Search results for "selection"

Progreso, complejidad y evolución

2020

Ensayos en honor de Eloy Rada. [ES]: El progreso biológico es un tema ampliamente debatido en biología evolutiva que tiene partidarios y detractores. Sin embargo, no es una cuestión, a pesar de su importancia, de la que podamos afirmar que está resuelta desde el punto de vista científico. En este trabajo presento un análisis del concepto basado en la teoría de la evolución por selección natural, sus paralelismos con el también debatido concepto de “progreso” en la historia de la humanidad y, finalmente, se intenta orientarlo hacia formas accesibles a la investigación científica. Para ello, en lugar del concepto de progreso, recurro al de “complejidad biológica”. Si tenemos formas de medirla…

The logic of forms in the light of developmental biology and palaeontology.

2010

11 pages; If you ask palaeontologists, and indeed anyone interested in the theory of evolution, for the key words that encapsulate it, you will obtain the following results: adaptation, natural selection, speciation, but also ontogeny and phylogeny. The first three key words apply to the future of the individual and by extension to the future of the species: we are therefore dealing with adults of a reproductive age. The two other key words concern (i) the evolution of the morphology from the egg to the adult (individual ontogeny: short timescale) and especially what goes on in the black box called embryogenesis, and (ii) the modification of ontogenetic sequences over time, resulting in cha…

Testis asymmetry in birds: the influences of sexual and natural selection

2014

Gonad size and shape asymmetries are particularly common in birds. Although some obvious size and shape differences between the left and right testes in birds were first documented more than a century ago, little is known about what influences the variation across species in either the degree or the direction of these asymmetries. Here we show that a left bias in size is the most likely ancestral state in most orders and families, and that there is a weak but significant negative relation between the degree of size and shape asymmetries. In extant species, testis size and shape symmetries increase with the degree of sperm competition (relative testes mass), but those relations are significa…

Parasite Infection and Host’s Behavior

2010

Animal behavior and parasitism are more tightly linked, from an ecological and evolutionary point of view, than commonly thought. In the past 30 years, the growing field of evolutionary parasitology has tackled both proximate and ultimate answers to the following question: Why and how should the behavior of hosts exposed to the risk of a disease or that of parasitized hosts be altered? Altered behavior may simply be a symptom of disease without obvious connection with host resistance or parasite-transmission strategies. However, natural selection may have shaped behavior to avoid infection, get rid of parasites, or limit their pathogenicity. Alternatively, manipulative parasites may alter t…

1993

From his studies on Invertebrate animals and fossils in the vicinity of Paris, J.-B. de Lamarck (1744–1829) formulated a number of conclusions in his Zoological Philosophy [1] (1809), the first coherent theory of evolution. However, in contrast to commonly held belief, this was not based purely on speculation, but was progressively elaborated.

Should the teaching of biological evolution include the origin of life?

2010

The development of mainstream research on the origin of life as an outcome of Darwinian evolution is discussed. It is argued that prebiotic evolution and the origin of life should not be excluded from the syllabus and should be part of classes on biological evolution, and that the transition from non-living to living matter is best understood when seen as part of evolutionary biology. The wide acceptance of evolutionary approaches to the study of the emergence of life in European and Latin American countries is discussed.

1993

We have pointed out that the history of the giraffe’s neck served as an example to explain the theoretical concepts of transformism, proposed by J.-B. Lamarck, and of Darwin’s natural selection. However, at that time it had not been substantiated by palaeontological data. Since then, the record has furnished a number of fossils which enable us to reconstruct the major trends in the evolution of the giraffides of Africa, Asia, and Europe [1,2, 3] (Fig. 16.1; Appendix 16.1).

Morphological variation of the Oncocyclus irises (Iris: Iridaceae) in the southern Levant

2002

Morphological traits of Iris section Oncocyclus (Siems.) Baker in the southern Levant (Israel, Jordan, The Palestinian Authority and Sinai/Egypt) were analysed in order to clarify taxonomic relationships among taxa and the validity of diagnostic characters. Floral and vegetative characters were measured in 42 populations belonging to nine species during the peak of the flowering season in 1998‐2000. Pearson’s Coefficient of Racial Likelihood (CRL) was used to calculate morphological distances between populations. Twelve of the measured populations, distributed along the north-south aridity gradient in Israel, were further explored for morphological changes along the gradient. Cluster analys…

Productivity increases with variation in aggression among group members in Temnothorax ants

2011

Social insect societies are characterized not only by a reproductive division of labor between the queen and workers but also by a specialization of workers on different tasks. However, how this variation in behavior or morphology among workers influences colony fitness is largely unknown. We investigated in the ant Temnothorax longispinosus whether aggressive and exploratory behavior and/or variation among nest mates in these behavioral traits are associated with an important fitness measure, that is, per worker offspring production. In addition, we studied how body size and variation in size among workers affect this colony fitness correlate. First, we found strong differences in worker b…

Rapid growth of Atlantic salmon juveniles in captivity may indicate poor performance in nature

2011

Abstract The hatchery environment often favours completely different traits than natural selection in the wild. Consequently, hatchery-reared fish are usually larger and more aggressive than their wild counterparts. Increased growth rate and aggression are predicted to be beneficial in feeding competition in hatcheries, but not necessarily in nature, where food resources are spatially and temporally more variable. We compared the growth, condition and mortality of landlocked Atlantic salmon (Salmo salar L.) juveniles in a common hatchery environment and when feeding on natural prey in semi-natural channels. We found that the growth and survival probability of the fish in the hatchery was ne…