^ Wilson Journal 
of Ornithology 
Published by the Wilson Ornithological Society 
VOL. 123, NO. 3 September 2011 PAGES 429-662 
The Wilson Journal of Ornithology 123(3):429-440. 2011 
VOCAL TRAIT EVOLUTION IN A GEOGRAPHIC LEAPFROG 
PATTERN: SPECIATION IN THE MAROON-CHINNED FRUIT DOVE 
(.PTILINOPUS SUBGUIARIS) COMPLEX FROM WALLACEA 
FRANK E. RHEINDT. 11 JAMES A. EATON, 2 AND FILIP VERBELEN 3 
ABSTRACT.—Leapfrog patterns are a peculiar and little-understood phenomenon in which similar populations at either 
end of a geographic continuum are divided by dissimilar intervening populations. Leapfrog patterns may be important in 
allopatric speciation. Most documented cases of biological leapfrog patterns refer to morphological traits in passerine birds, 
and only few have been reported from outside (lie Andean region. More importantly, the biological basis of leapfrog 
patterns continues to elude biologists. We document a vocal leapfrog pattern—possibly the second such case documented— 
in the Maroon-chinned Fruit Dove (Ptilinopus suhgularis ) complex, adding to the few known examples of leapfrog patterns 
from outside the Neotropics and in non-passerines. P. suhgularis is a Wallucean pigeon whose three taxa occur in a 
longitudinal continuum from Sulawesi in the west to the Sula Islands in the east. We used discriminant analysis and other 
statistical methods to demonstrate that terminal members of the complex differ in song from Lhe geographically 
intermediate taxon but resemble each other more closely. Plumage in P. subgularis does not exhibit the same geographic 
distribution of variability, a pattern that agrees with the only Other study reporting a vocal leapfrog pattern, and supports an 
earlier hypothesis that leapfrog patients arise from stochastic phenotypic changes in geographically intermediate taxa. We 
combine the new insights on the distribution of vocal trail variation in P. subgularis with Pleistocene earth-historic 
information to revise species in the complex, Received 1J September 2010. Accepted 20 January 2011. 
One of the most puzzling phenomena in trait 
evolution is the geographic leapfrog pattern. This 
pattern arises when populations from opposing 
ends of a geographic continuum resemble each 
other in a particular character and are divided by 
populations that differ in this trait. Leapfrog patters 
' Harvard University. Department of Organismic and 
Evolutionary Biology. MCZ Fifth Floor, 26 Oxford Street, 
Cambridge. MA 02138. USA. 
: Birdtour Asia Ltd.. 17 Keats Avenue. Littleover, Derby. 
DE23 4EE, United Kingdom. 
1 Auguste Van Ooststraat 28. 9050 Gentbrugge. Belgium. 
4 Corresponding author; e-mail: 
frankrheindt@yahoo.com.au 
were first characterized in birds (Remsen 1984b), 
the class in which most cases are reported. 
Leapfrog patterns are distinguished from ring 
species, which have geographically circular distri¬ 
butions in which terminal forms are phenotypically 
different and behave as different biological species 
where they overlap. Several cases of avian ring 
species were formerly reported, only one of 
which—the Greenish Warbler ( Phylloscopus tro- 
chiloides )—has survived genetic scrutiny (e.g., 
Irwin et al. 2005). Leapfrog patterns continue to be 
regularly documented (e.g.. Remsen 1984a, Re¬ 
msen and Graves 1995. Maijer and Fjeldsi 1997, 
Hayes 2001, Johnson 2002, Weir et al. 2008, 
Mauck and Bums 2009. Cadena and Cuervo 2010). 
429 
