Monarch butterflies help explain why parasites ...(the western population caused the butter...)

Aside from shedding light on the vexing evolutionary question of why parasites harm their hosts, the study has implications for the health of humans and butterflies.

In some cases, scientists have predicted how public health interventions can influence the evolution of disease virulence based on the trade-off hypothesis. Predictions require careful knowledge of host and parasite biology, but one idea is that interventions that block parasite transmission opportunities could cause natural selection to favor strains with lower virulence. The teams findings suggest that when transmission opportunities are more limited, such as in the eastern monarch populations, natural selection will favor parasites that can persist longer on infected hosts and cause less damage.

The study also calls into question the wisdom of captive breeding of monarchs for intentional release at events such as weddings. Captive rearing conditions can promote parasite transmission and favor more virulent parasite strains that have the potential to harm wild populations that come into contact with them.

Altizer points out that migratory monarchs are already facing challenges from climate change which reduces their migratory range and habitat destruction in their winter breeding grounds.

Theres a very real probability that the eastern migratory population will be lost sometime in the next 50 to 100 years, Altizer said. Smaller, non migratory populations will likely persist, but were expecting that many more butterflies will be infected and that the parasites could become more virulent.

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