Evolution Of Floral Characters Research Articles

Phylogenetic Analysis and Flower Color Evolution of the Subfamily Linoideae (Linaceae).

The taxonomy of the subfamily Linoideae at the intergeneric and section levels has been questioned throughout the years, and the evolution of floral characters remains poorly understood. In particular, the evolution of flower color is still uncertain, despite its ecological importance and being one of the most variable and striking traits in Angiospermae. We evaluated the phylogenetic relationships of the genera and sections and used the phylogeny to reconstruct the ancestral state of flower color. The results suggest reevaluating the taxonomic status of segregated genera and re-incorporating them into Linum. Four of the five sections currently accepted were recovered as monophyletic (Cathartolinum, Dasylinum, Linum, and Syllinum). We propose accepting the section Stellerolinon and reevaluating Linopsis, whose representatives were recovered in three separate clades. The ancestral flower color for Linoideae was yellow-white. The flower colors purple and yellow-white were recovered at the deepest nodes of the two main clades. Pink, blue, and red colors were the most recent to evolve. These results appear to be related to diversification events, biogeographical history, and ecological aspects of the subfamily. Our reconstruction constitutes the first plausible scenario that explores the evolution of flower color, leading to new testable hypotheses for future research on the flax group.

Evolution of floral characters and biogeography of Heloniadeae (Melanthiaceae): an example of breeding system shifts with inflorescence change

Heloniadeae (Melanthiaceae) presents an East Asia–North America disjunct distribution. Different molecular and morphological data nevertheless support the tribe as a monophyletic group. However, their phylogenetic relationships and biogeographic history, together with the character evolution, are not clear. Therefore, we constructed a Bayesian phylogenetic tree for Heloniadeae using cpDNA and inferred the historical biogeography and floral character evolution. The results revealed that Heloniadeae was distributed in high-latitudes of East Asia and North America, originating since 22.2 mya. The East Asia clade migrated into southwest China, and subsequently colonized the Korean Peninsula, Taiwan, the Ryukyus, and spread northward to Japan and southern Sakhalin. The evolution of the inflorescence and number of flowers were phylogenetically conserved, associated with the historical biogeography of Heloniadeae. The inflorescences transferred from raceme to sub-umbel, and the number of flowers decreased during the dispersal process, which may be accompanied by changes in the breeding system. Besides, the anthesis period was more affected by the habitat environment than phylogenetic constraints. The flowering temperature of Heloniadeae was below 20 °C in most species, except H. kawanoi. Such a low temperature might not be conductive to pollinator activities, but it could be compensated by sustaining seed production with long-lasting flowers.

Visits to manipulated flowers by Episyrphus balteatus (Diptera: Syrphidae) : Partitioning the signals of petals and anthers

In a number of previous studies attention has been directed to the selection on corolla dimensions by pollinator preference, but anthers may also be a signal. This experiment examined the relative importance of petals and anthers in the attraction of male Episyrphus balteatus (Diptera, Syrphidae) to individual oil-seed rape flowers (Bracus rapae oleifera). Rape flowers have four petals and six anthers. Nine treatments were created, of flowers with four, two, or zero petals and six, three, or zero anthers. Twenty males were tested for preference among the experimental flowers by recording the sequence and duration of their visits (which were all for feeding) to the flowers. The number of first visits and the duration of visits on each flower were significantly related to the number of anthers but not the number of petals. There was no correlation between petal area and pollen load of control flowers. It is suggested that Syrphidae may not always attend to petals, and variation in preference of different pollinator taxa should be taken into account when discussing the evolution of floral characters.

Developmental Homeostasis and Floral Form: Evolutionary Consequences and Genetic Basis

Plant biologists have largely ignored the role of developmental homeostasis in the evolution of floral traits. In this brief review, we discuss the relationship between floral form and developmental homeostasis, emphasizing that developmental homeostasis, as any other character, may respond to natural selection. We discuss the implications of developmental homeostasis being a selectively labile trait for the evolution of floral characters. A trait's ability to respond to selection is in part determined by its genetic basis. Therefore, we also discuss evidence for the genetic basis of developmental homeostasis and how it influences the evolution of developmental homeostasis and ultimately floral diversity. We conclude with a series of suggestions for future research, calling for a synthetic approach utilizing ecological, morphological, quantitative genetic, and molecular methodologies.

Phylogeny and Phylogeography of the Circumpolar GenusFraxinus(OLEACEAE) Based on Internal Transcribed Spacer Sequences of Nuclear Ribosomal DNA

The DNA sequences of the nuclear internal transcribed spacers (1 and 2) of nuclear ribosomal DNA were determined for 27 taxa ofFraxinusin an attempt to reconstruct the phylogeny of the genus and interpret its biogeographic history in a phylogenetic context. Minimal intraindividual and intraspecific polymorphisms were observed and infrageneric taxa were all recovered in phylogenetic analyses. The tree topologies estimated from parsimony and neighbor-joining analyses of one- and two-parameter substitution rates were congruent and supported by high bootstrap estimates. Indels were also found to be phylogenetically informative. The phylogenetic trees obtained were in quite good agreement with the current taxonomy of the genus but homoplasy was observed in the evolution of floral characters. Polyploidy also appeared to have evolved several times in the genus.Fraxinus nigrawas more closely related to European and Asian taxa than to the other American ashes. The AsianF. platypodahad a closer relationship to Asian and European ashes in sectionBumelioidesthan to its presumed North American allies of sectionMelioides.With respect to the position ofF. quadrangulataas sister group to the remainder to the remaining species, the subgenusFraxinusappeared paraphyletic. Phylogeographical analysis indicated thatFraxinuslikely originated in North America, with two subsequent events of intercontinental migration from North America to Asia.

Oviposition choices by a pre-dispersal seed predator (Hylemya sp.) : I. Correspondence with hummingbird pollinators, and the role of plant size, density and floral morphology.

Although the importance of pollinators has most often been examined in the evolution of floral characters, seed predators may also play a role in shaping floral evolution. In this study, I examined the role of interplant distance, plant size, and flower morphology on Ipomopsis aggregatás (Polemoniaceae) attractiveness to a pre-dispersal seed predator, Hylemya sp. (Anthomyiidae) and to hummingbird pollinators. The attractiveness of I. aggregata individuals to Hylemya was nonlinearly related to interplant distance in experimental arrays. Clumped and highly dispersed plants were preyed upon more frequently than those at intermediate distances. I found no relationship between interplant distance and visitation rates by hummingbird pollinators in these experimental arrays. However, in natural populations studied, clumped plants were more frequently approached by hummingbirds than those growing more widely dispersed. Display size was unrelated to visitation by Hylemya on inflorescences I clipped and maintained as "large", "small" and "control". Display size was also unrelated to the total number of visits by hummingbird pollinators to each of these experimental plants, however "large" display plants were more likely to be visited first in any given visitation sequence. Of various morphological measurements, corolla length showed the strongest positive correlation with Hylemya egg presence. To the extent that plant spacing and morphology is correlated with pollinator visits and ultimate seed set, Hylemya could be choosing flowers optimally, and playing a role in the evolution of floral traits.

VARIATION IN POLLEN FLOW WITHIN AND AMONG POPULATIONS OF IPOMOPSIS AGGREGATA.

Pollen dispersal is a major component of gene flow in plant populations. It can influence microevolution within and among populations as well as the evolution of floral characters that affect dispersal. Most previous studies have relied on point estimates to characterize dispersal distances, even though there is likely to be substantial intrapopulational and interpopulational variation. We measured variation in pollen dispersal for the hummingbird-pollinated herb Ipomopsis aggregata (Polemoniaceae), using powdered fluorescent dyes to estimate pollen movement. Analysis of 5-6 natural populations in each of three years indicated that mean and mean squared distances of pollen dispersal, measured over the reproductive lifespan of individual plants, varied more than threefold among populations and years. Dispersal distances also shifted over the season within a given population. Unlike the variation among populations, these seasonal changes were associated in part with changes in flower density. The mean distance of pollen dispersal from an individual plant was unrelated to the date of first flowering, but did reflect two floral characters. Plants with higher variance in stamen length across flowers delivered pollen farther on average, as predicted by computer simulations of pollen carryover. Plants with lower mean stamen lengths also delivered pollen farther. Such effects of plant characters on pollen dispersal are a critical prerequisite for dispersal to evolve in response to its effects on fitness.