Search

Over the last 50 years, sperm competition has become increasingly recognised as a potent evolutionary force shaping male ejaculate traits. One such trait is sperm swimming speed, with faster sperm associated with increased fertilisation success in some species. Consequently, sperm are often thought to have evolved to be longer in order to facilitate faster movement. However, despite the intrinsic appeal of this argument, sperm operate in a different biophysical environment than we are used to, and instead increasing length may not necessarily be associated with higher velocity. Here, we test four predictive models (ConstantPower Density, Constant Speed, Constant Power Transfer, Constant Force) of the relationship between sperm length and speed. We collated published data on sperm morphology and velocity from 141 animal species, tested for structural clustering of sperm morphology and then compared the model predictions across all morphologically similar sperm clusters. Within four of five morphological clusters of sperm, we did not find a significant positive relationship between total sperm length and velocity. Instead, in four morphological sperm clusters we found evidence for the Constant Speed model, which predicts that power output is determined by the flagellum and so is proportional to flagellum length. Our results show the relationship between sperm morphology (size, width) and swimming speed is complex and that traditional models do not capture the biophysical interactions involved. Future work therefore needs to incorporate not only a better understanding of how sperm operate in the microfluid environment, but also the importance of fertilising environment, i.e., internal and external fertilisers. The microenvironment in which sperm operate is of critical importance in shaping the relationship between sperm length and form and sperm swimming speed. [ABSTRACT FROM AUTHOR]

Males that exhibit alternative reproductive tactics (ARTs) often differ in the risk of sperm competition and the energetic trade-offs they experience. The resulting patterns of selection could lead to between-tactic differences in ejaculate traits. Despite extensive research on male ARTs, there is no comprehensive review of whether and what differences in sperm traits exist between male ARTs. We review existing theory on ejaculate evolution relevant to ARTs and then conduct a comprehensive vote-counting review of the empirical data comparing sperm traits between males adopting ARTs. Despite the general expectation that sneaker males should produce sperm that are more competitive (e.g. higher quality or performance), we find that existing theory does not predict explicitly how males adopting ARTs should differ in sperm traits. The majority of studies find no significant difference in sperm performance traits between dominant and sneaker males. However, when there is a difference, sneaker males tend to have higher sperm performance trait values than dominant males. We propose ways that future theoretical and empirical research can improve our understanding of the evolution of ejaculate traits in ARTs. We then highlight how studying ejaculate traits in species with ARTs will improve our broader knowledge of ejaculate evolution. [ABSTRACT FROM AUTHOR]

Copyright of Biotechnology in Animal Husbandry is the property of Institute for Animal Husbandry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Sperm number is an important predictor of paternity when there is sperm competition. Sperm number is often measured as maximum sperm reserves, but in species where mating is frequent, males will often be replenishing their reserves. Thus, variation in how quickly males can produce sperm is likely to be important in determining male success in sperm competition. Despite this, little is known about how male size, body condition or diet affects sperm production rates. We counted sperm number in large and small Gambusia holbrooki (eastern mosquitofish) after 3 weeks on either a high or low food diet. Sperm number was significantly higher in both larger males and in well-fed males. We then stripped ejaculates again either 1, 2, 3, 4 or 5 days later to investigate subsequent sperm production. The rate of sperm replenishment was influenced by an interaction between size and diet. Large, well-fed males had consistently high levels of sperm available over the 5 days (i.e. rapid replenishment), whereas small poorly fed males showed consistently low levels of sperm availability over the 5 days (i.e. slow replenishment). In contrast, large, poorly fed and small, well-fed males increased their sperm numbers over the first 3 days (i.e. intermediate replenishment). Our study highlights that when mating is frequent and sperm competition is high, size and condition dependence of maximal sperm number and of sperm production rate might both contribute to variation in male reproductive success. [ABSTRACT FROM AUTHOR]

The main objective of this study was to score variability of fertility traits of boars as influenced by breed, age at first ejaculation/collection (AFE), the lean meat content (LM), lifetime average daily gain (ADG) and age of boars. The following fertility traits were analysed: libido, duration of ejaculation (DE), ejaculate volume (VOL), the density of the ejaculate (DEN) and sperm motility (MO) of boars. Boars' libido was assessed on the basis of duration of preparing to collection (DPC). The study included 7987 ejaculates from 105 boars of three breeds: Swedish Landrace (SL; n=34), Large White (LW; n=39) and Duroc (n=32). Impact assessment was carried out using the GLM procedure of the statistical package SAS 9.1.3 (SAS Inst. Inc., 2002-2003). Of all the traits analysed, only the DPC and VOL varied under the influence of all investigated impacts. Boars of SL and LW breeds demonstrated superiority in the trait VOL (+12.53 and +11.25 ml) compared to Duroc. Ejaculates of boars with AFE from 23 to 27 weeks had the highest VOL, but with the lowest qualitative properties. Contrary to the negative trend in the manifestation of libido, increase of LM and ADG indicated the trend of increasing DE and VOL. Boars with LM of 61% and higher had the highest VOL, and the differences in relation to the first and second class were +6.32 ml (P<0.01) and +5.18 ml (P<0.05), respectively. The ejaculate volume of the boars with the highest ADG compared to the other classes was higher (P<0.001) by 10.88 and 9.81 ml. Boars in different ADG classes produced ejaculate with differing qualitative property DEN. Correlations between production traits and fertility traits were negligible, and unlike the ADG, only the correlation between LM and DPC was statistically significant (P<0.001). [ABSTRACT FROM AUTHOR]

Female sexual promiscuity is a prevalent element of mating systems. One consequence of female sexual promiscuity is that male-male competition often continues post-copulation within the female's reproductive tract. According to theory, the number of sperm a male inseminates relative to his rivals strongly predicts his fertilization success. However, sperm quality is also important, especially when males are sperm limited and female sperm storage is prevalent. In this study, we examined intrapopulational variation in sperm numbers and ejaculate quality (sperm mobility) in male red-sided garter snakes, T hamnophis sirtalis parietalis, and determined whether these traits varied with male body size and condition over successive matings. We obtained sperm by dissolving copulatory plugs collected from natural matings, which enabled us to also test whether males allocated more sperm to larger, more fecund females. We found significant variation in ejaculate quality among males and that small males transferred as many sperm as large males. Total sperm numbers declined significantly from a male's first to second ejaculate suggesting that males may become significantly sperm depleted across successive matings. The mass of the relatively sperm-free posterior portion of the copulatory plug that remained after liberation of sperm was correlated with copulation duration. Males copulated longer with larger females; however, longer copulation durations did not correlate with total sperm. Thus, males may allocate more copulatory plug material to larger females to guard against her remating, instead of allocating more sperm. [ABSTRACT FROM AUTHOR]

Sperm competition is a widespread phenomenon that shapes male reproductive success. Ejaculates present many potential targets for postcopulatory selection (e.g., sperm morphology, count, and velocity), which are often highly correlated and potentially subject to complex multivariate selection. Although multivariate selection on ejaculate traits has been observed in laboratory experiments, it is unclear whether selection is similarly complex in wild populations, where individuals mate frequently over longer periods of time. We measured univariate and multivariate selection on sperm morphology, sperm count, and sperm velocity in a wild population of brown anole lizards (Anolis sagrei). We conducted a mark-recapture study with genetic parentage assignment to estimate individual reproductive success. We found significant negative directional selection and negative quadratic selection on sperm count, but we did not detect directional or quadratic selection on any other sperm traits, nor did we detect correlational selection on any trait combinations. Our results may reflect pressure on males to produce many small ejaculates and mate frequently over a six-month reproductive season. This study is the first to measure multivariate selection on sperm traits in a wild population and provides an interesting contrast to experimental studies of external fertilizers, which have found complex multivariate selection on sperm phenotypes. [ABSTRACT FROM AUTHOR]