pre- and postmating reproductive isolation in populations of the red-sided garter snake by rachel...
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![Page 1: Pre- and Postmating Reproductive Isolation in Populations of the Red-sided Garter Snake By Rachel McAlister Mentors: Drs. Robert Mason, Suzanne Estes,](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cb05503460f94974bbf/html5/thumbnails/1.jpg)
Pre- and Postmating Reproductive Isolation in Populations of the Red-sided Garter Snake
By Rachel McAlisterMentors: Drs. Robert Mason, Suzanne Estes, & Steve ArnoldDepartment of Zoology
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Evolutionary theory predicts that during a speciation event, premating reproductive isolation will evolve faster than postmating reproductive isolation in populations undergoing sexual selection (R.A. Fisher 1930).
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premating reproductive isolation- behavior preventing individuals from mating and producing offspring.
Female gold finches choose mates based on the color and the brightness of their plumage.
Evolutionary theory predicts that during a speciation event, premating reproductive isolation will evolve faster than postmating reproductive isolation in populations undergoing sexual selection.
Male
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post-mating reproductive isolation- prevents a hybrid produced by two different species from developing into a viable, fertile adult.
Mule
=Donkey
XHorse (Sterility)
Evolutionary theory predicts that during a speciation event, premating reproductive isolation will evolve faster than postmating reproductive isolation in populations undergoing sexual selection.
![Page 5: Pre- and Postmating Reproductive Isolation in Populations of the Red-sided Garter Snake By Rachel McAlister Mentors: Drs. Robert Mason, Suzanne Estes,](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cb05503460f94974bbf/html5/thumbnails/5.jpg)
Postmating reproductive isolation also occurs as a result of reduced fitness and increased mortality of hybrid offspring.
HybridNon-hybrid
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sexual selection- A difference between the mating success of individuals with a particular phenotype versus individuals with a different phenotype.
Galapagos Island Marine Iguana Peacock
(Tail length and elaboration)(Body size and aggressiveness)Male-male competition Female choice
Evolutionary theory predicts that during a speciation event, premating reproductive isolation will evolve faster than postmating reproductive isolation in populations undergoing sexual selection.
![Page 7: Pre- and Postmating Reproductive Isolation in Populations of the Red-sided Garter Snake By Rachel McAlister Mentors: Drs. Robert Mason, Suzanne Estes,](https://reader036.vdocuments.mx/reader036/viewer/2022062423/56649cb05503460f94974bbf/html5/thumbnails/7.jpg)
Most research on reproductive isolation is conducted between species, not between populations—the level at which speciation generally occurs.
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Research Question
Does premating reproductive isolation evolve faster than postmating reproductive isolation in populations of the red-sided garter snake?
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Red-sided Garter Snake(Thamnophis sirtalis parietalis)
Mate after spring emergence
Females can store sperm
Highly philopatric-always return to the same den
Island-like populations (geographically distinct populations)
Populations differ phenotypically Body size Coloration Female pheromone composition Levels of premating isolation
Experience sexual selection on body size
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*
*
Snake Island *Inwood *
*
*
Methods:
Collected males and females from 2 populations in Manitoba, Canada during May 2003
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20 Inwood ♂1 Snake Island ♀1 Inwood ♀
20 Snake Island ♂1 Snake Island ♀1 Inwood ♀
Methods: Premating Reproductive Isolation
Simultaneous choice tests
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Results: No evidence (yet) for premating isolation
Male Population
Inwood Snake
-0.5
0.0
0.5
1.0
Pre
ma
tin
g I
sola
tio
n
N=6 N=6
Snake Islandmales MAY prefer theirown femalesover Inwoodfemales.
Snake Isl.
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Inwood ♀ X Inwood ♂
Snake Isl. ♀ X Snake Isl. ♂
Inwood ♀ X Snake Isl. ♂
Inwood ♂ X Snake Isl. ♀
Methods: Postmating Reproductive Isolation
Within- and between-population crosses:
{within
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Inwood ♀ X Inwood ♂
Snake Isl. ♀ X Snake Isl. ♂
Inwood ♀ X Snake Isl. ♂
Inwood ♂ X Snake Isl. ♀
Methods: Postmating Reproductive Isolation
Within- and between-population crosses:
{between
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Methods: Postmating Reproductive Isolation
Body Mass SVL (Snout-Vent Length) & Tail Length
Body Condition—regression of SVL on mass
Snout Vent/Genitalia
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Results: No evidence (yet) for postmating isolation
(Hybrids)
Cross
Sta
nd
ard
ize
d M
ean
s
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
Mass1
SVL1
Condition1
Tail length
Inwood♀ x Inwood♂
Inwood♀ x Snake♂
Snake ♀ x Snake♂
Snake♀ x Inwood♂
(Hybrids) (Hybrids)
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Results: No evidence (yet) for postmating isolation
(Hybrids)
Cross
Sta
nd
ard
ize
d M
ean
s
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
Mass1
SVL1
Condition1
Tail length
Inwood♀ x Inwood♂
Inwood♀ x Snake♂
Snake ♀ x Snake♂
Snake♀ x Inwood♂
(Hybrids) (Hybrids)
Postmating isolation reduction in hybrid fitness correlatescompared to within-population offspring
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Results: No evidence (yet) for postmating isolation
(Hybrids)
Cross
Sta
nd
ard
ize
d M
ean
s
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
Mass1
SVL1
Condition1
Tail length
Inwood♀ x Inwood♂
Inwood♀ x Snake♂
Snake ♀ x Snake♂
Snake♀ x Inwood♂
(Hybrids) (Hybrids)
Hybrid Vigor?
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BUT, because females store sperm, paternity of individual offspring is unknown…
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Paternity Assignment
Is postmating isolation data confounded by multiple paternity of litters?
How many fathers are responsible for a given litter?
Sperm precedence: How many offspring sired by experimental male vs. stored sperm?
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Methods: Paternity Assignment
Determining paternity using two microsatellite markers
a) Collect tail tips from known parents & offspring
b) Tissue digestion
c) DNA extraction
d) DNA amplification -Polymerase chain reaction (PCR)
e) Genotyping
f) Paternity assignment by exclusion
GCATACACACACACGAGGTGAC
microsatellite
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Results: Extensive multiple paternity
Multiple paternity was detected in 68% of the litters (15/22)
Most litters sired by at least 2 males
One litter sired by at least 3 males
0
2
4
6
8
10
12
14
16
1 2 3
Number of sires per litter
Fre
qu
en
cy
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Results: Sperm Precedence
Experimental males sire 63% of each litter on average.
However, for between-population crosses, experimental males sire fewer offspring than experimental males in within-population crosses.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Between-population Within-population
(non-significant)
Cross Type
Fra
ctio
n o
f lit
ters
sir
ed b
y e
xpe
rim
en
tal m
ale
N =11 N =11
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Conclusions
Multiple paternity is common in T. s. parietalis litters
68% of litters were sired by 2 or more males
Data on postmating reproductive isolation (i.e., offspring fitness) is likely confounded by multiple paternity.
Only about half of each litter was sired by the experimental male; half was sired by stored sperm
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Research Question
Does premating reproductive isolation evolve faster than postmating reproductive isolation in populations of the red-sided garter snake?
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(Hybrids)
Reanalyze offspring fitness data taking paternity into account
(Hybrids)
Future Directions
Cross
Sta
nd
ard
ize
d M
ean
s
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
Mass1
SVL1
Condition1
Tail length
Inwood♀ x Inwood♂
Inwood♀ x Snake♂
Snake ♀ x Snake♂
Snake♀ x Inwood♂
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Future Directions
Within- and between-population crosses were repeated and offspring await paternity analysis
Mating trials will be repeated in May 2005
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Acknowledgements
Dr. Suzanne Estes
Dr. Robert Mason
Dr. Steve Arnold
HHMI
Dr. Kevin Ahern
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Premating Isolation
Premating isolation = within-population – between-population pairings pairings
total number of pairings
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Results: Extensive Multiple Paternity
Hybrid (between-population) litters have more sires represented than do non-hybrid (within-population) ones
0.0
0.5
1.0
1.5
2.0
2.5
Between-population Within-population
NS(non-significant)
Cross Type
Av
era
ge
# o
f si
res
/litt
er
N =11 N =11