Journal of Heredity - current issue

The Ancestral Carnivore Karyotype (2n = 38) Lives Today in Ringtails

2008-04-11

Chromosome painting was used to investigate the conservation of high-resolution longitudinal 4',6-diamidino-2-phenylindole (DAPI)/G bands in Carnivore chromosomes. Cat (Felis catus) and raccoon dog (Nyctereutes procyonoides) painting probes were hybridized to the ringtail (Bassaricus astutus), dwarf mongoose (Helogale parvula), and Malagasy civet (Fossa fossa) to identify homologous chromosome elements. The patterns of chromosome segment homology among Carnivore species allowed us to reconstruct and propose the disposition of a high-resolution banded ancestral carnivore karyotype (ACK). Three bi-armed chromosomes consistently found among Caniformia species are represented as 6 homologous acrocentric chromosomes among Feliformia species of Carnivora. However, reexamination of the most basal of Feliformia species, the African palm civet Nandinia, revealed the presence of the 3 heretofore Caniformia bi-armed chromosomes. Because these 3 bi-armed chromosomes are found in both Caniformia and Feliformia lineages, they are presumed ancestral for all Carnivora, suggesting that the ACK chromosome number would be 38, rather than the previously supposed 42. Banded chromosomes of the ACK are used to evaluate the consistency between recently determined molecular phylogenetic relationships and postulated cytogenetic dynamics in the same Carnivore species.

Mitochondrial DNA Sequence Phylogeny of 4 Populations of the Widely Distributed Cynomolgus Macaque (Macaca fascicularis fascicularis)

Blancher, A., Bonhomme, M., Crouau-Roy, B., Terao, K., Kitano, T., Saitou, N. — 2008-04-11

We studied the mitochondrial DNA (mtDNA) polymorphism of 304 Macaca fascicularis fascicularis (M. f. fascicularis) individuals, representative of 4 cynomolgus macaque populations (Indochina, Indonesia, Philippines, and Mauritius). By sequencing a 590-bp fragment in the hypervariable II region of the D-loop region, we defined 70 haplotypes. The homologous region was also characterized in 22 Chinese Macaca mulatta and 2 Macaca sylvanus. The phylogenetic analysis confirms the monophyly of M. f. fascicularis and defines 2 haplotype groups inside the M. f. fascicularis clade: one "insular," encompassing 6 Philippines, 2 Mauritius, and 31 Indonesian haplotypes, the other "continental" that contains all Indochinese and 6 Indonesian haplotypes. Continental and insular group divergence time was estimated to be approximately 10⁶ years before present (BP). Among Indonesian haplotypes, some have a continental origin. This suggests either direct migration from mainland to Indonesia or that remnant lineages from an ancient population genetically close to the mainland (i.e., in the Sunda Shelf, <550 000 years BP) were subsequently brought southward to Indonesia. The low nucleotide diversity in the Philippines population suggests a bottleneck following colonization by Indonesian individuals, around 110 000 years BP. mtDNA and further observations of nuclear genetic data corroborate the mixed origin (Indonesian/continental) hypothesis of Mauritius individuals and a population bottleneck.

Deciphering Ecological Barriers to North American River Otter (Lontra canadensis) Gene Flow in the Louisiana Landscape

Latch, E. K., Scognamillo, D. G., Fike, J. A., Chamberlain, M. J., Rhodes, O. E. — 2008-04-11

For North American river otters (Lontra canadensis) in Louisiana, statewide distribution, availability of aquatic habitats, and the absence of physical barriers to dispersal might suggest that they exist as a large, panmictic population. However, the wide variety of habitat types in this region, and the dynamic nature of these habitats over time, could potentially structure river otter populations in accordance with cryptic landscape features. Recently developed landscape genetic models offer a spatially explicit approach that could be useful in identifying potential barriers to the movement of river otters through the dynamic aquatic landscape of Louisiana. We used georeferenced multilocus microsatellite genotypes in spatially implicit (STRUCTURE) and spatially explicit (GENELAND) models to characterize patterns of landscape genetic structure. All models identified 3 subpopulations of river otters in Louisiana, corresponding to Inland, Atchafalaya River, and Mississippi River regions. Variation in breeding seasonality, brought about by variation in prey abundance between inland and coastal populations, may have contributed to genetic differentiation among populations. It is also possible that the genetic discontinuities we observed indicate a correlation between otter distribution and access to freshwater. Regardless of the mechanism, it is likely that any genetic differentiation among subpopulations is exacerbated by relatively poor dispersal.

Fitness of Transgenic Anopheles stephensi Mosquitoes Expressing the SM1 Peptide under the Control of a Vitellogenin Promoter

Li, C., Marrelli, M. T., Yan, G., Jacobs-Lorena, M. — 2008-04-11

Three transgenic Anopheles stephensi lines were established that strongly inhibit transmission of the mouse malaria parasite Plasmodium berghei. Fitness of the transgenic mosquitoes was assessed based on life table analysis and competition experiments between transgenic and wild-type mosquitoes. Life table analysis indicated low fitness load for the 2 single-insertion transgenic mosquito lines VD35 and VD26 and no load for the double-insertion transgenic mosquito line VD9. However, in cage experiments, where each of the 3 homozygous transgenic mosquitoes was mixed with nontransgenic mosquitoes, transgene frequency of all 3 lines decreased with time. Further experiments suggested that reduction of transgene frequency is a consequence of reduced mating success, reduced reproductive capacity, and/or insertional mutagenesis, rather than expression of the transgene itself. Thus, for transgenic mosquitoes released in the field to be effective in reducing malaria transmission, a driving mechanism will be required.

Mapping Homologous Sequences for Determinacy and Photoperiod Sensitivity in Common Bean (Phaseolus vulgaris)

Kwak, M., Velasco, D., Gepts, P. — 2008-04-11

Determinacy and photoperiod insensitivity are agronomically important traits, selected during or after domestication in common bean. Determinacy reduces aboveground plant biomass and accelerates and synchronizes flowering. Photoperiod insensitivity allows common bean to be grown at higher latitudes under long days. In this study, we attempted to identify Phaseolus vulgaris homologues of 12 Arabidopsis genes that are involved in meristem identity determination and the photoperiod-dependent and autonomous flowering pathways. Amplification products with homology to the original Arabidopsis gene were obtained for 8 genes, 7 of which could be mapped onto the common bean-linkage map using the BAT93 x Jalo EEP 558 and Midas x G12873 recombinant inbred populations. Three Terminal Flower 1 homologues (PvTFL1x, PvTFL1y, and PvTFL1z) were mapped to B4, B1, and B7, respectively. PvTFL1y cosegregated with the determinacy locus, fin. In addition, PvTFL1z mapped near or at a second determinacy locus on B7. A Zeitlupe homologue mapped near a quantitative trait locus (QTL) for flowering time on linkage group B9. Constans, FCA, Flowering locus D, Gigantea, and Leafy homologues did not cosegregate with currently mapped flowering time QTLs and photoperiod insensitivity loci in common bean. Further studies are needed to confirm the role of these homologues as potential candidate genes.

Molecular Aspects of Anthocyanin fruit Tomato in Relation to high pigment-1

2008-04-11

The tomato Anthocyanin fruit (Aft) genotype is characterized by purple color in skin and outer pericarp of its fruits due to higher levels of anthocyanins—flavonoid metabolites. Our objectives were to carry out metabolic and molecular characterization of this genotype, emphasizing its interaction with the high pigment-1 (hp-1) mutation, known to increase flavonoids in tomato fruits. These objectives fit the growing interest in developing tomato fruits with higher levels of functional metabolites. Our results show that 1) Aft fruits are also characterized by significantly higher levels of the flavonols quercetin and kaempferol, thus enhancing their functional value; 2) the tomato Anthocyanin1 (Ant1) gene, encoding a Myb transcription factor, displayed nucleotide and amino acid polymorphisms between the Aft genotype and cultivated genotypes; 3) a DNA marker based on Ant1 showed that the Aft trait is encoded by a single locus on chromosome 10 fully associated with Ant1; and 4) double homozygotes Aft/Aft hp-1/hp-1 plants displayed a more-than-additive effect on the production of fruit anthocyanidins and flavonols. This effect was manifested by approximately 5-, 19-, and 33-fold increase of petunidin, malvidin, and delphinidin, respectively, in the double mutants compared with the cumulative levels of their parental lines.

ISSR and Isozyme Characterization of Androgenetic Dihaploids Reveals Tetrasomic Inheritance in Tetraploid Somatic Hybrids between Solanum melongena and Solanum aethiopicum Group Gilo

2008-04-11

Gene exchanges between Solanum melongena and its allied relative Solanum aethiopicum are a crucial prerequisite for introgression of useful traits from the allied species into the cultivated eggplant. In order to evaluate the extent of genetic recombination between the 2 species, biochemical and molecular markers were employed. A dihaploid population obtained through anther culture of the corresponding tetraploid somatic hybrids was genetically analyzed. The extent of disomic/tetrasomic inheritance and segregation ratios of 3 isozyme systems and intersimple sequence repeat (ISSR) markers were evaluated. The dihaploids, being derived from microspores, allowed for simple, complete, and accurate analyses. The segregation of 280 ISSR markers (110 aethiopicum-specific, 104 melongena-specific, and 66 monomorphic) were evaluated in 71 dihaploids. According to the genetic constitution (simplex/duplex/triplex), almost 64% of the fragments revealed the tetrasomic and/or disomic inheritance. With regard to the assigned species-specific fragments, 68% and 4% were unambiguously the result of tetrasomic and disomic inheritance, respectively. Twenty-four of the 66 monomorphic ISSRs were inherited according to random chromatid segregation. The phenotypes of glucose-6-phosphate dehydrogenase (G-6-PDH), 6-phosphogluconate dehydrogenase (6-PGDH), and shikimate dehydrogenase (SKDH) were studied in 70 dihaploids and inferences were made about the allelic state of their 5 loci. The isozyme markers segregated in the dihaploids in a distorted manner, their segregations did not fit in with any of the expected segregation ratios. However, tetrasomic inheritance might be suggested for G-6-PDH 2 and SKDH 1 loci. Our results demonstrated that gene exchanges occurred readily in the somatic hybrids between S. melongena and S. aethiopicum gr. Gilo.

Recombination in Interpopulation Hybrids of the Copepod Tigriopus californicus: Release of Beneficial Variation Despite Hybrid Breakdown

Edmands, S. — 2008-04-11

Crosses between divergent populations of the copepod Tigriopus californicus typically result in fitness reductions for both F₂ and backcross hybrids. Because females in this species lack chiasmatic meiosis, both recombinant and nonrecombinant backcross hybrids can be created. Recombinant hybrids were found to have significantly faster development time for both males and females in 2 pairs of crosses, indicating the creation of favorable gene combinations by disrupting parental linkage groups.

Genetic Mapping of Resistance to Purple Seed Stain in PI 80837 Soybean

Jackson, E. W., Feng, C., Fenn, P., Chen, P. — 2008-04-11

Purple seed stain (PSS) of soybean caused by Cercospora kikuchii is an important disease that reduces market grade and can affect seed germination and vigor. A single dominant gene was shown to confer PSS resistance in PI 80837. The objective of this research was to map the PSS resistance gene in PI 80837 using simple sequence repeat (SSR) markers. A cross was made between the PSS-susceptible cultivar Agripro 350 (AP 350) and PI 80837. The F₂ population and parents were grown in the field, and the resistance or susceptibility of individual plants was determined by assaying the seed for infection by C. kikuchii. DNA of parent and F₂ plants was extracted for SSR analysis and mapping. Segregation ratios for seed infection and for SSR markers showed that a single dominant gene conditions resistance to PSS in PI 80837. The candidate resistance gene was mapped between Sat_308 (6.6 cM) and Satt594 (11.6 cM) on molecular linkage group G. These markers may be useful in marker-assisted selection for utilizing PSS resistance from PI 80837 in a breeding program.

Parentage Analysis with Few Contributing Breeders: Validation and Improvement

Duchesne, P., Meldgaard, T., Berrebi, P. — 2008-04-11

Validation of parental allocation using PAPA software (Duchesne P, Godbout MH, Bernatchez L. 2002. PAPA (package for the analysis of parental allocation): a computer program for simulated and real parental allocation. Mol Ecol Notes. 2:191–193.) was investigated under the assumption that only a small proportion of potential breeders contributed to the offspring sample. Inbreeding levels proved to have a large impact on allocation error rate. Consequently, simulations from artificial, unrelated parents may strongly underestimate allocation error, and so, whenever possible, simulations based on the actual parental genotypes should be run. An unexpected and interesting finding was that ambiguity (the highest likelihood is shared by several parental pairs) rates below 10% stood very close to exact allocation error rates (true proportions of wrong allocations). Hence, the ambiguity rate statistic may be viewed as a ready-made indicator of the resolution power of a specific parental allocation run and, if not exceeding 10%, used as an estimate of allocation error rate. It was found that the PAPA simulator, even with few contributing breeders, can be trusted to output reasonably accurate estimates of allocation error as long as those estimates do not exceed 15%. Indeed, most discrepancies between exact and estimated error then stood below 3%. Reproductive success variance had little impact on error estimate discrepancies within the same range. Finally, a (focal set) method was described to correct the estimated family sizes computed directly from parental allocations. Essentially, this method makes use of the detailed structure of the allocation probabilities associated with each parental pair with at least 1 allocated offspring. The allocation probabilities are expressed in matrix form, and the subsequent calculations are run based on standard matrix algebra. On average, this method provided better estimates of family sizes for each investigated combination of parameter values. As the size of offspring samples increased, the corrections improved until a plateau was finally reached. Typically, samples comprising 250, 500, and 1000 offspring would bring corrections in the order of 10–20%, 20–30%, and 30–40%, respectively.

Announcements

2008-04-11