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PubMed2004

A genetic analysis of avian personality traits: correlated, response to artificial selection.

Individuals in a range of species consistently differ in their behavior towards mild challenges, over age and time. Differences have been found for several personality traits in a range of species. In great tits these traits have a genetic basis and are phenotypically correlated. Estimates of genetic correlations are, however, fundamental to understanding the evolution of consistent individual differences in behavior. This study analyzed two selection experiments on two avian personality traits, early exploratory behavior and risk-taking behavior. The selection lines used were both started using wild great tits (Parus major) from two natural populations. Genetic correlations were calculated using the response and the correlated response to artificial selection. We found genetic correlations ranging from 0.51 to 0.66, based on individual values, and from 0.84 to 1.00 based on nest means. Genetic correlations can be due to pleiotropic effects or to linkage disequilibrium. The different behavioral traits might therefore have a common genetic basis, possibly constraining independent evolution of personality traits in natural populations. These results are discussed in relation to domain generality and domain specificity of personalities.

Animals↗
PubMed2001

Artificial selection and heritability of sperm length in Gryllus bimaculatus.

The adaptive significance of variation in sperm size remains poorly understood but there has been even less attention focused on the genetic mechanisms controlling spermatozoal traits (only three species have been studied). Here we explore heritability and artificial selection of sperm length in the cricket Gryllus bimaculatus. Using a within-family selection design we selected sperm with increasing and decreasing sperm size and bred divergence across five generations. Although we recorded no significant parent-offspring heritability, realized heritability from a within-family analysis was significant at 0.52 +/- 0.06 SE (P = 0.01) and we successfully achieved significant divergence. However, we only achieved a response when the maternal line was incorporated into selection (from the F1 onwards) and our findings therefore suggest that sperm length in G. bimaculatus is a sex-linked trait that is influenced by genes which are active on the female chromosome. Accordingly, sperm length heritability in G. bimaculatus can only be measured using a within-family design because the spermatozoal phenotype is sex-limited (to males) while the genotype is sex-linked (to females). The evolutionary significance of the heritability of sperm length is discussed with reference to sex-linkage of this important sex-limited trait.

Animals↗
PubMed2004

Genetic constraints on floral evolution in a sexually dimorphic plant revealed by artificial selection.

Sexual dimorphism is one of the most widespread and recognizable patterns of phenotypic variation in the biotic world. Sexual dimorphism in floral display is striking in the dioecious plant Silene latifolia, with males making many, small flowers compared to females. We investigated this dimorphism via artificial selection on two populations to determine whether genetic variation exists within populations for flower size and the extent of the between-sex correlation, whether a flower size and number trade-off exists within each sex, and whether pollen and ovule production vary with flower size. We selected for decreased flower size (calyx width) in females and increased flower size in males and measured the response to selection in size and correlated responses in flower dry mass, flower number, and pollen or ovule number per flower. Four bouts of selection in each of two selection programs were performed, for a total of three selection lines to decrease size, three to increase it, and two control lines. Flower size always significantly responded to selection and we always found a significant correlated response in the sex not under selection. Selection decreased but did not eliminate the sexual dimorphism in flower dry mass and number. A negative relationship between flower size and number within each sex was revealed. Whereas ovule number showed a significant correlated response to selection on flower size, pollen number did not. Our results indicate that although substantial additive genetic variation for flower size exists, the high between-sex genetic correlation would likely constrain flower size from becoming more sexually dimorphic. Furthermore, floral display within each sex is constrained by a flower size and number trade-off. Given this trade-off and lack of variation in pollen production with flower size, we suggest that sexual dimorphism evolved via sexual selection to increase flower number in males but not females.

Biological Evolution↗
PubMed2005

Systemic oxygen transport in rats artificially selected for running endurance.

The relative contribution of genetic and environmental influences to individual exercise capacity is difficult to determine. Accordingly, animal models in which these influences are carefully controlled are highly useful to understand the determinants of intrinsic exercise capacity. Studies of systemic O(2) transport during maximal treadmill exercise in two diverging lines of rats artificially selected for endurance capacity showed that, at generation 7, whole body maximal O(2) uptake ((.)V(O(2)(max)) was 12% higher in high capacity (HCR) than in low capacity runners (LCR) during normoxic exercise. The difference in (.)V(O(2)(max) between HCR and LCR was larger during hypoxic exercise. Analysis of the linked O(2) conductances of the O(2) transport system showed that the higher (.)V(O(2)(max) was not due to a higher ventilatory response, a more effective pulmonary gas exchange, or an increased rate of O(2) delivery to the tissue by blood. The main reason for the higher (.)V(O(2)(max) of HCR was an increased tissue O(2) extraction, due largely to a higher tissue diffusive O(2) conductance. The enhanced tissue O(2) diffusing capacity was paralleled by an increased capillary density of a representative locomotory skeletal muscle, the gastrocnemius, in HCR. Activities of skeletal muscle oxidative enzymes citrate synthase and beta-HAD were also higher in HCR than LCR. Thus, the functional characteristics observed during exercise are consistent with the structural and biochemical changes observed in skeletal muscle that imply an enhanced capacity for muscle O(2) uptake and utilization in HCR. The results indicate that the improved (.)V(O(2)(max) is solely due to enhanced muscle O(2) extraction and utilization. However, the question arises as to whether it is possible to maintain a continually expanding capacity for O(2) extraction at the tissue level with successive generations, without a parallel improvement in the capacity to deliver O(2) to the exercising muscles.

Animals↗
PubMed2002

Direct and correlated responses to artificial selection on developmental time and wing length in Drosophila buzzatii.

Developmental time and body size are two positively correlated traits closely related to fitness in many organisms including Drosophila. Previous work suggested that these two traits are involved in a trade-off that may result from a negative genetic correlation between their effects on pre-adult and adult fitness. Here, we examine the evolution of developmental time and body size (indexed by wing length) under artificial selection applied to one or both traits in replicated D. buzzatii populations. Directional changes in both developmental time and wing length indicate the presence of substantial additive genetic variance for both traits. The strongest response to selection for fast development was found in lines selected simultaneously to reduce both developmental time and wing length, probably as an expected consequence of a synergistic effect of indirect selection. When selection was applied in the direction opposite to the putative genetic correlation, that is, large wing length but fast development, no responses were observed for developmental time. Lines selected to reduce both wing length and developmental time diverged slightly faster from the control than lines selected to increase wing length and reduce developmental time. However, wing length did not diverge from the control in lines selected only for fast development. These results suggest a complex genetic basis of the correlation between developmental time and wing length, but are generally consistent with the hypothesis that both traits are related in a trade-off. However, we found that this trade-off may disappear under uncrowded conditions, with fast-developing lines exhibiting a higher pre-adult viability than other lines when tested at high larval density.

Analysis of Variance↗
PubMed2004

Genetic analysis of rapid tolerance to ethanol's incoordinating effects in mice: inbred strains and artificial selection.

Ethanol tolerance, a decrease in drug responsiveness with repeated administrations, is an important diagnostic criterion for alcoholism. Rapid tolerance develops within 8-24 hours of an initial ethanol exposure and shares many similarities with chronic tolerance. The genetic contribution to rapid tolerance to ethanol-induced ataxia was estimated using a panel of inbred strains of mice. Strains differed significantly in the degree of rapid tolerance development, which had a broad-sense heritability estimate of 0.11. Artificial selection was carried out to develop lines of mice that would show High (HRT) and Low (LRT) levels of Rapid Tolerance. Starting with HS/Npt mice, derived from a systematic cross of eight inbred strains, a significant response to selection was seen in replicate 1 by the third selection generation. No difference was found in replicate 2. Heritability estimates after the fourth generation were 0.25 for HRT-1 mice and 0.06 for LRT-1 mice. HRT-1 and LRT-1 mice also differed significantly in chronic tolerance development to four doses of ethanol. These studies provide evidence for a genetic contribution to rapid tolerance and support a genetic link between rapid and chronic tolerance to ethanol's ataxic effects.

Animals↗
PubMed2006

Consequences of artificial selection on pre-adult development for adult lifespan under benign conditions in the butterfly Bicyclus anynana.

The genetic architecture underlying the regulation of lifespan is shaped by evolutionary history, thus, including selection in past environments. In particular, the developmental environment is important, because selection pressure for survival is highest during development. From this life-history point of view, the ageing phenotype is the outcome of these factors, and links between the developmental and adult life stage are expected. In this study, we specifically address whether genetic variation in pre-adult traits affects adult lifespan. We use lines artificially selected for divergence in development time, pupal mass or egg size, thus, exploiting the standing genetic variation in pre-adult traits present in natural populations of Bicyclus anynana. We then reared individuals from each line and the unselected base population in a common environment, and recorded each selected trait and adult longevity. In general, differences in adult lifespan across selection lines were small. This is not surprising given the benign conditions used here. The minor differences in adult survival were only partially the result of environmental influences, as indicated by low phenotypic correlations. However, significant genetic correlations point to possible intrinsic mechanisms involved in lifespan regulation. Genetic variation in egg mass or pupal mass did not contribute to variation in lifespan. However, we found a negative genetic correlation between developmental time and lifespan, suggesting a genetic coupling of faster development with a longer adult lifespan in this species. A follow-up study with an identical set-up that introduces stress during development should give a more detailed insight into the role of development in the regulation of lifespan.

Aging↗
PubMed1985

Constitutional biases in early perceptual learning: III. Similarities and differences between artificially selected and imprinted color preferences in quail chicks (Coturnix coturnix japonica).

Color preferences and preference generalization were tested in naive and imprinted Japanese quail chicks drawn from the 20th generation of a genetic control line and two genetic lines that were bidirectionally selected for preferences between blue and red. Twelve hours of imprinting to blue or red on the first posthatch day resulted in large preference changes in the genetic controls, and these subjects exhibited no or only small additional changes from 3 more days of imprinting (for the total of 66 hr of exposure time). By contrast, 12 hr of imprinting of artificially selected subjects did not change or only marginally changed their genetically manipulated preferences, but 66 hr of imprinting changed them by magnitudes as large as or larger than those in genetic controls. Reciprocal imprinting partially mimicked the phenotypic effects of bidirectional selection. Differences between transfer and generalization of phenotypically similar but genetically and experimentally different preferences indicated dissimilar mediation of the implicit gene effects and learning effects.

Animals↗
PubMed2005

The expression of brain sexual dimorphism in artificial selection of rat strains.

Central nervous system sex differences have two morphological patterns. In one pattern, males show larger measurements (volume, number of neurons) than females (male > female; m > f) and, in the other, the opposite is true (female > male; f > m). The bed nucleus of the stria terminalis (BST) is a unique model for the study of sex differences because it has dimorphic and isomorphic subdivisions, with the former showing the two sexually differentiated morphological patterns. Meanwhile, other CNS structures, like the locus coeruleus (LC), present the f > m pattern. The philogenetic maintenance of the two patterns of sexual differentiation can help to disentangle the functional meaning of sex differences. Laboratory rat strains, whether albino or pigmented, descend from the Wistar strain through artificial selection. The present work compares the BST and LC of Wistar and Long-Evans rats. The medial posterior subdivision of the BST (BSTMP) is sexually dimorphic (m > f pattern) in the original (Wistar) and derived (Long-Evans) strains, while the lateral anterior and medial anterior subdivisions of the BST and the LC only present sex differences (f > m pattern) in the ancestor Wistar strain. Isomorphic BST regions are the same in both strains. The fact that the BSTMP, which is implicated in male copulatory behavior, is sexually dimorphic in both strains, as well as in other species, including humans, indicates the relevance of this structure in male sexual behavior in mammals.

Animals↗
PubMedDate not supplied

Investigating the independent evolution of the size of floral organs via G-matrix estimation and artificial selection.

The attractiveness of a plant to pollinators is dependent on both the number of flowers produced and the size of the petals. However, limiting resources often result in a size/number trade-off, whereby the plant can make either more flowers or larger flowers, but not both. If developmental genes underlying sepal and petal identity (some of which overlap) also influence size, then this shared genetic basis could constrain the independent evolution of floral size and attractiveness. Here, we determined whether the size of sepals and petals in the dioecious perennial, Silene latifolia, are developmentally independent by performing two experiments: a genetic variance-covariance experiment to estimate genetic correlations between calyx width, petal-limb length, flower mass, and number and a four-bout artificial-selection experiment to alter calyx width and estimate the correlated response in petal-limb length. In addition, we determined whether variation in petal-limb length is the result of cell expansion or cell proliferation. The first experiment revealed that petal-limb length is not genetically correlated with calyx width, and the second experiment confirmed this; selection on calyx width did not result in a predictable or significant change in petal-limb length. Flower number was negatively correlated with all the floral traits measured, indicating a flower size/number trade-off. Cell number, but not size, explained a significant amount of the variation in petal-limb length. We conclude that the size of the two outer floral organs can evolve independently. This species can therefore increase the number of flowers produced by decreasing investment in the calyx without simultaneously decreasing petal size and the attractiveness of each individual flower to pollinators.

Biological Evolution↗
PubMed2000

Direct and correlated responses to artificial selection on acute thermal stress tolerance in a livebearing fish.

Tradeoffs in performance or fitness across environments have important implications regarding the nature of evolutionary constraints. It remains controversial whether tradeoffs such as these reflect genetic correlations that are genuine evolutionary constraints. However, if such long-term genetic constraints do exist, they must be due to underlying pleiotropy such that alleles that confer high performance in one environment invariably confer low performance in another. The distribution of genetic correlations within and among populations can provide insight about the existence of such pleiotropic tradeoffs. The long-term association of certain teleost fish taxa with particular abiotic environments suggests that tradeoffs in performance across environments have constrained the geographic distribution of those taxa. Here we report the results of an experiment in which we artificially selected on acute heat- and cold-stress tolerance in two stocks of the poeciliid fish Heterandria formosa from source populations with different thermal histories. Unexpectedly, we observed no direct responses to selection. Under certain conditions, fish from the different source populations differed significantly in cold tolerance, but not in heat tolerance. The results suggest there are no strong pleiotropic tradeoffs between heat- and cold-stress tolerance in these populations.

Animals↗
PubMed1997

[The possibility of performing artificial selection in vivo for a change in the mutability level in populations of mouse bone marrow stem cells].

Bone marrow cells of CBA males were transplanted to irradiated syngeneic females and after 13 days the mean frequency of blood erythrocytes with micronuclei, cloning efficiency of haemopoietic stem cells (HSC), and variability range of frequency of cells with micronuclei in spleen colonies were studied in 44 primary recipients. A wide range of variability has been shown for the indicators of mutability and cloning efficiency (0.1-1.8% for frequency of erythrocytes with micronuclei, 200-300-1500 for cloning efficiency, 0.1-0.5% for frequency of cells with micronuclei in spleen colonies of individual transplants). A weak negative correlation between the frequency of erythrocytes with micronuclei and the cloning efficiency was observed. We conclude that the difference in frequency of erythrocytes with micronuclei between HSC subpopulations is sufficiently high to carry out an artificial selection for high and low mutability in the course of transplantations. The cloning efficiency can be increased when spleen colonies are studied by micronuclear analysis. Data on the importance of such a selection in studying the behavior of "mutability" and "cloning efficiency" characters, immortalization, "aging", and death of HSC populations of CBA mice have been reported.

Animals↗
PubMed2001

Mutations that cause amino acid substitutions at the invariant positions in homeodomain of OSH3 KNOX protein suggest artificial selection during rice domestication.

KNOX homeodomain (HD) proteins encoded by KNOTTED1-like homeobox genes (KNOX genes) are considered to work as important regulators for plant developmental and morphogenetic events. We found that OSH3, one of the KNOX genes isolated from a cultivar of Oryza sativa (Nipponbare), encodes a novel HD, which has two amino acid substitutions at invariant positions. Sequence analysis of OSH3 from various domesticated and wild species of rice has revealed that these substitutions are distributed only in Japonica and Javanica type of O. sativa, two groups of domesticated rice in Asia. Surprisingly, nucleotide sequences in the first intron are almost conserved in the rice strains that have the substitutions at the invariant amino acids. Overexpression studies revealed that these invariant amino acids are critical for the function of OSH3 in vivo. The facts that these substitutions occurred specifically at the functionally important amino acids and the sequences are conserved in intron where neutral mutations accumulate suggest the substitutions at the invariant positions of OSH3 have been fixed by artificial selections during domestication. Based on these observations, we hypothesize that OSH3 is responsible for one of the traits that are selectively introduced during the domestication of most of Japonica and a part of Javanica type of rice.

Amino Acid Substitution↗
PubMed2005

Artificial selection and maintenance of genetic variance in the global dairy cow population.

Genetic improvement of dairy cows, which has increased the milk yield of cows in the UK by 1200 kg per lactation in 12 years, is an excellent example of the application of quantitative genetics to agriculture. The most important traits of dairy cattle are expressed only in females, but the main opportunity for selection is in males. Despite this, genetic improvement was achieved by the invention of a new statistical methodology, called 'best linear unbiased prediction' to estimate the breeding value of bulls. Intense selection of the best bulls, combined with the worldwide use of these bulls through artificial insemination and frozen semen, has created a global population and caused concern that the genetic variation available in the future will be reduced. Maintenance of genetic variation and long-term genetic gains would be aided by rational payment systems, use of crossbreeding where profitable, inclusion of all economically important traits in the breeding objective, recognition of genotype by environment interactions and the use of selection algorithms that balance estimated breeding value against the average relationship among the selected animals. Fortunately, all of these things are happening to some degree.

Animals↗
PubMed2001

Immune and artificial selection in the haemagglutinin (H) glycoprotein of measles virus.

We present a maximum likelihood (ML) analysis of the selection pressures that have shaped the evolution of the large (L) protein and the haemagglutinin (H) glycoprotein of measles virus (MV). A number of amino acid sites that have potentially been subject to adaptive evolution were identified in the H protein using sequences from every known genotype of MV. All but one of these putative positively selected sites reside within the ectodomain of the H protein, where they often show an association with positions of potential B-cell epitopes and sites known to interact with the CD46 receptor. This suggests that MV may be under pressure from the immune system, albeit relatively weakly, to alter sites within epitopes and hence evade the humoral immune response. The positive selection identified at amino acid 546 was shown to correlate with the passage history of MV isolates in Vero cells. We reveal that Vero cell passaging has the potential to introduce an artificial signal of adaptive evolution through selection for changes that increase affinity for the CD46 receptor.

Amino Acid Sequence↗
PubMed2001

Site-selective artificial ribonuclease using pinpoint RNA activation.

An acridine residue attached to the end or the inside of a DNA activates the target phosphodiester linkages in complementary RNA. Due to this pinpoint activation, the RNA is site-selectively and efficiently cleaved at these linkages by various free metal ions under mild condition. Spectroscopic analyses show that the acridine moiety is sandwiched between neighboring bases, and pushes the opposite nucleotide out of the hetero-duplex.

Acridines↗
PubMed1989

Simulated evolution and artificial selection.

A highly simplified evolving system was investigated by computer simulation. The genetic complement of each simulated organism in the population was represented by a single chromosome that consisted of a string of symbols. Individual fitness was measured as the number of symbols that corresponded to a specified rule. Reproduction was simulated with a non-breeding algorithm and two variants of a breeding algorithm, and was subject to random point mutations. In each generation, selection was effected by replacing the less fit members of the population with offspring of the more fit. The size of the population and the fraction replaced, though under experimental control, were constant for each simulation run. It was found that even such a simplified system is able to mimic a variety of properties observed in natural systems. In addition, the effect of the simulation parameters on the course of fitness increase provides a basis for using a genetic algorithm as an optimization technique.

Algorithms↗
PubMed1999

Behaviour of house mice artificially selected for high levels of voluntary wheel running.

We have developed a novel model to study the correlated evolution of behavioural and morphophysiological traits in response to selection for increased locomotor activity. We used selective breeding to increase levels of voluntary wheel running in four replicate lines of laboratory house mice, Mus domesticus, with four random-bred lines maintained as controls. The experiment presented here tested for correlated behavioural responses in the wheel-cage complex, with wheels either free to rotate or locked (environmental factor). After 13 generations, mice from selected lines ran 2.2 times as many revolutions/day as controls on days 5 and 6 of initial exposure to wheels (10 826 versus 4890 revolutions/day, corresponding to 12.1 and 5.5 km/day, respectively). This increase was caused primarily by mice from selected lines running faster, not more minutes per day. Focal-animal observations confirmed that the increase in revolutions/day involved more actual running (or climbing in locked wheels), not an increase in coasting (or hanging). Not surprisingly, access to free versus locked wheels had several effects on behaviour, including total time spent in wheels, sniffing and biting. However, few behaviours showed statistically significant differences between the selected and control lines. Selection did not increase the total time spent in wheels (either free or locked), the frequency of nonlocomotor activities performed in the wheels, nor the amount of locomotor activity in cages attached to the wheels; as well, selection did not decrease the amount of time spent sleeping. Thus, wheel running is, at the genetic level, a largely independent axis of behaviour. Moreover, the genetic architecture of overall wheel running and its components seem conducive to increasing total distance moved without unduly increasing energy or time-related costs. The selection experiment also offers a new approach to study the proximate mechanisms of wheel-running behaviour itself. For example, frequencies of sniffing and wire biting were reduced in selected females but not males. This result suggests that motivation or function of wheel running may differ between the sexes. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗