Abstract
Micropsectra sedna (Oliver, 1976) is a parthenogenetic midge from the Canadian Arctic. The parthenogenetic mechanism is apomictic thelytoky, with a restitutional division during oogenesis, as found in other parthenogenetic Chironomidae. It is triploid, with two similar chromosome sets, and the third is relatively dissimilar, pairing little with the diploid set. Two karyotypes were observed: a single individual with eight polytene elements in the salivary glands (3n=12), considered standard, while the majority of larvae showed only seven polytene chromosomes (3n=11). Hybrid speciation is considered likely, although chromosomal recombination following the origin of thelytoky has played some part in karyotype evolution. A single morphologically distinct larva was also found, which might be the donor of the haploid chromosome set. The apomictic restitutional system is compared to that of the other, independently derived, parthenogenetic Chironomids to assess the extent of similarity between species.
Highlights
Parthenogenesis, in the forms of arrhenotoky, deuterotoky, or thelytoky, is a quite common phenomenon in the animal kingdom (Suomalainen 1962)
There is some homology between members of the haploid and diploid sets, it is impossible to trace the banding pattern of one set completely in the other, and better material would have to be used in order for this to be achieved
Two of the haploid set have a large heterochromatic block, which is postulated to be the centromere, while there is no development of heterochromatin to indicate the centromere locations in the diploid set
Summary
Parthenogenesis, in the forms of arrhenotoky, deuterotoky, or thelytoky, is a quite common phenomenon in the animal kingdom (Suomalainen 1962). Thelytoky, in which females produce exclusively female progeny in the absence of genetic fertilization, is the most widespread and most mechanistically diverse form of parthenogenesis (Hartl 1971).
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