The Shape of the Trade-Off Function Between Reproduction and Future Performance in \u3cem\u3ePlantago major\u3c/em\u3e and \u3cem\u3ePlantago rugelii\u3c/em\u3e

There is a paucity of data describing the nature of the trade-off function between reproduction and future performance. Most studies implicitly assume it is a linear function such that allocation of resources to reproduction results in a proportional decline in future survival and reproduction. We reanalyse data from a field experiment with halfsib families of Plantago major L. that suggests this relationship is in fact curvilinear. Low levels of reproductive investment had relatively little impact on future performance and higher levels of investment had a larger impact. To explain this curvilinear pattern, we conducted an experiment to examine the effect of incremental increases in reproductive investment on rates of resource uptake in P. major and Plantago rugelii Decne. Results suggest that, because of differences in the resource requirements of vegetative versus reproductive tissues, reproduction will have little effect on growth, providing that the limiting resources are required in greater quantities for vegetative as compared with reproductive tissues. These results are in accord with a curvilinear trade-off function between reproduction and future performance and provide an explanation for the maintenance of sexual reproduction in species where seed production may contribute minimally to fitness in the short term

Temperature acclimation of root respiration in Douglas-fir and western red cedar seedlings

This study examined the ability of seedlings of coastal and interior provenances of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata Donn) to acclimate root respiration rates to growth temperature. A second objective was to determine whether acclimation involved an increase in activity and/or capacity of the alternative path of electron transport, a phenomenon observed in many crop species. Since western red cedar has less genetic variation than Douglas-fir, one might expect better acclimation in cedar. Seedlings were grown hydroponically in computer-controlled mist boxes placed inside an environmental chamber (18/6 hr photoperiod, day/night). This allowed for precise manipulation of root temperature (11, 18, 25°C), while shoot temperature was unchanged between treatments (25/18°C, day/night). Respiration of excised root segments was measured with an oxygen electrode. Potassium cyanide and salicylhydroxamic acid were used to estimate the activity and capacity of the alternative path. Oxygen response curves were constructed, seedling water potentials were determined and shoot samples were analyzed for carbon isotope discrimination. Total plant weight, root to shoot biomass and root density were also measured. The results showed that both the coastal and interior provenances of western red cedar and the coastal provenance of Douglas-fir were able to acclimate, while interior Douglas-fir was not. Acclimation did not seem to involve an increase in electron partitioning through the alternative path. It was suggested that the increase in alternative path respiration that is often seen at low temperatures is independent of compensatory respiration and sometimes occurs coincidentally with it to reduce the damage caused by active oxygen species, which can be a problem at those temperatures. There is evidence that the cold-grown roots were able to increase the supply of O₂ to the mitochondria, thus compensating for the increased O₂ demand that occurs upon acclimation, although the manner in which they did this remains unclear. Seedlings appeared to be able to adjust stomatal conductance in order to avoid experiencing water stress. The optimal root growth temperature was between 18 and 25°C for both species. It seems that root signalling could be involved in rhodoxanthin accumulation in cedar shoots.Forestry, Faculty ofGraduat

The shape of the trade-off function between reproduction and future performance

Abstract: There is a paucity of data describing the nature of the trade-off function between reproduction and future performance. Most studies implicitly assume it is a linear function such that allocation of resources to reproduction results in a proportional decline in future survival and reproduction. We reanalyse data from a field experiment with halfsib families of Plantago major L. that suggests this relationship is in fact curvilinear. Low levels of reproductive investment had relatively little impact on future performance and higher levels of investment had a larger impact. To explain this curvilinear pattern, we conducted an experiment to examine the effect of incremental increases in reproductive investment on rates of resource uptake in P. major and Plantago rugelii Decne. Results suggest that, because of differences in the resource requirements of vegetative versus reproductive tissues, reproduction will have little effect on growth, providing that the limiting resources are required in greater quantities for vegetative as compared with reproductive tissues. These results are in accord with a curvilinear trade-off function between reproduction and future performance and provide an explanation for the maintenance of sexual reproduction in species where seed production may contribute minimally to fitness in the short term. Key words: reproductive cost, resource allocation, life-history theory, nitrogen uptake, reproductive photosynthesis, Plantago major, Plantago rugelii. Résumé : Il y a peu de données décrivant la fonction d'échange entre la reproduction et la performance future. La plupart des études assument implicitement qu'il s'agit d'une fonction linéaire faisant en sortes que l'allocation des ressources à la reproduction résulte en un déclin proportionnel de la survie et de la reproduction futures. Les auteurs ont réexaminé les données d'une expérience sur le terrain impliquant des familles de demi-frères du Plantago major L., suggérant que cette relation est en fait curvilinéaire. De faibles niveaux d'investissement reproducteur ont relativement peu d'impact sur la performance future, et des niveaux plus élevés d'investissement ont des impacts plus marqués. Pour expliquer ce patron curvilinéaire, les auteurs ont conduit une expérience afin d'examiner l'effet d'augmentations graduelles de l'investissement reproducteur sur les taux d'accumulation des ressources chez le P. major et le Plantago rugelii Decne. Les résultats suggèrent que, compte tenu des différences de besoins en ressources des tissus végétatifs versus les tissus reproducteurs, le reproduction aurait peu d'effet sur la croissance, pourvu que les ressources limitantes soient nécessaires en quantités plus élevées pour les tissus végétatifs que pour les tissus reproducteurs. Ces résultats concordent avec la fonction d'échange curvilinéaire entre la reproduction et la performance future et fournit une explication pour le maintient de la reproduction sexuelle chez les espèces où la production de graines peut contribuer minimalement à l'adaptation à court terme