Eversion and withdrawal of an intromittent organ before sexual maturation prepares male beetles for copulation

Some species of criocerine beetles have a hyper-elongated part of the intromittent organ called a flagellum. In resting position, the flagellum is stored in a specialized internal sac in the intromittent organ. This specialized state of the flagellum and internal sac is indispensable during copulation for flagellar insertion into the female spermathecal duct for sperm transfer. However, the morphogenesis of the flagellum does not generate the active state of the flagellum; rather, the flagellum is generated in an inactive and completely coiled state. After eclosion, males of Lema coronata evert and withdraw the internal sac multiple times before sexual maturation, without mounting a female. This behaviour serves to uncoil the flagellum and guide it into the active state with the aid of surface structures on the internal sac. A closely related species, Lema dilecta , also has a long flagellum and undergoes the same behaviour to place the flagellum in the active position. However, some other species of criocerine beetles with much shorter flagella can attain the active state without exhibiting this behaviour. Based on a previously proposed phylogenetic tree, we discuss the evolutionary history of the hyper-elongation of the flagellum and associated behaviour.

Monte Carlo simulation of chromatin fibre confined in a nanochannel

We study 30-nm chromatin fibre restricted in a nanofluidic channel with square cross-section using Monte Carlo (MC) simulations. The chromatin fibre is modelled as cylinders-on-a-string with six alterable angles. The effects of the channel width and Emax on the configuration of the chromatin fibre are investigated in detail. Our results show that the channel width has a considerable influence on conformational characteristics of the chain. It is found that at large Emax, the chromatin fibre undergoes a conformational transition from stretched state to coiled state with increasing the channel width. Additionally, the influence of the channel width is lowered with enhancing Emax. At small values of the channel width, the chains for different Emax exhibit a similar structure, namely, a stretched conformation

Scattering Studies of Cyrstallization in Highly Oriented Polymers

The solidification of low molecular weight materials from their melts (in the absence of temperature fields) generally leads to a product with no preferred orientation, independent of the extent or rate of deformation of the melt. The solidification of polymers from a highly deformed melt or solution nearly always leads to a product with preferred molecular orientation. Further, the rate of solidification can be significantly increased by melt deformation. The change in rate, relative to that in a quiescent melt or solution, can be several orders of magnitude [1]. These differences, relative to small-molecule systems, arise from the degree to which orientation and local strain can be maintained in the melt. Due to the long-range connectivity within a polymer molecule, it is possible to impart large extensions to these molecules in the molten state, and significant time is often required for the molecules to relax back to their undistorted, coiled state. If crystallization or glass formation occurs before the chain can relax, an extended molecular configuration can be retained. Thus in the solidification of oriented polymers there exists a competition between the “freezing” of the molecular orientation and the relaxation (re-coiling) of the molecules.