L4 ecological speciation Flashcards
What are the two primary forms of speciation focused on in this course?
Ecological speciation (via divergent natural selection) and mutation-order speciation (differential fixation of mutations).
Why is speciation considered a continuous process rather than a single event?
Because reproductive barriers accumulate gradually, and markers (biological, morphological, phylogenetic, geographic) are proxies with exceptions.
Define vicariance in allopatric speciation.
Physical separation of a population by a barrier (e.g., uplift isolating a small population).
Define colonization in allopatric speciation.
Separation of a population by dispersal to a new area (e.g., mainland to island colonization).
What level of gene flow and selection characterizes parapatric speciation?
Medium gene flow and medium selection across adjacent or stepping-stone populations.
What conditions make sympatric speciation possible?
High gene flow but very strong divergent selection within overlapping distributions.
Why measure gene flow directly rather than using geographic distance as a proxy?
Because actual connectivity can vary (e.g., human‐introduced isolated populations have zero gene flow despite proximity).
How do selection, drift, and gene flow interact in speciation?
Their balance determines whether populations diverge to full reproductive isolation on a geographic stage.
Under what scenario can genetic drift alone lead to speciation?
In allopatry with very low gene flow, drift can suffice without strong selection.
What is the Biological Species Concept?
Groups of actually or potentially interbreeding natural populations that are reproductively isolated.
What is ecological speciation?
Evolution of reproductive barriers due to ecologically based divergent selection between environments.
What is mutation-order speciation?
Reproductive isolation arising because different populations fix the same beneficial mutations in different orders, causing incompatibilities.
How can sexual selection contribute to speciation?
By driving divergence in mating signals or preferences, leading directly to reproductive isolation.
What is an indirect mechanism of ecological speciation?
Reproductive isolation as a by-product of adaptive divergence in non-mating traits (e.g., genomic incompatibilities).
Why are plants more capable of sympatric speciation than animals?
Because plants can survive polyploid mutations, instantly creating reproductive barriers without geographic separation.
Give an example of hybrid speciation.
Formation of a new species through interbreeding of two distinct parent species.
How does mutation-order speciation explain divergence under similar ecological conditions?
Random order of mutation fixation leads to different genetic combinations and incompatibilities.
Summarize the roles of geography in speciation.
Geography (vicariance, parapatry, allopatry) sets the stage by modulating gene flow, serving as a proxy for connectivity.
What are the two broad categories of speciation via natural selection?
Ecological speciation and mutation-order speciation.
Why is it difficult to delineate species boundaries?
Because speciation is gradual, markers are proxies, and there is variability across taxa and exceptions.
What does the three-spined stickleback system illustrate about divergence and speciation?
Divergence along separate fitness peaks can occur (different morphotypes) without complete reproductive isolation, showing speciation is a continuum.
What are the three key requirements for ecological speciation?
(1) Source of divergent selection, (2) Pre- or post-mating reproductive isolation, (3) Genetic mechanisms linking ecological traits to isolation.
Give two abiotic factors that drive divergent selection.
Altitude (e.g., high versus low elevation), temperature extremes (very cold vs. very hot environments).
Name two biotic factors that can create divergent selection pressures.
Predation regimes (presence/absence of predators) and competition for food resources.
What is ecological character displacement?
Evolution of extreme, divergent phenotypes in sympatric species due to direct competition for similar resources.
How do reciprocal transplant experiments detect local adaptation?
By moving individuals between environments and observing ‘crossover’ fitness effects—high fitness in home habitat but low fitness in foreign habitat.
Describe a field-based method for measuring divergent selection.
Tracking survival, growth, or reproduction of individuals with varying traits in natural populations (e.g., Western chorus frogs’ body shape under different predator regimes).
How was the adaptive landscape ‘reverse-engineered’ in Darwin’s finch studies?
Measuring natural seed-size distributions on islands to model and predict corresponding beak-size adaptations across finch populations.
What is pre-mating reproductive isolation via habitat preference?
When individuals preferentially remain and mate in their native habitat, reducing interbreeding (e.g., lake vs. stream sticklebacks in mark–recapture studies).
What evidence shows sticklebacks exhibit habitat fidelity?
Mark–recapture data reveal that few individuals switch between lake and stream habitats, and those that do have intermediate morphologies.
Define immigrant inviability with an example.
Reduced survival of migrants in non-native habitats, as shown by Atlantic Molly from sulphidic vs. non-sulphidic waters performing poorly when transplanted.
What physiological adaptation allows Atlantic Molly to inhabit sulphide-rich waters?
Evolved detoxification and respiratory mechanisms counteracting hydrogen sulphide’s metabolic disruption.
Name a post-mating, post-zygotic isolation mechanism in ecological speciation.
Ecologically dependent selection against hybrids or intrinsic genetic incompatibilities reducing hybrid fitness.
Why might some divergent environmental factors fail to show selection effects?
Due to low statistical power or examining the wrong traits, making true divergent selection hard to detect.
How do genomic tools aid in linking selection to reproductive isolation?
Whole-genome sequencing can identify loci under divergent selection that also contribute to mate choice or incompatibilities.
Summarize how trade-offs underpin local adaptation in ecological speciation.
Organisms face fitness trade-offs across environments, so alleles beneficial in one habitat reduce fitness in another, promoting divergent adaptation and isolation.
What is ecologically dependent selection against hybrids?
Environment‐dependent fitness reduction in hybrids beyond intrinsic genomic incompatibilities.
In the leaf beetle study, how did F₁ hybrids perform compared to pure types?
F₁ hybrids had lower growth rates in both maple and willow environments, reflecting both environmental mismatch and intrinsic incompatibilities.
How did backcross experiments isolate ecological effects in the leaf beetle study?
By comparing F₁×maple and F₁×willow backcrosses (same genetic load) across both host environments, revealing environment‐specific fitness trade-offs.
What is sensory drive in ecological sexual isolation?
Adaptive divergence of signaling traits (e.g., coloration, calls) driven by habitat‐dependent signal transmission efficiency.
Give an example of ecology influencing bird mate choice.
In some species, feeding strategy–induced beak morphology alters song structure, leading to assortative mating based on habitat‐tuned signals.
Define pleiotropy linking ecological traits to reproductive barriers.
A single gene simultaneously affects an ecological adaptation and a mating or isolation trait, directly coupling divergence and isolation.
How does linkage disequilibrium facilitate ecological speciation?
Close chromosomal proximity of ecological‐trait genes and isolation genes prevents recombination from breaking their association.
What stickleback evidence suggests pleiotropy or tight linkage?
A ~16 Kb haplotype block shows high LOD scores for multiple phenotypes (e.g., armour plating), implying shared genetic control.
Why is pleiotropy stronger than linkage disequilibrium in maintaining trait associations?
Pleiotropy has no chance of recombination separating traits, whereas linkage disequilibrium can be eroded by crossovers.
How can reproductive isolation evolve without ecological divergence?
Geographic isolation and genetic drift can generate barriers first, with ecological differences arising later (e.g., Himalayan warblers).
What scenario defines mutation‐order speciation?
Parallel adaptation to the same environment via different mutational paths in allopatry, leading to genomic incompatibilities.
How do mitochondrial‐nuclear interactions drive mutation‐order speciation?
Different populations accumulate distinct mitochondrial mutations and compensatory nuclear restorers, causing hybrids to malfunction.
What is meiotic drive and its role in speciation?
Selfish elements bias gamete transmission (e.g., disabling rival sperm), creating fertility costs and divergent genetic conflicts.
How do transposons contribute to mutation‐order speciation?
Rapid movement creates lineage‐specific genomic changes, leading to incompatibilities and reduced hybrid fitness.
Describe the Monkey Flower example of mutation‐order speciation.
Lineages evolved different mitochondrial distortions and nuclear restorer genes, so hybrids suffer inviability when crossed.
Contrast gene‐flow requirements for ecological vs. mutation‐order speciation.
Ecological speciation can occur with gene flow under divergent selection; mutation‐order speciation requires reduced gene flow for distinct mutation paths.
Why can mutation‐order speciation not generate ecologically based isolating barriers?
Because selective pressures are concordant across populations, not divergent ecologies driving isolation traits.
How does ecologically dependent selection against hybrids reinforce reproductive isolation?
Hybrids incur additional environment‐specific fitness losses, strengthening postzygotic barriers via trade‐offs.
What two genetic mechanisms bridge ecological adaptation and reproductive isolation?
Pleiotropy and linkage disequilibrium coupling adaptive traits with isolating traits.
Why doesn’t every ecological divergence result in ecological speciation?
Divergence must evolve before or alongside isolation; if isolation precedes ecology, ecological differences are secondary, not causative.
