Origin of Polyploidy in Parthenogenetic Weevils

Saura, Anssi; Lokki, Juhani; Suomalainen, Esko

doi:10.1006/jtbi.1993.1130

Cited by 60 publications

(77 citation statements)

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“…This is consistent with findings on invertebrate unisexuals of hybrid origin, most of which are polyploids thought to form via backcrossing of F 1 hybrids with one of the parentals (Suomalainen et al 1987;Saura et al 1993;Simon et al 2003). Unisexual Calligrapha furthermore exhibit a form of chromosomal heteromorphy in which one set of chromosomes appears to differ structurally from the other three.…”

Section: Figsupporting

confidence: 89%

“…If asymmetric hybridization is followed by the backcrossing of hybrid offspring with the paternal species, all mtDNA in the resulting progeny will be from the original maternal species whereas the majority of nuclear alleles will be of paternal origin (Harrison et al 1987;Aubert and Solignac 1990;Saura et al 1993;Normark and Lanteri 1998). This scenario might explain the incongruence between mitochondrial and both nuclear loci in Calligrapha.…”

Section: Figmentioning

confidence: 99%

“…A related scenario has been specifically hypothesized for Otiorhynchus weevils. In this scenario, diploid unisexuality evolves from diploid bisexuality, and triploid and tetraploid unisexual forms arise from subsequent additions of haploid genomes (Saura et al 1993;Normark and Lanteri 1998). Because there is no evidence for extant diploid or triploid Calligrapha unisexuals, the intermediates would seem to have a brief existence if the above scenario holds.…”

Section: Figmentioning

confidence: 99%

“…Because there is no evidence for extant diploid or triploid Calligrapha unisexuals, the intermediates would seem to have a brief existence if the above scenario holds. However, intermediate ploidy levels are not a necessary precursor to tetraploidy if unreduced gametes are contributed during any interspecific crosses or backcrosses (Saura et al 1993). These mechanisms of unisexual polyploid origins are diagrammed in Figure 5.…”

Section: Figmentioning

confidence: 99%

“…5. Schematic representation of a scenario describing the origins of polyploid apomixis in Calligrapha (adapted from Saura et al 1993). This scenario is consistent with cytogenetic, molecular, and phenotypic findings described in this and previous studies.…”

Section: Identifying Parental Speciesmentioning

confidence: 99%

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The Evolution of Unisexuality in Calligrapha Leaf Beetles: Molecular and Ecological Insights on Multiple Origins via Interspecific Hybridization

2006

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Abstract. Interspecific hybridization is a well-established cause of unisexual origins in vertebrates. This mechanism is also suspected in other apomictic taxa, but compelling evidence is rare. Here, we evaluate this mechanism and other hypotheses for the evolutionary origins of unisexuality through an investigation of Calligrapha leaf beetles. This group provides an intriguing subject for studies of unisexual evolution because it presents a rare insect example of multiple apomictic thelytokous species within a primarily bisexual genus. To investigate unisexual evolution, this study conducts the first molecular systematic analysis of Calligrapha. This involved the collection and analysis of about 3000 bp of DNA sequences-representing RNA and protein-coding loci from mitochondrial and nuclear genomes-from 54 specimens of 25 Calligrapha species, including four unisexual tetraploid taxa. Phylogenetic and molecular clock analyses indicated independent and single evolutionary origins of each of these unisexual species during the Pleistocene. Significant phylogenetic incongruence was detected between mitochondrial and nuclear datasets and found to be especially associated with the asexual taxa. This pattern is expected when unisexual lineages arise via interspecific hybridization and thus represent genetic mosaics that possess certain nuclear alleles from the paternal species lineage and mitochondrial DNA (mtDNA) alleles from the maternal parent. Analyzing the mtDNA and nuclear relatedness of unisexuals with corresponding haplotypes of bisexual Calligrapha species allowed the putative identification of these maternal and paternal species lineages for each unisexual species. Strong phenotypic similarities between unisexual taxa and their paternal parent species supported a model that involves both backcrosses of interspecific hybrids with a paternal parent and unreduced gametes. This model accounts for the origins of apomixis, polyploidy, and an overrepresentation of paternal nuclear alleles (and associated phenotypes) in unisexuals. This model is also consistent with the tetraploid karyotypes of unisexual Calligrapha, in which three sets of chromosomes (of presumed paternal ancestry) are quite morphologically homogeneous compared to the fourth. Especially intriguing was a consistent association of unisexual species with the host plant of the paternal parent but never with the maternal host. The statistical implausibility of these patterns occurring by chance further supports our inference of parental species. Moreover, it points to a potentially critical role for host-association in the formation and preservation of unisexual lineages. These findings suggest that ecological factors are critical for the diversification of unisexual as well as bisexual taxa and thus point out new research directions in the area of ecological speciation.

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Section: Figsupporting

confidence: 89%

Section: Figmentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

Section: Identifying Parental Speciesmentioning

confidence: 99%

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The Evolution of Unisexuality in Calligrapha Leaf Beetles: Molecular and Ecological Insights on Multiple Origins via Interspecific Hybridization

2006

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When it only takes one to tango: assessing the impact of apomixis in the fern genus Pteris

Picard

Ranft

Grusz

et al. 2021

American J of Botany

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Premise Apomixis (asexual reproduction by seed, spore, or egg) has evolved repeatedly across the tree of life. Studies of animals and angiosperms show that apomictic lineages are often evolutionarily short‐lived and frequently exhibit different distributions than their sexual relatives. However, apomixis is rare in these groups. Less is known about the role of apomixis in the evolution and biogeography of ferns, in which ~10% of species are apomictic. Apomixis is especially common in the fern genus Pteris (34–39% of species); however, because of the limited taxonomic and geographic sampling of previous studies, the true frequency of apomixis and its associations with geography and phylogeny in this lineage remain unclear. Methods We used spore analyses of herbarium specimens to determine reproductive mode for 127 previously unsampled Pteris species. Then we leveraged biogeographic and phylogenetic analyses to estimate the global distribution and evolution of apomixis in Pteris. Results Among all Pteris species examined, we found that 21% are exclusively apomictic, 71% are exclusively sexual, and 8% have conflicting reports. Apomixis is unevenly distributed across the range of the genus, with the Paleotropics exhibiting the highest frequency, and has evolved numerous times across the Pteris phylogeny, with predominantly East Asian and South Asian clades containing the most apomictic species. Conclusions Apomixis arises frequently in Pteris, but apomictic species do not appear to diversify. Species that encompass both apomictic and sexual populations have wider ranges than exclusively sexual or apomictic species, which suggests that sexual and apomictic ferns could occupy separate ecological niches.

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