New User Special Price Expires in

Let's log you in.

Sign in with Facebook


Don't have a StudySoup account? Create one here!


Create a StudySoup account

Be part of our community, it's free to join!

Sign up with Facebook


Create your account
By creating an account you agree to StudySoup's terms and conditions and privacy policy

Already have a StudySoup account? Login here


by: La-Teisha Allen
La-Teisha Allen

GPA 3.52

Preview These Notes for FREE

Get a free preview of these Notes, just enter your email below.

Unlock Preview
Unlock Preview

Preview these materials now for free

Why put in your email? Get access to more of this material and other relevant free materials for your school

View Preview

About this Document

Natural Selection
John Howard Roe
Class Notes
artificalselection, natural selection, directional, mechanisms of selection, tradeoffs, constraints
25 ?




Popular in Evoloution

Popular in Biology

This 5 page Class Notes was uploaded by La-Teisha Allen on Saturday September 10, 2016. The Class Notes belongs to BIO 4220-001 at University of North Carolina at Pembroke taught by John Howard Roe in Fall 2016. Since its upload, it has received 3 views. For similar materials see Evoloution in Biology at University of North Carolina at Pembroke.


Reviews for Evolution


Report this Material


What is Karma?


Karma is the currency of StudySoup.

You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!

Date Created: 09/10/16
Natural Selection Notes Types, Dimensions, and Constraints Artificial Selection – modern examples • Illinois Long-Term Selection Experiment on Corn (1896 – current) – selectively bred corn for either high (top 20%) or low (bottom 20%) oil content – generated corn with extreme oil content well beyond the initial variation (limits of original population) • Russian Farm-Fox Experiment (1959 – current) – selectively bred silver foxes for tameness (behavior) – numerous other unintended traits (side-effects) became more common Population thinking • both Artificial Selection and Natural Selection – process of “sculpting phenotypes” by “sculpting the gene pool” – systematic increase or decrease in gene/phenotype in population = Evolution Linking Artificial and Natural Selection Scientific Thinking • Artificial Selection is a manipulative experiment • Hypothesis: non-random survival of random geneticàphenotypic variation as cause of evolution – Artificial: human eyes as selective agent – Natural: nature as selecting agent (differential survival and reproduction) Natural Selection – Directions A. Directional Selection (positive or negative) • Favors indiviudals near one end of phenotypic spectrum B. Stablizing Selection • Favors individuals with intermediate phenotypes C. Disruptive (Balancing) Selection • Favors indiviuals with both extreme phenotypes Disruptive (Balancing) Selection • European Garden Snails – variation in shell color – uniform dark morphs favored on forest floor – yellow striped morph favored in grass – habitat patchiness maintains variation • Pacific Salmon spp. males exhibit alternative life history and breeding strategies – Hooknose mature late (3 yr) at larger size (70 cm) • fighting, nest guarding – Jacks mature early (2 yr) at smaller size (40 cm) • hide and sneak fertilizations – Intermediate sizes? – Too small to fight, too large to hide ESS or BBS? Relative Fitness depends on not only own strategy, but strategy of competition • Evolutionarily Stable Strategy (ESS) – Where phenotypic strategy cannot be successfully invaded by variant (all individuals in a population employ the same) – Mixed ESS allows for multiple strategies to coexist at stable equilibrium • can change as Selective Environment shifts • Strategy= genetically hard wired • Best of a Bad Situation (BBS) – Where multiple phenotypic variants coexist in population with hierarchy of success • one best strategy has highest fitness payoff relative to alternate strategies • other lower fitness strategies represent individuals making the most of their constrained situation • Not genetically hard wired Frequency-Dependent Selection • Frequency-dependent selection: when selective advantage of a phenotype depends on its frequency in the population – rare phenotype is favored – adaptive trait shifts with Selective Environment Viability vs. Fecundity Selection • Male birds of paradise showy have plumage and attention-grabbing displays • - increase mating oppurtunities at expense of survival • Female drab coloring and secretive behavior • Increase survival by avoiding predators Phenotypic Variation Tradeoff: balance/compromise achieved among competing, incompatible features No such thing as a free lunch! Tradeoffs in Reproductive Investment • Invest in a few showy flowers and energy-rich nectar to attract pollinator (e.g., hummingbird) – targeted fertilization • Invest in millions of pollen grains and broadcast them into environment, dispersed by wind – non-targeted fertilization Tradeoffs in Survival Investments • Mexican cavefish divert resources from building/maintaining eyes to invest in sensory capacity of jaws, taste buds, teeth • Star-nosed moles divert resources from eyes to improving tactile and chemical sensitivity on nose tubercles Tradeoffs between Survival and Reproduction • Flightlessness common among island birds – diversion of resources from flight (energy, materials to build wings and muscles) – increased investment in larger body size and reproduction – How does the selective environment differ from mainland? Dimensions • Evolution can occur in two primary dimensions – Cladogenesis • temporal (vertical) change in a population – Anagenesis • spatial (horizontal) change between reproductively isolated populations Constraints adaptations are rarely perfect 1) Source of variation is random  no preordained directional goals 1) Tradeoffs • Competing allocations/functions within individual • Multiple selective agents in environment 1) Can only “tinker” with existing parts 1) Selective Environments change Source of Variation is Random • Lots of ways for variation to appear in a population (e.g., mutation), but limits on rate of occurrence – genetic mutations are usually repaired • If particular variation never occurs, trait variant never appears Tradeoffs competing allocations and functions in individual • Physical Constraints: • Investing in extra long legs could be beneficial (reaching higher food, running faster) • But they would more easily break ( inc. risk of injury) • Resource Allocation: • Investing more calcium in bones can strengthen them • But there would be less calcium for other uses ( feeding offsprng via lactation) • Owl has eyes that face forward • Pro: binocular vision improves visual acuity in front (catching food) • Con: limited field of view increases vulnerability to predators (mortality) • Ostrich has eyes on side of head • Pro: can see predators approaching from all sides (survival) • Con: harder to catch prey (food acquisition) Natural Selection can only tinker with existing parts • Freshwater mussels modify the mantle to crudely resemble a fish – larva require fish gills to develop – lure predatory fish close enough to infect (prey make false- positive error) • Anglerfish modify dorsal fin spine to vaguely resemble a food item – sit-and-wait predators – lure predators close enough to engulf (prey make false-positive error) • Bird feathers served original function of insulation and signaling – first fossil evidence of feathers in animals that did not fly – feathers later modified for flight as well • Snake venom original function for digestion – venom full of digestive enzymes, many snakes have mild venom for only digestive purposes – venom delivery apparatus later modified in some snakes for defense as well (spitting cobra) Adaptation or Exaptation? • Adaptations: – trait must be shaped by Natural Selection and serve the same primary function in current Selective Environment as it did in past • Exaptation: – trait must be shaped by Natural Selection and serve different primary function in current Selective Environment than it did in past • trait was co-opted, re-worked, and tweaked for new purpose • “Concluding that feathers evolved for flight is like maintaining that digits evolved for playing the piano” (Prum and Brush 2002) Selective Environments Change moving targets • Natural selection favors trait variants that are immediately beneficial, not variants that may be favorable in the future – shaped by past and current Selective Environments, cannot anticipate the future • Abiotic and biotic Selective Environments are constantly changing – abiotic: • climate shifts between ice age and hot periods (thousands to millions of years), flood and drought (years to centuries), seasonal variation in temperature and rainfall – biotic • predator/prey, host/parasite, competitive or mutualistic interactions


Buy Material

Are you sure you want to buy this material for

25 Karma

Buy Material

BOOM! Enjoy Your Free Notes!

We've added these Notes to your profile, click here to view them now.


You're already Subscribed!

Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'

Why people love StudySoup

Bentley McCaw University of Florida

"I was shooting for a perfect 4.0 GPA this semester. Having StudySoup as a study aid was critical to helping me achieve my goal...and I nailed it!"

Jennifer McGill UCSF Med School

"Selling my MCAT study guides and notes has been a great source of side revenue while I'm in school. Some months I'm making over $500! Plus, it makes me happy knowing that I'm helping future med students with their MCAT."

Steve Martinelli UC Los Angeles

"There's no way I would have passed my Organic Chemistry class this semester without the notes and study guides I got from StudySoup."

Parker Thompson 500 Startups

"It's a great way for students to improve their educational experience and it seemed like a product that everybody wants, so all the people participating are winning."

Become an Elite Notetaker and start selling your notes online!

Refund Policy


All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.