Article

2 Unifying Life History Analyses for Inference of Fitness and Population Growth

Department of Ecology, Evolution, and Behavior, Minnesota Center for Community Genetics, University of Minnesota, St. Paul, Minnesota 55108, USA.
(Impact Factor: 3.83). 08/2008; 172(1):E35-47. DOI: 10.1086/588063
Source: PubMed

ABSTRACT

The lifetime fitnesses of individuals comprising a population determine its numerical dynamics, and genetic variation in fitness results in evolutionary change. This dual importance of individual fitness is well understood, but empirical fitness records generally violate the assumptions of standard statistical approaches. This problem has undermined comprehensive study of fitness and impeded empirical synthesis of the numerical and genetic dynamics of populations. Recently developed aster models remedy this problem by explicitly modeling the dependence of later-expressed components of fitness (e.g., fecundity) on those expressed earlier (e.g., survival to reproduce). Moreover, aster models employ different sampling distributions for different components of fitness (e.g., binomial for survival over a given interval and Poisson for fecundity). Analysis is done by maximum likelihood, and the resulting distributions for lifetime fitness closely approximate observed data. We illustrate the breadth of aster models' utility with three examples demonstrating estimation of the finite rate of increase, comparison of mean fitness among genotypic groups, and analysis of phenotypic selection. Aster models offer a unified approach to addressing the breadth of questions in evolution and ecology for which life-history data are gathered.

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Available from: Julie R Etterson
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• "known generalizations for vector distributions (Gorban, 1984;Metz et al., 1992). However, there is no universal rule to measure various traits of organisms by the changes in the average reproduction coefficient, despite exerted efforts, development of special methods, and gaining some success (Haldane, 1954;Waxman and Welch, 2005;Kingsolver and Pfennig, 2007;Shaw et al., 2008;Karev and Kareva, 2014). There may be additional difficulties because the evolutionary optimality is not necessarily related to organisms, and the non-trivial question arises: 'what is optimal?' Another difficulty is caused by possible non-stationarity of the optimum: selected organisms change their environment and become non-optimal on the background of the new ecological situation (Gorban, 1984). "
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ABSTRACT: In 1938, H. Selye proposed the notion of adaptation energy and published "Experimental evidence supporting the conception of adaptation energy". Adaptation of an animal to different factors appears as the spending of one resource. Adaptation energy is a hypothetical extensive quantity spent for adaptation. This term causes much debate when one takes it literally, as a physical quantity, i.e. a sort of energy. The controversial points of view impede the systematic use of the notion of adaptation energy despite experimental evidence. Nevertheless, the response to many harmful factors often has general non-specific form and we suggest that the mechanisms of physiological adaptation admit a very general and nonspecific description. We aim to demonstrate that Selye's adaptation energy is the cornerstone of the top-down approach to modelling of non-specific adaptation processes. We analyse Selye's axioms of adaptation energy together with Goldstone's modifications and propose a series of models for interpretation of these axioms. {\em Adaptation energy is considered as an internal coordinate on the dominant path' in the model of adaptation}. The phenomena of oscillating death' and `oscillating remission' are predicted on the base of the dynamical models of adaptation. Natural selection plays a key role in the evolution of mechanisms of physiological adaptation. We use the fitness optimization approach to study of the distribution of resources for neutralization of harmful factors, during adaptation to a multifactor environment, and analyse the optimal strategies for different systems of factors.
Full-text · Article · Jan 2016 · Journal of Theoretical Biology
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• "Limited sample sizes within each block for each line–cross type combination for scoring survival as a binary trait also precluded the use of more sophisticated analyses of cumulative fitness (e.g. Aster models;Shaw et al. 2008). Because we are interested in differences in ratios (heterosis ) between mating system categories, it is appropriate to use natural-log-transformed data (Johnston and Schoen 1994). "
Article: Increased heterosis in selfing populations of a perennial forb
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ABSTRACT: Quantifying the importance of random genetic drift in natural populations is central to understanding the potential limits to natural selection. One approach is to estimate the magnitude of heterosis, the increased fitness of progeny derived from crosses between populations relative to crosses within populations caused by the heterozygous masking of deleterious recessive or nearly recessive alleles that have been fixed by drift within populations. Self-fertilization is expected to reduce the effective population size by half relative to outcrossing, and population bottlenecks may be common during the transition to selfing. Therefore, chance fixation of deleterious alleles due to drift in selfing populations should increase heterosis between populations. Increased homozygosity due to fixation or loss of alleles should also decrease inbreeding depression within populations. Most populations of the perennial herb Arabidopsis lyrata ssp. lyrata are self-incompatible, but several have evolved self-compatibility and are highly selfing. We quantified heterosis and inbreeding depression in two predominantly self-compatible (SC) and seven self-incompatible (SI) populations in a field common garden experiment within the species' native range, and examined the correlation between these metrics to gauge the similarity in their genetic basis. We measured proportion germination in the lab, and survival and fecundity (flower and seed production) for two years in the field, and calculated estimates of cumulative fitness. We found 7.2-fold greater heterosis in SC compared to SI populations, despite substantial heterosis in SI populations (56%). Inbreeding depression was >61%, and not significantly different between SC and SI populations. There was no correlation between population estimates of heterosis and inbreeding depression, suggesting that they have somewhat different genetic bases. Combined with other sources of information, our results suggest a history of bottlenecks in all of these populations. The bottlenecks in SC populations may have been severe, but their strong inbreeding depression remains enigmatic.
Full-text · Article · Oct 2015 · AoB PLANTS
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• "Aster models for life-history traits were used to characterize phenotypic selection on characteristics within each water treatment (aster package) [44]. These models utilize maximum likelihood linear methods and improve upon previous least squares methods by modeling multiple components of fitness into a single variable, as well as by specifying a particular distribution for each component of fitness [45] [46] [47]. All characteristics were regressed with the combined fitness variable based on two components: survival to reproduction (Bernoulli distribution) and fecundity (truncated Poisson distribution). "
Article: Selection on Crop-Derived Traits and QTL in Sunflower (Helianthus annuus) Crop-Wild Hybrids under Water Stress
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ABSTRACT: Locally relevant conditions, such as water stress in irrigated agricultural regions, should be considered when assessing the risk of crop allele introgression into wild populations following hybridization. Although research in cultivars has suggested that domestication traits may reduce fecundity under water stress as compared to wild-like phenotypes, this has not been investigated in crop-wild hybrids. In this study, we examine phenotypic selection acting on, as well as the genetic architecture of vegetative, reproductive, and physiological characteristics in an experimental population of sunflower crop-wild hybrids grown under wild-like low water conditions. Crop-derived petiole length and head diameter were favored in low and control water environments. The direction of selection differed between environments for leaf size and leaf pressure potential. Interestingly, the additive effect of the crop-derived allele was in the direction favored by selection for approximately half the QTL detected in the low water environment. Selection favoring crop-derived traits and alleles in the low water environment suggests that a subset of these alleles would be likely to spread into wild populations under water stress. Furthermore, differences in selection between environments support the view that risk assessments should be conducted under multiple locally relevant conditions.
Full-text · Article · Jul 2014 · PLoS ONE