On Great Tits, Parasitism, and Immunocompetence: The Trade-Offs

This paper in Proceedings of Royal Society Biology purports to show that there is an investment trade-off between immunocompetence and animal growth. In cases where parasitism is high, the trade-off tends to tilt towards investment in immunocompetence.

I love this article for two reasons.

1) It was conducted on a species that -- I &%^@ you not -- is called the Great Tit:

The study was performed in 2004 in a population of great tits breeding in nest boxes in a mixed forest near Bern, Switzerland. The great tit is a small (16-20 g) hole-nesting passerine that produces one or two broods per year.

I have to meet the people who are naming these birds. That is the most fantastic thing I have ever heard. And a lot of the study is done on the baby birds or the "nestlings." That's right...there is a model organism called the nestling great tit. Here would be a picture of the tit in question:

2) I think that they show rather elegantly that the investment of a species into a one area may make sense under one condition but may not in another. Evolution is a very dynamic business. Here is the money figure:

We found that after the experimental manipulation of the nestlings' investment in immune defence, i.e. after the methionine supplementation had stopped, immune-boosted nestlings grew at significantly faster rates in parasite-infested nests compared to controls, whereas in parasite-free nests, immune-boosted and control nestlings did not grow at significantly different rates. This result cannot be explained by compensatory growth alone because compensatory growth would lead to higher growth rates of methionine supplemented nestlings irrespective of their parasite treatment, (i.e. to a significant main effect of the methionine treatment, but a non-significant interaction effect between parasite treatment and methionine treatment). The significant interaction effect between parasite treatment and methionine supplementation thus emphasizes the beneficial effects of an increased investment in immune defence when exposed to parasites. This beneficial effect might be due to specific or unspecific immune reactions--against hen fleas and/or pathogens that are potentially transmitted by the fleas during the blood meal... -- which were stimulated by the methionine supplementation.

Hat-tip: Faculty of 1000.