Résumé
Spatio-temporal studies of hybrid zones provide an opportunity to test
evolutionary hypotheses of hybrid zone maintenance and movement. We
conducted a landscape genetics study on a classic hybrid zone of the
south-eastern Australian frogs, Litoria ewingii and L. paraewingi. This
hybrid zone has been comprehensively studied since the 1960s, providing
the unique opportunity to directly assess changes in hybrid zone structure
across time. We compared both mtDNA and male advertisement call data from
two time periods (present and 1960s). Clinal analysis of the coincidence
(same centre) and concordance (same width) of these traits indicated that
the centre of the hybrid zone has shifted 1 km south over the last 40
years, although the width of the zone and the rate of introgression
remained unchanged. The low frequency of hybrids, the strong concordance
of clines within a time period and the small but significant movement
across the study period despite significant anthropogenic changes through
the region, suggest the hybrid zone is a tension zone located within a low
density trough. Hybrid zone movement has not been considered common in the
past but our findings highlight that it should be considered a crucial
component to our understanding of evolution.