Meiosis and Its Deviations in Polyploid Animals

Abstract

We review the different modes of meiosis and its deviations encountered in polyploid animals. Bisexual reproduction involving normal meiosis occurs in some allopolyploid frogs with variable degrees of polyploidy. Aberrant modes of bisexual reproduction include gynogenesis, where a sperm stimulates the egg to develop. The sperm may enter the egg but there is no fertilization and syngamy. In hybridogenesis, a genome is eliminated to produce haploid or diploid eggs or sperm. Ploidy can be elevated by fertilization with a haploid sperm in meiotic hybridogenesis, which elevates the ploidy of hybrid offspring such that they produce diploid gametes. Polyploids are then produced in the next generation. In kleptogenesis, females acquire full or partial genomes from their partners. In pre-equalizing hybrid meiosis, one genome is transmitted in the Mendelian fashion, while the other is transmitted clonally. Parthenogenetic animals have a very wide range of mechanisms for restoring or maintaining the mother's ploidy level, including gamete duplication, terminal fusion, central fusion, fusion of the first polar nucleus with the product of the first division, and premeiotic duplication followed by a normal meiosis. In apomictic parthenogenesis, meiosis is replaced by what is effectively mitotic cell division. The above modes have different evolutionary consequences, which are discussed. See also the sister article by Grandont et al. in this themed issue.

Clonal Diversity of Otiorhynchus ligustici and O. raucus (Coleoptera, Curculionidae) in Central Ukraine

“…We suppose that two species studied are not only triploids but contain a tetraploids admixture, as was demonstrated earlier for O. scaber (Stenberg et al, 1997). At the moment, it is known that the ploidy level of the genus Otiorhynchus parthenogenetic forms varies from 2 n to 10 n (Stenberg, Saura, 2013). For this reason, the hypothesis of the presence in the population species we studied allotetraploids admixture is seemed to be quite probable.…”

Genome Architecture and Evolution of a Unichromosomal Asexual Nematode

“…Maintenance of heterozygosity during parthenogenesis can result from several types of modified meiosis: (1) pre-meiotic genome doubling where the entire genetic material from the mother along with its heterozygosity is preserved in the first meiotic division, which thus loses its reductional property; (2) central fusion, where two genetically distinct meiotic end-products fuse, forming a diploid heterozygous embryo; or (3) skipping of the first reductional division (Meiosis I), whereby the mother’s entire genetic material and its heterozygosity are also maintained [64, 65]. Complete heterozygosity is maintained unless crossing over or gene conversion occurs (in type 2 or 3) [64, 65]. …”

The parthenogenetic Marmorkrebs (Malacostraca: Decapoda: Cambaridae) is a triploid organism

“…Stöck et al. ; Stenberg and Saura ) – triploids are generally apomictic parthenogens (Saura et al. ).…”