DOES VARIATION IN SELECTION IMPOSED BY BEARS DRIVE DIVERGENCE AMONG POPULATIONS IN THE SIZE AND SHAPE OF SOCKEYE SALMON?

Few studies have determined whether formal estimates of selection explain patterns of trait divergence among populations, yet this is one approach for evaluating whether the populations are in equilibria. If adaptive divergence is complete, directional selection should be absent and stabilizing selection should prevail. We estimated natural selection, due to bear predation, acting on the body size and shape of male salmon in three breeding populations that experience differing predation regimes. Our approach was to (1) estimate selection acting within each population on each trait based on an empirical estimate of reproductive activity, (2) test for trait divergence among populations, and (3) test whether selection coefficients were correlated with trait divergence among populations. Stabilizing selection was never significant, indicating that these populations have yet to attain equilibria. Directional selection varied among populations in a manner consistent with trait divergence, indicating ongoing population differentiation. Specifically, the rank order of the creeks in terms of patterns of selection paralleled the rank order in terms of size and shape. The shortest and least deep-bodied males had the highest reproductive activity in the creek with the most intense predation and longer and deeper-bodied males were favored in the creeks with lower predation risk.     

DOES GENE FLOW CONSTRAIN ADAPTIVE DIVERGENCE OR VICE VERSA? A TEST USING ECOMORPHOLOGY AND SEXUAL ISOLATION IN TIMEMA CRISTINAE WALKING‐STICKS

Population differentiation often reflects a balance between divergent natural selection and the opportunity for homogenizing gene flow to erode the effects of selection. However, during ecological speciation, trait divergence results in reproductive isolation and becomes a cause, rather than a consequence, of reductions in gene flow. To assess both the causes and the reproductive consequences of morphological differentiation, we examined morphological divergence and sexual isolation among 17 populations of Timema cristinae walking-sticks. Individuals from populations adapted to using Adenostoma as a host plant tended to exhibit smaller overall body size, wide heads, and short legs relative to individuals using Ceonothus as a host. However, there was also significant variation in morphology among populations within host-plant species. Mean trait values for each single population could be reliably predicted based upon host-plant used and the potential for homogenizing gene flow, inferred from the size of the neighboring population using the alternate host and mitochondrial DNA estimates of gene flow. Morphology did not influence the probability of copulation in between-population mating trials. Thus, morphological divergence is facilitated by reductions in gene flow, but does not cause reductions in gene flow via the evolution of sexual isolation. Combined with rearing data indicating that size and shape have a partial genetic basis, evidence for parallel origins of the host-associated forms, and inferences from functional morphology, these results indicate that morphological divergence in T. cristinae reflects a balance between the effects of host-specific natural selection and gene flow. Our findings illustrate how data on mating preferences can help determine the causal associations between trait divergence and levels of gene flow.     

DOES INTERFERENCE COMPETITION AMONG POLLEN GRAINS OCCUR IN WILD RADISH?

Interest in the possibility of sexual selection in plants has focused primarily on competition among pollen donors based on the speed of pollen-tube growth. However, when pollen arrives on stigmas, there is the opportunity for both races for access to ovules (exploitation competition) and interference with the germination and growth of pollen from other donors (interference competition). We considered whether this second form of competition might occur among pollen grains of wild radish in two experiments. In the first, interference likely occurred because the amount of pollen germination was less in mixed-donor than in single-donor pollinations. This result was duplicated in a second experiment, which also showed that interference occurred only when pollen grains from different donors were in direct contact with each other. In addition, in the second experiment, the opportunity for interference affected the frequency of seeds sired by different pollen donors. Because pollen loads are often mixed in nature, interference competition among pollen grains may be important in the ecology and evolution of plant reproduction.     

DOES NICHE DIVERGENCE ACCOMPANY ALLOPATRIC DIVERGENCE IN APHELOCOMA JAYS AS PREDICTED UNDER ECOLOGICAL SPECIATION?: INSIGHTS FROM TESTS WITH NICHE MODELS

The role of ecology in the origin of species has been the subject of long‐standing interest to evolutionary biologists. New sources of spatially explicit ecological data allow for large‐scale tests of whether speciation is associated with niche divergence or whether closely related species tend to be similar ecologically (niche conservatism). Because of the confounding effects of spatial autocorrelation of environmental variables, we generate null expectations for niche divergence for both an ecological‐niche modeling and a multivariate approach to address the question: do allopatrically distributed taxa occupy similar niches? In a classic system for the study of niche evolution—the Aphelocoma jays—we show that there is little evidence for niche divergence among Mexican Jay (A. ultramarina) lineages in the process of speciation, contrary to previous results. In contrast, Aphelocoma species that exist in partial sympatry in some regions show evidence for niche divergence. Our approach is widely applicable to the many cases of allopatric lineages in the beginning stages of speciation. These results do not support an ecological speciation model for Mexican Jay lineages because, in most cases, the allopatric environments they occupy are not significantly more divergent than expected under a null model.     

DOES SELECTION ON FLORAL ODOR PROMOTE DIFFERENTIATION AMONG POPULATIONS AND SPECIES OF THE SEXUALLY DECEPTIVE ORCHID GENUS OPHRYS?

Sexually deceptive orchids from the genus Ophrys attract their pollinators primarily through the chemical mimicry of female hymenopteran sex pheromones, thereby deceiving males into attempted matings with the orchid labellum. Floral odor traits are crucial for the reproductive success of these pollinator-limited orchids, as well as for maintaining reproductive isolation through the attraction of specific pollinators. We tested for the signature of pollinator-mediated selection on floral odor by comparing intra and interspecific differentiation in odor compounds with that found at microsatellite markers among natural populations. Three regions from southern Italy were sampled. We found strong floral odor differentiation among allopatric populations within species, among allopatric species and among sympatric species. Population differences in odor were also reflected in significant variation in the attractivity of floral extracts to the pollinator, Colletes cunicularius. Odor compounds that are electrophysiologically active in C. cunicularius males, especially alkenes, were more strongly differentiated among conspecific populations than nonactive compounds in the floral odor. In marked contrast to these odor patterns, there was limited population or species level differentiation in microsatellites (FST range 0.005 to 0.127, mean FST 0.075). We propose that the strong odor differentiation and lack of genetic differentiation among sympatric taxa indicates selection imposed by the distinct odor preferences of different pollinating species. Within species, low FST values are suggestive of large effective population sizes and indicate that divergent selection rather than genetic drift accounts for the strong population differentiation in odor. The higher differentiation in active versus non-active odor compounds suggests that divergent selection among orchid populations may be driven by local pollinator preferences for those particular compounds critical for pollinator attraction.     

DOES GENETIC DIVERSITY REDUCE SIBLING COMPETITION?

An enduring hypothesis for the proximal benefits of sex is that recombination increases the genetic variation among offspring and that this genetic variation increases offspring performance. A corollary of this hypothesis is that mothers that mate multiply increase genetic variation within a clutch and gain benefits due to genetic diversity alone. Many studies have demonstrated that multiple mating can increase offspring performance, but most attribute this increase to sexual selection and the role of genetic diversity has received less attention. Here, we used a breeding design to generate populations of full-siblings, half-siblings, and unrelated individuals of the solitary ascidian Ciona intestinalis. Importantly, we preclude the potentially confounding influences of maternal effects and sexual selection. We found that individuals in populations with greater genetic diversity had greater performance (metamorphic success, postmetamorphic survival, and postmetamorphic size) than individuals in populations with lower genetic diversity. Furthermore, we show that by mating with multiple males and thereby increasing genetic variation within a single clutch of offspring, females gain indirect fitness benefits in the absence of mate-choice. Our results show that when siblings are likely to interact, genetic variation among individuals can decrease competition for resources and generate substantial fitness benefits within a single generation.     

ESTIMATING DIVERSIFICATION RATES: HOW USEFUL ARE DIVERGENCE TIMES?

The dynamics of species diversification rates are a key component of macroevolutionary patterns. Although not absolutely necessary, the use of divergence times inferred from sequence data has led to development of more powerful methods for inferring diversification rates. However, it is unclear what impact uncertainty in age estimates have on diversification rate inferences. Here, we quantify these effects using both Bayesian and frequentist methodology. Through simulation, we demonstrate that adding sequence data results in more precise estimates of internal node ages, but a reasonable approximation of these node ages is often sufficient to approach the theoretical minimum variance in speciation rate estimates. We also find that even crude estimates of divergence times increase the power of tests of diversification rate differences between sister clades. Finally, because Bayesian and frequentist methods provided similar assessments of error, novel Bayesian approaches may provide a useful framework for tests of diversification rates in more complex contexts than are addressed here.     

DOES PROFESSIONAL AUTONOMY PROTECT MEDICAL FUTILITY JUDGMENTS?

Despite substantial controversy, the use of futility judgments in medicine is quite common, and has been backed by the implementation of hospital policies and professional guidelines on medical futility. The controversy arises when health care professionals (HCPs) consider a treatment futile which patients or families believe to be worthwhile: should HCPs be free to refuse treatments in such a case, or be required to provide them? Most physicians seem convinced that professional autonomy protects them from being forced to provide treatments they judge medically futile, given the lack of patient benefit as well as the waste of medical resources involved. The argument from professional autonomy has been presented in a number of articles, but it has not been subjected to much critical scrutiny. In this paper I distinguish three versions of the argument: 1) that each physician should be free to exercise his or her own medical judgment; 2) that the medical profession as a whole may provide futility standards to govern the practice of its members; and 3) that the moral integrity of each physician serves as a limit to treatment demands. I maintain that none of these versions succeeds in overcoming the standard objection that futility determinations involve value judgments best left to the patients, their designated surrogates, or their families. Nor do resource considerations change this fact, since they should not influence the properly patient‐centered judgment about futility.     

DO PHAGES EFFICIENTLY SHUTTLE TRANSPOSABLE ELEMENTS AMONG PROKARYOTES?

The distribution, dynamics, and evolution of insertion sequences (IS), the most frequent class of prokaryotic transposable elements, are conditioned by their ability to horizontally transfer between cells. IS horizontal transfer (HT) requires shuttling by other mobile genetic elements. It is widely assumed in the literature that these vectors are phages and plasmids. By examining the relative abundance of IS in 454 plasmid and 446 phage genomes, we found that IS are very frequent in plasmids but, surprisingly, very rare in phages. Our results indicate that IS rarity in phages reflects very strong and efficient postinsertional purifying selection, mainly caused by a higher density of deleterious insertion sites in phages compared to plasmids. As they do not tolerate IS insertions, we conclude that phages may be rather poor vectors of IS HT in prokaryotes, in sharp contrast with the conventional view.     

DOES YOUR HOSPITAL NEED A RECOVERY ROOM?

In a survey made to estimate the need for a special room in which patients could recover from anesthesia after operation, it was found that of 475 cases in which this service might have been used, it would have been desirable in 296; that recovery room care would probably have relieved ward nurses of the duty of special care during their busiest hours; that recovery room care was indicated in a high percentage of cases in which certain anesthetics were employed, and that the need for recovery room care appeared to increase in proportion to the amount of pre-sedation given.     

DOES IMBALANCE IN PHYLOGENIES REFLECT ONLY BIAS?

Phylogenetic tree imbalance was originally believed to indicate differences in evolutionary rates within trees, but other sources of imbalance have been identified, such as tree incompleteness and low quality of the data. To examine the effect of data quality, I calculated Colless's index for 69 recent complete phylogenies. On average, these phylogenies were more unbalanced than phylogenies generated by the equal rates Markov (ERM) model. I tried Mooers's (1995) method to correct for tree size, but his measure appeared to become dependent on tree size when there are large trees (i.e., > 14 tips) in a collection. Instead I corrected for tree size by taking the difference between Colless's index of observed trees and the ERM model expectation for a tree of the same size. The balance measure thus obtained did not correlate significantly to consistency and retention indices as indicators of data quality. It was also independent of the factors kingdom (plants and animals) and taxon level at the tips and type of data (molecular, morphological, and combined).     

DOES JUSTICE REQUIRE THAT WE BE AGEIST?

This paper restates some of the principal arguments against an automatic preference for the young as advocated by Kappel and Sandøe, arguments many of which have been extant for over a decade but which Kappel and Sandøe largely ignore. It then goes on to demonstrate that Kappel and Sandøe's "indifference test" fails to do the work required of it because it can be met by unacceptable conceptions of justice. The paper develops a number of new arguments against what I have called "ageist" preferences for the young or for those with long life expectancy. Finally I show that Kappel and Sandøe must believe that murdering older people is less morally wrong than murdering the young and that people relying on arguments such as theirs will have to accept the moral respectability of killing the innocent in order to maximise units of lifetime.     

WHEN DOES POTENTIALITY COUNT? A COMMENT ON LOCKWOOD

Michael Lockwood's essay, "Warnock v. Powell (and Harradine): when does potentiality count?," and Hare's response are two of three articles in this issue of Bioethics discussing potentiality and its implications for experimentation with human embryos. (See also Stephen Buckle's "Arguing from potential.") Hare responds to Lockwood's arguments on potential, an embryo's "interests," and what obligations these interests entail. In Hare's view, the interests are those of the grown person the embryo (or fetus or neonate) will become. In formulating regulations on embryo research, legislators ought to be concerned chiefly with the interests of the persons who may come into existence, grading harms differently for gametes, embryos, fetuses, and neonates, and balancing these against the expected good from the experiments.