A citizen scientist is a volunteer who collects and/or processes data as part of a scientific enquiry. Projects that involve citizen scientists are burgeoning, particularly in ecology and the environmental sciences, although the roots of citizen science go back to the very beginnings of modern science itself.

A new dawn for citizen science.

All too often in evolutionary biology we are led to speculate or infer the mode of action of natural selection; we usually do not know why some individuals are more adaptive than others. Very often attempts to measure natural selection are unsuccessful, leading to heated arguments about' the relative importance of selection, genetic drift, and epistasis in evolution (Lewontin, 1974). Until we know more about how and why natural selection occurs, attempts to measure it are quixotic, and discussions of its importance are theandric. It is no coincidence that most of the successful studies of natural selection have dealt with animal color patterns; it should be obvious which color patterns are more adaptive in the presence of visually hunting predators. The adaptive significance of warning coloration and mimicry of distasteful species has been worked out (Cott, 1940; Wickler, 1968; Edmunds, 1974; Rothschild, 1975; Turner, 1977). But most species are neither distasteful nor mimetic; most have inconspicuous or cryptic color patterns in their natural habitats (Poulton, 1890; Thayer, 1909; Cott, 1940; Endler, 1978). Most field and experimental studies have shown that the overall color or tone of inconspicuous species matches or approximates the background (DiCesnola, 1904; Sumner, 1934, 1935; Isley, 1938; Popham, 1942; Dice, 1947; Kettlewell, 1956, 1973; Turner, 1961; Kaufman, 1974; Wicklund, 1975; Curio, 1976), but they treated species with solid colors or

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1980.tb04790.x

Natural selection on color patterns in poecilia reticulata.

It has long been known that the general colors and tones of animals tend to match their backgrounds (E. Darwin, 1794; Poulton, 1890). The adaptive significance of this has been borne out in numerous experimental studies (DiCesnola, 1904; Sumner, 1934, 1935; Isley, 1938; Popham, 1942; Dice, 1947; Turner, 1961; Kettlewell, 1956, 1973; Kaufman, 1974; Wiklund, 1975; Curio, 1976). There is also a good understanding of warning coloration (Cott, 1940; Wickler, 1968; Edmunds, 1974; Rothschild, 1975). However, the determinants of color pattern are poorly known, although it is known in a general way that the patterns and forms of animals are similar to their backgrounds (Poulton, 1890; Thayer, 1909; Cott, 1940; Wickler, 1968; Robinson, 1969; Edmunds, 1974; Fogden and Fogden, 1974). It is the purpose of this paper to explore the factors that determine color patterns under various specific conditions. The basic assumption is that a color pattern must resemble a random sample of the background seen by predators in order to be cryptic, and must deviate from the background in one or more ways in order to be conspicuous. As a result, the actual pattern evolved in a particular place represents a compromise between factors which favor crypsis and those which favor conspicuous color patterns.

A Predator’s View of Animal Color Patterns

The discovery in the last decade, using electrophoresis, of large amounts of genetic polymorphism in natural populations has had a tremendous effect on population genetics. Before then it was not clear how many polymorphic loci there were in a population and the single gene overdominance model generally seemed adequate to explain what polymorphism was documented. In an effort to explain the new-found genetic variation, two opposing camps surfaced in the late 1960s and still exist to some extent today. One group, often called neutralists, believes that most allozymic variants have a minimal effect on fitness and are in a population because of a combination of mutation, finite population size, and migration. In other words, in their view, selection plays little or no role in maintaining different electrophoretic alleles. The other group, sometimes known as selectionists, believes that some sort of balancing selection is responsible for the maintenance of the majority of electropho­ retic alleles. "Balancing selection" is a catch all term for any type of selection that can maintain a stable polymorphism. Among the types of balancing selection that are thought to play a significant role in maintaining genetic polymorphisms are the classical overdominance mode, frequency-dependent selection [see (8) for a recent review], differential selection between the two sexes or between different life stages, and variable selection in time and/or space. This last type of balancing selection is examined here in an effort to understand the importance of selection varying in time and/or space in maintaining genetic polymQrphisms. A significant body of literature demonstrates an association between the genetic attributes of a population and some aspect of the environment. Since much of this material has been reviewed elsewhere (2, 16,58, 165), we concentrate on two of the

Genetic Polymorphism in Heterogeneous Environments

Ten years ago, Joseph Felsenstein (35) and I (56) both wrote reviews discussing the maintenance of genetic polymorphisms in heterogeneous environments. I addressed the question of the importance in maintaining genetic variation of diversifying selection (sometimes called the niche-variation hypothesis), i.e. selection for different alleles in different environments. My focus was on the evidence and theory supporting the connection of a variable environment with genetic variation, particularly as an explanation for the large amounts of allozymic variation. At that time, the empirical evidence suggesting a genetic-environment connection for allozymic variation was mostly correlative and not in general experimentally based. Theory suggested, however, that polymorphism maintenance was possible in a variable environment; it was most likely when there was variable selection in space and limited gene flow and/or habitat selection. The purpose of this review is to evaluate the research of the intervening decade on genetic polymorphism in variable environments. The topics of this review are divided in a fashion similar to that of the earlier review. First, I mention some recent work in which there has been detailed investigation of the relationship of different environments and the maintenance of genetic variation. Second, I review the theoretical developments in the past decade. Finally, I discuss recent experimental work in some detail. An emphasis in the review is to evaluate these experimental studies, a number of which were designed specifically to determine the importance of heterogeneous environments in maintaining genetic variation.

Genetic polymorphism in heterogeneous environments: a decade later

When faced with a problem or a series of related problems, scientists tend to look for a single unifying solution. When alternative solutions present themselves, it is usually accepted that only one is likely to be true. Further research often justifies this assumption. The successes of this type of reasoning have tended to obscure the fact that not all biological observations must necessarily be explicable in a simple and unitary way and that not all hypotheses to be tested need be mutually exclusive. We hope to illustrate this by considering some of the evolutionary processes affecting one well known genetic polymorphism, that of shell pattern in the land snail Cepaea. rhe development of techniques for detecting molecular polymorphisms has led to considerable disagreement between those who believe that such genetic variation is actively maintained by natural selection and those who suggest that random processes are the only significant factor in its control. The most important lesson to be gained from an intensive study of the Cepaea polymorphism is that many types of evolutionary force act upon it and that their relative importance varies between different polymorphic loci, or even when the same locus is studied in different populations. It is largely meaningless to ask whether selection or drift explains the observed variation in gene frequency, or indeed to attempt to identify the single selective mechanism acting on the polymorphism. The nature of the evolutionary process means that the genetic structure of each Cepaea population usually requires a complex and perhaps a unique explanation. This is a point which has not been sufficiently emphasized by students of other polymorphic systems.

B. H. Leith

Papers

Polymorphism in Cepaea: A Problem with Too Many Solutions?