Triploidy and its evolutionary significance in Cystopteris protrusa

The most widely recognized mode of polyploid formation in homosporous ferns is allopolyploidy. There are taxa, however, that appear to have arisen through autopolyploidy. Several widely separated collections of the normally diploid species Cystopteris protrusa were found to be triploid. Plants in these collections were morphologically similar to typical, diploid C. protrusa, exhibited a significant number of trivalents during meiosis, and corresponded allozymically to heterozygotes from diploid populations. These plants probably arose through outcrossing between normal, haploid gametes and unreduced, diploid gametes. It is hypothesized that this mechanism of autopolyploid formation is stimulated by environmental stress and may be an intermediate stage in the formation of sexually reproductive tetraploids.

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Elimination of 5S DNA unit classes in newly formed allopolyploids of the genera Aegilops and Triticum

Genome ◽

10.1139/g10-017 ◽

2010 ◽

Vol 53 (6) ◽

pp. 430-438 ◽

Cited By ~ 13

Author(s):

B. R. Baum ◽

M. Feldman

Keyword(s):

Parental Species ◽

Chromosome Doubling ◽

Diploid Species ◽

Evolutionary Significance ◽

Intergeneric Hybridization ◽

Unit Classes ◽

5S Dna ◽

The Difference ◽

Natural And Synthetic

Two classes of 5S DNA units, namely the short (containing units of 410 bp) and the long (containing units of 500 bp), are recognized in species of the wheat (the genera Aegilops and Triticum ) group. While every diploid species of this group contains 2 unit classes, the short and the long, every allopolyploid species contains a smaller number of unit classes than the sum of the unit classes of its parental species. The aim of this study was to determine whether the reduction in these unit classes is due to the process of allopolyploidization, that is, interspecific or intergeneric hybridization followed by chromosome doubling, and whether it occurs during or soon after the formation of the allopolyploids. To study this, the number and types of unit classes were determined in several newly formed allotetraploids, allohexaploids, and an allooctoploid of Aegilops and Triticum. It was found that elimination of unit classes of 5S DNA occurred soon (in the first 3 generations) after the formation of the allopolyploids. This elimination was reproducible, that is, the same unit classes were eliminated in natural and synthetic allopolyploids having the same genomic combinations. No further elimination occurred in the unit classes of the 5S DNA during the life of the allopolyploid. The genetic and evolutionary significance of this elimination as well as the difference in response to allopolyploidization of 5S DNA and rDNA are discussed.

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Haplodiploidy, eusociality and absence of male parental and alloparental care in Hymenoptera: a unifying genetic hypothesis distinct from kin selection theory

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1993.0163 ◽

1993 ◽

Vol 342 (1302) ◽

pp. 335-352 ◽

Cited By ~ 17

Keyword(s):

Genetic Drift ◽

Maternal Care ◽

Kin Selection ◽

Paternal Care ◽

Diploid Species ◽

Alloparental Care ◽

Selection Theory ◽

Long Run ◽

Diploid Populations ◽

Genetic Hypothesis

Beginning with Hamilton ( J. theor. Biol. 7, 1-52 (1964)), evolutionary biologists have attempted to explain the apparent predisposition for the haplodiploid Hymenoptera to evolve both eusociality and female workers. As an alternative to kin selective, pre-adaptational, or ecological explanations for this association, I propose a new genetic hypothesis, the protected invasion hypothesis : dominant alleles for maternal care in finite haplodiploid populations are more resistant to loss from genetic drift than are paternal-care alleles in haplodiploid populations or than are either maternal or paternal-care alleles in diploid populations. Similarly, dominant alleles for female alloparental care in finite haplodiploid populations are more resistant to loss from genetic drift than are male alloparental alleles in haplodiploid populations or than are (male or female) alloparental alleles in diploid populations. A Markov model of phenotypic evolution describing the step-wise progress of a population toward one of two adaptive peaks demonstrates that even small differences in fixation probabilities among these alleles can translate into large differences in the long-run probabilities of observing the corresponding parental or alloparental strategies. Thus the protected invasion hypothesis immediately explains all of the peculiar social features of the haplodiploid Hymenoptera, namely: (i) the overwhelmingly greater tendency for maternal care than paternal care in Hymenoptera; (ii) the greater propensity for eusociality (alloparental sibling care) in Hymenoptera than in diploid insects; and (iii) the greater likelihood for females than males to become alloparents (workers) in the Hymenoptera. The hypothesis also correctly predicts (iv) the apparently higher frequency of paternal care in diploid species than in haplodiploid species, and (v) the lack of a sex-bias among workers of eusocial diploid species. The protected invasion hypothesis is distinct from relatedness-based explanations and provides a more comprehensive explanation for the repeated appearance of the distinctive social structures of the Hymenoptera than does the kin selection model. I show that the bias toward eusociality in Hymenoptera is produced by protected invasion effects even when there is no female-biased sex ratio and no asymmetry between a female’s relatedness to its siblings and to its own offspring. In addition, protected invasion effects create a bias for female versus male workers within the Hymenoptera even when there is no asymmetry between a female’s and male’s relatedness to its siblings. Furthermore, protected invasion effects create a bias toward eusociality in haplodiploid versus diploid populations even when the queen mates an indefinite number of times and there is no difference between haplodiploid and diploid colonies in the relatednesses of workers to their tended brood. Finally, the protected invasion hypothesis explains a phenomenon that cannot be explained by kin selection theory: the surprising overwhelming preponderance of maternal over paternal care in the Hymenoptera (because male and female parents have the same mean relatedness to their offspring when the female mates singly). An important implication of the protected invasion hypothesis is that synergistic co-operation among siblings is more likely to evolve in haplodiploid than in diploid species.

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Cytological relationships between three diploid species of the fern genus Ceratopteris

Canadian Journal of Botany ◽

10.1139/b77-194 ◽

1977 ◽

Vol 55 (12) ◽

pp. 1660-1667 ◽

Cited By ~ 14

Author(s):

Leslie G. Hickok

Keyword(s):

Diploid Species ◽

Genetic Differences ◽

Individual Chromosome ◽

Structural Rearrangements ◽

Species Relationships ◽

Genomic Level ◽

Cytological Data ◽

Homosporous Fern ◽

Homosporous Ferns ◽

Chromosomal Homologies

The cytological and reproductive characteristics of synthesized hybrids involving three diploid species of the homosporous fern genus Ceratopteris Brongn. have been examined. Cytological data indicate that the three species have major chromosomal homologies but differ with respect to a few structural rearrangements involving translocations and inversions. All of the hybrids were semi-sterile but F2 generations were obtained in which moderate to full fertility was evident. No relationship was evident between the degrees of morphological similarities between the species and the degrees of cytological and genetic differences expressed in the hybrids. These factors have confused species relationships among the diploid members of the genus. The behavior of the diploid hybrids is unique among the homosporous ferns in that cytological differences between the species involve individual chromosome differences rather than differences or similarities at the genomic level.

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Substantially adaptive potential in polyploid cyprinid fishes: evidence from biogeographic, phylogenetic and genomic studies

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2019.3008 ◽

2020 ◽

Vol 287 (1920) ◽

pp. 20193008 ◽

Cited By ~ 2

Author(s):

Xinxin Li ◽

Baocheng Guo

Keyword(s):

Environmental Changes ◽

Diploid Species ◽

Diversification Rate ◽

Evolutionary Significance ◽

Mean Annual Temperature ◽

The Tibetan Plateau ◽

Polyploid Species ◽

Adaptive Potential ◽

Fish Family ◽

Dead End

Whole genome duplication (WGD) is commonly believed to play key roles in vertebrate evolution. However, nowadays polyploidy exists in a few fish, amphibian and reptile groups only, and seems to be an evolutionary dead end in vertebrates. We investigate the evolutionary significance of polyploidization in Cyprinidae—a fish family that contains more polyploid species than any other vertebrate group—with integrated biogeographic, phylogenetic and genomic analyses. First, polyploid species are found to be significantly frequent in areas of higher altitude and lower mean annual temperature compared with diploid species in Cyprinidae. Second, a polyploidy-related diversification rate shift is observed in Cyprinidae. This increased net diversification rate is only seen in three polyploid lineages, and other polyploid lineages have similar net diversification rate as well as diploid lineages in Cyprinidae. Interestingly, significant ‘lag times’ existed between polyploidization and radiation in Cyprinidae. Multiple polyploid lineages were established approximately 15 Ma through recurrent allopolyploidization events, but the net diversification rate did not start to increase until approximately 5 Ma—long after polyploidization events. Environmental changes associated with the continuous uplift of the Tibetan Plateau and climate change have probably promoted the initial establishment and subsequent radiation of polyploidy in Cyprinidae. Finally, the unique retention of duplicated genes in polyploid cyprinids adapted to harsh environments is found. Taken together, our results suggest that polyploidy in Cyprinidae is far more than an evolutionary dead end, but rather shows substantially adaptive potential. Polyploid cyprinids thus constitute an ideal model system for unveiling largely unexplored consequences of WGD in vertebrates, from genomic evolution to species diversification.

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Genome-wide sequence information reveals recurrent hybridization among diploid wheat wild relatives

10.1101/678045 ◽

2019 ◽

Author(s):

Nadine Bernhardt ◽

Jonathan Brassac ◽

Xue Dong ◽

Eva-Maria Willing ◽

C. Hart Poskar ◽

...

Keyword(s):

Incomplete Lineage Sorting ◽

Diploid Species ◽

Wild Relatives ◽

Testable Hypothesis ◽

Sequence Information ◽

Genome Wide ◽

Wheat Group ◽

Polyploid Formation ◽

Extant Species ◽

Wheat Wild Relatives

AbstractMany conflicting hypotheses regarding the relationships among crops and wild species closely related to wheat (the genera Aegilops, Amblyopyrum, and Triticum) have been postulated. The contribution of hybridization to the evolution of these taxa is intensely discussed. To determine possible causes for this, and provide a phylogeny of the diploid taxa based on genome-wide sequence information, independent data was obtained from genotyping-by-sequencing and a target-enrichment experiment that returned 244 low-copy nuclear loci. The data were analyzed with Bayesian, likelihood and coalescent-based methods. D statistics were used to test if incomplete lineage sorting alone or together with hybridization is the source for incongruent gene trees. Here we present the phylogeny of all diploid species of the wheat wild relatives. We hypothesize that most of the wheat-group species were shaped by a primordial homoploid hybrid speciation event involving the ancestral Triticum and Am. muticum lineages to form all other species but Ae. speltoides. This hybridization event was followed by multiple introgressions affecting all taxa but Triticum. Mostly progenitors of the extant species were involved in these processes, while recent interspecific gene flow seems insignificant. The composite nature of many genomes of wheat group taxa results in complicated patterns of diploid contributions when these lineages are involved in polyploid formation, which is, for example, the case in the tetra-and hexaploid wheats. Our analysis provides phylogenetic relationships and a testable hypothesis for the genome compositions in the basic evolutionary units within the wheat group of Triticeae.

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Solar Filaments as Tracers of Subsurface Processes

International Astronomical Union Colloquium ◽

10.1017/s0252921100064459 ◽

2000 ◽

Vol 179 ◽

pp. 177-183

Author(s):

D. M. Rust

Keyword(s):

Magnetic Fields ◽

Magnetic Flux ◽

Coronal Mass Ejections ◽

Interplanetary Space ◽

Intermediate Stage ◽

Coronal Plasma ◽

Magnetic Helicity ◽

The Sun ◽

New Paradigm ◽

Solar Filaments

AbstractSolar filaments are discussed in terms of two contrasting paradigms. The standard paradigm is that filaments are formed by condensation of coronal plasma into magnetic fields that are twisted or dimpled as a consequence of motions of the fields’ sources in the photosphere. According to a new paradigm, filaments form in rising, twisted flux ropes and are a necessary intermediate stage in the transfer to interplanetary space of dynamo-generated magnetic flux. It is argued that the accumulation of magnetic helicity in filaments and their coronal surroundings leads to filament eruptions and coronal mass ejections. These ejections relieve the Sun of the flux generated by the dynamo and make way for the flux of the next cycle.

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