Abstract
For studying meiosis in males, large samples of Cacopsylla myrtilli (Wagner, 1947) (Hemiptera, Psyllidae) were collected in Norway, Sweden, Finland and northwest Russia. In addition to all-female populations, males were present in 10 out of 47 populations; still, all populations were highly female-biased, the proportion of males varying from 0.1% to 9.1%. These males are thus rare or so-called spanandric males. Males in northern Norway, Finland and northwest Russia showed normal chiasmate meiosis, while complete absence of chiasmata due to asynapsis was found in males collected in Norway and northern Sweden. In asynaptic meiosis, all univalent chromosomes divided during the first meiotic division resulting in incomplete second meiotic division and formation of diploid sperms. Hence, males in these populations are nonfunctional and do not contribute to the genetic constitution of the population, but appear in every generation as reversals from apomictic parthenogenesis and the mode of parthenogenesis is of obligatory type.
Highlights
For bisexual reproduction it is essential that the diploid chromosome complement is reduced to haploid during gametogenesis
In the present study we have established that none of the male-carrying populations in Norway, northern Sweden, Finland and northwest Russia were genuinely bisexual, but all were parthenogenetic with highly female-biased sex ratio
Males appear in every generation as reversals from apomictic parthenogenesis and reproduction in the populations is of obligatory parthenogenetic type
Summary
For bisexual reproduction it is essential that the diploid chromosome complement is reduced to haploid during gametogenesis. This is achieved by a specialized cell cycle, meiosis, where the chromosome number of germ line cells is reduced during two rounds of cell divisions after just one round of chromosome replication. In achiasmate meiosis, pairing, alignment and synapsis are normal, but no chiasmata are formed. In these cases, the paired condition of homologs is retained till the onset of anaphase I (for references see Nokkala and Nokkala 1983, Nokkala 1987, Grozeva et al 2010)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have