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.     

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.     

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.     

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.     

Peroxidase and polyphenol oxidase activities in Cyperus esculentus leaves following glyphosate applications

Following a 2-week treatment with glyphosate [N-(phosphonomethyl)glycine] changes in peroxidase (EC 1.11.1.7) and polyphenol oxidase (PPO; EC 1.14.18.1) activities of yellow nutsedge ( Cyperus esculentus L.) plants, were determined. Glyphosate caused significant increases of both activities. Isoelectric focusing gave 3 species (F₁, F₂ and F₃) of peroxidase activity, at pl 3.8, 4.4 and 4.8, and 4 species (F_a, F_b, F_c and F_d) of PPO activity at pl 7.0, 7.5, 7.8 and 9.5. The activity of the 4 active forms of PPO increased with increasing glyphosate dose up to 10⁻² M . The effect of the herbicide on the 3 fractions with peroxidase activity was to change their relative activities. Highest F₁ activity was found in control plants whereas the F₂ fraction was the predominant form in the plants treated with glyphosate at 10⁻² M and the highest F₃ activity occurred in plants treated with 5 × 10⁻³ M glyphosate. The increased PPO activity could produce phytotoxic o -quinones, and variations in peroxidase isoenzymes activity could enhance isoperoxidases with lignin biosynthetic activity.     

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.     

Genetic heterogeneity, reproductive isolation and host preferences in mealy aphids of the Hyalopterus pruni complex (Homoptera, Aphidoidea)

Three taxa were detected by allozyme markers within the mealy aphids of the Hyalopterus pruni complex, having different cultivated Prunus species as main primary hosts. The genetically closer H. pruni and H. amygdali A ( D _Nei= 0.10) never share primary hosts, whereas H. amygdali A and B ( D _Nei= 0.32) may occasionally share them, producing few F₁ hybrids. The three species proved reproductively isolated in the field, with no gene exchange. Their speciation seem to have occurred long before the agricultural revolution, crop colonization representing a host range expansion rather than a host shift, as in sympatric speciation.     

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.     

Genetic evidence for asymmetric hybridization between menhadens (Brevoortia spp.) from peninsular Florida

Hybridization between the North American menhadens Brevoortia smithi , Brevoortia tyrannus and Brevoortia patronus has been reported by numerous authors, based primarily on the morphological intermediacy of hybrids relative to each parental type. In this study, genetic characterization of individuals in areas previously designated as hybrid zones validates the presence of F₁ hybrids. Evidence from microsatellite genotypes indicates that B. patronus and B. smithi are parental species of hybrids on both sides of the Florida peninsula, and mitochondrial DNA (mtDNA) haplotypes suggest a maternal contribution by B. smithi in each case. Hybrids between B. tyrannus and B. smithi were not identified in this study. The presence of B. patronus on the Atlantic coast of Florida, coupled with admixture between this species and B. tyrannus , has likely influenced the mixed lineage assortment of mtDNA haplotypes demonstrated in this study and in previous studies.     

A morphometric analysis of spontaneous and artificial hybrids of Pinus mugo ×sylvestris (Pinaceae)

Hybridization among Pinus mugo and P.sylvestris is visualized in Wells' distance diagrams using either equally or differently weighted characters. Parents and hybrids are better resolved in diagrams using differently weighted characters. Putative hybrids from mixed, planted or naturalized stands of P. mugo and P. sylvestris in SW and NW Jutland, Denmark, are compared with artificial F₁ and spontaneous material of P. mugo × sylvestris (P. × rhaetica ) from the Alps and the Pyrenees. The natural hybrids are primary hybrids, rather than introgressants.     

Crossability variation in four South American Hordeum species

Andersson, 2. 1995. Crossability variation in four South American Hordeum species— Nord. J. Bot. IS: 355–364. Copenhagen. ISSN 0107–055X.
Intra- and interpopulation crosses within the four South American Hordeum species, H. cordobense, H. chilense, H. muticum and H. stenostachys were performed. Seeds were obtained in all intrapopulation crosses within all four species. Hordeum cordobense showed little variation in crossability of interpopulation crosses and the F₁-families had rather high fertility. A wide range in crossability between populations was observed in the three species H. chilense, H. muticum and H. stenostachys . Some combinations failed to set seed while others had high seed set. The fertility of the F₁-_- families varied from almost sterile to fully fertile. All parental plants, intra and interpopulation hybrids in the four species had very high meiotic pairing frequency with 12–14 chiasmata per cell. Hordeum cordobense is a homogeneous species while the other three species are heterogeneous and genetically diverse.     

The ATP-dependent synthesis of factor 390 by cell-free extracts of Methanobacterium thermoautotrophicum (strain ΔH)

Abstract Cell-free extracts of Methanobacterium thermoautotrophicum (strain ΔH) converted the 8-OH-5-deazaflavin coenzyme F₄₂₀ to factor 390, a 8-adenylyl derivative (F₄₂₀-AMP). Activity was only observed upon exposure of the crude cell-free extract to oxygen. The ability to synthesize F₃₉₀ was lost when crude cell-free extract was subsequently brought to an anaerobic reducing environment. The enzymatic reaction used ATP and oxidized coenzyme F₄₂₀ as substrates and inorganic pyrophosphate was formed next to F₃₉₀. GTP could be used instead of ATP resulting in a guanylylated derivative. The crude cell-free extract showed K _m values of 154 μM for coenzyme F₄₂₀ and 2.4 mM for ATP. A partially purified enzyme preparation exhibited a K _eq of 0.32. In accordance, coenzyme F₄₂₀ and ATP could be synthesized from F₃₉₀ and PPi by the reverse reaction.     

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.     

Resurrection of Aedes (Halaedes) ashworthi Edwards 1921: Morphological Characterisation and Separation from its Sibling Aedes (Halaedes) australis (Erichson) 1842 (Diptera: Culicidae)

The result of population crosses of members of the Ae. australis complex and the examination of the male genitalia of these populations have shown that Ae. ashworthi Edwards 1921 should be reinstated as a valid species. the parent females laid viable eggs when cross mated to males of different species, but the resulting F₁ females and males were largely sterile. When F₁ females were blood-fed and examined 3–8 d later, usually fewer than 10 ovarioles per ovary developed recognisable follicles and none of these formed eggs. F₁ males in nearly all cases possessed half-size testes, and there was no spermatid development in the reduced testes. A few males had normal-sized testes, but the spermatids were mostly tailless. the male of Ae. ashworthi can be separated from Ae. australis by the shape of the gonocoxite and the length of the gonostylus of the genitalia. the larvae of both species are identical, and the females differ only in the colour of some scale patches and the integument, which may prove to be too variable to be useful when more populations are compared. the morphological similarity of the two mosquitoes as larvae and adults supports the proposal that they should be recognised as sibling species, with Ae. ashworthi as the derived member of the Ae. australis complex. It is clear from morphological evidence, the viability of the F₁ hybrids and the unusual habitat occupied by both species, that they have diverged recently.     

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     

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.     

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.     

Some expression of heterosis in F1-hybrid barley

Small and large scale trials of F₁ barley hybrids were done in a glasshouse in the United Kingdom and in the field in the United Kingdom and Europe in 1970, 1971 and 1972. The results showed that there were few instances of significant positive heterosis in yield with either the small or field scale experiments. The hybrids studied were all derived from American varieties as male-sterile parents and therefore the hybrids were not adapted to European countries, thus the case for or against F₁-hybrids cannot be assessed solely on this material.