Logistic Regression for Empirical Studies of Multivariate Selection

Janzen, Fredric J.; Stern, Hal S.

doi:10.2307/2411330

Cited by 267 publications

(299 citation statements)

References 26 publications

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“…Many studies of selection use viability as their measure of fitness, so it is possible that any conclusions regarding power derived from the methods presented above might not be applicable to binomially distributed fitnesses (Janzen and Stern 1998). To test for this possibility, for a given theoretical correlation coefficient and sample size, sample datasets were generated under the assumption that the traits were normally distributed ( ϭ 0, 2 ϭ 1) but that fitness was binomially distributed (the probability of being alive, p ϭ 0.1, 0.5, and 0.9; BIVAR, ver.…”

Section: Methodsmentioning

confidence: 99%

Power and Potential Bias in Field Studies of Natural Selection

2004

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Abstract. The advent of multiple regression analyses of natural selection has facilitated estimates of both the direct and indirect effects of selection on many traits in numerous organisms. However, low power in selection studies has possibly led to a bias in our assessment of the levels of selection shaping natural populations. Using calculations and simulations based on the statistical properties of selection coefficients, we find that power to detect total selection (the selection differential) depends on sample size and the strength of selection relative to the opportunity of selection. The power of detecting direct selection (selection gradients) is more complicated and depends on the relationship between the correlation of each trait and fitness and the pattern of correlation among traits. In a review of 298 previously published selection differentials, we find that most studies have had insufficient power to detect reported levels of selection acting on traits and that, in general, the power of detecting weak levels of selection is low given current study designs. We also find that potential publication bias could explain the trend that reported levels of direct selection tend to decrease as study sizes increase, suggesting that current views of the strength of selection may be inaccurate and biased upward. We suggest that studies should be designed so that selection is analyzed on at least several hundred individuals, the total opportunity of selection be considered along with the pattern of selection on individual traits, and nonsignificant results be actively reported combined with an estimate of power.

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Section: Methodsmentioning

confidence: 99%

Power and Potential Bias in Field Studies of Natural Selection

2004

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“…As values for survival are binary, we used logistic regressions to estimate selection gradients (Schluter, 1988;Janzen & Stern, 1998). All the morphological traits were standardized to have a mean of zero and a standard deviation of 1 (Lande & Arnold, 1983;Janzen & Stern, 1998).…”

Section: Viability Selection In the Wildmentioning

confidence: 99%

“…Consequently, we transformed the logistic regression coefficients and obtained b avggrad , which is comparable to the linear selection gradient (b) obtained through multiple regressions (Janzen & Stern, 1998). Nonlinear selection gradients (c), which describe nonlinear selection on a trait, were calculated by adding the cross-product and squared standardized traits to the logistic regression.…”

Section: Researchmentioning

confidence: 99%

Environment-dependent intralocus sexual conflict in a dioecious plant

et al. 2011

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Summary Intralocus sexual conflict is a form of conflict that does not involve direct interactions between males and females. It arises when selection on a shared trait with a common genetic basis differs between the sexes. Environmental factors, such as resource availability, may influence the expression and evolutionary outcome of such conflict. We quantified the genetic variance‐covariance matrix, G, for both sexes of Silene latifolia for floral and leaf traits, as well as the between‐sex matrix, B. We also quantified selection on the sexes via survival for 2 yr in four natural populations that varied in water availability. Environment‐dependent intralocus sexual conflict exists for specific leaf area, a trait that is genetically correlated between the sexes. Males experienced significant negative selection, but only in populations with relatively limited water availability. Females experienced weakly positive or significant stabilizing selection on the same trait. Specific leaf area is genetically correlated with flower size and number, which are sexually dimorphic in this species. The extent of intralocus sexual conflict varied with the environment. Resolution of such conflict is likely to be confounded, given that specific leaf area is highly genetically integrated with other traits that are also divergent between the sexes.

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“…All analyses were conducted by using both linear and logistic regression, and the robustness of the results to method of analysis was evaluated. We note that our primary goal was parameter estimation rather than significance testing of individual differentials such that selection estimates from linear regression are likely appropriate (26,37). Whether selection differed significantly among treatments for individual traits was evaluated by using data from all treatments and then testing the significance of interaction between trait value (continuous covariate) and treatment (categorical covariate) in a selection analysis with survival as the dependent variable.…”

Section: )mentioning

confidence: 99%

Experimental evidence that predation promotes divergence in adaptive radiation

Nosil

Crespi²

2006

Proc. Natl. Acad. Sci. U.S.A.

225

242

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Adaptive radiation is the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. Recent studies have identified general patterns in adaptive radiation and inferred that resource competition is a primary factor driving phenotypic divergence. The role and importance of other processes, such as predation, remains controversial. Here we use Timema stick insects to show that adaptive radiation can be driven by divergent selection from visual predators. Ecotypes using different host-plant species satisfy criteria for the early stages of adaptive radiation and differ in quantitative aspects of color, color pattern, body size, and body shape. A manipulative field experiment demonstrates that the direction and strength of divergent selection on these traits is strongly positively correlated with the direction and magnitude of their population divergence in nature but only when selection is estimated in the presence of predation. Our results indicate that both competition and predation may commonly serve as mechanisms of adaptive radiation.T he ''ecological theory of adaptive radiation'' states that (i) divergent natural selection drives the phenotypic divergence and speciation of lineages and (ii) divergent selection itself stems from ecological differences between environments or from ecological interactions (1-3). A prediction of the theory is that the direction and magnitude of divergent selection in the wild is positively correlated with the direction and magnitude of trait divergence among natural populations (4, 5). Our understanding of adaptive radiation has been greatly increased by studies describing general patterns or documenting the process of divergent selection (6-11). However, such studies do not test the critical prediction of a correlation between selection and trait divergence. With respect to the causes of divergent selection, support for even the best-studied mechanism of interspecific competition is mostly indirect (2). The role of other processes, such as predation, has long been discussed (12-14) but remains controversial (2,(15)(16)(17)(18). Part of the controversy stems from the fact that predation is notoriously difficult to study in the wild. Here we demonstrate that divergent selection and trait divergence are strongly correlated in natural populations of walking stick insects, and we elucidate predation as the source of divergent selection by using a manipulative field experiment.Timema walking sticks are plant-feeding insects distributed throughout southwestern North America (19). The genus as a whole satisfies three of the four criteria for adaptive radiation (2): recent ancestry, environment-phenotype correlations, and rapid bursts of speciation (19,20). Only experimental tests for trait utility at the among-species level remain to be conducted. By contrast, all four criteria are satisfied for host-associated ecotypes of Timema cristinae adapted to feeding on two different host-plant species. Ecotypes are defined by which host-plant species they are found on...

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Logistic Regression for Empirical Studies of Multivariate Selection

Cited by 267 publications

References 26 publications

Power and Potential Bias in Field Studies of Natural Selection

Power and Potential Bias in Field Studies of Natural Selection

Environment-dependent intralocus sexual conflict in a dioecious plant

Experimental evidence that predation promotes divergence in adaptive radiation

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