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
In the previous post on The G-CAT, we talked about the role of maladaptation in the evolution of populations and species, and how this might impact their future. To summarise, maladaptation is the process (or trait responsible for) which causes a reduction in the fitness. As we discussed, this can come about a number of ways – such as from a shift in the selective environment or from fitness trade-offs in traits over time – and predominantly impacts on species by reducing their capacity to adapt. Particularly, this is important for small populations or those lacking in genetic diversity, which are already at risk of entering an extinction vortex and lack the capability to respond well to extreme selective changes (such as contemporary climate change).
Adaptation and natural selection
Adaptation via natural selection is one of the most fundamental components of understanding evolution. It describes how species can continually evolve new, innovative traits and produce the wondrous diversity of the natural world. This process is inevitably underpinned by particular heritable traits often linked to particular genetic variants (alleles). Remember that the underlying genetic trait (the allele) is referred to as the genotype; the physical outcomes of that allele (i.e. how it changes the physiological, behaviour or ecology of the organism) is the phenotype; and the scale of the benefit of possessing that trait is referred to as its fitness. Under the normal process of natural selection, phenotypes which increase fitness are selected for, which results in a shift in genotypes underpinning it.
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.
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.
Many things in life are the product of their history, and nothing exemplifies this better than evolution. Given the often-gradual nature of evolution by natural selection, environmental stressors and factors operating on long-term scales (i.e. over thousands or millions of years) can have major impacts on evolutionary changes across the diversity of biota. While many of these are specific to the characteristics of the target organism (i.e. are related to adaptive traits), non-adaptive (neutral) traits are also critically important in driving the path of evolution.
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.
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.
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.