Neutral markers confirm the octoploid origin and reveal spontaneous autopolyploidy in white sturgeon, Acipenser transmontanus

Abstract

SummaryThe role of polyploidy in vertebrate genome evolution remains a fertile area of research and sturgeons (order Acipenseriformes) provide a unique model of genome duplication, with species possessing 120, 250 or 360 chromosomes. Cytogenetic and molecular data have been used to support different hypotheses about the number of genome duplications in this polyploid series; however, few studies have examined inheritance in sturgeons, although evaluation of polysomic segregation ratios is crucial to inferring ancestral genome duplication level in a polyploid species. Here we examine the inheritance of eight microsatellite loci in fifteen white sturgeon (Acipenser transmontanus) families of known parentage to infer the level of genome duplication. Microsatellites were detected as four or eight copy loci. Numbers of alleles per locus, transmission frequencies of informative alleles, and gene copy numbers in parents reveal an ancient octoploid origin for white sturgeon.Comparison to the lake sturgeon genome suggests the 250 chromosome state in sturgeon was achieved by multiple independent polyploid events. The discovery of spontaneous autopolyploids via microsatellite analysis and flow cytometry provides additional evidence of the plasticity of highly duplicated sturgeon genomes.

Sturgeon conservation genomics: SNP discovery and validation using RAD sequencing

“…This high chromosome number is the result of two whole genome duplication (WGD) events, and for this reason, these species are considered to be evolutionary octoploid by some authors (Vasil'ev ; Drauch Schreier et al . ). However, between the two WGD events, a functional rediploidization took place, and these species should be better considered as functionally tetraploid (Fontana et al .…”

Resolving microsatellite genotype ambiguity in populations of allopolyploid and diploidized autopolyploid organisms using negative correlations between allelic variables

“…Using a real microsatellite dataset from natural populations of white sturgeon, we found that our method was useful for recoding over half of the markers into two independently segregating isoloci each. Given that white sturgeon are octoploid with two tetrasomic subgenomes (Drauch Schreier et al , 2011), we expected this dataset to be problematic; having tetrasomic isoloci as opposed to disomic isoloci would reduce the magnitude of the negative correlations between allelic variables, and was observed in simulations to reduce the accuracy of assignment using our method, although not nearly as severly as the reduction in efficacy of the Catalán et al (2006) method (Supplementary Table 1, Fig. 3).…”

“…To demonstrate the usefulness of our allele assignment method on a real dataset, we used previously published data from natural populations of octoploid white sturgeon ( Acipenser transmontanus ) [Drauch Schreier et al, 2012]. Previous studies of inheritance patterns in this species suggested that it possesses two tetrasomic subgenomes, at least for portions of its genome [Rodzen and May, 2002, Drauch Schreier et al, 2011]. We selected for analysis the eight microsatellite markers that, based on number of alleles per genotype, appeared to be present in eight copies rather than four.…”

A review of genetic evaluation tools for conservation and management of North American sturgeons: roles, benefits, and limitations

“…Some have argued that the 120 chromosome species should be considered diploid as their genomes have been largely diploidized (Fontana, 1994), which would lead to the designation of 250 and 360 chromosome species as tetraploid and hexaploid. However, the presence of microsatellite markers in ≥8 copies in the 250 chromosome white sturgeon suggests their classification should be octoploid rather than tetraploid (Drauch Schreier et al., 2011c). As a result of their largely diploidized genomes, species such as Atlantic sturgeon ( Acipenser oxyrinchus ), shovelnose sturgeon, ( Scaphirhynchus platorynchus ) and pallid sturgeon ( Scaphirhynchus albus ) possess most microsatellite markers in two copies, which allows for estimation of traditional population genetic metrics such as heterozygosity, F IS , F ST , and N e .…”

“…In the case of lake sturgeon and green sturgeon, many two‐copy markers have been developed, allowing traditional population genetic metrics to be used (Israel et al., 2004; Welsh et al., 2008, 2010). However, the 250 chromosome white sturgeon possesses most of its microsatellites in four or eight copies (Drauch Schreier et al., 2011c). Nonetheless, a number of microsatellite markers have been developed for white sturgeon (Rodzen and May, 2002; Börk et al., 2008).…”