Sunday, July 31, 2011
Centaurium bianoris, a species in formation
The gorgeous salmon color of the Centaurium bianoris flowers is perhaps most showy of this natural allotetraploid hybrid. Its genome still is not completely stabilized and defined, continues evolving for million years and this fact is the responsible of the great variability in the tonality of the color salmon of its petals, that can go from a sulphured color, Centaurium bianoris var. sulfureum, happening through the typical color more or less intense salmon, Centaurium bianoris var. bianoris, until a clearly pink tonality, Centaurium bianoris var. roseum. This great chromatic variability is consequence of the instability of its chromosomes and its genes, since in its tetraploid genome the complete genomes of two diploid species of the Centaurium sort coexist with different degrees of harmony. It belongs to the family of the Gentianaceae.
During many years the botanists thought that their ancestors were the Centaurium pulchellum and the Centaurium maritimum, since apparently their macrocospic characteristics made therefore it suppose. Recently the genetic engeneering has given an upset to this supposition and it has been possible to know finally without no sort of doubts that their parents are the diploid Centaurium tenuiflorum subsp. acutiflorum of pink flowers and the diploid Centaurium maritimum of yellow flowers. It has been possible to even find out that at the time of the hibridization makes million years the father who contributed with the pollen was the Centaurium tenuiflorum subsp. acutiflorum and the mother who contributed the ovule and therefore the metabolic system with the chloroplasts was the Centaurium maritimum. In the photo the flowers of the family are seen, above both ancestors and down the hybrid son.
The color salmon of its petals, a really little character in the nature, confers a great beauty to it. I recommend to extend the photos with a double click.
A very showy characteristic of the flowers are the spiraled anthers of stamens.
The chloroplasts in the plants are the equivalent to mitochondrias in the mammals, which always inherit themselves by maternal way through mitochondrial chromosome of the feminine ovule. As animal mitochondrias the vegetal chloroplasts regulate the metabolism in each individual, so that most living beings inherit the metabolism of their mothers and have therefore more maternal genetic load than paternal. In the case of the Centaurium bianoris the inherited genes of their mother, the Centaurium maritimum, weigh more that those of their father and this it have been able to state in the genetic studies. I recommend to read the magnificent article in pdf of the Dr. Alessia Guggisberg, the Dr. François Bretagnolle and the Dr. Guilhem Mansion Allopolyploid Origin of the Mediterranean Endemic, Centaurium Bianoris, Inferred by Molecular Markers
The genome of the Centaurium bianoris is very unstable and its phenotype is extraordinarily variable. Before the height of the genetic engeneering one assumed that the varieties roseum and sulfureum were fruit of the retro-hybridization with one of them of its ancestors, but the genetic studies have discarded this possibility and the differences in the color of the flowers have been attributed to genetic silencing, that is to say, the blockade of the gene of one tonality and to the activation of the gene of another tonality. Thus in the variety sulfureum it would be silenced or it blocked the pink gene coming from the ancestor Centaurium tenuiflorum, whereas in the variety roseum would be the yellow gene of the Centaurium maritimum the one that would be silenced. Also in the leaves and other parts of the plant they have been found phenotypical differences by genetic silencing.
It is evident that the Centaurium bianoris has still not arrived at the end of its process of speciation, continues trying and playing with its genes in the long search of its genetic stability that began with the original hibridization, from which a sterile allodiploid hybrid arose, Centaurium X bianoris (TM) with half of its genome of the Centaurium maritimum (MM) and the other half of the Centaurium tenuiflorum (TT). The absolute lack of homology in the chromosomes of its genome made impossible the formation of viable seeds. It was led the extinction after its death, since generally the allodiploid hybrids usually are individual unique that die without descendants. Nevertheless, after many tests during million years, the nature was able to meet this challenge and managed to generate a fertile allodiploid hybrid with an intelligent mutation in the meiosis, call apomeiosis (meiosis absence), that allowed him to produce diploid gametes (normally they are haploid) in each one of as there were all the chromosomes of its ancestor. This way a grain of diploid pollen (TM) fertilized a diploide ovule (TM) and generated a new allotetraploid plant (TTMM), with two whole genomes in its nucleus. It was just born the Centaurium bianoris.
The flowers have 5 petals and are tiny. In order to do an idea it is enough to compare the flower of the image with the yolk of the annular finger of my left hand.
The Centaurium bianoris loves the direct sun. Its ideal habitat are the clear sites very illuminated of the pine groves and Mediterranean dry Garriga on grounds with little substrate generally covered with mosses and lichens. Usually it shares the habitat with Cistus, Rosmarinus, Pistacia lentiscus, Olea, Phillyrea, Ophrys, Barlia, Merendera, Blackstonia, Asphodelus, Asparagus, etc… It is a grass of annual cycle with a rosette of basal leaves and a turgid stem that it finishes in a branched inflorescence. The leaves of the stem are opposed and ovate-lanceolate. Usually it blooms in May and June.
Variety roseum with a delicate pink tone, by the silencing of the yellow gene and predominance of the pink gene of the ancestor Centaurium tenuiflorum subsp. acutiflorum.
Variety sulfureum with predominance of the yellow gene of the ancestor Centaurium maritimum.
This gorgeous hybrid is endemic to Majorca, Ibiza and Formentera. Their two ancestors coexist in other many regions of Western Europe and North Africa, but they have peculiarly not been able to hybridize or if they have made it the hybrid has not managed to surpass sterility, when lacking the mutation that causes the apomeiosis during the formation of the gametes.