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.     

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.     

Animals in Schools: Processes and Strategies in Human-Animal Education

Abstract

In this study we tested the hypothesis that the process of training a non-human primate (NHP) affects it's general behavior patterns, outside of training. A group of Abyssinian colobus monkeys (Colobus guereza, n = 8), housed at Paignton Zoo, UK, were observed for four 12-day periods. Behaviors were noted prior to training, using positive reinforcement to achieve oral examinations, and each month for three months after training had started. These data were used to construct daily activity budgets and investigate social behaviors (both colobus–colobus and colobus–human). A comparison of these data (using doubly repeated measures MANOVAs) showed activity budget (F_(3,3) = 9.8, λ = 0.4, p < 0.001) and colobus-initiated interactions with people (F_(3,2) = 16.6, λ = 0.3, p < 0.001) differed significantly across the four observation periods. Resting behavior was negatively correlated with feeding behavior (Pearson: n = 56, r = -0.25, p < 0.05); this relationship was considered to be independent of the onset of training. The significant decline in colobus-initiated interactions with the public appeared to be a direct result of the training.

The results in this study showed that the implementation of training reduced colobus–human interactions. Two reasons are suggested in this paper to account for these unexpected results; either or both of these explanations may be true. The increased level of keeper–colobus interactions necessary for training may have acted to socialize the colobus to humans, so that they habituated to the general presence of humans. Equally, the training sessions may have provided the colobus with predictable interactions with humans that provided rewards, outside of which colobus-initiated interactions were not worthwhile.

Training in this situation was found to be beneficial for the colobus and did not adversely affect the behavior of the colobus outside of the training sessions. It is concluded that caution should be taken when instigating training as part of captive primate management, due to species differences and the paucity of studies that have quantified the impact of training on zoo primate biology. What is greatly needed is more studies which are able to empirically compare the biology (behavior and physiology) of zoo housed primates before and after training has been implemented.     

The Evolution of Life Histories in Holo-anhydrobiotic Animals: A First Approach

The life histories of holo-anhydrobiotic animals differ fromthose of all other organisms by a regular or irregular entranceinto an ametabolic state induced by desiccation. Such ametabolicperiods will arrest growth and reproduction completely and thusaffect primary life history parameters dramatically. The selectiveforces and the genetic and physiological trade-offs acting onanhydrobiotic animals are to a large extent unknown. Assuminglow growth rates and low juvenile to adult survival, generaltheoretical models on life history responses to stress predictthat anhydrobiotic animals will be selected for a high degreeof iteroparity, with low fecundity, large egg size, and lowtotal reproductive investment. A high degree of variabilityin growth and reproduction should create a selective force inthe same direction. Although basic empirical data on life historyparameters are very scarce, available observations seem to beconsistent with this prediction.     

The Changing State of Surfactant Lipids: New Insights from Ancient Animals

SYNOPSIS. Pulmonary surfactant is a mixture of phospholipids(including disaturated phospholipids), cholesterol and proteinslining the air-liquid interface within the lung. Surfactantacts to reduce surface tension, thereby increasing lungcomplianceand also preventing edema. The saccular lungs, or other gas-holdingstructures, of nonmammals have 7–70% more surfactant/cm²of surface than lungs of mammals. Nonmammalian surfactant actsas an antiglue that decreases the inflation pressures of collapsedlungs by reducing the adherence of apposing epithelial surfaces.The autonomic nervous system appears to be the primary systemcontrolling release of surfactant in nonmammals. The lipid compositionis highly conserved within the vertebrates, except that surfactantof teleost fish is dominated by cholesterol whereas tetrapodsurfactant consists primarily of disaturated phospholipids (DSP).The dipnoan Neoceratodus forsteri demonstrates a "fish-type"surfactant profile while the other derived dipnoans demonstratea surfactant profile similar to that of tetrapods. Homologyof the surfactant protein SP-A within the vertebrates pointsto a single evolutionaryorigin for the system and indicatesthat fish surfactant is a "protosurfactant". Amongst the tetrapods,the relative proportions of DSP and cholesterol vary in responseto lung structure, habitat, and body temperature (T_b) but notin relation to phytogeny. The cholesterol content of surfactantis elevated in species with simple saccular lungs, in aquaticspecies, and in species with low T_b. The DSP content is highestin complex lungs, particularly ofaquatic species or specieswith high T_b. The cholesterol content of surfactant also increasesin response to acute decreases in Tb in lizards and torpid marsupials,presumably to maintain fluidity of the lipid mixture.