Potential fitness benefits from mate selection in the Atlantic cod (Gadus morhua)

Variation in parasite resistance of Arctic charr, Salvelinus alpinus, between and within sympatric morphs

Genetic variation in resistance against parasite infections is a predominant feature in host-parasite systems. However, mechanisms maintaining genetic polymorphism in resistance in natural host populations are generally poorly known. We explored whether differences in natural infection pressure between resource-based morphs of Arctic charr (Salvelinus alpinus) have resulted in differentiation in resistance profiles. We experimentally exposed offspring of two morphs from Lake Þingvallavatn (Iceland), the pelagic planktivorous charr ("murta") and the large benthivorous charr ("kuðungableikja"), to their common parasite, eye fluke Diplostomum baeri, infecting the eye humor. We found that there were no differences in resistance between the morphs, but clear differences among families within each morph. Moreover, we found suggestive evidence of resistance of offspring within families being positively correlated with the parasite load of the father, but not with that of the mother. Our results suggest that the inherited basis of parasite resistance in this system is likely to be related to variation among host individuals within each morph rather than ecological factors driving divergent resistance profiles at morph level. Overall, this may have implications for evolution of resistance through processes such as sexual selection.

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.

Disentangling structural genomic and behavioural barriers in a sea of connectivity

Genetic divergence among populations arises through natural selection or drift and is counteracted by connectivity and gene flow. In sympatric populations, isolating mechanisms are thus needed to limit the homogenizing effects of gene flow to allow for adaptation and speciation. Chromosomal inversions act as an important mechanism maintaining isolating barriers, yet their role in sympatric populations and divergence with gene flow is not entirely understood. Here, we revisit the question of whether inversions play a role in the divergence of connected populations of the marine fish Atlantic cod (Gadus morhua), by exploring a unique data set combining whole‐genome sequencing data and behavioural data obtained with acoustic telemetry. Within a confined fjord environment, we find three genetically differentiated Atlantic cod types belonging to the oceanic North Sea population, the western Baltic population and a local fjord‐type cod. Continuous behavioural tracking over 4 year revealed temporally stable sympatry of these types within the fjord. Despite overall weak genetic differentiation consistent with high levels of gene flow, we detected significant frequency shifts of three previously identified inversions, indicating an adaptive barrier to gene flow. In addition, behavioural data indicated that North Sea cod and individuals homozygous for the LG12 inversion had lower fitness in the fjord environment. However, North Sea and fjord‐type cod also occupy different depths, possibly contributing to prezygotic reproductive isolation and representing a behavioural barrier to gene flow. Our results provide the first insights into a complex interplay of genomic and behavioural isolating barriers in Atlantic cod and establish a new model system towards an understanding of the role of genomic structural variants in adaptation and diversification.

No support for cryptic choice by ovarian fluid in an external fertilizer

Whether the ovarian fluid (OF) represents a selective environment influencing cryptic female choice was tested using an external fertilizer experiencing intense sperm competition and large effects of OF on sperm swimming behavior-the Arctic charr (Salvelinus alpinus). We physically separated the OF from the eggs of reproductively active females and reintroduced either their own OF or fluid from another female to the eggs. The eggs were then fertilized in vitro in a replicated split-brood design with sperm from two males under synchronized sperm competition trials, while also measuring sperm velocity of the individual males in the individual OFs. We found large effects of males, but no effect of females (i.e., eggs) on paternity, determined from microsatellites. More important, we found no effect of OF treatments on the relative paternity of the two competing males in each pair. This experimental setup does not provide support for the hypothesis that OF plays an important role as medium for cryptic female choice in charr. Power analyses revealed that our sample size is large enough to detect medium-sized changes in relative paternity (medium-sized effect sizes), but not large enough to detect small changes in relative paternity. More studies are needed before a conclusion can be drawn about OF's potential influence on paternity under sperm competition-even in charr.

A mitochondrial long noncoding RNA in atlantic cod harbors complex heteroplasmic tandem repeat motifs

A heteroplasmic tandem repeat (HTR) array occupies 100 to 300 bp of the mitochondrial DNA control region in the Atlantic cod, and recently we noted that the repeat appeared integrated in a polyadenylated mitochondrial long noncoding RNA. Here we provide a more detailed analysis of the mitochondrial HTR in the mitochondrial genome of 134 Atlantic cod specimens. We report all specimens to harbor mitochondrial HTRs in the control region, and identified 26 distinct variants among the 402 repeat motifs assessed. Whereas most specimens contained HTR profiles of 2-5 copies consisting of the same 40-bp motif, 22 specimens showed compound HTR arrays of at least two types of motifs present in the same mitochondrial DNA molecule. We found HTR profiles to be highly conserved between different tissue types of a single individual, and strictly maternally inherited in a mating experiment between parental Atlantic cod expressing different HTR profiles and array motifs. We conclude that mitochondrial heteroplasmy in the control region is very common in Atlantic cod, and results in length heterogenity of the long noncoding RNA lncCR-H.

Metapopulation patterns of additive and nonadditive genetic variance in the sea bass (Dicentrarchus labrax)

Describing and explaining the geographic within‐species variation in phenotypes (“phenogeography”) in the sea over a species distribution range is central to our understanding of a variety of eco‐evolutionary topics. However, phenogeographic studies that have a large potential to investigate adaptive variation are overcome by phylogeographic studies, still mainly focusing on neutral markers. How genotypic and phenotypic data could covary over large geographic scales remains poorly understood in marine species. We crossed 75 noninbred sires (five origins) and 26 dams (two origins; each side of a hybrid zone) in a factorial diallel cross in order to investigate geographic variation for early survival and sex ratio in the metapopulation of the European sea bass (Dicentrarchus labrax), a highly prized marine fish species. Full‐sib families (N = 1,950) were produced and reared in a common environment. Parentage assignment of 7,200 individuals was performed with seven microsatellite markers. Generalized linear models showed significant additive effects for both traits and pleiotropy between traits. A significant nonadditive genetic effect was detected. Different expression of traits and distinct relative performances were found for reciprocal crosses involving populations located on each side of the main hybrid zone located at the Almeria‐Oran front, illustrating asymmetric reproductive isolation. The poor fitness performance observed for the Western Mediterranean population of sea bass is discussed as it represents the main source of seed hatchery production, but also because it potentially illustrates nonadaptive introgression and maladaptation.

Effects of chronic dietary petroleum exposure on reproductive development in polar cod (Boreogadus saida)

Increasing human activities in the Arctic raise the risk of petroleum pollution, thus posing an elevated risk for Arctic organisms to be chronically exposed to petroleum compounds. The endocrine disrupting properties of some of these compounds (i.e. polycyclic aromatic hydrocarbons [PAHs]) present in crude oil may have negative effects on the long and energy intensive reproductive development of polar cod (Boreogadus saida), an Arctic keystone species. In the present study, selected reproductive parameters were examined in feral polar cod exposed to crude oil via a natural diet (0.11, 0.57 and 1.14μg crude oil/g fish/day [corresponding to low, medium and high treatments, respectively]) for 31 weeks prior to spawning. Fish maturing in the current reproductive period made up 92% of the experimental population while 5% were immature and 3% were identified as resting fish. Phase I metabolism of PAHs, indicated by ethoxyresorufin-O-deethylase (EROD) activity, showed a dose-dependent increase in high and medium crude oil treatments at week 6 and 22, respectively. Decreasing EROD activity and increasing PAH bile metabolite concentrations over the experimental period may be explained by reproductive maturity stage. Significant alterations in sperm motility were observed in crude oil exposed males compared to the controls. The investigated somatic indices (gonad and hepatic), germ cell development and plasma steroid levels (estradiol-17β [females], testosterone [males and females] and 11-ketotestosterone [males]) were not significantly altered by chronic dietary exposure to crude oil. The environmentally realistic doses polar cod were chronically exposed to in this study were likely not high enough to induce adverse effects in this ecologically important fish species. This study elucidated many baseline aspects of polar cod reproductive physiology and emphasized the influence of maturation state on biomarkers of PAH biotransformation (EROD and PAH bile metabolites).

Differential Survival among Batches of Atlantic Cod (Gadus morhua L.) from Fertilisation through to Post-Metamorphosis

Aquaculture production of cod has decreased from over 20,000 tonnes in 2009 to less than 2,000 tonnes in 2014 and the industry faces many challenges, one of which is high and unpredictably variable mortality rates in the early life stages. Hence, full-cycle farming with hatchery produced juveniles is still considered unprofitable compared to fisheries and on-growing of wild cod. In the present study, potential batch differences in progeny survival of wild-caught, hatchery-spawned Faroe Bank cod (Gadus morhua L.) were investigated at two defined periods during early life history; i) the embryo stage (60 day degrees post fertilisation) and ii) the fry stage (110 days post hatch), post metamorphosis. The fry stage experiment was conducted in three replicates (N = 300 per replicate), and a panel of three polymorphic microsatellite markers was used for parental analysis. Mean survival rate at the embryo stage was 69% (± 20% SD). Survival was positively associated with egg diameter (P < 0.01), explaining 90% of the variation in egg survival rates. The data were too scarce to conclude either way concerning a possible correlation between survival rates between the two periods (P < 0.10). Offspring from three batches (from a total of eight) dominated in the fry stage, contributing over 90% of the progeny, and results were consistent over all three replicate tanks. The skewed batch representation observed may be of relevance to the effective management of selective breeding programmes for cod.

Post-copulatory opportunities for sperm competition and cryptic female choice provide no offspring fitness benefits in externally fertilizing salmon

There is increasing evidence that females can somehow improve their offspring fitness by mating with multiple males, but we understand little about the exact stage(s) at which such benefits are gained. Here, we measure whether offspring fitness is influenced by mechanisms operating solely between sperm and egg. Using externally fertilizing and polyandrous Atlantic salmon (Salmo salar), we employed split-clutch and split-ejaculate in vitro fertilization experiments to generate offspring using designs that either denied or applied opportunities for sperm competition and cryptic female choice. Following fertilizations, we measured 140 days of offspring fitness after hatch, through growth and survival in hatchery and near-natural conditions. Despite an average composite mortality of 61%, offspring fitness at every life stage was near-identical between groups fertilized under the absence versus presence of opportunities for sperm competition and cryptic female choice. Of the 21 551 and 21 771 eggs from 24 females fertilized under monandrous versus polyandrous conditions, 68% versus 67.8% survived to the 100-day juvenile stage; sub-samples showed similar hatching success (73.1% versus 74.3%), had similar survival over 40 days in near-natural streams (57.3% versus 56.2%) and grew at similar rates throughout. We therefore found no evidence that gamete-specific interactions allow offspring fitness benefits when polyandrous fertilization conditions provide opportunities for sperm competition and cryptic female choice.

Conspicuous carotenoid-based pelvic spine ornament in three-spined stickleback populations-occurrence and inheritance

Reports on reddish carotenoid-based ornaments in female three-spined sticklebacks (Gasterosteus aculeatus) are few, despite the large interest in the species' behaviour, ornamentation, morphology and evolution. We sampled sticklebacks from 17 sites in north-western Europe in this first extensive study on the occurrence of carotenoid-based female pelvic spines and throat ornaments. The field results showed that females, and males, with reddish spines were found in all 17 populations. Specimens of both sexes with conspicuous red spines were found in several of the sites. The pelvic spines of males were more intensely red compared to the females' spines, and large specimens were more red than small ones. Fish infected with the tapeworm (Schistocephalus solidus) had drabber spines than uninfected fish. Both sexes had red spines both during and after the spawning period, but the intensity of the red colour was more exaggerated during the spawning period. As opposed to pelvic spines, no sign of red colour at the throat was observed in any female from any of the 17 populations. A rearing experiment was carried out to estimate a potential genetic component of the pelvic spine ornament by artificial crossing and rearing of 15 family groups during a 12 months period. The results indicated that the genetic component of the red colour at the spines was low or close to zero. Although reddish pelvic spines seem common in populations of stickleback, the potential adaptive function of the reddish pelvic spines remains largely unexplained.

Cryptic choice of conspecific sperm controlled by the impact of ovarian fluid on sperm swimming behavior

Despite evidence that variation in male-female reproductive compatibility exists in many fertilization systems, identifying mechanisms of cryptic female choice at the gamete level has been a challenge. Here, under risks of genetic incompatibility through hybridization, we show how salmon and trout eggs promote fertilization by conspecific sperm. Using in vitro fertilization experiments that replicate the gametic microenvironment, we find complete interfertility between both species. However, if either species' ova were presented with equivalent numbers of both sperm types, conspecific sperm gained fertilization precedence. Surprisingly, the species' identity of the eggs did not explain this cryptic female choice, which instead was primarily controlled by conspecific ovarian fluid, a semiviscous, protein-rich solution that bathes the eggs and is released at spawning. Video analyses revealed that ovarian fluid doubled sperm motile life span and straightened swimming trajectory, behaviors allowing chemoattraction up a concentration gradient. To confirm chemoattraction, cell migration tests through membranes containing pores that approximated to the egg micropyle showed that conspecific ovarian fluid attracted many more spermatozoa through the membrane, compared with heterospecific fluid or water. These combined findings together identify how cryptic female choice can evolve at the gamete level and promote reproductive isolation, mediated by a specific chemoattractive influence of ovarian fluid on sperm swimming behavior.

Genetic analysis of captive spawning strategies for the endangered Rio Grande Silvery Minnow

Captive breeding and rearing are central elements in conservation, management, and recovery planning for many endangered species including Rio Grande Silvery Minnow, a North American freshwater cyprinid. Traditionally, the sole purpose of hatcheries was to produce as many fish as feasible for stocking and harvest. Production quotas are also an important consideration in hatchery programs for endangered species, but they must also maintain and maximize genetic diversity of fish produced through implementation of best breeding practices. Here, we assessed genetic outcomes and measures of productivity (number of eggs and larval viability) for three replicates of three mating designs that are used for this small, pelagic-spawning fish. These were 1) monogamous mating, 2) hormone-induced communal spawning, and 3) environmentally cued communal spawning. A total of 180 broodstock and 450 progeny were genotyped. Genetic diversity and egg productivity did not differ significantly among spawning designs (H e : F = 0.52, P = 0.67; H o : F = 0.12, P = 0.89; number of eggs: F = 3.59, P = 0.09), and there was evidence for variance in reproductive success among individuals in all three designs. Allelic richness declined from the broodstock to progeny generation in all breeding designs. There was no significant difference in the genetic effective size (regardless of the method used) among designs. Significantly more viable eggs were produced in environmentally cued communal spawn compared to the alternative strategies (F = 5.72, P = 0.04), but this strategy is the most difficult to implement.

Parental identity influences progeny responses to incubation thermal stress in sockeye salmon Onchorhynchus nerka

The influence of individual parentage on progeny responses to early developmental temperature stress was examined in a cross-fertilization experiment using sockeye salmon Oncorhynchus nerka. Differences in survival, hatch timing and size were examined among five paternally linked and five maternally linked offspring families (Weaver Creek population, British Columbia, Canada) incubated at 12, 14 and 16° C from just after fertilization to hatch. Mean embryonic survival was significantly lower at 14 and 16° C; however, offspring families had substantially different survival responses across the thermal gradient (crossing reaction norms). Within temperature treatments, substantial variation in embryonic survival, alevin mass, time-to-hatch and hatch duration were attributable to family identity; however, most traits were governed by significant temperature-family interactions. For embryonic survival, large differences between families at 16° C were due to both female and male spawner influence, whereas inter-family differences were obscured at 14° C (high intra-family variation), and minimal at 12° C (only maternal influence detected). Despite post-hatch rearing under a common cool thermal regime, persistent effects of both temperature and parentage were detected in alevin and 3 week-old fry. Collectively, these findings highlight the crucial role that parental influences on offspring may have in shaping future selection within salmonid populations exposed to elevated thermal regimes. An increased understanding of parental and temperature influences and their persistence in early development will be essential to developing a more comprehensive view of population spawning success and determining the adaptive capacity of O. nerka populations in the face of environmental change.

Fertilization success and the estimation of genetic variance in sperm competitiveness

A key question in sexual selection is whether the ability of males to fertilize eggs under sperm competition exhibits heritable genetic variation. Addressing this question poses a significant problem, however, because a male's ability to win fertilizations ultimately depends on the competitive ability of rival males. Attempts to partition genetic variance in sperm competitiveness, as estimated from measures of fertilization success, must therefore account for stochastic effects due to the random sampling of rival sperm competitors. In this contribution, we suggest a practical solution to this problem. We advocate the use of simple cross-classified breeding designs for partitioning sources of genetic variance in sperm competitiveness and fertilization success and show how these designs can be used to avoid stochastic effects due to the random sampling of rival sperm competitors. We illustrate the utility of these approaches by simulating various scenarios for estimating genetic parameters in sperm competitiveness, and show that the probability of detecting additive genetic variance in this trait is restored when stochastic effects due to the random sampling of rival sperm competitors are controlled. Our findings have important implications for the study of the evolutionary maintenance of polyandry.

Parental effects on embryonic viability and growth in Arctic charr Salvelinus alpinus at two incubation temperatures

The parental influences on three progeny traits (survival to eyed-embryo stage, post-hatching body length and yolk-sac volume) of Arctic charr Salvelinus alpinus were studied under two thermal conditions (2 and 7 degrees C) using a factorial mating design. The higher temperature resulted in elevated mortality rates and less advanced development at hatching. Survival was mostly attributable to maternal effects at both temperatures, but the variation among families was dependent on egg size only at the low temperature. No additive genetic variation (or pure sire effect) could be observed, whereas the non-additive genetic effects (parental combination) contributed to offspring viability at 2 degrees C. In contrast, any observable genetic variance in survival was lost at 7 degrees C, most likely due to the increased environmental variance. Irrespective of temperature, dam and sire-dam interaction contributed significantly to the phenotypic variation in both larval length and yolk size. A significant proportion of the variation in larval length was also due to the sire effect at 2 degrees C. Maternal effects were mediated partly through egg size, but as a whole, they decreased in importance at the high temperature, enabling a concomitant increase in non-additive genetic effects. For larval length, however, the additive component, like maternal effects, decreased at 7 degrees C. The present results suggest that an exposure to thermal stress during incubation can modify the genetic architecture of early developmental traits in S. alpinus and presumably constrain their short-term adaptive potential and evolvability by increasing the amount of environmentally induced variation.

Chapter 3. Effects of climate change and commercial fishing on Atlantic cod Gadus morhua

During the course of the last century, populations of Atlantic cod Gadus morhua L. have undergone dramatic declines in abundance across their biogeographic range, leading to debate about the relative roles of climatic warming and overfishing in driving these changes. In this chapter, we describe the geographic distributions of this important predator of North Atlantic ecosystems and document extensive evidence for limitations of spatial movement and local adaptation from population genetic markers and electronic tagging. Taken together, this evidence demonstrates that knowledge of spatial population ecology is critical for evaluating the effects of climate change and commercial harvesting. To explore the possible effects of climate change on cod, we first describe thermal influences on individual physiology, growth, activity and maturation. We then evaluate evidence that temperature has influenced population-level processes including direct effects on recruitment through enhanced growth and activity, and indirect effects through changes to larval food resources. Although thermal regimes clearly define the biogeographic range of the species, and strongly influence many aspects of cod biology, the evidence that population declines across the North Atlantic are strongly linked to fishing activity is now overwhelming. Although there is considerable concern about low spawning stock biomasses, high levels of fishing activity continues in many areas. Even with reduced fishing effort, the potential for recovery from low abundance may be compromised by unfavourable climate and Allee effects. Current stock assessment and management approaches are reviewed, alongside newly advocated methods for monitoring stock status and recovery. However, it remains uncertain whether the rebuilding of cod to historic population sizes and demographic structures will be possible in a warmer North Atlantic.

Genetic compatibility and hatching success in the sea lamprey (Petromyzon marinus)

Recent discussion of genetic benefits of polyandry and female mate choice has distinguished between two potential factors influencing offspring quality: (i) some males carry higher quality genes and (ii) males and females differ in their degree of genetic compatibility. We examined evidence for effects of good genes and genetic compatibility on embryonic survival of sea lamprey (Petromyzon marinus), a fish species with external fertilization that spawns in North Atlantic rivers. Using in vitro fertilization, we made all possible crosses among 10 males and 5 females collected in the spawning grounds. Male identity did not have any significant effect on hatching success. However, female identity and male x female interactions had a highly significant effect on hatching success. Our results suggest that genetic compatibility between male and female genomes plays an important role in embryo survival during the early stages of development in the sea lamprey.

Male genetic quality and the inequality between paternity success and fertilization success: consequences for studies of sperm competition and the evolution of polyandry

Studies of postcopulatory sexual selection typically estimate a male's fertilization success from his paternity success (P2) calculated at hatching or birth. However, P2 may be affected by differential embryo viability, thereby confounding estimations of true fertilization success (F2). This study examines the effects of variation in the ability of males to influence embryo viability upon the inequality between P2 and F2. It also investigates the consequences of this inequality for testing the hypothesis that polyandrous females accrue viability benefits for their offspring through facilitation of sperm competition (good-sperm model). Simulations of competitive mating trials show that although relative measures of male reproductive success tend to underestimate the strength of underlying good-sperm processes, good-sperm processes can be seriously overestimated using P2 values if males influence the viability of the embryos they sire. This study cautions the interpretation of P2 values as a proxy for fertilization success or sperm competitiveness in studies of postcopulatory sexual selection, and highlights that the good-sperm hypothesis needs empirical support from studies able to identify and separate unequivocally the males' ability to win fertilizations from their ability to influence the development of embryos.

Viability of brown trout embryos positively linked to melanin-based but negatively to carotenoid-based colours of their fathers

‘Good-genes’ models of sexual selection predict significant additive genetic variation for fitness-correlated traits within populations to be revealed by phenotypic traits. To test this prediction, we sampled brown trout (Salmo trutta) from their natural spawning place, analysed their carotenoid-based red and melanin-based dark skin colours and tested whether these colours can be used to predict offspring viability. We produced half-sib families by in vitro fertilization, reared the resulting embryos under standardized conditions, released the hatchlings into a streamlet and identified the surviving juveniles 20 months later with microsatellite markers. Embryo viability was revealed by the sires' dark pigmentation: darker males sired more viable offspring. However, the sires' red coloration correlated negatively with embryo survival. Our study demonstrates that genetic variation for fitness-correlated traits is revealed by male colour traits in our study population, but contrary to predictions from other studies, intense red colours do not signal good genes.

SOURCES OF GENETIC AND PHENOTYPIC VARIANCE IN FERTILIZATION RATES AND LARVAL TRAITS IN A SEA URCHIN

In nonresource based mating systems females are thought to derive indirect genetic benefits by mating with high-quality males. Such benefits can be due either to the intrinsic genetic quality of sires or to beneficial interactions between maternal and paternal haplotypes. Animals with external fertilization and no parental care offer unrivaled opportunities to address these hypotheses. With these systems, cross-classified breeding designs and in vitro fertilization can be used to disentangle sources of genetic and environmental variance in offspring fitness. Here, we employ these approaches in the Australian sea urchin Heliocidaris erythrogramma and explore how sire-dam identities influence fertilization rates, embryo viability (survival to hatching), and metamorphosis, as well as the interrelationships between these potential fitness traits. We show that fertilization is influenced by a combination of strong maternal effects and intrinsic male effects. Our subsequent analysis of embryo viability, however, revealed a highly significant interaction between parental genotypes, indicating that partial incompatibilities can severely limit offspring survival at this life-history stage. Importantly, we detected no significant relationship between fertilization rates and embryo viability. This finding suggests that fertilization rates should not be inferred from hatching rates, which is commonly practiced in species in which it is not possible to estimate fertilization at conception. Finally, we detected significant additive genetic variance due to sires in rates of juvenile metamorphosis, and a positive correlation between fertilization rates and metamorphosis. This latter finding indicates that the performance of a male's ejaculate in noncompetitive IVF trials predicts heritable offspring traits, although the fitness implications of variance in rates of spontaneous juvenile metamorphosis have yet to be determined.

‘Good-genes’ and ‘compatible-genes’ effects in an Alpine whitefish and the information content of breeding tubercles over the course of the spawning season

Some models of sexual selection predict that individuals vary in their genetic quality and reveal some of this variation in their secondary sexual characteristics. Alpine whitefish (Coregonus sp.) develop breeding tubercles shortly before their spawning season. These tubercles are epidermal structures that are distributed regularly along the body sides of both males and females. There is still much unexplained variation in the size of breeding tubercles within both sexes and with much overlap between the sexes. It has been suggested that breeding tubercles function to maintain body contact between the mating partners during spawning, act as weapons for defence of spawning territories, or are sexual signals that reveal aspects of genetic quality. We took two samples of whitefish from their spawning place, one at the beginning and one around the peak of spawning season. We found that females have on average smaller breeding tubercles than males, and that tubercle size partly reveals the stage of gonad maturation. Two independent full-factorial breeding experiments revealed that embryo mortality was significantly influenced by male and female effects. This finding demonstrates that the males differed in their genetic quality (because offspring get nothing but genes from their fathers). Tubercle size was negatively linked to some aspects of embryo mortality in the first breeding experiment but not significantly so in the second. This lack of consistency adds to inconsistent results that were reported before and suggests that (i) some aspects of genetic quality are not revealed in breeding tubercles while others are, or (ii) individuals vary in their signaling strategies and the information content of breeding tubercles is not always reliable. Moreover, the fact that female whitefish have breeding tubercles of significant size while males seem to have few reasons to be choosy suggests that the tubercles might also serve some functions that are not linked to sexual signaling.

Sexual dimorphism in pelvic fin length of Atlantic cod

Behavioural differences between females and males may result in sexual dimorphism among morphological traits associated with these behaviours. In the broadcast-spawning Atlantic cod ( Gadus morhua L., 1758), release of gametes occurs during a “ventral mount” in which the male positions himself directly beneath the female while grasping her with his pelvic fins. Males also display the pelvic fins during agonistic encounters with other males. Based on data obtained from four Atlantic cod populations off Canada and Norway, we find clear evidence of sexual dimorphism in pelvic fin size, the fins being significantly larger in males than in females. Pelvic fin size was, however, not more variable than other morphological traits and was not correlated with body condition or drumming muscles mass (hypothesized to be a secondary sexual characteristic in this species). To our knowledge, this is the first study to demonstrate sexual dimorphism in any external morphological trait in a gadoid fish. Although the observed differences in pelvic fin size may be a product of sexual selection, we identify future work to test this hypothesis and to explore more fully the causes and fitness consequences of this sexual bias in Atlantic cod.