September 6, 2012

Magellanic Penguins Now Designated As “Near Vulnerable”

Brett Smith for redOrbit.com — Your Universe Online

The latest IUCN Red List registers Magellanic penguins as ℠Near Vulnerable´ from a conservation standpoint, however a group of scientists from Bowling Green State University want to see if concerns might be tempered or fueled by understanding the genetic diversity amongst the birds´ populations in South America.

To measure the amount of genetic diversity in the birds, the researchers focused on the Major Histocompatibility Complex (MHC), a cell surface molecule that determines the interactions of leukocytes, or white bloods cells. This meant that the factors of disease exposure and mate choice have a direct effect on how the genes responsible for the MHC are passed on from generation to generation.

According to the team´s report published in the Journal of Heredity this week, they first looked to determine the amount of diversity within the South American population of Magellanic penguins.

"By looking at the MHC genotypes of 50 breeding pairs of Magellanic penguins, we found considerable levels of genetic variation, detecting a significantly greater number of MHC variants or alleles than those reported for Galapagos penguins and Humboldt penguins,” said first author Gabrielle Knafler, a graduate student at Bowling Green University.

The report stated that 45 alleles were found at the MHC gene locus for the Magellanic penguins found in southern Patagonia, compared to 3 for Galapagos penguins and 7 for Humboldt penguins living in captivity.

After establishing a relatively high level of MHC genetic diversity for Magellanic penguins, the team looked at two potential mechanisms to explain how this might happen. One possible scenario could be balanced selection, in which certain individuals are better adapted to combat a wide range of diseases and are therefore more likely to survive.

Another possibility is disassortative mating, where the mate selection process is driven by a difference in MHC genotype. The study´s lead scientist, Juan Bouzat, said the penguins may be able to detect mates with different MHC genotypes based on factors like smell.

"In some species in which disassortative mating has been detected, individuals discriminate among potential mates by MHC type on the basis of olfactory cues,” he said.

The scientists tested this possibility by checking the diversity among their 50 breeding pair sample set versus the possibility of random encounters. The disassortative mating possibility was eliminated when they found no direct correlation between the genotypes of each individual within the breeding pairs.

However, the team did find that MHC diversity did translate into a great level of overall population fitness, as heterozygous females were found to produce significantly more viable fledglings than homozygous females. These results point to a mechanism for balancing selection that maintains MHC diversity.

"There are likely other mechanisms at work as well," said Bouzat. "Spatial and temporal patterns in exposure to different pathogens may shape which alleles are favored at different times," changing selection pressures on the MHC genes. "The direct association of MHC genes with mechanisms of disease resistance suggests that the maintenance of MHC diversity could be driven by periodic selection due to different pathogens, similar to epidemics in humans.”