Traditional models of sexual selection propose that partner choice increases both average male and average female fitness in a population. Recent theoretical and empirical work, however, has stressed that sexual conflict may be a potent broker of sexual selection. When the fitness interests of males and females diverge, a reproductive strategy that increases the fitness of one sex may decrease the fitness of the other sex. The chase-away hypothesis proposes that sexual conflict promotes sexually antagonistic, rather than mutualistic, coevolution, whereby manipulative reproductive strategies in one sex are counteracted by the evolution of resistance to such strategies in the other sex. In this paper, we consider the criteria necessary to demonstrate the chase-away hypothesis. Specifically, we review sexual conflict with particular emphasis on the chase-away hypothesis; discuss the problems associated with testing the predictions of the chase-away hypothesis and the extent to which these predictions and the predictions of traditional models of sexual selection are mutually exclusive; discuss misconceptions and mismeasures of sexual conflict; and suggest an alternative approach to demonstrate sexual conflict, measure the intensity of sexually antagonistic selection in a population, and elucidate the coevolutionary trajectories of the sexes.

The importance of accommodating the phylogenetic history of a group when performing a comparative analysis is now widely recognized. The typical approaches either assume the tree is known without error, or they base inferences on a collection of well-supported trees or on a collection of trees generated under a stochastic model of cladogenesis. However, these approaches do not adequately account for the uncertainty of phylogenetic trees in a comparative analysis, especially when data relevant to the phylogeny of a group are available. Here, we develop a method for performing comparative analyses that is based on an extension of Felsenstein's independent contrasts method. Uncertainties in the phylogeny, branch lengths, and other parameters are accommodated by averaging over all possible trees, weighting each by the probability that the tree is correct. We do this in a Bayesian framework and use Markov chain Monte Carlo to perform the high-dimensional summations and integrations required by the analysis. We illustrate the method using comparative characters sampled from Anolis lizards.

Cryptic animal coloration or camouflage is an adaptation that decreases the risk of detection. The study of the evolution of camouflage has strongly emphasized the minimization of visual information that predators receive from prey, by means of background matching. However, the evolutionary effects of information processing after its reception have been virtually ignored. I constructed a model that employs an artificial neural network and simulates the evolution of prey coloration in a visually complex and simple habitat. The model suggests: (1) the difficulty of a detection task is related to the visual complexity of the habitat; (2) it is easier to decrease the risk of detection by the means of camouflage in a visually complex habitat; (3) selection on camouflage can exploit limitations in predators information processing; and (4) there are shortcomings in using the degree of background matching as the measure of camouflage.

The interaction between Ficus (Moraceae) and their pollinating wasps (Chalcidoidea: Agaonidae; more than 700 species-specific couples) is one of the most specialized mutualisms found in nature. Both partners of this interaction show extensive variation in their respective biology. Here we investigate Ficus life-history trait evolution and fig/fig wasp coadaptation in the context of a well-resolved molecular phylogeny. Mapping out variations in Ficus life-history traits on an independently derived phylogeny constructed from ribosomal DNA sequences (external and internal transcribed spacer) reveals several parallel transitions in Ficus growth habit and breeding system. Convergent trait evolution might explain the discrepancies between morphological analyses and our molecular reconstruction of the genus. Morphological characters probably correlate with growth habit and breeding system and could therefore be subject to convergent evolution. Furthermore, we reconstruct the evolution of Ficus inflorescence characters that are considered adaptations to the pollinators. Our phylogeny reveals convergences in ostiole shape, stigma morphology, and stamen:ovule ratio. Statistical tests taking into account the phylogenetic relationship of the species show that transitions in ostiole shape are correlated with variation in wasp pollinator head shape, and evolutionary changes in stigma morphology and stamen:ovule ratio correlate with changes in the pollination behavior of the associated wasp. These correlations provide evidence for reciprocal adaptations of morphological characters between these mutualistic partners that have interacted over a long evolutionary time. In light of previous ecological studies on mutualism, we discuss the adaptive significance of these correlations and what they can tell us about the coevolutionary process occurring between figs and their pollinators.

Resistance and tolerance are widely viewed as two alternative adaptive responses to herbivory. However, the traits underlying resistance and tolerance remain largely unknown, as does the genetic architecture of herbivory responses and the prevalence of genetic trade-offs. To address these issues, we measured resistance and tolerance to natural apical meristem damage (AMD) by rabbits in a large field experiment with recombinant inbred lines (RILs) of Arabidopsis thaliana (developed from a cross between the Columbia × Landsberg erecta ecotypes). We also measured phenological and morphological traits hypothesized to underlie resistance and tolerance to AMD. Recombinant inbred lines differed significantly in resistance (the proportion of replicates within an RIL that resisted herbivory), and early flowering plants with tall apical inflorescences were more likely to experience damage. Tolerance (the difference in fitness between the damaged and undamaged states), also differed significantly among RILs, with some lines overcompensating for damage and producing more fruit in the damaged than undamaged state. Plastic increases in basal branch number, basal branch height, and senescence date in response to damage were all associated with greater tolerance. There was no evidence for a genetic trade-off between resistance and tolerance, an observation consistent with the underlying differences in associated morphological and phenological characters. Selection gradient analysis detected no evidence for direct selection on either resistance or tolerance in this experiment. However, a statistical model indicates that the pattern of selection on resistance depends strongly on the mean level of tolerance, and selection on tolerance depends strongly on the mean level of resistance. These observations are consistent with the hypothesis that selection may act to maintain resistance and tolerance at intermediate levels in spatially or temporally varying environments or those with varying herbivore populations.

The precise dependence of barnacle leg form on flow suggests the wave-swept environment imposes strong selection on suspension feeding limbs. I conducted three experiments to determine the mechanism, age dependence, and response time of cirrus variation in the acorn barnacle Balanus glandula. (1) To test whether cirrus variation arises via genetic or environmental mechanisms, I transplanted juvenile barnacles from one wave-exposed and one protected population into high and low flow conditions. Both populations exhibited similar abilities to modify cirri in response to experimental velocities: transplanted barnacles grew legs up to 84% longer in low flow. A small (up to 24%), but significant difference between source populations suggested slight genetic divergence in leg form. (2) Because flow is heterogeneous over space and time, I tested whether cirrus plasticity was limited to juveniles by transplanting both juveniles and adults from exposed and protected shores into quiet water. Remarkably, both juveniles and adults from the wave-exposed population produced legs over 100% longer than the original population, whereas protected barnacles remained unchanged. (3) A third transplant of adults into quiet water demonstrated that wave-exposed B. glandula modified cirrus form very quickly—within 18 days, or one to two molts. Results from these experiments suggest that variation in cirrus form is largely environmentally induced, but genetic differences may account for some variation observed among field populations; spatial and temporal flow heterogeneity appear to have selected for extreme flexibility of feeding form throughout a barnacle's life; and flow heterogeneity in the wave-swept environment appears to have selected for rapid ecophenotypic responses in the form of feeding structures.

Understanding the mode of origin of asexuality is central to ongoing debates concerning the evolution and maintenance of sexual reproduction in eukaryotes. This is because it has profound consequences for patterns of genetic diversity and ecological adaptability of asexual lineages, hence on the outcome of competition with sexual relatives both in short and longer terms. Among the possible routes to asexuality, hybridization is a very common mechanism in animals and plants. Aphids present frequent transitions from their ancestral reproductive mode (cyclical parthenogenesis) to permanent asexuality, but the mode of origin of asexual lineages is generally not known because it has never been thoroughly investigated with appropriate molecular tools. Rhopalosiphum padi is an aphid species with coexisting sexual (cyclically parthenogenetic) and asexual (obligately parthenogenetic) lineages that are genetically distinct. Previous studies have shown that asexual lineages of R. padi are heterozygous at most nuclear loci, suggesting either that they have undergone long-term asexuality (under which heterozygosity tends to increase) or that they have hybrid origins. To discriminate between these alternatives, we conducted an extensive molecular survey combining the sequence analysis of alleles of two nuclear DNA markers and mitochondrial DNA haplotypes in sexual and asexual lineages of R. padi. Both nuclear and cytoplasmic markers clearly showed that many asexual lineages have hybrid origins, the first such demonstration in aphids. Our results also indicated that asexuals result from multiple events of hybridization between R. padi and an unknown sibling species, and are of recent origin (contradicting previous estimates that asexual R. padi lineages were of moderate longevity). This study constitutes another example that putatively ancient asexual lineages are actually of much more recent origin than previously thought. It also presents a robust approach for testing whether hybrid origin of asexuality is also a common phenomenon in aphids.

Female response to male advertisement signals in lesser waxmoths showed substantial genetic variation, phenotypic plasticity across rearing environments, and genotype-by-environment interactions resulting in crossing reaction norms. These results represent two previously underemphasized means by which genetic variation may be maintained in sexually selected traits: genetic variation in female response to male traits, and variation in the selection acting on both males and females. Genotype-by-environment interactions and reaction norms that cross indicate that divergent selection may act on male and female sexual traits if the level of environmental change is high. The processes that contribute to the maintenance of genetic variation may thus also contribute to population differentiation.

We manipulated experimental populations of the housefly (Musca domestica L.) under three inbreeding schemes (fast, slow, and punctuated) to partition out the influences of different means and variances in the rate of inbreeding, per generation, while controlling for the final level of inbreeding as a constant. One treatment used constant fast inbreeding (11% per generation; N_e = 4 for 4 generations), for a comparison to one that was consistently slow (3% per generation; N_e = 16 for 14 generations). The third followed a model for serial founder-flush events. Each founder-flush episode involved a one-generation pulse of fast inbreeding (N_e = 4) followed by two generations of very low (or no) inbreeding, yielding high intergenerational variation (i.e., for an average inbreeding rate of 4% per generation). Allozyme assays showed that we achieved the intended final inbreeding coefficient of about 37%. All inbreeding schemes decreased fitness levels in terms of egg-to-adult viability, development time, and male mating success relative to the outbred control. The consistently fast inbreeding protocol had more pronounced reductions in fitness, relative to the other two inbreeding schemes. In comparison to the fast and punctuated regimes, the consistently slow protocol preserved evolutionary potential (as assayed by the genetic divergence of subpopulations exposed to different environments) in egg-to-adult viability, and (albeit anecdotally) reduced the extinction probabilities, especially in a novel environment. The punctuated treatment did not optimize the potential for purge as predicted, but instead reduced fitness, evolutionary potential, and environmental responsiveness (as measured by genotype-by-environment interactions). This founder-flush treatment also had the highest extinction probabilities. Longer periods of population flush might be necessary to purge effectively in a punctuated scheme. We conclude that the rate of inbreeding, independent from the final level, can have important effects on population fitness, environmental responsiveness, and evolutionary potential.

The role played by gene transpositions during the evolution of eukaryotic genomes is still poorly understood and indeed has been analyzed in detail only in nematodes. In Drosophila, a limited number of transpositions have been detected by comparing the chromosomal location of genes between different species. The relative importance of gene transposition versus other types of chromosomal rearrangements, for example, inversions, has not yet been evaluated. Here, we use physical mapping to perform an extensive search for long-distance gene transpositions and assess their impact during the evolution of the Drosophila genome. We compare the relative order of 297 molecular markers that cover 60% of the euchromatic fraction of the genome between two related Drosophila species and conclude that the frequency of gene transpositions is very low, namely one order of magnitude lower than that of nematodes. In addition, gene transpositions seem to be events almost exclusively associated with genes of repetitive nature such as the Histone gene complex (HIS-C).

We investigated sex allocation in a Mediterranean population of the facultatively polygynous (multiple queen per colony) ant Pheidole pallidula. This species shows a strong split sex ratio, with most colonies producing almost exclusively a single-sex brood. Our genetic (microsatellite) analyses reveal that P. pallidula has an unusual breeding system, with colonies being headed by a single or a few unrelated queens. As expected in such a breeding system, our results show no variation in relatedness asymmetry between monogynous (single queen per colony) and polygynous colonies. Nevertheless, sex allocation was tightly associated with the breeding structure, with monogynous colonies producing a male-biased brood and polygynous colonies almost only females. In addition, sex allocation was closely correlated with colony total sexual productivity. Overall, our data show that when colonies become more productive (and presumably larger) they shift from monogyny to polygyny and from male production to female production, a pattern that has never been reported in social insects.

One-third to two-thirds of all tropical carabids, or ground beetles, are arboreal, and evolution of arboreality has been proposed to be a dead end in this group. Many arboreal carabids have unusual morphological features that have been proposed to be adaptations for life on vegetation, including large, hemispheric eyes; an elongated prothorax; long elytra; long legs; bilobed fourth tarsomeres; adhesive setae on tarsi; and pectinate claws. However, correlations between these features and arboreality have not been rigorously tested previously. I examined the evolution of arboreality and morphological features often associated with this habitat in a phylogenetic context. The number and rates of origins and losses of arboreality in carabids in the subfamily Harpalinae were inferred with parsimony and maximum-likelihood on a variety of phylogenetic hypotheses. Correlated evolution in arboreality and morphological characters was tested with concentrated changes tests, maximum-likelihood, and independent contrasts on optimal phylogenies. There is strong evidence that both arboreality and the morphological features examined originated multiple times and can be reversed, and in no case could the hypothesis of equal rates of gains and losses be rejected. Several features are associated with arboreality: adhesive setae on the tarsi, bilobed tarsomeres, and possibly pectinate claws and an elongated prothorax. Bulgy eyes, long legs, and long elytra were not correlated with arboreality and are probably not arboreal adaptations. The evolution of arboreal carabids has not been unidirectional. These beetles have experienced multiple gains and losses of arboreality and the morphological characters commonly associated with the arboreal habitat. The evolutionary process of unidirectional character change may not be as widespread as previously thought and reversal from specialized lifestyles or habitats may be common.

Males of many insect species increase the fecundity and/or egg size of their mates through the amount or composition of their nuptial gifts or ejaculate. The genetic bases of such male effects on fecundity or egg size are generally unknown, and thus their ability to evolve remains speculative. Likewise, the genetic relationship between male and female investment into reproduction in dioecious species, which is expected to be positive if effects on fecundity are controlled by at least some of the same genes in males and females, is also unknown. Males of the seed beetle Stator limbatus contribute large ejaculates to females during mating, and the amount of donated ejaculate is positively correlated with male body mass. Females mated to large males lay more eggs in their lifetime than females mated to small males. We describe an experiment in which we quantify genetic variation in the number of eggs sired by males (mated to a single female) and found that a significant proportion of the phenotypic variance in the number of eggs sired by males was explained by their genotype. Additionally, the number of eggs sired by a male was highly positively genetically correlated with his body mass. The between-sex genetic correlation, that is, the genetic correlation between the number of eggs sired by males and the number of eggs laid by females, was highly positive when eggs were laid on Acacia greggii seeds. This indicates that males that sire many eggs have sisters that lay many eggs. Thus, some of the genes that control male ejaculate size (or some other fecundity-enhancing factor) when expressed in males appear to control fecundity when expressed in females. We found no significant interaction between male and female genotype on fecundity.

We explore the hypothesis that females choose to mate with heavier males for the genes for behavioral aggressiveness they offer their offspring in the desert spider, Agelenopsis aperta. Behavioral aggressiveness is important to competition for limited resources in the field and is thus correlated with the mass spiders achieve. We established four crosses based on the body mass relationships of parents subjected to selection in their natural environment (female mass/male mass: HI/HI, HI/LO, LO/HI, and LO/LO) and reared the F₁ offspring in a noncompetitive laboratory environment. Offspring size and mass at maturity were measured, life history parameters recorded, and behavioral aggressiveness scored in a series of tests. Significant familial effects were detected in all of these measures, but pertinent cross effects were observed only in the assays measuring behavioral aggressiveness. The results were summarized in terms of the fitness costs to HI females of mating with LO males (fewer female offspring of the more aggressive phenotypes) and the benefits to LO females of mating with HI males (fewer fearful offspring of both sexes).

Modern theory predicts that relative parental investment of the sexes in their young is a key factor responsible for sexual selection. Seahorses and pipefishes (family Syngnathidae) are extraordinary among fishes in their remarkable adaptations for paternal care and frequent occurrences of sex-role reversals (i.e., female-female competition for mates), offering exceptional opportunities to test predictions of sexual selection theory. During mating, the female transfers eggs into or onto specialized egg-brooding structures that are located on either the male's abdomen or its tail, where they are osmoregulated, aerated, and nourished by specially adapted structures. All syngnathid males exhibit this form of parental care but the brooding structures vary, ranging from the simple ventral gluing areas of some pipefishes to the completely enclosed pouches found in seahorses. We present a molecular phylogeny that indicates that the diversification of pouch types is positively correlated with the major evolutionary radiation of the group, suggesting that this extreme development and diversification of paternal care may have been an important evolutionary innovation of the Syngnathidae. Based on recent studies that show that the complexity of brooding structures reflects the degree of paternal investment in several syngnathid species, we predicted sex-role reversals to be more common among species with more complex brooding structures. In contrast to this prediction, however, both parsimony- and likelihood-based reconstructions of the evolution of sex-role reversal in pipefishes and seahorses suggest multiple shifts in sex roles in the group, independent from the degree of brood pouch development. At the same time, our data demonstrate that sex-role reversal is positively associated with polygamous mating patterns, whereas most nonreversed species mate monogamously, suggesting that selection for polygamy or monogamy in pipefishes and seahorses may strongly influence sex roles in the wild.

The gynogenetic Amazon molly (Poecilia formosa) is a clonal, all-female lineage of livebearing fish that faces an unusual obstacle to evolutionary persistence. Sperm from heterospecific males (either sailfin, P. latipinna, or Atlantic, P. mexicana, mollies) is necessary to trigger embryogenesis. However, none of the male's genes are incorporated into the genome of the gynogenetic offspring. Some investigators have proposed that the evolution of male mate discrimination is a result of this cost, leading to a coevolutionary arms race between male avoidance of P. formosa and P. formosa attractiveness. Given that P. formosa successfully reproduces and has not yet gone extinct, it is clear there are mechanisms by which they attract the sexual attention of males. Although a Red Queen coevolutionary process in typical host/parasite systems has been shown to favor the persistence of sexual species, in this system an arms race has been invoked to explain the reverse. Here I present behavioral data supporting a more parsimonious scenario: that mechanisms of attraction in P. formosa are simply a consequence of its hybrid origin. Poecilia latipinna and P. mexicana males do not discriminate between gynogenetic P. formosa females and first generation sexual hybrid females, and females do not differ in agonistic behaviors associated with competition for mates. Both results contradict predictions from the Red Queen hypothesis. Therefore, coevolution is not necessary to explain the apparent evolutionary persistence of P. formosa.

Species in Mimulus section Erythranthe (monkeyflowers) have become model systems for the study of the genetic basis of ecological adaptations. In this study, we pursued two goals. First, we reconstructed the phylogeny of species in Erythranthe using both DNA sequences from the ribosomal DNA ITS and ETS and AFLPs. Data from rDNA sequences support the monophyly of the section, including M. parishii, but provide little support for relationships within it. Analyses using AFLP data resulted in a well-supported hypothesis of relationships among all Erythranthe species. Our second goal was to reconstruct ancestral pollination syndromes and ancestral states of individual characters associated with hummingbird-pollinated flowers. Both parsimony and likelihood approaches indicate that hummingbird pollination evolved twice in Erythranthe from insect-pollinated ancestors. Our reconstruction of individual characters indicates that corolla color and some aspects of corolla shape change states at the same point on the phylogenetic tree as the switch to hummingbird pollination; however, a switch to secretion of high amounts of nectar does not. Floral trait transformation may have been more punctuational than gradual.

The study of the patterns of reproductive isolation in relation to species divergence is critical for the understanding of the process of speciation. Comparative analyses of this kind were previously conducted in Drosophila, Lepidoptera, frogs, ducks, and birds in general. In the present study, we used information from the literature to analyze hybrid inviability in relation to species divergence in pigeons and doves. Four main patterns arose from this analysis: (1) as in the other groups studied, F₁ hybrid inviability gradually increases as species diverge, the time needed to reach total inviability being higher in birds than in the other groups; (2) as expected, the presence of geographic overlap does not influence the evolution of postzygotic isolation; (3) the percentage of unhatched eggs does not differ between hybrids of the first generation and the backcrosses, but it increases in the second hybrid generation; and (4) pigeons and doves follow Haldane's rule, as found in the other groups studied so far. The similarity between the results of this and previous studies contributes to the growing evidence suggesting that the patterns of the evolution of postzygotic isolation, and the process of speciation in general, are shared among animal groups.

We report the results of one of the first intrageneric analyses to simultaneously survey mitochondrial, Y-chromosomal, and autosomal loci from the same individuals representing the same taxa. Phylogenetic trees were constructed for each of these genetic systems from a pool of 63 macaques, representing all 19 recognized species in this genus, and eight outgroup taxa. The mitochondrial locus analyzed here (1.5 Kb) spans the 3′ end of 12S rDNA, tRNA-VAL, and the 5′ end of 16S rDNA; the Y chromosome dataset (3.1 Kb) consists of the genes SRY and TSPY; the two autosomal datasets include IRBP intron 3 (1.6 Kb) and the 5′ half of C4 “long” intron 9 (3.3 Kb). A total of 1.35 million bases were read, revealing 682 variable sites within the genus Macaca. With regard to earlier unresolved issues of macaque evolution, a comparison of topologies reconstructed from each of the three genetic systems suggests: (1) four monophyletic species groups; (2) an initial bifurcation among Asian macaques between the silenus group progenitor and a M. fascicularis-like taxon, with the latter representing the probable common ancestor to all non-silenus group Asian macaques; (3) a possible hybrid origin of M. arctoides from proto-M. assamensis/thibetana and proto-M. fascicularis; and (4) contemporary introgression between M. mulatta and M. fascicularis in Indochina. Inferences 3 and 4 are of particular interest, because episodes of reticulate evolution often go undetected in analyses employing a single genetic system. Finally, divergence calculations suggest that, in female-philopatric taxa, mitochondrial bifurcations may typically predate Y-chromosomal divergences at the same node.

Ecological or geological phenomena can impose limits on geographic diversification that cause biogeographical patterns of distantly related but sympatrically occurring taxa to be similar. Concordant patterns of diversity facilitate conservation management because strategic designation of protected areas can capture complementary rather than redundant components of variation. Here we demonstrate that on the biodiverse Indonesian island of Sulawesi, seemingly idiosyncratic distributions of diversity in endemic monkeys (Macaca species) and toads (Bufo celebensis) are actually virtually identical on a fine geographic scale. It appears that range fragmentation has generated seven multi-taxon areas of genetic endemism, each of which should be targeted for conservation. Joint consideration of molecular phylogeography, morphology, and demography helps resolve apparent contradictions in paraphyletic macaque mitochondrial DNA and in undifferentiated toad morphology, and facilitates an understanding of biogeography and conservation genetics of Sulawesi fauna.

Hosts vary in both their strength of response to a general immunological insult and in their specific susceptibility to different parasite species or different strains of the same parasite. The variation in the general immune response is considered a result of the costs imposed by selection on defended individuals. The variation in the specific response may originate from variation in host and parasite genotypes and is a requirement for frequency-dependent selection. The relationship between these two fundamental aspects of defense has only rarely been studied. Using the bumblebee Bombus terrestris and its gut trypanosomal parasite Crithidia bombi we found that the host's specific response profile toward different strains correlates negatively with its level of response to a general insult. This is the opposite result one would expect if the level of general response were simply a measure of immunological quality (immunocompetence). Rather, it suggests that there is some form of a trade-off between these two fundamental aspects of the immune system. These results, therefore, shed an important light on the possible constraints that affect the evolution of the immune system and particularly the trade-off between different arms of the immune system.

Lipson et al. (2002) presented an elegant linear algebraic formalism to define and study the evolution of modularity in an artificial evolving system. They employed simulation data to support their suggestion that modularity arises spontaneously in temporally fluctuating systems in response to selection for enhanced evolvability. We show analytically and by simulation that their correlate of modularity is itself under selection and so is not a reliable indicator of selection for modularity per se. In addition, we question the relation between modularity and evolvability in their simulations, suggesting that this modularity cannot confer enhanced evolvability.