Journal Title - Oecologia
Article Title - Hybridization leads to host-use divergence in a 
polyphagous butterfly sibling species pair
Volume - Volume 158
Issue - 4
First Page - 651
Last Page - 662
Issue Cover Date - 2009-01-01

Author - R. J. Mercader
Author - M. L. Aardema
Author - J. M. Scriber
DOI - 10.1007/s00442-008-1177-9
Link - http://www.springerlink.com/content/461851215783q5mt

Abstract Climate warming has lead to increased genetic introgression 
across a narrow hybrid zone separating the eastern and Canadian tiger 
swallowtails (/Papilio glaucus/ and /Papilio canadensis/). This 
situation has led to the formation of an allochronically separated 
hybrid population with a delayed emerging phenotype or “late flight”. 
Here, we assess how the recombination of the parental genomes that lead 
to this phenotype may have facilitated another major ecological shift, 
host-use divergence. We first contrast the ovipositional profiles of the 
late flight population to that of the parental species /P. glaucus/ and 
/P. canadensis/. Subsequently we contrast the larval survival and growth 
of the late flight, a /P. canadensis/ and a /P. glaucus/ population, and 
a population from the northern edge of the hybrid zone on five hosts. 
Our results indicate that the ovipositional preference of this hybrid 
swarm is identical to that of the introgressing parental species, /P. 
glaucus/. Due to the absence of the preferred hosts of /P. glaucus/ 
(/Liriodendron tulipifera/ L. and /Ptelea trifoliata/ L.) where the late 
flight occurs/,/ this ovipositional pattern implies a functional 
specialization onto a secondary host of both parental species, /Fraxinus 
americana/ L. In contrast, the larval host-use abilities represent a 
mixture of /P. glaucus/ and /P. canadensis/, indicating divergence in 
larval host-use abilities has not taken place. However, high genetic 
variability (genetic coefficient of variation) is present for growth on 
/F. americana/ in the late flight hybrid swarm and tradeoffs for larval 
performance on the preferred hosts of the parental species are evident; 
indicating a strong potential for future specialization in larval 
host-use abilities. This current scenario represents an instance where a 
shift in a major ecological trait, host use, is likely occurring as a 
byproduct of a shift in an unrelated trait (delayed emergence) leading 
to partial reproductive isolation.

-- 
Kent McFarland
Vermont Center for Ecostudies
PO Box 420 • Norwich, VT 05055
802.649.1431
http://www.vtecostudies.org/