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Floral volatile alleles can contribute to pollinator‐mediated reproductive isolation in monkeyflowers ( M imulus )
Author(s) -
Byers Kelsey J. R. P.,
Vela James P.,
Peng Foen,
Riffell Jeffrey A.,
Bradshaw Harvey D.
Publication year - 2014
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.12702
Subject(s) - biology , pollinator , pollination , bumblebee , reproductive isolation , locus (genetics) , allele , botany , genetics , gene , pollen , population , demography , sociology
Summary Pollinator‐mediated reproductive isolation is a major factor in driving the diversification of flowering plants. Studies of floral traits involved in reproductive isolation have focused nearly exclusively on visual signals, such as flower color. The role of less obvious signals, such as floral scent, has been studied only recently. In particular, the genetics of floral volatiles involved in mediating differential pollinator visitation remains unknown. The bumblebee‐pollinated M imulus lewisii and hummingbird‐pollinated M imulus cardinalis are a model system for studying reproductive isolation via pollinator preference. We have shown that these two species differ in three floral terpenoid volatiles – d ‐limonene, β‐myrcene, and E ‐β‐ocimene – that are attractive to bumblebee pollinators. By genetic mapping and in vitro analysis of enzyme activity we demonstrate that these interspecific differences are consistent with allelic variation at two loci, LIMONENE ‐ MYRCENE SYNTHASE ( LMS ) and OCIMENE SYNTHASE ( OS ). M imulus lewisii LMS ( Ml LMS ) and OS ( Ml OS ) are expressed most strongly in floral tissue in the last stages of floral development. M imulus cardinalis LMS ( Mc LMS ) is weakly expressed and has a nonsense mutation in exon 3. M imulus cardinalis OS ( Mc OS ) is expressed similarly to Ml OS , but the encoded Mc OS enzyme produces no E ‐β‐ocimene. Recapitulating the M . cardinalis phenotype by reducing the expression of Ml LMS by RNA interference in transgenic M . lewisii produces no behavioral difference in pollinating bumblebees; however, reducing Ml OS expression produces a 6% decrease in visitation. Allelic variation at the OCIMENE SYNTHASE locus is likely to contribute to differential pollinator visitation, and thus promote reproductive isolation between M . lewisii and M . cardinalis . OCIMENE SYNTHASE joins a growing list of ‘speciation genes’ (‘barrier genes’) in flowering plants.