Episode 160: An introduction to Evolutionary Biology
The field of evolutionary biology has been greatly influenced by the development of modern genetic methodology. The understanding of genes, genomes and the molecular mechanisms key to life on Earth are all goals of evolutionary biology in the 21st century, yet its potential applications seem to be near limitless. Palaeontology and evolutionary biology continue to be closely related and both, with their deeply rooted origins, have been essential to our understanding of macroevolution (major evolutionary change over long periods of time) ever since the major development of the theory in the 19th century.
In this episode, Prof. Erica Bree Rosenblum introduces us to this diverse and constantly evolving field. We cover fundamental questions such as: what are genes and genomes and why does understanding them matter; which evolutionary roles do environmental and genetic mechanisms play; and what ultimately causes the rise and fall of species. In order to better understand life on Earth, we show how evolutionary biology brings together the fields of genetics, biochemistry, ecology, palaeontology and more.
The gypsum dune fields of White Sands (New Mexico, USA) where Bree and her group sample and study lizards. These geologically young dunes provide a dramatic environmental stage for fast-paced evolution to occur allowing Bree and her colleagues to address important questions about rapid organismal adaptation and ecological speciation. Photo credit: Bree Rosenblum.The three species of lizards from White Sands which evolved convergent light and dark ‘ecomorphs’ (forms which exhibit unique morphological traits that relate to their specific ecology) within the last few thousand years: Little Striped Whiptail (Aspidoscelis inornata), the Lesser Earless Lizard (Holbrookia maculata) and the Eastern Fence Lizard (Sceloporus undulatus). The ecomorphs of each species have proven themselves to be excellent model organisms for the study of rapid evolution via substrate matching for camouflage. Lighter colour morphs of each species inhabit the white gypsum dunes of White Sands, whilst brown colour morphs live on surrounding dark desert soils. Bree and her colleagues study them to unveil the genetic architecture of adaptation and demographic parameters like gene flow. Photo credit: Bree Rosenblum. Such genetics work often begins with tissue sampling in the field (e.g. skin, blood, muscle) and continues in the lab where genetic material (e.g. DNA, RNA) is extracted following standard or modified protocols depending on the quality of the material itself, preservation of DNA/RNA and the specific research questions. Once genetic material gets extracted, it is then used in a whole array of methodological procedures, from rather simple PCRs (Polymerase Chain Reactions) which amplify single targeted genes (for population genetics, for example) to the so called library preparation for Next Generation Sequencing, which enables evolutionary biologists to study larger sections or even whole genomes and transcriptomes (the subsection of the genome that actually gets expressed). Here is Bree in her lab at UC Berkeley where most of her groups molecular work is done. Photo credit: Elena Zhukova.Baby earless lizards (Holbrookia maculata) depicting the two different ecomorphs. Such a phenomenon could give rise to new species, provided some kind of reproductive isolation occurs. This does not necessarily need to be geographic and can occur, for example, if these lizards can’t recognise themselves as conspecific and thus don’t mate. In the absence of such genetic exchange, populations slowly diverge, each adapting in their own fashion through accumulation of unique changes that make it even less likely they will successfully mate again. What is a species, though? There are numerous different ‘species concepts‘ and ecologists, population geneticists and palaeontologists could all use different definitions by necessity. Photo credit: Bree Rosenblum.Whilst earless lizards retain their habitat-dependant colouration through life, it’s not uncommon for some organisms to exhibit ‘phenotypic plasticity’. This phenomenon occurs when the environment influences a physical or behavioural alteration in an organism via a change in how different genes are expressed. It enables organisms to adapt to an ever-changing environment (e.g. the vision of a salmon will change depending on which leg of its migratory journey it’s on). Photo credit: Bree Rosenblum.“Nothing in Biology Makes Sense Except in the Light of Evolution” is an essay published by the evolutionary biologist Theodosius Dobzhansky in 1973. Whilst the importance of evolution cannot be understated, some communities have difficulty in accepting evolutionary theory and so public engagement and science communication play an important role in society. Bree hosts elementary students in the UC Berkeley Museum of Vertebrate Zoology, showing examples of how evolution has shaped our world. Photo credit: Julie Gipple.Prof. Bree Rosenblum with her dear friend Sticky the Frog. Photo credit: Elena Zhukova.
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