PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Chapter 46: ANIMAL REPRODUCTIONMany aspects of animal form and function can be viewed as adaptations contributing to reproductive success. Individuals are transient. Individuals are transient. A population transcends finite life spans only by reproduction, the creation of new individuals from existing ones. There are two principal modes of animal reproduction. Asexual reproductionAsexual reproduction is the creation of new individuals whose genes all come from one parent without the fusion of egg and sperm. In most cases, just mitotic cell division w/o meiosis & syngamy. {fission, fragmentation, budding, parthenogenesis …}Sexual reproductionSexual reproduction is the creation of offspring by the fusion of haploid gametes to form a diploid zygote.Gametes are formed by meiosis. The female gamete, the ovumovum (unfertilized egg), is usually a relatively large and nonmotile cell. The male gamete, the spermatozoonspermatozoon, is generally a small, motile cell. Sexual reproduction increases genetic variability among offspring Sexual reproduction increases genetic variability among offspring by generating unique combinations of genes inherited from two parents. Sexual reproduction may enhance the {long-term} reproductive success of parents when environment changes or offspring disperse or pathogens evolve. {but there are short-term costs of sexual recombination: males & meiosis}Why sex and recombination?Why sex and recombination?Barton NH, Charlesworth BSCIENCE 281 (5385): 1986-1990 SEP 25 1998.Abstract:Most higher organisms reproduce sexually, Most higher organisms reproduce sexually, despite the automatic reproductive advantage experienced by asexual variantsdespite the automatic reproductive advantage experienced by asexual variants. This implies the operation of selective forces that confer an advantage to This implies the operation of selective forces that confer an advantage to sexuality and genetic recombinationsexuality and genetic recombination, at either the population or individual level. In a population of parthenogenetic females cloning selves:the pop. can produce babies faster – everyone’s a mom;& each baby reproduces 100% of a mom’s genes, not 50%;With sex, isolated mutations at diff loci in diff individuals can be combined in one individual: beneficial mutations can interact synergistically & deleterious mutations can be purged in batches – both processes can speed adaptation and select for sexual recombination.The effect of sex and recombination {combining isolated beneficial mutations at} different genetic loci, which increases the efficiency of natural selection, is likely to be a major factor favoring their evolution and maintenance. …But babies, families & the pop genetically more homogeneous;less variable ecology, more vulnerable to coevolving parasitesSee: http://www.pbs.org/wgbh/evolution/sex/advantage/index.htmlAnimals may reproduce asexually or sexually exclusively, or they may alternate between the two modes. {“alternation of generationsalternation of generations”}In aphids, rotifers, and the freshwater crustacean DaphniaDaphnia, X each female can produce eggs of two types, depending on environmental conditions such as the time of year. DaphniaDaphnia: AsexualAsexual reproduction occurs in good conditionsreproduction occurs in good conditions, early in the season. Females produce clonal parthenogenetic female offspring. SexualSexual reproduction occurs reproduction occurs during adverse environmental conditionsduring adverse environmental conditions: food shortages & end of season.Some males develop from parthenogenetic eggs and some females produce darker eggs that require fertilisation by the males. {males made only when times are tough & sex is apparently a good idea!}The fertilized eggs form dormant ephippia: resistant to freezing, desiccation and digestion and may remain viable in sediment for years, - disperse through time & space.The importance of sexual and asexual reproduction in the recent evolution of Allium vinealeCeplitis A. EVOLUTION 55 (8): 1581-1591 AUG 2001Abstract:In the weedy plant species Allium vineale (wild garlic), individuals may simultaneously produce sexually and asexually derived offspring, by seed and bulbils, respectively. In this study, genetic and genotypic diversity was determined in samples from 14 European A. vineale populations using nuclear (RAPD) and cytoplasmic (PCR-RFLP of cpDNA) markers to investigate the importance of the different reproductive modes. … Genotypic diversity was significantly lower than expected under free recombination in almost all populations, indicating that recruitment into populations is mostly by asexually produced offspring. Nevertheless, … many … genotypes have originated by sexual recombination … It is argued that the weedy habit of A. vineale is likely to have favored bulbil reproduction, {rapid population growth within habitats by asexual cloning – everyone’s a mom}whereas sexually generated genotypes may have facilitated local adaptation during the species' expansion across Europe.{a little sexual recombination increased the range of habitats invaded}Among vertebratesvertebrates, several genera of fishes, amphibians, and lizards reproduce exclusively by a complex form of parthenogenesisparthenogenesis that involves the doubling of chromosomes after meiosis to create diploid "zygotes." About 15 species of whiptail lizardswhiptail lizards reproduce exclusively by parthenogenesisparthenogenesis. There are no males in these species, but the lizards imitate courtship and mating behavior typical of sexual species of the same genus. During the breeding season, one female of each mating pair mimics a maleone female of each mating pair mimics a male. The roles change two or three times during the season, female behavior occurring when the level of estrogen is high prior to ovulation; male behavior occurring after ovulation when the level of estrogen drops.Ovulation is more likely to occur if one individual is mounted by anotherOvulation is more likely to occur if one individual is mounted by another; isolated lizards lay fewer eggs