Linkage Analysis of the Multilocus Glucosephosphate Isomerase Isozyme System in Sunfish (Centrarchidae, Teleostii)

The purpose of the present investigation is to determine whether the two duplicated glucosephosphate isomerase (EC 5.3.1.9) loci Gpi-A and Gpi-B reside on the same chromosome in teleostean fishes. Interspecific sunfish hybrids were employed for the cross because of the different species-specific electrophoretic mobilities of the allelic isozymes at each GPI locus and because of their genomic compatibility. F1 sunfish hybrids, formed from a male warmouth (Lepomis gulosus) X female green sunfish (L. cyanellus) cross, were mated to form the F2 generation. The number of each of the nine different isozyme phenotypes, revealed by starch gel electrophoresis, was determined using 256 F2 individuals. The high frequency of recombinant phenotypes in the F2 generation indicated that the two GPI loci are not linked. An excess of F2 individuals heterozygous at both loci was observed and is interpreted as being caused by heterosis. The absence of linkage for the homologous loci encoding GPI subunits and for other multilocus isozyme systems is consistent with the postulate that the genomes of present-day vertebrates arose through one or more polyploidization events early in vertebrate evolution.     

Relative developmental success of interspecific Lepomis hybrids as an estimate of gene regulatory divergence between species

The developmental success of interspecific Lepomis hybrids is used as an index of gene regulatory divergence between the green sunfish, L. cyanellus, and each of three other parental species, longear sunfish, L. megalotis, warmouth, L. gulosus, and bluegill, L. macrochirus. This gene regulatory divergence is compared to the degree of structural gene divergence among these four species (genetic distance [Nei, '78], D, ranged from 0.206 to 0.586). The developmental success of the hybrid embryos at the level of morphogenesis was higher than expected from the genetic distance between the parental species. The rates of morphogenesis of the hybrid embryos were the same as that for the green sunfish embryos. The percentage of embryos that hatched was relatively high in all crosses. However, two of the hybrid crosses resulted in enhanced percentages of hatched embryos. Slight increases in the extent of morphological abnormalities were observed in hybrids from crosses between more distantly related parental species. The schedules and levels of enzyme locus expression of the hybrids, assessed spectrophotometrically and electrophoretically for nine enzyme systems (encoded in a total of 14 loci), were different from each other and from those of the green sunfish embryos. Alterations in the time of first enzyme appearance and in the time of first increase in enzyme activity in the developing hybrid embryos were not correlated with genetic distance between parental species. However, the extents of alteration of enzyme activities over the entire period of hybrid embryogenesis were correlated with the genetic distance. We attribute the morphological and molecular anomalies observed in the hybrids to gene regulatory incompatibilities between species. Although the exact number of mutational differences and their relative developmental impacts are not known, some inferences can be drawn about the degree of divergence in gene regulation between species. It appears that an uncoupling of the rates of structural and regulatory gene evolution can occur between species of some taxa, an observation that has implications for the roles of gene regulatory differences in organismic evolution.     

Expression of lactate dehydrogenase phenotypes in intraspecific and interspecific matings of two species of Xenopus

Starch gel electrophoresis has been used to examine lactate dehydrogenase phenotypes in two species of Xenopus and their hybrids obtained from reciprocal crosses. The patterns are complex, consisting of as many as 18 bands in some material. Differences between laevis and mulleri isozymes allow an evaluation of the contribution of both parents to the phenotypes of their hybrid offspring, and the determination of approximate times of paternal allele expression. The phenotype of early embryos resembles that of the maternal parent until hatching, when evidence of paternal influence is first apparent. Regardless of the early appearance of paternal enzyme, reciprocal hybrids bear a stronger resemblance to the maternal parent until well after tadpole growth begins. Once this maternal effect disappears, both laevis and mulleri appear to contribute to the LDH phenotype without predominance of the isozymes of either species. Evidence for the possible formation of “hybrid” enzymes consisting of subunits of both species in one active enzyme molecule is presented. Expression of LDH phenotype is variable in the unfertilized eggs of fertile hybrid females.     

Linkage relationships of nine enzyme Loci in sunfishes (lepomis; centrarchidae)

Linkage relationships of nine enzyme loci; aconitase (Acon ), esterase (Est), glucosephosphate isomerase A and B ( Gpi), glycerate-2-dehydrogenase (G2dh), malic enzyme (Me ), phosphoglycerate kinase (Pgk), phosphoglucomutase (Pgm ) and superoxide dismutase (Sod), were investigated in sunfishes (Lepomis, Centrarchidae). Reciprocal F₁ hybrids produced from crosses between green sunfish (Lepomis cyanellus) and redear sunfish ( L. microlophus) were backcrossed with each of the two parental species. A three-point linkage map comprising G2dh, Pgk and Sod is reported. The frequencies of recombination between G2dh and Pgk and between Pgk and Sod are estimated as 45.3 and 24.7%. The remaining six loci assort independently. Possible linkage conservation and homology of this linkage group with those of other vertebrate species are discussed.     

Biochemical genetics of hybrid sunfish: Differential survival of heterozygotes

Allelic segregation in reciprocal backcrosses involving the largemouth bass (Micropterus salmoides) and the F₁ hybrid (largemouth bass × smallmouth bass, M. dolomieui) was investigated to determine the extent of euheterosis and luxuriance. The frequencies of allelic isozymes encoded in the lactate dehydrogenase E, malate dehydrogenase B, and isocitrate dehydrogenase loci were determined for reciprocal backcross progeny subjected to different selection pressures. The progeny of the backcross (male F₁ × female largemouth bass) underwent a rapid loss of heterozygous individuals in a natural pond environment. When the offspring of this same mating were placed in artificial pools, where cannibalism is the main source of mortality, heterozygosity was advantageous. There was a marked correlation of increased heterozygosity at these enzyme loci with an increased growth rate. None of the above responses to selection was observed when the F₁ hybrid served as the maternal parent in the reciprocal backcross. A maternal factor in the egg cytoplasm may influence the expression of heterosis.     

Asynchronous expression of the alcohol and supernatant malate dehydrogenase loci during Barbus hybrid development (Cypriniformes, Teleostei)

The tissue specificity and ontogeny of supernatant malate dehydrogenase (s-MDH) and alcohol dehydrogenase (ADH) are reported for the tiger barb (Barbus tetrazona), the rosy barb (Barbus conchonius) and their reciprocal hybrids. The tissue distribution of s-MDH and ADH isozymes in both species is consistent with spatial profiles reported for other teleosts. The expression of alleles of paternal origin at the s-Mdh-B and Adh loci are delayed in reciprocal hybrids as compared to their expression intraspecifically; suggestive of a low degree of affinity between maternally derived regulatory factors and paternal regulative elements controlling structural gene activation.     

Reciprocal effects in anther cultures of wheat hybrids

This study was conducted to determine the reciprocal effects for anther culture response in wheat (Triticum aestivum L.) using a set of 4 × 4 full diallel crosses. Both reciprocal and nuclear genetic effects were highly significant for anther culture response and useful for selection and breeding purposes. General combining ability (GCA) effects were predominant for all investigated anther culture traits. Also, significant differences for specific combining ability (SCA) effects were detected between reciprocal crosses. Although significant reciprocal differences for responding anther, callus number and green plant regeneration were recorded in some reciprocal crosses, there were no significant reciprocal differences for albino plant regeneration. The use of one parent as male or female could lead to change at the production of green plants from the F₁ hybrids and screening of inbred lines for response to anther culture, without reciprocal effects, could decrease the utilization of breeding material.     

Maternal and Reciprocal Effects on Seedling Characters in ARABIDOPSIS THALIANA (L.) Heynh

Five early growth characters were examined in six races of Arabidopsis thaliana (L.) Heynh, their reciprocal F₁ hybrids (1974) and F₁ by tester hybrids, using a seventh race as a paternal tester. Three of the five characters were also examined at two nutrient levels in reciprocal F₁ hybrids (1972) of all seven races. Analyses of F₁ and F₁ by tester hybrids revealed significant maternal effects in all characters examined in F₁ hybrids (1972) and in root length and plant weight of F₁ (1974) and F₁ by tester hybrids. Significant reciprocal effects were found for plant weight in F₁ by tester hybrids and for seed weight, percentage of germination and root length in F₁ (1974) and F₁ by tester hybrids. The presence of significant maternal and/or reciprocal components in both F₁ (1974) and F₁ by tester diallels suggests that differences in maternal cytoplasm rather than maternal genotype per se were responsible for much of the variation resulting from these non-direct genetic effects.     

Purification of the creatine kinase isozymes of the green sunfish (Lepomis cyanellus) with Blue Sepharose CL-6B.

Three homodimeric creatine kinase isozymes (A₂, B₂, and C₂) of the green sunfish (Lepomis cyanellus) were purified by a combination of affinity chromatography, gel filtration, and preparative starch gel electrophoresis. The final preparations were isozymically pure and were used to elicit antibodies in rabbits. The use of the group-specific adsorbant Blue Sepharose CL-6B (Pharmacia) and specific elution conditions for creatine kinase facilitated purification. Fish creatine kinase isozymes are sensitive to denaturation and cannot be readily purified by procedures routinely used for mammalian creatine kinase isozymes.     

Prey use of wetland benthivorous sunfishes: ontogenetic, interspecific and seasonal variation

The intensity of competitive interactions between fishes is partly determined by prey use and ontogenetic niche shifts. In a wetland where distinct habitat shifts are missing we compared prey use of three generalist benthivorous sunfishes to look for evidence of ontogenetic, interspecific, and “seasonal” variation in prey composition. Diet analysis revealed evidence of diet ontogeny in warmouth (Lepomis gulosus, 30–152 mm standard length, SL), but not in bluespotted sunfish (Enneacanthus gloriosus, 30–47 mm SL) or dollar sunfish (Lepomis marginatus, 30–60 mm SL). Bluespotted and dollar sunfishes consumed small dipteran and amphipod prey and had similar diets in both seasons suggesting a potential for strong interspecific competition. In the dry season, warmouth shifted from using smaller insect prey to larger decapod and fish prey with increasing size. This shift to prey types that were little used by the other species reduced dietary niche overlap with the other sunfishes. After drought and re-flooding (in the wet season), decapods and small fish were less abundant in the wetland and the warmouth ontogenetic shift was less distinct. When matched for gape width, prey composition differed between warmouth and both dollar and bluespotted sunfishes in the wet season, suggesting differences in sunfish foraging modes, but prey use differences were less clear in the dry season when prey were abundant. Both warmouth ontogenetic diet shifts and seasonal variation in prey use (probably mediated by prey abundance) had strong influences on diet overlap and therefore the potential for intra- and interspecific competition between sunfishes in this wetland ecosystem.     

What Causes Partial F1 Hybrid Viability? Incomplete Penetrance versus Genetic Variation

Background

Interspecific hybrid crosses often produce offspring with reduced but non-zero survivorship. In this paper we ask why such partial inviability occurs. This partial inviability could arise from incomplete penetrance of lethal Dobzhansky-Muller incompatibilities (DMIs) shared by all members of a hybrid cross. Alternatively, siblings may differ with respect to the presence or number of DMIs, leading to genotype-dependent variation in viability and hence non-Mendelian segregation of parental alleles in surviving F1 hybrids.

Methodology/Principal Findings

We used amplified fragment length polymorphisms (AFLPs) to test for segregation distortion in one hybrid cross between green and longear sunfish (Lepomis cyanellus and L. megalotis). Hybrids showed partial viability, and twice as much segregation distortion (36.8%) of AFLPs as an intraspecific control cross (18.8%). Incomplete penetrance of DMIs, which should cause genotype-independent mortality, is insufficient to explain the observed segregation distortion.

Conclusions/Significance

We conclude that F1 hybrid sunfish are polymorphic for DMIs, either due to sex-linked DMI loci (causing Haldane''s Rule), or polymorphic autosomal DMI loci. Because few AFLP markers were sex-linked (2%), the most parsimonious conclusion is that parents may have been heterozygous for loci causing hybrid inviability.     

Ontogeny of gene expression in Pomoxis (pisces: Centrarchidae)

The regulation of gene expression during embryogenesis was investigated in white and black crappie (Pomoxis spp.) and their reciprocal interspecific F₁ hybrids. The schedule of morphological development and the timing of isozyme expression were compared among the two species and both reciprocal maternal half-sibling F₁ hybrids. Although absolute rates of morphological development differed in response to incubation temperature, relative rates of morphological development (normalized to the onset of retinal pigment deposition) were similar among all crosses. Furthermore, these relative rates were similar to those previously documented for other centrarchid species. To assess differences in ontogenetic patterns of gene expression among the crosses, we examined expression for 39 enzymeencoding loci. Expression was not detected in the embryos for 16 loci due to low or nonexistent activity. Enzymatic activity from eight other loci were continuously detected throughout embryogenesis as a result of maternal enzyme in the egg. However, 15 loci initiated expression during the early development period investigated (fertilization through yolk sac absorption). We observed temporal variability in expression of these 15 loci among the crosses, either in the form of differential expression between parental species or as disturbances in the ontogeny of expression in interspecific hybrids. Such variability in expression suggests that some of the gene regulating mechanisms have diverged since Pomoxis species shared a common ancestral genome. © 1994 Wiley-Liss, Inc.     

Differences in tissue expressions of enzyme activities in interspecific sunfish (Centrarchidae) hybrids and their backcross progeny

The extent of naturally occurring variations of enzyme locus expression was determined for three tissues (liver, muscle, and eye) in two species of sunfish (Centrarchidae), the green sunfish (Lepomis cyanellus) and the redear sunfish (L. microlophus). The genetic basis for species differences in tissue enzyme specific activities of malate dehydrogenase (EC 1.1.1.37), lactate dehydrogenase (EC 1.1.1.27), phosphoglucomutase (EC 2.7.5.1), and glucosephosphate isomerase (EC 5.3.1.9) was investigated by determining enzyme specific activities in the tissues of the reciprocal F1 hybrids and of their backcross progenies. The specific activities for most enzymes in hybrids were intermediate between those of the parental species. Significant differences in enzyme specific activity were detected among the F1 progeny as well as those of backcrosses. Variations in specific activity levels in one tissue were often independent of variations in specific activities in a different tissue. However, the changes in the specific activities of different enzymes within the same tissue were often positively correlated. The tissue glucosephosphate isomerase activity differences appear not to be due to different functional contributions of the glucosephosphate isomerase allelic isozymes. Cluster analysis of distributions of specific activities revealed no simple Mendelian pattern of inheritance for control of tissue enzyme activity. Our results suggest a polygenic control of tissue enzyme specific activity levels.     

Chloroplast DNA inheritance in theStellaria longipes complex (Caryophyllaceae)

Inheritance of chloroplast DNA (cpDNA) was examined in F₁ progenies derived from three crosses and three corresponding reciprocal crosses betweenStellaria porsildii andS. longifolia. Chloroplast DNA restriction fragments were analyzed using methods of nonradioactive digoxigenin-11-dUTP labeling and chemiluminescent detection with Lumi-Phos 530. Distinct interspecific restriction fragment polymorphisms were identified and used to demonstrate the mode of cpDNA inheritance. Mode of cpDNA inheritance differed among crosses. Two crosses in whichS. porsildii, SP2920-21, was the maternal parent exhibited three different types of plastids, maternal, paternal and biparental, among the F₁ hybrids, suggesting a biparental cpDNA inheritance and plastid sorting-out inStellaria.     

Genetic control of seed proteins in wheat

Summary Electrophoretic profiles of crude protein extracts from seed of F₁ hybrids and reciprocal crosses among diploid, tetraploid and hexaploid wheats were compared with those of their respective parental species. The electrophoretic patterns within each of three pairs of reciprocal crosses, T.boeoticum X T.urartu, T.monococcun X T. urartu and T.dicoccum X T. araraticum, were different from one another but were identical with those of their respective maternal parents. Protein bands characteristic of the paternal parents were missing in F₁ hybrid seed suggesting that the major seed proteins in wheat were presumably regulated by genotype of the maternal parent rather than by the seed genotype. However, in another three pairs of reciprocal crosses, T.boeoticum X T. durum, T.dicoccum X T.aestivum and T. zhukovskyi x T. aestivum, protein bands attributable to the paternal parents were present in the F₁ hybrid seeds indicating that the seed proteins were not always exclusively regulated by the maternal genotype. The expression of paternal genomes is presumably determined by dosage and genetic affinity of the maternal and paternal genomes in the hybrid endosperm. The maternal regulation of seed protein content is probably accomplished through the maternal control over seed size. The seed protein quality may, however, depend upon the extent of expression of the paternal genome.     

Developmental Genetics of Fishes: Isozymic Analyses of Differential Gene Expression

SYNOPSIS. The fundamental evolutionary position of the fishesand the plasticity of their gene expression render them wellsuited for developmental genetic analyses. Isozymes, encodedin related loci, have proven to be effective probes of differentialgene expression in the fishes. The advanced bony fishes exhibita higher temporal and spatial specificity of isozyme locus expressionthan the primitive fishes. Some isozyme loci are limited intheir expression to specific developmental periods such as hatching.The more phylogenetically recently derived loci have a morerestricted tissue expression, and tend to be expressed laterin development than more ancient loci exhibiting a more generalizedtissue expression. More closely related isozyme loci tend tooverlap more in their cellular expressions than do more distantlyrelated loci. The role of gene and genome relatedness in regulatinggene expression also has been studied by the investigation ofpreferential allele expression in interspecific hybrids. Theschedules of gene expression are often perturbed in interspecificfish hybrids. A progressive increase in the severity of developmentalabnormalities, at the morphological and enzymatic levels, occursduring embryogenesis of hybrids formed from progressively moredistantly related species. In most instances of allelic repression,the paternal allele is preferentially inhibited but occasionallythe maternal allele is selectively repressed. A non-reciprocaldevelopmental success is often observed for hybrid embryos derivedfrom reciprocal crosses. These aberrant nucleocytoplasmic interactionshave been related to models of gene regulation and the evolutionarydivergence of gene regulatory mechanisms.     

Basis of difference between reciprocal crosses involving Triticum boeoticum and T. urartu

Summary The boeoticum () X urartu () F₁ hybrids gave small, plump and viable seeds while the reciprocal crosses with T. urartu as the female parent had long, shrivelled and non-viable seeds. Reciprocal nuclear-substitution lines comprising the nucleus of one species into the cytoplasm of the other were developed through repeated backcrossing and were crossed as female parents with respective non-recurrent parents (the cytoplasm donors). The difference between the reciprocal crosses was presumably attributable to different boeoticum urartu genomic ratios in the triploid endosperm rather than to the cytoplasmic difference between the diploid wheats. The endosperm with two doses of the boeoticum and one of the urartu genome resulted in small, plump and viable seed while the endosperm of the reciprocal crosses with two doses of the urartu and one of the boeoticum genome led to large but shrivelled and non-viable seeds irrespective of the cytoplasmic type. One dose of the paternal genome in the triploid endosperm is probably not expressed in the presence of two doses of the maternal genome thereby leading to the difference between the reciprocal crosses. The results reported here indicate that difference between reciprocal crosses may not always be attributed to cytoplasmic difference between the parental species.     

High transmission of paternal plastid DNA in alfalfa plants demonstrated by restriction fragment polymorphic analysis

Summary A high frequency of paternal plastid transmission occurred in progeny from crosses among normal green alfalfa plants. Plastid transmission was analyzed by hybridization of radiolabeled alfalfa plastid DNA (cpDNA) probes to Southern blots of restriction digests of the progeny DNA. Each probe revealed a specific polymorphism differentiating the parental plastid genomes. Of 212 progeny, 34 were heteroplastidic, with their cpDNAs ranging from predominantly paternal to predominantly maternal. Regrowth of shoots from heteroplasmic plants following removal of top growth revealed the persistence of mixed plastids in a given plant. However, different shoots within a green heteroplasmic plant exhibited paternal, maternal, or mixed cpDNAs. Evidence of maternal nuclear genomic influence on the frequency of paternal plastid transmission was observed in some reciprocal crosses. A few tetraploid F₁ progeny were obtained from tetraploid (2n=4x=32) Medicago sativa ssp. sativa x diploid (2n=2x=16) M. sativa ssp. falcata crosses, and resulted from unreduced gametes. Here more than the maternal genome alone apparently functioned in controlling plastid transmission. Considering all crosses, only 5 of 212 progeny cpDNAs lacked evidence of a definitive paternal plastid fragment.Contribution No. 89-524-J from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan