Phenotypic noise and the cost of complexity

Experimental studies demonstrate the existence of phenotypic diversity despite constant genotype and environment. Theoretical models based on a single phenotypic character predict that during an adaptation event, phenotypic noise should be positively selected far from the fitness optimum because it increases the fitness of the genotype, and then be selected against when the population reaches the optimum. It is suggested that because of this fitness gain, phenotypic noise should promote adaptive evolution. However, it is unclear how the selective advantage of phenotypic noise is linked to the rate of evolution, and whether any advantage would hold for more realistic, multidimensional phenotypes. Indeed, complex organisms suffer a cost of complexity, where beneficial mutations become rarer as the number of phenotypic characters increases. Using a quantitative genetics approach, we first show that for a one-dimensional phenotype, phenotypic noise promotes adaptive evolution on plateaus of positive fitness, independently from the direct selective advantage on fitness. Second, we show that for multidimensional phenotypes, phenotypic noise evolves to a low-dimensional configuration, with elevated noise in the direction of the fitness optimum. Such a dimensionality reduction of the phenotypic noise promotes adaptive evolution and numerical simulations show that it reduces the cost of complexity.     

Heritable morphological differentiation in salmonids from two distinct stream types

We tested for phenotype-to-habitat associations in brown trout Salmo trutta populations from two ecologically different habitat types; i.e., groundwater and surface-water-fed streams. Additionally, we raised captive offspring from two such populations under standardised conditions to test whether potential phenotypic differentiation would be passed on to offspring. We found analogous differentiation by habitat in multiple wild populations. Some of these morphological differences were at least partially inherited by offspring. We suggest that this could have implications for both scientists and fisheries authorities studying or managing trout populations.     

生态因子及其交互作用对拟南芥(Arabidopsis thaliana)表型可塑性的影响

以拟南芥(Arabidopsis thaliana)两种基因型(ws-0和col-0)材料,采用复因子混合水平正交试验设计开展盆栽实验,研究了土壤盐分、土壤水分、光照强度、去叶处理等生态因子及其交互作用对受试植株18个表型特征的影响.结果表明生态因子对植物表型可塑性的影响是有针对性的:土壤水分主要影响植物体构件数目;土壤盐分主要影响生物量、角果数及种籽总数等直接反映植株适合度的表型特征;光照条件则主要影响植物的物候表型特征.植物体表型可塑性的方向随水分梯度的变化而发生改变.生态因子交互作用对植物表型可塑性的影响效果不是各因子独立作用的简单加和:对某个表型特征都有显著影响的两个生态因子其交互作用对该特征可能没有影响;反之,受两个生态因子交互作用影响显著的表型特征也可能不受它们的独立影响.在对生态因子交互作用作出响应时,col-0的9个特征表现出可塑性,而ws-0仅有4个表型是可塑的;同一基因型内彼此相关的表型特征在可塑性上也具一致性.抽苔时莲座叶数与角果平均籽粒数不受任何生态因子及其交互作用的影响,这两个表型作为数量特征而未表现出可塑性.     

Phenotypic integration: studying the ecology and evolution of complex phenotypes

Phenotypic integration refers to the study of complex patterns of covariation among functionally related traits in a given organism. It has been investigated throughout the 20th century, but has only recently risen to the forefront of evolutionary ecological research. In this essay, I identify the reasons for this late flourishing of studies on integration, and discuss some of the major areas of current endeavour: the interplay of adaptation and constraints, the genetic and molecular bases of integration, the role of phenotypic plasticity, macroevolutionary studies of integration, and statistical and conceptual issues in the study of the evolution of complex phenotypes. I then conclude with a brief discussion of what I see as the major future directions of research on phenotypic integration and how they relate to our more general quest for the understanding of phenotypic evolution within the neo‐Darwinian framework. I suggest that studying integration provides a particularly stimulating and truly interdisciplinary convergence of researchers from fields as disparate as molecular genetics, developmental biology, evolutionary ecology, palaeontology and even philosophy of science.     

Reduction and variability of trunk spines in the acanthocephalan Corynosoma cetaceum: the role of physical constraints on attachment

Abstract. In this study, we investigated a functional trade-off between trunk attachment and trunk-spine development in the acanthocephalan Corynosoma cetaceum . The worms live attached to the stomach and upper intestine of their cetacean definitive hosts, using the proboscis and spiny foretrunk as the main holdfast; the spiny hindtrunk can also attach by bending ventrally. When the hindtrunk bends, ventral compression generates an anterior fold (AF) and a posterior fold (PF). A morphological analysis based on 7,823 individuals collected from 10 franciscana dolphins, Pontoporia blainvillei , revealed that spines were smaller and more variable in size and occurrence in the folds than on neighboring areas; the growth of fold spines seemed to be inhibited to various degrees. Spines were more reduced in the AF than in the PF, and spines of both folds were more reduced in females than in males. Patterns of reduction appeared to be directly related to the intensity of fold compression associated with hindtrunk bending. Fold compression could induce plastic inhibition of spine growth, and/or could make fold spines maladaptive, spines being reduced by natural selection. Apparently, fold spines neither contact the substrate, nor are they exposed to the environment when the hindtrunk attaches. Therefore, fold spines could have reduced, or lost, their primary function, at least in the definitive host. The reduction and variability of spines in C. cetaceum seem to be unique among Corynosoma species.     

ALBINISM AND PHENOTYPE OF BARN SWALLOWS (HIRUNDO RUSTICA) FROM CHERNOBYL

Abstract The effects of mutation on phenotypic expression are supposed to be mainly deleterious because mutations disrupt the expression of genes that function relatively well under current environmental conditions. Thus, mutations are assumed to give rise to deviant phenotypes that are generally selected against. Radioactive contamination in the Chernobyl region of Ukraine is associated with a significant increase by a factor two to 10 in mutation rate in microsatellite markers of the barn swallow, Hirundo rustica. Barn swallows from Chernobyl had a temporally constant, elevated frequency of partial albinism compared to the situation before radioactive contamination and compared to birds from a control area. Albinism disproportionately affected the carotenoid‐based plumage of the head, suggesting that carotenoid metabolism is particularly susceptible to the effects of radiation. Individuals with partially albinistic plumage had, on average, lower mean phenotypic values than other birds, and this was particularly the case for males. Furthermore, differences in phenotypic variation, as determined using Levene's test, were significantly larger in partial albinos compared to nonalbinos in males, but not in females, even though the null expectation would be the opposite due to the lower mean phenotypic values of partial albinos. Although small phenotypes were commonly associated with germline mutations, there was no general decrease in overall body size during the period 1991–2000, implying that small individuals were selected against. Because partial albinism is disfavored by natural selection, the effects of mutations are deleterious, giving rise to a balance between mutation and selection.     

Metabolic adjustment enhances food web stability

Understanding ecosystem stability is one of the greatest challenges of ecology. Over several decades, it has been shown that allometric scaling of biological rates and feeding interactions provide stability to complex food web models. Moreover, introducing adaptive responses of organisms to environmental changes (e.g. like adaptive foraging that enables organisms to adapt their diets depending on resources abundance) improved species persistence in food webs. Here, we introduce the concept of metabolic adjustment, i.e. the ability of species to slow down their metabolic rates when facing starvation and to increase it in time of plenty. We study the reactions of such a model to nutrient enrichment and the adjustment speed of metabolic rates. We found that increasing nutrient enrichment leads to a paradox of enrichment (increase in biomasses and oscillation amplitudes and ultimately extinction of species) but metabolic adjustment stabilises the system by dampening the oscillations. Metabolic adjustment also increases the average biomass of the top predator in a tri‐trophic food chain. In complex food webs, metabolic adjustment has a stabilising effect as it promotes species survival by creating a large diversity of metabolic rates. However, this stabilising effect is mitigated in enriched ecosystems. Phenotypic plasticity of organisms must be considered in food web models to better understand the response of organisms to their environment. As metabolic rate is central in describing biological rates, we must pay attention to its variations to fully understand the population dynamics of natural communities.     

Polypeptide analysis of genotypic variants of occluded Heliothis spp. baculoviruses

The structural polypeptides of 12 baculovirus isolates which included nuclear polyhedrosis viruses (NPVs) and granulosis viruses (GVs) obtained from four different species of the insect genus Heliothis collected in different geographical regions of the world were characterized using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The matrix proteins were compared according to their molecular weights and peptide profiles produced after limited proteolysis. Examination of the matrix and virion polypeptide profiles revealed three major polypeptide phenotypes which corresponded to the three baculovirus morphological groups; singly embedded nuclear polyhedrosis viruses (SNPVs), multiply embedded nuclear polyhedrosis viruses (MNPVs), and granulosis viruses (GVs). Enveloped nucleocapsid polypeptide profiles of isolates within each NPV phenotype differed in only one polypeptide whereas the two GV isolates differed by as many as five polypeptides. Nucleocapsid polypeptide profiles of isolates within each of the NPV subgroups were identical while those profiles from the GV nucleocapsids differed slightly in molecular weight of one polypeptide.     

The impact of plasticity and maternal effect on the evolution of leaf resin production in Diplacus aurantiacus

Our previous quantitative genetic study of leaf resin production in Diplacus aurantiacus revealed large environmental and maternal effects on variation in resin production, which suggests the possibility of a genotype×environment interaction for this trait when plants grow in heterogeneous environments. Our objectives in this study were to observe the genetic variation in plasticity of resin production under field and chamber conditions, compare phenotypic correlations of resin content with growth traits under these two environmental conditions, and distinguish the possible basis of the maternal effect on resin production using parents and half-sib progeny. A significant genotype×environment interaction (P<0.0001) in leaf resin production was found, which suggests a potential for the evolution of plasticity of these secondary metabolites under heterogeneous environments. The phenotypic correlation between resin content and growth rate also exhibited plasticity. In addition, the resin content of dam half-sib families grown in the chamber had a closer relationship with their maternal parents in the field (r=0.65, P=0.059) than in the chamber (r=0.39, P=0.34), suggesting an environmentally based maternal effect on the secondary chemicals. We suggest that the maternal environmental effect may act as a contributor to plasticity of resin production and, while it may not diminish the appearance of the genotype×environment interaction, the heritable variation of plasticity of resin production may be confounded.     

From icons to symbols: Some speculations on the origins of language

This paper is divided into three sections. In the first section we offer a retooling of some traditional concepts, namely icons and symbols, which allows us to describe an evolutionary continuum of communication systems. The second section consists of an argument from theoretical biology. In it we explore the advantages and disadvantages of phenotypic plasticity. We argue that a range of the conditions that selectively favor phenotypic plasticity also favor a nongenetic transmission system that would allow for the inheritance of acquired characters. The first two sections are independent, the third depends on both of them. In it we offer an argument that human natural languages have just the features required of an ideal transmission mechanism under the conditions described in section 2.We would like to thank Robert Boyd, Noam Chomsky, Gerald Feinberg, Ken Glander, David Hull, Ernst Mayr, John Rawls, Peter Richerson, william Wimsatt and Paul Ziff for helpful comments on earlier drafts of this paper. Special thanks go to Doug Stalker who was instrumental in both the origins and development of this work.