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Unformatted text preview: Lecture 26: Sexual Selection and Speciation and I. Sexual Selection & Speciation
Many organisms recognize members of their own species using highly specific… Many a. courtship behaviors b. songs (birds, insects) These evolve primarily by _sexual selection These _sexual c. chemical signals d. visual signals For example, male fireflies attract females of their own species (conspecifics) with species-specific set of flashes and flying patterns species-specific We already discussed that these signals We can act as reproductive isolating mechanisms: mechanisms Behavioral isolation Behavioral Because sexually-selected signals are Because used to recognize and choose mates, they may be particularly important in reproductive isolation reproductive I. Sexual Selection & Speciation I.
There are 2 primary means by which behavioral isolation via sexual selection can be important in speciation: selection 1._speciation by natural selection_: populations diverge due to natural populations selection and sexual traits change as a by-product, causing behavioral isolation. Here we expect the species to be different in many ways, including sexual signals sexual 2._speciation by sexual selection___: behavioral isolation evolves first, behavioral and other forms may (or may not) evolve later. Here we expect species to be similar, except for their sexual signals similar, These are not different modes of speciation from allopatric and These sympatric speciation. The key issue is whether divergent sexual traits cause genetic differentiation or are a consequence of it. cause Note that SS is a type of NS, but biologists often contrast them, with SS Note referring to traits that improve competition over mates and NS referring to all other traits that improve survival and fecundity. II. Speciation by Natural Selection
Behavioral isolation as a by-product of natural selection in Darwin’s finches selection Beak size diverged by natural selection as Beak finches colonized different islands; beak sizes are specialized to crack particular seeds are This caused behavioral isolation as a This _by-product_: Changes in head and beak morphology caused changes in song apparently as a bycaused product; song is used in _mate choice_ product; _mate II. Speciation by Natural Selection
Bill depth affects the relationship Bill between trill rate and bandwidth of trill (the diff between the max and min pitch) and Bigger bills lead to narrower Bigger frequency range and/or slower trills trills Species that have evolved Species large bills adapted for crushing big hard seeds cannot move their bills as quickly during trills, __so their songs change as you had diverging natural selection__ diverging
Podos, 2001 II. Speciation by Sexual Selection
Divergent sexual selection in allopatry or sympatry can lead Divergent to _behavioral isolation, and thus to speciation_ to
Example: In Vogelkop bowerbird, two isolated populations have Example: evolved very different sexual signals evolved Hut-building population: Males build elaborate huts Males and decorate with bright objects objects Females prefer larger huts Females and more colored decorations decorations BBC 2000 II. Speciation by Sexual Selection II.
Maypole-building population: population: Males build maypole Males bowers with no closed hut hut Males decorate with drab Males colors colors Hut and maypole males Hut are morphologically identical, and there is _almost no genetic divergence, suggesting that sexual signals are diverging first. II. Speciation by Sexual Selection
Why do sexual signals diverge in the first place? Could be _____________________running away in different directions OR sexually-selected signals used to advertise good genes OR or direct benefits may diverge to be more effective in different habitats So sexual signals may change so that they look better or sound better in their particular habitat, thus causing behavioral isolation better II. Speciation by Sexual Selection
Adaptive radiation from a single species of cichlid in multiple African lakes; African As the fish moved into diff As environments in the lake, there were different light spectra available for communication so the fish evolved colors to match the When they come into When secondary contact, ________ secondary _________________________ _________________________
Speciation in Cichlids II. Speciation by Sexual Selection
_eutrophication__resulting from industrial and agricultural processes has resulting caused phytoplankton blooms that filter out blue and red light caused Many Lake Victoria cichlids now hybridize because __they cant tell each Many other apart other
Pre-industrial: Pre-industrial: Full-spectrum Full-spectrum Post-industrial: Eutrophication Post-industrial: (Green water) (Green %R
blue red %R blue red green Blue and red cichlid fishes cooccur and don’t normally occur interbreed interbreed Hybridization and thus loss of 2 Hybridization species species
(Seehausen et al., Science 1997) (Seehausen 1997) III. Summary III.
Speciation does not always involve __behavioral isolation; BI is Speciation __behavioral BI only one of many types of reproductive isolation only However, because sexual traits are so important for finding and However, choosing a mate and because speciation requires reproductive reproductive isolation (it’s all about who does and doesn’t interbreed), isolation sexually-selected traits may play a particularly important role in sexually-selected speciation by causing __behavioral isoaltion_ __behavioral This is a huge area of research right now… ...
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This note was uploaded on 11/29/2010 for the course BIOLOGY 1211 taught by Professor Patricelli during the Spring '10 term at UC Davis.
- Spring '10