Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans

The Late Cretaceous (∼95–66 million years ago) western North American landmass of Laramidia displayed heightened non-marine vertebrate diversity and intracontinental regionalism relative to other latest Cretaceous Laurasian ecosystems. Processes generating these patterns during this interval remain poorly understood despite their presumed role in the diversification of many clades. Tyrannosauridae, a clade of large-bodied theropod dinosaurs restricted to the Late Cretaceous of Laramidia and Asia, represents an ideal group for investigating Laramidian patterns of evolution. We use new tyrannosaurid discoveries from Utah—including a new taxon which represents the geologically oldest member of the clade—to investigate the evolution and biogeography of Tyrannosauridae. These data suggest a Laramidian origin for Tyrannosauridae, and implicate sea-level related controls in the isolation, diversification, and dispersal of this and many other Late Cretaceous vertebrate clades.     

Habent Fata Sua: The Rise and Fall of Garden Plants

Background: Rare cactus in the Americas and other species worldwide are threatened species because of their high level of habitat specialisation, narrow distribution range and continuing population decline.

Aims: To identify management units (MUs) based on genetic variability and demographic structure in order to propose assertive conservation actions for Mammillaria crucigera and to provide a model case study for other species that are under similar threats.

Methods: We genotyped through eight microsatellite loci in 171 individuals and described demographic structures in six populations of this cactus based on plots of 1 m².

Results: Across populations with a mean density of 2.6 m^?2 and a total of ~500 individuals counted, 30% of the individuals were reproductive (diameter >2 cm). The total heterozygosity was low (H_O = 0.54), but the inbreeding coefficient (F_IS = 0.29) and the allele diversity (N_A = 20) were high. Four genetic groups were distinguished, although considering the demographic structure, we propose three MUs.

Conclusions: It is critical to maintain the genetic connectivity within and among MUs, which can only be achieved through cooperation between government authorities and local habitants to halt the degradation and further destruction of the remnant populations. Searching MUs allows the identification of critical areas for conservation issues for all species whose extant populations are in a fragmented landscape.     

Contrasting Strategies of Alfalfa Stem Elongation in Response to Fall Dormancy in Early Growth Stage: The Tradeoff between Internode Length and Internode Number

Fall dormancy (FD) in alfalfa (Medicago sativa L.) can be described using 11 FD ratings, is widely used as an important indicator of stress resistance, productive performance and spring growth. However, the contrasting growth strategies in internode length and internode number in alfalfa cultivars with different FD rating are poorly understood. Here, a growth chamber study was conducted to investigate the effect of FD on plant height, aboveground biomass, internode length, and internode number in alfalfa individuals in the early growth stages. In order to simulate the alfalfa growth environment in the early stage, 11 alfalfa cultivars with FD ratings from one to 11 were chosen and seeded at the greenhouse, and then were transplanted into an artificial growth chamber. The experimental design was a randomized complete block in a split-plot arrangement with three replicates. Plant height, above-ground biomass, internode length, and internode number were measured in early growth stage in all individuals. Our findings showed that plant height and the aboveground biomass of alfalfa did not significantly differ among 11 different FD rated cultivars. Also, internode length and internode number positively affected plant height and the aboveground biomass of alfalfa individuals and the average internode length significantly increased with increasing FD rating. However, internode number tended to sharply decline when the FD rating increased. Moreover, there were no correlations, slightly negative correlations, and strongly negative correlations between internode length and internode number in alfalfa individuals among the three scales, including within-FD ratings, within-FD categories and inter-FD ratings, respectively. Therefore, our results highlighted that contrasting growth strategies in stem elongation were adopted by alfalfa with different FD ratings in the early growth stage. Alfalfa cultivars with a high FD rating have longer internodes, whereas more dormant alfalfa cultivars have a larger number of internodes. There were tradeoffs between internode length and internode number in response to FD in alfalfa, which reflected certain scale-dependence.     

The Rise and Fall of HIV in High-Prevalence Countries: A Challenge for Mathematical Modeling

Several countries with generalized, high-prevalence HIV epidemics, mostly in sub-Saharan Africa, have experienced rapid declines in transmission. These HIV epidemics, often with rapid onsets, have generally been attributed to a combination of factors related to high-risk sexual behavior. The subsequent declines in these countries began prior to widespread therapy or implementation of any other major biomedical prevention. This change has been construed as evidence of behavior change, often on the basis of mathematical models, but direct evidence for behavior changes that would explain these declines is limited. Here, we look at the structure of current models and argue that the common “fixed risk per sexual contact" assumption favors the conclusion of substantial behavior changes. We argue that this assumption ignores reported non-linearities between exposure and risk. Taking this into account, we propose that some of the decline in HIV transmission may be part of the natural dynamics of the epidemic, and that several factors that have traditionally been ignored by modelers for lack of precise quantitative estimates may well hold the key to understanding epidemiologic trends.     

The Evolution of Evolutionary Thinking in Chile

The scientific study of evolution in Chile has experienced periods of diversification and stasis, depending upon the social and political context at different times. In the eighteenth century, most of the natural history research consisted of systematics and taxonomy and, as in most of South America, this task was performed mainly by natural historian theologists. Later, the immigration of European scientists to Chile after independence from Spain in 1810 improved substantially its knowledge of the local biota and stimulated the diversification of naturalists in the country. Research in modern biology and the teaching of genetics in Chile can be traced back to Giovanni Noe, an Italian zoologist who had a profound impact in the first third of the twentieth century. In the 1960s–70s, Danko Brncic, a population geneticist educated in the tradition of Dobzhansky and the modern synthesis, led the most important diversification process in the study of evolutionary biology in the country. However, the military coup in 1973 brought this radiation to a sudden stop and produced a stasis period associated with the subsequent 17-year dictatorship. Evolutionary biology recovered its status after the re-establishment of democracy, and it is currently experiencing an exciting and renewed diversification period that has led to the foundation of the Chilean Society of Evolutionary Biology, the only scientific society for the study of evolution in Latin America. One of the missions of the Society is to bridge the gap between scientists and science educators in order to improve the teaching of evolution at different levels both in secular and religious schools. Even though the Roman Catholic Church has been a pivotal institution in the development of Chilean society, debate on evolutionism—creationism issues has been largely absent both in public and academic discussions. The influence of religion on science education has been sporadic, and mostly related to omission rather than tergiversation of scientific information in biology textbooks. Currently, schools are obliged by law to teach the basics of evolution in K-12 and K-16 levels (or their local equivalents). Because of this, there is little at present that suggests an organized creationist or intelligent design movement surge in the near future. Nevertheless, the high percentage of religiosity in Chile, together with the observation that the moral values of Chilean society are among the most conservative in the world, provide good reasons to remain vigilant.     

动物内温性进化研究进展

对动物内温性进化的研究进行了较为系统的论述,包括内温性动物概念的由来、特点和起源的选择因子。内温性起源的选择因子包括8个模型：热生态位扩展模型、恒温与代谢效率模型、降低个体大小模型、姿势改变模型、增加脑大小模型、有氧呼吸能力模型、双亲行为模型和同化能力模型。其中后3个模型较为重要。有氧呼吸能力模型认为,选择提高支持物理运动的最大呼吸能力,而增加的静止代谢作为其相关反应而得以进化。该假说得到种内研究数据的支持,而种问的数据并小完全支持。双亲行为模型是指在鸟兽类中,内温性是对双亲行为选择的结果,因为内温性为双亲控制抚育温度提供了保证。同化能力模型认为,在鸟类和兽类中内温性进化由以下两个因素所推动：①子代出生后双亲行为加强;②为支持每日总体能量高速消耗所需,动物内脏器官能力增强而导致的较高维持消耗。     

Fixation of Strategies for an Evolutionary Game in Finite Populations

A stochastic evolutionary dynamics of two strategies given by 2x 2 matrix games is studied in finite populations. We focus on stochastic properties of fixation: how a strategy represented by a single individual wins over the entire population. The process is discussed in the framework of a random walk with site dependent hopping rates. The time of fixation is found to be identical for both strategies in any particular game. The asymptotic behavior of the fixation time and fixation probabilities in the large population size limit is also discussed. We show that fixation is fast when there is at least one pure evolutionary stable strategy (ESS) in the infinite population size limit, while fixation is slow when the ESS is the coexistence of the two strategies.