SIZE AS A LINE OF LEAST RESISTANCE II: DIRECT SELECTION ON SIZE OR CORRELATED RESPONSE DUE TO CONSTRAINTS?

Evolutionary change in New World Monkey (NWM) skulls occurred primarily along the line of least resistance defined by size (including allometric) variation ( g_max ). Although the direction of evolution was aligned with this axis, it was not clear whether this macroevolutionary pattern results from the conservation of within population genetic covariance patterns (long‐term constraint) or long‐term selection along a size dimension, or whether both, constraints and selection, were inextricably involved. Furthermore, G ‐matrix stability can also be a consequence of selection, which implies that both, constraints embodied in g_max and evolutionary changes observed on the trait averages, would be influenced by selection. Here, we describe a combination of approaches that allows one to test whether any particular instance of size evolution is a correlated by‐product due to constraints ( g_max ) or is due to direct selection on size and apply it to NWM lineages as a case study. The approach is based on comparing the direction and amount of evolutionary change produced by two different simulated sets of net‐selection gradients ( β ), a size (isometric and allometric size) and a nonsize set. Using this approach it is possible to distinguish between the two hypotheses (indirect size evolution due to constraints or direct selection on size), because although both may produce an evolutionary response aligned with g_max , the amount of change produced by random selection operating through the variance/covariance patterns (constraints hypothesis) will be much smaller than that produced by selection on size (selection hypothesis). Furthermore, the alignment of simulated evolutionary changes with g_max when selection is not on size is not as tight as when selection is actually on size, allowing a statistical test of whether a particular observed case of evolution along the line of least resistance is the result of selection along it or not. Also, with matrix diagonalization (principal components [PC]) it is possible to calculate directly the net‐selection gradient on size alone (first PC [PC1]) by dividing the amount of phenotypic difference between any two populations by the amount of variation in PC1, which allows one to benchmark whether selection was on size or not.     

SELECTION ON POLEMONIUM BRANDEGEEI (POLEMONIACEAE) FLOWERS UNDER HUMMINGBIRD POLLINATION: IN OPPOSITION,PARALLEL, OR INDEPENDENT OF SELECTION BY HAWKMOTHS?

Particular floral phenotypes are often associated with specific groups of pollinators. However, flowering plants are often visited, and may be effectively pollinated by more than one type of animal. Therefore, a major outstanding question in floral biology asks: what is the nature of selection on floral traits when pollinators are diverse? This study examined how hummingbirds selected on the floral traits of Polemonium brandegeei, a species pollinated by both hummingbirds and hawkmoths. In array populations of P. brandegeei, we measured pollen movement, and female (seeds set) and male (seeds sired) fitness under hummingbird pollination. We then compared the patterns of selection by hummingbirds with our previous study examining selection by hawkmoths. We documented contrasting selection on sex organ positioning through female function, with hummingbirds selecting for stigmas exserted beyond the anthers and hawkmoths selecting for stigmas recessed below the anthers. Furthermore, hummingbirds selected for longer and wider corolla tubes, and hawkmoths selected for narrower corolla tubes. Therefore, contrasting selection by hawkmoths and hummingbirds may account for variation in sex organ arrangements and corolla dimensions in P. brandegeei. We documented how floral traits under selection by multiple pollinators can result in either an intermediate “compromise” between selective pressures (sex organs) or apparent specialization (corolla tube length) to one pollinator.     

ESTIMATING NONLINEAR SELECTION GRADIENTS USING QUADRATIC REGRESSION COEFFICIENTS: DOUBLE OR NOTHING?

The use of regression analysis has been instrumental in allowing evolutionary biologists to estimate the strength and mode of natural selection. Although directional and correlational selection gradients are equal to their corresponding regression coefficients, quadratic regression coefficients must be doubled to estimate stabilizing/disruptive selection gradients. Based on a sample of 33 papers published in Evolution between 2002 and 2007, at least 78% of papers have not doubled quadratic regression coefficients, leading to an appreciable underestimate of the strength of stabilizing and disruptive selection. Proper treatment of quadratic regression coefficients is necessary for estimation of fitness surfaces and contour plots, canonical analysis of the gamma matrix, and modeling the evolution of populations on an adaptive landscape.     

COMPARING STRENGTHS OF DIRECTIONAL SELECTION: HOW STRONG IS STRONG?

The fundamental equation in evolutionary quantitative genetics, the Lande equation, describes the response to directional selection as a product of the additive genetic variance and the selection gradient of trait value on relative fitness. Comparisons of both genetic variances and selection gradients across traits or populations require standardization, as both are scale dependent. The Lande equation can be standardized in two ways. Standardizing by the variance of the selected trait yields the response in units of standard deviation as the product of the heritability and the variance-standardized selection gradient. This standardization conflates selection and variation because the phenotypic variance is a function of the genetic variance. Alternatively, one can standardize the Lande equation using the trait mean, yielding the proportional response to selection as the product of the squared coefficient of additive genetic variance and the mean-standardized selection gradient. Mean-standardized selection gradients are particularly useful for summarizing the strength of selection because the mean-standardized gradient for fitness itself is one, a convenient benchmark for strong selection. We review published estimates of directional selection in natural populations using mean-standardized selection gradients. Only 38 published studies provided all the necessary information for calculation of mean-standardized gradients. The median absolute value of multivariate mean-standardized gradients shows that selection is on average 54% as strong as selection on fitness. Correcting for the upward bias introduced by taking absolute values lowers the median to 31%, still very strong selection. Such large estimates clearly cannot be representative of selection on all traits. Some possible sources of overestimation of the strength of selection include confounding environmental and genotypic effects on fitness, the use of fitness components as proxies for fitness, and biases in publication or choice of traits to study.     

DOES TOTAL REPRODUCTIVE EFFORT EVOLVE INDEPENDENTLY OF OFFSPRING SIZE?

In all species, patterns of reproductive allocation have important fitness consequences and therefore important implications for life-history evolution. Nearly universally, theory in this field has modeled as independent the evolution of total allocation to offspring and the subsequent division of this allocation into many small versus few large offspring. Yet, some theory and a very small amount of experimental evidence suggest that these life-history traits may be evolutionarily linked. Using comparative analyses of copepod life histories, we illustrate that rather than being evolutionarily independent these traits can be linked, in this case, across a very large clade of invertebrates. Our results indicate that a more complete understanding of the evolution of these traits will require greater consideration of simultaneous allocation decisions, rather than sequential ones, and other genetic and selective mechanisms.     

ASCOMA ONTOGENY: IS THIS CHARACTER SET OF ANY USE IN THE SYSTEMATICS OF LICHENIZED ASCOMYCETES?

The use of ascoma ontogeny in the systematics of lichenized asco-mycetes is reviewed briefly. Two recently studied examples are discussed to illustrate the use of ontogenetic studies to discover phylogenetic relationships. As one example, theAgyriaceaewas mainly circumscribed by the ascus type and included diverse genera.Xylographais characterized by lirelliform apothecia. However, the ascoma development shares the ontogenetic pattern observed inTrapeliaand its placement in the family was confirmed. In contrast,Anamylopsoraexhibited a substantially different apothecial development and was separated as a family of its own. As a second example, theCandelariaceaeis based on chemical characters. With the detection of pulvinic acid derivatives also in the genusLecanora, the distinction of theCandelariaceaeandLecanoraceaebecame doubtful. Therefore, the ascoma ontogeny was employed to evaluate this classification and is illustrated here in detail forCandelaria fibrosa. The substantial similarity of the ascoma development found in both families suggests that both might be better united. Finally, a general discussion of the significance of ontogenetic characters in lichen taxonomy is included.     

EXPERIMENTALLY ENFORCED MONOGAMY: INADVERTENT SELECTION,INBREEDING, OR EVIDENCE FOR SEXUALLY ANTAGONISTIC COEVOLUTION?

There has been recent criticism of experiments that applied enforced monogamous mating to species with a long history of promiscuity. These experiments indicated that the newly introduced monogamy reversed sexually antagonistic coevolution and caused males to evolve to be less harmful to their mates and females to evolve reduced resistance to harm from males. Several authors have proposed alternative interpretations of these experimental results based on qualitative analysis. If well-founded, these criticisms would invalidate an important part of the empirical foundation for sexually antagonistic coevolution between the sexes. Although these criticisms have a reasonable basis in principle, we find that after quantitative evaluation that they are not supported.     

EVOLUTION OF REPRODUCTIVE STRATEGIES IN THE SEXUALLY DECEPTIVE ORCHID OPHRYS SPHEGODES: HOW DOES FLOWER‐SPECIFIC VARIATION OF ODOR SIGNALS INFLUENCE REPRODUCTIVE SUCCESS?

The orchid Ophrys sphegodes Miller is pollinated by sexually excited males of the solitary bee Andrena nigroaenea, which are lured to the flowers by visual cues and volatile semiochemicals. In O. sphegodes, visits by pollinators are rare. Because of this low frequency of pollination, one would expect the evolution of strategies that increase the chance that males will visit more than one flower on the same plant; this would increase the number of pollination events on a plant and therefore the number of seeds produced. Using gas chromatography-mass spectrometry (GC-MS) analyses, we identified more than 100 compounds in the odor bouquets of labellum extracts from O. sphegodes; 24 compounds were found to be biologically active in male olfactory receptors based on gas chromatography with electroantennographic detection (GC-EAD). Gas chromatography (GC) analyses of odors from individual flowers showed less intraspecific variation in the odor bouquets of the biologically active compounds as compared to nonactive compounds. This can be explained by a higher selective pressure on the pollinator-attracting communication signal. Furthermore, we found a characteristic variation in the GC-EAD active esters and aldehydes among flowers of different stem positions within an inflorescence and in the n-alkanes and n-alkenes among plants from different populations. In our behavioral field tests, we showed that male bees learn the odor bouquets of individual flowers during mating attempts and recognize them in later encounters. Bees thereby avoid trying to mate with flowers they have visited previously, but do not avoid other flowers either of a different or the same plant. By varying the relative proportions of saturated esters and aldehydes between flowers of different stem positions, we demonstrated that a plant may take advantage of the learning abilities of the pollinators and influence flower visitation behavior. Sixty-seven percent of the males that visited one flower in an inflorescence returned to visit a second flower of the same inflorescence. However, geitonogamy is prevented and the likelihood of cross-fertilization is enhanced by the time required for the pollinium deposited on the pollinator to complete its bending movement, which is necessary for pollination to occur. Cross-fertilization is furthermore enhanced by the high degree of odor variation between plants. This variation minimizes learned avoidance of the flowers and increases the likelihood that a given pollinator would visit several to many different plants within a population.     

NATURAL SELECTION FOR GRAZER RESISTANCE TO TOXIC CYANOBACTERIA: EVOLUTION OF PHENOTYPIC PLASTICITY?

Abstract We studied the selection response of the freshwater grazing zooplankter, Daphnia galeata, to increased abundance of cyanobacteria in its environment. Cyanobacteria are a poor‐quality and often toxic food. Distinct genotypes of D. galeata were hatched from diapausing eggs extracted from three time horizons in the sediments of Lake Constance, Europe, covering the period 1962 to 1997, a time of change in both the prevalence of planktonic cyanobacteria and levels of phosphorus pollution. We assessed whether the grazers evolved to become more resistant to dietary cyanobacteria by exposing genetically distinct clones to two diets, one composed only of the nutritious green alga, Scenedesmus obliquus (good food), and the other a mixture of S. obliquus and the toxic cyanobacterium Microcystis aeruginosa (poor food). Genotype performance was measured as the specific rate of weight gain from neonate to maturity (g_j). We evaluated evolutionary change in the Daphnia population using an analysis of reaction norms based on relative (log‐transformed) changes in g_j. Log(g_j) is a measure of the proportional effect of dietary cyanobacteria on other fitness components of the Daphnia phenotype. For comparison, we also analyze absolute (i.e., nontransformed) changes in g_j and discuss the interpretations of the two approaches. Statistical results using a general linear model demonstrate a significant effect of genotype (showing differences in g_j among genotypes), a significant genotype X food‐type interaction (showing differences in phenotypic plasticity among genotypes), and, in the case of log‐transformed data, a significant sediment‐genotype‐age X food‐type interaction. The latter shows that phenotypic plasticity evolved over the period studied. Two constraints act on response to selection in the D. galeata‐Lake Constance system. First, g_j on a diet containing poor food is highly correlated with g_j on a diet of good food, thus evolving resistance also meant evolving an increase in g_j on both diets. Second, because genotypes with a high g_j also grow to a large adult body size, which in turn increases Daphnia vulnerability to fish predation, we suggest that selection only acted to favor genotypes possessing a high potential g_j after cyanobacteria became prevalent. The presence of cyanobacteria depressed realized g_j and led to animals of small adult body size even if their genotypes had the potential for high g_j and large size. With realized g_j reduced, genotypes with an inherently high value could be selected even in the presence of predatory fish. The joint action of selection by dietary cyanobacteria and vulnerability to fish predation provides an explanation for the observed evolution of resistance to poor food through reduced phenotypic plasticity.     

TREATMENT OF MELANOMA—SUCCESS OR FAILURE?

The treatment of melanoma should be by radical surgical excision of the primary lesion and dissection of the regional nodes.Where possible this should be done in anatomic continuity; otherwise in physical discontinuity but at the same time.If maximum salvage is to be achieved the nodal dissection must be effected before there is clinical evidence of involvement by metastasis.Amputation of extremities should be reserved for cases in which there is evident metastasis between the original focus and the regional lymph node areas.     

MATHEMATICS OF KIN‐ AND GROUP‐SELECTION: FORMALLY EQUIVALENT?

Evolutionary game theory is a general mathematical framework that describes the evolution of social traits. This framework forms the basis of many multilevel selection models and is also frequently used to model evolutionary dynamics on networks. Kin selection, which was initially restricted to describe social interactions between relatives, has also led to a broader mathematical approach, inclusive fitness, that can not only describe social evolution among relatives, but also in group structured populations or on social networks. It turns out that the underlying mathematics of game theory is fundamentally different from the approach of inclusive fitness. Thus, both approaches—evolutionary game theory and inclusive fitness—can be helpful to understand the evolution of social traits in group structured or spatially extended populations.     

EGG FREEZING: A BREAKTHROUGH FOR REPRODUCTIVE AUTONOMY?

This article describes the relatively new technology of freezing human eggs and examines whether egg freezing, specifically when it is used by healthy women as 'insurance' against age-related infertility, is a legitimate exercise of reproductive autonomy. Although egg freezing has the potential to expand women's reproductive options and thus may represent a breakthrough for reproductive autonomy, I argue that without adequate information about likely outcomes and risks, women may be choosing to freeze their eggs in a commercially exploitative context, thus undermining rather than expanding reproductive autonomy.     

ENZYMATIC N-METHYLATION OF INDOLEAMINES BY MAMMALIAN BRAIN: FACT OR ARTEFACT?

Abstract— Indoleamine- N -methyltransferase (INMT) activity in brain and other tissues from various species was investigated. Using conventional radiochemical assay techniques it was found that apparent INMT activity in brain was linear with time and concentration of protein, indoleamine substrate and methyl donor ( S -adenosylmethionine). However, examination of the reaction products by means of exhaustive thin-layer chromatographic analysis failed to reveal evidence of significant N -methylation of tryptamine or N -methyltryptamine by S -adenosylmethionine. By contrast, with other tissues, notably rabbit lung. N -methylation of indoleamine was reproducibly demonstrable. The significance of these findings with reference to the transmethylation hypothesis of schizophrenia is discussed.     

THE POPCORN WOLBACHIA INFECTION OF DROSOPHILA MELANOGASTER: CAN SELECTION ALTER WOLBACHIA LONGEVITY EFFECTS?

Wolbachia popcorn ( w MelPop), a life-shortening strain of Wolbachia, has been proposed as an agent for suppressing transmission of dengue fever following infection of the vectoring mosquito Aedes aegypti . However, evolutionary changes in the host and Wolbachia genomes might attenuate any life span effects mediated by w MelPop. Here we test for attenuation by selecting strains of Drosophila melanogaster infected with w MelPop for early and late reproduction in three independent outcrossed populations. Selection caused divergence among the lines in longevity. This divergence was mostly associated with the host genetic background rather than the Wolbachia infection, although there were also interactions between the host and Wolbachia genomes. Development time, viability, and productivity were not altered by selection. The implications of these results are discussed in light of the intended use of w MelPop for suppressing disease transmission.     

GEOGRAPHICAL VARIATION IN THE RATE OF EVOLUTION: EFFECT OF AVAILABLE ENERGY OR FLUCTUATING ENVIRONMENT?

In a recent paper, Wright et al. (2003) argue for the hypothesis that greater biologically available energy elevates the rate of molecular evolution. However, their results are also consistent with alternative hypotheses that invoke either environmentally driven variation in effective population sizes, or natural selection, or both. The available energy gradient cited by Wright et al. is linearly correlated with temperature fluctuations, and the observed rate heterogeneity could be a consequence of this environmental variability. The distribution of phylogenetic branch lengths alone is insufficient to distinguish between the hypotheses, and complementary approaches are suggested.     

INTERSPECIFIC X‐CHROMOSOME AND MITOCHONDRIAL DNA INTROGRESSION IN THE IBERIAN HARE: SELECTION OR ALLELE SURFING?

Introgression from a resident species into an invading one is predicted to occur through the demographic process of "allele surfing," and to particularly affect genomic regions transmitted by the lower migrating sex, such as mtDNA. This could explain that northern Iberian populations of Lepus granatensis harbor high frequencies of mtDNA from L. timidus, an arctic hare it replaced there after deglaciation. We report that variation of introgressed timidus-like mtDNA reflects several predicted effects of this process: increasing frequency and diversity in the direction of expansion, strong perpendicular phylogeographic structure and signs of postglacial demographic growth. However, demographic inferences for the granatensis and timidus-like mtDNA lineages suggest the latter may have outcompeted the former in northern Iberia. Autosomal introgression occurs at low frequencies and species-wide rather than only in the north. If this difference with mtDNA resulted from sex-biased migration, an intermediate pattern should prevail for the X-chromosome, but we report species-wide and high-frequency introgression of an X-fragment. Either selection favored this ubiquitous X-introgression, or more complex postglacial expansion patterns prevailed, with different consequences depending on the genomic and geographic region. This illustrates the difficulty of distinguishing demographic and selective effects and the need for genome and species-wide based demographic models.     

HOW DEPRESSED? ESTIMATES OF INBREEDING EFFECTS DURING SEED DEVELOPMENT DEPEND ON REPRODUCTIVE CONDITIONS

Inbreeding depression can reduce the performance of offspring produced by mating between relatives, with consequences for population dynamics and sexual-system evolution. In flowering plants, inbreeding depression commonly acts most intensely during seed development. This predispersal component is typically estimated by comparing seed production following exclusive self- and cross-pollination, but such estimates are unbiased only if seed production is limited by ovule availability, rather than by pollen receipt or seed-development resources. To overcome this problem, we propose experimental and statistical methods based on a model of ovule fertilization and seed development that accounts for differential fertilization by self- and cross-pollen, limited ovule viability or receptivity, differential survival of self- and cross-zygotes and limited resource availability. Simulations illustrate that the proposed methods eliminate bias in estimated predispersal inbreeding depression caused by pollen limitation and can improve estimates under resource limitation. Application of these methods to two orchid species further demonstrates their utility in identifying and estimating diverse influences on reproductive performance under typical conditions. Although our theoretical results raise questions about the reported intensity of predispersal inbreeding depression, our proposed methods guard against bias while also providing insight into plant reproduction.