Retention of low-fitness genotypes over six decades of admixture between native and introduced tiger salamanders

Background  

Introductions of non-native tiger salamanders into the range of California tiger salamanders have provided a rare opportunity to study the early stages of secondary contact and hybridization. We produced first- and second-generation hybrid salamanders in the lab and measured viability among these early-generation hybrid crosses to determine the strength of the initial barrier to gene exchange. We also created contemporary-generation hybrids in the lab and evaluated the extent to which selection has affected fitness over approximately 20 generations of admixture. Additionally, we examined the inheritance of quantitative phenotypic variation to better understand how evolution has progressed since secondary contact.     

Fibrinogen and fibrin in strong magnetic fields. Complementary results and discussion

When fibrin polymerizes in a strong magnetic field, it can be highly oriented. The structural diffraction study of the oriented polymer becomes thus possible. The magnetic birefringence can also be used to study the development of the polymer Fibrinogen in solution is weakly oriented in high magnetic fields. In this work we present complementary results and discussion. The validity of the comparison of the orientation parameters of fibrinogen and fibrin with those of other orientable known biological structures is discussed. The orientation of fibrin formed from fibrin monomer solution is compared to that of fibrin formed by the action of thrombin on fibrinogen. The conditions to obtain highly oriented fibrin gels suitable for three dimensional structure studies are also briefly discussed.     

Chlorine resistance of poliovirus isolants recovered from drinking water

Poliovirus 1 isolants were recovered from finished drinking water produced by a modern, well-operated water treatment plant. These waters contained free chlorine residuals in excess of 1 mg/liter. The chlorine inactivation of purified high-titer preparations of two such isolants was compared with the inactivation behavior of two stock strains of poliovirus 1, LSc and Mahoney. The surviving fraction of virus derived from the two natural isolants was shown to be orders of magnitude greater than that of the standard strains. These results raise the question whether indirect drinking water standards based on free chlorine residuals are adequate public health measures, or whether direct standards based on virus determinations might be necessary.     

The Murray River's 'Sea to Hume Dam' fish passage program: Progress to date and lessons learned

Since its commencement in 2001, a program to facilitate fish passage on a major stretch of Australia's longest river has installed eight structures, testing and modifying their design as they go. What are the results so far and what are the implications for future directions?     

Fluorescence banding in four species of Microtidae: an analysis of the evolutive changes of the constitutive heterochromatin

Three different fluorochrome and specific counterstain combination (DAPI/AMD, DA/DAPI and CMA/DA) treatments were applied to the chromosomes of four Microtidae (Rodentia) species. The results complete the data obtained in our previous paper (Burgos, M., Jiménez, R., & Dìaz de la Guardia, R., Genome 30:540–546, 1988) and prove that the changes in the constitutive heterochromatin in the evolution of the karyotypes of these species are not only due to gain or loss of heterochromatin, but are qualitative with respect to their nucleotide composition, repeated base pair organization or DNA-protein complex modification. These variations lead to the differential response to the fluorescence dye combinations used.     

The Optimal Solution of a Non-Convex State-Dependent LQR Problem and Its Applications

This paper studies a Non-convex State-dependent Linear Quadratic Regulator (NSLQR) problem, in which the control penalty weighting matrix in the performance index is state-dependent. A necessary and sufficient condition for the optimal solution is established with a rigorous proof by Euler-Lagrange Equation. It is found that the optimal solution of the NSLQR problem can be obtained by solving a Pseudo-Differential-Riccati-Equation (PDRE) simultaneously with the closed-loop system equation. A Comparison Theorem for the PDRE is given to facilitate solution methods for the PDRE. A linear time-variant system is employed as an example in simulation to verify the proposed optimal solution. As a non-trivial application, a goal pursuit process in psychology is modeled as a NSLQR problem and two typical goal pursuit behaviors found in human and animals are reproduced using different control weighting . It is found that these two behaviors save control energy and cause less stress over Conventional Control Behavior typified by the LQR control with a constant control weighting , in situations where only the goal discrepancy at the terminal time is of concern, such as in Marathon races and target hitting missions.     

Natal recruitment and adult retention in a population of nine-banded armadillos

Nine-banded armadillosDasypus novemcinctus Linnaeus, 1758 are interesting in part because (a) they give birth to litters of genetically identical quadruplets, and (b) the species’ range has expanded rapidly throughout the southern United States during the last 150 years, suggesting substantial dispersal of individuals. Using data from 7 field seasons between 1992 and 1999, we examined the extent of juvenile recruitment and retention of adults in a population of armadillos from northern Florida. There were no sex differences in the likelihood of recruitment or most attributes of male and female recruits at any age. In the few cases where more than one littermate was recruited into the population, siblings were significantly more widely dispersed as adults than they were as juveniles, thus limiting opportunities for interaction among clonal siblings. There was some evidence that recruits ranged more widely than other individuals, suggesting recruits may have been searching for suitable sites to establish themselves. Recruits were heavier than non-recruits as both juveniles and yearlings, which may have aided in establishing a home range, but recruits were lighter than other animals as adults. Overall, slightly less than 50% of armadillos first captured as adults were never seen in a subsequent year, suggesting these individuals may have been transients. However, some adults remained in the population for multiple years, moving very little from the area where they were first sighted. As with recruits, there were no sex differences in the likelihood of adults being retained in the population nor in the attributes of retained males and females. Retained animals exhibited more extensive anatomical damage and moved farther between successive sightings within years than did non-residents. Adults were more likely to be retained in the population than juveniles were to be recruited, and retained adults were older, heavier, and exhibited more extensive anatomical damage than did recruits. Our data seem to indicate a population characterized by limited recruitment of juveniles (particularly of clonemates) and an adult population exhibiting considerable turnover from year to year, but with a core of individuals who are long-term residents.