scholarly journals The evolution of Daphnia pulex in a temporally varying environment

1998 ◽  
Vol 72 (1) ◽  
pp. 25-37 ◽  
Author(s):  
SAMUEL M. SCHEINER ◽  
LEV Yu YAMPOLSKY
Keyword(s):  
Genetic Variation ◽  
Temperature Change ◽  
Local Population ◽  
Daphnia Pulex ◽  
Selection Response ◽  
Clonal Variation ◽  
Offspring Size ◽  
Malthusian Parameter ◽  
Offspring Number ◽  
Variable Environments

We investigated three aspects of adaptation to variable environments in Daphnia pulex (Cladocera: Crustacea): (1) effects of temporal variation on the evolution of phenotypic plasticity ; (2) plasticity in sexual versus asexual lineages; (3) maintenance of genetic variation in variable environments. We performed a 72-day quasi-natural selection experiment comparing three patterns of variation: constant temperatures, varying but predictable temperature change, and unpredictable temperature change. All populations were begun with an identical array of 34 clones. During selection clonal variation declined in all populations and different patterns of environmental variation had little effect on amounts of genetic variation. Sexual and asexual lineages differed in size and growth rate, but did not differ in amounts of plasticity or in adaptation to variable environments. The primary target of selection was the Malthusian parameter (r) and life history traits of development time, offspring size and offspring number. The heritability of plasticity was generally lower than trait heritability. Because of this difference, the selection response on the mean of the traits overwhelmed the selection response on plasticity. Lower heritabilities of plasticity are very typical, suggesting that our results will be typical of responses to selection in nature. Our results suggest that selection will act mostly on trait means within environments and that plasticity will evolve often as a correlated trait. Because selection on plasticity is based on its across-deme, global fitness, this process will usually be slow. Comparative studies need to shift from closely related, local population differences to those of more distantly related populations or even different species.

scholarly journals Low but genetically variable male remating ability in a tropical Drosophila despite substantial fitness benefits

2018 ◽  
Author(s):  
Andrew D. Saxon ◽  
Natalie E. Jones ◽  
Eleanor K. O’Brien ◽  
Jon R. Bridle
Keyword(s):  
Genetic Variation ◽  
Mating Success ◽  
Local Population ◽  
Encounter Rate ◽  
Male Reproductive Success ◽  
Male Mating ◽  
Heritable Variation ◽  
Elevational Gradients ◽  
Offspring Number ◽  
Mating Latency

AbstractMating success is the main source of fitness variation in males, meaning that males should capitalise on all opportunities for mating. Strong selection on male mating success should also reduce genetic variation in male mating traits relative to other traits. We quantified mating latency, mating duration and productivity in males of the tropical fruitfly, Drosophila birchii, from 30 isofemale lines collected from across two elevational gradients, when they were given opportunities to mate with up to four females consecutively. Male remating rates were low compared to other Drosophila (only 14 – 27% of males achieved a fourth mating), with mean mating durations approximately doubling across successive copulations. However, although successive remating produced progressively fewer offspring, it consistently increased overall male reproductive success, with males that mated four times more than doubling offspring number compared to males mating only once. We also found no reduction in the productivity of sons emerging from later matings, indicating a sustained cumulative fitness benefit to remating. Heritable variation was observed for most traits (H2 = 0.035 – 0.292) except mating latency, but there was no divergence in trait means with elevation. The observed restricted remating ability of male D. birchii, despite the clear benefits of remating, may be due to a low encounter rate with females in the field, leading to high investment per gamete (or ejaculate). However, it remains unclear why genetic variation in these traits is high, given we observe no variation in these traits across elevational gradients known to affect local population density.

scholarly journals The alignment between phenotypic plasticity, the major axis of genetic variation and the response to selection

2015 ◽  
Vol 282 (1816) ◽  
pp. 20151651 ◽  
Author(s):  
Martin I. Lind ◽  
Kylie Yarlett ◽  
Julia Reger ◽  
Mauricio J. Carter ◽  
Andrew P. Beckerman
Keyword(s):  
Genetic Variation ◽  
Phenotypic Plasticity ◽  
Daphnia Pulex ◽  
Major Axis ◽  
Selection Response ◽  
Recent Theory ◽  
Response To Selection ◽  
Selection Gradients ◽  
Survival Selection ◽  
The Difference

Phenotypic plasticity is the ability of a genotype to produce more than one phenotype in order to match the environment. Recent theory proposes that the major axis of genetic variation in a phenotypically plastic population can align with the direction of selection. Therefore, theory predicts that plasticity directly aids adaptation by increasing genetic variation in the direction favoured by selection and reflected in plasticity. We evaluated this theory in the freshwater crustacean Daphnia pulex , facing predation risk from two contrasting size-selective predators. We estimated plasticity in several life-history traits, the G matrix of these traits, the selection gradients on reproduction and survival, and the predicted responses to selection. Using these data, we tested whether the genetic lines of least resistance and the predicted response to selection aligned with plasticity. We found predator environment-specific G matrices, but shared genetic architecture across environments resulted in more constraint in the G matrix than in the plasticity of the traits, sometimes preventing alignment of the two. However, as the importance of survival selection increased, the difference between environments in their predicted response to selection increased and resulted in closer alignment between the plasticity and the predicted selection response. Therefore, plasticity may indeed aid adaptation to new environments.

scholarly journals UNEQUAL CROSSING OVER AT THE rRNA TANDON AS A SOURCE OF QUANTITATIVE GENETIC VARIATION IN DROSOPHILA

Genetics ◽  
1980 ◽  
Vol 95 (3) ◽  
pp. 727-742 ◽  
Author(s):  
R Frankham ◽  
D A Briscoe ◽  
R K Nurthen
Keyword(s):  
Genetic Variation ◽  
Selection Response ◽  
Crossing Over ◽  
Wild Type ◽  
X Chromosomes ◽  
Unequal Crossing Over ◽  
Quantitative Genetic ◽  
Y Chromosomes ◽  
Homozygous Line ◽  
Minimum Estimate

ABSTRACT Abdominal bristle selection lines (three high and three low) and controls were founded from a marked homozygous line to measure the contribution of sex-linked "mutations" to selection response. Two of the low lines exhibited a period of rapid response to selection in females, but not in males. There were corresponding changes in female variance, in heritabilities in females, in the sex ratio (a deficiency of females) and in fitness, as well as the appearance of a mutant phenotype in females of one line. All of these changes were due to bb alleles (partial deficiencies for the rRNA tandon) in the X chromosomes of these lines, while the Y chromosomes remained wild-type bb+. We argue that the bb alleles arose by unequal crossing over in the rRNA tandon.—A prediction of this hypothesis is that further changes can occur in the rRNA tandon as selection is continued. This has now been shown to occur.—Our minimum estimate of the rate of occurrence of changes at the rRNA tandon is 3 × 10-4. As this is substantially higher than conventional mutation rates, the questions of the mechanisms and rates of origin of new quantitative genetic variation require careful re-examination.

scholarly journals Loci, genes, and gene networks associated with life history variation in a model ecological organism,Daphnia pulex(complex)

2018 ◽  
Author(s):  
Jacob W. Malcom ◽  
Thomas E. Juenger ◽  
Mathew A. Leibold
Keyword(s):  
Gene Expression ◽  
Genetic Variation ◽  
Life History ◽  
Molecular Basis ◽  
Life History Traits ◽  
Evolutionary Dynamics ◽  
Daphnia Pulex ◽  
Life History Trait ◽  
Life History Variation ◽  
Trait Variation

ABSTRACTBackgroundIdentifying the molecular basis of heritable variation provides insight into the underlying mechanisms generating phenotypic variation and the evolutionary history of organismal traits. Life history trait variation is of central importance to ecological and evolutionary dynamics, and contemporary genomic tools permit studies of the basis of this variation in non-genetic model organisms. We used high density genotyping, RNA-Seq gene expression assays, and detailed phenotyping of fourteen ecologically important life history traits in a wild-caught panel of 32Daphnia pulexclones to explore the molecular basis of trait variation in a model ecological species.ResultsWe found extensive phenotypic and a range of heritable genetic variation (~0 < H2< 0.44) in the panel, and accordingly identify 75-261 genes—organized in 3-6 coexpression modules—associated with genetic variation in each trait. The trait-related coexpression modules possess well-supported promoter motifs, and in conjunction with marker variation at trans- loci, suggest a relatively small number of important expression regulators. We further identify a candidate genetic network with SNPs in eight known transcriptional regulators, and dozens of differentially expressed genes, associated with life history variation. The gene-trait associations include numerous un-annotated genes, but also support several a priori hypotheses, including an ecdysone-induced protein and several Gene Ontology pathways.ConclusionThe genetic and gene expression architecture ofDaphnialife history traits is complex, and our results provide numerous candidate loci, genes, and coexpression modules to be tested as the molecular mechanisms that underlieDaphniaeco-evolutionary dynamics.

Characterization of Phytophthora infestans populations in Cyprus, the southernmost potato-producing European country.

Plant Disease ◽  
2021 ◽  
Author(s):  
Loukas Kanetis ◽  
Lambros Pittas ◽  
Nikolaos Nikoloudakis ◽  
David E. L. Cooke ◽  
Nicolas Ioannou
Keyword(s):  
Late Blight ◽  
Phytophthora Infestans ◽  
Local Population ◽  
Management Strategies ◽  
Population History ◽  
Clonal Variation ◽  
Limited Area ◽  
Asexual Population ◽  
Epidemic Period ◽  
Genotypic Analysis

Cyprus is the southernmost island country of Europe located in the Mediterranean and despite its limited area, potato production is considered an integral source of the national agricultural revenue. During 2010-2012, a late blight-epidemic period for the country, the population structure of Phytophthora infestans was analyzed via a sample of 539 isolates collected from all the main potato-cultivating regions of Cyprus. We determined mating type, mefenoxam sensitivity, and genetic polymorphism at 12 simple sequence repeat (SSRs) loci. Although both mating types were detected in the country, a gradual -but dynamic- shift towards A2 dominance was manifested over time. The pathogen population also demonstrated reduced sensitivity to the phenylamide fungicide, since 96.2% of the tested isolates had high (70.3%) and intermediate resistance (25.9%) to mefenoxam, suggesting it should be replaced with other active ingredients in local disease management strategies. The genotypic analysis also revealed the predominance of the highly aggressive, mefenoxam-insensitive EU_13_A2 lineage across the country with a frequency of 79.2%. Other samples comprised an older lineage EU_2_A1 (19.5%), a very low proportion of EU_23_A1 (0.37%), and others that did not match any known lineage (0.92%). SSRs data supported triploid genomes among the dominant lineages and patterns of their asexual population history were also apparent. High sub-clonal variation of the 13_A2 population was detected, suggesting introduction events of this widespread genotype to Cyprus from major tuber exporting countries. Present data indicate the severe impact of inoculum migration to the structure of the local population; thus, current phytosanitary procedures should be reconsidered and possibly attuned. This is the first comprehensive study to elucidate the diversity of P. infestans in Cyprus and could serve as a baseline for future monitoring of this highly adaptive plant pathogen since late blight management strategies should be constantly refined according to the traits of the dominant genotypes of P. infestans.

scholarly journals Geographical Gradients of Genetic Diversity and Differentiation among the Southernmost Marginal Populations of Abies sachalinensis Revealed by EST-SSR Polymorphism

Forests ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 233 ◽  
Author(s):  
Keiko Kitamura ◽  
Kentaro Uchiyama ◽  
Saneyoshi Ueno ◽  
Wataru Ishizuka ◽  
Ikutaro Tsuyama ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Genetic Variation ◽  
Local Population ◽  
Distribution Center ◽  
Population History ◽  
Peripheral Populations ◽  
Abies Sachalinensis ◽  
Marginal Populations ◽  
Local Populations ◽  
Longitudinal Gradients

Research Highlights: We detected the longitudinal gradients of genetic diversity parameters, such as the number of alleles, effective number of alleles, heterozygosity, and inbreeding coefficient, and found that these might be attributable to climatic conditions, such as temperature and snow depth. Background and Objectives: Genetic diversity among local populations of a plant species at its distributional margin has long been of interest in ecological genetics. Populations at the distribution center grow well in favorable conditions, but those at the range margins are exposed to unfavorable environments, and the environmental conditions at establishment sites might reflect the genetic diversity of local populations. This is known as the central-marginal hypothesis in which marginal populations show lower genetic variation and higher differentiation than in central populations. In addition, genetic variation in a local population is influenced by phylogenetic constraints and the population history of selection under environmental constraints. In this study, we investigated this hypothesis in relation to Abies sachalinensis, a major conifer species in Hokkaido. Materials and Methods: A total of 1189 trees from 25 natural populations were analyzed using 19 EST-SSR loci. Results: The eastern populations, namely, those in the species distribution center, showed greater genetic diversity than did the western peripheral populations. Another important finding is that the southwestern marginal populations were genetically differentiated from the other populations. Conclusions: These differences might be due to genetic drift in the small and isolated populations at the range margin. Therefore, our results indicated that the central-marginal hypothesis held true for the southernmost A. sachalinensis populations in Hokkaido.

scholarly journals How a Genetically Stable Extremophile Evolves: Modes of Genome Diversification in the Archaeon Sulfolobus acidocaldarius

2017 ◽  
Vol 199 (17) ◽  
Author(s):  
Dominic Mao ◽  
Dennis W. Grogan
Keyword(s):  
Dna Repair ◽  
Genetic Variation ◽  
Tandem Repeats ◽  
Local Population ◽  
Genome Structure ◽  
Sulfolobus Acidocaldarius ◽  
Hyperthermophilic Archaea ◽  
Wild Type ◽  
Induced Mutations ◽  
Content Type

ABSTRACT In order to analyze in molecular terms how Sulfolobus genomes diverge, damage-induced mutations and natural polymorphisms (PMs) were identified in laboratory constructs and wild-type isolates, respectively, of Sulfolobus acidocaldarius. Among wild-type isolates drawn from one local population, pairwise nucleotide divergence averaged 4 × 10−6, which is about 0.15% of the corresponding divergence reported for Sulfolobus islandicus. The most variable features of wild-type S. acidocaldarius genomes were homopolymer (mononucleotide) tracts and longer tandem repeats, consistent with the spontaneous mutations that occur under laboratory conditions. Natural isolates, however, also revealed large insertions/deletions and inversions, which did not occur in any of the laboratory-manipulated strains. Several of the large insertions/deletions could be attributed to the integration or excision of mobile genetic elements (MGEs), and each MGE represented a distinct system of site-specific recombination. The mode of recombination associated with one MGE, a provirus related to Sulfolobus turreted icosahedral virus, was also seen in certain chromosomal inversions. Artificially induced mutations, non-MGE insertions/deletions, and small PMs exhibited different distributions over the genome, suggesting that large-scale patterning of Sulfolobus genomes begins early in the divergence process. Unlike induced mutations, natural base pair substitutions occurred in clusters, and one cluster exhibited properties expected of nonreciprocal recombination (gene conversion) between dispersed imperfect repeats. Taken together, the results identify simple replication errors, slipped-strand events promoted by tandem repeats, homologous recombination, and rearrangements promoted by MGEs as the primary sources of genetic variation for this extremely acidophilic archaeon in its geothermal environment. IMPORTANCE The optimal growth temperatures of hyperthermophilic archaea accelerate DNA decomposition, which is expected to make DNA repair especially important for their genetic stability, yet these archaea lack certain broadly conserved types of DNA repair proteins. In this study, the genome of the extreme thermoacidophile Sulfolobus acidocaldarius was found to be remarkably stable, accumulating few mutations in many (though not all) laboratory manipulations and in natural populations. Furthermore, all the genetic processes that were inferred to diversify these genomes also operate in mesophilic bacteria and eukaryotes. This suggests that a common set of mechanisms produces most of the genetic variation in all microorganisms, despite the fundamental differences in physiology, DNA repair systems, and genome structure represented in the three domains of life.

Clonal variation in pollen-related characteristics of Douglas-fir

1982 ◽  
Vol 12 (2) ◽  
pp. 403-408 ◽  
Author(s):  
W. T. Adams
Keyword(s):  
Genetic Variation ◽  
Pollen Grains ◽  
Seed Orchard ◽  
Douglas Fir ◽  
Clonal Variation ◽  
Pollen Production ◽  
The Mean ◽  
Pollen Cone ◽  
Grain Diameter

The mean number of pollen grains produced per pollen cone (P) ranged from 37 310 to 62 960 ([Formula: see text], SE = 1584) among eight seed-orchard clones of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and correlated significantly (r = 0.87, p < 0.05) with the mean number of microsporophylls per cone but not significantly with pollen cone length. The number of pollen grains per milligram (G) also differed among clones (range 2323–3112; [Formula: see text], SE = 32) and correlated significantly and negatively (r = −0.86) with grain diameter. Although this study provides evidence for genetic variation in both P and G, the differences were relatively small. Adjusting pollen-cone counts for P would add little, if any, precision to estimates of pollen production in seed-orchard clones. If balanced clonal representation in pollen mixes is desired, equal weights of pollen would probably suffice for most breeding applications.

Number and Size of Offspring

2021 ◽  
pp. 115-128
Author(s):  
Jeffrey A. Hutchings
Keyword(s):  
Life History ◽  
Clutch Size ◽  
Parental Investment ◽  
Adaptive Significance ◽  
Offspring Size ◽  
Structural Constraints ◽  
Offspring Survival ◽  
Trade Off ◽  
Offspring Number ◽  
Parental Fitness

Offspring number and size are two of the most variable life-history traits. Among species, much of this variability can be attributed to genetic, developmental, physiological, or structural constraints. Some trait combinations are not possible because of differences associated with a species’ evolutionary history. Substantial variation in propagule number and size can exist among populations of the same species, generating questions concerning the adaptive significance of this variability. The most influential models are those attributed to Lack on clutch size and to Smith and Fretwell on offspring size. Fundamental to both sets of models is a trade-off between offspring number and parental investment per offspring. When offspring survival or fitness continuously varies with offspring size, the fitness of the parent depends on both offspring size and the number of offspring of that size that the parent can produce. If offspring survival is independent of offspring size, parental fitness is maximized when individuals maximize the production of minimally sized propagules.

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