasite resistance and longevity in tropical pythons

Using restriction fragment length polymorphism (RFLP) we identified 26 unique major histocompatibility complex (MHC) genotypes in 104 water pythons. We observed a significant independent association between reduced blood parasite load (Hepatozoon sp.) and python body length/age, presence of a specific RFLP fragment (C-fragment) and the overall number of fragments. The parasite has a negative impact on several python life-history traits such as growth, nutritional status and longevity. Thus, the C-fragment could be considered a 'good gene' (a fitness-enhancing genetic element). However, while the number of fragments affected parasite load, the association between level of parasitaemia and fragment number was not linear, and, hence, minimum parasite infection level was achieved at an intermediate number of fragments. Intermediate MHC fragment numbers were also observed among the largest/oldest pythons, suggesting that both a specific fragment and intermediate levels of MHC polymorphism enhanced python longevity. Thus, our results suggest python MHC is subject to both frequency-dependent and balancing selection.     

Low MHC DRB class II diversity in the mountain goat: past bottlenecks and possible role of pathogens and parasites

Major histocompatibility complex (MHC) genes are the most polymorphic in vertebrates and code for molecules playing a central role in pathogen resistance. We studied levels of MHC DRB class II diversity in a long-term study population of mountain goats (Oreamnos americanus) at Caw Ridge, Alberta, and two other populations from British Columbia, Canada. Only two alleles were found among the three populations sampled. The Caw Ridge population was fixed for one of the two MHC DRB alleles, but this lack of variation did not appear to have affected it negatively because the population doubled over two decades and had no history of any apparent infectious diseases. Past population bottlenecks during Pleistocene glaciations are thought to have been the main factor contributing to the low levels of MHC diversity in mountain goats, a hypothesis supported by our previous work reporting low polymorphism at neutral loci. Additionally, the limited MHC variability in mountain goats may be related to its northern distribution as we found that allelic diversity at MHC DRB class II in wild ungulates decreases with increasing latitude, possibly as a result of low parasite diversity at high latitudes. The low MHC variation in mountain goats and other northern ungulates such as muskoxen (Ovibos moschatus) may expose these species to population outbreaks that could be generated by introduced pathogens or northward shifts in the distribution of pathogens with global climate warming.     

Recombination and the origin of sequence diversity in the DRB MHC class II locus in chamois (Rupicapra spp.)

We examined the evolutionary processes contributing to genetic diversity at the major histocompatibility complex (MHC) class II DRB locus in chamois (Rupicapra spp., subfamily Caprinae). We characterised the pattern of intragenic recombination (or homologous gene conversion) and quantified the amount of recombination in the genealogical history of the two chamois species, Pyrenean chamois (Rupicapra pyrenaica) and Alpine chamois (Rupicapra rupicapra). We found evidence for intragenic recombination, and the estimated amount of population recombination suggests that recombination has been a significant process in generating DRB allelic diversity in the genealogical history of the genus Rupicapra. Moreover, positive selection appears to act on the same peptide-binding residues in both analysed chamois species, but not in identical intensity. Recombination coupled with positive selection drives the rapid evolution at the peptide-binding sites in the MHC class II DRB gene. Many chamois MHC class II DRB alleles are thus much younger than previously assumed.     

Trans-species polymorphism and evidence of selection on class II MHC loci in tuco-tucos (Rodentia: Ctenomyidae)

Balancing selection acting over the evolutionary history of a lineage can result in the retention of alleles among species for longer than expected under neutral evolution. The associated pattern of trans-species polymorphism, in which similar or even identical alleles are shared among species, is often used to infer that balancing selection has occurred. The genes of the major histocompatibility complex (MHC) are thought to be subject to balancing selection that maintains alleles associated with response to specific pathogens. To explore the role of balancing selection in shaping MHC diversity in ctenomyid rodents, we examined allelic variability at the class II DRB and DQA loci in 18 species in the genus Ctenomys. Previous studies of four of these species had revealed significant within-population evidence of positive selection on MHC loci. The current study expands upon these analyses to (1) evaluate among-species evidence of positive selection and (2) explore the potential for balancing selection on MHC genes. Interspecific nucleotide sequence variation revealed significant evidence of positive selection on the DRB and DQA loci. At the same time, comparisons of phylogenetic trees for these MHC loci with a putative species tree based on mitochondrial sequence data revealed multiple examples of trans-specific polymorphism, including sharing of identical DRB and DQA alleles among distantly related species of Ctenomys. These findings suggest that MHC genes in these animals have historically been subject to balancing selection and yield new insights into the complex suite of forces shaping MHC diversity in free-living vertebrates.