Species‐independent, geographical structuring of chloroplast DNA haplotypes in a montane herb Ipomopsis (Polemoniaceae)

Abstract

Two hypotheses have been proposed to explain the occurrence of hybrid zones between red‐flowered Ipomopsis aggregata and white‐flowered I. tenuituba. Either local adaptation to hummingbird and hawkmoth pollinators has given rise to sympatric (or parapatric) divergence of flower colour and morphology (primary intergradation at hybrid zones), or alternatively two previously allopatric species are coming into contact at several geographical areas of secondary intergradation. We examined restriction site patterns in nuclear DNA (nrDNA), chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) from populations of I. aggregata and I. tenuituba representing seven zones of sympatry. No variation was detected in a 350‐bp fragment of mtDNA and uninformative levels of variation were observed for nrDNA. We detected 22 potentially informative restriction site polymorphisms in cpDNA, all of which united geographical areas containing populations of both species. We detected no informative species‐specific markers. Studies of other species (e.g. oaks) have detected similar species‐independent geographical structure of cpDNA. However, in these cases secondary interegradation could be inferred from species‐specific nuclear alleles. The pattern in Ipomopsis is consistent with both primary intergradation (independent speciation in each area of sympatry) or secondary intergradation involving complete cytoplasmic replacement. Thus, additional data are needed to explain the origin of hybrid zones in Ipomopsis.

Contrasting Patterns of Floral and Molecular Variation Across a Cline in Mimulus Aurantiacus

“…obs.). Similar studies of floral variation across ecological gradients have found comparable patterns of strong morphological differentiation, little or no neutral differentiation, and the presence of both alternative pollinators on each side of the contact zone (Hodges and Arnold 1994;Wolf et. al.…”

Chloroplast DNA variation of white oaks in the alpine region

“…Recombination events can only take place between different cpDNA genomes of the same cell and could be an important mechanism of evolutionary change in this molecule (Gillham, 1994;Kanno et al, 1997;Higgs et al, 1998). In addition, cpDNA has a low mutation rate (Zurawski et al, 1984;Gaut et al, 1996;Wolfe et al, 1997;Lynch and Blanchard, 1998) and in conjunction with its maternal inheritance, make it a suitable marker for following seed movement and retracing historical postglacial migration events (e.g. Petit et al, 1993;Le Corre et al, 1997).…”

Intraspecific variation and geographic patterns of Fagus orientalis Lipsky chloroplast DNA

“…Many studies have reported geographic pattern in cpDNA variation below the species level (MAYER et al, 1994;SEWELL et al, 1996;DUMOLIN-LAPÉGUE et al, 1997; VAN DIJK and BAKX-SCHATMAN, 1997;WOLF et al, 1997;KING and FERRIS, 1998;TREMBLAY and SCHOEN, 1990;ABBOTT et al, 2000). Furthermore, intra-specific cpDNA variation has been observed among Fagus species including Fagus sylvatica (DEMESURE et al, 1996), F. crenata (FUJII et al, 2002).…”