Statistical Comparative Methods Research Articles

Geological influence on the terrestrial gamma radiation dose rate in Jos Plateau, Nigeria

Natural environmental terrestrial gamma radiation dose (TGRD) rate measurements have been carried out across the geological formations of Jos Plateau, Nigeria. External gamma radiation dose rates ranged between 11 and 714 nGy h-1 with a mean value of 204 nGy h-1. Relationship between TGRD levels and geological type was determined. Statistical comparative method one way analysis of variance (ANOVA) was used to compare the TGRD means for the various types. The statistical results revealed in some instances, significant differences among the mean values of TGRD rates for the different underlying geological structures. Annual effective dose and collective effective dose for the general public due to exposure to terrestrial gamma radiation were estimated at 0.25 mSv y-1 and 1.20x102 mSv y-1, respectively. Isodose map for exposure rate due to TGRD wasplotted using ArcGIS software. The results will serve as database for natural background radiation for the country.Keywords: Natural radiation; Terrestrial gamma radiation dose (TGRD); geological type; Analysis of variance (ANOVA)

DEFINING THE MORPHO-FUNCTIONAL INDICATORS FOR THE SELECTION OF FOOTBALLERS ACCORDING TO THEIR PLAY LINES

This study aims at defining the morphological and functional indicators for the selection of footballers according to the three play lines (defence, midfield, attack) for the category of under 18 years old. We will work on finding the differences in these morpho-functional indicators and their relation with the play lines and their requirements. For this, we made the morphological measurements, namely : height, weight, fat-weight, muscle weight, bone weight, and the functional tests, namely : Luc Leger’ Test to measure the maximal oxygen consumption (Vo2max), the retrieval capacity via Ruffier Dickson Test and Vitality Capacity Test V.C, for 10 first level clubs in the West of Algeria; as we selected 18 players from each team with the average of 6 players of each play line (180 players), making a rate of 32% of the original society as a sample. We also used the descriptive and statistical comparative methods among those indicators and each play line in order to know to what extent those morpho-functional variables cause differences among players according to their play lines, while defining those indicators as a reference to be adopted in the players selection process for this age category in order to support the selection process with observation. The results revealed clear differences in the morph-functional indicators among the target category of players according to the differences in their playing lines at the level of the height indicator, as the significance value of selection reached 0.015 which is less than the significance level of the null hypotheses, while we did not find significant differences between the other morphological indicators. Meanwhile, there was a difference in the functional indicator at the level of the retrieval capacity, as the significance value reached 0.011 which is less than the test significance level 0.05; there was no difference at the level the other significances. Thence, the researcher recommends the necessity of consolidating the selection process by the inclusion of observation through the use of some morphological measurements such as height, in addition to functional tests such as the retrieval capacity as important indicators in the players selection process according to the requirements of the play lines for this age category of players, in order to select the best talents that can be beneficial to Algerian football in the future. Article visualizations:

Using phylogenetics to detect pollinator-mediated floral evolution.

The development of comparative phylogenetic methods has provided a powerful toolkit for addressing adaptive hypotheses, and researchers have begun to apply these methods to test the role of pollinators in floral evolution and diversification. One approach is to reconstruct the history of both floral traits and pollination systems to determine if floral trait change is spurred by shifts in pollinators. Looking across multiple shifts, it is also possible to test for significant correlations between floral evolution and pollinators using parsimony, likelihood and Bayesian methods for discrete characters or using statistical comparative methods for continuous characters. Evolutionary shifts in pollinators and floral traits may cause changes in diversification rates, and new methods are available for simultaneously studying character evolution and diversification rates. Relatively few studies have yet used formal comparative methods to elucidate how pollinators affect floral evolution across the phylogeny, and fruitful directions for future applications are discussed.

The evolution of courtship display repertoire size in the dabbling ducks (Anatini)

Abstract Many animals possess multiple ornaments or behaviours that seem to have evolved via sexual selection. A complete understanding of sexual selection requires an explanation for such multiple traits. The dabbling ducks (Tribe: Anatini) exhibit considerable variation among species in the number of displays in the male courtship repertoire. I tested five hypotheses concerning the evolution of the variation in display repertoire size of dabbling ducks: (1) species recognition, (2) courtship habitat, (3) sexual selection intensity, (4) display media tradeoff and (5) time constraints on pair formation. I tested these hypotheses, using an explicit phylogenetic hypothesis developed from DNA sequences for the dabbling ducks, with two types of statistical comparative methods (discrete and continuous character). The variation observed in male courtship display repertoire size in dabbling ducks was consistent with the courtship habitat and sexual selection intensity hypotheses. Specifically, the size of the display repertoire was larger in species that exhibit courtship exclusively on water and larger in species with dimorphic plumage. These results suggest that ecological (habitat) as well as social (sexual selection) factors may be important in driving the evolution of displays in the dabbling ducks.

Comparative studies of sex differences in the song-control system of songbirds

Songbirds exhibit some of the most extreme sex differences in the brain of all vertebrates. Understanding the function of these sex differences has relied on making interspecies comparisons. In some species, females sing rarely or not at all, and the brain nuclei that control song are many times larger in volume in males than in females. In other species, males and females sing approximately equally, and the sizes of the brain nuclei that control song are approximately equal between the sexes. This article reviews sex differences in the song-control system of songbirds, and introduces statistical comparative methods developed by evolutionary biologists. These methods control for phylogenetic effects while comparing the co-evolution of traits. The extreme sex differences in song seem to have co-evolved with the extreme sex differences in singing behavior in songbird species.

Reappraising adaptive radiation

Reappraising adaptive radiation

STABILIZING SELECTION AND THE COMPARATIVE ANALYSIS OF ADAPTATION.

Comparative studies tend to differ from optimality and functionality studies in how they treat adaptation. While the comparative approach focuses on the origin and change of traits, optimality studies assume that adaptations are maintained at an optimum by stabilizing selection. This paper presents a model of adaptive evolution on a macroevolutionary time scale that includes the maintenance of traits at adaptive optima by stabilizing selection as the dominant evolutionary force. Interspecific variation is treated as variation in the position of adaptive optima. The model illustrates how phylogenetic constraints not only lead to correlations between phylogenetically related species, but also to imperfect adaptations. From this model, a statistical comparative method is derived that can be used to estimate the effect of a selective factor on adaptive optima in a way that would be consistent with an optimality study of adaptation to this factor. The method is illustrated with an analysis of dental evolution in fossil horses. The use of comparative methods to study evolutionary trends is also discussed.

Testing Hypotheses of Correlated Evolution Using Phylogenetically Independent Contrasts: Sensitivity to Deviations from Brownian Motion

We examined the statistical performance (in terms of type I error rates) of Felsenstein's (1985, Am. Nat. 125:1–15) comparative method of phylogenetically independent contrasts for testing hypotheses about evolutionary correlations of continuous-valued characters. We simulated data along two different phylogenies, one for 15 species of plethodontid salamanders and the other for 49 species of Carnivora and ungulates. We implemented 15 different models of character evolution, 14 of which deviated from Brownian motion, which is in effect assumed by the method. The models studied included the Ornstein–Uhlenbeck process and punctuated equilibrium (change allowed in only one daughter at each bifurcation) both with and without trends and limits on how far phenotypes could evolve. As has been shown in several previous simulation studies, a nonphylogenetic Pearson correlation of species' mean values yielded inflated type I error rates under most models, including that of simple Brownian motion. Independent contrasts yielded acceptable type I error rates under Brownian motion (and in preliminary studies under slight deviations from this model), but they were inflated under most other models. This new result confirms the model dependence of independent contrasts. However, when branch lengths were checked and transformed, then type I error rates of independent contrasts were reduced. Moreover, the maximum observed type I error rates never exceeded twice the nominal P value at α = 0.05. In comparison, the nonphylogenetic correlation tended to yield extremely inflated (and highly variable) type I error rates. These results constitute another demonstration of the general superiority of phylogenetically based statistical methods over nonphylogenetic ones, even under extreme deviations from a Brownian motion model. These results also show the necessity of checking the assumptions of statistical comparative methods and indicate that diagnostic checks and remedial measures can substantially improve the performance of the independent contrasts method.

Testing Hypotheses of Correlated Evolution Using Phylogenetically Independent Contrasts: Sensitivity to Deviations from Brownian Motion

We examined the statistical performance (in terms of type I error rates) of Felsenstein's (1985, Am. Nat. 125:1-15) comparative method of phylogenetically independent contrasts for test- ing hypotheses about evolutionary correlations of continuous-valued characters. We simulated data along two different phylogenies, one for 15 species of plethodontid salamanders and the other for 49 species of Carnivora and ungulates. We implemented 15 different models of character evolution, 14 of which deviated from Brownian motion, which is in effect assumed by the method. The models studied included the Ornstein-Uhlenbeck process and punctuated equilibrium (change allowed in only one daughter at each bifurcation) both with and without trends and limits on how far phenotypes could evolve. As has been shown in several previous simulation studies, a nonphylogenetic Pearson correlation of species' mean values yielded inflated type I error rates under most models, including that of simple Brownian motion. Independent contrasts yielded acceptable type I error rates under Brownian motion (and in preliminary studies under slight deviations from this model), but they were inflated under most other models. This new result confirms the model dependence of independent contrasts. However, when branch lengths were checked and transformed, then type I error rates of independent contrasts were reduced. Moreover, the maximum observed type I error rates never exceeded twice the nominal P value at a = 0.05. In comparison, the nonphylogenetic correlation tended to yield extremely inflated (and highly variable) type I error rates. These results constitute another demonstration of the general superi- ority of phylogenetically based statistical methods over nonphylogenetic ones, even under extreme deviations from a Brownian motion model. These results also show the necessity of checking the assumptions of statistical comparative methods and indicate that diagnostic checks and remedial measures can substantially improve the performance of the independent contrasts method. (Com- parative method; computer simulation; independent contrasts; phylogeny; hypothesis testing; sta- tistics; correlated evolution.)