Week’s Lab IV: Student-Driven Project 1 Complete Homework 6 at home: Correlation/Regression Bring 3 abstracts to trade with group + TA Complete SDP1 Proposal Worksheet - Indiv. Use pg DRESS WARM + DRY!!!

Next lecture Chapter 11: Sex and Evolution

EXAM 1 next Tuesday 12:30 here Lectures/Chapters thru Thursday Practice exam with answers: On course website on Exam date Format: Choice of ?s to answer Longer: 4 of 5 (interpret figures) Shorter: 4 of 6 Questions? 6

***Sample exam question. A species of scale insects extracts fluids from branches of pine trees. They have very limited movement. In an experiment, these insects were transplanted 1) between branches of the same pine tree, and 2) from one pine tree to another pine tree of the same size.

1.State the hypothesis/prediction that was being tested as an “If…then…” 2.Summarize the results in one concise sentence. 3.Do the results support the hypothesis? 4.Predict whether gene flow or natural selection would be a more powerful force affecting the genetic structure of this insect. Explain your choice. 5. Predict whether the genetic makeup of populations of the insect on adjacent trees would be homogeneous or differentiated. Explain your choice.

Today:Ch 10: Life Histories and Evolution

Objectives Define life history How to study life history? Correlated life history traits in contrasting environments Resource allocation and tradeoffs Age of maturity Fecundity Parity (no. times reproduce/lifetime) Aging and lifespan

*** Sample exam question Life history traits often represent ‘tradeoffs’. Graph the expected relationship for each pair of traits. Label axes. Then explain the nature of each tradeoff. A. Seed size vs. seed number 1. Graph 2. Explanation B.Number of offspring per breeding attempt vs. adult survival between successive breedings 1. Graph 2. Explanation

A search for a set of rules when particular traits affecting reproduction and survival may be favored by natural selection.

How study life history evolution? Wide variation among organisms in life history traits: use of comparative methods temperatetropical

Clutch size of birds increases with latitude. Latitude Clutch size ***Possible hypothesis?

***Experimental test of hypothesis: Number of eggs per clutch is limited by food supply. Normal clutch size = 7. Do the data support the hypothesis? What type of selection does this demonstrate? a.Directional b.Stabilizing c.Disruptive Is genetic variation being maintained or reduced?

Lack: life history in an evolutionary context. As life history traits contribute to reproductive success, they influence evolutionary fitness. Life histories vary consistently with environmental factors; hence may be molded by natural selection.

A search for a set of rules when particular traits affecting reproduction and survival may be favored by natural selection.

Life histories vary along a slow-fast continuum. Traits are correlated in contrasting environments. Slow (K-species) = in persistent habitats population near carrying capacity slow development delayed maturity large adult size low reproductive rate high parental investment/offspring low mortality long life low dispersal Fast (r-species) = in disturbed habitats population can grow rapidly opposite traits

Life history results from rules and choices influencing survival and reproduction. Juvenile survival

Life history: schedule of organism’s life, including: age at first reproduction (maturity) number and size of offspring (fecundity) number of reproductive events (parity) aging (life span) The values of these traits are solutions to the problem of allocating limited time and resources among various structures, physiological functions, and behaviors.

Resource Allocation Organisms face a problem of allocation of scarce resources. (or can organisms increase overall performance without trading off one function against another?)

Alternative pathways for resource allocation growth reproductionmaintenance Energy + matter reproduction increased survival increased competitive ability immediate profit delayed profit increased numbers

Tradeoffs: Allocation of time, energy, or materials devoted to one structure or function cannot be allotted to another. Costs: Allocation to current reproduction affects survival, growth, and future reproduction.

Investing in reproduction lowers survival.

***Tradeoffs 1.Graph 2.Explain Looking for correlation or cause/effect? Can axes be switched? Prob of survival for 15 yr No. fruits per year No. flowers in 1st season Plant size in 2nd season

Variation in one life history trait is often correlated with variation in other traits.

*** Explain this tradeoff: reproduction vs. mortality

***Does this experiment support the ‘tradeoff hypothesis’ of parental care vs. adult survival? Explain. Prop surviving Brood size

Life histories balance trade-offs between current reproduction and future reproduction. Great variation among organisms in resolving the fundamental tradeoff between fecundity and adult growth and survival. Principle: limited time and resources are allocated among competing functions so as to maximize lifetime reproductive success.

Major life history traits 1 Age of Maturity 2 Fecundity 3 Parity (# times reproduce) 4 Aging and lifespan

1) Age of Maturity When should an organism begin to breed?

*** Summarize the major result. What explains the pattern?

What determines age of maturity? Affects generation time and rate of entry of genes into gene pool Benefit to not delay: immediate fecundity Benefit to delay: (if have relatively long lifespan)  may have age-related gains in fecundity from growth or experience BUT cost to delay: May have risk of mortality with time May have reduced fecundity at later ages

***Is there a fecundity advantage by delaying age at first reproduction? When should an individual with a lifespan of 3 begin to reproduce? A lifespan of 7?

Growth vs. Fecundity If indeterminate growth, Fecundity is related to body size; Increased fecundity in one year reduces growth, and thus fecundity, in future. Short-lived emphasize fecundity over growth High extrinsic adult mortality rates favor increased reproductive effort, or investment in offspring, at expense of adult survival and future reproduction. Long-lived emphasize growth over fecundity

Reproductive value (V x ): takes into account prob. survival and future reproduction. It rises then falls during lifetime. Natural selection is strongest at highest V x..

2) Fecundity: How many offspring per reproductive bout? Fecundity vs. parental investment/offspring seed size vs. seed number egg size vs. egg number Variation in seed and egg size among species

3) Parity How many times to reproduce per lifetime? Semelparous (monocarpic) once Iteroparous (polycarpic) repeated

If semelparous, at what year to undergo ‘big-bang’ reproduction? Annual Biennial Long-lived

Semelparity: When payoff for reproduction is highly variable but favorable conditions are predictable from environmental cues? When pollinators attracted to massive display? When seed predators become satiated?

Semelparity: When preparation for reproduction is extremely costly?

Iteroparity: When low current reproduction results in maintaining high future reproduction.

Annual vs. Biennial vs. Perennial… How much fecundity is required so number of offspring of annual > perennial? F A > F P + S adult /S juvenile How high fecundity is required for delayed semelparity > no delay? F delayed > (S juvenile x F annual ) # yr delay What is proportion of annuals, biennials, perennials? Which is most rare? Why?

4) Aging and Lifespan Senescence is a decline in physiological function with age. Causes decline in fecundity and survival

Hypotheses Antagonistic pleiotrophy good early tied to bad late Accumulation of harmful mutations

Why does aging vary? Not all organisms senesce at same rate, suggesting that aging may be subject to natural selection and evolutionary modification. Strength of selection diminishes on traits expressed at progressively later ages.

Strength of selection varies with mortality rate. If high mortality, few reach old age  little selection for mechanisms to prolong life.

Individuals in populations with high extrinsic mortality rates age faster.

*** Sample exam question Life history traits often represent ‘tradeoffs’. Graph the expected relationship for each pair of traits. Label axes. Then explain the nature of each tradeoff. A. Seed size vs. seed number 1. Graph 2. Explanation B. Number of offspring per breeding attempt vs. adult survival between successive breedings 1. Graph 2. Explanation

Objectives Define life history How to study life history? Correlated life history traits in contrasting environments Resource allocation and tradeoffs Age of maturity Fecundity Parity (no. times reproduce/lifetime) Aging and lifespan

Vocabulary