Evolutionary mechanisms and practical significance of reproductive success and clonal diversity in unisexual vertebrate polyploids

Unisexual reproduction is generally relevant to polyploidy, and unisexual vertebrates are often considered an evolutionary “dead end” due to the accumulation of deleterious mutations and absence of genetic diversity. However, some unisexual polyploids have developed strategies to avoid genomic decay, and thus provide ideal models to unveil unexplored evolutionary mechanisms, from the reproductive success to clonal diversity creation. This article reviews the evolutionary mechanisms for overcoming meiotic barrier and generating genetic diversity in unisexual vertebrates, and summarizes recent research advancements in the polyploid Carassius complex. Gynogenetic gibel carp(Carassius gibelio) is a unique amphitriploid that has undergone a recurrent autotriploidy and has overcome the bottleneck of triploid sterility via gynogenesis. Recently, an efficient strategy in which ploidy changes, including from amphitriploid to amphitetraploid, then from amphitetraploid to novel amphitriploid, drive unisexual-sexual-unisexual reproduction transition and clonal diversity has been revealed.Based on this new discovery, multigenomic reconstruction biotechnology has been used to breed a novel strain with superior growth and stronger disease resistance. Moreover, a unique reproduction mode that combines both abilities of ameiotic oogenesis and sperm-egg fusion,termed as ameio-fusiongensis, has been discovered, and it provides an efficient approach to synthesize sterile allopolyploids. In order to avoid ecological risks upon escape and protect the sustainable property rights of the aquaculture seed industry, a controllable fertility biotechnology approach for precise breeding is being developed by integrating sterile allopolyploid synthesis and gene-editing techniques.This review provides novel insights into the origin and evolution of unisexual vertebrates and into the attempts being made to exploit new breeding biotechnologies in aquaculture.

Genetic basis and breeding application of clonal diversity and dual reproduction modes in polyploid Carassius auratus gibelio

A unisexual species is generally associated with polyploidy, and reproduced by a unisexual reproduction mode, such as gyno- genesis, hybridogenesis or parthenogenesis. Compared with other unisexual and polyploid species, gibel carp (Carassius au- ratus gibelio) has a higher ploidy level of hexaploid. It has undergone several successive rounds of genome polyploidy, and experienced an additional, more recent genome duplication event. More significantly, the dual reproduction modes, including gynogenesis and sexual reproduction, have been demonstrated to coexist in the polyploid gibel carp. This article reviews the genetic basis concerning polyploidy origin, clonal diversity and dual reproduction modes, and outlines the progress in new va- riety breeding and gene identification involved in the reproduction and early development. The data suggests that gibel carp are under an evolutionary trajectory of diploidization. As a novel evolutionary developmental (Evo-Devo) biology model, this work highlights future perspectives about the functional divergence of duplicated genes and the sexual origin of vertebrate animals.

Genetic Variation and Clonal Diversity of the Two Divergent Types of Clonal Populations of Leymus chinensis Tzvel on the Song Liao Steppe in the West of Northeastern China

: The genetic variation and clonal diversity of two divergent types (grey-green and yellow-green) of clonal populations of Leymus chinensis Tzvel at 14 loci were compared. Total gene diversity (HT) and the coefficient of genetic differentiation (GST) were all higher for the yellow-green type (HT=0.270; GST= 0.186) than for the grey-green type (HT= 0.250; GST= 0.157) of L. chinensis. Rare alleles usually occurred as heterozygotes rather than homozygotes and significant deviations from Hardy-Weinberg equilibrium were found only at a few loci. This indicated that these two types of populations were mainly out-crossing. Clonal diversity, evenness of clones, and mean clone size were not significantly different between the two types. We found that differences between the clone size and genetic variation of the yellow-green type of populations occurred with different climate and habitat population groups. However, for the grey-green type of populations, these genetic variations decreased under conditions of different climate and habitat population groups.

Effects of hydrological connection and human disturbance on genetic variation of submerged Vallisneria natans populations in four lakes in China

With the increase in the need for flood prevention and lake resource used by humans,the construction of floodgates and sluices has changed the hydrological connection between rivers and lakes,and between adjacent lakes.In river-disconnected lakes,exploitation and use of lake resources have resulted in water quality decline and mechanical disturbance intensification to a different degree.Of the large number of river-disconnected lakes in the middle-lower reaches of the Changjiang(Yangtze)River,the Futou Lake,and the Xiliang Lake lie close together and are,historically,directly connected,and so do Liangzi Lake and Baoan Lake.The extent of human disturbance is severe in the Futou Lake and the Baoan Lake,but relatively mild in the Xiliang Lake and Liangzi Lake.The freshwater rosette-forming submerged plant Vallisneria natans is one of the dominant species in the four lakes.Using microsatellite markers,we studied the genetic variation of V.natans subpopulations in lakes with different intensities of human disturbance and historical direct hydrological connections.Our results showed that human disturbance decreased plant density and clonal growth in V.natans,but might increase genetic and clonal diversity at a subpopulation level and enhance gene flow among subpopulations by sexual propagule movement.Under similar climatic conditions,different intensities of disturbance seem to have such a high selective potential to differentiate genetically adjacent lake populations that they outperform the forces of gene flow through historical direct hydrological interconnection,which tends to produce genetic homogeneity.Our findings imply that human disturbance has a profound eff ect on the evolutionary process of natural populations of submerged plants.Moreover,increased subpopulation genetic diversity can enhance resistance and resilience to environmental disturbances.To a certain degree,we could expect that disturbed populations have the possibility of restoring spontaneously if humans cease to perturb natural ecosystems in the future.

Local-scale patterns of genetic variation in coexisting floating-leaved Nymphoides peltata and submerged Myriophyllum spicatum in Donghu Lake

Coexisting floating-leaved and submerged plants experience similar environmental changes but may evolve different patterns of genetic variation.To compare local-scale genetic variation,we collected samples of floating-leaved Nymphoides peltata and submerged Myriophyllum spicatum coexisting in a disturbed urban lake in China.At the subpopulation level,using microsatellites,M.spicatum had higher clonal diversity than N.peltata.M.spicatum had 28.4%multilocus genotypes(MLGs)shared between subpopulations,but N.peltata had only one MLG shared between two adjacent subpopulations.N.peltata displayed more genetic variation between subpopulations than within subpopulations,but the reverse was true for M.spicatum.Principal components and Bayesian cluster analyses showed that individuals from each subpopulation of N.peltata tended to have relatively close genetic relationships.For M.spicatum,individuals from each subpopulation were genetically scattered with those from other subpopulations.Our results imply that in unpredictable adverse environments M.spicatum may be less subjected to local-deme extinction than N.peltata because of genetically diverse clones at the subpopulation level.This characteristic means that following adverse events,M.spicatum may rapidly restore subpopulation distributions via recolonization and intense gene flow among subpopulations.

Mixed reproduction strategy and polyploidy facilitate dominance of Kobresia pygmaea on the Tibetan Plateau

Aims The sedge Kobresia pygmaea is the dominant species of high-altitude pastures in Tibet,and it is the most important source of forage in animal husbandry.We present the first comprehensive reproduction study for this perennial key species that adopts a molecular approach and tests how sexual and vegetative reproduction,as well as ploidy,relate to survival and dominance under harsh conditions.Methods We assessed inflorescence numbers of K.pygmaea across two Tibetan alpine pastures with differing grazing regimes.Germination was tested in untreated diaspores and then following mechanical and chemical scarification.In a 4-year experiment,we assessed diaspore viability and seed bank formation.Using eight microsatellite markers,we recorded multilocus genotypes in hierarchical grids and measured their ploidy using flow cytometry.Adjusted analysis of variance models were used to analyse data on sexual reproduction,while the complement of the Simpson index and the Shannon diversity index were used to characterize the spatial distribution of multilocus genotypes and clonal richness.Important Findings Inflorescence production was high and differed significantly between years(2010:617±460 SD;2012:2015±1213 SD)but not between grazing regimes.Diaspore viability was high(94%)and gradually decreased after 3 and 4 years of storage in the soil.Diaspores not exposed to further scarification failed to germinate,while mechanical and chemical(H2SO4)scarification increased germination to 9 and 44%,respectively.Clonal diversity was high,although in situ germination was rarely observed.Multilocus genotypes intersected and covered a mean area of 0.74 m2.Most individuals were found to be tetraploid,with only 0.8%of all ramets being triploid.We conclude that K.pygmaea survives on the Tibetan Plateau by employing a mixed reproduction strategy involving both sexual and clonal propagation.The species’adaptability and dominance is further facilitated by its polyploidy.As pasture restoration using diaspores would be difficult,existing Kobresia pasture should be managed more sustainably.