Genetics of somatic fusion in a myxomycete: F2 studies

Summary Extensive genetic studies have been undertaken on the control of asexual cell (plasmodial) fusion inDidymium iridis. At least 6 loci control asexual cell fusion and mutual exchange of protoplasm in the Pan. 1 strain. In this study it was determined that labor-saving use of backcrosses provides reliable genetic data which is in accord with more extensive F₂ studies. Additional fusion data on 45 Pan. 1 clones are reported and possible biochemical control mechanisms of the fusion loci are discussed.     

SOMATIC CELL INCOMPATIBILITY IN DIDYMIUM IRIDIS: LOCUS IDENTIFICATION AND FUNCTION

Somatic incompatibility in two strains of the myxomycete Didymium iridis is controlled by at least 13 loci: seven fusion loci and six clear-zone loci. Details on correlating loci of the Hon 1 strain with Pan 1 loci are given and a unified nomenclature, applicable to both strains, has been developed from data presented in this paper. Although fusion loci generally prevent fusion between different plasmodial incompatibility phenotypes, studies on individual loci have shown that a limited transient fusion may occasionally take place. Thus, the differences between the fusion and clear-zone loci are not as distinct as once thought. However, the 13 somatic incompatibility loci are still easily designated as either fusion or clear-zone loci, and no locus has thus far been found with true intermediate function. Studies on individual locus function are also discussed.     

GENETICS OF SOMATIC CELL FUSION IN TWO ISOLATES OF DIDYMIUM IRIDIS

Analysis of progeny from a cross between a Honduran clone and a Panamanian clone of Didymium iridis has revealed existence of five new plasmodial fusion loci in the Panamanian isolate. These are in addition to six which were previously known.     

CYTOPHOTOMETRIC MEASUREMENT OF NUCLEAR DNA IN SEVEN HETEROTHALLIC ISOLATES OF DIDYMIUM IRIDIS,A MYXOMYCETE

Absorption cytophotometry was used to measure nuclear Feulgen-DNA content of myxamoebae and Plasmodia in seven heterothallic isolates of Didymium iridis. Measurements of myxamoebal nuclei from clones of four isolates (Hon 1, Pan 1, Pan 2, and CR 5) gave a mean DNA value of 0.34, whereas the nuclei of Plasmodia which develop from each of the four intraisolate crosses had a mean value of 0.63. These values correspond to the 2C haploid level in myxamoebae and the 4C diploid level in Plasmodia. DNA values in two additional isolates (Pan 3 and CR 2) are much higher than the mean for the other five. Accordingly, it is proposed that these may be polyploid. The question of polyploidy in D. iridis and in other myxomycetes is evaluated. The seventh isolate, Ky 1, is taxonomically very close to D. nigripes and was not included in calculations of mean values for D. iridis.     

NUCLEAR DNA CONTENT OF MYXAMOEBAE AND PLASMODIA IN SIX NON-HETEROTHALLIC ISOLATES OF A MYXOMYCETE,DIDYMIUM IRIDIS

The nuclear DNA content of six non-heterothallic isolates of the myxomycete Didymium iridis was measured by combining the Feulgen reaction with absorption microspectrophotometry. This allowed us to distinguish between homothallic (sexual) and apogamic (non-sexual) isolates. Four of the isolates studied, Panamanian 4 and 5, California 1, and Missouri 1 are homothallic. Moreover, the average DNA content of the myxamoebal and plasmodial nuclei (0.32 and 0.61 respectively) does not differ significantly from the calculated haploid and diploid values for heterothallic isolates of D. iridis (0.34 and 0.63). Hence, it is concluded that in each of these isolates the myxamoebae are haploid and the plasmodia diploid. In two of the isolates investigated, Georgia 1 and Hawaii 1, the DNA content of the myxamoebal and plasmodial nuclei did not differ significantly. Therefore, in both of these isolates the plasmodia appear to develop apogamically. In addition the mean DNA values recorded for the Ha-1 isolate suggest that it is aneuploid.     

Pigmentation and sporulation in selected Myxomycetes

Chemical, chromatographic and spectrometric methods are used to characterize plasmodial pigments and determine relationships between pigmentation and sporulation in selected Myxomycetes. In Physarum gyrosum (white) a single pigment is identified and characterized as a flavone. Physarum polycephalum (yellow) and Didymium iridis (brown) contain four and six components, respectively, in their plasmodial pigments which test negatively for flavones but show the presence of some type of phenolic compound. No detectable component is identified in the white plasmodium of Didymium squamulosum which proved to be independent of light for fruiting. The absorption spectra of all species that were light sensitive for fruiting showed common peaks in the 300–400-mμ region, among others. Pigment changes associated with light absorption are reported for some white, yellow and brown plasmodial types. In Physarum gyrosum a yellow pigment forms in light which did not show the characteristic flavones present in the white plasmodial stage. Changes in absorption spectra are reported for Physarum polycephalum, Didymium iridis and Didymium squamulosum as the plasmodial pigments change prior to fruiting. Results show a close relationship between the physiology of plasmodial pigmentation and sporulation in the Myxomycete species studied.     

Sex linkage in salmonids: Evidence from a hybridized genome of brook trout and arctic charr

In second-generation sparctics (Salvelinus fontinalis × Salvelinus alpinus) backcrossed toS. fontinalis, we have identified tight classical linkage of phenotypic sex withLdh-1, Aat-5, andGpi-3. We designate this locusSex-1 and suggest that it may be the primary sex-determining locus in salmonids. Cumulative salmonid gene-to-centromere map distances for the three biochemical loci put the order as centromere—Ldh-1—(Aat-5 andGpi-3), with the latter two loci being tightly linked. An absence of association of phenotypic sex (presumably Sex-1) with these same three loci and other loci known to be linked to these loci is shown in splakes (S. fontinalis × Salvelinus namaycush) and cutbows (Salmo gairdneri × Salmo clarki). These data imply that the linkage ofSex-1 with these loci is found only inS. alpinus and support the view thatSex-1 lies across the centromere from these three loci inS. alpinus, representing a Robertsonian fusion not found in any of the other four species. A similar specific Robertsonian fusion is argued forS. gairdneri, whereSex-1 may be linked across a centromere to another biochemical locus (Ha). These linkage results and chromosomal observations of other investigators suggest thatSex-1 lies on an information-depauperate arm.     

Mucisphaera calidilacus gen. nov., sp. nov., a novel planctomycete of the class Phycisphaerae isolated in the shallow sea hydrothermal system of the Lipari Islands

For extending the current collection of axenic cultures of planctomycetes, we describe in this study the isolation and characterisation of strain Pan265^T obtained from a red biofilm in the hydrothermal vent system close to the Lipari Islands in the Tyrrhenian Sea, north of Sicily, Italy. The strain forms light pink colonies on solid medium and grows as a viscous colloid in liquid culture, likely as the result of formation of a dense extracellular matrix observed during electron microscopy. Cells of the novel isolate are spherical, motile and divide by binary fission. Strain Pan265^T is mesophilic (temperature optimum 30–33 °C), neutrophilic (pH optimum 7.0–8.0), aerobic and heterotrophic. The strain has a genome size of 3.49 Mb and a DNA G?+?C content of 63.9%. Phylogenetically, the strain belongs to the family Phycisphaeraceae, order Phycisphaerales, class Phycisphaerae. Our polyphasic analysis supports the delineation of strain Pan265^T from the known genera in this family. Therefore, we conclude to assign strain Pan265^T to a novel species within a novel genus, for which we propose the name Mucisphaera calidilacus gen. nov., sp. nov. The novel species is the type species of the novel genus and is represented by strain Pan265^T (=?DSM 100697^T?=?CECT 30425^T) as type strain.

     

A MORPHOMETRIC ANALYSIS OF CYTOLOGICAL CHANGES DURING SPORE MATURATION IN THE MYXOMYCETE DIDYMIUM IRIDIS

Ultrastructure of spore maturation in the myxomycete Didymium iridis was investigated using morphometric analytical techniques. Changes in actual volume (μm³) and relative volume (Vv) of nuclei, autophagic vacuoles, mitochondria, microbodies, lipid droplets, and spore wall were described for spores in three stages of development. Stage I spores were newly formed, surrounded only by the cell membrane. Stage II spores were approximately 1 hr older than Stage I spores and possessed surface spines, but little if any additional wall material. Stage III spores were 24 hr old and possessed a fully formed, multilayered wall. The results of this study indicate that spore maturation in D. iridis is a multistep process involving a decrease in spore volume and coordinated changes in specific organelle compartments. From Stage I to Stage III, mean spore volume decreased by more than 50%. Percent volume data (Vv) showed that Stage I spores allocated volume equally to all measured organelles except microbodies and the spore wall, the latter of which had not yet begun to develop. By Stage II, only the nucleus and spore wall showed significant changes in Vv values, both increasing. In terms of actual volume, the nucleus, autophagic vacuole and spore wall increased by Stage II. Between Stages II and III the cell wall was the only component to increase in volume, all others decreased in volume. Our data indicate a close relationship between a decrease in organelle volume and an increase in cell wall volume in the Stage III spore. The autophagic vacuole and the cell wall dominated the volume of the Stage III spore while the remaining volume was allocated unequally to the other components.     

Mobility of short interspersed repeats within the chimpanzee lineage

The PV subfamily of Alu repeats in human DNA is largely composed of recently inserted members. Here we document additional members of the PV subfamily that are found in chimpanzee but not in the orthologous loci of human and gorilla, confirming the relatively recent and independent expansion of this Alu subfamily in the chimpanzee lineage. As further evidence for the youth of this Alu subfamily, one PV Alu repeat is specific to Pan troglodytes, whereas others are present in Pan paniscus as well. The A-rich tails of these Alu repeats have different lengths in Pan paniscus and Pan troglodytes. The dimorphisms caused by the presence and absence of PV Alu repeats and the length polymorphisms attributed to their A-rich tails should provide valuable genetic markers for molecular-based studies of chimpanzee relationships. The existence of lineage-specific Alu repeats is a major sequence difference between human and chimpanzee DNAs. Correspondence to: C.W. Schmid     

Ectocranial suture fusion in primates: pattern and phylogeny

Patterns of ectocranial suture fusion among Primates are subject to species‐specific variation. In this study, we used Guttman Scaling to compare modal progression of ectocranial suture fusion among Hominidae (Homo, Pan, Gorilla, and Pongo), Hylobates, and Cercopithecidae (Macaca and Papio) groups. Our hypothesis is that suture fusion patterns should reflect their evolutionary relationship. For the lateral‐anterior suture sites there appear to be three major patterns of fusion, one shared by Homo‐Pan‐Gorilla, anterior to posterior; one shared by Pongo and Hylobates, superior to inferior; and one shared by Cercopithecidae, posterior to anterior. For the vault suture pattern, the Hominidae groups reflect the known phylogeny. The data for Hylobates and Cercopithecidae groups is less clear. The vault suture site termination pattern of Papio is similar to that reported for Gorilla and Pongo. Thus, it may be that some suture sites are under larger genetic influence for patterns of fusion, while others are influenced by environmental/biomechanic influences. J. Morphol. 275:342–347, 2014. © 2013 Wiley Periodicals, Inc.     

Allozyme genotype-environment relationships in natural populations of Drosophila buzzatii

Allozyme frequency data from natural populations of Drosophila buzzatii were analyzed for genotype-environment relationships. Allele frequency and heterozygosity at six loci polymorphic throughout eastern Australia and a number of environmental factors (both means and variabilities) were examined by a variety of multivariate techniques. Significant genotype-environment associations were found for five of the six loci, and after correcting for geographic location significant associations remained for Est-2 and Adh-1 gene frequencies and heterozygosities and for Pgm gene frequencies. The results are discussed in relation to selection and gene flow and provide the basis for laboratory studies to disentangle confounded effects of (1) environmental means and environmental variabilities and (2) allele frequency and heterozygosity, and thus to further test for and determine the nature of any natural selection at particular allozyme loci.This work was supported by a grant from the Australian Research Grants Committee to J. S. F. B.     

EVOLUTIONARY GENETICS OF ALLORECOGNITION IN THE COLONIAL HYDROID HYDRACTINIA SYMBIOLONGICARPUS

Many sedentary, clonal marine invertebrates compete intensively with conspecifics for habitable space. Allorecognition systems mediate the nature and outcome of these intraspecific competitive interactions, such that the initiation of agonistic behavior and the potential for intergenotypic fusion depend strongly on the relatedness of the contestants. The dependence of these behaviors on relatedness, along with the extraordinary precision with which self can be discriminated from nonself, suggest that allorecognition systems are highly polymorphic genetically. However, allotypic specificity of this sort could be produced by any number of genetic scenarios, ranging from relatively few loci with abundant allelic variation to numerous loci with relatively few alleles per locus. At this point, virtually nothing is known of the formal genetics of allorecognition in marine invertebrates; consequently, the evolutionary dynamics of such systems remain poorly understood. In this paper, we characterize the formal genetics of allorecognition in the marine hydrozoan Hydractinia symbiolongicarpus. Hydractinia symbiolongicarpus colonizes gastropod shells occupied by hermit crabs. When two or more individuals grow into contact, one of three outcomes ensues: fusion (compatibility), transitory fusion (a temporary state of compatibility), and rejection (incompatibility, often accompanied by the production of agonistic structures termed hyperplastic stolons). Observed patterns of compatibility between unrelated, half-sib pairs, and full-sib pairs show that unrelated and half-sib pairs under laboratory culture have a very low probability of being fusible, whereas full sibs have a roughly 30% rate of fusion in experimental pairings. The genetic simulations indicate that roughly five loci, with 5–7 alleles per locus, confer specificity in this species. In ecological terms, the reproductive ecology of H. symbiolongicarpus should promote the cosettlement of kin, some of which should be full sibs, and some half sibs. Thus, there is potential for kin selection to play a major role in the evolution of the H. symbiolongicarpus allorecognition system. In genetic terms, this system conforms to theoretical predictions for a recognition system selected to distinguish among classes of kin, in addition to self from nonself.     

CYTOPLASMIC INCOMPATIBILITY STUDIES IN THE MYXOMYCETE DIDYMIUM IRIDIS: RECOVERY AND NUCLEAR SURVIVAL IN HETEROKARYONS

At least eleven somatic compatibility loci exist in the myxomycete Didymium iridis. Cell fusion is controlled by at least seven fusion loci (Fus1–Fus7). Cytoplasmic compatibility is controlled by at least four clear-zone loci (Cz1–Cz4). Plasmodia with identical phenotypes at all seven fusion loci, but different phenotypes at the clear-zone loci, will fuse temporarily, but fusion is soon blocked by cytoplasmic reactions which prevent complete mixing. Areas which contain cytoplasm from two incompatible Plasmodia become clearly delineated from healthy cytoplasm. Such areas, termed clear zones, have been isolated and found to recover. If clear zones are sectioned into several small pieces, not all pieces will recover, indicating that toxic cytoplasmic reactions have occurred. Plasmodial fusion studies and F₁ studies of recovered clear zones indicate that the clear-zone loci may also control nuclear survival in heterokaryons.     

A STUDY OF SPATIAL FEATURES OF CLONES IN A POPULATION OF BRACKEN FERN,PTERIDIUM AQUILINUM (DENNSTAEDTIACEAE)

Allozymes were used to study the spatial attributes of clones (genets) comprising a population of Pteridium aquilinum (L.) Kuhn var. latiusculum (Desv.) Underw. ex Heller (bracken fern) in the Appalachian Mountains of Virginia. Ramets (individual leaves) were sampled at intervals of 165 m (or less in some cases) and genotyped for six polymorphic isozyme loci to produce a map depicting the spatial patterning of genets. Forty-five distinct genotypes were detected, 14 of which were sampled more than once, five of these more than four times. Genotype proportions at all loci except Pgm-1 conformed to Hardy-Weinberg expectations. Estimation of allele frequencies in the population used a “round-robin” approach that removed any upward bias for rare alleles that distinguish genets. Based on these allele frequencies, the probability that each genotype could arise independently and be sampled was calculated. Some genotypes represented by widely separated ramets had very low probabilities of re-encounter, documenting fragmentation of widespread genets. Coarse-scale mapping indicated a population consisting of many small genets and a few very large ones (up to 1,015 m across). The larger genets tended to be irregular in shape, fragmented, and overlapping. Fine scale mapping of individual fronds in spatially discrete patches of ramets revealed extensive intergrowth of genets, indicating that P. aquilinum exhibits a “guerrilla-type” clonal morphology.     

Genetic diversity within and among Atlantic cod (Gadus morhua) farmed in marine cages: a proof-of-concept study for the identification of escapees

This study presents a molecular genetic characterization of Atlantic cod reared in commercial marine farms. Samples consisted of approximately 47 fish collected from nine cages located on four farms throughout Norway. In addition, 28 farmed escapees were recaptured in the sea (443 fish in total). Nine microsatellite loci and the Pan I gene were analysed, revealing a total of 181 alleles. Each sample contained 43–63% of total allelic variation. Comparing variation with published data for wild cod indicates that lower genetic variation exists within single cages than in wild populations. Significant linkage disequilibrium was observed amongst pairs of loci in all samples, suggesting a low number of contributing parental fish. Global F_ST was 0.049, and the highest pairwise F_ST value (pooled loci) was 0.085. For single loci, the Pan I gene was the most diagnostic, displaying a global F_ST of 0.203. Simulations amongst the samples collected on farms revealed an overall correct self-assignment percentage of 75%, demonstrating a high probability of identifying individuals to their farm of origin. Identification of the 28 escapees revealed a single cage as the most likely source of origin for half of the escapees, whilst the remaining fish were assigned to a mixture of samples, suggesting more than one source of escapees.     

QUANTITATIVE MICROSPECTROPHOTOMETRY OF NUCLEAR DNA IN SELFING STRAINS OF THE MYXOMYCETE DIDYMIUM IRIDIS

Genetic and cytochemical investigations of the origin, development, nuclear activity, and ploidy level of Plasmodia obtained from selfed clones S-2 and B₁P-33 of the heterothallic myxomycete, Didymium iridis, are presented. To demonstrate that selfing did not result from contamination of the clones, or mutations at the mating-type locus, crosses were made between F₁ clones and clones of known mating types. The data were inconsistent with these two possibilities. DNA was quantified by Feulgen-DNA microspectrophotometry. All cellular phases studied (logarithmic amoebae, swarmers, and encysted amoebae) appear to be haploid, with the nuclear DNA being in the replicated (2C) state. The plasmodia are in all cases diploid; however, the data indicate that the selfed Plasmodia are in an extended G₁ condition. The nuclear DNA content of these is therefore 2C, whereas that of the cross Plasmodium is 4C. Sporangial nuclei exhibit DNA in diploid replicated (4C) category.     

Distances électrophorétiques entre l'Homme,le Chimpanzé (Pan troglodytes) et le Gorille (Gorilla gorilla) basées sur la mobilité des enzymes érythrocytaires

Summary Electrophoretic mobilities of homologous erythrocyte enzymes at 21 loci studied in man (Homo sapiens), chimpanzee (Pan troglodytes) and gorilla (Gorilla gorilla) led to estimations of the genetic distances between the three species: If each form is placed at a corner of an isoscele triangle, the distance between the chimpanzee and either of the other two is greater than that between the latter two.     

Inheritance of the human salivary proline-rich proteins: A reinterpretation in terms of six loci forming two subfamilies

DNA studies suggest that six loci control the synthesis of human salivary proline-rich proteins (PRPs). Genes at two of these loci (proposed names, PRH1 and PRH2) contain regions that strongly hybridize to a probe made from a cDNA in which sites for the restriction enzyme HaeIII occur repeatedly; they code for the acidic PRPs. Genes at the remaining four loci (PRB1, PRB2, PRB3, and PRB4) contain regions that strongly hybridize to a probe with repeated BstN1 sites; they probably code for the basic and glycosylated PRPs. In contrast to these data suggesting six loci forming two gene subfamilies, studies of protein polymorphisms and families have led to the postulation of 13 loci with 11 common null alleles. The discrepancy in the number of loci is partly resolved by the hypothesis that the three acidic PRPs, Db, Pa, and PIF, are coded for by alleles at one of the HaeIII-type loci rather than by three discrete loci.This work was supported by National Institutes of Health Grants DEO 3658-19 (E.A.) and GM 20069 (O.S.). This is paper No. 2774 from the Laboratory of Genetics, University of Wisconsin—Madison.     

Inter-menstrual intervals in captive bonobosPan paniscus

In this study we provide new data on the duration of the inter-menstrual intervals of six captive female bonobos (Pan paniscus). We found that the mean duration of the inter-menstrual interval was about 34 days. This lies close to the average value of 37 days that has been reported for common chimpanzees (Pan troglodytes).