Triiodothyronine (T3) effect on red crossbill (Loxia curvirostra) colouration
The mechanisms underlying the evolution of carotenoid-based colouration as a reliable signal of individual quality are still poorly understood. The Resource Allocation Trade-off hypothesis (RATH) asserts that honesty is maintained as only good-quality individuals have enough carotenoids to invest bo...
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| Tipo de recurso: | tesis de maestría |
| Fecha de publicación: | 2020 |
| País: | España |
| Institución: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositorio: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:dnet:digitalcsic_::88ca81ff9adbbb9c2b57fbdd495bc40e |
| Acceso en línea: | http://hdl.handle.net/10261/426880 |
| Access Level: | acceso abierto |
| Palabra clave: | Carotenoid-based colouration Ketocarotenoids Loxia curvirostra Mitochondrial metabolism Mito-targeted antioxidants MitoTEMPO Sexual selection Shared-pathway hypothesis Thyroid hormones Triiodothyronine Antioxidantes dirigidos a la mitocondria Coloración basada en carotenoides Hipótesis de la vía compartida Hormonas tiroideas Metabolismo mitocondrial Quetocarotenoides Selección sexual Triyodotironina |
| Sumario: | The mechanisms underlying the evolution of carotenoid-based colouration as a reliable signal of individual quality are still poorly understood. The Resource Allocation Trade-off hypothesis (RATH) asserts that honesty is maintained as only good-quality individuals have enough carotenoids to invest both in vital functions and ornamentation. Individuals would face a fitness cost when investing more in signalling. The Shared-Pathway hypothesis (SPH), in contrast, upholds that the honesty of some signals (not only carotenoid-based) rely on biochemical pathways shared between the signal production and homeostasis, making the signal unfalsifiable. Here, no resource allocation trade-off would be involved and no cost of signal production would have promoted signal evolution. The Inner Mitochondrial Membrane hypothesis (IMMH) is a specific case of the shared-pathway hypothesis. Red carotenoids in many species are produced by oxidizing yellow dietary carotenoids by enzymes (ketolases). The oxidative process would be made by enzymes placed in the inner mitochondria sharing its activity with cell respiration. Early studies suggested that birds in captivity lost its red carotenoid-produced plumage due to a decline in the oxidative metabolism. To prove the link among both processes, we performed a two-factorial experiment on captive male red crossbills (Loxia curvirostra). Half of the birds were treated with subcutaneous implants filled with triiodothyronine (T3-treated birds) or empty (hormone-controls). T3 is a hormone with known hypermetabolic effects. Also, half of the birds in each group were injected with mitoTEMPO (mitoTEMPO-treated birds), a mito-targeted antioxidant designed to penetrate the IMM, or vehicle (antioxidant controls). The hormone reduced plumage redness, perhaps due to the high production of reactive oxygen species (ROS) often demonstrated under high T3 levels. These ROS would have interfered the enzymatic activity involved in carotenoid biosynthesis. MitoTEMPO, instead, did not induce a significant effect on coloration, contradicting a recent study in the same species. Differences in diet composition between both studies and/or oxidative stress derived from subcutaneous implant rejection could explain this discrepancy. We suggest that the resource trade-off hypothesis and the shared-pathway hypothesis could not be mutually exclusive. |
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