Complex meiotic configuration of the holocentric chromosomes: the intriguing case of the scorpion Tityus bahiensis

Mitotic and meiotic chromosomes of Tityus bahiensis were investigated using light (LM) and transmission electron microscopy (TEM) to determine the chromosomal characteristics and disclose the mechanisms responsible for intraspecific variability in chromosome number and for the presence of complex chromosome association during meiosis. This species is endemic to Brazilian fauna and belongs to the family Buthidae, which is considered phylogenetically basal within the order Scorpiones. In the sample examined, four sympatric and distinct diploid numbers were observed: 2n = 5, 2n = 6, 2n = 9, and 2 = 10. The origin of this remarkable chromosome variability was attributed to chromosome fissions and/or fusions, considering that the decrease in chromosome number was concomitant with the increase in chromosome size and vice versa. The LM and TEM analyses showed the presence of chromosomes without localised centromere, the lack of chiasmata and recombination nodules in male meiosis, and two nucleolar organiser regions carrier chromosomes. Furthermore, male prophase I cells revealed multivalent chromosome associations and/or unsynapsed or distinctly associated chromosome regions (gaps, less-condensed chromatin, or loop-like structure) that were continuous with synapsed chromosome segments. All these data permitted us to suggest that the chromosomal rearrangements of T. bahiensis occurred in a heterozygous state. A combination of various factors, such as correct disjunction and balanced segregation of the chromosomes involved in complex meiotic pairing, system of achiasmate meiosis, holocentric nature of the chromosomes, population structure, and species dispersion patterns, could have contributed to the high level of chromosome rearrangements present in T. bahiensis.

A Comparative Cytogenetic Analysis of 2 Bothriuridae Species and Overview of the Chromosome Data of Scorpiones

The order Scorpiones is one of the most cytogenetically interesting groups within Arachnida by virtue of the combination of chromosome singularities found in the 59 species analyzed so far. In this work, mitotic and meiotic chromosomes of 2 species of the family Bothriuridae were detailed. This family occupies a basal position within the superfamily Scorpionoidea. Furthermore, review of the cytogenetic data of all previously studied scorpions is presented. Light microscopy chromosome analysis showed that Bothriurus araguayae and Bothriurus rochensis possess low diploid numbers compared with those of species belonging to closely related families. Gonadal cells examined under light and in transmission electron microscopy revealed, for the first time, that the Bothriuridae species possess typical monocentric chromosomes, and male meiosis presented chromosomes with synaptic and achiasmatic behavior. Moreover, in the sample of B. araguayae studied, heterozygous translocations were verified. The use of techniques to highlight specific chromosomal regions also revealed additional differences between the 2 Bothriurus species. The results herein recorded and the overview elaborated using the available cytogenetic information of Scorpiones elucidated current understanding regarding the processes of chromosome evolution that have occurred in Bothriuridae and in Scorpiones as a whole.

The medical zoologist - Ronald Vernon Southcott

Dr Ronald Vernon Southcott (1918–1998) was amongst the greatest of the Australian doctor-naturalists. His toxinological contributions included the description and naming of the box-jellyfish, Chironex fleckeri, the first definitive study (1950–1957) of the toxinology, taxonomy and biology of Australian scorpions; and the first observations in Australia of the introduced fiddleback spider, Loxosceles. His research into the medical effects of toxic fungi, poisonous plants and Australian insects was extensive. He was a founding member of the International Society on Toxinology and served on the Toxicon Editorial Board for more than 30 years. He also made extensive contributions to acarology, and to the taxonomy of mites, specifically the sub-families and genera of the Erythraeoidea. This prodigious output was achieved by one who, with the exception of war service (1942–1946), almost never travelled outside South Australia, was almost entirely self-funded and worked from his home laboratory. With Dr. P.D. Scott and C.J. Glover, he was also the authority on the fish of South Australia. Dr. Southcott was also a medical epidemiologist and senior medical administrator (1949–1978) with the Australian Commonwealth Department of Veterans’ Affairs. He served for 30 years as an Honorary Consultant in Toxicology to the Adelaide Children's Hospital. As a zoologist and botanist of astounding breadth, he worked indefatigably in a voluntary capacity for the South Australian Museum, of which he was Museum Board Chairman from 1974 to 1982. In the pantheon of the great doctor-naturalists who have worked in Australia, he stands with Robert Brown and Thomas Lane Bancroft.