S. trenchii is a coral symbiont that can persist in 1-2 degrees C higher temperatures than can other symbionts. It fixes similar amounts of carbon compared to other symbionts but significantly decreases the instantaneous calcification rate of corals. (compare against non-instantaneous rate?) (Treating is like a pathogen.) In the Greater Atlantic area, S. trenchii is generally clonal and the same genotype, and the Indo-Pacific has more MLG. (define multilocus genotype?) Seeing as S. trenchii is clonal in much of the Atlantic suggests that there were multiple, separate introductions of the symbiont.
What are MLG's? Is it a strain or an isolate, etc.? multiple loci and at each there is a genotype. Taking microsatellites and grind up sample of symbiont and characterize with the microsatellite. just a characterization of the lineage/isolate/strain.
genotype: two alleles and any one locus
allele sizes: genes are different sizes (lengths of base pairs)?
marker type: microsatellites - simple sequence repeat locus. may have a motif (such as TCG) that repeats. in one region of genome it is likely that a section of 4 TCG's will mutate to 5.
There are symbionts that did not co-evolve with the Caribbean corals, how do we know? Because there are no alleles that are restricted to the Greater Caribbean. It originated from Indo-Pacific and lost variation as it moved into the Atlantic due to the founder effect. Demographic argument trying to characterize the species interaction as recently introduced. The Indo-Pacific corals have evolved to work with S. trenchii which require less calcification, so they are fine with these symbionts while the Greater Atlantic corals suffer.
What is a pathogen?
An individual that is affected by an interaction with another thing has its fitness decreased while the infecting agent has its fitness increased. S. trenchii is a symbiont that are decreasing the fitness of of Atlantic corals when compared to the fitness of the symbiont naturally present in Atlantic corals, but without a symbiont the coral cannot exist at all, and the natural symbionts are nonpresent due to environmental effects raising the temperature of the ocean. Is it a pathogen? Is it infectious? Symbiosis is where both require each other to survive. The coral and S. trenchii both need each other to survive. Could the coral co-evolve with the S. trenchii in the Greater Atlantic to eventually be able to thrive with the S. trenchii as well as the Indo-Pacific corals? (there are variations in both populations of host and symbiont) If this were to occur then I would not consider it a pathogen. Could it replace other symbionts that existed in the Atlantic corals before S. trenchii were introduced? It's currently a "pathogen" of the Atlantic corals because the host is the incorrect host compared to the Pacific hosts.
Rephrase "pathogen" - any thing that can induce replication of itself and uses another to replicate. (ecologically it's a parasitic relationship) Level of interaction? Specific genome-by-genome interactions. Traits like disease response are not at the level of species. Evolution of infectious diseases involves evolution of host and parasite.
Atlantic and Pacific basins have been separated since 3 and a half million years ago. Implications: There should be some novel diversity in S. trenchii if it's been in an area since that time.
(Already there is de-calcification of oceans that are selecting for all organisms that can use less calcium for their shells and structures.)