Use of Conifer Resin to Create a Hostile Environment for Pathogens in Wood Ant Colonies
Wood ants ( Formica paralugubris ) have been observed gathering pieces of solidified conifer resin for use as nest material . This behavior can inhibit the growth of bacteria and fungi within the nest, and can even protect wood ants against a variety of pathogens . Experiments testing the intentionality of this behavior have demonstrated that wood ants prefer to collect the resin over alternative building materials in the spring and summer months . This preference for resin seems to waver in autumn . No concrete answers have been given for this seasonal variation in behavior, but several hypotheses have been proposed to explain the phenomenon . One leading thought is that the proportion of resin gathered drops as the ants focus on gathering twigs to prepare for the cold winter months . Another possibility is that because parasites can often be observed to time their reproduction with that of their host, the need for resin is much more significant in the spring and summer months, while the new brood of wood ant larvae is reared . Regardless of why this seasonal variation exists, the wood ants appear to recognize conifer resin through olfactory cues . The resin also appears to be used to prevent illness rather than treat it, as the proportion of resin gathered by infected ants is no higher than that gathered by uninfected ants . This behavior is a leading example of self medication behaviors in animals . Wood ants appear to gather the resin intentionally through olfactory cues, conifer resin is detrimental to a variety of wood ant pathogens, and this behavior does appear to have a positive effect on the fitness of wood ants in contact with pathogens .
Benefits of Conifer resin for wood ant health
The presence of conifer resin has a variety of demonstrable positive effects on the health, immune function, and survivability of wood ants. Immune function is an important characteristic for protecting species from parasitic and pathogenic organisms . However, constant activation and maintenance of the immune system greatly reduces the fitness of most organisms . This phenomenon has been directly observed in bumblebees, whose survivability under starvation conditions drops significantly with immune activation . Behavioral strategies for pathogen resistance, such as self-medication, are a useful biological strategy for mitigating these costs without compromising protection from pathogens . It is important to note that behavioral strategies are no more immune to costly trade offs than traditional immune activities . Behavioral defenses can often be energetically costly, but the costs of behavioral resistance can also come in the form of reduced time for other beneficial tasks . Still, behavioral strategies are often highly effective in increasing the overall fitness of an organism .
This principle can be demonstrated by the decrease of immune function that occurs when wood ants are in close proximity to conifer resin . Ants in resin-rich nests have been shown to have decreased antibacterial and lytic activities as compared to ants in resin-free environments . This decrease in immune function allows the ants to focus energy on beneficial metabolic pathways separate from immune function . This decrease also appears to have no detrimental effect on microbial resistance in the affected wood ants, since the presence of conifer resin has also been shown to increase survival rates in colonies affected by a variety of pathogens . When infected with Pseudomonas fluorescens, soil bacteria generally considered to be weakly pathogenic, except for some strains which have severely detrimental effects for insects, both worker ants and larvae had significantly increased survival rates when nest material contained conifer resin . When infected with another pathogen, the parasitic fungus Metarhizium anisopliae, results were more mixed (3). While conifer resin had little effect on the survival rate of adult worker ants exposed to Metarhizium anisopliae, it did appear to greatly increase the survival rate of ant larvae infected with the pathogen . It was also shown that the conifer resin had no positive or negative effects on ants in a pathogen free environment . This data is a testament to the strong beneficial effects incorporating conifer resin into wood ant nesting materials has on wood ant pathogen resistance.
Antimicrobial properties of Conifer resin
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- Castella G, Chapuisat M, Moret Y, Christe P. The presence of conifer resin decreases the use of the immune system in wood ants. Ecological Entomology. 2008 Jun;33(3):408-12.
- Castella G, Chapuisat M, Christe P. Prophylaxis with resin in wood ants. Animal Behaviour. 2008 Apr 1;75(4):1591-6.
- Chapuisat M, Oppliger A, Magliano P, Christe P. Wood ants use resin to protect themselves against pathogens. Proceedings of the Royal Society B: Biological Sciences. 2007 Aug 22;274(1621):2013-7.
- Martin D, Tholl D, Gershenzon J, Bohlmann J. Methyl jasmonate induces traumatic resin ducts, terpenoid resin biosynthesis, and terpenoid accumulation in developing xylem of Norway spruce stems. Plant physiology. 2002 Jul 1;129(3):1003-18.
- Phillips MA, Croteau RB. Resin-based defenses in conifers. Trends in plant science. 1999 May 1;4(5):184-90.