Christine M. Janis

Bio: Christine M. Janis is an academic researcher from University of Bristol. The author has contributed to research in topics: Ungulate & Neogene. The author has an hindex of 40, co-authored 114 publications receiving 8505 citations. Previous affiliations of Christine M. Janis include University of Chicago & Brown University.

Phylogenetic Analysis of Covariance by Computer Simulation

Abstract: Biologists often compare average phenotypes of groups of species defined cladistically or on behavioral, ecological, or physiological criteria (e.g., carnivores vs. herbivores, social vs. nonsocial species, endotherms vs. ectotherms). Hypothesis testing typically is accomplished via analysis of variance (ANOVA) or covariance (ANCOVA; often with body size as a covariate). Because of the hierarchical nature of phylogenetic descent, however, species may not represent statistically independent data points, degrees of freedom may be inflated, and significance levels derived from conventional tests cannot be trusted. As one solution to this degrees of freedom problem, we propose using empirically scaled computer simulation models of continuous traits evolving along «known» phylogenetic trees to obtain null distributions of F statistics for ANCOVA of comparative data sets

The Origins of C4 Grasslands: Integrating Evolutionary and Ecosystem Science

Abstract: The evolution of grasses using C4 photosynthesis and their sudden rise to ecological dominance 3 to 8 million years ago is among the most dramatic examples of biome assembly in the geological record. A growing body of work suggests that the patterns and drivers of C4 grassland expansion were considerably more complex than originally assumed. Previous research has benefited substantially from dialog between geologists and ecologists, but current research must now integrate fully with phylogenetics. A synthesis of grass evolutionary biology with grassland ecosystem science will further our knowledge of the evolution of traits that promote dominance in grassland systems and will provide a new context in which to evaluate the relative importance of C4 photosynthesis in transforming ecosystems across large regions of Earth.

The evolutionary strategy of the equidae and the origins of rumen and cecal digestion.

Abstract: There are two main groups of ungulates or hoofed mammals living today, perissodactyls and artiodactyls. They are distinguished by a basic difference in foot morphology, which indicates that the two groups arose independently from a basal "proto-ungulate" stock (the order Condylarthra) in the early Tertiary. This difference involves the axis of symmetry of the foot. In perissodactyls it passes through the third metapodial, while in artiodactyls it passes between the third and fourth metapodials. The perissodactyls surviving today are horses, rhinos and tapirs. The recent artiodactyls are a much larger and more diverse group, broadly covering all "cloven-hoofed" animals such as pigs, hippos, camels, deer, giraffes, antelope, cattle and sheep. The perissodactyls must have evolved by the late Paleocene, as by the early Eocene four out of five of the known superfamilies are already distinguishable (Romer, 1966). Artiodactyls are also seen in the early Eocene (Romer, 1966), but the two major groups of ruminant artiodactyls, the tylopods and the pecorans, do not appear in the fossil record until the late Eocene (Gazin, 1955) (see Fig. 1). The perissodactyls were the dominant medium to largesized herbivores during the Eocene, and in the early Oligocene a reduction in their diversity coincided with the beginning radiations of the ruminant groups of artiodactyls. These latter animals were the dominant medium-sized herbivores throughout the remainder of the Tertiary, at least in terms of species diversity. The perissodactyls originated in North America; the origin of the artiodactyls, whether in North America or in Eurasia, is still in question (Olson, 1971). As the rise of the artiodactyls at the Eocene-Oligocene boundary coincides with the decrease in the diversity of the perissodactyls, theories have been advanced to explain this coincidence in terms of perissodactyls being competitively inferior to artiodactyls. One obvious difference between the two groups is the difference in limb morphology. Although the axis of symmetry of the foot seems an unlikely candidate for conferring a selective advantage, artiodactyls do possess a unique double trochleared tarsal or ankle joint. This structure has been regarded as a key feature of the group and contributory to their evolutionary success, on the grounds that it has enabled artiodactyls to achieve rapid acceleration for predator escape (e.g., Schaeffer, 1947; Romer, 1968; Colbert, 1969). While there is little doubt that this particular adaptation was of value to the artiodactyls themselves, I do not think, however, that it had a great deal to do with the relative competitive efficiencies of these two ungulate groups. For a start, this tarsus appeared in a highly advanced condition in the first artiodactyls in the early Eocene (Schaeffer, 1947) long before their radiation and diversification, and is found in noncursorial as well as cursorial forms. In addition, modern ecological work demonstrates that predation is not necessarily detrimental

Tertiary mammal evolution in the context of changing climates, vegetation, and tectonic events

Abstract: Evolutiona ry trends among mammals over the past 66 Myr have been profou ndly influenced by changing climat es, in tum the result of tectonic events. The global trop ical forest type of ecosystem of the early Tertiary was disrupted by Late Eocene climatic changes, with the extinction of most archaic mammalian lineages and the appearance of most modem famil ies. Later Tertiary trends reflect increasing aridity, with the appearance of open-habitat mammals such as grazing ungulate s, although true grasslands probably did not appear until the Late Miocene in the New World and the Pliocene in the Old World. Patterns of mammalian diversity track paleote mperature curves for the northern latitudes, with maxima in the early Mid dle Eocene and early Middle Miocene. Major dispersals occurred at times of sea level lows, resulting in loss of endemism in originally isolated continents such as South America and Afr ica, and changes in faunal composition across Holarctica. Dispersal in con junction with climatic changes accounted for maj or extinction events in the Late Eocene to Early Oligoce ne, at the end of the Miocene , and in the mid Pliocene. Outstanding problems include the origin and dispersal routes of many extant orders that appeared at the start of the Eocene and the

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

phytools: an R package for phylogenetic comparative biology (and other things)

Abstract: Summary 1. Here, I present a new, multifunctional phylogenetics package, phytools, for the R statistical computing environment. 2. The focus of the package is on methods for phylogenetic comparative biology; however, it also includes tools for tree inference, phylogeny input/output, plotting, manipulation and several other tasks. 3. I describe and tabulate the major methods implemented in phytools, and in addition provide some demonstration of its use in the form of two illustrative examples. 4. Finally, I conclude by briefly describing an active web-log that I use to document present and future developments for phytools. I also note other web resources for phylogenetics in the R computational environment.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Testing for phylogenetic signal in comparative data: behavioral traits are more labile.

Abstract: The primary rationale for the use of phylogenetically based statistical methods is that phylogenetic signal, the tendency for related species to resemble each other, is ubiquitous. Whether this assertion is true for a given trait in a given lineage is an empirical question, but general tools for detecting and quantifying phylogenetic signal are inadequately developed. We present new methods for continuous-valued characters that can be implemented with either phylogenetically independent contrasts or generalized least-squares models. First, a simple randomization procedure allows one to test the null hypothesis of no pattern of similarity among relatives. The test demonstrates correct Type I error rate at a nominal α = 0.05 and good power (0.8) for simulated datasets with 20 or more species. Second, we derive a descriptive statistic, K, which allows valid comparisons of the amount of phylogenetic signal across traits and trees. Third, we provide two biologically motivated branch-length transformat...