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