Trypanosoma cruzi: distinct patterns of infection in the sibling caviomorph rodent species Thrichomys apereoides laurentius and Thrichomys pachyurus (Rodentia, Echimyidae)

Thrichomys apereoides, a caviomorph rodent species common in a highly endemic area for Chagas disease in Brazil, may act as reservoir of the parasite. However, no information is available concerning its sibling species Thrichomys pachyurus, found in the Pantanal region, where Trypanosoma cruzi is found only in the enzootic cycle. We followed up the cross infection of these cryptic species with two isolates derived from naturally infected T. pachyurus and Thrichomys apereoides laurentius. No regional co-adaptation between Thrichomys species and the regional isolates were noticed. However, significant differences in the outcome of the infection were observed. T. a. laurentius was more resistant than T. pachyurus, as expressed by lower parasitemia and less histopathological damage. The routine biochemical markers used for laboratory rodents were unsuitable for follow up of infection in Thrichomys spp, since they did not correlate with the histopathological findings or allowed the kinetic follow-up of tissue colonization by the parasite.     

Maintenance and breeding of Thrichomys (Trouessart, 1880) (Rodentia: Echimyidae) in captivity

South American histricognath rodents Thrichomys apereoides laurentius and Thrichomys pachyurus are natural hosts of Trypanosoma cruzi, agent of Chagas disease. We established breeding colonies of these species to serve as experimental models in various parasitological studies. Both species of Thrichomys have all the requirements necessary to become excellent laboratory models: they can be easily maintained in the standard laboratory conditions and breed throughout the year and they do not have any special dietary demands and can be fed by standard food pellets designed for laboratory mice. Both species produce precocious offspring that have their eyes and ears open, teeth erupted, fur well developed, and can eat solid food in the first week of life. T. a. laurentius has larger litter sizes and lower body masses at birth and weaning than T. pachyurus. Moreover, females of T. a. laurentius reach puberty earlier and with lower body mass than T. pachyurus.     

Karyologic evidence of diversification of the genus Thrichomys (Rodentia,Echimyidae)

Karyologic analysis of Thrichomys specimens from different Brazilian localities, in Pantanal, Cerrado and Caatinga biomes, shows different chromosome complements. The 2n = 34, FN = 64 karyotype is found in Mato Grosso do Sul state; the 2n = 30, FN = 54 karyotype in Bahia, Pernambuco, Piauí and Ceará states; the 2n = 30, FN = 56 karyotype in Goiás and Tocantins states, the 2n = 28, FN = 50 karyotype in Minas Gerais state, the 2n = 28, FN = 52 and 2n = 26, FN = 48 karyotypes in Bahia state. Comparisons of G-band patterns allowed the identification of homologies shared by all karyotypes and show that the two karyotypes with the lowest diploid number (2n = 26 and 2n = 28) belong to two different evolutionary lineages. The most proper names for each karyomorphic population are: Thrichomys pachyurus for 2n = 34; Thrichomys apereoides apereoides for 2n = 28, FN = 50; Thrichomys apereoides laurentius for 2n = 30, FN = 54 and Thrichomys inermis for 2n = 26. Two karyotypes (2n = 28, FN = 52 and 2n = 30, FN = 56) could not be attributed to any subspecies. These different karyomorphotypes are allopatric and/or parapatric.     

Cranial differentiation and evolution in Thrichomys apereoides (Rodentia: Echinyidae)

Thrichomys apereoides is an echimyid rodent which ranges in distribution from north-eastern and central Brazil into Paraguay, and currently five subspecies are recognized. Recent morphometric analyses of population samples formally assignable to T. a. laurentius and T. a. inermis , which occur in north-eastern Brazil, have shown that a major group of populations including both subspecies differ in cranial shape from a single population allocated to T. a. laurentius . In this study we employed mathematical models of evolutionary quantitative genetics to assess the role that random drift and selection may have played in the evolution of cranial shape differences in T. apereoides . The hypothesis of evolution due to drift was rejected and the selective forces necessary to account for shape differences were estimated. Minimum selective mortalities of the order of 10^-3 of per generation were sufficient to explain the observed morphologic differentiation.     

INTERGENERIC HYBRIDIZATION AMONG FIVE GENERA OF THE FAMILY LESSONIACEAE (PHAEOPHYCEAE) AND EVIDENCE FOR POLYPLOIDY IN A FERTILE PELAGOPHYCUS×MACROCYSTIS HYBRID

Hybridization was attempted by combining gametophytes between intergeneric pairs among the following taxa in the Lessoniaceae: Macrocystis pyrifera ( L.) C. Agardh , M. integrifolia Bory, M. angustifolia Bory , Pelagophycus porra ( Leman) Setch ., Nereocystis luetkeana ( Mert.) Post & Rupr ., Dictyoneurum californicum Rupr ., and Dictyoneuropsis reticulata ( Saud.) Smith. Hybrid sporophytes were produced in some combinations involving Macrocystis × Pelagophycus and Macrocystis × Dictyoneurum, and in all combinations of Dictyoneuropsis × Dictyoneurum. This is the first report of intergeneric hybrids involving Dictyoneurum. Gametophytes of P. porra had 16–24 chromosomes. Gametophytes from a fertile Macrocystis-Pelagophycus hybrid were crossed with Macrocystis and Pelagophycus gametophytes. Hybrid male gametophytes and Pelagophycus female gametophytes produced sporophyte progeny, but hybrid males with Macrocystis females did not. A single hybrid female gametophyte did not produce gametophytes in combination with hybrid males , Pelagophycus males or Macrocystis males. The hybrid gametophytes had approximately 30 chromosomes. It is hypothesized that the hybrid is an alloploid, containing a complete set of Macrocystis and Pelagophycus chromosomes, which may have allowed meiosis and sporogenesis to proceed normally in the hybrid sporophyte found in the sea. Thus, reproductive isolating mechanisms appear to operate at both pre- and postzygotic stages, and both can be overcome in intergeneric hybrids .     

Hybridization studies in the Schistocerca americana complex. I. The specific status of the Central American Locust

The Central American Locust has previously been identified as Schistocerca paranensis (Burmeister), the Argentinian Locust, and it has been suggested that S. americana of North America represents its solitarious phase. Hybrids of locusts from the Yucatan peninsula of Mexico with locusts from Argentina and Florida were reared, their fertility measured and meiosis in the males examined. It was found that: (1) sex ratios in the F, hybrids were distorted; (2) hybrids had reduced fertility; (3) female hybrids were more fertile than male hybrids; (4) meiosis in hybrid males was disturbed; (5) these effects were more pronounced in die hybrids with the Argentinian Locust than in those with Florida locusts.
These results are discussed in relation to Haldane's rule and the biogeography of die group. It is concluded that the Central American and Argentinian Locusts are separate species, but that the relationship of the former to S. americana americana requires further investigation.     

Fertility in first-generation hybrids of roach, Rutilus rutilus (L.), and silver bream, Blicca bjoerkna (L.)

Fertility in first‐generation hybrids of roach, Rutilus rutilus, and silver bream, Blicca bjoerkna, was investigated. Sperm and egg production of hybrids at first sexual maturity were examined. Eggs from female hybrids were artificially fertilized with the sperm of a corresponding hybrid male; a hybrid male from the reciprocal crossbreeding; a parental species male R. rutilus; and a parental species male B. bjoerkna. The results revealed that gametogenesis was normal in female hybrids. However, in male hybrids, a low efficiency of gametogenesis was observed. The semen of male hybrids was extremely dilute, with spermatozoa concentration lower than that in parental species. Nevertheless, these F1 hybrids (males and females) from reciprocal crossbreeding were fertile. F2 and backcross generations were produced, but F2 crosses from the female hybrid and corresponding hybrid male displayed a drastically slower hatching rate. Also higher proportions of deformed embryos were hatched than in other post‐F1‐generation crosses.     

Genetic and reproductive potential of spermatozoa of diploid and triploid males obtained from interspecific hybridization of Misgurnus anguillicaudatus female with M. mizolepis male

Diploid and triploid interspecific hybrid male progeny obtained from mating Misgurnus anguillicaudatus with M. mizoleis were reported to have histologically fertile and sterile testes, respectively. However, their reproductive capacity is still unclear because mating tests have not been examined using mature hybrids. Here, we examined physiological and genetic characteristics of spermatozoa of diploid and triploid hybrids. In diploid hybrid males, 1n, 2n and 4n spermatozoa showing low motility were detected. However, spermatozoa of three diploid hybrid males could generate 2n larvae. Therefore, only 1n spermatozoa of diploid hybrid males was fertile to produce larva. The chromosomes of diploid hybrid males were transmitted to spermatozoa by random segregation between the homologous chromosomes because most larvae had one allele derived from both M. anguillicaudatus and M. mizolepis at all loci examined. In triploid hybrid males, spermatozoa could be categorized to three different types based on their ploidy status. Type 1: In the first and second males, sperm samples mainly comprised 6n spermatozoa. Motility and fertility were not recorded. Type 2: The third male gave a large proportion of 6n spermatozoa as well as a small proportion of 1n spermatozoa. Although no motility was observed, larvae arose from eggs inseminated with such spermatozoa. Type 3: In the fourth male, only 1n spermatozoa were detected and their motility was vigorous. When eggs were fertilized with such 1n spermatozoa, normal larvae hatched. 1n spermatozoa of the triploid hybrid male only included the M. anguillicaudatus genome. In Misgurnus fishes, diploid hybrid males exhibited semi-sterility or slight fertility. On the contrary, triploid hybrid males were sometime fertile due to the production of 1n spermatozoa by a kind of transformation of meiosis like meiotic hybridogenesis.     

An examination of hybridization between the cattail species typha latifolia and typha angustifolia using random amplified polymorphic DNA and chloroplast DNA markers

Typha glauca represents a significant portion of the biomass of the wetlands surrounding the Great Lakes, USA. It is generally accepted to be a form of hybrid between T. latifolia and T. angustifolia, which itself appears to be an exotic introduction from Europe. Based on morphological and isozyme data, conflicting theories have been proposed for the hybrid nature of T. glauca: it has been described as a hybrid swarm, a distinct hybrid species and an F1 hybrid. Therefore, we developed random amplified polymorphic DNA (RAPD) and chloroplast DNA markers, specific to the parental species, to assess hybrids. Ten RAPD primers gave 17 fragments specific to T. angustifolia and 13 fragments specific to T. latifolia. All of the interspecific hybrids contained each of the species-specific markers, indicating an F1 hybrid status. Furthermore, all hybrids tested contained the T. angustifolia chloroplast haplotype, which is consistent with differential interspecific crossing success found previously. Additional confirmation of an F1 hybrid status was gained by examining seedlings from T. glauca. These progeny were expected to be advanced-generation hybrids, as opposed to the F1 hybrid parent. Analysis of the seedlings revealed segregating marker patterns consistent with patterns observed in experimental advanced-generation hybrids, although these advanced hybrids do not appear to be a significant part of mature stands. Our data do not provide support for extensive gene flow between T. latifolia and T. angustifolia. However, our results suggest that hybridization between the native and introduced Typha species has impacted the native population through the spread of the F1 hybrid, T. glauca.     

Masculinization mechanism of hybrids in bitterlings (Teleostei: Cyprinidae)

The sex ratio of bitterling hybrids (subfamily: Acheilognathinae) is often likely to be biased toward males. Artificial hybridization was carried out in 10 species of bitterlings (three genera) in order to elucidate the masculinization mechanism of hybrids. Tanakia himantegus never produced viable F1 hybrids with other species, while hybrids of most other species were viable. In terms of sex ratio and fertility, hybrids were clearly divided into two groups: congeneric Tanakia hybrids and others. Both male and female congeneric Tanakia hybrids were fertile. The sex ratio was nearly 1:1 in all groups of Tanakia hybrids. Except for the congeneric Tanakia hybrids, sterile males appeared predominantly in groups of hybrids in which females were very rare but remained fertile. Sterile intersexes were also observed in five hybrid groups: T. lanceolata (female) x Acheilognathus cyanostigma (male), Rhodeus uyekii (female) x T. lanceolata (male), A. rhombeus (female) x T. lanceolata (male), A. rhombeus (female) x T. limbata (male), and A. tabira tabira (female) x A. cyanostigma (male). In the development of male-predominant hybrids, although hybrid and control (parental species) hatching and survival rates do not differ, no females appeared in hybrids, contrary to the controls. Taking the female heterogametic sex-determining system (ZW) and the phylogenetic relationship of bitterlings into consideration, the masculinization mechanism of hybrids in bitterlings can be explained by the interaction of two sex chromosomes, derived from each parental species. The basic genetic sex in bitterlings is male (ZZ) and the derivative is female (ZW). When parental species are related, the sex phenotype of hybrids coincides with the genetic sex. However, when the parental species differ, the sex phenotype of the ZW genotype is reversed to become male by an abnormal interaction between the Z and W chromosomes. The rare appearance of females and intersexes in male-predominant hybrids might be due to complete or partial functional expression of the W chromosome.     

Acute SLE in F1 hybrids between SB/Le and NZW mice; prominently enhanced formation of gp70 immune complexes by a Y chromosome-associated factor from SB/Le mice

Both sexes of the F1 hybrids between SB/Le and NZW mice developed a spontaneous lupus-like disease. Their disease is essentially identical in time course and nature with autoimmune responses that are seen in the F1 hybrids between BXSB and NZW mice. The presence of abnormal Y chromosomes in the SB/Le strain was proved by the finding that the accelerated disease occurred in the F1 hybrid males only when the male parent was SB/Le but not NZW. The acceleration of disease in male F1 hybrids with abnormal Y chromosome was significantly associated with the enhanced formation of gp70 IC but not anti-DNA antibodies. These results indicate that all or almost all of the genetic abnormalities expressed in the BXSB strain are contributed by the SB/Le strain, and the Y chromosome-associated factor enhances the autoimmune response to serum gp70 antigen more markedly than to DNA antigens.     

Speciation and reduced hybrid female fertility in house mice

In mammals, intrinsic postzygotic isolation has been well studied in males but has been less studied in females, despite the fact that female gametogenesis and pregnancy provide arenas for hybrid sterility or inviability that are absent in males. Here, we asked whether inviability or sterility is observed in female hybrids of Mus musculus domesticus and M. m. musculus, taxa which hybridize in nature and for which male sterility has been well characterized. We looked for parent‐of‐origin growth phenotypes by measuring adult body weights in F1 hybrids. We evaluated hybrid female fertility by crossing F1 females to a tester male and comparing multiple reproductive parameters between intrasubspecific controls and intersubspecific hybrids. Hybrid females showed no evidence of parent‐of‐origin overgrowth or undergrowth, providing no evidence for reduced viability. However, hybrid females had smaller litter sizes, reduced embryo survival, fewer ovulations, and fewer small follicles relative to controls. Significant variation in reproductive parameters was seen among different hybrid genotypes, suggesting that hybrid incompatibilities are polymorphic within subspecies. Differences in reproductive phenotypes in reciprocal genotypes were observed and are consistent with cyto‐nuclear incompatibilities or incompatibilities involving genomic imprinting. These findings highlight the potential importance of reduced hybrid female fertility in the early stages of speciation.     

Hybridization studies in the planthopper genus Ribautodelphax (Homoptera,Delphacidae)

Seven known Ribautodelphax species and four recently discovered taxa were crossed. Forty-three percent of the interspecific crosses were successful. Interspecific crosses generally resulted in low numbers of hybrids. In some combinations prolonged larval development of the hybrid males was observed. Backcrosses showed that both male and female hybrids were fertile. Reproductive isolation was mainly maintained by premating barriers. Insemination tests revealed that prolonged confinement of males and females lowered mating thresholds. The taxonomic status of the known species and new taxa was shown to be in need of revision. No indications for a hybrid origin of the pseudogamous triploid Ribautodelphax females were found.     

Meiosis and fertility of reciprocal triploid hybrids of Lolium multiflorum with Festuca pratensis

Diploid and tetraploid forms of Lolium multiflorum and Festuca pratensis were crossed under controlled conditions and after embryo rescue all four combinations of autoallotriploid hybrids were obtained. Male and female fertility and chromosome pairing at metaphase I of meiosis were studied in several plants from each hybrid combination. The hybrids with two genomes of L. multiflorum and one of F. pratensis (genomic formulae LmLmFp and FpLmLm) were male and female fertile while the hybrids with two genomes of F. pratensis and one of L. multiflorum had a reduced fertility (FpFpLm) or were completely sterile (LmFpFp). Chromosome pairing at metaphase I varied among hybrid combinations depending on their genomic composition. LmLmFp and FpLmLm hybrids had similar patterns of pairing (1.83I + 5.29II + 2.85III and 2.22I + 5.22II + 2.75III, respectively) but they differed from those of FpFpLm (3.65I + 4.65II + 2.68III) and especially from LmFpFp (4.78I + 5.87II + 1.49III). Conventional analysis of meiosis failed to explain the differences in chromosome behaviour and fertility/sterility levels between the autoallotriploid hybrids with two Lolium or two Festuca genomes.     

小麦遗传背景对普通小麦×6x小簇麦杂种F_1减数分裂行为的影响及育性

利用普通小麦与6x小簇麦杂交转移簇毛麦有利基因的过程中,发现由小麦品系J－11为亲本的杂种F1花粉具有高可育的特性,研究结果表明,它可能是由小麦品系J－11核基因组上所携带的基因与簇毛麦染色体相互作用影响杂种F1减数分裂四分体时期的行为而形成的,导致其花粉育性及结实性的增高和外源染色体传递行为的不同。结果指出了可能存在一类影响远缘杂种减数分裂四分体时期行为的新基因,这种基因与外源染色体的相互作用对控制远缘杂种结实性及其外源基因的转移具有重要意义。     

Natural and sexual selection against hybrid flycatchers

While sexual selection is generally assumed to quickly cause or strengthen prezygotic barriers between sister species, its role in causing postzygotic isolation, through the unattractiveness of intermediate hybrids, is less often examined. Combining 24 years of pedigree data and recently developed species-specific molecular markers from collared (Ficedula albicollis) and pied (Ficedula hypoleuca) flycatchers and their hybrids, we were able to quantify all key components of fitness. To disentangle the relative role of natural and sexual selection acting on F1 hybrid flycatchers, we estimated various fitness components, which when combined represent the total lifetime reproductive success of F1 hybrids, and then compared the different fitness components of F1 hybrids to that of collared flycatchers. Female hybrid flycatchers are sterile, with natural selection being the selective force involved, but male hybrids mainly experienced a reduction in fitness through sexual selection (decreased pairing success and increased rate of being cuckolded). To disentangle the role of sexual selection against male hybrids from a possible effect of genetic incompatibility (on the rate of being cuckolded), we compared male hybrids with pure-bred males expressing intermediate plumage characters. Given that sexual selection against male hybrids is a result of their intermediate plumage, we expect these two groups of males to have a similar fitness reduction. Alternatively, hybrids have reduced fitness owing to genetic incompatibility, in which case their fitness should be lower than that of the intermediate pure-bred males. We conclude that sexual selection against male hybrids accounts for approximately 75% of the reduction in their fitness. We discuss how natural and sexual selection against hybrids may have different implications for speciation and conclude that reinforcement of reproductive barriers may be more likely when there is sexual selection against hybrids.     

Meiosis in gray voles of the subgenus microtus (rodentia, arvicolinae) and in their hybrids

The results of light and electron microscopic (EM) studies of meiosis in Microtus arvalis males of the karyoform "arvalis" (2n = 46, NFa = 80), in hybrids between the chromosomal forms arvalis and obscurus (2n = 46, NFa = 68), in M. rossiaemeridionalis voles (2n = 54, NFa = 54), and in a hybrid between the species M. rossiaemeridionalis and M. kermanensis (2n = 54, NFa = 54) are presented. SC (synaptonemal complex) karyotypes of the parental forms and the hybrids were constructed on the basis of measurements of the length ofautosomal SCs revealed by the EM analysis in spermatocytes at the stage of middle pachytene. The SC karyotypes of M. arvalis and the hybrids female obscurus x male arvalis consist of 22 synaptonemal complexes of autosomal bivalents and the axial elements of the synaptonemal complexes of the sex chromosomes X and Y. The SC karyotypes of M. rossiaemeridionalis and the hybrid M. rossiaemeridionalis x M. kermanensis consist of 26 synaptonemal complexes of autosomal bivalents and a sex bivalent; they differ only in the length of the Y chromosome axis (Y chromosome in the hybrid was inherited from M. kermanensis). Asynaptic configurations of the autosomal SCs were not observed in the hybrids. The SC axial elements of the X and Y chromosomes in the parental forms and in the hybrids were located close to each other throughout pachytene, but they did not form a synaptic region. The normal synapsis in sterile hybrids (M. rossiaemeridionalis x M. kermanensis) and the behavior of the sex chromosomes in meiosis in fertile and sterile hybrids are discussed in the context of specific features of meiosis and reproductive isolation.     

甘蔗-滇蔗茅杂交F_1花粉母细胞减数分裂过程GISH分析

研究甘蔗属与滇蔗茅属间远缘杂交F1染色体遗传行为具有重要科学意义,可为发掘利用滇蔗茅野生优异基因资源提供细胞学依据。本研究采用常规压片技术对可育父本及不育杂交F1花粉母细胞减数分裂过程进行比较观察,结果显示可育父本云南95-19减数分裂正常,而不育杂交F1分裂异常;进一步对F1花粉母细胞减数分裂过程进行基因组荧光原位杂交(GISH,genome in situ hybridization)分析,结果表明:滇蔗茅与甘蔗属热带种的亲缘关系较远,双亲染色体在F1细胞中不能进行同源配对,终变期,15条滇蔗茅染色体以单价体形式存在,花粉母细胞减数分裂细胞中存在滞后染色体、染色体丢失和不均衡分离现象。甘蔗-滇蔗茅属间远缘杂交F1花粉母细胞减数分裂异常因而杂交F1花粉完全败育。     

Allelic interaction of F1 pollen sterility loci and abnormal chromosome behaviour caused pollen sterility in intersubspecific autotetraploid rice hybrids

The intersubspecific hybrids of autotetraploid rice has many features that increase rice yield, but lower seed set is a major hindrance in its utilization. Pollen sterility is one of the most important factors which cause intersubspecific hybrid sterility. The hybrids with greater variation in seed set were used to study how the F(1) pollen sterile loci (S-a, S-b, and S-c) interact with each other and how abnormal chromosome behaviour and allelic interaction of F(1) sterility loci affect pollen fertility and seed set of intersubspecific autotetraploid rice hybrids. The results showed that interaction between pollen sterility loci have significant effects on the pollen fertility of autotetraploid hybrids, and pollen fertility further decreased with an increase in the allelic interaction of F(1) pollen sterility loci. Abnormal ultra-structure and microtubule distribution patterns during pollen mother cell (PMC) meiosis were found in the hybrids with low pollen fertility in interphase and leptotene, suggesting that the effect-time of pollen sterility loci interaction was very early. There were highly significant differences in the number of quadrivalents and bivalents, and in chromosome configuration among all the hybrids, and quadrivalents decreased with an increase in the seed set of autotetraploid hybrids. Many different kinds of chromosomal abnormalities, such as chromosome straggling, chromosome lagging, asynchrony of chromosome disjunction, and tri-fission were found during the various developmental stages of PMC meiosis. All these abnormalities were significantly higher in sterile hybrids than in fertile hybrids, suggesting that pollen sterility gene interactions tend to increase the chromosomal abnormalities which cause the partial abortion of male gametes and leads to the decline in the seed set of the autotetraploid rice hybrids.