Integration of a B chromosome into the A genome of a wasp, revisited

Abstract

A previous study showed that in the haplodiploid solitary wasp Trypoxylon albitarse, most individuals carry one B chromosome per haploid genome, the same dosage as the standard (A) chromosomes, indicating a possible regularization of B-chromosome meiotic behaviour and its integration into the A genome. In a new sampling, we have analysed 15 populations (including 9 out of the 10 previously analysed) to test the evolution of this integration process. The new results provide a direct report of the invasion process in the Porto Firme population, where B frequency has dramatically increased in only four generations. In the populations from the Viçosa region, however, B frequency has remained stable, although the principal B type, the metacentric one, has increased in frequency at the expense of the acrocentric one in several populations. The implications of these new results on the hypothesis of the integration of these B chromosomes, as regular members of the A genome, are discussed.

B-chromosome frequency stability in Prochilodus lineatus (Characiformes, Prochilodontidae)

“…In the grasshopper Eyprepocnemis plorans, the parasitic B 24 variant invaded the Torrox (Málaga, Spain) population replacing the neutralized B 2 (Zurita et al 1998), and the B 1 variant invaded the Pollensa (Mallorca, Spain) population increasing very much in frequency in only 10 years (Riera et al 2004). Likewise, in the wasp Trypoxylon albitarse, B-chromosome frequency increased from 0.133 to 0.962 in the Nova Ilha population (Porto Firme, Brazil) between 1997and 1999(Araújo et al 2002.…”

B Chromosomes and Sex in Animals

“…The observation of the rapid invasion of this B chromosome in a natural population led Araújo et al [2002] to postulate that drive is necessary for initial invasion by this B chromosome, but it is directly suppressed by the B tendency to pair and segregate in 2B females. Differently to other B chromosome systems, host-mediated suppression of the B-drive Brett, 1985, 1987;Shaw and Hewitt, 1985;Herrera et al, 1996;Camacho et al, 1997] is not necessary in this case because, as argued by Araújo et al [2002] and Rocha-Sanchez and Pompolo [2004], it is performed by the parasite itself through its tendency to pair during female meiosis.…”

The U2 snDNA Is a Useful Marker for B Chromosome Detection and Frequency Estimation in the Grasshopper <b><i>Abracris flavolineata</i></b>

“…These data also indicate that there is no sex-specific mechanism for B accumulation in A. flavolineata . The fluctuation of B chromosome frequency in natural populations throughout the years was studied in a few species, i.e., in the grasshoppers E. plorans [Camacho et al, 2015], Myrmeleotettix maculatus [Shaw, 1983], and Acrida lata [Kayano et al, 1970], in the fish Prochilodus lineatus [Cavallaro et al, 2000], and the wasp Trypoxylon albirtase [Araújo et al, 2002]. In some species, the frequency remained constant throughout the years, while in other ones this frequency rapidly was changed, as in P. lineatus and T. albirtase caused by accumulation mechanisms or advantage for host.…”