L5 adaptive radiation 1 Flashcards
What is adaptive radiation?
A pattern of rapid species diversification where a lineage evolves into multiple forms occupying diverse ecological roles, with coupled ecological and phenotypic divergence.
What key features characterize adaptive radiation?
Diversification into many forms with new phenotypes that improve organismal fitness in specific ecologies.
What essential criteria define adaptive radiation?
Evolution of tightly linked phenotypic and ecological traits initiating rapid diversification driven by ecological opportunity.
How does species diversification rate change over time in adaptive radiations?
It initially increases rapidly as niches are filled, then diminishes as ecological space saturates.
What is phenotypic disparity?
The increase in morphological and physiological differences among new forms as they specialize into distinct ecological niches.
Why does diversification slow down in adaptive radiations?
Because available ecological niches (adaptive peaks) become filled, reducing opportunities for further divergence.
What is ecological opportunity?
The availability of unoccupied or newly available niches that drive adaptive radiation.
How do new resources drive ecological opportunity? Provide an example.
Emergence of new resources (e.g., expansion of grasslands) opens niches for radiation, as seen in concurrent insect–plant radiations.
How can extinction of species create ecological opportunity? Provide an example.
Removal of dominant species frees niches for radiating lineages, as after the K–Pg extinction mammals and birds diversified.
How does colonisation of new environments drive ecological opportunity? Provide an example.
Entering isolated settings like islands or lakes with few competitors allows rapid niche filling, as early colonists diversify before others arrive.
What are key innovations? Provide an example.
Novel traits that open access to new environments (e.g., wings in birds enabling flight into aerial niches).
What occurs as lineages radiate and fill adaptive peaks?
The rate of new phenotypic and species diversification slows as niches become saturated.
What are the two main categories of drivers of adaptive radiation?
Extrinsic drivers (ecological opportunity) and intrinsic drivers (evolvability).
What role does standing genetic variation play in evolvability?
High genetic diversity in populations provides raw material for rapid evolutionary change under new ecological opportunities.
How does introgressive hybridisation enhance evolvability?
It transfers genetic information between species through hybridisation and backcrossing, expanding variation and evolutionary potential.
How do modularity and integration affect evolutionary change?
Modularity allows traits to change independently for diverse outcomes, while integration links traits, directing coordinated adaptations.
What role does phenotypic plasticity play in adaptive radiation?
It enables flexible trait expression in new environments, allowing initial survival and subsequent genetic assimilation of beneficial traits.
What are dynamic genomes and how do they drive diversity?
Structural genomic changes (e.g., inversions, transposable elements) provide new genetic material for adaptive evolution.
What is the debate between trait modularity and integration?
Whether trait independence (modularity) facilitates diverse phenotypes or trait linkage (integration) coordinates adaptations but may constrain variation.
Why are Darwin’s finches a model system for adaptive radiation?
They exhibit rapid phenotypic divergence in beak morphology tied to ecological resource use, illustrating extrinsic and intrinsic drivers at work.
How do Darwin’s finches demonstrate the link between phenotypic and ecological divergence?
Variation in beak shapes corresponds to specialized feeding niches, showing morphological adaptation to ecological roles.
What does convergent evolution in Caribbean anole lizards illustrate?
Independent lineages evolving similar phenotypes in similar island habitats due to geographic isolation and ecological opportunity.
How do fitness landscapes help visualize adaptive radiation?
They depict adaptive peaks (niches) and valleys, showing how lineages diversify rapidly into peaks then slow as peaks fill.
What explains the lag phase in Darwin’s finch speciation?
After arrival, ~1.3 M years passed before rapid speciation began, indicating ecological opportunity alone isn’t enough—intrinsic evolvability factors must align with external drivers.
What diversity of bill forms occurs in Darwin’s finches?
Bills vary (crushing, probing, sharp, parrot-like), each matched to distinct diets and ecological niches.
What sequence of geographic phases drove finch diversification?
Initial allopatry (island isolation → drift, local adaptation, beak/song divergence) followed by sympatry with character displacement and reinforcement via song differences.
How does song divergence act as a pre-mating barrier?
Juveniles imprint on father’s bill appearance and song, guiding mate choice to reduce gene flow, though some hybridisation persists.
How does hybridisation influence finch phenotypic variation?
Introgressive hybridisation increases heterozygosity and beak-shape variance, adding raw material for selection.
What did whole-genome analyses reveal about finch species and beak genes?
There are 18 species (including cryptic ones); key beak-development genes predate the radiation and are repeatedly reused during speciation.
What three components underlie Darwin’s finch radiation?
Geography (isolated archipelago with new islands), ecological opportunity (early arrival, environmental fluctuations), and high evolvability (standing variation, hybridisation, modularity/integration, behavioral flexibility).
How does introgression help maintain adaptive potential?
By replenishing genetic diversity lost to drift or fixation, ensuring capacity to adapt to environmental changes.
What do haplotype blocks tell us about beak-shape genetics?
~28 distinct genomic blocks on different chromosomes control beak variation, indicating a modular genetic architecture.
What proportion of SNPs are shared between tree and ground finches, and why is that important?
~40% shared SNPs, showing ancient standing variation recycled across lineages.
Which loci are key for beak shape and size in finches?
The ALX1 locus (shape) and HMGA2 locus (size).
How is craniofacial integration measured, and what pattern emerges?
Landmark-based morphometrics show a strong positive correlation between beak and skull shape, reflecting tight integration.
How does craniofacial integration relate to radiation rates across bird groups?
Groups with higher integration (Darwin’s finches, Hawaiian honeycreepers) radiate faster; those with lower integration (some mockingbirds, honeyeaters) radiate less despite similar niches.
What are the contrasting views on modularity vs. integration?
One view: integration channels rapid shifts along a ‘line of least resistance.’ The other: modularity enables independent trait variation. Both may operate at different scales or phases.
Give examples of behavioral flexibility in Darwin’s finches.
Vampire finch blood-feeding on seabirds; ground finches innovating seed- and egg-cracking techniques.
What does the Flexible Stem Hypothesis propose?
Ancestral behavioral flexibility lets populations exploit niches first, with genetic assimilation later fixing advantageous behaviors.
How does genetic assimilation follow behavioral innovation?
Initially plastic behaviors become genetically encoded over generations, stabilizing new ecological adaptations.
What ecomorphs do Anoles in the Antilles evolve into?
Grass–bush, trunk–ground, trunk–crown, and crown–giant types, each adapted to distinct vegetation structures.
How do morphological and molecular analyses of Anoles differ?
Morphology groups by similar ecomorph; molecular phylogeny groups by island, indicating single colonization followed by in situ radiation.
What factors underlie convergent evolution in Antillean Anoles?
Similar adaptive landscapes across islands, evolutionary constraints, and historical contingency producing recurrent ecomorphs.
How do evolutionary constraints channel Anoles trait evolution?
Genetic correlations and developmental pathways direct change along ‘lines of least resistance,’ although alternative morphologies can arise.
What is historical contingency in adaptive radiation?
The initial ancestral phenotype of colonists biases which adaptive peak they occupy, leading to predictable outcomes when starting points match.
How do single-peak vs. rugged adaptive landscapes affect radiation?
Single-peak landscapes yield similar endpoints regardless of start; rugged landscapes lead to different peaks based on starting conditions.
What distinguishes microevolutionary from macroevolutionary adaptive radiations?
Micro: ~1–2 M yr in confined locales, filling fine niches (e.g., island finches). Macro: deep time, broad ranges, great morphological disparity (e.g., all bird bills).
What pattern is seen in phylogenetic morphospace analyses of bird bills?
A rapid early increase in disparity (steep slope) followed by a plateau or decline as niches saturate.
What are the two models describing micro vs. macro radiation?
Early morphospace expansion (quantum leaps) and later morphospace packing (fine-scale niche partitioning).
Give an example of macroscale bill diversity in birds.
The wide range from long, curved hummingbird bills to large, pouch-bearing pelican bills.
Why is ecological opportunity necessary but not sufficient for adaptive radiation?
Intrinsic evolvability (genetic variation, developmental features) must align with available niches for radiation to proceed.
What intrinsic features predispose lineages to radiation?
Genetic variation, developmental modularity, evolutionary constraints, and historical contingency.
Why shouldn’t micro- and macroevolutionary radiations be equated directly?
They operate on different timescales with potentially distinct dominant processes at each scale.
Which methodologies are essential to study adaptive radiation comprehensively?
Morphological studies, molecular phylogenetics, and ecological modeling.
Why is the Antillean Anoles radiation a prime example of convergence?
Independent island radiations repeatedly yield the same ecomorphs, showing predictable evolution under similar ecological pressures and constraints.
