Table 1. Analysis of molecular variance indicated significant population substructure in both B. bicaudatus and B. tricaudatus.

		(Φct) Among drainages	(Φsc) Among sites within drainages	(Φst) Among all sites	Total
B. bicaudatus	df	2	14	585	601
	SumSq	2604.2	9560.7	107740.4	119905.4
	MeanSq	1302.1	682.9	184.2	199.5
	%	1.4%	7.1%	91.4%	100%
	Phi	0.014	0.072	0.086	–
	P-value	0.5	0.001	0.001	–
B. tricaudatus	df	2	5	221	228
	SumSq	561.6	976.9	23699.2	25137.7
	MeanSq	280.8	175.3	107.2	110.2
	%	1.0%	2.4%	96.6%	100%
	Phi	0.010	0.023	0.034	–
	P-value	0.057	0.003	0.003	–

In B. bicaudatus, structure was significant within and among sites, but was not significant at the largest spatial scale (that is, drainages were not a meaningful grouping of genetic variation). In B. tricaudatus, population structure was also significant within and among sites, and was approaching significance even at the largest spatial scale. Only sites with n⩾9 were included in the analysis of molecular variance analysis. P-values were corrected for multiple tests.