Transcript Document

http://atlas.geo.cornell.edu/education/instructor/topography/hawaii_seamounts.html
http://www.dnr.state.sc.us/marine/sertc/images/photo%20gallery/alpheus.jpg
Alpheus
snapping shrimp
Knowlton et al. 1993
Mechanisms of
species formation
• Darwin: geographic separation followed by
adaptation to different ecological circumstances
eventually leads to reproductive isolation
• Two alternatives:
– FOOD: Sympatric speciation due to shifts in
host (e.g., in specialized herbivores/parasites)
– SEX: Speciation due to divergent sexual
selection (evolution of mate preference)
Model of sympatric speciation
via shifts to new host (FOOD)
2
2
1
2
Host shift
1
Population uses
ancestral host 1
1
New population
founded via shift
to derived host 2
1
2
Populations on two
hosts become
reproductively
isolated
Eurosta solidaginis – an example of
sympatric speciation via host-plant shifts
Illustration from
Abrahamson and
Weis (1997)
Photo courtesy of Warren Abrahamson
Speciation via SEXual selection
Females in
ancestral
populations prefer
blue males
Geographic
barrier divides
populations
Female preference
for male trait
diverges due to
genetic drift
Upon
recontact,
populations
reproductively
isolated due
ONLY to
female
preference
Signatures of sympatric
speciation via host/habitat shift
(after Via 2001)
• Sympatric overlap of host patches
• Mating on the host causes reproductive
isolation between races
• Host phenology differs
• Divergent selection on different
hosts/habitats
Signatures of speciation via
sexual selection
(after Panhuis et al. 2001)
• Populations within species vary in sexually selected traits
and associated preferences, resulting in partial pre-mating
isolation
• Closely related species differ markedly in mating signals
and preferences, which constitute the primary barrier to
gene exchange
• Species differ in few other traits besides those involved in
mate choice
North American Enallagma
•37 spp. North America
•Species restricted either to lakes with or without fish (F and D lakes)
•Distribution mediated by differences in anti-predator behavior
•Species richness 3-5x higher in fish lakes
Brown, McPeek and May.2000
Syst. Biol. 49:697-712.
Robertson and
Paterson, 1982.
Evolution.
Brown, McPeek and May.2000
Syst. Biol. 49:697-712.
boreale
laterale
clausum
cyathigerum
hageni
davisi
recurvatum
minusculum
ebrium
Images from Westfall and May, 1996
Selection and the Enallagma
radiation
• Four damselfly-lake species generated by
habitat shifts and adaptive evolution
(morphological, behavioral and
physiological)
• Many fish-lake species generated during
recent radiations (associated with glacial
retreat?), possibly via founder effects on
mechanical mate recognition system