Paternal identity impacts embryonic development for two species of freshwater fish

Paternal-effect-genes revealed through sperm cryopreservation in Perca fluviatilis

Knowledge about paternal-effect-genes (PEGs) (genes whose expression in the progeny is influenced by paternal factors present in the sperm) in fish is very limited. To explore this issue, we used milt cryopreservation as a specific challenge test for sperm cells, thus enabling selection amidst cryo-sensitivity. We created two groups of Eurasian perch (Perca fluviatilis) as a model - eggs fertilized either with fresh (Fresh group) or cryopreserved (Cryo group) milt from the same male followed by phenotypic-transcriptomic examination of consequences of cryopreservation in obtained progeny (at larval stages). Most of the phenotypical observations were similar in both groups, except the final weight which was higher in the Cryo group. Milt cryopreservation appeared to act as a "positive selection" factor, upregulating most PEGs in the Cryo group. Transcriptomic profile of freshly hatched larvae sourced genes involved in the development of visual perception and we identified them as PEGs. Consequently, larvae from the Cryo group exhibited enhanced eyesight, potentially contributing to more efficient foraging and weight gain compared to the Fresh group. This study unveils, for the first time, the significant influence of the paternal genome on the development of the visual system in fish, highlighting pde6g, opn1lw1, and rbp4l as novel PEGs.

Evidence that genetic compatibility underpins female mate choice in a monandrous amphibian

Mate choice for genetic benefits remains controversial, largely because few studies have estimated the relative contributions of additive and non-additive sources of genetic variation to offspring fitness. Moreover, there remains a deficit of these estimates for species where female-mate preferences have been quantified in the wild, especially species characterized by monandry or monogamy. Here, we use artificial fertilization techniques combined with a cross-classified breeding design to simultaneously test for "good genes" and "compatible genes" benefits of mate choice in the monandrous red backed toadlet (Pseudophryne coriacea). In addition, we used a genomic approach to estimate effects of parental-genetic relatedness (assessed using 27, 768 single nucleotide polymorphisms) on offspring fitness. Our results revealed no significant additive genetic effects (sire effects), but highly significant non-additive genetic effects (sire × dam interaction effects), on fertilization success, survival during embryonic development, and hatching success. We also found significant associations between parental genetic similarity and offspring survival (whereby survival was higher when parents were more related), and significant positive relationships between fertilization success and embryo survival through to hatching. These results indicate that offspring viability is significantly influenced by the genetic compatibility of parental genotypes, that more related parents are more genetically compatible, and that gametes with greater compatibility at fertilization produce more viable offspring. More broadly, our findings provide new quantitative genetic evidence that genetic incompatibility underpins female mate preferences. Continued quantitative genetic assessment of the relative importance of good genes versus compatible genes is needed to ascertain the general importance of genetic benefits as a driver of female mate choice.

Parental transgenerational epigenetic inheritance related to dietary crude oil exposure in Danio rerio

Transgenerational inheritance from both parental lines can occur by genetic and epigenetic inheritance. Maternal effects substantially influence offspring survival and fitness. However, investigation of the paternal contribution to offspring success has been somewhat neglected. In the present study, adult zebrafish were separated into female and male groups exposed for 21 days to either a control diet or to a diet containing water accommodated fractions of crude oil. Four F1 offspring groups were obtained: (1) control (non-exposed parents), (2) paternally exposed, (3) maternally exposed and (4) dual-parent-exposed. To determine the maternal and paternal influence on their offspring, we evaluated responses from molecular to whole organismal levels in both generations. Growth rate, hypoxia resistance and heart rate did not differ among parental groups. However, global DNA methylation in heart tissue was decreased in oil-exposed fish compared with control parents. This decrease was accompanied by an upregulation of glycine N-methyltransferase. Unexpectedly, maternal, paternal and dual exposure all enhanced survival of F1 offspring raised in oiled conditions. Regardless of parental exposure, however, F1 offspring exposed to oil exhibited bradycardia. Compared with offspring from control parents, global DNA methylation was decreased in the three offspring groups derived from oil-exposed parents. However, no difference between groups was observed in gene regulation involved in methylation transfer, suggesting that the changes observed in the F1 populations may have been inherited from both parental lines. Phenotypic responses during exposure to persistent environmental stressors in F1 offspring appear to be influenced by maternal and paternal exposure, potentially benefitting offspring populations to survive in challenging environments.

Impact of long-term parental exposure to Tamiflu metabolites on the development medaka offspring (Oryzias latipes)

Despite the widespread use of the antiviral drug, Tamiflu®, little is known about the long-term toxic effects of drug or its metabolites in an aquatic ecosystem. This study integrated epidemiological and ecotoxicological methods to determine environmentally relevant concentrations of Tamiflu. A model based on the species medaka (Oryzias latipes) was then used to determine the health status and reproductivity of adults exposed to the drug as well as the embryonic development of offspring. The proposed ecotoxicological model was also used to quantitatively and qualitatively evaluate the toxicodynamic parameters related to egg production, hatchability, and development. Our results revealed that at an environmentally relevant exposure, Tamiflu and its metabolites had no adverse effects on growth, survival, or fecundity of adult medaka. Nonetheless, we observed a reduction in hatchability under exposure to 300 μg L^-1 and a reduction in body length under exposure exceeding 90 μg L^-1. Under exposure to 300 μg L^-1, the estimated spawning time to reach 50% of the maximum percentage of cumulative egg production (ET50) far exceeded that of the control group (without exposure to Tamiflu). We also observed a ∼ 3-fold decrease in maximum egg hatching (E_max). Based on an integrated epidemiological and ecotoxicological model, predictions of environmental concentrations of Tamiflu and its metabolites revealed that the influenza subtypes associated with increases in environmental concentrations: A(H3N2) > A(H1N1) > type B (in order of their effects). We also determined that A(H3N2) posed a potential risk to hatchability and development. Note however, the environmental concentrations of Tamiflu and its metabolites in most countries are lower than the effect concentrations derived in this study, indicating no hazards for aquatic environments. We recommend the use of hatchability and embryonic development as indicators in assessing the effects of long-term parental exposure to Tamiflu metabolites.

Sex-specific effects of outbreeding on offspring quality in pike (Esox lucius)

Intraspecific genetic admixture occurs when previously separated populations within a species start interbreeding, and it can have either positive, negative, or neutral effects on reproductive performance. As there currently is no reliable predictor for the outcome of admixture, an increased knowledge about admixture effects in different species and populations is important to increase the understanding about what determines the response to admixture. We tested for effects of admixture on F1 offspring quality in three subpopulations of pike (Esox lucius). Gametes were collected in the field, and eggs from each female were experimentally fertilized with milt from a male from each population (one "pure" and two "admixed" treatments). Three offspring quality measures (hatching success, fry survival, and fry length) were determined and compared between (a) pure and admixed population combinations and (b) the sex-specific treatments within each admixed population combination (based on the origin of the male and female, respectively). The results suggested that although there were no overall effects of admixture on offspring quality, the consequences for a given population combination could be sex-specific and thus differ depending on which of the parents originated from one or the other population. All offspring quality traits were influenced by both maternal ID and paternal ID. Sex- and individual-specific effects can have implications for dispersal behavior and gene flow between natural populations, and are important to consider in conservation efforts.

Effect of parental origin on early life history traits of European eel

Establishment of European eel (Anguilla anguilla) hatchery production will rely on selectively bred individuals that produce progeny with the best traits in successive generations. As such, this study used a quantitative genetic breeding design, between four females and nine males (four wild-caught and five cultured), to investigate the effect of paternal origin (wild-caught vs. cultured) and quantify the relative importance of parental effects, including genetic compatibility, on early life history (ELH) performance traits (i.e. fertilization success, embryonic survival at 32 hr post-fertilization, hatch success and larval deformities at 2 days post-hatch) of European eel. Wild-caught males had higher (56%) spermatocrit values than cultured males (45%), while fertilization success, embryonic survival, hatch success and larval deformities were not significantly impacted by paternal origin. This demonstrates that short-term domestication of male eels does not negatively affect offspring quality and enables the consideration of cultured male broodstock in future breeding programmes. Moreover, paternity significantly explained 9.5% of the variability in embryonic survival, providing further evidence that paternal effects need to be taken into consideration in assisted reproduction protocols. Furthermore, maternity significantly explained 54.8% of the variation for fertilization success, 61.7% for embryonic survival, 88.1% for hatching success and 62.8% for larval deformities, validating that maternity is a major factor influencing these "critical" ELH traits. At last, the parental interaction explained 12.8% of the variation for fertilization success, 8.3% for embryonic survival, 4.5% for hatch success and 20.5% for larval deformities. Thus, we conclude that eggs of one female can develop more successfully when crossed with a compatible male, highlighting the importance of mate choice for successful propagation of high-quality offspring. Together, this knowledge will improve early offspring performance, leading to future breeding programmes for this critically endangered and economically important species.