The effect of ploidy level on fitness in parthenogenetic flatworms

D’Souza, Thomas G.; Storhas, Martin; Michiels, Nico K.

doi:10.1111/j.1095-8312.2005.00543.x

Cited by 8 publications

(22 citation statements)

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“…In S. polychroa, it has been observed that reciprocal transitions between triploid and tetraploid pseudogamic populations were occasionally caused by genome gain of paternal chromosomes derived from haploid sperm (D'Souza et al 2004(D'Souza et al , 2005(D'Souza et al , 2006. This phenomenon was referred to as "occasional sex".…”

Section: Discussionmentioning

confidence: 99%

Production of diploid and triploid offspring by inbreeding of the triploid planarian Dugesia ryukyuensis

et al. 2008

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Triploidy has generally been considered to be an evolutionary dead end due to problems of chromosomal pairing and segregation during meiosis. Thus, the formation of tetraploids and diploids from triploid types is a rare phenomenon. In the present study, we demonstrated that inbreeding of the triploid planarian Dugesia ryukyuensis resulted in both diploid and triploid offspring in nature. In the triploids of D. ryukyuensis, chiasmata between homologous chromosomes were observed in both female and male germ lines. This result suggests that both diploid and triploid offspring of this species are produced bisexually by zygotic fusion between sperm and eggs. Hence, this phenomenon may be a novel mechanism in planarian for escaping the triploid state.

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Section: Discussionmentioning

confidence: 99%

Production of diploid and triploid offspring by inbreeding of the triploid planarian Dugesia ryukyuensis

et al. 2008

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“…It has been repeatedly suggested that for a colonization of extreme environments, rapid changes of the organization of the genome such as polyploidization are adaptive and more important than the slower processes of mutation and recombination (Stebbins 1971). Polyploidization may increase fitness due to higher genetic flexibility, pre-adaptation, neo-functionalization, and sophisticated modifications in epigenetic regulation of gene expression (Bierzychudek 1985 of mechanistic explanations for this increased fitness have been suggested, such as increased heterozygosity, higher selfing rates (Soltis and Soltis 2000), gene dosage effects (Durka 2002), heterosis (Grant 1971), bigger cells (Stebbins 1971;Comai 2005), a higher intrinsic growth rate, and a higher rate of gene expression (Stebbins 1971;D'Souza et al 2005). The increased fitness also facilitates invasion of new habitats (Kearney 2005) and thereby causes range expansions (Hijmans et al 2007).…”

Section: Discussionmentioning

confidence: 99%

“…Environmental conditions at high latitudes (and elevations) may therefore repeatedly induce the formation of polyploids (Ramsey and Schemske 1998;Hijmans et al 2007;te Beest et al 2011). Furthermore, neopolyploids suffer from high genomic instabilities (Comai 2005;D'Souza et al 2005); thus, diploidization and genome downsizing enhance stability and reduce biochemical costs (Leitch and Bennett 2004;Comai 2005;Mr az et al 2009). As a result of the elimination of single chromosomes, the frequency of aneuploidy and of the CV of a population increases.…”

Section: Discussionmentioning

confidence: 99%

“…2 Another hypothesis is based on the observation that at higher latitudes parthenogenetic reproduction is more common than sexual reproduction ("geographic parthenogenesis, " Vandel 1928). In addition, parthenogenetic species or populations often show higher levels of ploidy than species or populations with sexual reproduction (e.g., Bierzychudek 1985;Suomalainen et al 1987;Turgeon and Hebert 1994;Beukeboom et al 1998;Durka 2002;Comai 2005;D'Souza et al 2005;Kearney 2005;Adolfsson et al 2010;D'Souza and Michiels 2010). Although counterexamples exist (e.g., Salmonidae, Philipps and R ab 2001;Acipenseriformes, Birstein and Vasiliev 1987), exceedingly high or uneven numbers of chromosomes tend to impair sexual reproduction (Adolfsson et al 2010).…”

Section: Introductionmentioning

confidence: 99%

“…This may allow some polyploids to be successful in fluctuating environments and predicts an increase of the variability of chromosome numbers within individuals or among individuals within populations with harsh and more variable conditions. In freshwater flatworms (Platyhelminthes), chromosome numbers and levels of ploidy vary considerably across species, populations within species, individuals within populations (D'Souza et al 2005), and even within individuals (Dahm 1958). Some Tricladida such as Polycelis nigra have B chromosomes and/or an extra A chromo-some (aneuploidy; Beukeboom et al 1998).…”

Section: Introductionmentioning

confidence: 99%

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Chromosome numbers in three species groups of freshwater flatworms increase with increasing latitude

Lorch

Zeuss

Brandl

et al. 2016

Ecology and Evolution

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Polyploidy in combination with parthenogenesis offers advantages for plasticity and the evolution of a broad ecological tolerance of species. Therefore, a positive correlation between the level of ploidy and increasing latitude as a surrogate for environmental harshness has been suggested. Such a positive correlation is well documented for plants, but examples for animals are still rare. Species of flatworms (Platyhelminthes) are widely distributed, show a remarkably wide range of chromosome numbers, and offer therefore good model systems to study the geographical distribution of chromosome numbers. We analyzed published data on counts of chromosome numbers and geographical information of three flatworm “species” (Phagocata vitta, Polycelis felina and Crenobia alpina) sampled across Europe (220 populations). We used the mean chromosome number across individuals of a population as a proxy for the level of ploidy within populations, and we tested for relationships of this variable with latitude, mode of reproduction (sexual, asexual or both) and environmental variables (annual mean temperature, mean diurnal temperature range, mean precipitation and net primary production). The mean chromosome numbers of all three species increased with latitude and decreased with mean annual temperature. For two species, chromosome number also decreased with mean precipitation and net primary production. Furthermore, high chromosome numbers within species were accompanied with a loss of sexual reproduction. The variation of chromosome numbers within individuals of two of the three species increased with latitude. Our results support the hypothesis that polyploid lineages are able to cope with harsh climatic conditions at high latitudes. Furthermore, we propose that asexual reproduction in populations with high levels of polyploidization stabilizes hybridization events. Chromosomal irregularities within individuals tend to become more frequent at the extreme environments of high latitudes, presumably because of mitotic errors and downsizing of the genome.

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Polyploidy Is Genetic Hence May Cause Non‐Adaptive Radiations, Whereas Pseudopolyploidy Is Genomic Hence May Cause Adaptive Non‐Radiations

Gorelick

Olson

2013

J Exp Zool Pt B

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There are two ways eukaryotes double number of chromosomes: (1) whole genome duplication (polyploidy), in which all nuclear DNA is replicated, and (2) karyotypic fission (pseudopolyploidy), in which all chromosomes are physically bifurcated. We contrast polyploidy with pseudopolyploidy, highlighting when it is crucial to look at genetic vs. genomic levels. We review history of pseudopolyploidy, including recent mechanisms by which chromosomal bifurcation may occur and outline methods for detecting such genomic changes. We then delve into the evolutionary implications, with particular focus on adaptive potential, of these two forms of doubling chromosome numbers. We address the common assertion that polyploidy induces adaptive radiations, which contains three fallacies. First, while polyploidy causes quantum speciation, evolutionary theory implies that these radiations should be non-adaptive. Polyploidy causes reproductive isolation, minute effective population sizes, and increased mutation rates, which all imply a diminished role for selection. Second, due to lack of karyotyping in recent decades and lack of distinction between genomic and genetic effects, it is usually impossible to detect pseudopolyploids. Third, pseudopolyploids lack minority cytotype exclusion because they readily backcross with their progenitors, which thereby means no reproductive isolation for newly formed pseudopolyploids. Pseudopolyploidy will thereby not result in radiations until pseudopolyploid descendants undergo subsequent chromosome rearrangements or grow new centromeres. Pseudopolyploids may have a modest selective advantage over their progenitors due to diminished linkage disequilibrium. Thus, pseudopolyploidy may induce adaptive non-radiations. We encourage a renaissance of karyotyping to distinguish between these two mechanisms and a renaissance in genomic perspectives in evolution.

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The effect of ploidy level on fitness in parthenogenetic flatworms

Abstract: We apologize for this error. REFERENCE D'Souza TG, Storhas M, Michiels NK. 2005. The effect of ploidy level on fitness in parthenogenetic flatworms. Biological Journal of the Linnean Society 85: 191-198.

Cited by 8 publications

References 2 publications

Production of diploid and triploid offspring by inbreeding of the triploid planarian Dugesia ryukyuensis

Production of diploid and triploid offspring by inbreeding of the triploid planarian Dugesia ryukyuensis

Chromosome numbers in three species groups of freshwater flatworms increase with increasing latitude

Polyploidy Is Genetic Hence May Cause Non‐Adaptive Radiations, Whereas Pseudopolyploidy Is Genomic Hence May Cause Adaptive Non‐Radiations

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