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PubMed1999

Primates and their pinworm parasites: the cameron hypothesis revisited.

A morphologically based cladistic analysis of the Enterobiinae, which includes most of the Oxyuridae parasitic in Primates, allows a reevaluation of the Cameron's hypothesis of close coevolution with cospeciation between hosts and parasites. Each of the three genera separated in the Enterobiinae fits with one of the suborders defined in Primates: Lemuricola with the Strepsirhini, Trypanoxyuris with the Platyrrhini, and Enterobius with the Catarrhini. Inside each of the three main groups, the subdivisions observed in the parasite tree also fit with many of the subdivisions generally accepted within the Primate order. These results confirm the subgroups previously described in the subfamily and support Cameron's hypothesis in its aspect of association by descent. Although the classification of the Enterobiinae generally closely underlines the classification of Primates, several discordances also are observed. These are discussed case by case, with use of computed reconstruction scenarios. Given that the occurrences of the same pinworm species as a parasite for several congeneric host species is not the generalized pattern, and given that several occurrences also are observed in which the speciations of the parasites describe a more complex network, Cameron's hypothesis of a slower rhythm of speciation in the parasites can be considered partly refuted. The presence of two genera parasitic on squirrels in a family that contains primarily primate parasites also is discussed. The cladistic analysis does not support close relationships between the squirrel parasites and suggests an early separation from the Enterobiinae for the first (Xeroxyuris), and a tardy host-switching from the Platyrrhini to the squirrels for the second (Rodentoxyuris).

Animals↗

PubMed2005

Genotypes of JC virus, DNA of cytomegalovirus, and proviral DNA of human immunodeficiency virus in eyes of acquired immunodeficiency syndrome patients.

JC virus (JCV) is a human polyomavirus that exists in at least eight different genotypes as a result of coevolution with different human populations all over the world. Well adapted to its host, it usually persists in the kidneys and possibly the brain. If the host becomes immunodeficient, JCV can cause the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). There is increasing evidence that JCV is transactivated by cytomegalovirus (CMV) and the human immunodeficiency virus (HIV). Both CMV and HIV can infect the retina of acquired immunodeficiency syndrome (AIDS) patients, causing severe necrosis in the case of CMV retinitis or a mild HIV-associated vasculopathy, with bleeding and cotton wool spots. The authors therefore investigated by polymerase chain reaction (PCR) whether DNA of these three viruses was detectable in paraffin-embedded eyes of AIDS patients with a clinical history of CMV retinitis. From a total of 65 eyes, JCV was detected in 21 (32%). Thirty-six (55%) were positive for CMV and 6 (9%) for proviral DNA of HIV. JCV and CMV were found in 13 eyes, JCV and HIV in 3 eyes, CMV and HIV in 1 eye, and DNA from all three viruses in 1 eye. The JCV genotypes were types 1A, 2A, 2E, 3, and 4. In 21 eyes of patients without AIDS, only one sample was JCV positive. In conclusion, JCV DNA can be detected in ocular tissue of AIDS patients at a significantly higher level than in eyes of nonimmunosuppressed patients. Further investigations will help to decide if JCV contributes to the retinopathy caused by CMV and HIV.

Acquired Immunodeficiency Syndrome↗

PubMed2004

Sperm competition in mammals.

Although Darwin identified the evolutionary significance of competition between males in the context of reproduction, it is only in the past few decades that we have begun to appreciate the importance of competition at the gametic level. Sperm competition, defined as competition between the sperm of two or more males for fertilization of the same set of ova, is now recognised as a key selective force shaping male reproductive anatomy, physiology and behaviour across diverse animal groups, including mammals. The aim of this article is to provide a brief review of the selective consequences of sperm competition in mammals, with emphasis on recent theoretical advances and empirical controversies. Evidence of female influences on sperm competition outcomes in mammals is also discussed, and it is concluded that understanding the selective pressures driving coevolution between male and female reproductive traits remains a major challenge for researchers in this field.

Animals↗

PubMed2005

Schistosoma mansoni secretes a chemokine binding protein with antiinflammatory activity.

The coevolution of humans and infectious agents has exerted selective pressure on the immune system to control potentially lethal infections. Correspondingly, pathogens have evolved with various strategies to modulate and circumvent the host's innate and adaptive immune response. Schistosoma species are helminth parasites with genes that have been selected to modulate the host to tolerate chronic worm infections, often for decades, without overt morbidity. The modulation of immunity by schistosomes has been shown to prevent a range of immune-mediated diseases, including allergies and autoimmunity. Individual immune-modulating schistosome molecules have, therefore, therapeutic potential as selective manipulators of the immune system to prevent unrelated diseases. Here we show that S. mansoni eggs secrete a protein into host tissues that binds certain chemokines and inhibits their interaction with host chemokine receptors and their biological activity. The purified recombinant S. mansoni chemokine binding protein (smCKBP) suppressed inflammation in several disease models. smCKBP is unrelated to host proteins and is the first described chemokine binding protein encoded by a pathogenic human parasite and may have potential as an antiinflammatory agent.

Animals↗

PubMed2000

Local Competition, Inbreeding, and the Evolution of Sex-Biased Dispersal.

Using game theory, we developed a kin-selection model to investigate the consequences of local competition and inbreeding depression on the evolution of natal dispersal. Mating systems have the potential to favor strong sex biases in dispersal because sex differences in potential reproductive success affect the balance between local resource competition and local mate competition. No bias is expected when local competition equally affects males and females, as happens in monogamous systems and also in polygynous or promiscuous ones as long as female fitness is limited by extrinsic factors (breeding resources). In contrast, a male-biased dispersal is predicted when local mate competition exceeds local resource competition, as happens under polygyny/promiscuity when female fitness is limited by intrinsic factors (maximal rate of processing resources rather than resources themselves). This bias is reinforced by among-sex interactions: female philopatry enhances breeding opportunities for related males, while male dispersal decreases the chances that related females will inbreed. These results meet empirical patterns in mammals: polygynous/promiscuous species usually display a male-biased dispersal, while both sexes disperse in monogamous species. A parallel is drawn with sex-ratio theory, which also predicts biases toward the sex that suffers less from local competition. Optimal sex ratios and optimal sex-specific dispersal show mutual dependence, which argues for the development of coevolution models.

kin selection↗

PubMed2000

Long-Term Experimental Evolution in Escherichia coli. VIII. Dynamics of a Balanced Polymorphism.

We describe the short- and long-term dynamics of a phenotypic polymorphism that arose in a population of Escherichia coli while it was serially propagated for almost 20,000 generations in a glucose-limited minimal medium. The two types, designated L and S, differ conspicuously in the size of the colonies they form on agar plates as well as the size of their individual cells, and these differences are heritable. The S type reached a detectable frequency (>1%) at generation 6,000, and it remained above that frequency throughout the subsequent generations. In addition to morphological differences, L and S diverged in important ecological properties. With clones isolated at 18,000 generations, L has a maximal growth rate in fresh medium that is ∼20% higher than that of S. However, experiments with conditioned media demonstrate that L and S secrete one or more metabolites that promote the growth of S but not of L. The death rate of L during stationary phase also increases when S is abundant, which suggests that S may either secrete a metabolite that is toxic to L or remove some factor that enables the survival of L. One-day competition experiments with the clones isolated at generation 18,000 show that their relative fitness is frequency dependent, with each type having an advantage when rare. When these two types are grown together for a period of several weeks, they converge on an equilibrium frequency that is consistent with the 1-d competition experiments. Over the entire 14,000-generation period of coexistence, however, the frequency of the S type fluctuated between approximately 10% and 85%. We offer several hypotheses that may explain the fluctuations in this balanced polymorphism, including the possibility of coevolution between the two types.

Escherichia coli↗

PubMed2000

Conservation of Helicobacter pylori genotypes in different ethnic groups in Houston, Texas.

This study was concerned with whether the Helicobacter pylori strains circulating among ethnic groups living in the same region differ. The polymerase chain reactions to genotype (cagA, vacA, and iceA) H. pylori isolates from healthy volunteers from 4 ethnic groups (black, n=35; white Hispanic, n=31; whites, n=30; Vietnamese, n=29) residing in Houston were examined. The Vietnamese volunteers had the "East Asian"-type cagA 3' repeat region structure, and the others had the "non-Asian" type. The most common genotypes were delineated as follows: blacks and Hispanics, cagA+, vacA s1b-m1, and iceA2; whites, cagA+, vacA s1a-m2, and iceA2; and Vietnamese, cagA+, vacA s1c-m2, and iceA2. Two Hispanic families were also examined. H. pylori isolates from the children and their mothers had the same genotype and were different from those associated with the children's fathers or brothers-in-law. Conservation of an H. pylori genotype within ethnic groups over the course of generations will prove useful for epidemiological study of the coevolution of humans and H. pylori.

Adult↗

PubMedDate not supplied

Evolvability of Hsp70 expression under artificial election for inducible thermotolerance in independent populations of Drosophila melanogaster.

To test whether expression of the inducible heat-shock protein Hsp70 increases under selection for inducible thermotolerance in Drosophila melanogaster, we performed artificial selection on replicate sets of Drosophila lines founded from two independent populations. Selection entailed pretreatment at 36 degrees C to induce thermotolerance and Hsp70 expression, followed by a more severe heat shock, whose temperature varied between sexes and among generations to achieve 50% mortality. Inducible thermotolerance increased slowly and continuously in selected lines and was 37%-50% greater than in controls after 10-11 generations. Lines founded from the two populations differed in their coevolution of Hsp70 expression. In lines founded from Evolution Canyon, Israel, Hsp70 level initially increased and thereafter was unchanged; replicate lines exhibited two temporal patterns of response to selection. In lines founded from Australia, Hsp70 levels increased throughout selection. In both cases, however, the increase in Hsp70 level averaged only 15%, suggesting that pleiotropy in Hsp70 function constrains evolutionary increase in its expression.

Adaptation, Physiological↗

PubMed2003

Shared control of epidemiological traits in a coevolutionary model of host-parasite interactions.

Most models concerning the evolution of a parasite's virulence and its host's resistance assume that each component of the relationship (transmission, virulence, recovery, etc.) is controlled by either the host or the parasite but not by both. We present a model that describes the coevolution of host and parasite, assuming that the rate of transmission or the virulence depends on both genotypes. The evolution of these traits is constrained by trade-offs that account for costs of defense and attack strategies, in line with previous studies on the separate evolution of the host and the parasite. Considering shared control by the host and the parasite in determining the traits of the relationship leads to several novel predictions. First, the host should evolve maximal investment in defense against parasites with an intermediate replication rate. Second, the evolution of the parasite strongly depends on the way the host's defense is described. Third, the coevolutionary process may lead to decreasing the parasite's virulence as a response to a rise in the host's background mortality, contrary to classical predictions.

Adaptation, Physiological↗

PubMed2004

Host sex and local adaptation by parasites in a snail-trematode interaction.

One of the leading theories for the evolutionary stability of sex in eukaryotes relies on parasite-mediated selection against locally common host genotypes (the Red Queen hypothesis). As such, parasites would be expected to be better at infecting sympatric host populations than allopatric host populations. Here we examined all published and unpublished infection experiments on a snail-trematode system (Potamopyrgus antipodarum and Microphallus sp., respectively). A meta-analysis demonstrated significant local adaptation by the parasite, and a variance components analysis showed that the variance due to the host-parasite interaction far exceeded the variance due to the main effects of host source and parasite source. The meta-analysis also indicated that asexual host populations were more resistant to allopatric sources of parasites than were (mostly) sexual host populations, but we found no significant differences among parasite populations in the strength of local adaptation. This result suggests that triploid asexual snails are more resistant to remote sources of parasites, but the parasite has, through coevolution, overcome the difference. Finally, we found that the degree of local adaptation did not depend on the genetic distance among host populations. Taken together, the results demonstrate that the parasites are adapted, on average, to infecting their local host populations and suggest that they may be a factor in selecting against common host genotypes in natural populations.

Adaptation, Physiological↗

PubMed2004

The evolution of virulence when parasites cause host castration and gigantism.

It has been suggested that the harm parasites cause to their hosts is an unavoidable consequence of parasite reproduction with costs not only for the host but also for the parasite. Castrating parasites are thought to minimize their costs by reducing host fecundity, which may minimize the chances of killing both host and parasite prematurely. We conducted a series of experiments to understand the evolution of virulence of a castrating bacterium in the planktonic crustacean Daphnia magna. By manipulating food levels during the infection of D. magna with the bacterium Pasteuria ramosa, we showed that both antagonists are resource-limited and that a negative correlation between host and parasite reproduction exists, indicating resource competition among the antagonists. Pasteuria ramosa also induces enhanced growth of its hosts (gigantism), which we found to be negatively correlated with host fecundity but positively correlated with parasite reproduction. Because infected hosts never recovered from infections, we concluded that gigantism is beneficial only for the parasite. Hosts, however, have evolved counteradaptations. We showed that infected hosts have enhanced reproduction before castration. This shift to earlier reproduction increases overall host fecundity and compromises parasite reproduction. Finally, we showed that this resource conflict is subject to genetic variation among host and parasite genotypes within a population and is therefore likely to be an important force in the coevolution of virulence in this system. A verbal model is presented and suggests that the adaptive value of gigantism is to store host resources, which are liberated after parasitic castration for later use by the growing parasite. This hypothesis assumes that infections are long lasting, that is, that they have a high life expectancy.

Adaptation, Physiological↗

PubMed2005

Host specialization and geographic localization of avian malaria parasites: a regional analysis in the Lesser Antilles.

We recovered 26 genetically distinct avian malaria parasite lineages, based on cytochrome b sequences, from a broad survey of terrestrial avifauna of the Lesser Antilles. Here we describe their distributions across host species within a regional biogeographic context. Most parasite lineages were recovered from a few closely related host species. Specialization on one host species and distribution across many hosts were both rare. Geographic patterns of parasite lineages indicated limited dispersal and frequent local extinction. The central islands of the archipelago share similar parasite lineages and patterns of infection. However, the peripheral islands harbor well-differentiated parasite communities, indicating long periods of isolation. Nonetheless, 20 of 26 parasite lineages were recovered from at least one of three other geographic regions, the Greater Antilles, North America, and South America, suggesting rapid dispersal relative to rate of differentiation. Six parasite lineages were restricted to the Lesser Antilles, primarily to endemic host species. Host differences between populations of the same parasite lineage suggest that host preference may evolve more rapidly than mitochondrial gene sequences. Taken together, distributions of avian malarial parasites reveal evidence of coevolution, host switching, extinction, and periodic recolonization events resulting in ecologically dynamic as well as evolutionarily stable patterns of infection.

Animals↗

PubMed2005

Sexual conflict in the wild: elevated mating rate reduces female lifetime reproductive success.

Sexual conflict over mating rate is suggested to play a pivotal role in male-female coevolution, and females are predicted to reject superfluous mating attempts. Recent work suggests that direct effects of multiple mating on female fitness are not fully understood. A major concern in studies of sexual conflict is how well the data obtained under controlled laboratory settings relate to natural conditions. We tested the effect of female multiple mating on reproductive success in a natural population of a polyandrous spider, Stegodyphus lineatus. Previous studies show that a male who succeeds in entering a female nest also mates with her; therefore, we used male encounter rate as a proxy of female mating rate. We further elevated female mating rate by introducing males into females' nests. Female lifetime reproductive success was assessed as the likelihood of successful reproduction, offspring production, and juvenile offspring body mass. Increased mating rate increased the time to oviposition and reduced the likelihood of successful reproduction. Female mating rate negatively affected offspring body mass. Manipulated females produced fewer offspring than control females. The observed patterns imply a net cost of polyandry to females and suggest that natural mating rates can be suboptimal for females under natural conditions.

Animals↗

PubMed2005

Quantitative genetic models of sexual conflict based on interacting phenotypes.

Evolutionary conflict arises between reproductive partners when alternative reproductive opportunities are available. Sexual conflict can generate sexually antagonistic selection, which mediates sexual selection and intersexual coevolution. However, despite intense interest, the evolutionary implications of sexual conflict remain unresolved. We propose a novel theoretical approach to study the evolution of sexually antagonistic phenotypes based on quantitative genetics and the measure of social selection arising from male-female interactions. We consider the phenotype of one sex as both a genetically influenced evolving trait as well as the (evolving) social environment in which the phenotype of the opposite sex evolves. Several important points emerge from our analysis, including the relationship between direct selection on one sex and indirect effects through selection on the opposite sex. We suggest that the proposed approach may be a valuable tool to complement other theoretical approaches currently used to study sexual conflict. Most importantly, our approach highlights areas where additional empirical data can help clarify the role of sexual conflict in the evolutionary process.

Animals↗

PubMed2005

Identification of selective sources: partitioning selection based on interactions.

Interspecific interactions are an inescapable reality in nature. The evolution of a species is largely determined by the environment, abiotic or biotic, in which selection occurs. Quantifying the magnitude of selection is crucial to understanding which aspects of the environment are important to the evolution of a species. Such knowledge is particularly important to fields such as conservation biology, which attempts to maintain a suitable environment for the prosperity of a species, or coevolution, where dynamics are determined by the strength of reciprocal selection between species. I present a general method by which selection due to interspecific interactions may be quantified. This technique is based on past quantitative genetic models of selection and can be used with other methodologies that build on these standard models. The approach may be expanded to account for n-species interactions (e.g., a plant with two pollinators). Simulation studies conducted using this method indicate that the magnitude of selection between two species is strongly correlated with the presence of nonrandom interactions.

Biological Evolution↗

PubMed2005

Science and the French Empire.

Scholarly interest in French colonial science, interpreted to include colonial medical and scientific institutions as well as personages and other "actors" in France serving colonial agendas, has been robust for some two decades. This essay characterizes the complex and interlinked historical relationships between French metropolitan and colonial science as one of asymmetric coevolution. In analyzing scholarship on diverse topics from physics and military technology to colonial botany, medicine, geography, and racial theory, it interrogates the concepts of French nation and French empire and questions the historiographical and explanatory utility of the core-periphery model. Special scrutiny falls on a trope common to historigraphical studies of the postrevolutionary era, that of a firm French nationalism enabling largely rational colonial agendas and the promotion of these agendas by highly centralized Parisian bureaucracies. The essay calls for a reading of French history inclusive of regional colonialist activities and argues for the prevalence of municipal and regional maritime, technological, scientific, and military interests in constructing the modern French empire.

Colonialism↗

PubMed2005

Maladaptation and natural selection.

The transformations George Williams initiated in evolutionary biology seem so blindingly obvious in retrospect that they spur the question of why he saw what no one else did. While most humans are prone to see only what theory predicts, Williams sees in bold relief whatever does not fit. Not an adaptationist or an anti-adaptationist, Williams is better described as a maladaptionist. The challenge of finding evolutionary explanations for apparent maladaptations has been overlooked with casualness akin to that once typical for group selection. Suboptimal traits tend to be dismissed as illustrations of the weakness and stochastic nature of selection compared with mutation and drift. A closer look suggests that such constraints are only one of six possible kinds of explanations for apparently suboptimal designs: mismatch, coevolution, tradeoffs, constraints, reproductive advantage at the expense of the individual, and defenses that are aversive but useful Medicine has asked proximate questions at every possible level but has only begun to ask evolutionary questions about why bodies are vulnerable to disease. Considering all six possible evolutionary reasons for apparently suboptimal traits will spur progress not only in medicine but also more generally in biology. 'Williams Vision" may not yield a net benefit to the possessor, but it is invaluable for the species.

Adaptation, Physiological↗

PubMed2005

Divergent mating systems and parental conflict as a barrier to hybridization in flowering plants.

Parental conflicts can lead to antagonistic coevolution of the sexes and of parental genomes. Within a population, the resulting antagonistic effects should balance, but crosses between populations can reveal conflict. Parental conflict is less intense in self-pollinating plants than in outcrossers because outcrossing plants are pollinated by multiple pollen donors unrelated to the seed parent, while a self-pollinating plant is primarily pollinated by one individual (itself). Therefore, in crosses between plants with differing mating systems, outcrossing parents are expected to "overpower" selfing parents. We call this the weak inbreeder/strong outbreeder (WISO) hypothesis. Prezygotically, such overpowering can alter pollination success, and we argue that our hypothesis explains a common pattern of unilateral incompatibility, in which pollen from self-incompatible populations fertilizes ovules of self-compatible individuals but the reciprocal cross fails. A postzygotic manifestation of overpowering is aberrant seed development due to parent-of-origin effects such as genomic imprinting. We evaluate evidence for the WISO hypothesis by reviewing published accounts of crosses between plants of different mating systems. Many, but not all, of such reports support our hypothesis. Since parental conflicts can perturb fertilization and development, such conflicts may strengthen reproductive barriers between populations, contributing to speciation.

Flowers↗