Pre- and Postmating Reproductive Isolation in Populations of the Red-sided Garter Snake By Rachel...
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Transcript of Pre- and Postmating Reproductive Isolation in Populations of the Red-sided Garter Snake By Rachel...
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
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).
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
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.
Postmating reproductive isolation also occurs as a result of reduced fitness and increased mortality of hybrid offspring.
HybridNon-hybrid
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.
Most research on reproductive isolation is conducted between species, not between populations—the level at which speciation generally occurs.
Research Question
Does premating reproductive isolation evolve faster than postmating reproductive isolation in populations of the red-sided garter snake?
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
*
*
Snake Island *Inwood *
*
*
Methods:
Collected males and females from 2 populations in Manitoba, Canada during May 2003
20 Inwood ♂1 Snake Island ♀1 Inwood ♀
20 Snake Island ♂1 Snake Island ♀1 Inwood ♀
Methods: Premating Reproductive Isolation
Simultaneous choice tests
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.
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
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
Methods: Postmating Reproductive Isolation
Body Mass SVL (Snout-Vent Length) & Tail Length
Body Condition—regression of SVL on mass
Snout Vent/Genitalia
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)
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
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?
BUT, because females store sperm, paternity of individual offspring is unknown…
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?
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
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
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
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
Research Question
Does premating reproductive isolation evolve faster than postmating reproductive isolation in populations of the red-sided garter snake?
(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♂
Future Directions
Within- and between-population crosses were repeated and offspring await paternity analysis
Mating trials will be repeated in May 2005
Acknowledgements
Dr. Suzanne Estes
Dr. Robert Mason
Dr. Steve Arnold
HHMI
Dr. Kevin Ahern
Premating Isolation
Premating isolation = within-population – between-population pairings pairings
total number of pairings
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