Assessing Differences in Sperm Competitive Ability in Drosophila

Competition among conspecific males for fertilizing the ova is one of the mechanisms of sexual selection, i.e. selection that operates on maximizing the number of successful mating events rather than on maximizing survival and viability ¹. Sperm competition represents the competition between males after copulating with the same female ², in which their sperm are coincidental in time and space. This phenomenon has been reported in multiple species of plants and animals ³. For example, wild-caught D. melanogaster females usually contain sperm from 2-3 males ⁴. The sperm are stored in specialized organs with limited storage capacity, which might lead to the direct competition of the sperm from different males ^2,5.Comparing sperm competitive ability of different males of interest (experimental male types) has been performed through controlled double-mating experiments in the laboratory ^6,7. Briefly, a single female is exposed to two different males consecutively, one experimental male and one cross-mating reference male. The same mating scheme is then followed using other experimental male types thus facilitating the indirect comparison of the competitive ability of their sperm through a common reference. The fraction of individuals fathered by the experimental and reference males is identified using markers, which allows one to estimate sperm competitive ability using simple mathematical expressions ^7,8. In addition, sperm competitive ability can be estimated in two different scenarios depending on whether the experimental male is second or first to mate (offense and defense assay, respectively) ⁹, which is assumed to be reflective of different competence attributes.Here, we describe an approach that helps to interrogate the role of different genetic factors that putatively underlie the phenomenon of sperm competitive ability in D. melanogaster.     

Morphological and Biochemical Alterations of Abalone Testicular Germ Cells and Spawned Sperm and their Fertilizing Ability

In this study, we aimed to detect morphological and biochemical changes in developing germ cells (Gc), testicular sperm (Tsp), and spawned sperm (Ssp) using capacitation-associated characteristics. Gradual changes in the profiles of two membrane proteins, namely NaCl- and detergent-extractable proteins, were observed as compared Gc with Tsp and Tsp with Ssp. These membrane modifications were accomplished mostly through the introduction of new protein sets, both peripheral and integral, into Tsp and Ssp membranes. Activation of serine proteases, particularly in Ssp detergent-extracted proteins with the molecular masses of 38-130 kDa was evident and marked a major difference between Ssp and Tsp. An increase in the level of tyrosine phosphorylation of the proteins ranging from 15 to 20 kDa was noted in Tsp and remained constant in Ssp. Specifically, these three capacitation-associated characteristics could be detected in Ssp, possessing full fertilizing capacity. The lack of an activated proteolytic activity in Tsp resulted in a delayed fertilization, but not affected fertilizing ability. We believe that these characteristics should be advantageous in predicting abalone sperm fertilizing capability, particularly in cases when isolated germ cells or purified Tsp are used in place of spawned sperm in abalone aquaculture.     

Effect of Salt Concentration in the Recovery Medium on Heat-injured Streptococcus faecalis

Properties relating to the recovery of three heat-injured strains of Streptococcus faecalis were studied. All strains were cultured in all purpose plus Tween broth (APT) at 30 C for 24 hr before being subjected to heat in fresh APT broth. APT recovery medium containing various added amounts of NaCl, KCl, MgCl(2), or KCl and MgCl(2) was used to assess the effect of salts on the recovery of thermally injured S. faecalis. It was evident that, upon exposure to heat, S. faecalis cells became sensitive to increased salt concentrations. Analyses to determine the ribonucleic acid (RNA) content of heated cells showed a reduction of cellular RNA, but the per cent reduction was not directly proportional to the per cent reduction of the viable cells.     

Effect of Salt Concentration on Regeneration Rate in Blepharisma Acclimated to High Salt Levels*

SYNOPSIS. Individuals of Blepharisma intermedium (Rao A race) acclimated by prolonged growth in axenic medium containing 8X, 16X, 24X and 32X the concentration of salts in unit standard balanced salt solution (USBSS) used for fresh-water protozoans were tested for rate of regeneration at various salt concentrations, the time for 50% regeneration being used for comparisons. Blepharismas acclimated to axenic medium (of osmolality 10 × USBSS) containing 16X USBSS regenerated at about the same rate as those grown in axenic medium but were delayed at higher salt concentrations. The same was true for those grown in axenic medium containing 32X USBSS, except that the range of higher salt concentration tolerated was much greater. Those acclimated to higher salt concentrations were delayed in regeneration by exposure to lower salt concentrations tolerated by controls. Because growth was very slow in media of higher osmolal concentration, it was not possible to determine the internal concentration of salts in acclimated cells. The morphogenetic process as measured by rate of regeneration, appeared to be less sensitive to increased salt concentration than growth, as measured by cell division.