Lecture 14 - 10/2/15
Lecture 14 - 10/2/15 EEOB 3310 - 200
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This 2 page Class Notes was uploaded by an elite notetaker on Friday October 2, 2015. The Class Notes belongs to EEOB 3310 - 200 at Ohio State University taught by Joan Herbers,Zakee Sabree in Summer 2015. Since its upload, it has received 37 views. For similar materials see Evolution in Ecology at Ohio State University.
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Date Created: 10/02/15
Lecture 14 Hybrid zones regions where interbreeding between diverged populationslineages species occurs and hybrid offspring are frequent Apple trees are newly introduced causing fairly rapid speciation among Rhagoletis Hybrid zones help us to understand reproductive isolation Key is fitness of hybrid in comparison to that of the parents In many cases hybrids are at a disadvantage If fitness is higher than parental forms the effect depends on whether fitness advantage occurs in an ecotone or new a habitat Ecotone mix between two habitats If speciation is an ongoing process how do we actually identify species Speciation is a three step process Mayr thought a radial genomic reorganization was required and hybridization would be impossible Land 1980 and Barton amp Charlesworth 1984 showed theoretically that these types of largescale changes are unlikely and unnecessary What are the number and nature of alleles that distinguish closelyrelated species Aphids feed on sap of plants There are alfalfa populations and red clover populations Assess fitness on host plant and then force it to feed on a plant it is not adapted to fit on fitness is in uenced survival rate is much higher on host plant Linkage map how are genes packaged Alleles that increase fecundity on one plant but not the other and vice versa This suggests that large scale genomic recombination might not be required Evidence to support Darwin s theory that species will specialize on resources Evolution of reproductive isolation between Drosophila species Many places throughout the genome that affect hybrid viability Found 20 different regions that were capable independently of causing hybrid inviability Used genetic mapping traced deletions Implies that in the case of Drosophila it s not necessarily big changes it is adaptation and the cause of many small areas that cause the inviability Hemizygous is when you only have one chromosome when you re supposed to have two We 2001 genic view of speciation this is the way most biologist feel speciation happens today Speciation initially happens when there are small loci showing a clear difference between different copies As populations continue to diverge linkage disequilibrium begins to accumulative around these selected on Genetic hitchhiking is gradually becoming more divergent as a function of hitchhiking around these single loci that are being selected on At some point the divergence is complete and there is no more gene ow Classifying species is very difficult because under the biological species definition you must breed the species and determine hybrid fertility and what not Also it is a continual process 50 different species concepts studied in the last 50 years A lot of debate about this because it s something that is very difficult Only real progress made speciation is an ongoing process Rieseberg 2006 what proportion of described species represented reproductively isolated clusters of individuals Fraction of species taxa that represent reproductively independent lineages in major taxonomic groups of plants and animals Prominent criteria reproductive isolation morphological differentiation associated with different concepts Coyne and Orr 2004 1 Classification can occur 2 Corresponds to discrete groups of similar organisms 3 Helps us to understand how these clusters arise in nature 4 Represents the products of evolutionary history 5 Applies to the largest possible variety of organisms de Querioz operational species concept that treats species as separately evolving metapopulation lineage of species Different criteria can diverge in different orders Entities that are actively in the process of diversifying Carol Eunmi Lee 2000 Marine species are difficult to diagnose due in part to a lack of obvious morphological differences and in part to the absence of biological barriers Copepod Phylogenetic data indicate that there are multiple clades with high levels of support that correspond to geographic regions If there was no relationship between geography and phylogeny then it may be concluded that this is all one species this is why phylogenetic data is necessary What would happen if we took Copepods from here and Europe and allowed them to reproduce who would reproduce with whom Many didn t actively reproduce evidence that they were reproductively isolated and different species or clades Things that we define as one species are often composed of multiple cryptic species however they are not always functionally different even if they are reproductively isolated Number of described species vs number of actual species Threespined sticklebacks Very small ancestors live in the ocean where they are food for a lot of bigger fish Very good at colonizing fresh water Two different morphologies limnetic species top of lake benthic species bottom of lake In small lakes in British Columbia it appears that each form has evolved from marine ancestor However this process has occurred dozens to hundreds of times Has happened independently in every lake Challenge because the limnetic species is not a monophyletic species and neither is the benthic species Classifying these as two species is an issue because many people feel that a species should re ect the evolution of the spec1es