Effects of the Landscape on Gene Flow and Connectivity of Boreal Toads Jennifer Moore, Julie...
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Transcript of Effects of the Landscape on Gene Flow and Connectivity of Boreal Toads Jennifer Moore, Julie...
Effects of the Landscape on Gene Flow and Connectivity of Boreal Toads
Jennifer Moore, Julie Nielsen, David Tallmon, Sanjay PyareUniversity of Alaska Southeast
Landscapes have profound effects on species ecology
Colonization
Movement
DispersalPopulation dynamics
Geographic distributions
Landscape genetics
Landscape ecology + population genetics
• Aims to quantify the effects of the landscape on microevolutionary processes– Cryptic boundaries– Secondary contact among previously isolated pops
• Hypothesis driven• Novel individual-based methods
Landscape genetics
Two key steps:1. Detect genetic discontinuities2. Correlate these with landscape and
environmental features
Amphibians
• Good models for studies of connectivity– Function as metapopulations– Patchy distributions = limited connectivity
• Population dynamics difficult to understand with traditional ecological methods– High population stochasticity
Boreal toads
• Widespread• IUCN listed as near
threatened• Status in Alaska?– northern range
margin
Boreal toads
• Pond breeding, but variable habitat and climate tolerance
• Capable of long distance movements• High breeding site fidelity
Highly differentiated?Strongly affected by the landscape?
Study sitesAdmiralty Island Haines
Hypotheses• H1: Isolation by distance– Euclidean distance
• H2-n: Isolation by landscape resistance– Habitat structure (x 5)– Insolation– Rugosity– Saltwater– Permanent snow and ice– Roads (Haines only)G
eneti
c di
stan
ceGeographic distance
Methods
1. Sample breeding populations2. Amplify microsatellites3. Calculate genetic distance (Fst)4. Generate GIS models, calculate
geographic distances5. Correlate pairwise genetic with
pairwise geographic distance (Mantel tests)
Geographic distance
Least cost paths Circuit theory• Distance that incorporates
multiple potential paths of least resistance
• Single path of least resistance
Mcrae et al. 2008
Wolverine gene flowMcRae and Beir 2007, PNAS
Circuit theory outperforms traditional methods
Circuitscape software
Sample locations + resistance surface
Circuitscape current map=
Results
Toad populations moderately differentiated on a small scale
• Mean pairwise FstANM = 0.061, 0.008 - 0.122HNS = 0.053, 0.006 – 0.143
• Mean pairwise Euclidean distanceANM = 14.5 km, 0.33-45 kmHNS = 11.4 km, 0.11-50 km
Small effective population sizes (Ne)
0 2 4 6 8 10 120
50
100
150
200
250HNSANM
Population
Effec
tive
Popu
latio
n Si
ze
Permanent snow/ice strongest single factor model
euclid ice ru
gg salt
solar
struct1
struct2
struct3
struct4
struct5
road
s-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0.60ANM
HNS
Model
r
Permanent snow and ice affects genetic connectivity
0 0.05 0.1 0.15 0.2 0.250
1
2
3
4
5
6
Pairwise Fst
Pair
wis
e Re
sist
ance
- Ic
e
R = 0.59
Summary and conclusions
• Limited gene flow, small scale differentiation• Small Ne for many populations• Gene flow strongly affected by permanent
snow/ice– Differs from other parts of range– Barrier due to physiological/thermal limits
Summary and conclusions
• Impacts of climate change?
Glaciers, permanent snow and ice
= Toad connectivity?
Future directions
• Improve model fit– Combine surfaces, multiple parameters
• Compare methods: least cost path vs. circuit theory
• Broad-scale phylogeographic analysis– Do patterns hold true at different scales?
Thanks
• NSF Alaska EPSCoR• ADF&G Non Game program• USFS• USGS• Emma Caragano, Ray Slayton, Tim Shields, Kim
Obermeyer, Karin McCoy, Colin Shanley, Iris Shields, Robbie Piehl, Lance Lerum, Brett Addis, Cat Frock, Dave Moore