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.     

GROWTH TEMPERATURE AND ADULT PIGMENTATION IN TWO DROSOPHILA SIBLING SPECIES: AN ADAPTIVE CONVERGENCE OF REACTION NORMS IN SYMPATRIC POPULATIONS?

Phenotypic plasticity of abdomen pigmentation was investigated in populations of the sibling species Drosophila melanogaster and D. simulans, living in sympatry in two French localities. Ten isofemale lines of each population and species were grown at different constant temperatures spanning their complete thermal range from 12 to 31°C. Genetic variability between isofemale lines was not affected by growth temperature, but was consistently less in D. simulans. For all traits, the dark pigmentation of the abdominal segments decreased according to growth temperature, in agreement with the thermal budget adaptive hypothesis. The shapes of the response curves were different between the abdominal segments, but for a given segment, quite similar in the two species. On average D. simulans was lighter than D. melanogaster, but the difference was mainly expressed at higher temperatures. An interesting result was the difference observed between the two localities: flies from the colder locality (Villeurbanne) were found to be darker than flies from the warmer locality (Bordeaux). Interestingly, this difference was expressed only at low temperatures, 21°C and below, that is, at temperatures encountered in natural conditions. This suggests an adaptive response resulting in a change of the shape of reaction norm and involving genotype-environment interactions. When comparing the genetic structure of geographic populations for quantitative traits, several laboratory environments should be preferred to a single one.     

MULTIPLE MATING IN THE GLANVILLE FRITILLARY BUTTERFLY: A CASE OF WITHIN‐GENERATION BET HEDGING?

Many hypotheses have been proposed to explain multiple mating in females. One of them is bet hedging, that is avoiding having no or very few offspring in any given generation, rather than maximizing the expected number of offspring. However, within-generation bet hedging is generally believed to be an unimportant evolutionary force, except in very small populations. In this study, we derive predictions of the bet-hedging hypothesis for a case in which local insect populations are often small, offspring performance varies, for example, due to inbreeding depression, and the groups of gregarious larvae have to exceed a threshold size before they are likely to survive throughout the larval stage. These conditions exist for populations of the Glanville fritillary butterfly (Melitaea cinxia), potentially making bet-hedging benefits larger than usual. We observed matings in a field cage, which allowed detailed observations under practically natural conditions, and analyzed genetic paternity of egg clutches laid by females under direct observation. The egg-laying and survival patterns are in line with the predictions, supporting the hypothesis that multiple mating in M. cinxia presents a rare case of within-generation bet hedging.     

ONE HOST SHIFT LEADS TO ANOTHER? EVIDENCE OF HOST‐RACE FORMATION IN A PREDACEOUS GALL‐BORING BEETLE

Abstract.— We show that a predator, the tumbling flower beetle Mordellistena convicta (Coleoptera: Mordellidae), has formed host races in response to a host-plant shift and subsequent host-race formation by its prey, the gall-inducing fly Eurosta solidaginis (Diptera: Tephritidae). This fly has formed two host races, one that induces stem galls on the ancestral host plant, Solidago altissima (Compositae), and another that induces stem galls on the closely related S. gigantea . We found that subpopulations of M. convicta that attack E. solidaginis galls on the different host plants have significantly different emergence times and, although slight, these allochronic differences are consistent across a range of temperatures. More importantly, we found that beetles assortatively mate according to their natal host plants, and female M. convicta preferentially attack and/or their offspring have higher survival in galls on natal host plants. Our data suggest that subpopulations of M. convicta that attack E. solidaginis galls on S. altissima and S. gigantea have formed host races. This is one of the first studies to demonstrate that a host shift and subsequent host-race formation by an herbivorous insect may have resulted in subsequent diversification by one of its natural enemies.     

LINKAGE BETWEEN NUCLEAR AND MITOCHONDRIAL DNA SEQUENCES IN AVIAN MALARIA PARASITES: MULTIPLE CASES OF CRYPTIC SPECIATION?

Analyses of mitochondrial cytochrome b diversity among avian blood parasites of the genera Haemoproteus and Plasmodium suggest that there might be as many lineages of parasites as there are species of birds. This is in sharp contrast to the approximately 175 parasite species described by traditional methods based on morphology using light microscopy. Until now it has not been clear to what extent parasite mitochondrial DNA lineage diversity reflects intra- or interspecific variation. We have sequenced part of a fast-evolving nuclear gene, dihydrofolate reductase-thymidylate synthase (DHFR-TS), and demonstrate that most of the parasite mitochondrial DNA lineages are associated with unique gene copies at this locus. Although these parasite lineages sometimes coexist in the same host individual, they apparently do not recombine and could therefore be considered as functionally distinct evolutionary entities, with independent evolutionary potential. Studies examining parasite virulence and host immune systems must consider this remarkable diversity of avian malaria parasites.     

SPECIFIC BINDING AND STABILIZATION OF DNA AND PHOSPHOROTHIOATE DNA BY AMPHIPHILIC α-HELICAL PEPTIDES

Synthetic cationic peptides with amphiphilic α-helical structure were found to have DNA binding ability to stabilize double and triple stranded DNA. The stabilization effect was significant for cationic α-helical peptides indicating the importance of an electrostatic interaction of a positive charge of peptides and a negative charge of DNAs.     

IS GLOBAL ETHICS MORAL NEO‐COLONIALISM? AN INVESTIGATION OF THE ISSUE IN THE CONTEXT OF BIOETHICS

This paper considers the possibility and desirability of global ethics in light of the claim that ‘global ethics’ in any form is not global, but simply the imposition of one form of local ethics – Western ethics – and, as such, a form of moral neo‐colonialism. The claim that any form of global ethics is moral neo‐colonialism is outlined using the work of a group of ‘developing world bioethicists’ who are sceptical of the possibility of global ethics. The work of virtue ethicists is then introduced and compared to the position of the developing world bioethicists in order to show that the divide between ‘Western’ and ‘non‐Western’ ethics is exaggerated. The final section of the paper turns to the practical arena and considers the question of global ethics in light of practical issues in bioethics. The paper concludes that practical necessity is driving the creation of global ethics and thus the pertinent question is no longer ‘Whether global ethics?’, but ‘Why global ethics?’.     

PERSPECTIVE: MODELS OF SPECIATION: WHAT HAVE WE LEARNED IN 40 YEARS?

Theoretical studies of speciation have been dominated by numerical simulations aiming to demonstrate that speciation in a certain scenario may occur. What is needed now is a shift in focus to identifying more general rules and patterns in the dynamics of speciation. The crucial step in achieving this goal is the development of simple and general dynamical models that can be studied not only numerically but analytically as well. I review some of the existing analytical results on speciation. I first show why the classical theories of speciation by peak shifts across adaptive valleys driven by random genetic drift run into trouble (and into what kind of trouble). Then I describe the Bateson-Dobzhansky-Muller (BDM) model of speciation that does not require overcoming selection. I describe exactly how the probability of speciation, the average waiting time to speciation, and the average duration of speciation depend on the mutation and migration rates, population size, and selection for local adaptation. The BDM model postulates a rather specific genetic architecture of reproductive isolation. I then show exactly why the genetic architecture required by the BDM model should be common in general. Next I consider the multilocus generalizations of the BDM model again concentrating on the qualitative characteristics of speciation such as the average waiting time to speciation and the average duration of speciation. Finally, I consider two models of sympatric speciation in which the conditions for sympatric speciation were found analytically. A number of important conclusions have emerged from analytical studies. Unless the population size is small and the adaptive valley is shallow, the waiting time to a stochastic transition between the adaptive peaks is extremely long. However, if transition does happen, it is very quick. Speciation can occur by mutation and random drift alone with no contribution from selection as different populations accumulate incompatible genes. The importance of mutations and drift in speciation is augmented by the general structure of adaptive landscapes. Speciation can be understood as the divergence along nearly neutral networks and holey adaptive landscapes (driven by mutation, drift, and selection for adaptation to a local biotic and/or abiotic environment) accompanied by the accumulation of reproductive isolation as a by-product. The waiting time to speciation driven by mutation and drift is typically very long. Selection for local adaptation (either acting directly on the loci underlying reproductive isolation via their pleiotropic effects or acting indirectly via establishing a genetic barrier to gene flow) can significantly decrease the waiting time to speciation. In the parapatric case the average actual duration of speciation is much shorter than the average waiting time to speciation. Speciation is expected to be triggered by changes in the environment. Once genetic changes underlying speciation start, they go to completion very rapidly. Sympatric speciation is possible if disruptive selection and/or assortativeness in mating are strong enough. Sympatric speciation is promoted if costs of being choosy are small (or absent) and if linkage between the loci experiencing disruptive selection and those controlling assortative mating is strong.     

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.     

WHAT USE IS AN INFERTILE SPERM? A COMPARATIVE STUDY OF SPERM‐HETEROMORPHIC DROSOPHILA

Sperm size and number are important determinants of male reproductive success. The genus Drosophila exhibits a remarkable diversity of sperm production strategies, including the production of multiple sperm morphs by individual males, a phenomenon called sperm heteromorphism. Sperm-heteromorphic Drosophila species in the obscura group produce large numbers of infertile "parasperm" in addition to fertile eusperm. Parasperm have been hypothesized to perform a number of roles in place of fertilization, predominantly focused on their potential function in postcopulatory sexual selection. However, the evolutionary significance of parasperm remains unknown. Here we measured several male and female morphological, behavioral, and life-history traits in 13 obscura group species to test competing hypotheses of parasperm function using comparative methods. We found that parasperm size was unrelated to female reproductive tract morphology but was negatively related to our two indices of sperm competition, suggesting that postcopulatory sexual selection may indeed have shaped the evolution of parasperm. We also found abundant coevolution between male and female reproductive traits. Some of these relationships have been found in both sperm-monomorphic and sperm-heteromorphic taxa, but others are dissimilar. We discuss the significance of our results to the evolution of reproductive traits and the elusive function of Drosophila parasperm.     

CLINAL DISTRIBUTION OF A CHROMOSOMAL REARRANGEMENT: A PRECURSOR TO CHROMOSOMAL SPECIATION?

Geographically structured genetic variants provide an effective means to assess sources of natural selection and mechanisms of adaptation to local environments. Correlated selection pressures along environmental gradients favor subdivision of genomes through chromosomal rearrangement. This study examines populations of Drosophila americana to evaluate selection pressures affecting chromosomal forms distinguished by a centromeric fusion. Analyses of chromosomal polymorphism throughout the Mississippi River Valley in the central United States reveal the presence of a distinct latitudinal cline for the chromosomal rearrangement. The cline has a width of 623 km centered at 35.97 degrees N and displays a characteristic sigmoid shape consistent with a balance between selection and dispersal. Extreme low temperature during January, an indicator of winter severity, was identified as the environmental variable that most accurately predicts arrangement frequency. An intriguing relationship identified between the chromosomal cline and operational sex ratio indicates that these alternative arrangements of the X chromosome may influence sex-specific survival. A hypothesis for the cline is presented wherein variation associated with the alternative chromosome forms influences distinct overwintering strategies. The resulting subdivision within the genome embodies a transitory stage of a speciation process in which locally adapted gene complexes provide a foundation for species formation.     

HOST‐ASSOCIATED GENETIC DIFFERENTIATION IN PHYTOPHAGOUS INSECTS: GENERAL PHENOMENON OR ISOLATED EXCEPTIONS? EVIDENCE FROM A GOLDENROD‐INSECT COMMUNITY

There is growing awareness of the importance of natural selection in driving genetic divergence and speciation, and several of the most apparent cases of this ecological speciation are provided by the existence of genetically distinct host forms in phytophagous insects. Such examples of host-associated differentiation (HAD) have become increasingly documented, and the implications of this phenomenon for the diversification of insects are becoming widely appreciated. However, instances of HAD remain rare relative to insect diversity and are sparsely distributed both ecologically and taxonomically. We sought to assess the frequency of HAD in a model herbivore community by examining genetic divergence in a variety of herbivores that feed on two closely related and broadly sympatric species of goldenrod (Solidago altissima and S. gigantea). Using mitochondrial DNA and allozyme data, in conjunction with previously published studies, we found that four of nine herbivores exhibited evidence of HAD, including possible host races or cryptic species. Using a range of reasonable substitution rate estimates for cytochrome oxidase I mitochondrial DNA, we found that HAD appears to have proceeded asynchronously across taxa. This pattern, along with the broadly sympatric distribution of host plants and the specialized life histories of the phytophagous insects, is consistent with sympatric divergence in some or all of these taxa. Although further behavioral and ecological study is needed, our survey of HAD in a community of herbivores indicates that ecological (perhaps sympatric) speciation may have been responsible for generating a significant fraction of the extant diversity of phytophagous insects.