Cordia danosa

Disponível somente no TrabalhosFeitos
  • Páginas : 10 (2406 palavras )
  • Download(s) : 0
  • Publicado : 7 de maio de 2012
Ler documento completo
Amostra do texto
Nectar production, visitors and deposition of pollen in flowers of Cordia nodosa: a species with atypical distyly in the National Forest of Caxiuanã – Melgaço (PA)



Keywords: distyly, Cordia, reciprocal herkogamy


The old family Boraginaceae is presentedfrom small herbs, shrubs, saplings to large trees (Barroso et al., 1991), and differed in four subfamilies that with molecular assessments were raised to the level of families (Gottschling et al. 2001). Among the elevated subfamilies we can highlight the Cordiaeceae family, which has about 350 species (Judd et al. 1999) and 65 of them in Brazil (Taroda & Gibbs 1986) with a wide diversity in the NewWorld, many with heterostylous feature.

The heterostyly is a genetically controlled floral polymorphism, which are species with two or three floral morphs, distinguishing the height of the anthers and stigma (Ganders 1979, Barrett 1992). Species with two floral morphs that differ in longistylis and brevistylus, the longistylis have low stamens and high stigma and the brevistylus with highstamens and low stigma, in different individuals are called distylous species.
Other dimorphisms have been identified in distylous species, such as size and
amount of pollen grains, stigmatic surface, stigmatic papillae (Hamilton 1990; Lloyd & Webb 1992). When the species has three morphs: brevistylus (high and medium stamens and low stigma), medistylus (high and low stamens and medium stigma) andlongistylous (low and medium stamens and high stigma ) are called trístilicas (Ganders 1979).
The distylous condition is the most common, occurring in 27 of 28 families of Angiosperms that have heterostyly (Barrett 1992).
An interesting feature in distylous populations is the discrete distribution of morphs, due to the genetic control of this trait, but recent studies show that people havea continuous variation in the characteristics distylous, presenting what we call distyly atypical, as is the case of polymorphism styles (Richards and Koptur, 1993, Sánchez et al. 2010; Ferrero et al. 2011).
The ratio between the number of individuals with pin and thrum flowers, according to the type of inheritance they show, can also greatly influence the reproductive process of thepopulation. This ratio is usually 1:1 (isopletia) (Ganders 1979), but due to an asymmetrical pollen flow, affecting the reproductive success, or causing variations in heterostylous systems, this ratio can be skewed, as is the case of monomorphic populations (Hamilton 1990), or homostylous populations (Coelho & Almeida, 2003). These deviations in the ratio between the morphs are often caused by thepresence of self-compatibility in the population (Ganders 1979), and / or a high rate of vegetative reproduction (Sobrevila et al. 1983).
          Several studies highlight the presence of reciprocal herkogamy (HR) as important for the maintenance of distyly because it is responsible for pollen flow between morphs through flower visitors (Heuchera 1979, Barrett 1992, Faivre & McDade 2001), yet otherauthors have questioned the actual efficiency and also its precise manifestation as a basic requirement to assign a typical distyly to a species (1992 Dulberger, Pailler & Thompson 1997).
The absence of typical distyly may result from variation in the supergene, in response to factors related to environmental disturbance (Barrett 1988, Agren 1996), geographic isolation or reduction in populationsize (Jennersten 1988) often the result is the formation of variant morphs and / or the situation of total loss of one of the morphs (Ganders 1979, Hamilton 1990, Matsumura & Washitani 2000). These variants can be classified as Homostyly brevistylous, Homostyly longistylous, Homostyly intermediate and eventual total loss of one and thrum morphs as monomorphism monomorphy (Bawa & Beach 1983,...