The evolutionary history of Antirrhinum suggests that ancestral phenotype combinations survived repeated hybridizations

Abstract

SUMMARYThe model species Antirrhinum majus (the garden snapdragon) has over 20 close wild relatives that are morphologically diverse and adapted to different Mediterranean environments. Hybrids between Antirrhinum species have been used successfully to identify genes underlying their phenotypic differences, and to infer how selection acts on them. To better understand the genetic basis for this diversity, we have examined the evolutionary relationships between Antirrhinum species and how these relate to geography and patterns of phenotypic variation in the genus as a whole. Large population samples and both plastid and multilocus nuclear genotypes resolved the relationships between many species and provided some support for the traditional taxonomic division of the genus into morphological subsections. Morphometric analysis of plants grown in controlled conditions supported the phenotypic distinction of the two largest subsections, and the involvement of multiple underlying genes. Incongruence between nuclear and plastid genotypes further suggested that several species have arisen after hybridization between subsections, and that some species continue to hybridize. However, all potential hybrids appear to have retained a phenotype similar to one of their ancestors, suggesting that ancestral combinations of characters are maintained by selection at many different loci.

The influence of pigmentation patterning on bumblebee foraging from flowers of Antirrhinum majus

“…Although the two phenotypes are readily distinguishable under differential conditioning, bees did not innately prefer either line. This result at first seems surprising in light of the relative frequency of veined phenotypes in wild species of Antirrhinum (Shang et al, 2011;Wilson and Hudson, 2011). Furthermore, the venation patterns slightly reduce the overall reflectivity of the veined flowers.…”

“…It contains approximately 20 species distributed in the Mediterranean region, many of which produce flowers with pale pigmentation but deeply pigmented venation patterns (Wilson and Hudson, 2011;Shang et al, 2011). The common genetic model Antirrhinum majus is usually fully pigmented red.…”

The genetic basis for natural variation in heteroblasty in Antirrhinum

“…-that are largely natural (Rothmaler, 1956;Wilson & Hudson, 2010). Species in subsection Kickxiella were found to share low PC1 spp values, while most members of subsection Antirrhinum and Streptosepalum had higher values, reflecting their larger leaves and narrower leaf shapes (Fig.…”

“…Measures of allometric variation between leaves and flowers of different Antirrhinum L. (snapdragon) species have previously been made with computational models that captured variation in organ outlines as a limited number of orthogonal principal components, providing a low-dimensional description of much of the difference between species (Langlade et al, 2005;Feng et al, 2009;Wilson & Hudson, 2010).…”

“…All are able to form fertile hybrids with each other (Stubbe, 1966;Wilson & Hudson, 2010), allowing allometry genes to be identified as quantitative trait loci (QTLs; Langlade et al, 2005;Feng et al, 2009). Antirrhinum also includes the genetic model Antirrhinum majus L., in which a number of phase transitions have been studied, including variations in leaf size, hair density, phyllotaxy and the ability of plants to flower in response to an inductive photoperiod (Bradley et al, 1996;Cremer et al, 1998;Preston & Hileman, 2010).…”