Sperm death and dumping in Drosophila

Mating with more than one male is the norm for females of many species. In addition to generating competition between the ejaculates of different males, multiple mating may allow females to bias sperm use. In Drosophila melanogaster, the last male to inseminate a female sires approximately 80% of subsequent progeny. Both sperm displacement, where resident sperm are removed from storage by the incoming ejaculate of the copulating male, and sperm incapacitation, where incoming seminal fluids supposedly interfere with resident sperm, have been implicated in this pattern of sperm use. But the idea of incapacitation is problematic because there are no known mechanisms by which an individual could damage rival sperm and not their own. Females also influence the process of sperm use, but exactly how is unclear. Here we show that seminal fluids do not kill rival sperm and that any 'incapacitation' is probably due to sperm ageing during sperm storage. We also show that females release stored sperm from the reproductive tract (sperm dumping) after copulation with a second male and that this requires neither incoming sperm nor seminal fluids. Instead, males may cause stored sperm to be dumped or females may differentially eject sperm from the previous mating

Negative phenotypic and genetic associations between copulation duration and longevity in male seed beetles

Reproduction can be costly and is predicted to trade-off against other characters. However, while these trade-offs are well documented for females, there has been less focus on aspects of male reproduction. Furthermore, those studies that have looked at males typically only investigate phenotypic associations, with the underlying genetics often ignored. Here, we report on phenotypic and genetic trade-offs in male reproductive effort in the seed beetle, Callosobruchus maculatus. We find that the duration of a male's first copulation is negatively associated with subsequent male survival, phenotypically and genetically. Our results are consistent with life-history theory and suggest that like females, males trade-off reproductive effort against longevity

Probabilistic Study on the Geotechnical Behavior of Fiber Reinforced Soil

Expansive soils which are considered extremely problematic due to their potential to create swell and shrinkage-related distresses. In order to satisfy the geotechnical requirements, these soils are fiber reinforced to sustain dynamic loads as a subgrade material. Polypropylene fiber materials when amended with soil medium, have proven functionality in the long run. Usually, a binder is required to ensure proper bonding between discrete/random fiber elements and the clay particulates. In the current study, lime is a proposed binder and its dosage is fixed at 6% satisfying initial lime consumption and optimum lime requirements. Two types of fiber materials (Fiber Cast® and Fiber Mesh®) at varying dosages (0.2, 0.4, and 0.6% by weight of soil) and having different lengths (6 and 12 mm) are considered for the present study and its inclusion effect on the hydraulic conductivity, unconfined compression strength behavior and California bearing ratio behavior has been studied. The focus of this paper is in determining the optimum fiber reinforcement parameters (fiber type, length, dosage, etc.) for the stabilization of selected expansive Al-Ghat soil. Probabilistic analysis has been performed to correlate the targeted properties with aspect parameters (i.e., dosage and length) for fiber-reinforced soil. In addition to this, reliability analysis has been performed to examine the applicability of this fiber-reinforced soil in municipal solid waste (MSW) landfills for waste containment. The probabilistic analysis revealed that both aspect parameters play a crucial role in fiber-reinforced soils. Further, it is concluded that the target reliability approach (TRA) gives a valuable insight with regards to choosing optimum aspect parameters for effective soil stabilization practice