The ongoing creation-evolution controversy in North America thrives on the widespread special creationist beliefs of a significant portion of the public. Creation science supports a literal interpretation of the Judeo-Christian Bible, an earth that is no more than 10,000 years old and created ex nihilo in six days by a monotheistic God, with no new kinds arising since the period of creation, and with a single flood of staggering force shaping layers of rocks and trapping the organisms fossilized within them. Despite decisions in numerous court cases that specifically exclude creationism and creation science from primary and secondary biology classes in America's public schools, creationists now work locally to minimize or remove evolution from science teaching standards. The nationally organized movement to resist the teaching of evolution has proven highly effective, influencing state and district school boards in addition to individual teachers and schools. Thus, if teaching about evolution and the nature of science is to survive in America's primary and secondary schools, scientists must likewise work with teachers and reach out to state and local school boards. In this perspective we outline the typical creationist arguments we encounter from students, teachers, school board members, and neighbors. We explain briefly how knowledge of both microevolution and macroevolution is important in medicine, agriculture, and biotechnology. We describe a science education controversy that arose within our own school district, how we responded, and what we learned from it. Finally, we argue that even modest outreach efforts to science teachers will be richly repaid.

Corresponding Editor: J. Mitton

A mathematical model is presented that explores the relationship between transmission patterns and the evolution of virulence for horizontally transmitted parasites when only a single parasite strain can infect each host. The model is constructed by decomposing parasite transmission into two processes, the rate of contact between hosts and the probability of transmission per contact. These transmission rate components, as well as the total parasite mortality rate, are allowed to vary over the course of an infection. A general evolutionarily stable condition is presented that partitions the effects of virulence on parasite fitness into three components: fecundity benefits, mortality costs, and morbidity costs. This extension of previous theory allows us to explore the evolutionary consequences of a variety of transmission patterns. I then focus attention on a special case in which the parasite density remains approximately constant during an infection, and I demonstrate two important ways in which transmission modes can affect virulence evolution: by imposing different morbidity costs on the parasite and by altering the scheduling of parasite reproduction during an infection. Both are illustrated with examples, including one that examines the hypothesis that vector-borne parasites should be more virulent than non-vector-borne parasites (Ewald 1994). The validity of this hypothesis depends upon the way in which these two effects interact, and it need not hold in general.

Corresponding Editor: P. Jarne

Species that exist in heterogeneous environments experience selection for specialization that is opposed by the homogenizing forces of migration and recombination. Migration tends to reduce associations between alleles and habitats, whereas recombination tends to break down associations among loci. The idea that heterogeneity should favor the evolution of isolating mechanisms has motivated evolutionary studies of reduced migration, habitat preference, and assortative mating. However, costly female choice of high-quality males can also evolve in heterogeneous populations and is not hindered by either recombination or migration. When information on male fitness is available through indicator traits, female choice based on these traits increases associations between female choice alleles and locally adapted alleles. Not only does female choice evolve in a heterogeneous environment, it acts to enhance the level of genetic variation and is thus self-reinforcing. The amount of female choice at equilibrium depends on how well mixed the habitats are, how much information on male genotype is available, and how different the habitats are. Female choice reaches the highest levels for intermediate levels of heterogeneity, because at such levels of heterogeneity there is both a high risk and high cost of mismating.

Corresponding Editor: M. Whitlock

I investigate the competition between two quasispecies residing on two disparate neutral networks. Under the assumption that the two neutral networks have different topologies and fitness levels, it is the mutation rate that determines which quasispecies will eventually be driven to extinction. For small mutation rates, I find that the quasispecies residing on the neutral network with the lower replication rate will disappear. For higher mutation rates, however, the faster replicating sequences may be outcompeted by the slower replicating ones if the connection density on the second neutral network is sufficiently high. The analytical results are in excellent agreement with flow-reactor simulations of replicating RNA sequences.

Corresponding Editor: M. Riley

The genotype of an individual for allozymes such as phosphoglucoisomerase (Pgi) is often not neutral with regard to fitness. Studies of several taxa have found consistent fitness differences among Pgi genotypes expressing different allozymes. We conducted a greenhouse experiment with Clarkia unguiculata to determine whether allelic variation at the Pgi-C1 locus may affect components of male and female function. We found significant differences in siring success between pollen donors homozygous for different Pgi alleles. When a mixture of pollen was applied to stigmas under conditions of gametophytic competition (more pollen deposited on stigmas than there are ovules available to fertilize), donors homozygous for the C allele of Pgi sired more seeds per fruit than B-allele donors. Differences between genotypes with respect to female fertility per fruit contrasted with the male advantage associated with the C allele. Recipients homozygous for the C allele produced fruits with more aborted seeds and fewer viable seeds than recipients homozygous for the B allele. These results suggest that allelic variation at a single locus may have opposing effects on male and female reproductive success in C. unguiculata, and that trade-offs between the two types of reproductive success could contribute to the maintenance of variation at the Pgi-C1 locus.

Corresponding Editor: O. Savolainen

Across large spatial scales, plants often exhibit genetically based differentiation in traits that allow adaptation to local sites. At smaller spatial scales, sharp boundaries between edaphic conditions also can create strong gradients in selection that counteract gene flow and result in local adaptation. Few studies, however, have examined the degree to which continuous populations of perennial plants exhibit genetically based differentiation in life-history traits over small spatial scales. We quantified the degree of genetically based differentiation in adaptive traits among bush lupine (Lupinus arboreus) from nearby dune and grassland sites (sites separated by <0.75 km) that formed part of a larger continuous population of L. arboreus. We also investigated the spatial genetic structure of bush lupine by examining how genetic structure differed between seeds and juvenile plants that were less than two years old. We calculated F-statistics from gel electrophoresis of 10 polymorphic loci. We then used these values to infer levels of gene flow. To examine differentiation in adaptive traits, we created full-sibling/half-sibling families of lupine within each area and established reciprocal common gardens at each site. Across two years, we measured canopy volume, flowering time, seed set, and mortality of progeny planted in each garden. Spatial genetic structure among seeds was virtually nonexistent (F_ST = 0.002), suggesting that gene flow between the three areas could be quite high. However, genetic structure increased 20-fold among juvenile plants (F_ST = 0.041). We found strong evidence for fine-scale genetically based differentiation and local adaptation in adaptive traits such as plant size, flowering phenology, fecundity, and mortality. Thus, it is likely that strong but differing selection regimes within each area drive spatial differentiation in lupine life-history traits.

Corresponding Editor: S. Tonsor

Theory predicts that selection should favor genotypes that can vary their tendency to disperse in habitats that are spatially or temporally variable or those that remain near their carrying capacity. Although many marine habitats appear to fit these criteria, confirmed examples of dispersal polymorphism among marine invertebrates are exceedingly rare. Competent larvae of the gregarious tubeworm, Hydroides dianthus, settle specifically in response to living conspecific worms, but a small proportion of each spawn settle nonspecifically on uninhabited substrata concurrently with their gregarious siblings. Here, using a parental half-sib analysis, we show that the proportion of a spawn settling in response to uninhabited biofilm is highly heritable. When estimated as a continuous trait based on a one-way ANOVA, heritability is estimated to be 0.83 ± 0.31. When founder production was analyzed as a threshold trait, heritability was estimated to be 0.68 ± 0.10 based on the breeding design experiment and 0.65 ± 0.09 based on the artificial selection experiments. Realized heritability based on the selection experiments was considerably lower, however (0.17 per generation and 0.02 cumulative). Artificial selection was ineffectual at sequentially increasing the proportion of founder larvae among inbred family lines, but after three generations of selection, the proportion of larvae settling in response to biofilm was significantly higher among inbred lines than among the field-collected parents. The obligate planktonic larval stage common among so many marine invertebrates is thought to preclude the evolution of dispersal polymorphisms in these animals. Theoretical expectations of variable dispersal may instead be realized through individual behavioral differences resulting in differential transport or settlement preference, but this possibility remains largely unexplored among marine invertebrates.

Corresponding Editor: R. Burton

Recent glaciation covered the full extent of rocky intertidal habitat along the coasts of New England and the Canadian Maritimes. To test whether this glaciation in fact caused wholesale extinction of obligate rocky intertidal invertebrates, and thus required a recolonization from Europe, we compared American and European populations using allelic diversity and techniques adapted from coalescent theory. Mitochondrial DNA sequences were collected from amphi-Atlantic populations of three cold-temperate obligate rocky intertidal species (a barnacle, Semibalanus balanoides, and two gastropods, Nucella lapillus and Littorina obtusata) and three cold-temperate habitat generalist species (a seastar, Asterias rubens; a mussel, Mytilus edulis, and an isopod, Idotea balthica). For many of these species we were able to estimate the lineage-specific mutation rate based on trans-Arctic divergences between Pacific and Atlantic taxa. These data indicate that some obligate rocky intertidal taxa have colonized New England from European populations. However, the patterns of persistence in North America indicate that other life-history traits, including mechanisms of dispersal, may be more important for surviving dramatic environmental and climatic change.

Corresponding Editor: R. Burton

In broadcast-spawning marine organisms, chronic sperm limitation should select for traits that improve chances of sperm-egg contact. One mechanism may involve increasing the size of the physical or chemical target for sperm. However, models of fertilization kinetics predict that increasing egg size can reduce net zygote production due to an associated decline in fecundity. An alternate method for increasing physical target size is through addition of energetically inexpensive external structures, such as the jelly coats typical of eggs in species from several phyla. In selection experiments on eggs of the echinoid Dendraster excentricus, in which sperm was used as the agent of selection, eggs with larger overall targets were favored in fertilization. Actual shifts in target size following selection matched quantitative predictions of a model that assumed fertilization was proportional to target size. Jelly volume and ovum volume, two characters that contribute to target size, were correlated both within and among females. A cross-sectional analysis of selection partitioned the independent effects of these characters on fertilization success and showed that they experience similar direct selection pressures. Coupled with data on relative organic costs of the two materials, these results suggest that, under conditions where fertilization is limited by egg target size, selection should favor investment in low-cost accessory structures and may have a relatively weak effect on the evolution of ovum size.

Corresponding Editor: D. Wheeler

Organisms with external fertilization are often sperm limited, and in echinoids, larger eggs have a higher probability of fertilization than smaller eggs. This difference is thought to be a result of the more frequent sperm-egg collisions experienced by larger targets. Here we report how two components of egg target size, the egg cell and jelly coat, contributed to fertilization success in a selection experiment. We used a cross-sectional analysis of correlated characters to estimate the selection gradients on egg and jelly-coat size in five replicate male pairs of the sand dollar Dendraster excentricus. Results indicated that eggs with larger cells and jelly coats were preferentially fertilized under sperm limitation in the laboratory. The selection gradients were an average of 922% steeper for egg than for jelly-coat size. The standardized selection gradients for egg and jelly-coat size were similar. Our results suggest that fertilization selection can act on both egg-cell and jelly-coat size but that an increase in egg-cell volume is much more likely to increase fertilization success than an equal change in jelly-coat volume. The strengths of the selection gradients were inversely related to the correlation of egg traits across replicate egg clutches. This result suggests the importance of replication in studies of selection of correlated characters.

Corresponding Editor: D. Wheeler

Ecological constraints on effective dispersal have been suggested to be a key factor influencing social evolution in animal societies as well as the shift from single queen colonies (monogyny) to multiple queen colonies (polygyny) in ants. However, little is known about the effective dispersal patterns of ant queens. Here we investigate the microgeographic genetic structure of mitochondrial haplotypes in polygynous populations of the ant Formica exsecta, both between pastures and among nests within pastures. An analysis of molecular variance revealed a very high genetic differentiation (Φ_ST = 0.72) between pastures, indicating that queens rarely disperse successfully between pastures, despite the fact that pastures were sometimes as close as 1 km. Most of the pastures contained only a single haplotype, and haplotypes were frequently distinct between nearby pastures and even between groups of nests within the same pasture. In the three pastures that contained several haplotypes, haplotypes were not randomly distributed, the genetic differentiation between nests being Φ_ST = 0.17, 0.52, and 0.69. This indicates that most queens are recruited within their parental colonies. However, a large proportion of nests contained more than one haplotype, demonstrating that colonies will sometimes accept foreign queens. The relatedness of mitochondrial genes among nestmates varied between 0.62 and 0.75 when relatedness was measured within each pasture and ranged between 0.72 and 1.0 when relatedness was assessed with all pastures as a reference population. Neighboring nests were more genetically similar than distant ones, and there was significant isolation by distance. This pattern may be due to new nests being formed by budding or by limited effective queen dispersal, probably on foot between neighboring nests. These results show that effective queen dispersal is extremely restricted even at a small geographical scale, a pattern consistent with the idea that ecological constraints are an important selective force leading to the evolution and maintenance of polygyny.

Corresponding Editor: D. Wheeler

Selection for late-life fecundity and longevity in adult Drosophila melanogaster is well known to modify numerous characteristics of life history and physiology. We report experiments here in which selection applied to behavior affects features in an identical fashion. Selection for feeding rate of larval D. melanogaster modifies caloric intake, as measured by the uptake and incorporation of labeled glucose. Selection for slow larval feeding produced lines of D. melanogaster in which larvae synthesized significantly less lipid prior to pupation and eclosed to have low early-life fecundity and a long life as adults. They also had greater lifetime fecundity, but lower viability of egg to hatched adult. Alternatively, fast-feeding larvae incorporated more lipid before pupation and eclosed with high early-fecundity that declined rapidly throughout their short adult life. Slow-feeding populations also had a significantly enhanced expression of the stress-resistance genes CuZn-SOD, CATALASE, and HSP70. Selection on larval feeding behavior reproduced the antagonistic evolutionary trade-off found under selection for adult life span and mimicked the physiological response in life span as seen in many species when dietary restriction is imposed on adults. Thus, nutrient acquisition during development appears to share a common evolutionary and genetic basis with the allocation processes that determine adult life-history traits and the related phenotypic dietary restriction phenomena.

Corresponding Editor: S. Pitnick

Gall wasps, or cynipids, form the second largest radiation of galling insects with more than 1300 described species. According to current views, the first cynipids were phytophagous and developed in herb stems of the Asteraceae without modifying plant growth or development. The first galls were supposedly multichambered stem swellings, and subsequent trends involved increase in gall complexity and reduction in the number of larval chambers. Gall wasps also have many of the features believed to be characteristic for phytophagous insects radiating in parallel with their host plants. We tested these hypotheses by mapping characters onto a recent estimate of higher cynipid relationships from a morphology-based analysis of exemplar taxa, controlling for phylogenetic uncertainty using bootstrapping. Characters were also mapped onto a metatree including all gall wasps, assembled from phylogenetic analyses as well as recent classifications. The results contradict many of the current hypotheses. The first cynipids with extant descendants were not Asteraceae stem feeders but induced distinct single-chambered galls in reproductive organs of herbaceous Papaveraceae, or possibly Lamiaceae. There has been a general trend toward more complex galls but the herb-stem feeders evolved from ancestors inducing distinct galls and their larval chambers are best understood as cryptic galls. Woody hosts have been colonized only three times, making the apparently irreversible transition from herbs to woody hosts one of the most conservative features of the gall wasp–host plant association. The evolution of host plant preferences is characterized by colonization of preexisting host-plant lineages rather than by parallel cladogenesis. Cynipids are mono- or oligophagous and host-plant choice is strongly phylogenetically conserved. Yet, the few major host shifts have involved remarkably distantly related plants. Many shifts have been onto plant species already exploited by other gall wasps, suggesting that interspecific parasitism among cynipids facilitates colonization of novel host plants.

Corresponding Editor: K. Shaw

In general, squamate reptiles follow the converse to Bergmann's rule, attaining smaller sizes in cooler environments, whereas other vertebrate groups follow Bergmann's rule, attaining larger sizes in cooler areas. Intensive studies of body size evolution for species of squamates are necessary to understand the processes responsible for this trend. Here I present data on body size variation among mainland populations of the western rattlesnake, Crotalus viridis. This species consists of two well-differentiated phylogenetic clades, therefore all analyses were performed for the C. viridis group as a whole and separately for each of the two clades within the C. viridis group. Although both phylogenetic and nonphylogenetic analyses were performed, the data did not show phylogenetic conservatism, and therefore the nonphylogenetic results are preferred. I found no significant relationships between mean adult female snout-vent length and any of the physical and climatic variables that were examined for the C. viridis group using simple linear regression analysis. Examined separately, I found that individuals of the western clade, C. oreganus, were smaller in cooler and more seasonal environments, whereas individuals of the eastern clade, C. viridis sensu stricto, were larger in cooler and more seasonal areas. Thus, the observed size trends were in opposite directions for the two clades. Multiple regression analysis revealed that seasonality was a stronger predictor of body size variation than was temperature for both clades. The differences in body size trends between these clades may be due to differences in mortality rates among populations.

Corresponding Editor: T. Mousseau

Differences among taxa in sexual size dimorphism of adults can be produced by changes in distinct developmental processes and thus may reflect different evolutionary histories. Here we examine whether divergence in sexual dimorphism of adults between recently established Montana and Alabama populations of the house finch (Carpodacus mexicanus) can be attributed to population differences in growth of males and females. In both populations, males and females were similar at hatching, but as a result of sex-specific growth attained sexual size dimorphism by the time of independence. Timing and extent of growth varied between the sexes: Females maintained maximum rates of growth for a longer time than males, whereas males had higher initial growth rates and achieved maximum growth earlier and at smaller sizes than females. Ontogeny of sexual dimorphism differed between populations, but in each population, sexual dimorphism in growth parameters and sexual dimorphism at the time of nest leaving were similar to sexual dimorphism of adults. Variation in growth of females contributed more to population divergence than did growth of males. In each population, we found close correspondence between patterns of sexual dimorphism in growth and population divergence in morphology of adults: Traits that were the most sexually dimorphic in growth in each population contributed the most to population divergence in both sexes. We suggest that sex-specific expression of phenotypic and genetic variation throughout the ontogeny of house finches can result in different responses to selection between males and females of the same age, and thus produce fast population divergence in the sexual size dimorphism.

Corresponding Editor: J. Merilä

Robust phylogenies for brood-parasitic birds, their hosts, and nearest nesting relatives provide the framework to address historical questions about host-parasite coevolution and the origins of parasitic behavior. We tested phylogenetic hypotheses for the two genera of African brood-parasitic finches, Anomalospiza and Vidua, using mitochondrial DNA sequence data from 43 passeriform species. Our analyses strongly support a sister relationship between Vidua and Anomalospiza, leading to the conclusion that obligate brood parasitism evolved only once in African finches rather than twice, as has been the conventional view. In addition, the parasitic finches (Viduidae) are not recently derived from either weavers (Ploceidae) or grassfinches (Estrildidae), but represent a third distinct lineage. Among these three groups, the parasitic finches and estrildids, which includes the hosts of all 19 Vidua species, are sister taxa in all analyses of our full dataset. Many characters shared by Vidua and estrildids, including elaborate mouth markings in nestlings, unusual begging behavior, and immaculate white eggs, can therefore be attributed to common ancestry rather than convergent evolution. The host-specificity of mouth mimicry in Vidua species, however, is clearly the product of subsequent host-parasite coevolution. The lineage leading to Anomalospiza switched to parasitizing more distantly related Old World warblers (Sylviidae) and subsequently lost these characteristics. Substantial sequence divergence between Vidua and Anomalospiza indicates that the origin of parasitic behavior in this clade is ancient (∼20 million years ago), a striking contrast to the recent radiation of extant Vidua. We suggest that the parasitic finch lineage has experienced repeated cycles of host colonization, speciation, and extinction through their long history as brood parasites and that extant Vidua species represent only the latest iterations of this process. This dynamic process may account for a significantly faster rate of DNA sequence evolution in parasitic finches as compared to estrildids and other passerines. Our study reduces by one the tally of avian lineages in which obligate brood parasitism has evolved and suggests an origin of parasitism that involved relatively closely related species likely to accept and provide appropriate care to parasitic young. Given the ancient origin of parasitism in African finches, ancestral estrildids must have been parasitized well before the diversification of extant Vidua, suggesting a long history of coevolution between these lineages preceding more recent interactions between specific hosts and parasites.

Corresponding Editor: B. Crespi

Bird song often varies geographically within a species; when this geographic variation has distinct boundaries, the shared song types are referred to as song dialects. How dialects are produced and their adaptive significance are longstanding problems in biology, with implications for the role of culture in the evolution and ecology of diverse organisms, including humans. Here we test the hypothesis that song dialect, a culturally transmitted trait, is related to the population genetic structure of mountain white-crowned sparrows (Zonotrichia leucophrys oriantha). To address this, we compared microsatellite allele frequencies from 18 sample sites representing eight dialect regions in the Sierra Nevada. Pairwise genetic distances were not significantly correlated with geographic distances either within or between dialects, nor did dialect groups form distinct genetic groups according to neighbor-joining or UPGMA analysis, and most variation in allele frequencies occurred among individuals rather than at higher levels. However, most of the remaining variation was attributable to differences among, rather than within, dialect regions, and this among-dialect component of variance was statistically significant. Moreover, when controlling for the effect of geographic distance, song dissimilarity and genetic distance between site pairs were significantly correlated. Thus, song dialects appear to be associated with reductions in, but not strict barriers to, gene flow among dialect regions.

Corresponding Editor: P. Dunn

Similarity of genetic and phenotypic variation patterns among populations is important for making quantitative inferences about past evolutionary forces acting to differentiate populations and for evaluating the evolution of relationships among traits in response to new functional and developmental relationships. Here, phenotypic covariance and correlation structure is compared among Platyrrhine Neotropical primates. Comparisons range from among species within a genus to the superfamily level. Matrix correlation followed by Mantel's test and vector correlation among responses to random natural selection vectors (random skewers) were used to compare correlation and variance/covariance matrices of 39 skull traits. Sampling errors involved in matrix estimates were taken into account in comparisons using matrix repeatability to set upper limits for each pairwise comparison.

Results indicate that covariance structure is not strictly constant but that the amount of variance pattern divergence observed among taxa is generally low and not associated with taxonomic distance. Specific instances of divergence are identified. There is no correlation between the amount of divergence in covariance patterns among the 16 genera and their phylogenetic distance derived from a conjoint analysis of four already published nuclear gene datasets. In contrast, there is a significant correlation between phylogenetic distance and morphological distance (Mahalanobis distance among genus centroids). This result indicates that while the phenotypic means were evolving during the last 30 millions years of New World monkey evolution, phenotypic covariance structures of Neotropical primate skulls have remained relatively consistent.

Neotropical primates can be divided into four major groups based on their feeding habits (fruit-leaves, seed-fruits, insect-fruits, and gum-insect-fruits). Differences in phenotypic covariance structure are correlated with differences in feeding habits, indicating that to some extent changes in interrelationships among skull traits are associated with changes in feeding habits. Finally, common patterns and levels of morphological integration are found among Platyrrhine primates, suggesting that functional/developmental integration could be one major factor keeping covariance structure relatively stable during evolutionary diversification of South American monkeys.

Corresponding Editor: T. Mousseau

We consider a method of approximating Weir and Cockerham's θ, an unbiased estimator of genetic population structure, using values readily available from published studies using biased estimators (Wright's F_ST or Nei's G_ST). The estimation algorithm is shown to be useful for both model populations and real-world avian populations. However, the correlation between Wright's F_ST and Weir and Cockerham's θ is strong when compared among 39 empirical avian datasets. Thus, the advantage of approximating an unbiased estimator is unclear considering the small actual effect of θ's bias-removing power on empirical datasets.

Corresponding Editor: S. Karl

Population bottlenecks affect the dynamics of evolution, increasing the probability that beneficial mutations will be lost. Recent protocols for the experimental study of evolution involve repeated bottlenecks—when fresh media are inoculated during serial transfer or when chemostat tubes are changed. Unlike population reductions caused by stochastic environmental factors, these bottlenecks occur at known, regular intervals and with a fixed dilution ratio. We derive the ultimate probability of extinction for a beneficial mutation in a periodically bottlenecked population, using both discrete and continuous approaches. We show that both approaches yield the same approximation for extinction probability. From this, we derive an approximate expression for an effective population size.

Corresponding Editor: M. Morgan

Although fitness depends on both survivorship and fecundity, we tend to assume fecundity relates to fitness more directly than survivorship. In fact, several recent ecological studies suggest fitness depends more heavily on annual survivorship than annual fecundity for most taxa with lifespans longer than one year. These studies review elasticities of transition matrices for a broad range of taxa. Elasticities covary monotonically with selection gradients for demographic rates and are identical to selection gradients for traits rescaled to have mean values of zero and variance of one. For all taxa except semelparous perennial plants, adult survivorship has consistently higher elasticity than other suites of demographic rates. Fecundity only rarely has the highest elasticity. Thus, differences in yearly survival affect fitness disproportionately more than differences in yearly fecundity, even in many exponentially growing populations. This pattern reinforces the importance of interpreting the contribution of vital rates to fitness in the context of life history and population dynamics.

Corresponding Editor: T. Mousseau

We tested for the occurrence of oviposition acceptance for different media prepared with cactus tissues of three alternative cactus hosts: Opuntia sulphurea, O. quimilo and Trichocereus terschekii for 4 consecutive days in lines of two Drosophila buzzatii populations and one population of D. koepferae. Our results showed that the former laid significantly more eggs on both Opuntia cacti than on T. terschekii, whereas D. koepferae preferred T. terschekii. In addition, fecundity schedules differed between species: D. buzzatii laid similar numbers of eggs along the four-day sampling period, whereas D. koepferae showed an oviposition peak on the second day of egg collection on T. terschekii. We suggest that the between-species disparities observed in oviposition acceptance and fecundity schedule may be related to the temporal and spatial predictability of Opuntia versus T. terschekii (cardón) as part of the different adaptive strategies that have evolved after the split of D. koepferae and D. buzzatii from their recent common ancestor. Therefore, the willingness to accept hosts would be an important factor in the habitat selection and in the maintenance of species diversity.

Corresponding Editor: M. Noor

Corresponding Editor: D. Futuyma

Corresponding Editor: D. Futuyma