Ecological genetics is the study of genetics in natural populations. It combines ecology, evolution, and genetics to understand the processes behind adaptation. It is virtually synonymous with the field of molecular ecology.
This contrasts with classical genetics, which works mostly on crosses between laboratory strains, and DNA sequence analysis, which studies genes at the molecular level.
Research in this field is on traits of ecological significance—traits that affect an organism's fitness, or its ability to survive and reproduce. Examples of such traits include flowering time, drought tolerance, polymorphism, mimicry, and avoidance of attacks by predators.Ruxton G.D. Sherratt T.N. and Speed M.P. 2004. Avoiding attack: the evolutionary ecology of crypsis, warning signals & mimicry. Oxford University Press.
Research usually involves a mixture of field and laboratory studies.Ford E.B. 1981. Taking genetics into the countryside. Weidenfeld & Nicolson, London. Samples of natural populations may be taken back to the laboratory for their genetic variation to be analyzed. Changes in the populations at different times and places will be noted, and the pattern of mortality in these populations will be studied. Research is often done on organisms that have short generation times, such as insects and microbial communities.
History Although work on natural populations had been done previously, it is acknowledged that the field was founded by the English biologist E.B. Ford (1901–1988) in the early 20th century. Ford started research on the genetics of natural populations in 1924 and worked extensively to develop his formal definition of genetic polymorphism.Ford E.B. 1940. Polymorphism and taxonomy. In Huxley J. The new systematics. Oxford University Press.Ford E.B. 1965. Genetic polymorphism. All Souls Studies, Faber & Faber, London. Ford's magnum opus was Ecological Genetics, which ran to four editions and was widely influential.Ford E.B. 1975. Ecological genetics, 4th ed. Chapman and Hall, London.
Other notable ecological geneticists include R. A. Fisher and Theodosius Dobzhansky. Fisher helped form what is known as the modern synthesis of ecology, by mathematically merging the ideas of Darwin and Mendel. Dobzhansky worked on chromosome polymorphism in fruit flies. He and his colleagues carried out studies on natural populations of Drosophila species in western USA and Mexico over many years.Dobzhansky, Theodosius. Genetics and the origin of species. Columbia, N.Y. 1st ed 1937; second ed 1941; 3rd ed 1951.Dobzhansky, Theodosius 1970. Genetics of the evolutionary process. Columbia, New York.Dobzhansky, Theodosius 1981. Dobzhansky's genetics of natural populations I-XLIII. R.C. Lewontin, J.A. Moore, W.B. Provine & B. Wallace, eds. Columbia University Press, New York 1981. (reprints the 43 papers in this series, all but two of which were authored or co-authored by Dobzhansky)
Philip Sheppard, Cyril Clarke, Bernard Kettlewell and A.J. Cain were all strongly influenced by Ford; their careers date from the post World War II era. Collectively, their work on lepidoptera and on human blood groups established the field and threw light on selection in natural populations, where its role had been once doubted.
Research
Inheritance and Natural Selection Ecological genetics is closely tied to the concept of natural selection. Many classical ecology works have employed aspects of ecological genetics, investigating how inheritance and the environment affect individuals.
Ecological genetics further explores how inherited genetic variation influences an organism's ability to survive and reproduce in specific environments. Natural selection favours traits that enhance fitness, while other evolutionary forces, including mutations, gene flow, and genetic drift can play crucial roles in shaping the genetic makeup of populations. These interactions can drive local adaptation and evolutionary change. Earlier discussions questioned whether random mutation alone could account for the complexity observed in genetic sequences. While this remains a point of theoretical interest, molecular tools in modern ecological genetics have enabled researchers to identify genetic variants under selection in natural populations.
Industrial Melanism in Peppered Moths
Industrial melanism in the peppered moth Biston betularia is a well-known example of the process of natural selection. The typical wing colour phenotype of B. betularia is black and white flecks, but variant 'melanic' phenotypes with increased amounts of black also occur. In the nineteenth century, the frequency of these melanic variants increased rapidly. Many biologists proposed explanations for this phenomenon. It was demonstrated in the early 1910s, and again in many later studies, that the melanic variants were a result of dominant alleles at a single locus in the B. betularia genome. The proposed explanations, then, centered around various environmental factors that could contribute to natural selection. In particular, it was proposed that bird predation was selecting for the melanic moth forms, which were more cryptic in industrialized areas. H. B. D. Kettlewell investigated this hypothesis extensively in the early 1950s.
Uncertainty surrounding whether birds preyed on moths at all posed an initial challenge, leading Kettlewell to perform a series of experiments with captive birds. These experiments, while initially unsuccessful, found that when a variety of insects are provided, the birds did preferentially prey on the most conspicuous moths: those with coloration unmatched to their surroundings. Kettlewell then performed field experiments using mark-recapture techniques to investigate the selective predation of moths in their natural habitat. These experiments found that in woods near industrialized areas, melanic moth forms were recaptured at much higher rates than the traditional lighter-coloured forms, while in non-industrialized woods, the reverse held true.
More recent research has further emphasized the role of genetics in the case of industrialized melanism in B. betularia. While research had already emphasized the role of alleles in determining wing-color phenotype, it was still unknown whether the melanic alleles had a single origin or had arisen multiple times independently. The use of molecular marking and chromosomal mapping in conjunction with population surveys demonstrated in the early 2010s that the melanic B. betularia variants have one single ancestral origin. Additionally, the melanic variants appear to have arisen by mutation from a typical wing-colour phenotype.
Another classic example is warning coloration and mimicry in butterflies, which Ford and colleagues studied to understand polymorphism maintained by predation. In tropical American butterflies of the genus ''Heliconius'', multiple species share bright wing color patterns as part of Müllerian mimicry rings (where toxic species mimic each other for mutual benefit). Within a single ''Heliconius'' species, populations can display strikingly different color forms, each form matching the local co-mimic community. For instance, ''Heliconius erato'' and ''Heliconius melpomene'' co-occur across many locales, and in each locale they have evolved nearly identical wing patterns – red band and yellow spots in one region, orange and black in another, and so on – despite being distinct species. The maintenance of multiple color morphs within species, each favored in its specific geographic region, is an ecological genetics phenomenon: the different morphs are tied to survival, because local predators learn the warning pattern. A butterfly with a non-matching pattern is more likely to be mistaken for an edible insect and attacked. Research by ecological geneticists showed that these color pattern differences are under simple genetic control (often a few major loci, sometimes characterized as a "supergene"), and that gene flow between populations is counteracted by strong local selection favoring the regional pattern. In the case of ''Heliconius'', modern genomic studies have identified specific genes (such as variants of the gene ''optix'') that create the red wing band in multiple species – an example of convergent evolution at the genetic level. Ford's protégé Philip Sheppard and geneticist Sir Cyril Clarke also famously studied Batesian mimicry in African swallowtail butterflies (''Papilio'') during the 1950s–60s, uncovering polymorphic female forms: some females mimic toxic butterflies (to avoid predation), while others do not. They found that a single genetic locus with multiple alleles produces the different female morphs in ''Papilio polytes'', and frequency-dependent selection (predators being more likely to attack the rarer-looking forms) helped maintain the polymorphism. These butterfly studies demonstrated how complex interactions between predators, prey, and the environment can maintain balanced polymorphisms in nature. The work on mimicry, spanning over a century and continuing today, underscores a key theme of ecological genetics: natural selection can preserve genetic diversity when different environments or ecological interactions favor different genotypes, leading to a patchwork of adaptations across the landscape.
Polygenic Selection Research on ecologically important traits has traditionally focused on single alleles. However, in many cases, phenotypes are controlled by multiple alleles. Complex traits, such as traits involved in morphology, behaviour, life history or disease are often controlled by multiple alleles and are therefore polygenic traits. Through the use of genome-wide association studies (GWAS), researchers are able to scan genomes and identify loci associated with complex traits. Observing changes in allele frequency across a population can provide insight into polygenic adaptation.
A major line of evidence for polygenic traits can be drawn from artificial selection. Many experiments involving artificial selection have shown that traits often respond rapidly and steadily, suggesting they are influenced by many genes with small effects. For example, between 1957 and 2001, the weight of eight-week-old chickens increased by 4 times. This sustained improvement over time wouldn't make sense if only a few alleles of large effect were responsible for this phenotype, as the alleles would rapidly reach fixation, causing phenotypic change to plateau.
The prevalence of traits with a polygenic basis poses some issues when researching traits and adaptation in natural populations. With complex traits, it may be hard to separate the effects of genes, environmental factors, and random genetic drift.
Technology Ecological genetics combines various technologies to study the genetics underlying adaptive behaviours in populations.
Animal Tracking Technologies Animal instrumentation provides different types of biological information, involving migration patterns, habitat selection, energy spent and temporal patterns, which are used to study population dynamics. These tools include:
Heart-rate monitors: Assesses stress levels. Accelerometers: Measures acceleration of an object for activities such as diving or foraging. Acoustic recorders: Captures communication between organisms. Video recorders: Observes foraging behaviour, habitat interface and social interaction. Temperature loggers: Devices that measure body temperature patterns. Automated image-based tracking: Tracks behavioural patterns, social interactions and predator-prey interactions.
DNA Sequencing