Evolutionary Engineering Mark D. Rausher Department of Biology Duke University

Evolutionary Biology—largely an academic science Until recently, few applied applications May explain reluctance of many to accept fact of evolution

Evolutionary Biology—largely an academic science Until recently, few applied applications May explain reluctance of many to accept fact of evolution Recent applications of evolutionary principles disease management fisheries management biomolecular engineering computer design

Evolutionary Biology—largely an academic science Until recently, few applied applications May explain reluctance of many to accept fact of evolution Recent applications of evolutionary principles disease management fisheries management biomolecular engineering computer design resistance management

Evolutionary Biology—largely an academic science Until recently, few applied applications May explain reluctance of many to accept fact of evolution Recent applications of evolutionary principles disease management fisheries management biomolecular engineering computer design resistance management biological control

resistance management The Problem: Pests evolve counter-resistance to resistant crops, often within 5-10 years Genetically engineered crops cost millions of $$ and take up to a decade to develop Genetically engineered crops need an expected lifetime of more than 10 years to recoup investment

resistance management The Problem: Pests evolve counter-resistance to resistant crops, often within 5-10 years Genetically engineered crops cost millions of $$ and take up to a decade to develop Genetically engineered crops need an expected lifetime of more than 10 years to recoup investment How can the evolution of counter-resistance be delayed or prevented?

resistance management The Solution: Evolutionary Engineering Active manipulation of the evolutionary process for desired outcomes Involves manipulation of environment or genetics of pest population Relies on population genetic principles to guide manipulation

resistance management The Strategy: HDR motivated by desire to develop strategy for delaying evolution of counter-resistance by insects to Bt toxins pest-management workers, U.S. EPA, large corporations implementing HDR strategy engineer crops to produce High Dose of toxin intermix Refuges of susceptible plants with resistant plants

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles R recessive if rr, Rr have same value of trait RR has different value of trait R dominant if RR, Rr have same value of trait rr has different value of trait

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles Equation for change in gene frequency at a counter-resistance locus: p R = p R (p R W RR + p r W Rr )/ (p R W RR + 2p R p r W Rr + p r W rr ) 2 2 ’ p R, p r = frequencies of counter-resistant and susceptible alleles W ij = fitness of genotype ij W RR > W rr

W RR = 1.0, W rr = 0.5

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles make counter-resistance recessive

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles make counter-resistance recessive use High Dose of toxin

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles make counter-resistance recessive use High Dose of toxin

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles make counter-resistance recessive use High Dose of toxin

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles make counter-resistance recessive use High Dose of toxin 2.Rate of increase of advantageous allele is proportional to the difference in fitness between genotypes.

resistance management s = W RR - W rr

resistance management Evolutionary Principles Underlying HDR Strategy 1.Advantageous recessive alleles increase in frequency much more slowly than dominant or co-dominant alleles make counter-resistance recessive use High Dose of toxin 2.Rate of increase of advantageous allele is proportional to the difference in fitness between genotypes. reduce fitness advantage of resistant homozygote use Refuges

resistance management Evolutionary Principles Underlying HDR Strategy Refuge: plants lacking resistance gene interplanted among resistant plants. Resistant Plant

resistance management Evolutionary Principles Underlying HDR Strategy Refuge: plants lacking resistance gene interplanted among resistant plants. Resistant PlantSusceptible Plant

resistance management Evolutionary Principles Underlying HDR Strategy Refuges reduce fitness difference Insect Fitness GenotypeNon-Refuge rr 0 Rr 0 RR 1

resistance management Evolutionary Principles Underlying HDR Strategy Refuges reduce fitness difference Insect Fitness GenotypeNon-Refuge Refuge rr 0 1 Rr 0 1 RR 1 1

resistance management Evolutionary Principles Underlying HDR Strategy Refuges reduce fitness difference Insect Fitness GenotypeNon-Refuge Refuge rr 0 1 Rr 0 1 RR 1 1 If β is the proportion of plants that are refuge plants, then...

resistance management Evolutionary Principles Underlying HDR Strategy Refuges reduce fitness difference Insect Fitness Overall GenotypeNon-Refuge Refuge Fitness rr 0 1 β Rr 0 1β RR 1 11

resistance management Simulation of HDR strategy W RR = 1, W rr = W RR = 0 βββ

resistance management Conclusions: 1. HDR Strategy can delay evolution of counter-resistance 2. Refuges constituting 10-20% or more of plants are needed to delay evolution of counter-resistance for substantial periods

biological control Genetic control of pest organisms Introduction of low-fitness genotypes into a population by mass release sterile male eradication of screwworm populations attempts to suppress sheep blowfly by introducing lethal alleles

biological control Genetic control of pest organisms Introduction of low-fitness genotypes into a population by mass release sterile male eradication of screwworm populations attempts to suppress sheep blowfly by introducing lethal alleles often unsuccessful require ability to mass rear organism sustained release required—natural selection opposes

biological control Evolutionary control of pest organisms Manipulate evolutionary process to force evolutionary fixation of lethal or sterile mutants

biological control Evolutionary control of pest organisms Manipulate evolutionary process to force evolutionary fixation of lethal or sterile mutants Meiotic drive (Segregation Distortion) o preferential inheritance of one allele over another in gametes of heterozygotes Normal Mendelian Segregation 50% of gametes R Rr 50% of gametes r

biological control Evolutionary control of pest organisms Manipulate evolutionary process to force evolutionary fixation of lethal or sterile mutants Meiotic drive (Segregation Distortion) o preferential inheritance of one allele over another in gametes of heterozygotes Segregation Distortion 100% of gametes R Rr 0% of gametes r

biological control Evolutionary control of pest organisms Manipulate evolutionary process to force evolutionary fixation of lethal or sterile mutants Meiotic drive (Segregation Distortion) o preferential inheritance of one allele over another in gametes of heterozygotes o driven allele rapidly increases in population o link lethality or sterility to driven allele

biological control Evolutionary control of pest organisms Normal Chromosome Driven Chromosome Recessive Female Sterility elementDrive element

biological control Evolutionary control of pest organisms

biological control Evolutionary control of pest organisms

biological control Evolutionary control of pest organisms

biological control Evolutionary control of pest organisms

biological control Evolutionary control of pest organisms

biological control Evolutionary control of pest organisms

biological control Evolutionary control of pest organisms

biological control Evolutionary control of pest organisms EXTINCTION

biological control Evolutionary control of pest organisms EXTINCTION Will this really work?

biological control Model Assumptions SD is partial to complete SD may affect male gametes, female gametes, or both Female homozygotes for driven allele sterile or inviable Female heterozygotes may have reduced fitness Male heterozygotes may have reduced fitness

biological control Model Equations Male gamete freq.: p = (P+γαQ)/(P+αQ+R) Female gamete freq: p = (P+δβQ)/(P+βQ) P, Q, R are genotype frequencies p = [pp+γα(pq+qp)]/ [pp+α(pq+qp)+qq] p = [pp+δβ (pq+qp)]/ [pp+β (pq+qp)] N = [R + βQ] N e r(1—N/K) ˜ ’ ˜ ’ ˜˜ ˜˜˜˜˜˜ ˜˜˜˜˜ ’

biological control Case 1 Complete male drive No drive in females Female fertility of heterozygotes = 0.5 — 1

biological control Case 1 Complete male drive No drive in females Female fertility of heterozygotes = 0.5 — 1 Genotype FrequenciesPopulation Size P Q R r = 7.4 r = 7.4, β=1 r = 2.7, β=1 r = 2.7, β=0.5

biological control Case 2 Complete female drive No drive in males Female fertility of heterozygotes = 0.5 — 1

biological control Case 2 Complete female drive No drive in males Female fertility of heterozygotes = 0.5 — 1 Genotype FrequenciesPopulation Size P Q R

biological control Conclusions By linking a female-sterile or female-fertile mutant to a meiotic drive agent, pest populations can be forced to evolve to extinction Female-drive likely to be more effective than male drive Male drive can be effective if population rate of increase is high enough A single, small release can be effective

biological control Caveats It will be some time before drive elements can be genetically engineered/manipulated Efficacy of strategy needs experimental verification Likely to be just one more tool in biological control arsenal

Evolutionary Engineering Altering the course of evolution in desirable directions by manipulating the environment and genetics of pest organisms has begun and shows promise.