Hydrodynamics of the double-wave structure of insect spermatozoa flagella

In addition to conventional planar and helical flagellar waves, insect sperm flagella have also been observed to display a double-wave structure characterized by the presence of two superimposed helical waves. In this paper, we present a hydrodynamic investigation of the locomotion of insect spermatozoa exhibiting the double-wave structure, idealized here as superhelical waves. Resolving the hydrodynamic interactions with a non-local slender body theory, we predict the swimming kinematics of these superhelical swimmers based on experimentally collected geometric and kinematic data. Our consideration provides insight into the relative contributions of the major and minor helical waves to swimming; namely, propulsion is owing primarily to the minor wave, with negligible contribution from the major wave. We also explore the dependence of the propulsion speed on geometric and kinematic parameters, revealing counterintuitive results, particularly for the case when the minor and major helical structures are of opposite chirality.

Reduced metabolic rate and oxygen radicals production in stored insect sperm

Females of internally fertilizing species can significantly extend sperm lifespan and functionality during sperm storage. The mechanisms for such delayed cellular senescence remain unknown. Here, we apply current hypotheses of cellular senescence developed for diploid cells to sperm cells, and empirically test opposing predictions on the relationship between sperm metabolic rate and oxygen radical production in an insect model, the cricket Gryllus bimaculatus . Using time-resolved microfluorimetry, we found a negative correlation between metabolic rate (proportion of protein-bound NAD[P]H) and in situ intracellular oxygen radicals production in freshly ejaculated sperm. In contrast, sperm stored by females for periods of 1 h to 26 days showed a positive correlation between metabolic rate and oxygen radicals production. At the same time, stored sperm showed a 37 per cent reduced metabolic rate, and 42 per cent reduced reactive oxygen species (ROS) production, compared with freshly ejaculated sperm. Rank differences between males in ROS production and metabolic rate observed in ejaculated sperm did not predict rank differences in stored sperm. Our method of simultaneously measuring ROS production and metabolic rate of the same sample has the advantage of providing data that are independent of sperm density and any extracellular antioxidants that are proteins. Our method also excludes effects owing to accumulated hydrogen peroxide. Our results unify aspects of competing theories of cellular ageing and suggest that reducing metabolic rate may be an important means of extending stored sperm lifespan and functionality in crickets. Our data also provide a possible explanation for why traits of ejaculates sampled from the male may be rather poor predictors of paternity in sexual selection studies and likelihood of pregnancy in reproductive medicine.