Genomic evolution in parental and hybrid taxa of the genusBacillus(Insecta Phasmatodea)

Abstract

(D, 0.31-0.36) than to B. rossius (D = 1.82). Furthermore, SEM and allozymatic investigations allowed it to be established that body and egg characters are more conserved than gene-enzyme systems. Recently, satellite DNA sequences (the Bag320 family) and a mitochondrial coding gene (COII) were also analysed. It could be noticed that Bag sequences provided differentiation values among taxa higher than coding nuclear genes. Furthermore, it was discovered that, while parthenogenesis in B. atticus leaves random levels of individual variability of repeats -likely due to the absence of chromosome shuffling in the progeny -, the nucleotide sequences of B. grandii split into subspecific clusters, indicating that sequence variant homogenization/fixation are at work in Mendelian reproducing species. In B. whitei and B, lynceorum, only a limited sequence variability of grandii-like repeats was observed, that suggested a rather recent origin for them, although sufficiently old to allow gene-conversion to start between grandii-like and atticus-like sequences in B. lynceorum. The invention of both grandii-like and atticus-like Bag 320 clones also established beyond doubt the B. atticus contibution to the structure of this triploid hybrid. MtDNA of the COII gene gave indications of a more homogeneous degree of differentiation among taxa than that suggested by nuclear compartments, since B. rossius, B. grandii, and B. atticus appear to be differentiated from each other to a similar degree. Furthermore, COII unexpectedly demonstrated that, in addition to hybridogens and B. whitei, also B. lynceorum has B. rossius as the maternal ancestor, thus indicating a hybridization route different from that previously thought for this hybrid. Finally, mtDNA served as a genetic marker to demonstrate that androgenesis does occur in nature, since from hybridogenetic females, B. grandii specimens were produced, carrying mtDNA of B. rossius. Androgens provide an unusual opportunity of genome evolution since gene-size fragments of DNA can escape from mitochondria and migrate to the nucleus.

The Leptynia hispanica species complex (Insecta Phasmida): polyploidy, parthenogenesis, hybridization and more

“…4). For the unisexuals, two different haplotype clusters found within triploids suggest that L. hispanica 3n is a hybrid taxon, as found in other parthenogenetic stick insects (Mantovani et al . 1999; Morgan‐Richards & Trewick 2005).…”

Nonrandom Patterns of Genetic Admixture Expose the Complex Historical Hybrid Origin of Unisexual Leaf Beetle Species in the GenusCalligrapha

“…Classical unisexual vertebrate systems include wellknown examples of these tri-and even tetramodal complex hybridization scenarios, including Aspidoscelis whiptail lizards (Lowe and Wright 1966), Ambystoma mole salamanders (Bogart et al 2007), and Leuciscus (Alves et al 2001) and Poeciliopsis (Mateos and Vrijenhoek 2002) fish. There are known cases among the invertebrates, too, such as stick insects in the genera Bacillus (Mantovani et al 1999) and Leptynia (Ghiselli et al 2007).…”

Linkage between sexual and asexual lineages: genome evolution in Bacillus stick insects

“… Map of the Mediterranean Basin showing the distribution of Bacillus parental ( B. rossius , B. grandii and B. atticus ) and hybrid taxa. From Mantovani et al. (1999).…”

“…2). In Sicily, B. grandii and B. rossius have also hybridized to produce two different hybridogenetic strains ( sensu Schultz, 1961), which pass on to their progeny an invariant maternal rossius haploset, while renewing the paternal genome each generation (hemiclonal reproduction) (Mantovani & Scali, 1992; Mantovani, Passamonti & Scali, 1999). Mitochondrial DNA analysis has shown that unisexual Bacillus arose through asymmetrical hybridization events, with only one cross direction of the two possible being realized in nature, B. rossius always being the maternal parent.…”