Evolution Going Great, Reports Trilobite
Evolution Going Great, Reports Trilobite:
"Things are looking mighty fine," announced the prehistoric invertebrate, taking measure of his surroundings through a series of small, hexagonal eyelets located at the tip of his thorax. "Sulfurous gas seems to be bubbling up to the surface pretty good, and several single-cell organisms appear to be mutating at a rather steady pace. Also, just today, I developed the ability to roll into a small protective shell in order to avoid predators".
Predicting the direction of ornament evolution in guppies
Predicting the direction of ornament evolution in Trinidadian guppies Poecilia reticulata:
Sexual selection is thought to be opposed by natural selection such that ornamental traits express a balance between these two antagonistic influences. Phenotypic variation among populations may indicate local shifts in this balance, or that different stable ‘solutions’ are possible, but testing these alternatives presents a major challenge. In the guppy Poecilia reticulata, a small freshwater fish with male-limited ornamental coloration, these issues can be addressed by transplanting fish among sites of varying predation pressure, thus effectively manipulating the strength and nature of natural selection.
Here, we contrast the evolutionary outcome of two such introductions conducted in the Trinidadian El Cedro and Aripo Rivers. We use sophisticated colour appraisal methods that account for full spectrum colour variation and which incorporate the very latest visual sensitivity data for guppies and their predators.
Our data indicate that ornamentation evolved along different trajectories: whereas Aripo males evolved more numerous and/or larger orange, black and iridescent markings, El Cedro males only evolved more extensive and brighter iridescence. Examination of the El Cedro experiment also revealed little or no ornamental evolution at the control site over 29 years, which contrasts markedly with the rapid approx. 2–3 years changes reported for introduction populations.
Finally, whole colour-pattern analysis suggested that the greatest visual difference between El Cedro introduction and control fish would be perceived by the two most salient viewers: guppies and the putatively dangerous predator Crenicichla alta. We discuss whether and how these evolutionary trajectories may result from founder effects, population-specific mate preferences and/or sensory drive.
30 years of adaptationism
Rasmus Nielsen in today's issue of Evolution discusses what's happened to the concept of adaptationism in the 30 years since Gould and Lewontin published one of the most infamous critiques in evolutionary biology:
In 1979, Stephen Jay Gould and Richard C. Lewontin (Gould and Lewontin 1979), published their highly influential paper on adaptionism entitled “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme.” In this paper, Gould and Lewontin warned against confusing function with adaptation. Functional observations may not always have adaptive explanations—existence of form does not prove purpose.
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So should we give up making claims about selection and adaptation in humans and other similar organisms? Yes and no.
Altruism vs. Selfishness: Case Closed
David Sloan Wilson in Seed Magazine
The idea that evolution explains selfishness well and altruism poorly is so dead that it is beginning to smell. Can we please bury it now? Evolution explains the full range of behaviors, from extreme selfishness to extreme altruism. What evolves in any particular case depends upon the underlying environmental conditions, which are fairly well specified by now. No one should be surprised anymore by the raw fact that kindness exists in nature. The frontier of science has moved on to a more refined set of questions.
Using Phylogenetics to trace morphological evolution
Using Phylogenetics to trace morphological evolution.
Melanism in evolution
Sean Carroll in The Smithsonian Magazine talks about how the alternative color forms of some animals are providing new insights into how animals adapt and evolve:
One of the most widespread phenomena in the animal kingdom is the occurrence of darkly pigmented varieties within species. All sorts of moths, beetles, butterflies, snakes, lizards and birds have forms that are all or mostly black. Perhaps most familiar are the dark big cats, such as the black leopard and black jaguar. These beautiful animals are often displayed in zoos as curiosities, but they also occur in the wild in significant numbers.
The feeding biomechanics and dietary ecology of Australopithecus africanus
In today's PNAS, The feeding biomechanics and dietary ecology of Australopithecus africanus:
The African Plio-Pleistocene hominins known as australopiths evolved a distinctive craniofacial morphology that traditionally has been viewed as a dietary adaptation for feeding on either small, hard objects or on large volumes of food. A historically influential interpretation of this morphology hypothesizes that loads applied to the premolars during feeding had a profound influence on the evolution of australopith craniofacial form.
Here, we test this hypothesis using finite element analysis in conjunction with comparative, imaging, and experimental methods. We find that the facial skeleton of the Australopithecus type species, A. africanus, is well suited to withstand premolar loads. However, we suggest that the mastication of either small objects or large volumes of food is unlikely to fully explain the evolution of facial form in this species.
Rather, key aspects of australopith craniofacial morphology are more likely to be related to the ingestion and initial preparation of large, mechanically protected food objects like large nuts and seeds. These foods may have broadened the diet of these hominins, possibly by being critical resources that australopiths relied on during periods when their preferred dietary items were in short supply.
Our analysis reconciles apparent discrepancies between dietary reconstructions based on biomechanics, tooth morphology, and dental microwear.