Habitat fragmentation produces inbred bumble bees
A recent article in the BBC news reports that bumble bees in the UK may be experiencing increased susceptibility to parasites due to inbreeding. The inbreeding is due to habitat fragmentation. Habitat fragmentation causes populations of bees to be cut off from other populations, such that they cannot breed with each other.
If this is confusing, try to follow this story. Let’s say we are in the United States and suddenly people from one city cannot leave that city and no one new can come in. The situation is permanent, so people in each city intermarry because there is no other choice. They have children who also intermarry. Many generations pass.
After a long time, certain traits appear in each different city. Let’s pretend that people from Detroit begin having long noses, people from Miami get hiccups, and people from Denver are especially prone to catching the flu. These changes occur because the frequency of certain genes in a population changes when that population is forced to interbreed. So a person prone to hiccups has a high probability of marrying someone else prone to hiccups because there are a lot of hiccup genes in that population. The children of these people are also prone to hiccups. As time goes on, the hiccup gene is everywhere.
People like Penelope Whitehorn—the researcher in the BBC story—study island populations of various organisms to learn how fragmented populations will respond to the environment. Fragmented populations are very much like islands because the individuals are cut off from the rest of the world.
Bumble bees, for example, don’t travel very far. If you have a population of bumble bees in Central Park, there is a very low chance they will mate with bumble bees outside the city, because there are too many barriers. Skyscrapers, freeways, apartment buildings, shopping malls, and industrial complexes provide virtually un-crossable barriers to the bumble bees.
As a result, the bees interbreed. Whitehorn, studying bumble bees (Bombus muscorum) on nine islands off the coast of Scotland, found the isolated populations to be very susceptible to a parasite called Crithidia bombi that lives in the bee’s gut. The populations also produced a very high percentage of infertile males. Based on this evidence, it is easy to see that mainland populations that are cut off from each other may develop these or similar problems.
The study of populations on islands is called “island biogeography.” Those of us in grad school who studied this phenomenon had a favorite book entitled The Song of the Dodo by David Quammen. This book—affectionately known as “the dodo book”—walks you through the main concepts of this science in a readable and engaging history of island biogeography and its relationship to the evolution, extinction, and transformation of living things. I highly recommend it.
Honey Bee Suite