Fig. 2: Extensive gene flow among three Hawaiian island populations of T. oceanicus.

a ABBA–BABA tests illustrate significant gene flow among all three Hawaiian populations on the X chromosome. Sites used in the test are derived in T. oceanicus compared to the outgroup (T. commodus) but differ among P1 and P2 T. oceanicus individuals. Tests with Australian T. oceanicus populations are included as control comparisons (left three bars) and the plot shows all possible topological permutations of the three Hawaiian island populations relevant for the ABBA–BABA test (right three bars). The null expectation of no gene flow is indicated by D = 0. Positive D indicates an excess of shared derived alleles—evidence for greater gene flow—between populations 2 and 3 in the comparison (ABBA excess), whereas negative D indicates evidence for greater gene flow between populations 1 and 3 in the comparison (BABA excess). The significance of gene flow among island populations was also supported by all comparisons between all Hawaiian scenarios and Australian scenarios (two-sided t-tests: all P < 0.001; n = 700 independent D-values for each Australian control; n = 1000 each for Kauai and Hilo; n = 2000 for Oahu. Statistical details are provided in Supplementary Table 4). Box plots show upper quartile, median, and lower quartile values, 1.5× interquartile ranges, and outliers. Multiple individuals’ D tests using a smaller block size are represented by red diamonds. Source data are provided as a Source Data file. b The most likely demographic history of Hawaiian T. oceanicus populations reconstructed using Fastimcoal2 indicates recent, extensive gene flow among all islands. The ancestral population is shown in grey. Bar width for each population indicates estimated effective population sizes (numbers indicated in each block) and black horizontal lines represent population divergence. Blue horizontal arrows and the numbers underneath them indicate per-generation migration rates, i.e. the estimated rate of symmetrically exchanged migrants between populations every generation; these episodes of gene flow were inferred to have started approximately within the past 300–400 years and are ongoing. This reconstruction provided evidence that all three populations experienced ancient bottlenecks, plus recent population expansions accompanied by gene flow. An approximate timeframe indicating initial human colonisation of the Hawaiian archipelago, agricultural activity, and European contact is provided on the right of the panel. The population demographic reconstruction for T. oceanicus indicates that the crickets are likely to have accompanied the first human arrivals to Hawaii.