Reproductive relationships and degree of synapsis in the polytene chromosomes of the Drosophila buzzatii species cluster

Abstract

The process of speciation occurs through the evolution of any of several forms of reproductive isolation between taxa, including inviability of hybrids. In this work, strains derived from allopatric populations of Drosophila buzzatii cluster species were experimentally crossed in order to evaluate their reproductive and cytogenetic relationships, and to contribute toward understanding the reproductive isolation in this group of sibling species. Although intrastrain crosses were highly fertile, we consider it relevant to discuss the differences in intra-and interspecific fertility and fecundity here. Among 30 interspecific crosses, about 63% were partially or completely sterile. Fifty three percent of interspecific F1 crosses (female and male F1 crossed) were also partially or completely sterile, in contrast to only one out of 24 intraspecific F1 crosses that was partially sterile. An analysis of hybrid polytene chromosomes revealed complete synapsis, except in the microchromosomes (VI) and in the proximal region of the X chromosome. The intraspecific divergence observed in this study and the variable degree of chromosome pairing shown here reveal part of the complexity of the speciation process pertinent to Drosophila buzzatii cluster, which is consistent with different traits studied in this cluster.Keywords: Drosophila buzzatii cluster, reproductive isolation, polytene chromosome synapse. RESUMORelações reprodutivas e grau de sinapse nos cromossomos politênicos de espécies de Drosophila do cluster buzzatii O processo de especiação ocorre pela evolução de qualquer uma das diversas formas de isolamento reprodutivo entre táxons, incluindo inviabilidade de híbridos. Neste trabalho, linhagens provenientes de populações alopátricas de espécies de Drosophila do cluster buzzatii foram cruzadas experimentalmente com o objetivo de avaliar suas relações reprodutivas e citogenéticas, e contribuir para o entendimento do isolamento reprodutivo neste grupo de espécies intimamente relacionadas. Os cruzamentos dentro de uma mesma linhagem foram altamente férteis, contudo as diferenças na fertilidade e fecundidade encontradas intra e interespecificamente são discutidas neste artigo. Dos 30 cruzamentos interespecíficos, 63% foram parcialmente ou completamente estéreis. Cinqüenta e três por cento dos cruzamentos de F1 interespecíficos (fêmeas e machos F1 cruzados entre si) também foram parcialmente ou completamente estéreis, em contraste com apenas um, em 24 cruzamentos de F1 intra-específicos, que foi parcialmente estéril. A análise dos cromossomos politênicos nos híbridos revelou sinapse completa, exceto nos microcromossomos (VI) e na região proximal do cromossomo X. A divergência intra-específica e o grau variável de pareamento 280 MACHADO, L. P. B., MADI-RAVAZZI, L. and TADEI, W. J.

Mitotic and polytene chromosomes analysis of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

“…Asynapsis is frequently observed in hybrid chromosomes of inter-or intra-specific crosses in Dipteran species [e.g. (Machado et al 2006;Cáceres et al 2009)] and in the presence of heterozygous chromosome rearrangements (Lefevre 1976). Kounatidis et al (2008) reported a high frequency of asynapsis distributed over several chromosomal regions of R. cerasi in four natural Greek populations.…”

Intra- and interspecific divergence in the nuclear sequences of the clock gene period in species of the Drosophila buzzatii cluster

“…2008). Giving support to this hypothesis, these species are sympatric in many locations of the Chaco Domain, and laboratory experiments indicate that these species are capable of gene exchange (Machado et al. 2006; Soto et al.…”

“…The species of the Drosophila buzzatii cluster comprise a range of divergences, degrees of reproductive isolation (Machado et al. 2006; Manfrin and Sene 2006), ecological restrictions and cacti hosts (Sene et al.…”

Molecular characterization of SSS139, a new satellite DNA family in sibling species of the Drosophila buzzatii cluster

“…Furthermore, among the species of the cluster, D. buzzatii has a primitive pattern of chromosome inversions (Ruiz and Wasserman, 1993) and is the most reproductively isolated species (Marin et al, 1993;Madi-Ravazzi et al, 1997;Machado et al, 2006). Morphologically, the aedeagus and wing morphometry of this species is different from that of the other species of the cluster (Tidon-Sklorz and Sene 2001; Moraes et al, 2004;Manfrin and Sene, 2006).…”