When Polyploidy is Going to Sleep: Tempo and Modes of Karyotype evolution in Holocentrics
| Authors | |
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| Year of publication | 2012 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | In contrast to monocentric chromosomes with a single kinetochore, holocentric chromosomes attach spindle microtubules to kinetochores that cover most of their poleward surfaces. While in monocentrics, polyploidy can be easily detected based on periodicity of chromosome number, in holocentrics, it can be masked by chromosomal fusion/fission, which are considered the key mechanisms of karyotype evolution in holocentric taxa. Even if chromosome counting is combined with the measurement of DNA amount generally used for polyploidy detection is also not sufficient if repetitive DNA proliferation/removal acts in genome size evolution as was detected in some holocentrics. The role of polyploidy remains therefore unrecognized in holocentrics. To solve this problem we designed a model, which identifies four possible mechanisms of karyotype evolution in holocentrics (aneuploidy, polyploidy, fusion/fission and repetitive DNA proliferation/removal). For a given phylogeny and corresponding data for genome size and chromosome numbers, the algorithm (1) determines a mechanism (combination of mechanisms) for each branch, (2) estimates ancestral node states, and (3) quantifies (in pg or chromosome number) the role of particular mechanisms at each branch or whole tree. (4) The rate of particular mechanism can be estimated based on branch or tree length and proportions of mechanisms in karyotype evolution of a given phylogeny (genus, family, ...). Using a proposed model we analyzed 105 and 14 species of holocentric genera Carex and Eleocharis (Cyperaceae), respectively. While in Eleocharis, polyploidy is dominant mechanism driving 72 % of evolution in genome size, in Carex, the repetitive DNA proliferation/removal plays a key role (75 %). In Eleocharis the rate of aneuploidy is 67x higher, repetitive DNA proliferation/removal 14x higher and polyploidy 351x higher than in Carex. |
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