Sperm senescence, a decline in sperm quality caused by male ageing and by sperm ageing before or after copulation, may have fitness costs manifested as infertility or lowered genetic quality of offspring. This thesis tested the distinct evolutionary roles of sperm senescence using a laboratory-adapted population of Drosophila melanogaster. We developed a practical approach to avoid confounding male age with sperm age by standardizing pre-copulatory sperm age and mating history in young and old male age groups. Applying this approach, we documented sperm senescence in D. melanogaster and discussed its potential evolutionary importance. First, ageing males declined in fitness as evidenced by the reduction in fertilization potential of their ejaculates but not by decreased offspring fitness (the ability that a fly can survive to adulthood, successfully mate and produce viable offspring). This suggests a decline in the quality or quantity of seminal fluid or spermatozoa, with no decline in the genetic quality of sperm that actually fertilized ova. Second, post-copulatory sperm senescence has significant negative impacts on offspring fitness, indicating degraded genetic integrity of the spermatozoa stored in females. In both cases, male ageing and sperm ageing had similar fitness impact on male and female offspring, different from what has been suggested by previous work. In addition, We demonstrated that female fecundity, fertility, and length of the fertile period after a single mating were positively associated with the concentration of yeast in their food, and were negatively associated with the duration of yeast restriction in their diet, which suggested that sperm storage is affected by the nutritional status of the females. By revealing the significance of sperm senescence on male and female fertilization success and the fitness of the next generation, this thesis sheds light on a number of evolutionary and applied issues, and provokes new questions for future research on sperm senescence. / Thesis (Ph.D, Biology) -- Queen's University, 2014-03-07 10:38:12.879

Sexually reproducing eukaryotes are typically going through a biphasic life cycle with a diploid and a haploid phase. Unlike in plants where selection on haploid pollen genotypes is well established, the possibility of selection occurring in animal sperm is currently not known. One of the main reasons for this lack of knowledge is the general assumption that due to the shortness and the apparent absence of gene expression in haploid sperm, selection during that phase is unlikely to occur. The aim of this thesis was to fill this gap and address some of the main fundamental questions. I investigated the interaction between sperm phenotype and offspring phenotype with a focus on the trans-generational effects of (i) selection on the haploid sperm genotype, (ii) sperm ageing and (iii) sperm-mediated epigenetic effects. For one, we performed several experimental studies to investigate how selection on the sperm phenotype affects offspring performance in two externally fertilizing fishes, Atlantic salmon and zebrafish. We found that in Atlantic salmon, sperm of intermediate post-activation longevity sire offspring that hatch earlier. In zebrafish, longer living sperm sire more viable offspring with a higher fitness than their short-lived sibling sperm. We explored the mechanisms of these trans-generational effects and found that neither intrinsic post-ejaculation sperm ageing (Atlantic salmon and zebrafish) nor pre-ejaculation sperm ageing (zebrafish) affect offspring performance. However, we identified genetic differences between sperm pools that were obtained by selecting different phenotypes within ejaculates of zebrafish males. These results suggest a genetic basis for intra-ejaculate sperm phenotype variation and show that there is potential for haploid selection in sperm. In a separate experiment, we explored the role of sexual selection in shaping sperm-mediated epigenetic effects, and found that short-time changes in male-male competition affect offspring hatching time and survival. In conclusion, this thesis provides evidence that sperm phenotype affects offspring phenotype, and that sperm phenotype is affected by both epigenetic changes influenced by the male environment and differences in the haploid genome of sperm.

Sperm phenotype is an essential indicator of the male ejaculate quality and may have a significant impact on male reproductive success. Sperm phenotypes are considerably variable across species but variation is also found among males within species. This thesis examines (1) variation in sperm phenotypes among males in barn swallows (Hirundo rustica), (2) changes in male ejaculate quality with age, (3) relationships between sperm morphology and motility, (4) effects of sperm phenotypes (morphology and motility) on male fertilization success, using a large dataset of 174 observation for 130 males, and (5) the influence of female reproductive environment on sperm motility. From the tested variables, only midpiece length correlated with male age. Older males had shorter midpiece but no relationship between male age and reproductive success was found. Sperm length negatively affected sperm motility and, simultaneosly, relative midpiece length posively correlated with sperm motility. No correlation was found between the male reproductive success and sperm motility, presence of abnormalities, length of outermost tail feathers or age. Males with shorter relative midpiece were more successful in within-pair paternity, and males with shorter sperms but longer relative midpiece were more successful in...