Cross-Dressing Salmon By Tom Horvath (adapted with changes by Julie Korb) SUNY College at Oneonta

CQ#1: Which statement best describes natural selection? Survival of the fittest. The strongest individuals get to reproduce. The best adapted individuals survive and reproduce. Survival and reproduction is a matter of luck.

http://www.youtube.com/watch?v=5DqjsWsY8-g

CQ#2: Out of all the eggs a female lays, how many hatchlings (or smolts) do you think will survive to spawn? 50% (50 out of 100) 10% (10 out of 100) 1% (1 out of 100) 0.1% (1 out of 1000) Less than 0.1 % Mass of fertilized salmon eggs

About 0.03% survive & reproduce themselves Source: http://www.fws.gov/r5cneafp/survival.gif About 0.03% survive & reproduce themselves

Which are the lucky few who make it to reproduce? Rhetorical

Charles Darwin’s Theory of Natural Selection It is not just random luck. Some individuals have a better chance of surviving and reproducing than others. Source: http://en.wikipedia.org/wiki/Image:Charles_Darwin_by_G._Richmond.jpg

CQ#3: Are all these smolts ABSOLUTELY identical? A: Yes B: No http://www.bpa.gov/corporate/BPANews/Library/images/fish/

Variation in salmon translates into variations in survival and reproductive success.

Theory of Evolution by Natural Selection More offspring produced than survive to adulthood (OVERPRODUCTION). Variation among individuals of a species.

What good is variation? Talk to your neighbor and list as many characteristics a salmon may possess that helps it survive.

ADAPTATION Any characteristic that improves the survival or reproductive success of an organism. Often the result of natural selection. Organisms match closely with their environment.

Survival is only half the story – you have to reproduce to pass on those good traits that aided survival to this point.

Theory of Evolution by Natural Selection More offspring produced than survive to adulthood (OVERPRODUCTION). Inheritable variation among individuals of a species. Best adapted individuals survive and reproduce (UNEQUAL REPRODUCTIVE SUCCESS).

Typical Dominant Male Phenotype www.fws.gov http://www.arkive.org/atlantic-salmon/salmo-salar/video-09a.html?offset=0pt

The most dominant males (usually largest and most aggressive) successfully defend their redds and inseminate the eggs. Smaller males that also have the kype lose out in head-to-head competition with larger males. CQ#4: Are we seeing “survival of the fittest” in action here? A. Yes B. No www.salmonsociety.com

A Different Type of Male Female Mimic http://www.pac.dfo-mpo.gc.ca/recfish/Species/sockeye_e.htm Lack dominant male characteristics (e.g., no kype). Appear more female-like. Disadvantage: They can’t compete head-to-head with dominant males either, but….

Why don’t female mimics get weeded out through natural selection if they are not fit?

CQ#5: Why are female mimics still found in each generation? Some outcompete the dominant males in the redds. They appear from mutations randomly each generation. They have a different reproductive strategy from dominant males and it works. Some females change into males under stressful environmental conditions. http://www.fs.fed.us/r10/tongass/districts/mendenhall/fishcam/images/sockeye_female.jpg

Cross-Dressing Salmon Female mimics can stay near the redds because dominant males don’t see them as competition; they think they are females. These fish get a brief chance to inseminate a few eggs before being ultimately bumped out by dominant males. http://www.pac.dfo-mpo.gc.ca/recfish/Species/sockeye_e.htm

CQ#6: Even though female mimics are not dominant, are they fit. A CQ#6: Even though female mimics are not dominant, are they fit? A. Yes B. No www.salmonsociety.com

Survival of the Fittest? Source: http://www.arkive.org/species/ARK/fish/Salmo_salar/Salmo_salar_09a.html?movietype=rpMed Darwinian fitness: contribution an individual makes to the gene pool of the next generation relative to the contribution of others.

Fitness can be compared with relative values (values from 1 to 0) A fitness value of 1 is assigned to the phenotype with the highest representation. All other phenotypes are assigned based on their reproductive success relative to the dominant type.

Fitness Value Example Dominant male phenotype produces 300 male offspring in the next generation. Female mimic phenotype produces 50 male offspring in the next generation. Small male phenotype produce only 5 male offspring. Dominant Male Phenotype – Fitness = 300/300 = 1.0 Female Mimic Phenotype – Fitness = 50/300 = 0.17 Small Male Phenotype – Fitness = 5/300 = 0.02

Natural Selection Analyzing change in frequency of traits in a population: Three patterns emerge: Directional selection Stabilizing selection Diversifying selection

Natural Selection Directional Selection -Individuals of one extreme phenotype favored. Stabilizing Selection - Individuals with intermediate phenotype favored; Extreme phenotypes selected against. Diversifying Selection - Both extreme phenotypes favored; intermediate phenotypes selected against.

Directional Selection Individuals of one extreme phenotype favored Population under directional selection Population with no natural selection Frequency Similar (and better) images can be found in most text books Body Size of Salmon

Stabilizing Selection Individuals with intermediate phenotype favored; extreme phenotypes selected against Population under stabilizing selection Frequency Population with no natural selection Similar (and better) images can be found in most text books Body Size of Salmon

Diversifying Selection Both extreme phenotypes favored; intermediate phenotypes selected against Population with no natural selection Population under disruptive selection Frequency Similar (and better) images can be found in most text books Body Size of Salmon

CQ#7: Given our fitness value from the example, which pattern of selection would we expect in the salmon population? Directional selection Stabilizing selection Diversifying selection Unnatural selection

CQ#8: Do individuals have to be the “strongest” to be fit? Yes No

CQ#9: Which of these traits might confer fitness upon an individual? Being sneaky and tricking the dominant males into letting you hang around the spawning females. Having an awesome hook on your jaw and large body size. Having sperm that are extra good at finding and fertilizing eggs. Being extra good at storing fat, which will fuel all that waterfall jumping while migrating upstream. Any of the above will increase fitness.