Internal Seminar: Mikheyev Unit and Sowwan Unit

Ecology and Evolution Unit (Alexander Mikheyev)

Speaker : Misato Okamoto

Title : Unique reproduction system of invasive ants avoids genetic bottlenecks

Abstract : In the Hymenoptera, sex is usually determined by a single locus. Heterozygotes are female and hemizygotes are male. Inbreeding leads to homozygosity at the sex determining and the production of diploid males, which are typically sterile, and act as a major burden for the colony. Hymenoptera employ a range of strategies such as outbreeding, or gender-specific reproduction to avoid diploid male production. Recently, an extraordinary reproduction system has been reported in the ants Wasmannia auropunctata, Vollenhovia emeryi, and Paratrechina longicornis. In this system queens and males are produced clonally, receiving only maternal and paternal genomes, respectively. Workers are produced sexually, but are sterile. Thus, gene pools are separated between sexes. Because all three of these species employing this strategy are invasive, it may have some strategic advantage, namely to avoid inbreeding during low population sizes at the start of an invasion (Pearcy et al. 2011, Proc. R. Soc. B). However, the existence of clonal males has never been documented in these species, so the extent to which inbreeding will affect their production remains unknown.

Using the facultatively clonal species V. emeryi, we crossed sexually produced queens (with both parental genomes) with their brothers, with which the queens shared half their genomes. 25 to 30% of the resulting offspring were diploid males. Ordinarily, haploid males are produced only in autumn in nature and lab. By contrast, we observed continuous diploid male production from March to December, suggesting a high cost of inbreeding in this species.

The significant deviation from a 50:50 Mendelian ratio it is clear that at least two loci underlie sexual development. Using FASSST ddRAD tagging, we compared genomes of diploid males and their full sisters in order to identify regions containing gender-determining elements. These data should help to narrow the field of candidate genes related to sex determination.

Nanoparticles by Design Unit (Ibrahim Sowwan)

Speaker : Panagiotis Grammatikopoulos

Title : Nanoparticles by Design: Computer Simulations of Nanoparticle Growth and Coalescence

Abstract : Nanoparticle deposition has opened new paths in nanotechnology that had not been accessible to conventional deposition methods in the past. Possessing an extra degree of freedom, i.e. their size, these “artificial atoms” have tunable properties that can lead to novel materials with bespoke structures and potential applications. Moreover, each nanoparticle has an internal atomic structure randomly oriented with respect to those of other nanoparticles or the substrate, a fact that also accounts for specific physical properties.

OIST’s Nanoparticles by Design Unit specialises in growth, deposition and characterisation of nanoparticles for various technological, chemical and medical applications. In parallel, we perform computational simulations to assist in better understanding the mechanisms that lead to the formation of various structures.

In this seminar, nanoparticle growth and coalescence processes will be described from a simulation point of view, with emphasis on the sensitive dependence of the final structures on the growth conditions. A good control of these conditions can lead to optimised nanoparticles for catalysts, gas sensors, prosthetics, photonics, etc.