How strong is selection for cheating in mutualisms? The answer depends on the type and magnitude ... more How strong is selection for cheating in mutualisms? The answer depends on the type and magnitude of the costs of the mutualism. Here we investigated the direct and ecological costs of plant defense by ants in the association between Cordia nodosa, a myrmecophytic plant, and Allomerus octoarticulatus, a phytoecious ant. Cordia nodosa trees produce food and housing to reward ants that protect them against herbivores. For nearly 1 year, we manipulated the presence of A. octoarticulatus ants and most insect herbivores on C. nodosa in a full-factorial experiment. Ants increased plant growth when herbivores were present but decreased plant growth when herbivores were absent, indicating that hosting ants can be costly to plants. However, we did not detect a cost to ant colonies of defending host plants against herbivores. Although this asymmetry in costs suggests that the plants may be under stronger selection than the ants to cheat by withholding investment in their partner, the costs to C. nodosa are probably at least partly ecological, arising because ants tend scale insects on their host plants. We argue that ecological costs should favor resistance or traits other than cheating and thus that neither partner may face much temptation to cheat.
1. Ants provide variable protection against herbivores to ant-plants (i.e. myrmecophytes and myrm... more 1. Ants provide variable protection against herbivores to ant-plants (i.e. myrmecophytes and myrmecophiles). The ways in which ant-plants dynamically adjust both their direct (chemical and physical) and indirect (biotic) defences in response to varying levels of herbivory are not well understood. 2. We experimentally generated a broad range of ant-attendance levels and herbivory pressures in a tropical myrmecophyte, Cordia nodosa, which allowed exploration of the inducibility of and interactions between direct and indirect resistance traits. 3. In response to increased herbivory, host plants encouraged indirect (biotic) defence by increasing domatium volume, regardless of whether ants were present on the plant. When ants were present, larger domatia housed more workers, which in turn decreased herbivory on adjacent leaves. 4. Independent of the presence of ants, plants responded to increased herbivory by inducing both chemical (phenolics) and structural (leaf toughness, trichomes) resistance traits; these traits were associated with reduced palatability to a folivorous beetle. 5. Synthesis. Our results show that both direct and indirect defences are inducible in C. nodosa, which suggests that C. nodosa may retain direct defences as insurance against varying levels of protection from its ant bodyguards. Thus, the predictions of optimal defence theory are not violated: although C. nodosa invests in multiple forms of defence, they are not redundant.
Clinical presentation and histopathology of autoimmune hepatitis (AIH) and primary sclerosing cho... more Clinical presentation and histopathology of autoimmune hepatitis (AIH) and primary sclerosing cholangitis (PSC) overlap syndrome (OS) are similar, but their management is different. We conducted a pediatric retrospective cross-sectional study of 34 patients with AIH and PSC. AIH had female predominance (74%) and was lower in PSC (45%). There was a trend toward higher frequency of blacks in PSC/OS (55%) compared to Caucasians (36%) and Hispanics (9%), but not race differences in AIH. Inflammatory bowel disease (IBD) was present in 75% of PSC/OS. Plasma cells were not specific for AIH (found in 42% of PSC). Concentric fibrosis was not reliable for PSC as was found in 46% of AIH. A combination of clinical history, laboratory tests, imaging studies and liver biopsy are required to confirm and properly treat AIH and PSC. Liver biopsy should be used to grade severity and disease progression, but cannot be used alone to diagnose these conditions.
Gastroenterology, Volume 138, Issue 5, Pages S-786, May 2010, Authors:LinaHernandez; Eddie Island... more Gastroenterology, Volume 138, Issue 5, Pages S-786, May 2010, Authors:LinaHernandez; Eddie Island; Andreas G. Tzakis; Gennaro Selvaggi; Akin Tekin; Amber H. Langshaw; Lesley J. Smith. Gastroenterology - Click here ...
How strong is selection for cheating in mutualisms? The answer depends on the type and magnitude ... more How strong is selection for cheating in mutualisms? The answer depends on the type and magnitude of the costs of the mutualism. Here we investigated the direct and ecological costs of plant defense by ants in the association between Cordia nodosa, a myrmecophytic plant, and Allomerus octoarticulatus, a phytoecious ant. Cordia nodosa trees produce food and housing to reward ants that protect them against herbivores. For nearly 1 year, we manipulated the presence of A. octoarticulatus ants and most insect herbivores on C. nodosa in a full-factorial experiment. Ants increased plant growth when herbivores were present but decreased plant growth when herbivores were absent, indicating that hosting ants can be costly to plants. However, we did not detect a cost to ant colonies of defending host plants against herbivores. Although this asymmetry in costs suggests that the plants may be under stronger selection than the ants to cheat by withholding investment in their partner, the costs to C. nodosa are probably at least partly ecological, arising because ants tend scale insects on their host plants. We argue that ecological costs should favor resistance or traits other than cheating and thus that neither partner may face much temptation to cheat.
1. Ants provide variable protection against herbivores to ant-plants (i.e. myrmecophytes and myrm... more 1. Ants provide variable protection against herbivores to ant-plants (i.e. myrmecophytes and myrmecophiles). The ways in which ant-plants dynamically adjust both their direct (chemical and physical) and indirect (biotic) defences in response to varying levels of herbivory are not well understood. 2. We experimentally generated a broad range of ant-attendance levels and herbivory pressures in a tropical myrmecophyte, Cordia nodosa, which allowed exploration of the inducibility of and interactions between direct and indirect resistance traits. 3. In response to increased herbivory, host plants encouraged indirect (biotic) defence by increasing domatium volume, regardless of whether ants were present on the plant. When ants were present, larger domatia housed more workers, which in turn decreased herbivory on adjacent leaves. 4. Independent of the presence of ants, plants responded to increased herbivory by inducing both chemical (phenolics) and structural (leaf toughness, trichomes) resistance traits; these traits were associated with reduced palatability to a folivorous beetle. 5. Synthesis. Our results show that both direct and indirect defences are inducible in C. nodosa, which suggests that C. nodosa may retain direct defences as insurance against varying levels of protection from its ant bodyguards. Thus, the predictions of optimal defence theory are not violated: although C. nodosa invests in multiple forms of defence, they are not redundant.
Clinical presentation and histopathology of autoimmune hepatitis (AIH) and primary sclerosing cho... more Clinical presentation and histopathology of autoimmune hepatitis (AIH) and primary sclerosing cholangitis (PSC) overlap syndrome (OS) are similar, but their management is different. We conducted a pediatric retrospective cross-sectional study of 34 patients with AIH and PSC. AIH had female predominance (74%) and was lower in PSC (45%). There was a trend toward higher frequency of blacks in PSC/OS (55%) compared to Caucasians (36%) and Hispanics (9%), but not race differences in AIH. Inflammatory bowel disease (IBD) was present in 75% of PSC/OS. Plasma cells were not specific for AIH (found in 42% of PSC). Concentric fibrosis was not reliable for PSC as was found in 46% of AIH. A combination of clinical history, laboratory tests, imaging studies and liver biopsy are required to confirm and properly treat AIH and PSC. Liver biopsy should be used to grade severity and disease progression, but cannot be used alone to diagnose these conditions.
Gastroenterology, Volume 138, Issue 5, Pages S-786, May 2010, Authors:LinaHernandez; Eddie Island... more Gastroenterology, Volume 138, Issue 5, Pages S-786, May 2010, Authors:LinaHernandez; Eddie Island; Andreas G. Tzakis; Gennaro Selvaggi; Akin Tekin; Amber H. Langshaw; Lesley J. Smith. Gastroenterology - Click here ...
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