Correction to “Genetic variability and the ecology of geographic range: A test of the central‐marginal hypothesis in Australian scincid lizards”

Singhal S, Wrath J, Rabosky DL. Genetic variability and the ecology of geographic range: A test of the central‐marginal hypothesis in Australian scincid lizards. Molecular Ecology. 2022 Aug;31(16):4242–53.

We used the rangeExpansion program to infer if the genetic data for our focal lizard species showed evidence for a range expansion and, if so, the likely origin of the range expansion. We were informed that the program contains a coding error that changes our results. When rerunning our analysis using the corrected code, our results changed as follows:

Twenty of the 25 OTUs showed significant evidence for range expansion (Figure 5b). We measured significance by the significance of the correlation of the directionality index ($\psi$; a measure of asymmetry in two‐dimensional site frequency spectra) and geographic distance from the origin. The origins of the range expansion were generally inferred to be towards the edge of the range; on average, the centre–edge distance ratio of origins was 0.76 (Figure S6).

FIGURE 5.

Demographic inference for OTUs included in this study. (a) Ratio of current effective population size (N _e) to ancestral Ne as inferred using dadi. All 25 OTUs best fit the two‐epoch model, in which populations expanded instantly in the past (see Figure S3). (b) For the 20 OTUs that showed significant evidence for range expansion, we plot the strength of the range expansion, as measured by the correlation between allele frequency clines and geographic distance from the expansion origin.

FIGURE S6.

Estimated location of range expansion for the 20 OTUs inferred to have significant evidence for a range expansion. We inferred which OTUs showed evidence of a range expansion and inferred its likely origin using rangeExpansion (Peter & Slatkin, 2013). Shown here is where the origin is located relative to the current range, calculated as the ratio of the origin distance to range centre to the radius of the range through the origin. Most origins were inferred to be relatively far from the centre and closer to the edge (mean ratio distance = 0.76).

We found that no variables significantly predicted whether we recovered the central‐marginal hypothesis (Figure 6). The best overall model included sampling coverage (e.g. what proportion of the species range was sampled), but even in this best model, sampling coverage was not a significant predictor of the central‐marginal hypothesis (r ² = .05; p‐value = .14).

FIGURE 6.

(a) Model fitting for nine variables that span three possible factors for whether or not we recover support for the central‐marginal hypothesis in a given taxon: (1) biological factors: Isolation‐by‐distance (IBD) slope, biome; (2) historical factors: strength of range expansion, population size change; and (3) methodological factors: range eccentricity, sampling coverage, number of individuals sampled, range size and mean genetic diversity. Shown are the relative importance of each variable and the sign of its coefficient. Sampling coverage was the best predictor of all tested variables, however, it was non‐significant.

Updated figures follow.

We thank Paolo Momigliano & Petri Mikael Kemppainen for alerting us to this error and for sharing corrected code.

We apologize for this error.