scholarly journals Seaweed reproductive biology: environmental and genetic controls

2017 ◽  
Vol 60 (2) ◽  
Author(s):  
Xiaojie Liu ◽  
Kenny Bogaert ◽  
Aschwin H. Engelen ◽  
Frederik Leliaert ◽  
Michael Y. Roleda ◽  
...  
Keyword(s):  
Life Cycle ◽  
Current Knowledge ◽  
Natural Populations ◽  
Life Cycles ◽  
Research Papers ◽  
Cycle Progression ◽  
Vast Number ◽  
Endogenous Factors ◽  
Trade Offs ◽  
Excellent Control

AbstractKnowledge of life cycle progression and reproduction of seaweeds transcends pure academic interest. Successful and sustainable seaweed exploitation and domestication will indeed require excellent control of the factors controlling growth and reproduction. The relative dominance of the ploidy-phases and their respective morphologies, however, display tremendous diversity. Consequently, the ecological and endogenous factors controlling life cycles are likely to be equally varied. A vast number of research papers addressing theoretical, ecological and physiological aspects of reproduction have been published over the years. Here, we review the current knowledge on reproductive strategies, trade-offs of reproductive effort in natural populations, and the environmental and endogenous factors controlling reproduction. Given that the majority of ecophysiological studies predate the “-omics” era, we examine the extent to which this knowledge of reproduction has been, or can be, applied to further our knowledge of life cycle control in seaweeds.

scholarly journals A key role for UV sex chromosomes in the regulation of parthenogenesis in the brown algaEctocarpus

2018 ◽  
Author(s):  
Laure Mignerot ◽  
Komlan Avia ◽  
Remy Luthringer ◽  
Agnieszka P. Lipinska ◽  
Akira F. Peters ◽  
...  
Keyword(s):  
Life Cycle ◽  
Asexual Reproduction ◽  
Sex Chromosome ◽  
Natural Populations ◽  
Life History Evolution ◽  
Life Cycles ◽  
Negative Effects ◽  
Evolutionary Transitions ◽  
Trade Offs ◽  
Sexual And Asexual Reproduction

AbstractAlthough evolutionary transitions from sexual to asexual reproduction are frequent in eukaryotes, the genetic bases of these shifts remain largely elusive. Here, we used classic quantitative trait analysis, combined with genomic and transcriptomic information to dissect the genetic basis of asexual, parthenogenetic reproduction in the brown algaEctocarpus. We found that parthenogenesis is controlled by the sex locus, together with two additional autosomal loci, highlight the key role of the sex chromosome as a major regulator of asexual reproduction. Importantly, we identify several negative effects of parthenogenesis on male fitness, but also different fitness effects between parthenogenesis and life cycle generations, supporting the idea that parthenogenesis may be under both sexual selection and generation/ploidally-antagonistic selection. Overall, our data provide the first empirical illustration, to our knowledge, of a trade-off between the haploid and diploid stages of the life cycle, where distinct parthenogenesis alleles have opposing effects on sexual and asexual reproduction and may contribute to the maintenance of genetic variation. These types of fitness trade-offs have profound evolutionary implications in natural populations and may structure life history evolution in organisms with haploid-diploid life cycles.

scholarly journals Phenotypic plasticity and diversity in insects

2010 ◽  
Vol 365 (1540) ◽  
pp. 593-603 ◽  
Author(s):  
Armin P. Moczek
Keyword(s):  
Gene Expression ◽  
Phenotypic Plasticity ◽  
Natural Populations ◽  
Evolutionary Developmental Biology ◽  
Life Cycles ◽  
Biological Organization ◽  
Trade Off ◽  
Evolutionary Innovation ◽  
Trade Offs ◽  
Evolutionary Trajectories

Phenotypic plasticity in general and polyphenic development in particular are thought to play important roles in organismal diversification and evolutionary innovation. Focusing on the evolutionary developmental biology of insects, and specifically that of horned beetles, I explore the avenues by which phenotypic plasticity and polyphenic development have mediated the origins of novelty and diversity. Specifically, I argue that phenotypic plasticity generates novel targets for evolutionary processes to act on, as well as brings about trade-offs during development and evolution, thereby diversifying evolutionary trajectories available to natural populations. Lastly, I examine the notion that in those cases in which phenotypic plasticity is underlain by modularity in gene expression, it results in a fundamental trade-off between degree of plasticity and mutation accumulation. On one hand, this trade-off limits the extent of plasticity that can be accommodated by modularity of gene expression. On the other hand, it causes genes whose expression is specific to rare environments to accumulate greater variation within species, providing the opportunity for faster divergence and diversification between species, compared with genes expressed across environments. Phenotypic plasticity therefore contributes to organismal diversification on a variety of levels of biological organization, thereby facilitating the evolution of novel traits, new species and complex life cycles.

scholarly journals Annual dynamics of Zymoseptoria tritici populations in wheat cultivar mixtures: a compromise between the efficiency and durability of a recently broken-down resistance gene?

2021 ◽  
Author(s):  
Carolina Orellana-Torrejon ◽  
Tiphaine Vidal ◽  
Anne-Lise Boixel ◽  
Sandrine Gélisse ◽  
Sébastien Saint-Jean ◽  
...  
Keyword(s):  
Resistance Gene ◽  
Fungal Pathogen ◽  
Current Knowledge ◽  
Natural Populations ◽  
Pure Stand ◽  
Zymoseptoria Tritici ◽  
Trade Offs ◽  
Pathogen Populations ◽  
Dual Objectives ◽  
Cultivar Mixtures

AbstractCultivar mixtures slow polycyclic epidemics but may also modify the evolution of pathogen populations by diversifying the selection pressures exerted by their plant hosts at field scale. We compared the dynamics of natural populations of the fungal pathogen Zymoseptoria tritici in pure stands and in three binary mixtures of wheat cultivars (one susceptible cultivar and one cultivar carrying the recently broken-down Stb16q gene) over two annual field epidemics. We combined analyses of population ‘size’ based on disease severity, and of population ‘composition’ based on assessments of changes in the frequency of virulence against Stb16q in seedling assays with more than 3000 strains. In the field, disease levels were lower in mixtures, with each cultivar providing the other with reciprocal protection. The three cultivar proportions in the mixtures (0.25, 0.5 and 0.75) modulated the decrease in (i) the size of the pathogen population relative to the two pure stands, (ii) the size of the virulent subpopulation, and (iii) the frequency of virulence relative to the pure stand of the cultivar carrying Stb16q. Our findings suggest that optimal proportions may differ slightly between the three indicators considered. We identified potential trade-offs that should be taken into account when deploying a resistance gene in cultivar mixtures: between the dual objectives ‘efficacy’ and ‘durability’, and between the ‘size’ and ‘frequency’ of the virulent subpopulation. Based on current knowledge, it remains unclear whether virulent subpopulation size or frequency has the largest influence on interepidemic virulence transmission.

scholarly journals Comparative analysis of helminth infectivity: growth in intermediate hosts increases establishment rates in the next host

2021 ◽  
Vol 288 (1947) ◽  
Author(s):  
Spencer Froelick ◽  
Laura Gramolini ◽  
Daniel P. Benesh
Keyword(s):  
Life Cycle ◽  
Life Cycles ◽  
Complex Life Cycle ◽  
Life Stages ◽  
Intermediate Hosts ◽  
Cycle Progression ◽  
Recovery Rates ◽  
High Doses ◽  
Parasitic Worms ◽  
Higher Doses

Parasitic worms (i.e. helminths) commonly infect multiple hosts in succession before reproducing. At each life cycle step, worms may fail to infect the next host, and this risk accumulates as life cycles include more successive hosts. Risk accumulation can be minimized by having high establishment success in the next host, but comparisons of establishment probabilities across parasite life stages are lacking. We compiled recovery rates (i.e. the proportion of parasites recovered from an administered dose) from experimental infections with acanthocephalans, cestodes and nematodes. Our data covered 127 helminth species and 16 913 exposed hosts. Recovery rates increased with life cycle progression (11%, 29% and 46% in first, second and third hosts, respectively), because larger worm larvae had higher recovery, both within and across life stages. Recovery declined in bigger hosts but less than it increased with worm size. Higher doses were used in systems with lower recovery, suggesting that high doses are chosen when few worms are expected to establish infection. Our results indicate that growing in the small and short-lived hosts at the start of a complex life cycle, though dangerous, may substantially improve parasites' chances of completing their life cycles.

scholarly journals Selection and the evolution of genetic life cycles.

Genetics ◽  
1993 ◽  
Vol 133 (2) ◽  
pp. 401-410
Author(s):  
C D Jenkins
Keyword(s):  
Genetic Variation ◽  
Life Cycle ◽  
Genetic Control ◽  
Relative Length ◽  
Mortality Rates ◽  
Life Cycles ◽  
Stability Conditions ◽  
Viability Selection ◽  
Trade Offs

Abstract The evolution of haploid and diploid phases of the life cycle is investigated theoretically, using a model where the relative length of haploid and diploid phases is under genetic control. The model assumes that selection occurs in both phases and that fitness in each phase is a function of the time spent in that phase. The equilibrium and stability conditions that allow for all-haploid, all-diploid, or polyphasic life cycles are considered for general survivorship functions. Types of stable life cycles possible depend on the form of the viability selection. If mortality rates are constant, either haploidy or diploidy is the only stable life cycle possible. Departures from constant mortality can give qualitatively different results. For example, when survivorship in each phase is a linear, decreasing function of the time spent in the phase, stable haploid, diploid or polyphasic life cycles are possible. The addition of genetic variation at a coevolving viability locus does not qualitatively affect the outcome with respect to the maintenance of polyphasic cycles but can lead to situations where more than one life cycle is concurrently stable. These results show that trade-offs between the advantages of being diploid and of being haploid may help explain the patterns of life cycles found in nature and that the type of selection may be critical to determining the results.

scholarly journals Cyclical environments drive variation in life history strategies: a general theory of cyclical phenology

2018 ◽  
Author(s):  
John S. Park
Keyword(s):  
Life History ◽  
Life History Theory ◽  
Natural Populations ◽  
Life History Evolution ◽  
Life Cycles ◽  
Life History Strategies ◽  
Life History Variation ◽  
Trade Offs ◽  
Overwhelming Evidence ◽  
Phenological Shifts

ABSTRACTCycles, such as seasons or tides, characterize many systems in nature. Overwhelming evidence shows that climate change-driven alterations to environmental cycles—such as longer seasons— are associated with phenological shifts around the world, suggesting a deep link between environmental cycles and life cycles. However, general mechanisms of life history evolution in cyclical environments are still not well understood. Here I build a demographic framework and ask how life history strategies optimize fitness when the environment perturbs a structured population cyclically, and how strategies should change as cyclicality changes. I show that cycle periodicity alters optimality predictions of classic life history theory because repeated cycles have rippling selective consequences over time and generations. Notably, fitness landscapes that relate environmental cyclicality and life history optimality vary dramatically depending on which trade-offs govern a given species. The model tuned with known life history trade-offs in a marine intertidal copepod T. californicus successfully predicted the shape of life history variation across natural populations spanning a gradient of tidal periodicities. This framework shows how environmental cycles can drive life history variation—without complex assumptions of individual responses to cues such as temperature—thus expanding the range of life history diversity explained by theory and providing a basis for adaptive phenology.

scholarly journals Cyclical environments drive variation in life-history strategies: a general theory of cyclical phenology

2019 ◽  
Vol 286 (1898) ◽  
pp. 20190214 ◽  
Author(s):  
John S. Park
Keyword(s):  
Life History ◽  
Life History Theory ◽  
Natural Populations ◽  
Life History Evolution ◽  
Life Cycles ◽  
Life History Strategies ◽  
Life History Variation ◽  
Trade Offs ◽  
Overwhelming Evidence ◽  
Phenological Shifts

Cycles, such as seasons or tides, characterize many systems in nature. Overwhelming evidence shows that climate change-driven alterations to environmental cycles—such as longer seasons—are associated with phenological shifts around the world, suggesting a deep link between environmental cycles and life cycles. However, general mechanisms of life-history evolution in cyclical environments are still not well understood. Here, I build a demographic framework and ask how life-history strategies optimize fitness when the environment perturbs a structured population cyclically and how strategies should change as cyclicality changes. I show that cycle periodicity alters optimality predictions of classic life-history theory because repeated cycles have rippling selective consequences over time and generations. Notably, fitness landscapes that relate environmental cyclicality and life-history optimality vary dramatically depending on which trade-offs govern a given species. The model tuned with known life-history trade-offs in a marine intertidal copepod Tigriopus californicus successfully predicted the shape of life-history variation across natural populations spanning a gradient of tidal periodicities. This framework shows how environmental cycles can drive life-history variation—without complex assumptions of individual responses to cues such as temperature—thus expanding the range of life-history diversity explained by theory and providing a basis for adaptive phenology.

Size reduction, reproductive strategy and the life cycle of a centric diatom

1992 ◽  
Vol 336 (1277) ◽  
pp. 191-213 ◽  
Keyword(s):  
Life Cycle ◽  
Sexual Reproduction ◽  
Natural Populations ◽  
Life Cycles ◽  
Size Reduction ◽  
Centric Diatom ◽  
Low Light ◽  
Low Frequencies ◽  
Diatom Population ◽  
Regeneration Cycle

The life cycle of Aulacoseira subarctica (O. Müller) Haworth in Lough Neagh, Northern Ireland, is described. Cell numbers can reach up to 17000 per millilitre in spring. Most cells sediment to the bottom after silica limitation and go into a resting state during summer. The inoculum in autumn partly comes from resuspension, with the surviving cells (0.5-5%) continuing to grow through the winter, doubling every one to two weeks. T he population goes through a size reduction and regeneration cycle linked to sexual reproduction. Gametes are only produced in narrower cells (3.8-7.4 um diameter), usually after interruptions in growth caused by low light conditions (surface irradiance 100-150 pE m -2 s-1), but availability of nutrients, especially silica and nitrogen, is also important. Even the highest densities of auxospores (20 m1 -1) represent only a small proportion of the total cells present (0.16%). Size regeneration results in initial cells with diameters (14.8 ± 2 pm) about three times those of the parent. Larger parent cells usually give rise to larger initial cells. Subsequently, cell division leads to a decrease in population diameter, because of the way new valves are laid down below the girdle bands. Reductions are largest in broader cells (0.32 um per division) and gradually decrease as cells get narrower. Occasionally large reductions, up to 1 um, follow periods of environmental stress. By combining these results with studies of changes in cell size (width, length and volume) in related individuals along filaments, it was possible to explain why there have been difficulties in applying the MacDonald-Pfitzer hypothesis to natural populations. Theoretically, the life cycle in L. Neagh might extend over 100 divisions or 15 years but, in practice, cells reach a sexually inducible size in 4-6 years. The discrepancy is because environmental factors (e.g. sedimentation, resuspension, parasitism, etc.) are also important in size selectivity. The interaction of these factors, when combined with intermittent sexual reproduction at low frequencies, results in a relatively stable population size distribution, where there are always some cells in the size range in which sexual differentiation can be induced. Overall, the results demonstrate, that for a full understanding of diatom population dynamics, it is important to quantify events over complete life cycles.

scholarly journals Does a complex life cycle affect adaptation to environmental change? Genome-informed insights for characterizing selection across complex life cycle

2021 ◽  
Vol 288 (1964) ◽  
Author(s):  
Molly A. Albecker ◽  
Laetitia G. E. Wilkins ◽  
Stacy A. Krueger-Hadfield ◽  
Samuel M. Bashevkin ◽  
Matthew W. Hahn ◽  
...  
Keyword(s):  
Life Cycle ◽  
Empirical Studies ◽  
Life Cycles ◽  
Complex Life Cycle ◽  
Ecological Niches ◽  
Life Stages ◽  
Complex Life Cycles ◽  
High Fecundity ◽  
Trade Offs ◽  
Frequency Changes

Complex life cycles, in which discrete life stages of the same organism differ in form or function and often occupy different ecological niches, are common in nature. Because stages share the same genome, selective effects on one stage may have cascading consequences through the entire life cycle. Theoretical and empirical studies have not yet generated clear predictions about how life cycle complexity will influence patterns of adaptation in response to rapidly changing environments or tested theoretical predictions for fitness trade-offs (or lack thereof) across life stages. We discuss complex life cycle evolution and outline three hypotheses—ontogenetic decoupling, antagonistic ontogenetic pleiotropy and synergistic ontogenetic pleiotropy—for how selection may operate on organisms with complex life cycles. We suggest a within-generation experimental design that promises significant insight into composite selection across life cycle stages. As part of this design, we conducted simulations to determine the power needed to detect selection across a life cycle using a population genetic framework. This analysis demonstrated that recently published studies reporting within-generation selection were underpowered to detect small allele frequency changes (approx. 0.1). The power analysis indicates challenging but attainable sampling requirements for many systems, though plants and marine invertebrates with high fecundity are excellent systems for exploring how organisms with complex life cycles may adapt to climate change.

MERGERS AND ACQUISITIONS AND THEIR CORRELATION WITH THE LIFE CYCLES OF MEMBER COMPANIES ON THE EXAMPLE OF THE RUSSIAN MARKET 2017–2019

2020 ◽  
Vol 1 (10) ◽  
pp. 26-35
Author(s):  
E. A. SHUBINA ◽  
◽  
Yu. A. KOMAROVSKY ◽  
A. V. MERKUSHEV ◽  
◽  
...  
Keyword(s):  
Life Cycle ◽  
Mergers And Acquisitions ◽  
Life Cycles ◽  
Russian Market

The article is devoted to the study of the largest mergers and acquisitions (M&A, “Mergers & Acquisitions”) in Russia for 2017–2019. (the acquired block of shares is not less than 99%). The concept of life cycles of organizations and theoretical aspects of mergers and acquisitions are described. The stages of the life cycle of the merged and reorganized companies, the goals of mergers and acquisitions, depending on the stages of the life cycle are analyzed.

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