Every Friday at Nothing in Biology Makes Sense! our contributors pass around links to new scientific results, or science-y news, or videos of adorable wildlife, that they’re most likely to bring up while waiting in line for a latte.
To get things started, CJ found a depressing study (depending on your perspective anyway) about how your attitude can affect your health. It’s not what you would expect a study to find, but there are additional conflicting studies so take it as you will. However, she follows it up with another article about how the privatization of space flight has a long way to go before we can all reach for the stars.
From Amy, a new variant in the African-American Y-chromosome leads to the speculation on how long ago the common ancestor of modern humans existed and/or whether there was potential interbreeding between Neanderthals and modern humans.
To follow that up, Jeremy found an interesting video that shows a morphing of the faces of human ancestry.
From Sarah, a rather fun blog post on Scientific American on how one individual looked for answers to questions and found lots of information, but failed to answer the original question.
Finally, to return to the spring break theme, the CDC reports in its weekly grand rounds about multi-drug resistant gonorrhea.
Over the past several years there has been a growing trend of parents that are terrified of vaccinating their kids citing reasons such as the debunked link to autism or that it just isn’t “natural.” A healthcare blog run by several infectious disease doctors called Controversies in Hospital Infection Prevention has run frequent stories reporting on the declining vaccination rates as well as problems that ensue because of that, most recently about the whooping cough epidemic in Washington and wondering why Jenny McCarthy has so much influence on national views on vaccinations.
What happens when two parasites infect the same host individual? Is the outcome similar to the Thunderdome: two parasites enter, one parasite leaves? Host-parasite interactions are rarely so simple. While a reductionist approach to understanding the interaction of a parasite or pathogen with its host may decompose the system to a single infection, nature is full of much more complex puzzles. Within the host, the battle itself raging between parasites (within-host competition) may have cascading effects on the host.
A recent paper on virulence caught my eye (Bashey et al., 2012) which provides an update to a very interesting result from the group a few years ago. The system includes bacterial parasites, along with parasitic nematodes, that infect insect larvae and eat/digest them from the inside out. Vigneux et al. (2008) found that when multiple parasite isolates are mixed in a host, the host mortality decreased. However, this only occurred when the isolates were not related. In the experiment, the researchers created low relatedness by mixing populations with migration. I reviewed the 2008 paper over at the Coevolvers blog, my personal science blog. The hypothesis was that chemical warfare among the parasites decreased the parasite load and reduced the negative effects on the host, virulence.
What are the evolutionary consequences of parasite superinfection (i.e. simultaneous infection by multiple parasites)? When parasites are genetically distinct, coexistence within a host generates conflict because of limited resources. How this conflict is resolved is the source of evolutionary research on the evolution of parasite life history traits such as virulence, the negative effects on the host caused by infection, and transmission mode, how parasites infect a new host. The transmission mode of a parasite is often characterized as occurring in one of two different modes: vertical or horizontal. With vertical transmission, an offspring obtains its parasites directly from its parents. In contrast, with horizontal transmission, infections occur either directly from the environment or contagiously by infection from other individuals.
My interest in the evolution of transmission mode in parasites and symbionts led me to a recent paper (Ben-Ami et al. 2011), which addresses the consequences of superinfection by two different parasites with different transmission modes of the waterflea, Daphnia magna, on virulence and parasite fecundity. Pasteuria ramosa is a castrating, horizontally transmitted, blood-infecting bacterium where spores are produced from the cadaver of the host Daphnia. Octosporea bayeri, a microsporidium, utilizes both vertical transmission to eggs and horizontal transmission via waterborne spores.