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Lecture 7

Lecture 7 and 8 on Evilutionary Analysis II (fall2011)

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Biological Sciences
Maydianne Andrade

BIOB51Fall2011 Chapter 4 and Chapter 10 Lecture 78 Evolutionary Analysis II Phylogeny and Comparative Method The Comparative Methodo Examine how comparisons among species can be used to study the evolution of form and functiono The comparative method seeks to evaluate hypotheses by testing for patterns across species such as correlations among traits or correlations between traits and features of the environment o The comparative method deals with macroevolutionary questions questions of patternsorigin of major differences among taxa o Factors leading to the evolution of a trait and the hypotheses about the origin of these adaptations o Technique comparison of patterns of origin of traits across taxa Why do some bats have bigger testes than others o Males in some of the bat species have larger testes for their body size o Hosken hypothesized that large testes are an adaptation for sperm competition o Sperm competition occurs when a female mates with 2 or more males during a single cycle and the sperm from the different males are in a race to the egg o One way in which males can increase their success is to produce larger ejaculatesthe way to produce larger ejaculates is to have larger testes o To evaluate the sperm competition hypothesis Hosken needed a testable hypothesiso He knew that fruit bats and flying foxes roost in groups and that the size of a typical group varies dramatically among species from 23 to thousands o Females living in larger groups would have more opportunities for multiple matingso Males living in larger groups would experience greater sperm competition as a result o Predictionwhenever a bat species evolves a preference for roosting in larger groups the males would also evolve larger testes for their body sizeo Simplest way to test is to gather data for a variety of species and put it on a scatterplot showing the relative testes seize as a function of roost group size o He found that the 2 variable are strongly correlatedbat species that live in larger group have larger testes size oBUT consider that species A B and C are closely related to each other while D E F are also close to one another phylogeny V with 3 legs on each end o A B and C have smaller testes sizewhile D E and F have bigger testes sizefollows trend form other scatterplot o Species A B and C maybe inherited their small testes size from their common ancestoro Species D E and F inherited their bigger testes size from their ancestoro The possibility that these 6 species inherited their teste size from just 2 common ancestors deflates the strength of evidence 1
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