Testing adaptive hypotheses: a case study Appl;y what you;ve learned so far in class Thought exercise: go basically a lot like an exam questio. Purpose of today is to have some discussion, ask questions, do some critiacal thinking and proactice applying the concepts you learned on Tuesday Going to go through a scenario... Similar to what you might see on an exam, should also help you figure out if you understand what’s going on or not in class so far.

Trinidad Venezuela John Endler Poecilia reticulata ...the wild guppy

Poecilia reticulata Lives in gravel-bottomed forest streams: headwaters to lowlands

Poecilia reticulata Lives in gravel-bottomed forest streams: headwaters to lowlands Great variation in coloration from population to population, even within the same stream

Poecilia reticulata Lives in gravel-bottomed forest streams: headwaters to lowlands Great variation in coloration from population to population, even within the same stream Lots of natural predators; generally more and the most ferocious are at lower elevations (downstream)

Poecilia reticulata Lives in gravel-bottomed forest streams: headwaters to lowlands Great variation in coloration from population to population, even within the same stream Up to 7 natural predators; generally more and the most ferocious are at lower elevations (downstream) Brightest guppy populations tend to live upstream: populations downstream are duller in color

Lives in gravel-bottomed forest streams: headwaters to lowlands Poecilia reticulata Lives in gravel-bottomed forest streams: headwaters to lowlands Great variation in coloration from population to population, even within the same stream Up to 7 natural predators; generally more and the most ferocious are at lower elevations (downstream) Brightest guppy populations tend to live upstream: populations downstream are duller in color Females are dull gray (and blend in with the stream bed) in all populations Females (always look like this)

Forming an adaptive hypothesis about wild guppies What are the necessary conditions for evolution by natural selection? 1. variation 2. heritability: offspring resemble parents 3. survival and reproduction are not random: consistent relationship between phenotype and fitness

Forming an adaptive hypothesis about wild guppies What are the necessary conditions for evolution by natural selection? 1. variation 2. heritability: offspring resemble parents 3. SELECTION: consistent relationship between phenotype and survival and reproduction What is an adaptation? The phenotypic variant that results in the highest fitness in a given environment

You can: Move and remove guppies and predators from streams Maintain and breed guppies in a laboratory Cross guppies from different populations Determine paternity/maternity of individual guppies Genetically engineer and clone guppies Spend years of your life on this project (i.e. allow many, many guppy generations to pass Anything else (within reason)

Endler’s experiments: The phenotype of each population is adapted, and is the result of the local balance of sexual and predator selection If the balance of sexual and predator selection is changed, the phenotype should evolve in response Environment-dependent

Endler’s experiments: Greenhouse pool experiment Set up guppy populations in pools in a greenhouse Foundation population highly variable Sexual selection constant (always) Vary predation pressure Vary environment Track phenotypes through time: number, size, location, color variation of spots

Endler’s results: “innocuous” predator Ponds with no predators (K) showed a steady increase in the # of spots control “voracious” predator Little change in spot # (compared to the control) after addition of the innocuous predator (R) Pools that received a voracious predator treatment (C) showed a marked decrease in the # of spots Foundation population Treatments applied

Summary of greenhouse experiment: Phenotypes evolved in response to changes in the balance of sexual and predation selection

Endler’s experiments: 2. Field transplant in Trinidad Each population has an adapted phenotype, reflecting the local balance of sexual and predation selection. If evolution was “replayed”, the same adapted phenotype would evolve.

Endler’s experiments: 2. Field transplant in Trinidad Each population has an adapted phenotype, reflecting the local balance of sexual and predation selection. Trinidad stream: 3 sites... 1 2 3 2 km Guppies, innocuous predator and dangerous predator present No guppies: innocuous predator present Both guppies and innocuous predator present Transplanted 200 guppies from site 3 to site 1, measured phenotypes 10 months later. Population 1 should evolve the same phenotypes as population 2 (site 1 = site 2).

Endler’s field experiment: results In site 1 (x).... Spot size, number and color diversity increased Color pattern converged on that of fish in site 2 (r) c = site 3 (source pop), x = site 1 (transplant site), r = site 2

Endler’s work: Conclusions Demonstration of natural selection in action Evolutionary hypotheses are experimentally testable