Genetic monitoring is the use of molecular markers to (i) identify individuals, species or populations, or (ii) to quantify changes in population genetic metrics (such as effective population size, genetic diversity and population size) over time. Genetic monitoring can thus be used to detect changes in species abundance and/or diversity, and has become an important tool in both conservation and livestock management. The types of molecular markers used to monitor populations are most commonly mitochondrial, microsatellites or single-nucleotide polymorphisms (SNPs), while earlier studies also used allozyme data. Species gene diversity is also recognized as an important biodiversity metric for implementation of the Convention on Biological Diversity. [1]
Types of population changes that can be detected by genetic monitoring include population growth and decline, spread of pathogens, adaptation to environmental change, hybridization, introgression and habitat fragmentation events. Most of these changes are monitored using ‘neutral’ genetic markers (markers for which mutational changes do not change their adaptive fitness within a population). However markers showing adaptive responses to environmental change can be ‘non-neutral’ (e.g. mutational changes affect their relative fitness within a population).
Two broad categories of genetic monitoring have been defined: [2] Category I encompasses the use of genetic markers as identifiers of individuals (Category Ia), populations and species (Category Ib) for traditional population monitoring. Category II represents the use of genetic markers to monitor changes of population genetic parameters, which include estimators of effective population size (Ne), genetic variation, population inter-mixing, structure and migration.
At the individual level, genetic identification can enable estimation of population abundance and population increase rates within the framework of mark-recapture models. The abundance of cryptic or elusive species that are difficult to monitor can be estimated by collecting non-invasive biological samples in the field (e.g. feathers, scat or fur) and using these to identify individuals through microsatellite or single-nucleotide polymorphism (SNP) genotyping. This census of individuals can then be used to estimate population abundance via mark-recapture analysis. For example, this technique has been used to monitor populations of grizzly bear, [3] brush-tailed rock-wallaby, [4] Bengal tiger [5] and snow leopard. [6] Population growth rates are a product of rates of population recruitment and survival, and can be estimated through open mark-recapture models. For example, DNA from feathers shed by the eastern imperial eagle shows lower cumulative survival over time than seen for other long-lived raptors. [7]
Use of molecular genetic techniques to identify species can be useful for a number of reasons. Species identification in the wild can be used to detect changes in population ranges or site occupancy, rates of hybridization and the emergence and spread of pathogens and invasive species. Changes in population ranges have been investigated for Iberian lynx [8] and wolverine, [9] while monitoring of westslope cutthroat trout shows widespread ongoing hybridization with introduced rainbow trout [10] (see cutbow) and Canada lynx-bobcat hybrids have been detected at the southern periphery of the current population range for lynx. [11] [12] The emergence and spread of pathogens can be tracked using diagnostic molecular assays – for example, identifying the spread of West Nile virus among mosquitoes in the eastern US to identify likely geographical origins of infection [13] and identifying gene loci associated with parasite susceptibility in bighorn sheep. [14] Genetic monitoring of invasive species is of conservation and economic interest, as invasions often affect the ecology and range of native species and may also bring risks of hybridization (e.g. for copepods, [15] ducks, [16] barred owl and spotted owl, [17] and Lessepsian rabbitfish [18] ).
Species identification is also of considerable utility in monitoring fisheries and wildlife trade, where conventional visual identification of butchered or flensed products is difficult or impossible. [19] Monitoring of trade and consumption of species of conservation interest can be carried out using molecular amplification and identification of meat or fish obtained from markets. For example, genetic market surveys have been used to identify protected species and populations of whale (e.g., North Pacific minke whale) and dolphin species appearing in the marketplace. [20] Other surveys of market trade have focused on pinnipeds, [21] sea horses [22] and sharks. [23] Such surveys are used to provide ongoing monitoring of the quantity and movement of fisheries and wildlife products through markets and for detecting poaching or other illegal, unreported or unregulated (IUU) exploitation [19] (e.g. IUU fishing).
Although initial applications focused on species identification and population assessments, market surveys also provide the opportunity for a range of molecular ecology investigations including capture-recapture, assignment tests and population modeling. [19] These developments are potentially relevant to genetic monitoring Category II.
Monitoring of population changes through genetic means can be done retrospectively, through analysis of 'historical' DNA recovered from museum-archived species and comparison with contemporary DNA of that species. It can also be used as a tool for evaluating ongoing changes in the status and persistence of current populations. Genetic measures of relative population change include changes in diversity (e.g. heterozygosity and allelic richness). Monitoring of relative population changes through these metrics has been performed retrospectively for Beringian bison, [24] Galapagos tortoise, [25] houting, [26] Atlantic salmon, [27] northern pike, [28] New Zealand snapper, [29] steelhead trout, [30] greater prairie chicken, [31] Mauritius kestrel [32] and Hector's dolphin [33] and is the subject of many ongoing studies, including Danish and Swedish brown trout populations. [34] [35] Measuring absolute population changes (e.g. effective population size (Ne)) can be carried out by measuring changes in population allele frequencies (‘Ftemporal’) or levels of linkage disequilibrium over time (‘LDNe’), while changing patterns of gene flow between populations can also be monitored by estimating differences in allele frequencies between populations over time. Subjects of such studies include grizzly bears, [3] [36] [37] cod, [38] red deer, [39] Leopard frogs [40] and Barrel Medic. [41] [42]
Genetic monitoring has also been increasingly used in studies that monitor environmental changes through changes in the frequency of adaptively selected markers. For example, the genetically controlled photo-periodic response (hibernating time) of pitcher-plant mosquitos ( Wyeomyia smithii ) has shifted in response to longer growing seasons for pitcher plants brought on by warmer weather. [43] Experimental wheat populations grown in contrasting environments over a period of 12 generations found that changes in flowering time were closely correlated with regulatory changes in one gene, suggesting a pathway for genetic adaptation to changing climate in plants. [44] [45]
Genetic monitoring is also useful in monitoring the ongoing health of small, relocated populations. Good examples of this are found for New Zealand birds, many species of which were greatly impacted by habitat destruction and the appearance of numerous mammalian predators in the last century and have recently become part of relocation programs that transfer a few ‘founder’ individuals to predator-free offshore “ecological” islands. E.g. black robin, [46] and kākāpō. [47]
Category II genetic monitoring of population genetic diversity (PGD) of wild species, for purposes of biodiversity conservation and sustainable management, is unevenly distributed among countries in Europe. Country size and per capita Gross Domestic Product (GDP) are statistically associated in different ways with the number of documented monitoring projects, suggesting that available habitat for species and country financial resources influence monitoring effort. There is relatively little genetic monitoring for PGD conducted in southeastern Europe. Much attention has been directed towards monitoring of large carnivores, and relatively little effort towards monitoring species in other groups, such as amphibians. [48]
In February 2007 an international summit was held at the Institute of the Environment at UCLA, concerning ‘Evolutionary Change in Human Altered Environments: An International Summit to translate Science into Policy’. This led to a special issue of the journal of Molecular Ecology [49] organized around our understanding of genetic effects in three main categories: (i) habitat disturbance and climate change (ii) exploitation and captive breeding (iii) invasive species and pathogens.
In 2007 a Working Group on Genetic Monitoring was launched with joint support from NCEAS [50] and NESCent [51] to further develop the techniques involved and provide general monitoring guidance for policy makers and managers. [52]
Currently the topic is covered in several well known text books, including McComb et al. (2010) and Allendorf et al. (2013).
Many natural resource agencies see genetic monitoring as a cost-effective and defensible way to monitor fish and wildlife populations. As such scientists in the U.S. Geological Survey, U.S. Forest Service, [53] National Park Service, and National Marine Fisheries Service have been developing new methods and tools to use genetic monitoring, and applying such tools across broad geographic scales. [2] [36] Currently the USFWS hosts a website that informs managers as to the best way to use genetic tools for monitoring (see below).
A microsatellite is a tract of repetitive DNA in which certain DNA motifs are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. They have a higher mutation rate than other areas of DNA leading to high genetic diversity. Microsatellites are often referred to as short tandem repeats (STRs) by forensic geneticists and in genetic genealogy, or as simple sequence repeats (SSRs) by plant geneticists.
Phylogeography is the study of the historical processes that may be responsible for the past to present geographic distributions of genealogical lineages. This is accomplished by considering the geographic distribution of individuals in light of genetics, particularly population genetics.
Coregonus lavaretus is a species of freshwater whitefish, in the family Salmonidae. It is the type species of its genus Coregonus.
Peripatric speciation is a mode of speciation in which a new species is formed from an isolated peripheral population. Since peripatric speciation resembles allopatric speciation, in that populations are isolated and prevented from exchanging genes, it can often be difficult to distinguish between them. Nevertheless, the primary characteristic of peripatric speciation proposes that one of the populations is much smaller than the other. The terms peripatric and peripatry are often used in biogeography, referring to organisms whose ranges are closely adjacent but do not overlap, being separated where these organisms do not occur—for example on an oceanic island compared to the mainland. Such organisms are usually closely related ; their distribution being the result of peripatric speciation.
Genetic viability is the ability of the genes present to allow a cell, organism or population to survive and reproduce. The term is generally used to mean the chance or ability of a population to avoid the problems of inbreeding. Less commonly genetic viability can also be used in respect to a single cell or on an individual level.
Molecular ecology is a field of evolutionary biology that is concerned with applying molecular population genetics, molecular phylogenetics, and more recently genomics to traditional ecological questions. It is virtually synonymous with the field of "Ecological Genetics" as pioneered by Theodosius Dobzhansky, E. B. Ford, Godfrey M. Hewitt, and others. These fields are united in their attempt to study genetic-based questions "out in the field" as opposed to the laboratory. Molecular ecology is related to the field of conservation genetics.
A null allele is a nonfunctional allele caused by a genetic mutation. Such mutations can cause a complete lack of production of the associated gene product or a product that does not function properly; in either case, the allele may be considered nonfunctional. A null allele cannot be distinguished from deletion of the entire locus solely from phenotypic observation.
Deborah Charlesworth is a population geneticist from the UK, notable for her important discoveries in population genetics and evolutionary biology. Her most notable research is in understanding the evolution of recombination, sex chromosomes and mating system for plants.
Inbreeding depression is the reduced biological fitness that has the potential to result from inbreeding. Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. Inbreeding depression is often the result of a population bottleneck. In general, the higher the genetic variation or gene pool within a breeding population, the less likely it is to suffer from inbreeding depression, though inbreeding and outbreeding depression can simultaneously occur.
Genetic equilibrium is the condition of an allele or genotype in a gene pool where the frequency does not change from generation to generation. Genetic equilibrium describes a theoretical state that is the basis for determining whether and in what ways populations may deviate from it. Hardy–Weinberg equilibrium is one theoretical framework for studying genetic equilibrium. It is commonly studied using models that take as their assumptions those of Hardy-Weinberg, meaning:
Patricia G. Parker is a North American evolutionary biologist who uses molecular techniques to assess social structures, particularly in avian populations. Her interests have shaped her research in disease transmission and population size, particularly in regard to bird conservation. She received her B.S. in Zoology in 1975 and her Ph.D. in Behavioral Ecology in 1984, both from the University of North Carolina at Chapel Hill. From 1991 to 2000, Parker was an Assistant and Associate Professor in the Department of Evolution, Ecology, and Organismal Biology at Ohio State University. Since 2000, she is the Des Lee Professor of Zoological Studies at the University of Missouri–St. Louis.
The stepwise mutation model (SMM) is a mathematical theory, developed by Motoo Kimura and Tomoko Ohta, that allows for investigation of the equilibrium distribution of allelic frequencies in a finite population where neutral alleles are produced in step-wise fashion.
Carol Ann Stepien is an American ecologist at the National Museum of Natural History of the Smithsonian Institution. She was elected a fellow of the American Association for the Advancement of Science in 2016.
The Calabrian black squirrel is a species of tree squirrel in the genus Sciurus, endemic to the forests of the regions of Calabria and Basilicata, in the south of the Italian Peninsula.
Landscape genetics is the scientific discipline that combines population genetics and landscape ecology. It broadly encompasses any study that analyses plant or animal population genetic data in conjunction with data on the landscape features and matrix quality where the sampled population lives. This allows for the analysis of microevolutionary processes affecting the species in light of landscape spatial patterns, providing a more realistic view of how populations interact with their environments. Landscape genetics attempts to determine which landscape features are barriers to dispersal and gene flow, how human-induced landscape changes affect the evolution of populations, the source-sink dynamics of a given population, and how diseases or invasive species spread across landscapes.
DNA barcoding in diet assessment is the use of DNA barcoding to analyse the diet of organisms. and further detect and describe their trophic interactions. This approach is based on the identification of consumed species by characterization of DNA present in dietary samples, e.g. individual food remains, regurgitates, gut and fecal samples, homogenized body of the host organism, target of the diet study.
Invasion genetics is the area of study within biology that examines evolutionary processes in the context of biological invasions. Invasion genetics considers how genetic and demographic factors affect the success of a species introduced outside of its native range, and how the mechanisms of evolution, such as natural selection, mutation, and genetic drift, operate in these populations. Researchers exploring these questions draw upon theory and approaches from a range of biological disciplines, including population genetics, evolutionary ecology, population biology, and phylogeography.
Libby Liggins is an evolutionary ecologist and a Senior Lecturer in the School of Natural and Computational Science at Massey University, Auckland, New Zealand, as well as a research associate at Auckland Museum. Her research uses genetic and genomic data to explore the biogeography, population ecology, and biodiversity of marine organisms.
In quantitative genetics, QST is a statistic intended to measure the degree of genetic differentiation among populations with regard to a quantitative trait. It was developed by Ken Spitze in 1993. Its name reflects that QST was intended to be analogous to the fixation index for a single genetic locus (FST). QST is often compared with FST of neutral loci to test if variation in a quantitative trait is a result of divergent selection or genetic drift, an analysis known as QST–FST comparisons.
Iliana B. Baums is a professor at Pennsylvania State University known for her work on coral reef ecology.