Calcium taste preferences: genetic analysis and genome screen of C57BL/6J x PWK/PhJ hybrid mice

To characterize the genetic basis of voluntary calcium consumption, we tested C57BL/6J mice (B6; with low avidity for calcium), PWK/PhJ mice (PWK; with high avidity for calcium) and their F₁ and F₂ hybrids. All mice received a series of 96-h two-bottle preference tests with a choice between water and the following: 50 m m CaCl₂, 50 m m calcium lactate, 50 m m MgCl₂, 100 m m KCl, 100 m m NH₄Cl, 100 m m NaCl, 5 m m citric acid, 30 μ m quinine hydrochloride and 2 m m saccharin. Most frequency distributions of the parental and F₁ but not F₂ groups were normally distributed, and there were few sex differences. Reciprocal cross analysis showed that B6 × PWK F₁ mice had a non-specific elevation of fluid intake relative to PWK × B6 F₁ mice. In the F₂ mice, trait correlations were clustered among the divalent salts and the monovalent chlorides. A genome screen involving 116 markers showed 30 quantitative trait loci (QTLs), of which six involved consumption of calcium chloride or lactate. The results show pleiotropic controls of calcium and magnesium consumption that are distinct from those controlling consumption of monovalent chlorides or exemplars of the primary taste qualities.     

Genetic and in vitro molecular hybridization of malate dehydrogenase isozymes in interspecific bass (Micropterus) hybrids

Supernatant malate dehydrogenase (MDH) isozymes (as visualized by starch gel electrophoresis) are encoded by two distinct gene loci in both the largemouth and smallmouth bass. When an interspecific F₁ hybrid is formed between these two fish, a unique MDH isozyme is generated. The results of freeze-thaw molecular hybridization (which is the first application of this technique to MDH) indicate that this unique isozyme in the F₁ hybrid is a heterodimer composed of one subunit of each parental type. The F₁ hybrids produced F₂ hybrids which in turn formed the F₃ hybrid population. The inheritance of alleles at the MDH-B locus is consistent with a single Mendelian autosomal locus. Furthermore, there is no evidence of linkage between the lactate dehydrogenase-E locus and the MDH-B locus.     

ASYMMETRIC VIABILITY OF RECIPROCAL-CROSS HYBRIDS BETWEEN CRESTED AND MARBLED NEWTS (TRITURUS CRISTATUS AND T. MARMORATUS)

Hybridization between divergent lineages often results in reduced hybrid viability. Here we report findings from a series of independent molecular analyses over several seasons on four life stages of F₁ hybrids between the newts Triturus cristatus and T. marmoratus . These two species form a bimodal hybrid zone of broad overlap in France, with F₁ hybrids making up about 4% of the adult population. We demonstrate strong asymmetry in the direction of the cross, with one class ( cristatus -mothered) making up about 90% of F₁ hybrids. By analyzing embryos and hatchlings, we show that this asymmetry is not due to prezygotic effects, as both classes of hybrid embryos are present at similar frequencies, implicating differential selection on the two hybrid classes after hatching. Adult F₁ hybrids show a weak Haldane effect overall, with a 72% excess of females. The rarer marmoratus -mothered class, however, consists entirely of males. The absence of females from this class of adult F₁ hybrids is best explained by an incompatibility between the cristatus X chromosome and marmoratus cytoplasm. It is thus important to distinguish the two classes of reciprocal-cross hybrids before making general statements about whether Haldane's rule is observed.     

Fertility of roach × bream hybrids, Rutilus rutilus (L.) ×Abramis brama (L.), and their identification

Adult roach, bream and their presumed F₁ hybrid from an Anglian Water reservoir were identified on the basis of morphological and meristic characteristics. The hybrid was clearly intermediate. Four hybrid breeding crosses were induced to spawn by hypophysis. A bream × roach cross (female named first) failed to produce fertile eggs, whereas F₁ hybrid × roach, roach × F₁ hybrid and F₁ hybrid × F₁ hybrid all produced fry. Fertility (defined as survival of eggs to hatching) was high for the F₁ hybrid × roach back-cross (56%) but low for the others (<2%), in comparison to the pure species controls (roach 69%, bream 76%). Progeny from these crosses were reared until anal fin rays could be counted. These counts indicated intermediacy between the parents and back-crossed individuals, and similarity between F₁ hybrids and their F₂ progeny.     

Breeding experiments to distinguish two sibling species of Halicarcinus (Crustacea, Brachyura)

Hybridization experiments and various salinities were used in investigating the status of two Halicarcinus lacustris-like , forms, one of which has no free larval stages (direct-development) and the other of which has normal larval stages (indirect-development).
Hybrids were produced, at least from indirect-development female x direct-development male crosses, but introgression of genetic material was limited to F₂ hybrids from the female parental form. There were no intergrades between the two modes of development in F₁ and F₂ hybrids or as a response to salinity.
These forms are established as sibling species. The name lacustris applies to the direct-development form and the other is a new species, H. paralacustris , which is described. Hybridization in the field is unlikely due to geographical and reproductive isolating mechanisms. Contrary to a previous view, it seems that H. lacustris had a recent origin in Australia and transport by water birds is suggested as the mode of dispersal through south-east Australasia.     

Can Extensive Reticulation and Concerted Evolution Result in a Cladistically Structured Molecular Data Set?

Hierarchy is the main criterion for informativeness in a data set, even if no explicit reference to evolution as a causal process is provided. Sequence data (nuclear ribosomal DNA ITS) from Armeria (Plumbaginaceae) contains a certain amount of hierarchical structure as suggested by data decisiveness and distribution of tree lengths. However, ancillary evidence suggests that extensive gene flow and biased concerted evolution in these multicopy regions have significantly shaped the ITS data set. This argument is discussed using parsimony analysis of four data sets, constructed by combining wild sequences with those from different generations of artificial hybrids (wild + F₁, F₂, and backcrosses; wild + backcrosses; wild + F₁; wild + F₂). Compared to the F₁ hybrids, F₂ show a certain degree of homogenization in polymorphic sites. This effect reduces topological disruption caused by F₁ and is considered to be illustrative of how extensive gene flow and biased concerted evolution may have modeled the wild ITS data. The possibility that hierarchy has arisen as a result of—or despite a significant contribution from—those two such potentially perturbing forces raises the question of what kind of signal are we recovering from this molecular data set.     

Mating patterns of Darwin's Finch hybrids determined by song and morphology

Three species of Darwin's Finches hybridize on the Galapagos island of Daphne Major. We examined mating patterns to determine if hybrids exhibit mate preferences. Geospiza fortis x G. scandens F₁ hybrids backcrossed to both of the parental species, whereas all backcrosses bred with the parental species to which they were most related, or with hybrids. Paternal song was shown to be the crucial factor determining the mating pattern of G. fortis x G. scandens F₁ hybrids and their offspring. Song is culturally inherited, transmitted faithfully from father to son (with few exceptions) as a result of an imprinting-like process. Size also contributes to the choice of mates. G. fortis x G. scandens F₁ hybrid females paired with large G. scandens -like G. fortis males. G. fortis x G. fuliginosa F₁ hybrids paired negatively assortatively with respect to the size of their G. fortis mates. Non-random mating of hybrids based on song, a non-generic trait, has interesting evolutionary consequences. Song characteristics and nuclear and mitochondrial genes flow from G. fuliginosa into the G. fortis population, whereas the direction of transfer of genetic and song information between G. fortis and G. scandens depends on which song was sung by the father of the hybrids.     

The evolution of F1 postzygotic incompatibilities in birds

Abstract.— We analyzed the rate at which postzygotic incompatibilities accumulate in birds. Our purposes were to assess the role of intrinsic F₁ hybrid infertility and inviability in the speciation process, and to compare rates of loss of fertility and viability between the sexes. Among our sample more than half the crosses between species in the same genus produce fertile hybrids. Complete loss of F₁ hybrid fertility takes on the order of millions of years. Loss of F₁ hybrid viability occurs over longer timescales than fertility: some viable hybrids have been produced between taxa that appear to have been separated for more than 55 my. There is strong support for Haldane's rule, with very few examples where the male has lower fitness than the female. However, in contrast to Drosophila , fertility of the homogametic sex in the F₁ appears to be lost before viability of the heterogametic sex in the F₁. We conclude that the time span of loss of intrinsic hybrid fertility and viability is often, but not always, longer than the time to speciation. Premating isolation is an important mechanism maintaining reproductive isolation in birds. In addition, other factors causing postzygotic reproductive isolation such as ecological causes of hybrid unfitness, reduced mating success of hybrids, and genetic incompatibilities in the F₂s and backcrosses may often be involved in the speciation process.     

Large-scale purification procedure of spinach leaf mitochondria —isolation and immunological studies of the F1–ATPase

A large–scale purification procedure for mitochondria from spinach ( Spinacia oteracea L, cv Medania) leaves is described. It involves differential centrifugation and density gradient centrifugation on a self–generating gradient of Percoll, From 3 kg of spinach leaves, 150 mg mitochondrial protein are obtained. The thylakoid contamination is lower than 0.2% on a chlorophyll basis. The mitochondria oxidize malate and glycine with state 3 rates of 108 and 140 nmol (mg protein)^-1 min^-1, with respiratory control ratios of 2,7 and 3,8 and ADP/O ratios of 2,0 and 2.1, respectively. The present large–scale purification procedure will facilitate further biochemical and molecular biological studies of leaf mitochondrial proteins.
A pure and active catalytic moiety of the F₁–ATPase (EC 3,6,1,3) was purified from the isolated mitochondria. The yield was 5 mg of F₁–ATPase from 150 mg mitochondria. The F₁–ATPase contained five polypeptides of apparent molecular mass 54 kDa (α), 52 kDa (β), 33 kDa (γ), 22 kDa (ω) and 11 kDa (ɛ). An additional component at 24 kDa was present in variable amounts in some preparations and was therefore not ascribed to the ATPase complex. The enzyme catalyzed ATP hydrolysis at a rate of 12.5 nmol (mg protein)^-1 min^-1. Antibodies against the spinach mitochondrial F₁–ATPase cross–reacted only with the a and β subunits of F₁–ATPases of spinach chloroplasts, photosynthetic bacteria Rhodospirillum rubrum and beef heart mitochondria.     

INHERITANCE OF RESISTANCE TO CYHALOTHRIN IN THE HOUSEFLY (DIPTERA: MUSCIDAE)

Abstract The genetic inheritance of resistance to cyhalothrin in housefly, Musca domstica (L) was investigated.
Reciprocal crosses between susceptible (S) and resistant (R) strains were used to determine the characteristics of resistance. Analysis of probit line from the F₁ generation and F₂ generation obtained by inbreeding the F₁ hybrids indicated that cyhalothrin resistance was controlled by more than one factors and degree of resistance dominance to cyhalothrin was -0.10, indicating cyhalothrin resistance is conferred by incompletely recessive gene(s). The realized heritability of resistance to cyhalothrin cyhalothrin calculated from data collected routinely from laboratory selection was 0.12.     

Time-resolved microfluorescence for measuring coenzyme F420 in Methanobacterium thermoautotrophicum

Abstract The time course of photobleaching and the nanosecond fluorescence decay have been measured from microscopic samples of methanogenic bacteria, to our knowledge the first application of these methods in this field. Decay times of about 1 ns and 3 ns were obtained for the specific coenzymes F₄₂₀ and 7-methylpterin, respectively. In contrast to methylpterin and other fluorescent compounds the intensity of F₄₂₀ fluorescence was reduced selectively due to photobleaching. This effect, as well as the different decay time constants could be used to discriminate F₄₂₀ from other fluorescent components. In addition, active and inactive bacterial cells could be differentiated following the course of photobleaching.     

Electron transfer reactions for the reduction of NADP+ in Methanosphaera stadtmanae

Abstract Methanosphaera stadtmanae , a member of the Methanobacteriales reduces methanol, but not CO₂ with H₂ or 2-propanol to produce methane. In cell-free extracts of M. stadtmanae the activities of several enzymes involved in electron transfer were measured. The activities of an F₄₂₀-nonreactive hydrogenase, NADP⁺: F₄₂₀ oxidoreductase, NADP⁺-dependent 2-propanol dehydrogenase, and a methyl viologen dependent F₄₂₀ dehydrogenase were observed. Based on the presence of these particular enzyme activities, their cofactor requirements and the absence of F₄₂₀-dependent hydrogenase activity, a model of the electron transport pathway through the coenzyme F₄₂₀ to provide electrons for biosynthesis, was formulated.     

The F1FO ATP synthase genes in Methanosarcina acetivorans are dispensable for growth and ATP synthesis

There is a long-standing discussion in the literature, based on biochemical and genomic data, whether some archaeal species may have two structurally and functionally distinct ATP synthases in one cell: the archaeal A₁A_O together with the bacterial F₁F_O ATP synthase. To address a potential role of the bacterial F₁F_O ATP synthase, we have exchanged the F₁F_O ATPase gene cluster in Methanosarcina acetivorans against a puromycin resistance cassette. Interestingly, the mutant was able to grow with no difference in growth kinetics to the wild type, and cellular ATP contents were identical in the wild type and the mutant. These data demonstrate that the F₁F_O ATP synthase is dispensable for the growth of M. acetivorans .     

Spontaneous hybridizations between oilseed rape and wild radish

The occurence of spontaneous hybridization between Brassica napus (oilseed rape) and Raphanus raphanistrum (wild radish) was investigated under different density conditions in cages and open-field experiments. Hybrids with wild radish as the seed parent were identified by screening for herbicide resistance belonging to rape. Small seed size and intermediate morphology were used to screen for hybrids with rape as the seed parent. Leaf isozyme patterns and flow cytometry provided confirmation of hybrids. Wild radish in an oilseed rape field produced as many as three interspecific hybrids per 100 plants. This is the first report of such a spontaneous event. The frequency of hybrids is expected to range from 0.006 to 0.2% of the total seed produced, at P = 0.05. Male-sterile oilseed rape plants surrounded by wild radish can produce up to 37 hybrids per plant. Seed production of the F₁ hybrids and their F₂ descendants was up to 0.4% and 2%, respectively, of that of wild radish. Gene escape from transgenic oilseed rape to wild related species is discussed.     

Chloroplast ultrastructure in two Crassulacean species and an F1 hybrid with differing biomass δ13C values

Abstract. The chloroplasts of two species of the Crassulaceae and their F₁ hybrid were compared by electron microscopy. The two species had contrasting leaf tissue δ¹³C values of −25°/_∞ ( Sedum greggii ) and −13°/_∞ ( Cremnophila linguifolia ), and the F₁ hybrid had a value of − 18°/_∞. S. greggii had a mean of 8.9 thylakoids per granum in contrast to C. linguifolia which had a mean of only 3.8 thylakoids per granum. The F₁ hybrid had a mean of 6.4 thylakoids per granum. Crystaloids were observed in S. greggii and the hybrid but not in C. linguifolia     

Measurement of intracellular pH in maize root tissue with α-methyl fluorinated alanines and in-vivo 19F NMR spectroscopy

Methods for the simultaneous measurement of vacuolar and cytoplasmic pH in plant tissues currently have significant limitations. This study demonstrates the usefulness of methyl difluoro alanine (F₂ALA) and methyl trifluoro alanine (F₃ALA) with in-vivo ¹⁹F NMR spectroscopy to measure vacuolar and cytoplasmic pH in maize root tissue. The pH dependence of the chemical shift of F₂ALA and F₃ALA is greater than either the commonly used ³¹P NMR signal of inorganic phosphate or the ¹³C NMR signals of trans-aconitic acid, which is also found in some plant cells. F₂ALA and F₃ALA were also able to detect changes over a greater range of pH. When maize root tissue was incubated in the presence of 0.35 m m F₂ALA or F₃ALA, these accumulated to significant concentrations in two compartments of different pH with no significant effect on growth rate of root tips. The time course of accumulation and the pH of the two compartments were consistent with one being the cytoplasm and the other the vacuole. The chemical shift of both C₂ of trans-aconitic acid and vacuolar F₃ALA indicated that the mean vacuolar pH of maize root cells was 4.6 and that the pH gradient across the tonoplast membrane was about 2.8 units. Under a variety of conditions, there was considerable heterogeneity in the pH of the vacuoles in maize root tissue as indicated by the peak width of the signal from F₃ALA. The significance of these values is discussed in terms of the bioenergetics of proton transport across the tonoplast membrane in vivo.     

Non-association between Rfp-Y major histocompatibility complex-like genes and susceptibility to Marek's disease virus-induced tumours in 63× 72 F2 intercross chickens

Marek's disease (MD) is a lymphoproliferative disease caused by a member of the herpesvirus family, and the best understood genetic resistance to MD involves the chicken major histocompatibility complex (MHC) B -complex. Preliminary observations have suggested that MHC-like Rfp-Y genes might also influence the incidence of MD. This study describes the differentiation and definition of unique Rfp-Y genes in inbred lines 6₃ and 7₂, lines that possess identical B -complex genes, but that are resistant or susceptible to MD, respectively. To assess if Rfp-Y genes affect susceptibility to MD, 265 6₃× 7₂ F₂ chickens were challenged with the JM strain of MD virus at 1 week of age and were evaluated for MD lesions at up to 10 weeks of age. Genotyping of the F₂ chickens for Rfp-Y haplotypes was performed by restriction fragment length polymorphism analysis of genomic DNA using Taq I and a B-FIV probe. Analysis of variance and interval mapping procedures were used to determine association between the Rfp-Y haplotypes and the phenotypic MD values of the F₂ chickens. The cosegregation analysis of 265 F₂ chickens indicated that there was no association between Rfp-Y haplotypes and MD susceptibility. Furthermore, the fact that the Rfp-Y haplotypes fit the 1:2:1 segregation ratio and the Rfp-Y allele frequencies did not differ significantly from 0·5 in the full population or in selected subpopulations (of either 40 MD-resistant or 39 MD-susceptible chickens) also indicated that Rfp-Y haplotypes do not significantly influence MD susceptibility. We conclude that Rfp-Y haplotypes do not play a major role in determining the genetic susceptibility to MD in 6₃× 7₂ F₂ White Leghorn chickens.     

A test of ecological selection against young-of-the-year hybrids of sympatric sticklebacks

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.     

Ploidy levels in silverside fishes (Atherinidae, Menidia) on the Texas coast: flow-cytometric analysis of the occurrence of allotriploidy

Flow cytometry of nuclear DNA fluorescence in erythrocytes, coupled with gene dosage assessments derived from electrophoresis of proteins, reaffirmed that the Menidia clarkhubbsi complex of unisexual atherinid fishes is diploid. Non-recombinant hybrids between M. beryllina and M. peninsulae represented 18% (108 specimens) of the Menidia collected from three pools in the Copano Bay area and 9-6% (42 specimens) of those from a pool on Galveston Island. Of those hybrids, 35 and 5%, respectively, were triploids. Zymograms indicated that the triploids either had two doses of genes from M. beryllina and one from M. peninsulas or they had one from the former species and two from the latter. The hybrids seem to be maintained primarily, if not entirely, by ongoing hybridization and back-crossing of F₁ hybrids to the parental species. Triploids apparently result from the combination of unreduced, diploid gametes from F₁ hybrids with haploid gametes from either M. beryllina or M. peninsulae.