BIOL 203 Lecture 06: Evolutionary Ecology - Fall 2024 PDF

Lecture 06 Evolutionary Ecology BIOL 203 October 9th, 2024 1 Learning objectives 1. Describe how the process of evolution depends on genetic variation 2. Clarify how evolution can occur through random processes 3. Explain how evolution can also occur through sele...

Lecture 06 Evolutionary Ecology BIOL 203 October 9th, 2024 1 Learning objectives 1. Describe how the process of evolution depends on genetic variation 2. Clarify how evolution can occur through random processes 3. Explain how evolution can also occur through selection, which is a non- random process 4. Illustrate how microevolution operates at the population level 5. Describe the way that macroevolution operates at the species level and higher levels of taxonomic organization 2  The process of Key Concept evolution depends on genetic variation 3 The process of evolution depends on genetic variation 4 The process of evolution depends on genetic variation Evolution requires variation among individuals/populations Gene Contained in DNA → chromosomes Chromosome Regions of DNA which encode proteins = genes Alleles Different forms of a gene = alleles Genotype = combination of alleles 5 The process of evolution depends on genetic variation Phenotypes = physical expression of genes Some determined by a single gene, while others are determined by several/many genes E.g.) height in humans 6 The process of evolution depends on genetic variation Gene pool = collection of all the alleles for every individual in a population Populations can vary greatly in their gene pools E.g.) ABO blood type in humans 7 The process of evolution depends on genetic variation Several biological processes generate genetic variation Sexual reproduction = combining DNA from two different organisms Haploid (1n) gametes from parents combine to generate diploid (2n) offspring; results in new combinations of alleles 2n 2n 1n 2n + 1n 8 The process of evolution depends on genetic variation Chromosomes in a gamete are a random assortment of chromosomes in parent’s genome 9 The process of evolution depends on genetic variation Chromosomes in a gamete are a random assortment of chromosomes in parent’s genome 10 The process of evolution depends on genetic variation Recombination (reshuffling of genes during meiosis) also creates new variation 11 The process of evolution depends on genetic variation Mutations are random changes in the sequence of nucleotides Can be silent/synonymous (no detectable change in phenotype) Others alter phenotype If better suited for environment → natural selection Can be detrimental (e.g., sickle cell anemia) 12 The process of evolution depends on genetic variation Mutation rate is affected by: Expressed gene/non-coding region Number of genes (more genes = higher probability of mutation) Size of population (more chances for mutation to occur) Ranges from 1 in 100 to 1 in 1,000,000 generations Many mutations create selectable variation 13 Concept check What is the difference between genes and alleles? What are the three primary sources of genetic variation? 14  Evolution can Key Concept occur through random processes 15 Evolution can occur through random processes Random changes in allele frequencies can lead to evolution Random processes which affect allele frequencies include: Genetic drift Bottlenecks Founder effect 16 Evolution can occur through random processes Genetic drift is a process which occurs when genetic variation is lost due to random variation in mating, mortality, fecundity, or inheritance Primarily affects small populations Male #Mates Black 4 Brown 4 AA Aa aa 17 Evolution can occur through random processes Genetic drift is a process which occurs when genetic variation is lost due to random variation in mating, mortality, fecundity, or inheritance Primarily affects small populations AA Aa aa 18 Evolution can occur through random processes A severe reduction in population size can lead to genetic drift = bottleneck effect Survivors carry only a fraction of the diversity of original population Can be due to natural causes (e.g., drought) or anthropogenic causes (e.g., habitat loss) 19 Evolution can occur through random processes E.g.) Greater prairie chicken (Tympanuchus cupido) 20 Evolution can occur through random processes Reduction in diversity can prevent populations from adapting to future environmental changes (less variation for selection) E.g.) African cheetah (Acinonyx jubatus) Bottleneck ~10 kya; current population has very little genetic variation More susceptible to pathogens; AA amyloidosis kills up to 70% of captive cheetahs 21 Evolution can occur through random processes The founder effect occurs when a small number of individuals leave a large population and colonize a new area “Founders” will represent only a fraction of diversity of originating population 4 black (AA) A = 16/38 = 42% 7 brown (aa) a = 22/38 = 58% 8 grey (Aa) 22 Evolution can occur through random processes The founder effect occurs when a small number of individuals leave a large population and colonize a new area “Founders” will represent only a fraction of diversity of originating population 4 black (AA) A = 16/38 = 42% 7 brown (aa) a = 22/38 = 58% 8 grey (Aa) 0 black (AA) A = 1/6 = 17% 2 brown (aa) a = 5/6 = 83% 1 grey (Aa) 23 Evolution can occur through random processes E.g.) Water hyacinth (Eichhornia crassipes) 24 Activity Go to https://tinyurl.com/ys7n47e4 and explore how drift, the bottleneck effect, and the founder effect can affect genetic variation of a population 25  Evolution can Key Concept occur through non-random selection 26 Evolution can also occur through selection Selection is the non-random process by which certain phenotypes are favoured to survive and reproduce over other phenotypes Can influence the distribution of heritable traits in three ways: Stabilizing selection Directional selection Disruptive selection 27 Evolution can also occur through selection When individuals with intermediate phenotypes have higher survival and reproductive success = stabilizing selection Often begins with a wide distribution of phenotypes, progressively narrow distributions with offspring “Sweeps away” harmful genetic variation 28 Evolution can also occur through selection E.g.) Sociable weaver (Philetairus socius) 29 Evolution can also occur through selection Directional selection occurs when an extreme phenotype experiences higher fitness than the average phenotype Alters the appearance/behaviour of the population 30 Evolution can also occur through selection E.g.) Medium ground finch (Geospiza fortis) 1976 1978 pre-drought post-drought 31 Evolution can also occur through selection Disruptive selection occurs when extreme phenotypes at both ends of distribution have higher fitness than intermediate phenotypes Increases phenotypic/genetic variation Can lead to speciation 32 Evolution can also occur through selection E.g.) Tadpoles of spadefoot toad (Spea multiplicata) in New Mexico 33 Genetic drift or selection? Often, evolution occurs via both random (drift) and non-random (selection) processes E.g.) Mexican cavefish (Astyanax mexicanus) 34 Concept check Why do we consider selection to be a non-random process? 35  Microevolution Key Concept operates at the population level 36 Microevolution operates at the population level Microevolution = evolution of populations Responsible for producing different breeds of crops (e.g., Brassica) & domesticated animals, distinct populations of wild organisms IMPORTANT: Populations evolve, NOT individuals! Selection occurs via two ways: artificial selection and natural selection 37 Microevolution operates at the population level Artificial selection = selection in which humans determine which individuals will survive and breed (e.g., dogs) Can be intentional or unintentional 38 Microevolution operates at the population level Artificial selection can be used for de-extinction E.g.) Auroch, ancestor to modern- day cattle; extinct in 1627 Selective breeding of cattle with auroch genes Re-introduce to allow for return of natural grazing patterns 39 Microevolution operates at the population level Artificial selection can be used for conservation E.g.) American chestnut Introduced fungus in 1900s caused chestnut blight; led to death of ~4 billion trees Selective breeding/genetic modification to produce chestnut with fungal resistance 40 Microevolution operates at the population level Artificial selection can happen inadvertently E.g.) White-tail deer in New York state White deer protected, brown could be hunted 41  Microevolution operates at the population level Artificial selection can happen inadvertently E.g.) Horn size in bighorn sheep Pigeon et al. 2016 42  Microevolution operates at the population level Natural selection favours any phenotypes with the highest fitness Acts on existing variation among individuals Origins of new traits arise as undirected (random) mutations Traits are inherited regardless if they are beneficial or detrimental (no pre-ordained target) Adaptation results from non-random differences in survival/reproduction among variable individuals over many generations (accumulation) 43 Gregory 2009 Microevolution operates at the population level Natural selection has been the primary driver of the diversification of organisms over the history of Earth Due to ecological interactions: physical conditions, food resources, predators, competition, etc. 44 Microevolution operates at the population level E.g.) Industrial melanism in the peppered moth (Biston betularia) Consumed: Consumed: 45 Microevolution operates at the population level Natural selection can lead to potentially maladaptive traits E.g.) Long-tailed widowbird (Euplectes progne) 46 Concept check What traits are favoured by natural selection? 47  Macroevolution operates at the Key Concept species level and higher levels of taxonomic organization 48 Macroevolution operates at higher levels of organization Macroevolution = evolution of higher levels of organization, including species, genera, families, orders, and phyla Leads to speciation = evolution of new species Four main types: Allopatric speciation Sympatric speciation Parapatric speciation* Peripatric speciation* 49 Macroevolution operates at higher levels of organization Allopatric speciation is the evolution of new species through geographic isolation 50 Macroevolution operates at higher levels of organization Allopatric speciation is the evolution of new species through geographic isolation 51 Macroevolution operates at higher levels of organization Allopatric speciation is the evolution of new species through geographic isolation 52 Macroevolution operates at higher levels of organization Allopatric speciation is the evolution of new species through geographic isolation 53 Macroevolution operates at higher levels of organization Allopatric speciation is thought to be the most common mechanism of speciation E.g.) Darwin’s finches Common ancestor likely came from South American mainland Isolated on different islands Adaptive radiation = many new species arising from one common ancestor in a relatively short period of time 54 Macroevolution operates at higher levels of organization Sympatric speciation gives rise to new species without geographic isolation Can be facilitated by distinct habitats, resources, niches, etc. (environmental variation) E.g.) African cichlids in Lake Tanganyika Habitat ranges from rocky shores to sandy shorelines >200 species from a single ancestor 55 Macroevolution operates at higher levels of organization Sympatric speciation can occur through polyploidy = a species which contains 3+ sets of chromosomes Arises when homologous chromosomes fail to separate during mitosis/meiosis 56 Macroevolution operates at higher levels of organization 57 Macroevolution operates at higher levels of organization Some polyploid individuals cannot interbreed with diploid individuals → instant new species Reproductive isolation E.g.) Tremblay’s salamander (Ambystoma tremblayi) 58 Macroevolution operates at higher levels of organization Plant breeders intentionally cause polyploidy to produce more desirable traits (what is this an example of?) Polyploid plants tend to be larger, produce bigger fruits/flowers E.g.) cultivated strawberries are octoploid E.g.) wheat (2n → 6n) 59 Macroevolution operates at higher levels of organization Parapatric speciation occurs when a continuous population covers a large area (no geographical barriers) Over time, populations so distinct that they are separate species 60 Macroevolution operates at higher levels of organization Peripatric speciation occurs when a small group of individuals leave and colonize a new area (what random process is this?) Geographic isolation leads to speciation 61 Macroevolution operates at higher levels of organization How do we visualize evolution/speciation through time? Phylogenetic trees = hypothesized patterns of relatedness among different groups Relationships can be inferred using fossil data, morphology, behaviour, genetics/genomics 62 Macroevolution operates at higher levels of organization 63 Macroevolution operates at higher levels of organization Root 64 Macroevolution operates at higher levels of organization Node Root 65 Macroevolution operates at higher levels of organization Node Root Branch 66 Macroevolution operates at higher levels of organization Terminal taxa/external node Node Root Branch 67 Macroevolution operates at higher levels of organization Why use phylogenetic trees? Allows us to attempt to understand the order in which groups evolved from each other Better understanding how species evolved over time E.g.) loss of flight in ratites 68 Concept check What is one requirement of allopatric speciation? How does a polyploidy event immediately give rise to a new species? 69 Next class Adaptation to variable environments (Chapter 5) Next week: Monday, no classes (Thanksgiving) No labs 70