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Origins of asexuality in Bryobia mites (Acari: Tetranychidae).

ABSTRACT: BACKGROUND: Obligate asexual reproduction is rare in the animal kingdom. Generally, asexuals are considered evolutionary dead ends that are unable to radiate. The phytophagous mite genus Bryobia contains a large number of asexual species. In this study, we investigate the origin and evolution of asexuality using samples from 111 populations in Europe, South Africa and the United States, belonging to eleven Bryobia species. We also examine intraspecific clonal diversity for one species, B. kissophila, by genotyping individuals from 61 different populations. Knowledge on the origin of asexuality and on clonal diversity can contribute to our understanding of the paradox of sex. RESULTS: The majority (94%) of 111 sampled populations reproduces asexually. Analysis of part of nuclear 28S rDNA shows that these asexuals do not form a monophyletic clade. Analysis of the mitochondrial COI region shows that intraspecific variation is extensive (up to 8.8%). Within B. kissophila, distinct clades are found, which are absent at the nuclear 28S rDNA level. Moreover, paraphyletic patterns are found at the mitochondrial DNA. CONCLUSION: Asexuality is widespread in the genus Bryobia, signifying that some animal taxa do contain a high number of asexuals. We argue that asexuality originated multiple times within Bryobia. Wolbachia bacteria cause asexuality in at least two Bryobia species and may have infected different species independently. The high intraspecific clonal diversity and the patterns of paraphyly at the mitochondrial DNA in B. kissophila might be explained by a high mutation fixation rate and past hybridization events. Reproductive parasites like Wolbachia and Cardinium might influence these processes. We discuss the role these bacteria could play in the evolutionary success of asexual species.

SUBMITTER: Ros VI

PROVIDER: S-EPMC2426695 | biostudies-literature | 2008

REPOSITORIES: biostudies-literature

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Origins of asexuality in Bryobia mites (Acari: Tetranychidae).

Ros Vera I D VI Breeuwer Johannes A J JA Menken Steph B J SB

BMC evolutionary biology 20080519

<h4>Background</h4>Obligate asexual reproduction is rare in the animal kingdom. Generally, asexuals are considered evolutionary dead ends that are unable to radiate. The phytophagous mite genus Bryobia contains a large number of asexual species. In this study, we investigate the origin and evolution of asexuality using samples from 111 populations in Europe, South Africa and the United States, belonging to eleven Bryobia species. We also examine intraspecific clonal diversity for one species, B. ...[more]

PMID: 18489749

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Project description:BackgroundBy segregating somatic and germinal functions into large, compound macronuclei and small diploid micronuclei, respectively, ciliates can explore sexuality in ways other eukaryotes cannot. Sex, for instance, is not for reproduction but for nuclear replacement in the two cells temporarily joined in conjugation. With equal contributions from both conjugants, there is no cost of sex which theory predicts should favor asexuality. Yet ciliate asexuality is rare. The exceptional Tetrahymena has abandoned sex through loss of the micronucleus; its amicronucleates are abundant in nature where they reproduce by binary fission but never form conjugating pairs. A possible reason for their abundance is that the Tetrahymena macronucleus does not accumulate mutations as proposed by Muller's ratchet. As such, Tetrahymena amicronucleates have the potential to be very old. This study used cytochrome oxidase-1 barcodes to determine the phylogenetic origin and relative age of amicronucleates isolated from nature.ResultsAmicronucleates constituted 25% of Tetrahymena-like wild isolates. Of the 244 amicronucleates examined for cox1 barcodes, 237 belonged to Tetrahymena, seven to other genera. Sixty percent originated from 12 named species or barcoded strains, including the model Tetrahymena thermophila, while the remaining 40% represent 19 putative new species, eight of which have micronucleate counterparts and 11 of which are known only as amicronucleates. In some instances, cox1 haplotypes were shared among micronucleate and amicronucleates collected from the same source. Phylogenetic analysis showed that most amicronucleates belong to the "borealis" clade in which mating type is determined by gene rearrangement. Some amicronucleate species were clustered on the SSU phylogenetic tree and had longer branch lengths, indicating more ancient origin.ConclusionsNaturally occurring Tetrahymena amicronucleates have multiple origins, arising from numerous species. Likely many more new species remain to be discovered. Shared haplotypes indicate that some are of contemporary origin, while phylogeny indicates that others may be millions of years old. The apparent success of amicronucleate Tetrahymena may be because macronuclear assortment and recombination allow them to avoid Muller's ratchet, incorporate beneficial mutations, and evolve independently of sex. The inability of amicronucleates to mate may be the result of error(s) in mating type gene rearrangement.

Dataset Information

Origins of asexuality in Bryobia mites (Acari: Tetranychidae).

Publications

Origins of asexuality in Bryobia mites (Acari: Tetranychidae).

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