Saturday, September 12, 2009

Horizontal transfer and invasive species

The latest issue of PNAS has two articles of interest to creation biology. The first is a piece on the origin of cholera. Chun et al. studied 23 genome sequences of pathogenic Vibrio cholerae isolated over the past 98 years. They found that recombination and lateral gene transfer are important factors in the emergence of different strains of the pathogen. As I noted before with malaria, the origin of pathogens and natural evil can be quite complicated. In this case, the origin and persistence of Vibrio pathogens by lateral gene transfer is quite interesting, given what I've speculated in the past about genomic modularity.

The next article is on one of my new favorite topics: invasive species. I've come to suspect that invasives could be a good model for recovery after the Flood. Lankau et al. studied the production of secondary compounds in populations of garlic mustard (Alliaria petiolata), a Eurasian plant that is invasive in the eastern US. In plants, secondary compounds are (more or less) a class of substances that includes fragrant oils and noxious chemicals. They can serve to repel herbivores or to attract pollinators. They're called secondary because they're not part of the primary metabolism that allows the plant to live and grow. In the case of A. petiolata, the secondary compounds appear to inhibit growth of other plants in the same soil. Lankau et al. found that the amount of these secondary compounds in the roots of A. petiolata decreases with the age of the population. In other words, populations of A. petiolata that have been here longer produce lower amounts of inhibitory root compounds, which allows nearby species to grow better. Lankau et al. attribute this change to natural selection, which I'm not really prepared to comment on. Suffice it to say that (as far as I can tell) their evidence for selection is indirect and would not preclude some kind of direct adaptation, a la Lamarck.

Chun et al. 2009. Comparative genomics reveals mechanism for short-term and long-term clonal transitions in pandemic Vibrio cholerae. PNAS 106:15442-15447.

Lankau et al. 2009. Evolutionary limits ameliorate the negative impact of an invasive plant. PNAS 106:15362-15367.