Haploid selection within a single ejaculate increases offspring fitness

Diploid organisms produce haploid gametes for sexual reproduction, resulting in a biphasic life cycle. Although selection during the diploid phase is well understood, selection during the haploid gametic stage and its consequences are largely ignored despite its potential importance for fundamental evolutionary processes, including the rate of adaptation and inbreeding depression, as well as for applied research into fertilization technology. A current dogma assumes that in animals selection on the haploid gametic genotype is minimal. We examined the importance of haploid selection in the zebrafish and found strong fitness consequences of selection on sperm phenotype in the resulting offspring. Genomic data support the idea that these effects may well be the consequence of selection on the haploid sperm genotype

Paternal starvation affects metabolic gene expression during zebrafish offspring development and lifelong fitness

Dietary restriction in the form of fasting is a putative key to a healthier and longer life, but these benefits may come at a trade‐off with reproductive fitness and may affect the following generation(s). The potential inter‐ and transgenerational effects of long‐term fasting and starvation are particularly poorly understood in vertebrates when they originate from the paternal line. We utilised the externally fertilising zebrafish amenable to a split‐egg clutch design to explore the male‐specific effects of fasting/starvation on fertility and fitness of offspring independently of maternal contribution. Eighteen days of fasting resulted in reduced fertility in exposed males. While average offspring survival was not affected, we detected increased larval growth rate in F1 offspring from starved males and more malformed embryos at 24 h post‐fertilisation in F2 offspring produced by F1 offspring from starved males. Comparing the transcriptomes of F1 embryos sired by starved and fed fathers revealed robust and reproducible increased expression of muscle composition genes but lower expression of lipid metabolism and lysosome genes in embryos from starved fathers. A large proportion of these genes showed enrichment in the yolk syncytial layer suggesting gene regulatory responses associated with metabolism of nutrients through paternal effects on extra‐embryonic tissues which are loaded with maternal factors. We compared the embryo transcriptomes to published adult transcriptome datasets and found comparable repressive effects of starvation on metabolism‐associated genes. These similarities suggest a physiologically relevant, directed and potentially adaptive response transmitted by the father, independently from the offspring's nutritional state, which was defined by the mother

Sperm selection by thermotaxis improves ICSI outcome in mice

Abstract The ejaculate is a heterogeneous pool of spermatozoa containing only a small physiologically adequate subpopulation for fertilization. As there is no method to isolate this subpopulation, its specific characteristics are unknown. This is one of the main reasons why we lack effective tools to identify male infertility and for the low efficiency of assisted reproductive technologies. The aim of this study was to improve ICSI outcome by sperm selection through thermotaxis. Here we show that a specific subpopulation of mouse and human spermatozoa can be selected in vitro by thermotaxis and that this subpopulation is the one that enters the fallopian tube in mice. Further, we confirm that these selected spermatozoa in mice and humans show a much higher DNA integrity and lower chromatin compaction than unselected sperm, and in mice, they give rise to more and better embryos through intracytoplasmic sperm injection, doubling the number of successful pregnancies. Collectively, our results indicate that a high quality sperm subpopulation is selected in vitro by thermotaxis and that this subpopulation is also selected in vivo within the fallopian tube possibly by thermotaxis

Brood‐stock management and early hatchery rearing of Arctic charr (Salvelinus alpinus (Linnaeus))

Arctic charr (Salvelinus alpinus (Linnaeus)) is a stenothermic cold‐water fish, which has been cultured in Northern Europe and North America since the 1980s. The industry has remained relatively small with an annual production between 6000 and 10 000 tonnes, and is still challenged by an unreliable offspring production. This review focuses on offspring production in Arctic charr aquaculture including holding conditions for brood‐stock, fertilisation and egg rearing until hatch. Brood‐stock requires low temperatures during summer (<12°C) with the optimum still unknown. The temperature maximum for egg incubation lies between 6 and 8°C. The composition of an optimal brood‐stock diet is debated regarding fatty acids. A demand for a freshwater‐based diet rich in omega‐6 fatty acids is indicated, but results remain inconclusive. Extensive knowledge has been gained on the timing of spawning and its manipulation through photoperiod, temperature and hormone treatments; spawning can be induced by short‐day photoperiod; and temperature drops to 5°C. Eggs are fertilised dry in ovarian fluid. Egg quality is highly variable and positively related to egg size and energy density. Contrary, little information is available on sperm quality and its impact on egg survival. There may also be profound differences between Arctic charr of stationary or anadromous origin regarding requirements for holding conditions of brood‐stock and their diet. However, these differences have received little attention, and direct comparative studies are in demand