Monday 6 August 2012

A new, diploid, Pincushion Plant, from the Rocky Mountains.

Most eukaryotic organisms (organisms with cell nuclei; basically everything accept bacteria, archaea and viruses) are diploid, that is to say they have two sets of chromosomes, which are recombined during sexual reproduction. Sometimes this process goes wrong, creating new organisms with additional chromosomes, known as polyploid species. The most common way this happens is that an incomplete cell division during reproduction leaves two sets of chromosome pairs (i.e. four of each chromosome) in each cell, which is known as tetraploidy, although more complex species with six sets of chromosomes (hexaploids) or even higher numbers are known. 

Individuals with higher chromosome numbers are not necessarily physically any different from their parents, but they will not be able to reproduce with diploid individuals, due to the different chromosome number. In animals, which usually reproduce only with other individuals, this typically means tetraploid individuals die without reproducing, but many species of plants can reproduce asexually, or sexually with themselves (self-fertilization), so changes in chromosome number are an important method of speciation (the formation of new species), creating reproductive isolation between identical populations, which can then follow different evolutionary paths. New species can also be created when tetraploid species loose chromosomes

In a paper published in the journal Phytotaxa on 30 January 2012, a team of scientists led by Leigh Johnson of the Department of Biology and M.L. Bean Museum at Brigham Young University, describe the discovery of a new species of diploid Pincushion Plant, Navarretia, from Utah, Idaho, Wyoming, Montana, and Colorado. 

Pincushion Plants are spiny, herbaceous members of the Phlox family (Polemoniaceae), found throughout North America, but at their most diverse in California.

The new plant is named Navarretia furnissii in honour of Blaine Furniss a retired professor of Botany at Brigham Young University. It is a diploid version of the widespread, tetraploid, Rocky Mountain Pincushion Plant, Navarretia saximontana, implying that one species arose from the other, either by chromosome-loss or chromosome-gain. The most closely related species is the diploid Navarretia propinqua, suggesting that Navarretia saximontana arose from Navarretia furnissii via chromosome doubling, but since  Navarretia propinqua is probably really a complex of cryptic species (species which appear identical but which are reproductively isolated by genetic differences), this is not certain.

Navarretia furnissii is essentially similar to Navarretia saximontana, although some differences have started to appear, most notably shorter flowers in Navarretia furnissii and longer in Navarretia saximontana, suggesting that the pair have been reproductively isolated for a while. The new plant is an annual herbaceous plant 1-6 cm tall, it occurs in moist pockets in woodlands and grasslands, and at the margins of pools. It forms large colonies of hundreds or thousands of individuals, and is not thought to be under any conservation threat; the new species was not recognized before due to its similarity to Navarretia saximontana, rather than because it is rare in any way.

The flowers of (A) Navarretia furnissii, (B) Navarretia saximontana, and (C) Navarretia propinqua. Scale bar is 5 mm. Johnson et al. (2012).

Entire Navarretia furnissii plant, excluding root system. Scale bar is 1 cm. Johnson et al. (2012).

Detailof flowering head of Navarretia furnissii. Scale bar is 5 mm. Johnson et al. (2012).

Pollen of Navarretia furnissii. Scale bar is 10 μm. Johnson et al. (2012).

Follow Sciency Thoughts on Facebook.