Fig 1.
(A) The Gulf and Atlantic seaboards of the Eastern United States. States harboring terrapin populations along their coastlines are faded red. (B) All terrapin populations under ΔK = 2. (C) All terrapin populations under ΔK = 4. (D) All terrapin populations under ΔK = 7. Subsections B,C, and D depict the same analysis, explored under different genotypic partitions. (E) Mid- and north Atlantic terrapins under K = 2. In this scenario, NY and NJ terrapins constitute a single population. (F) Mid- and north Atlantic terrapins under K = 3. In this scenario, NY and NJ form separate populations. Subsections F and G depict the same analysis under two values of K with similar likelihood scores. (G) SC terrapins investigated with Gulf populations. TX and FL form separate populations and SC1-6 constitute a single cluster. No substructure is present within SC1-6. TX, FL, SC, and MD are diagnosable clusters. If NY and NJ form a single cluster (subsection E), there are five total clusters. If NY and NJ form separate clusters (subsection F), there are six total clusters.
Fig 2.
The eight models of population structure derived from STRUCTURE, DAPC, and Δm results.
Black lines denote naturally occurring gene flow while red lines indicate gene flow possibly arising from translocation. Model A is a linear stepping-stone; Model B added gene flow from TX to SC and from NC to NY; Model C removed all gene flow to and from FL while retaining translocation; Model D treated FL as a sink population; Model E allowed gene flow with FL on the Atlantic coast; Model F allowed gene flow with FL on the Gulf Coast; Model G depicts the Suwannee Seaway with completely isolated FL populations; Model H depicts the Suwannee Seaway with FL as a sink population.
Fig 3.
BIC scores indicating k = 6 is the preferred value of genetic clusters when retaining 60 PC axes.
Fig 4.
DAPC for 60 retained axes and four discriminate functions.
Six clusters are recovered with this model. The top half contains populations along the Atlantic coast while Gulf populations are found on the right half of the diagram. SC terrapins are present within each cluster.
Fig 5.
Membership probabilities for 60 retained PC axes and six genetic clusters.
Warmer colors denote more certainty in membership probabilities to each respective cluster. Cluster numbers correspond with populations denoted in Fig 4.
Fig 6.
DAPC for 60 retained axes on sampling localities (k = 12).
Clusters in the model resemble the spatial distribution of sampling localities along the Gulf and Atlantic seaboards (see Fig 1). FL exhibits no admixture with any cluster while TX shows overlap with populations found in SC.
Fig 7.
Membership probabilities for 60 retained PC axes and 12 genetic clusters (sampling localities).
Warmer colors denote more certainty in membership probabilities to each respective cluster. Cluster numbers correspond with populations denoted in Fig 6.
Table 1.
Historical gene flow (mh) estimates from MIGRATE among coastal populations; gene flow is measured by the proportion of migrants per generation, ranging from 0.0–1.0.
Populations on the left are sending gene flow into recipient populations listed above columns.
Table 2.
Contemporary gene flow (m) estimates from BAYESASS among coastal populations; gene flow is measured by the proportion of migrants per generation, ranging from 0.0–1.0.
Populations on the left are sending gene flow into recipient populations listed above columns.
Table 3.
Temporal changes in gene flow (Δm) among all populations; values in italics denote gene flow routes under a linear stepping-stone; bolded values denote an increase in contemporary gene flow (+Δm) of >0.010.
Populations on the left are sending gene flow into recipient populations listed above columns.
Table 4.
BOTTLENECK results by sampling locality and STRUCTURE cluster.
Shown are P-values for a genetic bottleneck under the SMM and TPM. An “L-Shaped” distribution under a Mode-Shift test indicates a bottleneck was not detected.