A New Tradeoff Model for Fuzzy Supply Chain Network Design and Optimization

This article proposes a novel mixed integer linear programming model for solving a fuzzy supply chain network (SCN) design problem. This problem includes fuzzy parameters, choosing suppliers according to their quality of raw materials, and the supplier's engagement contracts. There is a tradeoff between raw material quality, and its purchasing and reprocessing costs. If a decision-maker (DM) wishes to work with a supplier that supplies a low-quality raw material, this raw material may be in need of reprocessing. To avoid the reprocessing costs, a supplier that provides a high-quality raw material can be chosen, but in this case the DM faces a high purchasing cost. An integrated fuzzy SCN system that consists of multiple suppliers, manufacturers, distribution centers, and retailers is considered in order to address problems under the aforementioned tradeoffs. Finally, concluding remarks and suggestions for future work are presented.     

Environment-dependent metabolic investments in the mixotrophic chrysophyte Ochromonas

Mixotrophic protists combine photosynthesis and phagotrophy to obtain energy and nutrients. Because mixotrophs can act as either primary producers or consumers, they have a complex role in marine food webs and biogeochemical cycles. Many mixotrophs are also phenotypically plastic and can adjust their metabolic investments in response to resource availability. Thus, a single species's ecological role may vary with environmental conditions. Here, we quantified how light and food availability impacted the growth rates, energy acquisition rates, and metabolic investment strategies of eight strains of the mixotrophic chrysophyte, Ochromonas. All eight Ochromonas strains photoacclimated by decreasing chlorophyll content as light intensity increased. Some strains were obligate phototrophs that required light for growth, while other strains showed stronger metabolic responses to prey availability. When prey availability was high, all eight strains exhibited accelerated growth rates and decreased their investments in both photosynthesis and phagotrophy. Photosynthesis and phagotrophy generally produced additive benefits: In low-prey environments, Ochromonas growth rates increased to maximum, light-saturated rates with increasing light but increased further with the addition of abundant bacterial prey. The additive benefits observed between photosynthesis and phagotrophy in Ochromonas suggest that the two metabolic modes provide nonsubstitutable resources, which may explain why a tradeoff between phagotrophic and phototrophic investments emerged in some but not all strains.     

Children's Help and the Pace of Reproduction: Cooperative Breeding in Humans

Because children's ability to support themselves falls below their consumption, human young are subsidized by others throughout much of their growth and development. Mothers, however, who often have multiple dependents of different ages, are faced with an allocation problem (Fig. 1). This has led to important debate about the evolution of a long period dependence and the development of nonmaternal strategies to provision young. This article focuses on the critical role that children themselves play. Because the human subsistence niche incorporates a broad diversity of resources that require variable procurement and processing costs, dependent children can also be important producers, furthering both a need and an opportunity for cooperative breeding.     

Macroclimatic and maternal effects on the evolution of reproductive traits in lizards

Much of life‐history theory rests on fundamental assumptions about constraints on the acquisition and allocation of energy to growth and reproduction. In general, the allocation of energy to reproduction depends on maternal size, which in turn depends on environmental factors experienced throughout the life of the mother. Here, we used phylogenetic path analyses to evaluate competing hypotheses about the environmental and maternal drivers of reproductive traits in lizards. In doing so, we discovered that precipitation, rather than temperature, has shaped the evolution of the life history. Specifically, environments with greater rainfall have enabled the evolution of larger maternal size. In turn, these larger mothers produce larger clutches of larger offspring. However, annual precipitation has a negative direct effect on offspring size, despite the positive indirect effect mediated by maternal size. Possibly, the evolution of offspring size was driven by the need to conserve water in dry environments, because small organisms are particularly sensitive to water loss. Since we found that body size variation among lizards is related to a combination of climatic factors, mainly precipitation and perhaps primary production, our study challenges previous generalizations (e.g., temperature‐size rule and Bergmann''s rule) and suggests alternative mechanisms underlying the evolution of body size.     

GENETIC CONSTRAINTS TO LIFE-HISTORY EVOLUTION IN THE PITCHER-PLANT MOSQUITO,WYEOMYIA SMITHII

Life-history theory relies heavily on the hypothesis that genetic tradeoffs among the components of fitness constrain their independent evolution and joint maximization. Herein we show that selection on preadult development time in the pitcher-plant mosquito, Wyeomyia smithii, leads to a correlated response in cohort mean generation time but no correlated response in survivorship, fecundity, or cohort replacement rate. Lines selected for fast development achieve a higher capacity for increase (r_c) than lines selected for slow development, independently of larval density. These results imply that tradeoffs due to underlying antagonistic pleiotropy affecting growth, development, survivorship, and reproduction are not necessary constraints to life-history evolution. Previous work with W. smithii has shown a positive genetic correlation between development time and a general, genetically coordinated diapause syndrome. We propose that the observed nontradeoffs among the components of r_c may be subsumed into an even more fundamental tradeoff between performance during the summer generations and synchronization of development and reproduction with the changing seasons. Consequently, critical tests of genetic tradeoffs as a constraint to the independent evolution or simultaneous optimization of fitness components may need to consider the seasonal context.     

Factors affecting soldier allocation in clonal aphids: a life-history model and test

Aphid species using a defensive soldier caste offer us the opportunityto study allocation decisions by eusocial groups, without thehindrance of genetic dissimilarity between colony members, whichoften impair studies involving Hymenopteran or Isopteran systems.When the entire aphid clone is considered the adaptive unitof organization, understanding soldier allocation strategiesis tantamount to understanding the outcome of the tradeoff betweenclonal growth (i.e., asexual reproduction) and clonal defense.Under this framework, we present the results of a dynamic programmingeffort aimed at determining the optimal ontogeny of defensiveallocation strategies by eusocial clonal organisms. We considerthe allocation decision for clones with both obligately andfacultatively sterile soldiers, under various levels of predation,and favorable and unfavorable ecological conditions. We testpredictions of the model with the eusocial aphid, Pemphigusspyrothecae. Our model predicts that defensive investment shouldbe dependent on the time of the season, with clones discountingdefense nearer the end of season. Defensive investment shouldalso vary inversely with clonal productivity and be sensitiveto the current state (e.g., level of defense) of the clone.Census data collected in Burnaby, British Columbia, Canada,conform to patterns of clonal composition derived from allocationdecisions generated in the model. Finally, qualitative predictionsabout patterns of clonal organization under "good" and "poor"ecological conditions were upheld by comparing clones in preferredand less-preferred galling sites.     

Individual variation in testosterone and parental care in a female songbird; The dark-eyed junco (Junco hyemalis)

When competition for sex-specific resources overlaps in time with offspring production and care, trade-offs can occur. Steroid hormones, particularly testosterone (T), play a crucial role in mediating such trade-offs in males, often increasing competitive behaviors while decreasing paternal behavior. Recent research has shown that females also face such trade-offs; however, we know little about the role of T in mediating female phenotypes in general, and the role of T in mediating trade-offs in females in particular. Here we examine the relationship between individual variation in maternal effort and endogenous T in the dark-eyed junco, a common songbird. Specifically, we measure circulating T before and after a physiological challenge (injection of gonadotropin releasing hormone, GnRH), and determine whether either measure is related to provisioning, brooding, or the amount of T sequestered in egg yolk. We found that females producing more T in response to a challenge spent less time brooding nestlings, but provisioned nestlings more frequently, and deposited more T in their eggs. These findings suggest that, while T is likely important in mediating maternal phenotypes and female life history tradeoffs, the direction of the relationships between T and phenotype may differ from what is generally observed in males, and that high levels of endogenous T are not necessarily as costly as previous work might suggest.     

Influence of Predator Presence and Prey Density on Behavior and Growth of Damselfly Larvae (Ischnura elegans) (Odonata: Zygoptera)

Foraging behavior is often determined by the conflicting benefits of energy gain and the risk of mortality from predation or other causes. Theory predicts that animals should have lower activity levels when either the risk of predation or the availability of resources in the environment is high. We investigated the adjustment of the behavior of I. elegans larvae to predator presence (Anax imperator) and prey density (Daphnia sp.) and their interaction in a completely crossed factorial experiment in the lab and the effect of behavior on growth. The foraging activity of the I. elegans larvae was significantly reduced in the presence of a free-swimming predator but not a caged predator. Abdominal movements were significantly reduced at a low prey density. Growth was significantly reduced by the presence of a free swimming predator and low prey densities. These results provide evidence that these damselfly larvae adjust their behavior to the presence of predators to increase their survival at the expense of reduced growth and development.