Natural selection

Natural selection

Natural selection • Concept of natural selection is simple, but mechanism is subtile • Deals with survival and reproduction • Comprises the only known process that offers an explanation for the origin of adaptations

11.1 Different forms of leaves on the aroid vine Monstera tenuis in tropical American forests • Different forms of leaves on the vine Monstera tenuis in tropical American forests • Example of adaptive development in relation to environmental parameters

11.2 Pseudocopulatory pollination • Adaptive shapes of flowers for pseudocopulatory pollination in the Australian orchid Chiloglottis formicifera • Shape is combined with other traits such as odour

11.3(2) The kinetic skull of snakes • Adaptive skeletal structure of poisonous snakes

11.3(1) The kinetic skull of snakes • Adaptive skeletal structure of poisonous snakes • Form complex mechanisms “redesigned” through modification of existing skeletal structures in other reptiles

11.4 Weaver ants (Oecophylla) constructing a nest • Level of complexity of cooperative behaviour reaches climax in social insects • Genetically inherited behaviour increases the reproductive success of the queen

Process of natural selection • Design and function • Consistent difference in fitness among phenotypically different classes of biological entities • Fitness as a product of survival and reproductive success • Individual versus genic selection • Natural selection versus chance effects

11.5 A child’s toy that selects small balls • Selection for small size results in selection of red balls • By chance, natural selection can lead to selection for correlated traits • Selection always acts for a particular phenotypic trait, but results in selection of the genes that code for this trait

11.7 Allele frequency fluctuates due to hitchhiking in a laboratory population of Escherichia coli • Example of hitchhiking through fluctuations in frequency of his- and his+ alleles in E. Coli • Illustrates selection for new advantagous mutations and selection of neutral alleles at the linked his locus

11.9(1) A male long-tailed widowbird in flight • Male body traits used for display are often strongly developed • Relationships with fitness can be examined through correlative or experimental studies

11.9(2) Effects of experimental alterations of tail length on males’ mating success • Male body traits used for display are often strongly developed • Relationships with fitness can be examined through correlative or experimental studies

11.9(3) Effects of experimental alterations of tail length on males’ mating success • Male body traits used for display are often strongly developed • Relationships with fitness can be examined through correlative or experimental studies

11.11(1) Effects of individual selection and group selection on population size in the flour beetle • Study on effects of selection for different population sizes

11.11(2) Effects of individual selection and group selection on population size in the flour beetle • Study on effects of selection for different population sizes

11.11(3) Effects of individual selection and group selection on population size in the flour beetle • Study of effects of selection for different population sizes • Treatment C shows characteristics of individual selection • Treatments A and B show characteristics of group selection • Selection can act both within and between populations • Selfish genetic elements

11.12 The mythical self-sacrificial behavior of lemmings • Mytical self-sacrificial behaviour of lemmings • Altruists versus cheaters • Lower average turn-over of populations than of individuals reduces likelihood of strong group selection

11.13(1) Conflict between group and individual selection • Conflict between group selection and individual selection • Altruistic traits may evolve through group selection if the rate of extinction of populations with selfish genotypes is very high

11.13(2) Conflict between group and individual selection • Conflict between group selection and individual selection • Altruistic traits may evolve through group selection if the rate of extinction of populations with selfish genotypes is very high

11.13(2) Conflict between group and individual selection • Because individual selection works faster than group selection, selfish individuals rapidly increase within populations • May spread towards neighbouring populations though gene flow • Leads to fixation of selfish genotypes (even if causing population extinction)

11.14(1) The evolution of altruism and selfishness by kin selection • Evolution of altruisim and selfishness by kin selection • Kin selection operates at the level of individual genes • Both behavioural strategies potentially increase the inclusive fitness of the actor

11.14(2) The evolution of altruism and selfishness by kin selection • Evolution of altruisim and selfishness by kin selection • Kin selection operates at the level of individual genes • Both behavioural strategies potentially increase the inclusive fitness of the actor

11.17 Exaptation and adaptation • ‘Preadaptation’ versus ‘exaptation’ • Wings in alcids can be regarded as exaptations • Wings in penguins can be regarded as adaptations

11.18 Cross section of a bird’s eye, showing the pecten • Non-adaptive explanations: by-product of selection, correlated selection (hitchhiking, pleiotropy), random genetic drift, ancestral character state • Indications for adaptation: complexity

11.19 Small surfaces shed the hot boundary layer of air more readily than large surfaces • Non-adaptive explanations: by-product of selection, correlated selection (hitchhiking, pleiotropy), random genetic drift, ancetsral character state • Indications for adaptation: design (functional, morphological, fysiological)

11.9(3) Effects of experimental alterations of tail length on males’ mating success • Non-adaptive explanations: by-product of selection, correlated selection (hitchhiking, pleiotropy), random genetic drift, ancetsral character state • Indications for adaptation: experimental evidence

11.20 Testes versus body weight among polygamous and monogamous primate taxa • Non-adaptive explanations: by-product of selection, correlated selection (hitchhiking, pleiotropy), random genetic drift, ancestral character state • Indications for adaptation: comparative studies • Convergent evolution as natural evolutionary experiments • Hypothetico-deductive methods

11.21 The problem of phylogenetic correlation in employing the comparative method • Hypothesis testing assumes statistically independent data • Study of convergent evolution for hypothesis testing on adaptations assumes independent convergent evolutionary events

Conclusive remarks • Necessity of adaptation ? • Perfection ? • Progression ? • Harmony and balance ? • Morality and ethics ?

Natural selection