Abstract
BackgroundUnisexuals of the blue-spotted salamander complex are thought to reproduce by kleptogenesis. Genome exchanges associated with this sperm-dependent mode of reproduction are expected to result in a higher genetic variation and multiple ploidy levels compared to clonality. However, the existence of some populations exclusively formed of genetically identical individuals suggests that factors could prevent genome exchanges. This study aimed at assessing the prevalence of genome exchange among unisexuals of the Ambystoma laterale-jeffersonianum complex from 10 sites in the northern part of their distribution.ResultsA total of 235 individuals, including 207 unisexuals, were genotyped using microsatellite loci and AFLP. Unisexual individuals could be sorted in five genetically distinct groups, likely derived from the same paternal A. jeffersonianum haplome. One of these groups exclusively reproduced clonally, even when found in sympatry with lineages presenting signature of genome exchange. Genome exchange was site-dependent for another group. Genome exchange was detected at all sites for the three remaining groups.ConclusionPrevalence of genome exchange appears to be associated with ecological conditions such as availability of effective sperm donors. Intrinsic genomic factors may also affect this process, since different lineages in sympatry present highly variable rate of genome exchange. The coexistence of clonal and genetically diversified lineages opens the door to further research on alternatives to genetic variation.
Highlights
Unisexuals of the blue-spotted salamander complex are thought to reproduce by kleptogenesis
Genetic analyses revealed a high proportion of unisexuals (n = 207, 88%) compared to A. laterale (LL), the unique contributing sexual species captured
Most of the sites included individuals of different ploidy levels, except two sites exclusively composed of diploid unisexual individuals (E01 and E02) (Fig. 1)
Summary
Unisexuals of the blue-spotted salamander complex are thought to reproduce by kleptogenesis. Genome exchanges associated with this sperm-dependent mode of reproduction are expected to result in a higher genetic variation and multiple ploidy levels compared to clonality. Most unisexual vertebrates reproduce clonally and preserve F1 heterosis acquired through interspecific hybridization. Because of their sexually-derived ancestors, these unisexual species still produce gametes. In the other two reproductive modes, females can discard a whole haploid set of chromosomes (haplome) before meiosis to produce reduced eggs that will be combined with the genome of a sexual male from a closely related species. The male haplome is always discarded and replaced de novo, while the same female genome is conserved across generations, resulting in a semi clonal reproduction, as seen in the complex of Pelophylax esculentus (formerly Rana esculenta) [7].
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