Sperm traits in farmed and wild Atlantic salmon Salmo salar.

Differences in sperm metabolism and morphology between wild and non-local farmed Atlantic salmon Salmo salar were assessed by measuring metabolic enzyme activities and length of sperm flagella. No differences were observed between wild and farmed S. salar sperm with regards to cell counts or any of the biochemical variables assessed. Flagella of sperm cells were significantly longer in wild than farmed S. salar; however, this did not result in higher energy levels or different fertilization rates.

Inter-population ovarian fluid variation differentially modulates sperm motility in Atlantic cod Gadus morhua.

This study tested the hypothesis that the effects of Atlantic cod Gadus morhua ovarian fluid on sperm motility variables are population specific. Sperm from a northern G. morhua population were activated in the presence of ovarian fluid from either northern or southern G. morhua at different concentrations. Ovarian fluid acted as a filter, in some cases reducing sperm swimming performance compared with seawater. Fluid from females foreign in population (southern) to the males (northern) had a greater inhibiting effect than those from the native population. Follow-up analysis indicated that the ovarian fluids had lower Ca(2+) concentration in northern than southern G. morhua, which could be the causative mechanism. If widespread, such cryptic female choice could reduce the incidence of intraspecific hybridization among diverged populations and contribute to reproductive isolation.

The effects of sexual selection on life-history traits: an experimental study on guppies.

Sexual selection is often prevented during captive breeding in order to maximize effective population size and retain genetic diversity. However, enforcing monogamy and thereby preventing sexual selection may affect population fitness either negatively by preventing the purging of deleterious mutations or positively by reducing sexual conflicts. To better understand the effect of sexual selection on the fitness of small populations, we compared components of female fitness and the expression of male secondary sexual characters in 19 experimental populations of guppies (Poecilia reticulata) maintained under polygamous or monogamous mating regimes over nine generations. In order to generate treatments that solely differed by their level of sexual selection, the middle-class neighbourhood breeding design was enforced in the monogamous populations, while in the polygamous populations, all females contributed similarly to the next generation with one male and one female offspring. This experimental design allowed potential sexual conflicts to increase in the polygamous populations because selection could not operate on adult-female traits. Clutch size and offspring survival showed a weak decline from generation to generation but did not differ among treatments. Offspring size, however, declined across generations, but more in monogamous than polygamous populations. By generation eight, orange- and black-spot areas were larger in males from the polygamous treatment, but these differences were not statistically significant. Overall, these results suggest that neither sexual conflict nor the purging of deleterious mutation had important effects on the fitness of our experimental populations. However, only few generations of enforced monogamy in a benign environment were sufficient to negatively affect offspring size, a trait potentially crucial for survival in the wild. Sexual selection may therefore, under certain circumstances, be beneficial over enforced monogamy during captive breeding.

An experimental study of the multiple effects of brown trout Salmo trutta on the bioenergetics of two Arctic charr Salvelinus alpinus morphs.

This study investigated the importance of competition with brown trout Salmo trutta as a driver of the morphological and behavioural divergence of two morphs of Arctic charr Salvelinus alpinus. The morphs originated from two lakes differing in absence or presence of the competitor. The bioenergetics and behaviour of S. alpinus were quantified in replicate experimental enclosures (mean volume: 150 m(3)) stocked with 15 S. alpinus of one morph or the other and in the absence or presence of nine S. trutta. The presence of S. trutta decreased growth rate, affected food consumption and increased activity costs in S. alpinus, but provided little support for the hypothesis that competition with S. trutta is a major driver of the divergence of the two S. alpinus morphs. Both morphs responded similarly in terms of mean growth and consumption rates per enclosure, but the association between individual morphology and growth rate reversed between allopatric and sympatric enclosures. While the activity patterns of the two morphs were unaffected by the presence of S. trutta, their swimming speed and activity rate differed. Since the profound differences in the structure of the physical habitat of the source lakes provided a more likely explanation for the difference observed among these two morphs than interspecific competition, it is hypothesized that physical habitat may sometimes be a significant driving force of the phenotypic divergence.

Temporal change in inbreeding depression in life-history traits in captive populations of guppy (Poecilia reticulata): evidence for purging?

Inbreeding depression, which generally affects the fitness of small populations, may be diminished by purging recessive deleterious alleles when inbreeding persists over several generations. Evidence of purging remains rare, especially because of the difficulties of separating the effects of various factors affecting fitness in small populations. We compared the expression of life-history traits in inbred populations of guppy (Poecilia reticulata) with contemporary control populations over 10 generations in captivity. We estimated inbreeding depression as the difference between the two types of populations at each generation. After 10 generations, the inbreeding coefficient reached a maximum value of 0.56 and 0.16 in the inbred and control populations, respectively. Analysing changes in the life-history traits across generations showed that inbreeding depression in clutch size and offspring survival increased during the first four to six generations in the populations from the inbred treatment and subsequently decreased as expected if purging occurred. Inbreeding depression in two other traits was weaker but showed similar changes across generations. The loss of six populations in the inbred treatment indicates that removal of deleterious alleles also occurred by extinction of populations that presumably harboured high genetic load.

Growth hormone transgenesis does not influence territorial dominance or growth and survival of first-feeding Atlantic salmon Salmo salar in food-limited stream microcosms.

This study explored the relative competitive ability and performance of first-feeding growth hormone (GH) transgenic and non-transgenic Atlantic salmon Salmo salar fry under low food conditions. Pair-wise dominance trials indicated a strong competitive advantage for residents of a contested foraging territory. Transgenic and non-transgenic individuals, however, were equally likely to be dominant. Similarly, in stream environments with limited food, the transgene did not influence the growth in mass or survival at high or low fry densities. Fry in low-density treatments, however, performed better than fry in high-density treatments. These results indicate that, under the environment examined, the growth performance of GH-transgenic and non-transgenic S. salar may be similar during first feeding, an intense period of selection in their life history. Similarities in competitive ability and growth performance with wild-type fish suggest that the capacity of transgenic S. salar to establish in natural streams may not be inhibited during early life history.

Selection against late emergence and small offspring in Atlantic salmon (Salmo salar).

Timing of breeding and offspring size are maternal traits that may influence offspring competitive ability, dispersal, foraging, and vulnerability to predation and climatic conditions. To quantify the extent to which these maternal traits may ultimately affect an organism's fitness, we undertook laboratory and field experiments with Atlantic salmon (Salmo salar). To control for confounding effects caused by correlated traits, manipulations of the timing of fertilization combined with intraclutch comparisons were used. In the wild, a total of 1462 juveniles were marked at emergence from gravel nests. Recapture rates suggest that up to 83.5% mortality occurred during the first four months after emergence from the gravel nests, with the majority (67.5%) occurring during the initial period ending 17 days after median emergence. Moreover, the mortality was selective during this initial period, resulting in a significant phenotypic shift toward an earlier date of and an increased length at emergence. However, no significant selection differentials were detected thereafter, indicating that the critical episode of selection had occurred at emergence. Furthermore, standardized selection gradients indicated that selection was more intense on date of than on body size at emergence. Timing of emergence had additional consequences in terms of juvenile body size. Late-emerging juveniles were smaller than early-emerging ones at subsequent samplings, both in the wild and in parallel experiments conducted in seminatural stream channels, and this may affect success at subsequent size-selective episodes, such as winter mortality and reproduction. Finally, our findings also suggest that egg size had fitness consequences independent of the effects of emergence time that directly affected body size at emergence and, in turn, survival and size at later life stages. The causality of the maternal effects observed in the present study supports the hypothesis that selection on juvenile traits may play an important role in the evolution of maternal traits in natural populations.

Lifetime success and interactions of farm salmon invading a native population.

Farm Atlantic salmon escape and invade rivers throughout the North Atlantic annually, which has generated growing concern about their impacts on native salmon populations. A large-scale experiment was therefore undertaken in order to quantify the lifetime success and interactions of farm salmon invading a Norwegian river. Sexually mature farm and native salmon were genetically screened, radio tagged and released into the River Imsa where no other salmon had been allowed to ascend. The farm fishes were competitively and reproductively inferior, achieving less than one-third the breeding success of the native fishes. Moreover, this inferiority was sex biased, being more pronounced in farm males than females, resulting in the principal route of gene flow involving native males mating with farm females. There were also indications of selection against farm genotypes during early survival but not thereafter. However, evidence of resource competition and competitive displacement existed as the productivity of the native population was depressed by more than 30%. Ultimately, the lifetime reproductive success (adult to adult) of the farm fishes was 16% that of the native salmon. Our results indicate that such annual invasions have the potential for impacting on population productivity, disrupting local adaptations and reducing the genetic diversity of wild salmon populations.

Dipyridamole-dobutamine stress with Tc-99m sestamibi tomographic myocardial perfusion imaging.

In 66 patients unable to exercise referred for pharmacologic stress single-photon emission computed tomographic myocardial perfusion imaging, a moderate dose of dobutamine was combined with intravenous dipyridamole and the results were compared with standard intravenous dipyridamole stress. The combined stress protocol resulted in increased defect size and reversibility with technetium-99m sestamibi single-photon emission computed tomographic myocardial perfusion imaging.

Genetically enhanced growth causes increased mortality in hypoxic environments.

Rapid growth and development are associated with several fitness-related benefits. Yet, organisms usually grow more slowly than their physiological maximum, suggesting that rapid growth may carry costs. Here we use coho salmon (Oncorhynchus kisutch) eggs of wild and transgenic genotypes to test whether rapid growth causes reduced tolerance to low levels of oxygen (hypoxia). Eggs were exposed to four different durations of hypoxia, and survival and growth were recorded until the end of the larval stage. Survival rates decreased with increasing duration of hypoxia, but this decrease was most pronounced for the transgenic group. Larval mass was also negatively affected by hypoxia; however, transgenic genotypes were significantly larger than wild genotypes at the end of the larval stage. Oxygen can be a limiting factor for survival and development in a wide range of organisms, particularly during the egg stage. Thus, the reduced ability of fast-growing genotypes to cope with low oxygen levels identified in the present study may represent a general constraint on evolution of rapid growth across taxa.

A critical review of adaptive genetic variation in Atlantic salmon: implications for conservation.

Here we critically review the scale and extent of adaptive genetic variation in Atlantic salmon (Salmo salar L.), an important model system in evolutionary and conservation biology that provides fundamental insights into population persistence, adaptive response and the effects of anthropogenic change. We consider the process of adaptation as the end product of natural selection, one that can best be viewed as the degree of matching between phenotype and environment. We recognise three potential sources of adaptive variation: heritable variation in phenotypic traits related to fitness, variation at the molecular level in genes influenced by selection, and variation in the way genes interact with the environment to produce phenotypes of varying plasticity. Of all phenotypic traits examined, variation in body size (or in correlated characters such as growth rates, age of seaward migration or age at sexual maturity) generally shows the highest heritability, as well as a strong effect on fitness. Thus, body size in Atlantic salmon tends to be positively correlated with freshwater and marine survival, as well as with fecundity, egg size, reproductive success, and offspring survival. By contrast, the fitness implications of variation in behavioural traits such as aggression, sheltering behaviour, or timing of migration are largely unknown. The adaptive significance of molecular variation in salmonids is also scant and largely circumstantial, despite extensive molecular screening on these species. Adaptive variation can result in local adaptations (LA) when, among other necessary conditions, populations live in patchy environments, exchange few or no migrants, and are subjected to differential selective pressures. Evidence for LA in Atlantic salmon is indirect and comes mostly from ecological correlates in fitness-related traits, the failure of many translocations, the poor performance of domesticated stocks, results of a few common-garden experiments (where different populations were raised in a common environment in an attempt to dissociate heritable from environmentally induced phenotypic variation), and the pattern of inherited resistance to some parasites and diseases. Genotype x environment interactions occurr for many fitness traits, suggesting that LA might be important. However, the scale and extent of adaptive variation remains poorly understood and probably varies, depending on habitat heterogeneity, environmental stability and the relative roles of selection and drift. As maladaptation often results from phenotype-environment mismatch, we argue that acting as if populations are not locally adapted carries a much greater risk of mismanagement than acting under the assumption for local adaptations when there are none. As such, an evolutionary approach to salmon conservation is required, aimed at maintaining the conditions necessary for natural selection to operate most efficiently and unhindered. This may require minimising alterations to native genotypes and habitats to which populations have likely become adapted, but also allowing for population size to reach or extend beyond carrying capacity to encourage competition and other sources of natural mortality.

Highly fecund mothers sacrifice offspring survival to maximize fitness.

Why do highly fecund organisms apparently sacrifice offspring size for increased numbers when offspring survival generally increases with size? The theoretical tools for understanding this evolutionary trade-off between number and size of offspring have developed over the past 25 years; however, the absence of data on the relation between offspring size and fitness in highly fecund species, which would control for potentially confounding variables, has caused such models to remain largely hypothetical. Here we manipulate egg size, controlling for maternal trait interactions, and determine the causal consequences of offspring size in a wild population of Atlantic salmon. The joint effect of egg size on egg number and offspring survival resulted in stabilizing phenotypic selection for an optimal size. The optimal egg size differed only marginally from the mean value observed in the population, suggesting that it had evolved mainly in response to selection on maternal rather than offspring fitness. We conclude that maximization of maternal fitness by sacrificing offspring survival may well be a general phenomenon among highly fecund organisms.