Selective and genetic constraints on the evolution of body size in a stream-dwelling salmonid fish

To examine constraints on evolution of larger body size in two stunted populations of brook charr (Salvelinus fontinalis) from a single river in Cape Race, Newfoundland, Canada, we measured viability selection acting on length-at-age traits, and estimated quantitative genetic parameters in situ (following reconstruction of pedigree information from microsatellite data). Furthermore we tested for phenotypic differentiation between the populations, and for association of high juvenile growth with early maturity that is predicted by life history theory. Within each population, selection differentials and estimates of heritabilities for length-at-age traits suggested that evolution of larger size is prevented by both selective and genetic constraints. Between the populations, phenotypic differentiation was found in length-at-age and age of maturation traits, whereas early maturation was associated with increased juvenile growth (relative to adult growth) both within and between populations. The results suggest an adaptive plastic response in age of maturation to juvenile growth rates that have a largely environmental basis of determination.     

Individual variation in movement throughout the life cycle of a stream-dwelling salmonid fish

Stream-dwelling fish populations have long served as important models of animal movement. Populations of adult stream-dwelling fishes are generally composed of a mix of relatively sedentary and mobile individuals. However, we do not know whether this pattern that we typically observe among adults is indicative of patterns of movement that occur throughout the life cycle. Therefore, we do not know whether we can apply these patterns to understanding or predicting processes such as migration and thus the potential for the evolution of genetic differences among populations. We test the general hypothesis that patterns of movement throughout the life cycle are consistent with patterns of movement inferred by indirect genetic methods and, more specifically, that the characteristics of the mobile fraction of the population are consistent with patterns of genetic differentiation. We used parentage analyses to infer the movements of alevin brook charr (Salvelinus fontinalis) in Freshwater River, Newfoundland, Canada, and a capture-recapture study of one cohort in this population to infer movement throughout the rest of the life cycle. We found that alevins move large distances shortly after emergence, primarily in the downstream direction, and that the population is composed of a mix of relatively sedentary and mobile individuals throughout all other intervals of the life cycle. In contrast, when we considered movements of individuals first captured as juveniles and eventually recovered as reproductively mature adults, we found relatively large and uniform distributions of net movement distance. Thus, heterogeneity in individual movement of adults is not representative of patterns of movement throughout the life cycle and therefore may provide only limited inference of population-level processes such as gene flow.     

Spatial and temporal scale of density-dependent body growth and its implications for recruitment, population dynamics and management of stream-dwelling salmonid populations

Density-dependent variations in body growth and size have important consequences for the population dynamics of stream-dwelling salmonid populations, since body size is related to a variety of ecologically relevant characteristics. These include survival and fecundity, competitive and predatory abilities, and foraging behavior. However, little work has been done to understand how density-dependent body growth varies across temporal and spatial scales and when this compensatory process is relevant for recruitment and population dynamics of stream-dwelling salmonids. Increased intra- or inter-cohort competition reduces growth rates of juveniles. Both within- and among-cohort differences at the juvenile stage are likely to be maintained through the lifetime. Limited movement or dispersal can lead to subdivision of a population into several local populations with independent dynamics. The spatial and temporal variation in movement and the patchy distribution of resources make fish likely to experience density-dependence across location, life-stage, and season. The relaxation of density-dependent suppression of body growth at low densities constitutes a potential mechanism for salmonids to persist in the face of environmental perturbation and may contribute to explaining the peculiar resilience to population collapses often showed by salmonids. The inclusion of density-dependent growth in population models may increase the usefulness of model predictions in management contexts. Models not accounting for density-dependent growth may underestimate the recovery potential of resident salmonid populations when they collapse to low densities.     

Sex-specific mutation rates in salmonid fish

If germline mutations arise because of replication errors, the mutation rate may differ between males and females given that they differ in their number of germ cell divisions. As males of many higher organisms produce more gametes than females, this has led to the idea of "male-driven evolution." The extent of such male bias to the mutation rate is currently debated. For human some recent data suggest a very low bias, at a factor 1.7 only, while other approaches have given values of alpha(m) (the male-to-female mutation rate ratio) of 5, which is more close to what might be expected from male and female germ cell biology. Comparative analyses of sex-specific mutation rates in other organisms may be necessary for understanding the generality of an effect of sex and the number of germline DNA replications on the mutation rate. In this study we estimate for the first time sex-specific mutation rates in fish. Comparing the intronic substitution rates of the autosomal GH- 2 gene and its duplicated Y-linked and male-specific copy GH- 2Y (447-468 bp of each gene), we estimate alpha(m) to be 5.35-6.60 in salmonid fish of the genus Oncorhynchus. To the observations previously made among mammals and birds, this adds evidence from another class of vertebrates showing that a majority of mutations are of paternal origin. This would suggest that replication errors play a major role for the generation of new mutations.     

Medical and genetic consequences of radiation catastrophes (Review)

The data from publications about radiation catastrophes that occurred in the world were analyzed. We focused on the causes that led to catastrophes and the scale and peculiarities of clinical and genetic effects. Much attention was paid to early and distant consequences of the Chernobyl Nuclear Plant catastrophe.     

Physiological causes and consequences of social status in salmonid fish

Social interactions in small groups of juvenile rainbow trout(Oncorhynchus mykiss) lead to the formation of dominance hierarchies.Dominant fish hold better positions in the environment, gaina larger share of the available food and exhibit aggressiontowards fish lower in the hierarchy. By contrast, subordinatefish exhibit behavioural inhibition, including reduced activityand feeding. The behavioural characteristics associated withsocial status are likely the result of changes in brain monoaminesresulting from social interactions. Whereas substantial physiologicalbenefits, including higher growth rates and condition factor,are experienced by dominant trout, low social status appearsto be a chronic stress, as indicated by sustained elevationof circulating cortisol concentrations in subordinate fish.High cortisol levels, in turn, may be responsible for many ofthe deleterious physiological consequences of low social status,including lower growth rates and condition factor, immunosuppressionand increased mortality. Circulating cortisol levels may alsobe a factor in determining the outcome of social interactionsin pairs of rainbow trout, and hence in determining social status.Rainbow trout treated with cortisol were significantly morelikely to become subordinate in paired encounters with smalleruntreated conspecifics.     

A stationary distribution for the growth of a population subject to random catastrophes

The problem of the existence of a stationary distribution and the convergence towards it in a certain semistochastic model for the growth of a population is considered. It is assumed that the population grows according to a deterministic equation, but at certain times there are catastrophes, which lead to a decrease in the population level. The hazard function for the occurrence of catastrophes is a function of the population level only. The size of these jumps have a distribution that depends on the population size immediately before the catastrophe. A constructive method for finding the stationary distribution is given.     

Complex evolution of a salmonid microsatellite locus and its consequences in inferring allelic divergence from size information

Sequence analysis of 78 alleles of a microsatellite locus was resolved atvarious taxonomic levels among salmonid fishes to test for congruencebetween size and sequence information. Allelic variability of this locusinvolved changes in number of dinucleotide repeats as expected formicrosatellite loci. However, additional mutational events involving largeindels and base substitutions also occurred frequently among and withinspecies. These caused the evolution of different imperfect microsatellitevariants, from an ancestral perfect one, which was undetectable fromallelic size information only. Alleles of the same length resulting fromdifferent mutational events were also observed among and within species.Altogether, these results revealed the incongruence between size and numberof mutation events, implying that it may be imprecise to interpretmutational rates and relationships on the basis of size information alonein interspecific comparisons and, to a lesser extent, within species.     

Intraspecific variation in competitive ability and food intake in salmonids: consequences for energy budgets and growth rates

The interactions between dominance status, feeding rate and growth in rainbow trout, Salmo gairdneri Richardson, were analyzed using published data on experimental populations. There was a positive correlation between metabolic expenditure and food intake in both dominant and subordinate fish, but dominants obtained a greater intake for a given expenditure than did subordinates. Subordinates that adopted a high–return/high–cost foraging strategy actually expended more energy than they acquired, whereas those that minimized energy expenditure obtained a net energy gain. This led to the surprising finding that the growth rate of subordinates was negatively correlated with food intake.     

Sex‐biased dispersal in a salmonid fish: implications for growth rate and survival

Migration is widespread among marine fishes, yet little is known about variation in the migration of individuals within localities. We tested the hypothesis that variation in the migratory behaviour among plaice ( Pleuronectes platessa ) in the North Sea could be explained by large‐scale differences in the speed and directions of the tidal streams, which the fish use as a transport mechanism. Towards this end, 752 mature female plaice tagged with electronic data storage tags were released at eight locations with contrasting tidal flow properties, between December 1993 and September 1999. The experiment yielded 20 403 days of data from 145 plaice. The position of each fish was determined at intervals throughout the liberty period using the tidal location method. The results show 3 geographically discrete feeding aggregations during the summer, which dispersed over the southern North Sea and Eastern English Channel to spawn during winter. Our results re‐affirmed the major role of the tidal streams in the southern North Sea in structuring plaice dispersion, both by providing transport and guidance, and by delimiting the extent of distribution due to thermal stratification during the summer. These results confirm the prediction that large‐scale variation in migration behaviour can be explained in part by the tidal guidance and transport mechanisms available. They have revealed features of spatial dynamics not previously observed from a century of conventional tagging experiments and illustrate how the study of individual fish can successfully define the migratory characteristics of populations.     

Evolutionary consequences of asymmetric dispersal rates

We study the consequences of asymmetric dispersal rates (e.g., due to wind or current) for adaptive evolution in a system of two habitat patches. Asymmetric dispersal rates can lead to overcrowding of the downstream habitat, resulting in a source-sink population structure in the absence of intrinsic quality differences between habitats or can even cause an intrinsically better habitat to function as a sink. Source-sink population structure due to asymmetric dispersal rates has similar consequences for adaptive evolution as a source-sink structure due to habitat quality differences: natural selection tends to be biased toward the source habitat. We demonstrate this for two models of adaptive evolution: invasion of a rare allele that improves fitness in one habitat but reduces it in the other and antagonistic selection on a quantitative trait determined by five additive loci. If a habitat can sustain a population without immigration, the conditions for adaptation to that habitat are most favorable if there is little or no immigration from the other habitat; the influence of emigration depends on the magnitude of the allelic effects involved and other parameters. If, however, the population is initially unable to persist in a given habitat without immigration, our model predicts that the population will be most likely to adapt to that habitat if the dispersal rates in both directions are high. Our results highlight the general message that the effect of gene flow upon local adaptation should depend profoundly on the demographic context of selection.     

Sex-biased dispersal in a salmonid fish

We tested the hypothesis that dispersal is sex biased in an unexploited population of brook trout, Salvelinus fontinalis, on Cape Race, Newfoundland, Canada. Based on the assumptions that trout are promiscuous and that reproductive success is limited primarily by either number of mates (males) or fecundity (females), we predicted that males would disperse greater distances than females. We also tested the hypothesis that trout populations comprise stationary and mobile individuals, predicting that males have greater mobility than females. Based on a mark-recapture study of 943 individually tagged fishes, 191 of which were recaptured over 5 years, we find strong support for our hypothesis of male-biased dispersal in brook trout. Averaged among all 11 resampling periods, males dispersed 2.5 times as far as females; during the spawning period only, male dispersal exceeded that by females almost fourfold. Both sexes were heterogeneous with respect to movement, with a lower incidence of mobility among females (29.6%) than males (41.1%); mobile males dispersed six times further than mobile females. We conclude that this sex bias reduces mate competition among male kin and decreases the probability that males will reproduce with related females.     

Plasticity in probabilistic reaction norms for maturation in a salmonid fish

The relationship between body size and the probability of maturing, often referred to as the probabilistic maturation reaction norm (PMRN), has been increasingly used to infer genetic variation in maturation schedule. Despite this trend, few studies have directly evaluated plasticity in the PMRN. A transplant experiment using white-spotted charr demonstrated that the PMRN for precocious males exhibited plasticity. A smaller threshold size at maturity occurred in charr inhabiting narrow streams where more refuges are probably available for small charr, which in turn might enhance the reproductive success of sneaker precocious males. Our findings suggested that plastic effects should clearly be included in investigations of variation in PMRNs.     

Ontogenetic shifts in habitat use and activity in a stream-dwelling isopod

We examined ontogenetic changes in diel patterns of habitat use and activity of the lotic isopod Lirceus fontinalis in relation to differences in predation risk from green sunfish, Lepomis cyanellus. Juveniles are ≤5 mm total length (TL), individuals 6-9 mm TL are mature females (c. 90%) and immature males, and mature males are ≥10 mm TL. Isopods of all sizes were far more dense in Cladophora , a filamentous green algae, than in open silt/sand substrates in fish pools. Densities of each size did not increase in open areas at night in fish pools when risk of predation presumably decreases. Few individuals of any size class occurred in open silt/sand areas in fish pools. However, habitat use did not depend on fish presence. Densities and relative abundances of all sizes were similar between algal and open habitats in fishless pools both day and night, except for mature males which were more abundant in open areas during daylight. All sizes of isopods were significantly more dense in fishless versus fish pools, and density of a size class was influenced by fish presence. Densities of size classes were typically juveniles > individuals 6-9 mm TL > mature males. Green sunfish are size selective feeders on isopods, thus demography of isopods within pools may be partially influenced by the size structure of the fish population.
Isopods reduced their activity, as measured by captures in benthic traps, in the presence of caged green sunfish only at night. This behavior coupled with relatively high activity levels during daylight regardless of fish presence suggests other predators or factors may influence diel activity. Mature males were overrepresented in traps relative to their occurrence in fish runs, indicating high activity levels. Mature males were also more active than gravid and nongravid females and juveniles in the presence of fish in laboratory aquaria. Number of male encounters with nongravid females depended on activity level.     

Ovarian follicle growth and consequences for fertility in sheep

Understanding the pattern of ovarian follicle development is seen as an important step leading to the development of techniques that maximise fertility in sheep. Repeated observations of the growth of individual follicles have led to the understanding that follicles develop in a wave-like pattern during the oestrous cycle, with two to four waves per cycle being the most common. The ease with which follicle waves are described seems to depend on the their frequency and the number of follicles per wave. There is evidence for the largest follicle(s) of a follicle wave inhibiting the development of other follicles; however, in some cases this is not apparent as other follicle waves emerge when a previous large, healthy follicle is still present. Follicle development can be manipulated using exogenous gonadotrophins or progestagens and these have been shown to alter the number or age profile of developing follicles. The ovulation of aged follicles in cattle clearly has a detrimental effect on fertility, but this relationship is less clear and seems to be less critical in sheep. Recent findings at the molecular level show that the bone morphogenetic proteins (BMP) and their receptors are critically involved in the control of ovulation rate, but fully understanding their mechanism remains to be described. This highlights the potential for the integration of molecular and physiological findings to better develop methods to manipulate follicle development and reproduction in sheep.     

Partitioning of nitrogen and biomass at a range of N-addition rates and their consequences for growth and gas exchange in two perennial grasses from inland dunes

This paper describes the effects of nitrgen supply on the partitioning of biomass and nitrogen of Agrostis vinealis (L.) Schreber and Corynephorus canescens (L.) Beauv., two perennial grasses of dry, nutrient-poor inland dunes, and their consequences for growth and gas exchange. At a given plant nitrogen concentration (PNC) the two species allocate the same relative amount of dry matter and nitrogen to their leaves. However, A. vinealis allocates more dry matter and nitrogen to its roots and less to its above-ground support tissue than C. canescens . Both the leaf weight ratio and leaf nitrogen ratio increase with increasing PNC. Despite species-specific differences in growth form and leaf morphology, the leaf area ratio and specific leaf area of the two species are similar, both at high and low PNC. At intermediate nitrogen supply, and thus intemediate PNC, however, A. vinealis has a higher leaf area ratio and specific leaf area than C. canescens .
The two species exhibit a similar positive relationship when either the rate of net photosynthesis or the rate of shoot respiration are compared to the leaf nitrogen concentration, all expressed per unit leaf weight. The rate of net photosynthesis per unit Jeafnitrogen (PNUE) of the two species increases with decreasing leaf nitrogen concentration per unit leaf weight. C. canescens has a higher PNUE at low, and a lower PNUE at high leaf nitrogen concentration per unit leaf weight than A. vinealis . At non-limiting nitrogen supply, A. vinealis has a higher nitrogen productivity and net assimilation rate and a similar PNC and leaf area ratio as compared to C. canescens , which explains the higher relative growth rate (RGR_max) of A. vinealis. At growth-limiting nitrogen supply C. canescens achieves a similar relative growth rate at a lower PNC than A. vinealis.     

Fish growth hormone genes: Divergence of coding sequences in salmonid fishes

Comparison of coding nucleotide sequences of the paralogous GH1 and GH2 genes, as well as of the growth hormone amino acid sequences, in the species of closely related salmonid genera Salvelinus, Oncorhynchus, and Salmo was performed. It was demonstrated that, in different groups of salmonids, the amino acid substitution rates were considerably different. In some cases, an obvious discrepancy between the divergence of growth hormone genes and phylogenetic schemes based on other methods and approaches was revealed. These findings suggest that the reason may be multidirectional selection at duplicated genes at different stages of evolution.