Possible origin of polymorphism for chromosome number in the assassin bugZelurus femoralis longispinis(Reduviidae: Reduviinae)

Abstract

In this study, we analysed a population of Zelurus femoralis longispinis polymorphic for chromosomal number. The fundamental karyotype of this subspecies is 2n = 22 = 20A + XY (male), but individuals with 2n = 23 = 20A + XY + extra chromosome have been found at high frequency and collected at different time periods. We examined male meiotic behaviour, average length as percentage of the sex chromosomes, the content, distribution and composition of heterochromatin, and the number and location of ribosomal DNA in the two cytotypes found. The meiotic behaviour of the extra chromosome was highly regular and similar to that of sex chromosomes. The average length of the sex chromosomes in individuals not carrying the extra chromosome was significantly greater than in those carrying it. The results support a hypothesis that the extra chromosome might have originated by fragmentation of the original X chromosome into two unequal‐sized chromosomes (X1 and X2), leading to an X1X2Y multiple system. Maintenance of the polymorphism with time appears to indicate that the new chromosomal variant is neutral or at least not detrimental, or that it could be selectively advantageous. This polymorphic population represents direct evidence of a multiple sex chromosome system originating through fragmentation of a single X in Reduviidae as well as in Heteroptera. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 757–764.

Karyotype diversity among predatory Reduviidae (Heteroptera)

“…However, our data on Cosmoclopius nigroannulatus , which shows fragmentation of the X chromosome, suggests an additional situation for the distribution of 18S rDNA sites, since the rDNA signals appeared on both one of the fragmented X chromosomes and Y chromosome. The presence of 18S or 45S rDNA loci in one or more sex chromosomes has also been observed in several reduviid species from the subfamilies Triatominae (Severi-Aguiar et al 2006, Panzera et al 2012) and Reduviinae (Poggio et al 2013a) with multiple sex chromosome system. There is at least one example, Dysdercus albofasciatus , where the original X chromosome was inserted into the NOR-autosome next to the rDNA cluster in an ancestor carrying the X0 system, resulting in a neo-sex-chromosome system (Bressa et al 2009).…”

“…Due to the lack of phylogenetic analyses as well as the absence of chromosome markers for most heteropterans, the evolutionary direction for certain rearrangements is very speculative, especially in heteropteran predators. However, there are sporadic examples where chromosome rearrangements can be supposed, as observed in Cosmoclopius nigroannulatus , where numerical diversity is clearly linked to the fragmentation of sex chromosomes (Papeschi 1994, 1996, Poggio et al 2007, 2013a, 2014). …”

“…The 18S rDNA locus is the principal marker on chromosomes of Nepomorpha, Pentatomomorpha and Cimicomorpha (González-García et al 1996, Papeschi et al 2003, Cattani et al 2004, Cattani and Papeschi 2004, Dias de Campos Severi-Aguiar and Azeredo-Oliveira 2005, Severi-Aguiar et al 2006, Morielle-Souza and Azeredo-Oliveira 2007, Bressa et al 2008, 2009, Grozeva et al 2010, 2011, Poggio et al 2011, 2013a, 2014, Panzera et al 2012, Chirino et al 2013a, Bardella et al 2013). Of the 36 species of Pentatomomorpha studied until now, the rDNA loci are preferably located in autosomes with only four species with rDNA loci on the sex chromosomes (González-García et al 1996, Bressa et al 2009, Grozeva et al 2011, Bardella et al 2013).…”

“…Of the 36 species of Pentatomomorpha studied until now, the rDNA loci are preferably located in autosomes with only four species with rDNA loci on the sex chromosomes (González-García et al 1996, Bressa et al 2009, Grozeva et al 2011, Bardella et al 2013). On the contrary, in Cimicomorpha, the location of rDNA loci are more heterogeneous: the hybridization sites are observed on autosomes, sex chromosomes or both simultaneously (Dias de Campos Severi-Aguiar and Azeredo-Oliveira 2005, Severi-Aguiar et al 2006, Morielle-Souza and Azeredo-Oliveira 2007, Grozeva et al 2010, 2011, 2013, 2014, Panzera et al 2012, 2014, Poggio et al 2011, 2013a, 2013b). …”

Comparison of different cytogenetic methods and tissue suitability for the study of chromosomes in Cimex lectularius (Heteroptera, Cimicidae)

“…The spreading technique was also modified by Traut (1976) for male and female meiotic studies in lepidopteran species. Following his procedure, spreading was used successfully for chromosome studies of other heteropteran taxa, namely Corixidae: Micronectinae (Ituarte and Papeschi 2004), Reduviidae: Hammacerinae (Poggio et al 2011), Triatominae (Morielle-Souza and Azeredo-Oliveira 2007, Poggio et al 2013a), Reduviinae (Poggio et al 2013b), Coreidae (Bressa et al 2008), Pyrrhocoridae ), and Belostomatidae (Bardella et al 2012, Chirino et al 2013.…”