Jarle Tryti Nordeide

Large-scale sequence analyses of Atlantic cod.

The Atlantic cod (Gadus morhua) is a key species in the North Atlantic ecosystem and commercial fisheries, with increasing aquacultural production in several countries. A Norwegian effort to sequence the complete 0.9Gbp genome by the 454 pyrosequencing technology has been initiated and is in progress. Here we review recent progress in large-scale sequence analyses of the nuclear genome, the mitochondrial genome and genome-wide microRNA identification in the Atlantic cod. The nuclear genome will be de novo sequenced with 25 times oversampling. A total of 120 mitochondrial genomes, sampled from several locations in the North Atlantic, are being completely sequenced by Sanger technology in a high-throughput pipeline. These sequences will be included in a new database for maternal marker reference of Atlantic cod diversity. High-throughput 454 sequencing, as well as Evolutionary Image Array (EvoArray) informatics, is used to investigate the complete set of expressed microRNAs and corresponding mRNA targets in various developmental stages and tissues. Information about microRNA profiles will be essential in the understanding of transcriptome complexity and regulation. Finally, developments and perspectives of Atlantic cod aquaculture are discussed in the light of next-generation high-throughput sequence technologies.

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

Little evidence of benefits from female mate choice has been found when males provide no parental care or resources. Yet, good genes models of sexual selection suggest that elaborated male sexual characters are reliable signals of mate quality and that the offspring of males with elaborate sexual ornaments will perform better than those of males with less elaborate ornaments. We used cod (Gadus morhua L.), an externally fertilizing species where males provide nothing but sperm, to examine the potential of optimal mate selection with respect to offspring survival. By applying in vitro fertilizations, we crossed eight females with nine males in all possible combinations and reared each of the 72 sib groups. We found that offspring survival was dependent on which female was mated with which male and that optimal mate selection has the potential to increase mean offspring survival from 31.9 to 55.6% (a 74% increase). However, the size of the male sexual ornaments and sperm quality (i.e. sperm velocity and sperm density) could not predict offspring survival. Thus, even if there may be large fitness benefits of mate selection, we might not yet have identified the male characteristics generating high offspring survival.

Female ornaments revisited – are they correlated with offspring quality?

The evolution and signalling content of female ornamentation has remained an enduring challenge to evolutionary biologists, despite the fact that secondary sexual characters are widespread in females. While females usually invest significant amounts of their resources, including carotenoids, in offspring, all the resources allocated to elaborate ornamentation reduce resources available for other purposes. This may in turn constrain female fitness leading to dishonest female signalling. We review the literature for empirical studies on mutually ornamented species with conventional sex roles, by focusing on the association between female ornaments and quality of their offspring. We found 43 papers where 33 (77%) are bird-studies, nine (21%) are on fishes, and one (2%) is a lizard-study. Nine of these report negative, 14 non-existing, and 20 positive associations between female ornament and offspring quality. Eighteen of the bird studies (55%) show a positive association between the two traits investigated, whereas five (15%) of the studies report a negative association. The number of fish studies, although few, is skewed in the opposite direction with two (22%) and four (44%) studies supporting positive and negative association, respectively. A minority of studies on carotenoids-based ornaments reports a positive association (4 of 18 studies, or 22%) between the traits, which is low compared to studies on non-carotenoids-based ornaments (16 of 25 studies, or 64%). The above-mentioned relative large number of studies with negative association, especially common in studies on fishes and in carotenoids-based-ornaments, challenges the generality of the direct selection hypothesis to account for female fineries. This is important because this hypothesis seems to have strong support in recent literature on the topic. In the present paper, we also propose possible explanations for the observed differences between taxa and suggest directions and ideas for future research on the evolution of female ornamentation.

Genomic divergence between the migratory and stationary ecotypes of Atlantic cod

Atlantic cod displays a range of phenotypic and genotypic variations, which includes the differentiation into coastal stationary and offshore migratory types of cod that co‐occur in several parts of its distribution range and are often sympatric on the spawning grounds. Differentiation of these ecotypes may involve both historical separation and adaptation to ecologically distinct environments, the genetic basis of which is now beginning to be unravelled. Genomic analyses based on recent sequencing advances are able to document genomic divergence in more detail and may facilitate the exploration of causes and consequences of genome‐wide patterns. We examined genomic divergence between the stationary and migratory types of cod in the Northeast Atlantic, using next‐generation sequencing of pooled DNA from each of two population samples. Sequence data was mapped to the published cod genome sequence, arranged in more than 6000 scaffolds (611 Mb). We identified 25 divergent scaffolds (26 Mb) with a higher than average gene density, against a backdrop of overall moderate genomic differentiation. Previous findings of localized genomic divergence in three linkage groups were confirmed, including a large (15 Mb) genomic region, which seems to be uniquely involved in the divergence of migratory and stationary cod. The results of the pooled sequencing approach support and extend recent findings based on single‐nucleotide polymorphism markers and suggest a high degree of reproductive isolation between stationary and migratory cod in the North‐east Atlantic.

RNA deep sequencing of the Atlantic cod transcriptome

The Atlantic cod (Gadus morhua) is an emerging aquaculture species. Efforts to develop and characterize its genomic recourses, including draft-grade genome sequencing, have been initiated by the research community. The transcriptome represents the whole complement of RNA transcripts in cells and tissues and reflects the expressed genes at various life stages, tissue types, physiological states, and environmental conditions. We are investigating the Atlantic cod transcriptome by Roche 454, Illumina GA, and ABI SOLiD deep sequencing platforms and corresponding bioinformatics. Both embryonic developmental stages and adult tissues are studied. Here we summarize our recent progress in the analyses of nuclear and mitochondrial polyA mRNAs, non-protein-coding intermediate RNAs, and regulatory microRNAs.

Ornaments or offspring? Female sticklebacks (Gasterosteus aculeatus L.) trade off carotenoids between spines and eggs

Hypotheses and models to explain female ornaments often assume that the elaborated traits are condition dependent; nevertheless, few empirical studies have addressed this topic. We studied a population of three‐spined sticklebacks (Gasterosteus aculeatus) in which the females have conspicuous, carotenoid‐based red coloration to their pelvic spines. The red coloration seems not to be condition dependent, as coloration is negatively associated with age and body length and not associated with condition. Furthermore, redder females did not have a lower density of leucocytes. We found a negative association between the females’ red carotenoid‐based coloration in the spines and the amount of carotenoids in the females gonads. Males choosing red‐coloured females will fertilize eggs with small amounts of carotenoids and appear not to gain any benefit from their mates’ phenotypic quality that could result in offspring of improved quality. These results do not support the ‘direct selection hypothesis’ to explain the existence of the female ornaments.

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.

Mitogenome sequence variation in migratory and stationary ecotypes of North-east Atlantic cod.

Sequencing of mitochondrial gene fragments from specimens representing a wide range of geographical locations has indicated limited population structuring in Atlantic cod (Gadus morhua). We recently performed whole genome analysis based on next-generation sequencing of two pooled ecotype samples representing offshore migratory and inshore stationary cod from the North-east Atlantic Ocean. Here we report molecular features and variability of the 16.7kb mitogenome component that was collected from the datasets. These sequences represented more than 25 times coverage of each individual and more than 1100 times coverage of each ecotype sample. We estimated the mitogenome to have evolved 14 times more rapidly than the nuclear genome. Among the 365 single nucleotide polymorphism (SNP) sites identified, 121 were shared between ecotypes, and 151 and 93 were private within the migratory and stationary cod, respectively. We found 323 SNPs to be located in protein coding genes, of which 29 were non-synonymous. One synonymous site in ND2 was likely to be under positive selection. FST measurements indicated weak differentiation in ND1 and ND2 between ecotypes. We conclude that the Atlantic cod mitogenome and the nuclear genome apparently evolved by distinct evolutionary constraints, and that the reproductive isolation observed from whole genome analysis was not visible in the mtDNA sequences.

On the relative effect of spawning asynchrony, sperm quantity, and sperm quality on paternity under sperm competition in an external fertilizer

How much of a fitness benefit is obtained by dominant males of external fertilizers from releasing ejaculates in synchrony with female egg-release when engaging in sperm competition, and what is the most important sperm trait for paternity in these situations? The Arctic charr (Salvelinus alpinus) is an external fertilizer experiencing intense male-male competition over reproductive opportunities including sperm competition. To compensate for their disadvantage the sneaker males, which often spawn out of synchrony with the female, produce more and faster sperm than the guarding males. We used controlled in vitro fertilization trials with experimentally produced dominant and subordinate, sneaker males to test what effect relative synchrony in gamete release, sperm quality (i.e., motility and velocity) and sperm quantity have on a male’s fertilization success in pair-wise sperm competitions. When the sneaker males released ejaculates after the guarding male there was no overall difference in fertilization success. The quality (i.e., motility and velocity) of a male’s sperm relative to that of the competing male was the best predictor of male fertilization success regardless of their mating tactic and spawning synchrony. The relative number of sperm cells also had an effect on fertilization success, but mainly when the dominant and sneaker male ejaculated synchronously. Our close imitation of natural sperm competition in charr shows that the sneaker males of external fertilizing species may fully compensate for their disadvantaged mating role by producing ejaculates of higher quality - an adjustment strangely not met by dominants.

Status specific tailoring of sperm behavior in an external fertilizer

Why dominant males experiencing intense sperm competition sometimes show low investments in sperm production is not always obvious. One well-documented example is that of the external fertilizing teleost, the Arctic charr (Salvelinus alpinus), where individuals becoming dominant reduce sperm production and sperm swimming speed in water compared to subordinates. Here we report how ovarian fluid differentially influences sperm velocity of dominant and subordinate male Arctic charr. That is, sperm from dominant males increase their velocity in water diluted ovarian fluid compared to that observed in water, while sperm from subordinates, on the other hand, decrease velocity in ovarian fluid compared to that observed in water. Thus, subordinates, who invest more resources in their sperm and usually show the highest sperm velocity in water, have lower gains from their investment than dominant males when sperm are swimming in ovarian fluid. In sum, our result suggests that ovarian fluid increase sperm velocity more in dominant males than in subordinate males. Although this finding could partly be caused by cryptic female choice exerted by the ovarian fluid for sperm from dominant males, an alternative and more parsimonious explanation is that sperm from dominant males may simply be better designed for swimming in ovarian fluid compared to sperm from subordinate males. Thus, sperm production in the two reproductive roles seems to be adaptively tailored to different external environments.