Seperating the role of biotic interactions and climate in determining adaptive response of plants to climate change
Tomiolo, S. ; Putten, W.H. van der; Tielbörger, K. - \ 2015
Ecology 96 (2015)5. - ISSN 0012-9658 - p. 1298 - 1308.
local adaptation - environmental gradients - positive interactions - species interactions - soil feedback - ecological responses - aridity gradient - global change - evolutionary - communities
Altered rainfall regimes will greatly affect the response of plant species to climate change. However, little is known about how direct effects of changing precipitation on plant performance may depend on other abiotic factors and biotic interactions. We used reciprocal transplants between climatically very different sites with simultaneous manipulation of soil, plant population origin, and neighbor conditions to evaluate local adaptation and possible adaptive response of four Eastern Mediterranean annual plant species to climate change. The effect of site on plant performance was negligible, but soil origin had a strong effect on fecundity, most likely due to differential water retaining ability. Competition by neighbors strongly reduced fitness. We separated the effects of the abiotic and biotic soil properties on plant performance by repeating the field experiment in a greenhouse under homogenous environmental conditions and including a soil biota manipulation treatment. As in the field, plant performance differed among soil origins and neighbor treatments. Moreover, we found plant species-specific responses to soil biota that may be best explained by the differential sensitivity to negative and positive soil biota effects. Overall, under the conditions of our experiment with two contrasting sites, biotic interactions had a strong effect on plant fitness that interacted with and eventually overrode climate. Because climate and biotic interactions covary, reciprocal transplants and climate gradient studies should consider soil biotic interactions and abiotic conditions when evaluating climate change effects on plant performance.
Environmental proxies of antigen exposure explain variation in immune investment better than indices of pace of life
Horrocks, N.P.C. ; Hegemann, A. ; Ostrowski, S. ; Ndithia, H. ; Shobrak, M. ; Williams, J.B. ; Matson, K.D. ; Tieleman, B.I. - \ 2015
Oecologia 177 (2015)1. - ISSN 0029-8549 - p. 281 - 290.
female pied flycatchers - tropical birds - trade-offs - ecological immunology - microbial diversity - natural antibodies - aridity gradient - south-africa - history - patterns
Investment in immune defences is predicted to covary with a variety of ecologically and evolutionarily relevant axes, with pace of life and environmental antigen exposure being two examples. These axes may themselves covary directly or inversely, and such relationships can lead to conflicting predictions regarding immune investment. If pace of life shapes immune investment then, following life history theory, slow-living, arid zone and tropical species should invest more in immunity than fast-living temperate species. Alternatively, if antigen exposure drives immune investment, then species in antigen-rich tropical and temperate environments are predicted to exhibit higher immune indices than species from antigen-poor arid locations. To test these contrasting predictions we investigated how variation in pace of life and antigen exposure influence immune investment in related lark species (Alaudidae) with differing life histories and predicted risks of exposure to environmental microbes and parasites. We used clutch size and total number of eggs laid per year as indicators of pace of life, and aridity, and the climatic variables that influence aridity, as correlates of antigen abundance. We quantified immune investment by measuring four indices of innate immunity. Pace of life explained little of the variation in immune investment, and only one immune measure correlated significantly with pace of life, but not in the predicted direction. Conversely, aridity, our proxy for environmental antigen exposure, was predictive of immune investment, and larks in more mesic environments had higher immune indices than those living in arid, low-risk locations. Our study suggests that abiotic environmental variables with strong ties to environmental antigen exposure can be important correlates of immunological variation.
Seasonal patterns in immune indices reflect microbial loads on birds but not microbes in the wider environment
Horrocks, N.P.C. ; Matson, K.D. ; Shobrak, M. ; Tinbergen, J.M. ; Tieleman, B.I. - \ 2012
Ecosphere 3 (2012)2. - ISSN 2150-8925 - 14 p.
feather-degrading bacteria - arabian desert - saudi-arabia - life-history - trade-offs - ecological immunology - evolutionary ecology - atmospheric bacteria - airborne particles - aridity gradient
Documenting patterns in immune function is a first step to understanding immune variation, but to comprehend causes and consequences, antigen and parasite exposure that may drive such variation must be determined. We measured host-independent microbial exposure in five species of larks (Alaudidae) in the Arabian Desert by sampling ambient air for culturable microbes during late spring and winter, two periods with contrasting environmental conditions. We developed a novel technique to assay densities of microbes shed from birds, and we quantified four indices of constitutive innate immunity. Birds shed significantly more microbes during spring than winter, and all immune indices except one were also significantly higher during spring. In contrast, concentrations of airborne environmental microbes were higher in winter. Among all birds in both seasons, lysis titers were positively correlated with total densities of microbes shed from birds, suggesting that immune defenses are directed towards the microbes that birds carry, rather than microbes in the wider environment. Our findings highlight the relevance of quantifying non-specific immune challenges in ecological immunology studies, and reinforce the importance of both host-dependent and host-independent measures of antigenic pressure for understanding immune variation. Read More: http://www.esajournals.org/doi/abs/10.1890/ES11-00287.1