Surviving despite difficulties: amphibians and the perpetuation of the species

Els amfibis són actualment un dels grups de vertebrats més amenaçats del món. Les causes són diverses i quasi totes d’origen antròpic. Malgrat aquest declivi generalitzat, encara existeix una gran biodiversitat d’amfibis. En general, aquest grup, com que tenen un cicle biològic bifàsic (fase larvària aquàtica i fase adulta terrestre) és especialment sensible a la disminució i a la desaparició de les seves poblacions, fonamentalment per modificació dels seus hàbitats. Es pot pensar que, com a grup, els amfibis tenen dificultats intrínseques per a la seva supervivència, però la realitat està molt lluny d’aquesta afirmació. L’inici de la història evolutiva d’aquest grup, a partir dels peixos sarcopterigis, representa el primer pas per accedir a terra ferma i aprofitar uns recursos que abans no estaven al seu abast. Així doncs, la seva diversificació ha comportat una variabilitat d’estratègies de reproducció sorprenents. Aquest article esmenta el pas a terra ferma i fa una revisió de les estratègies reproductores dels amfibis que els han permès, malgrat les adversitats, distribuir-se àmpliament i sobreviure fins als nostres dies.Amphibians are currently one of the most threatened vertebrate groups in the world. There are many reasons for this problem, but almost all of them are of anthropogenic origin. However, despite this widespread decline, there is still a great biodiversity of amphibians. They have a biphasic life cycle (an aquatic larval stage and a terrestrial adult stage) and are usually especially prone to reduction and extinction of their populations, particularly as a result of modification of their habitats. It might therefore be thought that amphibians have intrinsic difficulties for survival, but this is far from being true. The beginning of their evolutionary history, from sarcopterygian fishes, was the first step towards reaching land and taking advantage of new resources, and their diversification has led to a surprising variety of reproduction strategies. This paper deals with the move to land and reviews the reproductive strategies of amphibians that have allowed them, despite adversity, to spread widely and survive to this day

Microcanonical versus Canonical Analysis of Protein Folding

The microcanonical analysis is shown to be a powerful tool to characterize the protein folding transition and to neatly distinguish between good and bad folders. An off-lattice model with parameter chosen to represent polymers of these two types is used to illustrate this approach. Both canonical and microcanonical ensembles are employed. The required calculations were performed using parallel tempering Monte Carlo simulations. The most revealing features of the folding transition are related to its first-order-like character, namely, the S-bend pattern in the caloric curve, which gives rise to negative microcanonical specific heats, and the bimodality of the energy distribution function at the transition temperatures. Models for a good folder are shown to be quite robust against perturbations in the interaction potential parameters.Comment: 4 pages, 4 figure

Minimum phi-divergence estimator and hierarchical testing in loglinear models

In this paper we consider inference based on very general divergence measures, under assumptions of multinomial sampling and loglinear models. We define the minimum phi-divergence estimator, which is seen to be a generalization of the maximum likelihood estimator. This estimator is then used in a phi-divergence goodness-of-fit statistic, which is the basis of two new statistics for solving the problem of testing a nested sequence of loglinear models

Get Rid of Unanimity Rule: The Superiority of Majority Rules with Veto Power

We study unanimous decision making under incomplete information. We argue that all unanimous decision rules are not equivalent. We show that majority rules with veto power are (i) Pareto superior to commonly used unanimous rules, and (ii) ex-ante efficient in a broad class of situations