Trends of Karyotype Evolution in Neotropical Oedionychina (Coleoptera: Chrysomelidae: Alticinae)

Abstract

Although the cytology of the Oedionychina flea beetles is unorthodox in many ways, their karyotypes are conservative in chromosome number and sex chromosome system: typically 2n = 22(X, y); 10 + X + y. Differences between karyotypes are expressed mainly in arm length ratios. This study describes instances where this conservatism is broken and new karyotypes have emerged or seem to be emerging. The cases include distance sex multivalents up to 7x + Y (Asphaera spp. and Aspicela scutata), a full series of autosomal centric fusions: 5 + X + y (Alagoasa equestris), up to 17 B chromosomes (“Al. transparent” and Al. oblecta), and erosion of achiasmate arms (Al. januaria).

Comparative Cytogenetics of <b><i>Omophoita abbreviata</i></b> and <b><i>O. aequinoctialis </i></b>(Coleoptera, Chrysomelidae, Alticini) from the Adolpho Ducke Forest Reserve in Brazilian Amazonia: Intrapopulation Variation in Karyotypes

“…B chromosomes have been reported in other alticins, such as Alagoasa arcifera , A. fasciaticollis , A. equestris , A. transparente , A. oblecta , and Aedmon eugeniae [Petitpierre et al, 1988;Virkki and Santiago-Blay, 1993]. Chromosomal fragments have been observed in meiosis I cells in Alagoasa januaria , A. equestris , O. personata , and O. aequinoctialis [Virkki and Santiago-Blay, 1993]. However, our results show that this chromosome can not be classified as a fragment, but as a B chromosome.…”

“…This is the second record of B chromosomes in an Omophoita species; they were previously described only in O. inscipiens [Virkki and Santiago-Blay, 1996]. B chromosomes have been reported in other alticins, such as Alagoasa arcifera , A. fasciaticollis , A. equestris , A. transparente , A. oblecta , and Aedmon eugeniae [Petitpierre et al, 1988;Virkki and Santiago-Blay, 1993]. Chromosomal fragments have been observed in meiosis I cells in Alagoasa januaria , A. equestris , O. personata , and O. aequinoctialis [Virkki and Santiago-Blay, 1993].…”

“…Some genera, as Omophoita , Alagoasa , Asphaera , and Walterianella , have been the focus of several studies [Smith and Virkki, 1978;Virkki and Santiago-Blay, 1993;Petitpierre, 2006;Almeida et al, 2009;Mello et al, 2014]. This is due, in part, to the unique features of the subtribe Oedionychina, such as its giant sex chromosomes, which are asynaptic during meiosis and are oriented distantly from each other during metaphase I [Smith and Virkki, 1978;Santiago-Blay, 1993, 1998;Almeida et al, 2009].…”

“…The cytogenetic traits of the subtribe Oedionychina are relatively conserved, with a prevailing diploid chromosome number of 2n = 22, metacentric chromosome morphology, and a meiotic formula of 10II + X + y [Smith and Virkki, 1978;Virkki et al, 1991;Virkki and Santiago-Blay, 1993;Almeida et al, 2009].…”

Evolution of the Sex Chromosomes in Beetles. I. The Loss of the Y Chromosome

“…The incidence of additional B chromosomes (+Bs and +s, in the entomological terminology of that time) is 25.30% among X0, 3.7% among neoXY, and 1% among XY (Xy p ) formulae. Indeed, other XY+Bs males were found later in this family [Virkki and Santiago-Blay, 1993] and exist in other families, but this example shows that the lack of the Y and the presence of Bs may not be independent. This finding can be interpreted differently: either Bs derive from modified Ys, or Bs are preferentially retained in X0 males.…”