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OSU / Biology / BIOLOGY 1114 / parthenogenosis




School: Ohio State University
Department: Biology
Course: Form, Function and Ecology
Professor: James chiucchi
Term: Summer 2015
Tags: Biology, ecology&evolution, evolution, and Biology: Ecology and Evolution
Cost: 25
Name: Biology 1114, Week 6 Notes
Description: These notes cover everything that was gone over in lecture on Sex and Sexual Selection
Uploaded: 02/21/2017
4 Pages 95 Views 0 Unlocks

What mating strategy would optimize fitness for individuals of each sex?

Why is it usually males competing for females?

Why is variation beneficial?

Biology 1114 Sex and Sexual Selection 1. SEX AND SEXUAL SELECTION A. Modes of reproduction a. Asexual Reproduction i. Formation of offspring without the fusion of egg and sperm ii. Offspring are genetically identical to parent iii. Modes of asexual reproduction: 1. Budding- offspring develop as outgrowth of pareIf you want to learn more check out judson jahn clemson
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nt  2. Fission- parent splits into 2 organisms of roughly equal size 3. Root Suckering- many clonal individuals sprout from  the roots of an individual a. EX: Pando the quaking aspen (“I spread” in Latin) i. Started roughly 80,000 years ago ii. Started with one single aspen iii. Covers more than 100 acres iv. Is Pando one individual or many close  individuals? 4. Parthenogenosis- unfertilized egg develops into  offspring a. Whiptail lizards i. Entire species is female, reproduce  parthenogenically ii. Still display courtship/mating behavior 1. Associated with hormone levels during breeding season iii. Females mounted by “male-like” females  more likely to ovulate and lay more eggs b. Sexual Reproduction i. Formation of offspring by fusion of a female gamete (egg) and male gamete (sperm) ii. Offspring are genetically distinct and inherit traits form both  parents iii. Offspring are not identical to either parent B. Does Sex Make Sense? a. From evolutionary perspective, the reproductive mode that  produces the most offspring should be the most frequent  b. Sexual reproduction: i. Leads to a stable population number 1. Only half of individuals can bear offspring (limited to  females) ii. Cannot mate in isolation; a mate that wants to mate with you  is required c. Asexual reproduction:i. Leads to a much bigger population 1. Not limited by the number of females 2. All individuals can bear offspring  ii. Can reproduce in isolation d. So why sex? i. Ubiquity- seen in eukaryotes 1. Prokaryotes also have modes of recombination ii. Historic extinction rates 1. Asexual lineages have higher extinction rates than  sexual lineages do C. Advantages of Sex a. Variation i. Sexual 1. Beneficial alleles can be rapidly combined in offspring a. Can rapidly spread through a population 2. Produces new combinations of alleles ii. Asexual 1. Offspring are clones of parents a. Beneficial alleles are not combined in offspring 2. Each lineage would have to independently gain  beneficial alleles a. Since mutation is random, takes much longer iii. Why is variation beneficial? 1. Allows population response to changing environment via selection 2. Makes a population more likely to survive future  environmental changes b. Fewer Deleterious Alleles i. Sexual 1. Elimination of deleterious phenotypes 2. Results in a much more vigorous population ii. Asexual 1. Since offspring are clones, all parental mutations are  passed to offspring 2. Over time, due to random chance, all subsets of the  population acquire deleterious alleles a. Now 1 deleterious allele is the norm 3. Over time more and more deleterious alleles will  become the norm in a population 4. Mutation meltdown- over time in asexual populations, proportions of low fitness individuals with many  deleterious alleles increases a. Eventual consequence = extinction b. Mutation meltdown + lower variation explains  greater extinction rates of asexual lineagesD. Sexual Selection- individuals with certain inherited characters are more  likely than others to attract mates a. Form of natural selection b. Why is it usually males competing for females? i. Reproductive differences E. Reproductive Differences Between Males and Females a. Females i. Gametes: eggs are limiting 1. Produce limited number per breeding opportunity  ii. Parental care 1. When it occurs, often falls on female a. Gestation, lactation, guarding, feeding, etc… 2. Greater energetic cost to raising young iii. Gametes limited, high PI b. Males i. Gametes: excess of sperm 1. Not limited by sperm available during breeding season ii. Parental care 1. Males often provide no parental care- mate and leave 2. Lower energetic cost to raise young iii. Gametes NOT limited, low PI c. Operational sex ratio (OSR) – ratio of males in a population that  are ready to mate with females in that population that are ready to  mate i. Skewed male OSR results from differences in number of ready  gametes produced between males and females 1. Lots of male, few of female d. Differential parental investment (PI) – measured as each  parent’s contribution to rearing offspring  e. What mating strategy would optimize fitness for individuals of each  sex? i. Female: 1. Find a mate with beneficial alleles or good resources so  offspring have a better chance of survival 2. Be very choosy ii. Male: 1. Mate with as many partners as possible and leave  rearing to them if possible  iii. These strategies are in direct conflict  1. Average reproductive output = the same between sexes F. Variation within Selection  a. Female reproductive success: Relatively uniform i. Not limited by mating opportunities because males are trying  to mate with as many as possible ii. Limited egg resourcesiii. Limited by resources required to raise young b. Male reproductive success: Variable i. Limited by mating opportunities 1. Females chose only high quality males 2. Males that can demonstrate quality are preferred  c. Average reproductive success between sexes it equal, but males  experience the most variation within themselves on who is having  the most offspring G. Variable reproductive success a. Selection acts on variation i. Stronger in males because of greater variation in  reproductive success b. Selection for characteristics that allow greater access to mates i. Characteristics that allow defense of territories/resources and  thus greater access/opportunity to mate ii. Characteristics that result in greater female choice

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