scholarly journals Fragmentation modes and the evolution of life cycles

2017 ◽  
Author(s):  
Yuriy Pichugin ◽  
Jorge Peña ◽  
Paul B. Rainey ◽  
Arne Traulsen
Keyword(s):  
Growth Rate ◽  
Life Cycle ◽  
Population Growth ◽  
Population Growth Rate ◽  
Single Cells ◽  
Adaptive Significance ◽  
Life Cycles ◽  
Mode Of Reproduction ◽  
Size Groups ◽  
Multicellular Organisms

AbstractReproduction is a defining feature of living systems. To reproduce, aggregates of biological units (e.g., multicellular organisms or colonial bacteria) must fragment into smaller parts. Fragmentation modes in nature range from binary fission in bacteria to collective-level fragmentation and the production of unicellular propagules in multicellular organisms. Despite this apparent ubiquity, the adaptive significance of fragmentation modes has received little attention. Here, we develop a model in which groups arise from the division of single cells that do not separate but stay together until the moment of group fragmentation. We allow for all possible fragmentation patterns and calculate the population growth rate of each associated life cycle. Fragmentation modes that maximise growth rate comprise a restrictive set of patterns that include production of unicellular propagules and division into two similar size groups. Life cycles marked by single-cell bottlenecks maximise population growth rate under a wide range of conditions. This surprising result offers a new evolutionary explanation for the widespread occurrence of this mode of reproduction. All in all, our model provides a framework for exploring the adaptive significance of fragmentation modes and their associated life cycles.Author SummaryMode of reproduction is a defining trait of all organisms, including colonial bacteria and multicellular organisms. To produce offspring, aggregates must fragment by splitting into two or more groups. The particular way that a given group fragments defines the life cycle of the organism. For instance, insect colonies can reproduce by splitting or by producing individuals that found new colonies. Similarly, some colonial bacteria propagate by fission or by releasing single cells, while others split in highly sophisticated ways; in multicellular organisms reproduction typically proceeds via a single cell bottleneck phase. The space of possibilities for fragmentation is so vast that an exhaustive analysis seems daunting. Focusing on fragmentation modes of a simple kind we parametrise all possible modes of group fragmentation and identify those modes leading to the fastest population growth rate. Two kinds of life cycle dominate: one involving division into two equal size groups, and the other involving production of a unicellular propagule. The prevalence of these life cycles in nature is consistent with our null model and suggests that benefits accruing from population growth rate alone may have shaped the evolution of fragmentation mode.

scholarly journals Population growth rate as a basis for ecological risk assessment of toxic chemicals

2002 ◽  
Vol 357 (1425) ◽  
pp. 1299-1306 ◽  
Author(s):  
Valery E. Forbes ◽  
Peter Calow
Keyword(s):  
Risk Assessment ◽  
Growth Rate ◽  
Life Cycle ◽  
Population Growth ◽  
Ecological Risk ◽  
Population Growth Rate ◽  
Toxic Chemicals ◽  
Ecological Risks ◽  
Individual Level ◽  
Rate Analysis

Assessing the ecological risks of toxic chemicals is most often based on individual–level responses such as survival, reproduction or growth. Such an approach raises the following questions with regard to translating these measured effects into likely impacts on natural populations. (i) To what extent do individual–level variables underestimate or overestimate population–level responses? (ii) How do toxicant–caused changes in individual–level variables translate into changes in population dynamics for species with different life cycles? (iii) To what extent are these relationships complicated by population–density effects? These issues go to the heart of the ecological relevance of ecotoxicology and we have addressed them using the population growth rate as an integrating concept. Our analysis indicates that although the most sensitive individual–level variables are likely to be equally or more sensitive to increasing concentrations of toxic chemicals than population growth rate, they are difficult to identify a priori and, even if they could be identified, integrating impacts on key life–cycle variables via population growth rate analysis is nevertheless a more robust approach for assessing the ecological risks of chemicals. Populations living under density–dependent control may respond differently to toxic chemicals than exponentially growing populations, and greater care needs to be given to incorporating realistic density conditions (either experimentally or by simulation) into ecotoxicological test designs. It is impractical to expect full life–table studies, which record changes in survival, fecundity and development at defined intervals through the life cycle of organisms under specified conditions, for all relevant species, so we argue that population growth rate analysis should be used to provide guidance for a more pragmatic and ecologically sound approach to ecological risk assessment.

scholarly journals Life cycle and population growth rate of Caenorhabditis elegans studied by a new method

BMC Ecology ◽  
2009 ◽  
Vol 9 (1) ◽  
pp. 14 ◽  
Author(s):  
Daniel Muschiol ◽  
Fabian Schroeder ◽  
Walter Traunspurger
Keyword(s):  
Growth Rate ◽  
Life Cycle ◽  
Caenorhabditis Elegans ◽  
Population Growth ◽  
Population Growth Rate ◽  
New Method

scholarly journals Full life-cycle models from ring-recovery data: estimating fecundity from age ratios at capture

2018 ◽  
Author(s):  
Todd. W. Arnold
Keyword(s):  
Growth Rate ◽  
Life Cycle ◽  
Population Growth ◽  
Population Growth Rate ◽  
Large Scale ◽  
Adult Survival ◽  
List Type ◽  
Vital Rates ◽  
Full Life Cycle ◽  
Full Life

AbstractTag-recovery data from organisms captured and marked post breeding are commonly used to estimate juvenile and adult survival. If annual fecundity could also be estimated, tagging studies such as European and North American bird-ringing schemes could provide all parameters needed for building full life-cycle projection models.I modified existing tag-recovery models to allow estimation of annual fecundity using age composition and recapture probabilities obtained during routine banding operations of northern pintails (Anas acuta) and dark-eyed juncos (Junco hyemalis), and I conducted simulations to assess estimator performance in relation to sample size.For pintails, population growth rate from band-recovery data (λ = 0.929, SD 0.060) was similar but less precise than count-based estimates from the Waterfowl Breeding Pair and Habitat Survey (λ 0.945, SE 0.001). Models with temporal variation in vital rates indicated that annual population growth in pintails was driven primarily by variation in fecundity. Juncos had lower survival but greater fecundity, and their estimated population growth rate (λ 1.01, SD 0.19) was consistent with count-based surveys (λ 0.986).Simulations indicated that reliable (CV < 0.10) estimates of fecundity could be obtained with >1000 same-season live encounters. Although precision of survival estimates depended primarily on numbers of adult recoveries, estimates of population growth rate were most sensitive to total number of live encounters.Synthesis and applications: Large-scale ring-recovery programmes could be used to estimate annual fecundity in many species of birds, but the approach requires better data curation, including accurate assessment of age, better reporting of banding totals and greater emphasis on obtaining and reporting same-season live encounters.

scholarly journals Biological scaling in green algae: the role of cell size and geometry

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Helena Bestová ◽  
Jules Segrestin ◽  
Klaus von Schwartzenberg ◽  
Pavel Škaloud ◽  
Thomas Lenormand ◽  
...  
Keyword(s):  
Growth Rate ◽  
Population Growth ◽  
Population Growth Rate ◽  
Internal Diffusion ◽  
Scaling Exponent ◽  
Power Scaling ◽  
Nutrient Distribution ◽  
Metabolic Scaling ◽  
Key Factor ◽  
Size And Morphology

AbstractThe Metabolic Scaling Theory (MST), hypothesizes limitations of resource-transport networks in organisms and predicts their optimization into fractal-like structures. As a result, the relationship between population growth rate and body size should follow a cross-species universal quarter-power scaling. However, the universality of metabolic scaling has been challenged, particularly across transitions from bacteria to protists to multicellulars. The population growth rate of unicellulars should be constrained by external diffusion, ruling nutrient uptake, and internal diffusion, operating nutrient distribution. Both constraints intensify with increasing size possibly leading to shifting in the scaling exponent. We focused on unicellular algae Micrasterias. Large size and fractal-like morphology make this species a transitional group between unicellular and multicellular organisms in the evolution of allometry. We tested MST predictions using measurements of growth rate, size, and morphology-related traits. We showed that growth scaling of Micrasterias follows MST predictions, reflecting constraints by internal diffusion transport. Cell fractality and density decrease led to a proportional increase in surface area with body mass relaxing external constraints. Complex allometric optimization enables to maintain quarter-power scaling of population growth rate even with a large unicellular plan. Overall, our findings support fractality as a key factor in the evolution of biological scaling.

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