Striking convergence in the mouthpart evolution of stream-living algae grazers

This scanning-electron microscopic study demonstrates the convergent evolution of the mouthparts of various herbivorous stream animals (insects from different orders, an isopod, snails, fish, and a tadpole) feeding on epilithic algal pastures. This food source is rich but is often difficult to harvest. Nevertheless, a large number of species can live on it because they have evolved highly specialized mouthparts. There are four functional problems that an algae grazer has to solve: the algae must be removed from the stone, they have to be collected and crushed, and a current shield is needed to prevent the water flow sweeping away the food. Among the 30 algae grazers examined in this study, a limited number of morphological solutions have been found for each of these adaptational problems. There are multiple evolutionary pathways for mouthpart adaptation and even closely related species have often evolved different types of tools for the same function. This refects the existence of a certain amount of evolutionary scope. Such freedom of evolution is present, however, only at the beginning of the adaptiogenesis of an algae grazer. Once one of the evolutionary pathways is taken, further improvement of the mouthparts is possible only by the refinement of the ‘chosen’ type of tools. The consequence of this is that a large number of astonishing convergences have occurred in algae grazers that have independently trodden the same evolutionary pathway.     

Evolutionary genetics of ruminant lysozymes

Comparative studies of mammalian lysozymes and their genes have contributed to knowledge of how new functions arise during evolution. The recruitment of lysozymes for functioning in the stomach fluid of ruminants has occurred in response to selection pressures that are partly known and on a time-scale that is known. A semiquantitative analysis of adaptive evolution is thus made possible by the ruminant lysozyme system. Large-scale production of lysozyme by the stomach lining entailed gene duplication as well as a change in gene expression. Remoulding of the lysozyme for working and lasting in the stomach fluid involved accelerated amino acid replacements, which may have been facilitated by intergenic recombination. The possibility that multigene families can accelerate adaptive evolution, by virtue of their capacity for bringing together functionally coupled substitutions, receives emphasis in this review.     

The Genetic Basis of Morphological Diversity in Domesticated Goldfish

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Increase in body size is correlated to warmer winters in a passerine bird as inferred from time series data

Climate change is expected to affect natural populations in many ways. One way of getting an understanding of the effects of a changing climate is to analyze time series of natural populations. Therefore, we analyzed time series of 25 and 20 years, respectively, in two populations of the citril finch (Carduelis citrinella) to understand the background of a dramatic increase in wing length in this species over this period, ranging between 1.3 and 2.9 phenotypic standard deviations. We found that the increase in wing length is closely correlated to warmer winters and in one case to rain in relation to temperature in the summer. In order to understand the process of change, we implemented seven simulation models, ranging from two nonadaptive models (drift and sampling), and five adaptive models with selection and/or phenotypic plasticity involved and tested these models against the time series of males and females from the two population separately. The nonadaptive models were rejected in each case, but the results were mixed when it comes to the adaptive models. The difference in fit of the models was sometimes not significant indicating that the models were not different enough. In conclusion, the dramatic change in mean wing length can best be explained as an adaptive response to a changing climate.     

The insufficience of supervenient explanations of moral actions: Really taking Darwin and the naturalistic fallacy seriously

In a recent paper in this journal (Rottschaefer and Martinsen 1990) we have proposed a view of Darwinian evolutionary metaethics that we believe improves upon Michael Ruse's (e.g., Ruse 1986) proposals by claiming that there are evolutionary based objective moral values and that a Darwinian naturalistic account of the moral good in terms of human fitness can be given that avoids the naturalistic fallacy in both its definitional and derivational forms while providing genuine, even if limited, justifications for substantive ethical claims. Jonathan Barrett (this issue) has objected to our proposal contending that we cannot hold for the reality of supervenient moral properties without either falling foul of the naturalistic fallacy or suffering the consequences of postulating inexplicable moral properties. In reply, we show that Barrett's explicit arguments that we commit either the definitional or derivational form of the naturalistic fallacy fail and that his naturalistic intuitions that supervenience explanations of moral properties by nonmoral properties force us into what we call the explanatory form of the naturalistic fallacy also fail. Positively, his objections help us to clarify the nature of the naturalistic fallacy within an evolutionary based naturalistic ethics and to point out the proper role of both supervenience explanations and moral explanations in such an ethics.     

Pathogenic Allodiploid Hybrids of Aspergillus Fungi

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Distinguishing Drift and Selection Empirically: “The Great Snail Debate” of the 1950s

Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature, particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case – Maxime Lamotte’s study of natural populations of the land snail, Cepaea nemoralis in the 1950s – shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for a significant role for␣drift. It may be difficult to disentangle the causes of drift and selection acting in a population, but it is not (always) impossible.