Sweeping under the genomic rug: hard and soft sweeps

Of alleles and selection

If you’ve read this blog more than once before, you’re probably sick of hearing about how genetic variation underlies adaptation. It’s probably the most central theme of this blog, and similarly one of the biggest components of contemporary biology. We’ve talked about different types of selection; different types of genes; different ways genes and selection can interact. And believe it or not, there’s still heaps to talk about! Continue reading

Managing genes in conservation and industry

The fundamentals of population genetics

Many times in the past, we’ve discussed the importance of genetic diversity within populations as a foundation for adaptation and evolution. It includes both adaptive variation (which encompasses genetic variation directly under natural selection), as well as neutral variation (which is predominantly generated and maintained by non-selective forces such as demographic history and genetic drift). This pool of genetic variation acts as the underlying architecture for evolution by natural selection, and is a critically important component for future and ongoing evolution.

This all sounds important from an academic perspective: that population genetics can reveal a significant amount of information about the processes and outcomes of evolution and provide novel insights into concepts that have been around for ages. But how can this information be applied to real scenarios? With the ever-growing availability of massive genetic datasets for an increasing number of species, the sheer volume of information in existence that can be used is monumental.

Continue reading

Rebuilding the genomic architecture of evolution

Beyond mutations in the genome

Although genetic variation is, in itself, often considered to be one of the fundamental underpinnings of adaptation by natural selection, it can appear through a number of different forms. Typically, we think of genetic variation in terms of individual mutations at a single site (referred to as ‘single nucleotide polymorphisms’, or SNPs), which may vary in frequency across a population or species in response to selective pressures. However, we’ve also discussed some other types of genetic-related variation within The G-CAT before, such as differential gene expression or epigenetic markers.

Continue reading

Scanning for causes: an introduction to genome-wide association studies

Understanding genetic determinants

You’ve probably been exposed to one news headline or another in the recent past (let’s say the last 5 years) that reads something like “SCIENTISTS DISCOVER GENES THAT CAUSE (X).” X, of course, varies massively based on the study itself (and sometimes the bastardisation of said study by media): it can include describing medical conditions such as cancer, autism or congenital diseases; behavioural traits, such as sexual preferences; or broad physical traits, such as the classic problem of the inheritability of height. Unsurprisingly, you may think that trying to find the genes responsible for some traits should be either a) super easy, or b) super hard, depending on your own philosophical preference or the trait in question. So how do these studies come about, anyway?

Continue reading

What’s yours is mine: evolution by adaptive introgression

Gene flow and introgression

Genetic variation remains a key component of not only understanding the process and history of evolution, but also for allowing evolution to continue into the future. This is the basis of the concept of ‘evolutionary potential’ – the available variation within a population or species which may enable them to adapt to new environmental stressors as they occur. With the looming threat of contemporary climate change and environmental transformations by humanity, predicting and supporting evolutionary potential across the diversity of life is critical for conserving the stability of our biosphere.

Continue reading

Islands of speciation and speciation on islands

The concept of a species

We’ve spent some time before discussing the nature of the term ‘species’ and what it means in reality. Of course, answers to questions in biology are always more complicated than we wish they might be, and despite the common nomenclature of the word ‘species’ the underlying definition is convoluted and variable.

Continue reading

Evolutionary clocks out of sync

Evolutionary time

It shouldn’t come as a surprise to anyone with a basic understanding of evolution that it is a temporal (and also spatial concept). Time is a fundamental aspect of the process of evolution by natural selection, and without it evolution wouldn’t exist. But time is also a fickle thing, and although it remains constant (let’s not delve into that issue here) not all things experience it in the same way.

Continue reading

Genes in parallel

Adaptation from genetic variation

One of the central themes of this blog, and indeed of evolutionary biology as a whole, is the notion that adaptation is often underpinned by genes. Genetic variation acts as the basis for natural selection to favour or disfavour traits: while this is directly through phenotypic traits (e.g. fur colour, morphology, behaviour), these traits are typically determined by a genetic component. In the early stages of adaptation, evolution can often be observed by changes in the frequency of genetic variants (alleles) within a species or population over time as natural selection acts, gradually leading to the observable (and sometimes dramatic) change in species over time.

Continue reading

UnConservation Genetics: tools for managing invasive species

Conservation genetics

Naturally, all species play their role in the balancing and functioning of ecosystems across the globe (even the ones we might not like all that much, personally). Persistence or extinction of ecologically important species is a critical component of the overall health and stability of an ecosystem, and thus our aim as conservation scientists is to attempt to use whatever tools we have at our disposal to conserve species. One of the most central themes in conservation ecology (and to The G-CAT, of course) is the notion that genetic information can be used to better our conservation management approaches. This usually involves understanding the genetic history and identity of our target threatened species from which we can best plan for their future. This can take the form of genetic-informed relatedness estimates for breeding programs; identifying important populations and those at risk of local extinction; or identifying evolutionarily-important new species which might hold unique adaptations that could allow them to persist in an ever-changing future.

Applications of conservation genetics.jpg
Just a few applications of genetic information in conservation management, such as in breeding programs and pedigrees (left), identifying new/cryptic species (centre) and identifying and maintaining populations and their structure (right).

The Invaders

Contrastingly, sometimes we might also use genetic information to do the exact opposite. While so many species on Earth are at risk (or have already passed over the precipice) of extinction, some have gone rogue with our intervention. These are, of course, invasive species; pests that have been introduced into new environments and, by their prolific nature, start to throw out the balance of the ecosystem. Australians will be familiar with no shortage of relevant invasive species; the most notable of which is the cane toad, Rhinella marina. However, there are a plethora of invasive species which range from notably prolific (such as the cane toad) to the seemingly mundane (such as the blackbird): so how can we possibly deal with the number and propensity of pests?

Table of invasive species in Australia
A table of some of the most prolific mammalian invasive species in Australia, including when they were first introduced and why, and their (relatively) recently estimated population sizes. Source: Wikipedia (and studies referenced therein). Some estimated numbers might not reflect current sizes as they were obtained from studies over the last 10 years.

Tools for invasive species management

There are a number of tools at our disposal for dealing with invasive species. These range from chemical controls (like pesticides), to biological controls and more recently to targeted genetic methods. Let’s take a quick foray into some of these different methods and their applications to pest control.

Types of control tools for invasive species
Some of the broad categories of invasive species control. For any given pest species, such as the cane toad (top), we might choose to use a particular set of methods to reduce their numbers. These can include biological controls (such as the ladybird, for aphid populations (left)); chemical controls such as pesticides; or even genetic engineering technologies.

Biological controls

One of the most traditional methods of pest control are biological controls. A biological control is, in simple terms, a species that can be introduced to an afflicted area to control the population of an invasive species. Usually, this is based on some form of natural co-evolution or hierarchy: species which naturally predate upon, infect or otherwise displace the pest in question are preferred. The basis of this choice is that nature, and evolution by natural selection, often creates a near-perfect machine adapted for handling the exact problem.

Biological controls can have very mixed results. In some cases, they can be relatively effective, such as the introduction of the moth Cactoblastis cactorum into Australia to control the invasive prickly pear. The moth lays eggs exclusively within the tissue of the prickly pear, and the resultant caterpillars ravish the plant. There has been no association of secondary diet items for caterpillars, suggesting the control method has been very selective and precise.

Moth biological control flow chart
The broad life cycle of the cactus moth and how it controls the invasive prickly pear in Australia. The ravenous caterpillar larvae of the moth is effective at decimating prickly pears, whilst the moth’s specificity to this host means there is limited impact on other plant species.

On the contrary, bad biological controls can lead to ecological disasters. As mentioned above, the introduction of the cane toad into Australia has been widely regarded as the origin of one of the worst invasive pests in the nation’s history. Initially, cane toads were brought over in the 1930s to predate on the (native) cane beetle, which was causing significant damage to sugar cane plantations in the tropical north. Not overly effective at actually dealing with the problem they were supposed to deal with, the cane toad rapidly spread across northern portion of the continent. Native species that attempt to predate on the cane toad often die to their defensive toxin, causing massive ecological damage to the system.

The potential secondary impact of biological controls, and the degree of unpredictability in how they will respond to a new environment (and how native species will also respond to their introduction) leads conservationists to develop new, more specific techniques. In similar ways, viral and bacterial-based controls have had limited success (although are still often proposed in conservation management, such as the planned carp herpesvirus release).

Genetic controls?

It is clear that more targeted and narrow techniques are required to effectively control pest species. At a more micro level, individual genes could be used to manage species: this is not the first way genetic modification has been proposed to deal with problem organisms. Genetic methods have been employed for years in crop farming through genetic engineering of genes to produce ‘natural’ pesticides or insecticides. In a similar vein, it has been proposed that genetic modification could be a useful tool for dealing with invasive pests and their native victims.

Gene drives

One promising targeted, genetic-based method that has shown great promise is the gene drive. Following some of the theory behind genetic engineering, gene drives are targeted suites of genes (or alleles) which, by their own selfish nature, propagate through a population at a much higher rate than other alternative genes. In conjunction with other DNA modification methods, which can create fatal or sterilising genetic variants, gene drives present the opportunity to allow the natural breeding of an invasive species to spread the detrimental modified gene.

Gene drive diagram
An example of how gene drives are being proposed to tackle malaria. In this figure, the pink mosquito at the top has been genetically engineered using CRISPR to possess two important genetic elements: a genetic variant which causes the mosquito to be unable to produce eggs or bite (the pink gene), and a linked selfish genetic element (the gene drive itself; the plus) which makes this detrimental allele spread more rapidly than by standard inheritance. Sources: Nature and The Australian Academy of Science.

Although a relatively new, and untested, technique, gene drive technology has already been proposed as a method to address some of the prolific invasive mammals of New Zealand. Naturally, there are a number of limitations and reservations for the method; similar to biological control, there is concern for secondary impact on other species that interact with the invasive host. Hybridisation between invasive and native species would cause the gene drive to be spread to native species, counteracting the conservation efforts to save natives. For example, a gene drive could not reasonably be proposed to deal with feral wild dogs in Australia without massively impacting the ‘native’ dingo.

Genes for non-genetic methods

Genetic information, more broadly, can also be useful for pest species management without necessarily directly feeding into genetic engineering methods. The various population genetic methods that we’ve explored over a number of different posts can also be applied in informing management. For example, understanding how populations are structured, and the sizes and demographic histories of these populations, may help us to predict how they will respond in the future and best focus our efforts where they are most effective. By including analysis of their adaptive history and responses, we may start to unravel exactly what makes a species a good invader and how to best predict future susceptibility of an environment to invasion.

Table of genetic information applications
A comprehensive table of the different ways genetic information could be applied in broader invasive species management programs, from Rollins et al. (2006). This paper specifically relates to pest management within Western Australia but the concepts listed here apply broadly. Many of these concepts we have discussed previously in a conservation management context as well.

The better we understand invasive species and populations from a genetic perspective, the more informed our management efforts can be and the more likely we are to be able to adequately address the problem.

Managing invasive pest species

The impact of human settlement into new environments is exponentially beyond our direct influences. With our arrival, particularly in the last few hundred years, human migration has been an effective conduit for the spread of ecologically-disastrous species which undermine the health and stability of ecosystems around the globe. As such, it is our responsibility to Earth to attempt to address our problems: new genetic techniques is but one growing avenue by which we might be able to remove these invasive pests.

The human race(s)? Perspectives from genetics

The genetic testing of race

In one form or another, you may have been (unfortunately) exposed to the notion of ‘testing for someone’s race using genetics.’ In one sense, this is part of the motivation and platform of ‘23andMe’, which maps the genetic variants across the human genome back to likely origin populations to determine the relative ancestry of a person. In a much darker sense, the connection between genetic identity and race is the basis of eugenics, by suggesting genetic “purity” (this concept is utter nonsense, for reference) of a population as justification for some racist hierarchy. Typically, this is associated with Hitler’s Nazism, but more subversive versions of this association still exist in the world: for Australian readers, most notably when the far-right conservative minor party One Nation suggested that people claiming to be Indigenous should be subjected to genetic testing to verify their race.

DNA Ancestry map.jpg
A simplified overview of how DNA Ancestry methods work, by associating particular genetic variants within your genome to likely regions of origin. Note the geographic imprecision in the method on the map on the right, as well as the clear gaps. Source: Ancestry blog.

The biological concept of a ‘race’

Beyond the apparent ethical and moral objections to the invasive nature of demanding genetic testing for Indigenous peoples, a crucial question is one of feasibility: even if you decided to genetically test for race, is this possible? It might come as a surprise to non-geneticists that actually, from a genetic perspective, race is not a particularly stable concept.

The notion of races based on genetics has been a highly controversial topic throughout the development of genetic theory and research. Even recently, James Watson (as in of Watson & Crick, who were credited with the discovery of the structure of DNA) was stripped of several titles (including Chancellor Emeritus) following some controversial (and scientifically invalid) comments on the nature of race, genetics and intelligence. Comfortingly, the vast majority of the scientific community opposed his viewpoints on the matter, and in fact it has long been held that a ‘genetic race’ is not a scientifically stable concept.

James Watson.jpg
James Watson himself. I bet Rosalind Franklin never said anything like this… Source: Wikipedia.

You might ask: why is that? There are perceivable differences in the various peoples of the world, surely some of those could be related to both a ‘race’ and a ‘genetic identity’, right? Well, the issue is primarily due to the lack of identifiability of genetic variants that can be associated with a race. Decades of research in genetic variation across the global human population indicates that, due to the massive size of the human population and levels of genetic variation, it is functionally impossible to pinpoint down genetic variants that uniquely identify a ‘race’. Human genetic variation is such a beautiful spectrum of alleles that it becomes impossible to reliably determine where one end of the spectrum ends or begins, or to identify a strict number of ‘races’ within the kaleidoscope of the human genome.

How does this relate to 23AndMe?

How does this relate to your ‘23AndMe’ results? Well, chances are that some genetic variants might be able to be traced back to a particular region (e.g. Europe, somewhere). But naturally, there’s a significant number of limitations to this kind of inference; notably, that we don’t have reliable references from ancient history to draw upon very often. This, combined with the fact that humans have mixed among ourselves (and even with other species) for millennia, means that tracing back individual alleles is exceedingly difficult.

Genetic variation and non-identifiability of race figure
A diagram of exactly why identifying a genetic basis for race is impossible in humans. A) The ‘idealised’ version of race; people are easily classified by their genetic identity, with some variation within each classification (in this case, race) but still distinctiveness between them. B) The reality of human genetic variation, which makes it exceedingly difficult to make any robust or solid boundaries between groups of people due to the sheer amount of variation. Source: Harvard University blog.

This is exponentially difficult for people who might have fewer sequenced ancestors or relatives; without the reference for genetic variation, it can be even harder to trace their genetic ancestry. Such is the case for Indigenous Australians, for which there is a distinct lack of available genetic data (especially compared to European-descended Australians).

The non-genetic components

The genetic non-identifiability of race is but one aspect which contradicts the rationality of genetic race testing. As we discussed in the previous post on The G-CAT, the connection between genetic underpinning and physicality is not always clear or linear. The role of the environment on both the expression of genetic variation, as well as the general influence of environment on aspects such as behaviour, philosophy, and culture necessitate that more than the genome contributes to a person’s identity. For any given person, how they express and identify themselves is often more strongly associated with their non-genetic traits such as beliefs and culture.

genetic vs cultural inheritance.jpg
A comparison of genetic vs. cultural inheritance, which demonstrates (as an example) how other factors (in this case, other people) influence the passing on of cultural traits. Remember that this but one aspect of the factors that determine culture and identity, and equally (probably more) complex networks exist for other influences such as environment and development. Source: Creanza et al. (2017), PNAS.

These factors cannot reliably be tested under a genetic framework. While there may be some influence of genes on how a person’s psychology develops, it is unlikely to be able to predict the lifestyle, culture and complete identity of said person. For Indigenous Australians, this has been confounded by the corruption and disruption of their identity through the Stolen Generation. As a result, many Indigenous descendants may not appear (from a genetic point of view) to be purely Indigenous but their identity and culture as an Indigenous person is valid. To suggest that their genetic ancestry more strongly determines their identity than anything else is not only naïve from a scientific perspective, but nothing short of a horrific simplification and degradation of those seeking to reclaim their identity and culture.

The non-identifiability of genetic race

The science of genetics overwhelmingly suggests that there is no fundamental genetic underpinning of ‘race’ that can be reliably used. Furthermore, the impact of non-genetic factors on determining the more important aspects of personal identity, such as culture, tradition and beliefs, demonstrates that attempts to delineate people into subcategories by genetic identity is an unreliable method. Instead, genetic research and biological history fully acknowledges and embraces the diversity of the global human population. As it stands, the phrase ‘human race’ might be the most biologically-sound classification of people: we are all the same.