Song divergence at the edge of Amazonia: an empirical test of the
peripatric speciation model
NATHALIE SEDDON
Biological Journal of the Linnean Society, 2007, 90, 173-188.
Abstract
The evolutionary divergence of mating signals provides a powerful basis for
animal speciation. Divergence in sympatry strengthens reproductive isolation,
and divergence in allopatry can reduce or eliminate gene flow between
populations on secondary contact. In birds, the first of these processes has
empirical support, but the second remains largely hypothetical. This is perhaps
because most studies have focused on oscine passerines, whose song learning
ability may reduce the influence of vocalizations in reproductive isolation. In
suboscine passerines, the role of learning in song development is thought to be
minimal, and the resultant signals are relatively fixed. To investigate the
role of song in the early stages of peripatric speciation, we therefore studied
a suboscine, the chestnut-tailed antbird Myrmeciza hemimelaena. We recorded
male songs in a natural forest island (isolated for < 3000 years) at the
southern fringe of Amazonia, and at two nearby sites in continuous!
forest. A previous study found the isolated population to be weakly
differentiated genetically from the ancestral population suggesting that
peripatric speciation was underway. In support of this, although we detected
minor but significant differences in song structure between each site, the most
divergent songs were those of island birds. On simulating secondary contact
using playback, we found that pairs from the forest island responded more
strongly to island (i.e. local) songs than to those from both non-island sites,
and vice versa. This pattern was not observed in pairs from one non-island
site, which responded with equal strength to local songs and songs from the
other non-island site. Island females were more likely to approach and sing
after hearing local male songs, rather than songs from the non-island
populations, and vice versa; non-island females did not appear to discriminate
between local songs and those from the other non-island site. These findings
are co!
nsistent with the idea that vocal divergence arising in small !
populati
ons at the edge of Amazonia may result in partial reproductive isolation when
contact is resumed. They also suggest the possibility that song divergence in
peripatry may, after much longer time-frames, act as a barrier to gene flow in
suboscines, perhaps because of an inability to learn or recognize divergent
songs on secondary contact.
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Dr. Alan McElligott
The School of Biology
Biology Building
The University of Nottingham
University Park
Nottingham NG7 2RD
UK
Tel + 44 (0) 115 951 3231
Fax + 44 (0) 115 951 3251
http://www.nottingham.ac.uk/biology/
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