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PubMed1998

Coevolution of immunoglobulin heavy- and light-chain variable-region gene families.

The gene families encoding the immunoglobulin variable regions of heavy (VH) and light (VL) chains in vertebrates are composed of many genes. However, the gene number and the extent of diversity among VH and VL gene copies vary with species. To examine the causes of this variation and the evolutionary forces for these multigene families, we conducted a phylogenetic analysis of VH and VL genes from the species of amniotes. The results of our analysis showed that for each species, VH and VL genes have the same pattern of clustering in the trees, and, according to this clustering pattern, the species can be divided into two groups. In the first group of species (humans and mice), VH and VL genes were extensively intermingled with genes from other organisms; in the second group of species (chickens, rabbits, cattle, sheep, swine, and horses), the genes tended to form clusters within the same group of organisms. These results suggest that the VH and VL multigene families have evolved in the same fashion: they have undergone coordinated contraction and expansion of gene repertoires such that each group of organisms is characterized by a certain level of diversity of VH and VL genes. The extent of diversity among copies of VH and VL genes in each species is related to the mechanism of generation of antibody variety. In humans and mice, DNA rearrangement of immunoglobulin variable, diversity, and joining-segment genes is a main source of antibody diversity, whereas in chickens, rabbits, cattle, sheep, swine, and horses, somatic hypermutation and somatic gene conversion play important roles. The evolutionary pattern of VH and VL multigene families is consistent with the birth-and-death model of evolution, yet different levels of diversifying selection seem to operate in the VH and VL genes of these two groups of species.

Animals↗
PubMed2002

The evolutionary response of predators to dangerous prey: hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts.

The "geographic mosaic" approach to understanding coevolution is predicated on the existence of variable selection across the landscape of an interaction between species. A range of ecological factors, from differences in resource availability to differences in community composition, can generate such a mosaic of selection among populations, and thereby differences in the strength of coevolution. The result is a mixture of hotspots, where reciprocal selection is strong, and coldspots, where reciprocal selection is weak or absent, throughout the ranges of species. Population subdivision further provides the opportunity for nonadaptive forces, including gene flow, drift, and metapopulation dynamics, to influence the coevolutionary interaction between species. Some predicted results of this geographic mosaic of coevolution include maladapted or mismatched phenotypes, maintenance of high levels of polymorphism, and prevention of stable equilibrium trait combinations. To evaluate the potential for the geographic mosaic to influence predator-prey coevolution, we investigated the geographic pattern of genetically determined TTX resistance in the garter snake Thamnophis sirtalis over much of the range of its ecological interaction with toxic newts of genus Taricha. We assayed TTX resistance in over 2900 garter snakes representing 333 families from 40 populations throughout western North America. Our results provide dramatic evidence that geographic structure is an important component in coevolutionary interactions between predators and prey. Resistance levels vary substantially (over three orders of magnitude) among populations and over short distances. The spatial array of variation is consistent with two areas of intense evolutionary response by predators ("hotspots") surrounded by clines of decreasing resistance. Some general predictions of the geographic mosaic process are supported, including clinal variation in phenotypes, polymorphism in some populations, and divergent outcomes of the interaction between predator and prey. Conversely, our data provide little support for one of the major predictions, mismatched values of interacting traits. Two lines of evidence suggest selection is paramount in determining population variation in resistance. First, phylogenetic information indicates that two hotspots of TTX resistance have evolved independently. Second, in the one region that TTX levels in prey have been quantified, resistance and toxicity levels match almost perfectly over a wide phenotypic and geographic range. However, these results do not preclude the role the nonadaptive forces in generating the overall geographic mosaic of TTX resistance. Much work remains to fill in the geographic pattern of variation among prey populations and, just as importantly, to explore the variation in the ecology of the interaction that occurs within populations.

Adaptation, Physiological↗
PubMed2026

Parasites and allergies: a complex bidirectional relationship from evolutionary origins to modern therapeutics.

Parasites and allergic diseases are linked by a complex, bidirectional relationship shaped by long-term host-parasite coevolution. This review discusses how different parasites may either promote or attenuate allergic responses through immunological, epithelial, and microbiome-mediated mechanisms. IgE-mediated immunity, mast cell activation, eosinophilia, and pruritus may have evolved as protective responses against helminths and blood-feeding ectoparasites. In contrast, modern allergies may partly reflect misdirected responses to harmless environmental antigens. The effects of parasites on allergy are not uniform and depend on parasite type, infection site, exposure intensity and chronicity, host immune status, and the degree of host-parasite adaptation. Protozoa such as Giardia intestinalis may contribute to food allergy-related manifestations by disrupting the intestinal barrier, altering gut microbiota composition, and modifying mucosal immune responses, particularly in atopic individuals. In contrast, selected helminths may attenuate allergic inflammation by inducing regulatory T and B cells, anti-inflammatory cytokines, antigen-presenting cell modulation, and IgG4-associated mechanisms that can limit IgE-mediated effector responses. Molecular similarities between parasite-derived antigens and environmental allergens, including conserved protein families and carbohydrate epitopes, may contribute to cross-reactive IgE responses and complicate allergy diagnostics. Therefore, current research is shifting from live helminth therapy toward defined parasite-derived molecules and immunomodulatory pathways that may inspire safer and more controlled therapeutic strategies. A clearer understanding of parasite-allergy interactions may improve diagnostic interpretation and support the development of new approaches to the management of allergic disease.

Humans↗
PubMed1998

The coevolution of human fertility and wealth inheritance strategies.

Life history theory concerns the scheduling of births and the level of parental investment in each offspring. In most human societies the inheritance of wealth is an important part of parental investment. Patterns of wealth inheritance and other reproductive decisions, such as family size, would be expected to influence each other. Here I present an adaptive model of human reproductive decision-making, using a state-dependent dynamic model. Two decisions made by parents are considered: when to have another baby, and thus the pattern of reproduction through life; and how to allocate resources between children at the end of the parents' life. Optimal decision rules are those that maximize the number of grandchildren. Decisions are assumed to depend on the state of the parent, which is described at any time by two variables: number of living sons, and wealth. The dynamics of the model are based on a traditional African pastoralist system, but it is general enough to approximate to any means of subsistence where an increase in the amount of wealth owned increases the capacity for future production of resources. The model is used to show that, in the unpredictable environment of a traditional pastoralist society, high fertility and a biasing of wealth inheritance to a small number of children are frequently optimal. Most such societies are now undergoing a transition to lower fertility, known as the demographic transition. The effects on fertility and wealth inheritance strategies of reducing mortality risks, reducing the unpredictability of the environment and increasing the costs of raising children are explored. Reducing mortality has little effect on completed family sizes of living children or on the wealth they inherit. Increasing the costs of raising children decreases optimal fertility and increases the inheritance left to each child at each level of wealth, and has the potential to reduce fertility to very low levels. The results offer an explanation for why wealthy families are frequently also those with the smallest number of children in heterogeneous, post-transition societies.

Africa↗
PubMed1997

Host-parasite coevolution: comparative evidence for covariation of life history traits in primates and oxyurid parasites.

The environmental factors that drive the evolution of parasite life histories are mostly unknown. Given that hosts provide the principal environmental features parasites have to deal with, and given that these features (such as resource availability and immune responses) are well characterized by the life history of the host, we may expect natural selection to result in covariation between parasite and host life histories. Moreover, some parasites show a high degree of host specificity, and cladistic analyses have shown that host and parasite phylogenies can be highly congruent. These considerations suggest that parasite and host life histories may covary. The central argument in the theory of life history evolution concerns the existence of trade-offs between traits. For parasitic nematodes it has been shown that larger body sizes induce higher fecundity, but this is achieved at the expense of delayed maturity. As high adult mortality would select for reduced age at maturity, the selective benefit of increased fecundity is expressed only if adult mortality is low. Parasite adult mortality may depend on a number of factors, including host longevity. Here we tested the hypothesis concerning the positive covariation between parasite body size (which reflects parasite longevity) and host longevity. To achieve this goal, we used the association between the pinworms (Oxyuridae, Nematoda) and their primate hosts. Oxyurids are highly host specific and are supposed to be involved in a coevolutionary process with their hosts. We found that female parasite body length was positively correlated with host longevity after correcting for phylogeny and host body mass. Conversely, male parasite body length and host longevity were not correlated. These results confirm that host longevity may represent a constraint on the evolution of body size in oxyurids, at least in females. The discrepancy between female and male oxyurids is likely to depend on the particular mode of reproduction of this taxon (haplodiploidy), which should result in weak (or even null) selection pressures to an increase of body size in males.

Animals↗
PubMed1980

Atmospheric constraints on the evolution of metabolism.

Earth's early history may have been characterized by coevolution of microbial metabolism and atmospheric composition. Metabolic developments affected the composition of the atmosphere and the resultant changes in the atmosphere stimulated the evolution of new metabolic capabilities. The first organisms were presumably fermenting heterotrophs, exploiting organic molecules abiotically synthesized. These organisms multiplied, developing new biosynthetic capabilities to overcome deficiencies in the abiotic supply of particular compounds, until their growth was limited by the energy source provided by abiotic synthesis of fermentable organic compounds. Further growth required a new energy source, which may have been the chemical energy represented by the mixture of carbon dioxide and hydrogen in the primitive atmosphere. Chemotrophic organisms resembling methane bacteria may have evolved to exploit this source. They would have flourished, along with the heterotrophs that fed on them, until they had decreased the level of atmospheric hydrogen to the point where further extractions of chemical energy from the atmosphere was not possible. Once again, the expansion of life was limited by the availability of energy. The origin of bacterial photosynthesis overcame the second energy crisis. Photosynthetic bacteria could exploit the abundant energy of sunlight while using atmospheric hydrogen and reduced compounds derived from it only as electron donors. Life flourished again, drawing atmospheric hydrogen (replenished only by volcanoes) down to levels so low as to limit even bacterial photosynthesis. Before the full potential of photosynthesis could be exploited the evolution of the metabolic apparatus to process an electron donor of unlimited abundance was necessary. This donor, of course, was water, and the new metabolic process was algal photosynthesis. The oxygen released changed the world from anaerobic to aerobic and made possible the last great advance in energy-yielding metabolism, aerobic respiration.

Aerobiosis↗
PubMed1987

An evaluation of the interactions between freshwater pulmonate snail hosts of human schistosomes and macrophytes.

An account is given of a laboratory investigation designed to evaluate the extent to which the freshwater pulmonate snail Biomphalaria glabrata (Say) can utilize various species of aquatic plants, mainly macrophytes, when presented in the following forms over different time scales: normal plants; dried plant material; homogenized plant material in calcium alginate matrices; water-soluble filtrates of plant homogenates in the medium. The following propositions, derived from the theory of phased coevolution of components of the module consisting of the epiphytic bacteria, algae, snails and macrophytes, are evaluated on the basis of the present results and others including those obtained in this laboratory. That as the snails had become specialized to exploit surface communities of epiphytic algae, decaying plant material and dissolved organic matter (DOM) early in their evolutionary history they would continue to exploit these resources when they later become associated with aquatic macrophytes. That pulmonate snails would tend to be feeding generalists capable of adapting to food of varying chemical composition, given sufficient time, provided it was sufficiently small or flaccid. That although macrophytes and snails show a strong positive relationship, the living macrophyte tissue would be little used by the snails. That the hard outer envelope, inherited from their terrestrial ancestors, would remain as the major defence mechanism of aquatic macrophytes against attack by snails and other aquatic invertebrates. That aquatic macrophytes would invest little in the nutrient deficiency strategy to reduce attack by invertebrates such as snails. That truly aquatic submerged macrophytes would not possess secondary plant compounds (SPC) that would be molluscicidal. Emergent parts of subaquatic or aquatic plants might be expected to be better sources of SPC with molluscicidal factors than submerged aquatic plants. Species of epiphytic or planktonic algae might be better sources of SPC with molluscicidal effects than aquatic macrophytes. That the strategies developed by pulmonate snails for obtaining their energy supplies would not be conducive to rapid speciation. The analysis of the present and other related results supports these propositions. Predictions based on the theory of mutualism involving the snails, macrophytes and other components of the module also receive some support from an analysis of the present results. The additional empirical work that could be undertaken to test this theory is briefly discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Sexual conflict and speciation.

We review the significance of two forms of sexual conflict (different evolutionary interests of the two sexes) for genetic differentiation of populations and the evolution of reproductive isolation. Conflicting selection on the alleles at a single locus can occur in males and females if the sexes have different optima for a trait, and there are pleiotropic genetic correlations between the sexes for it. There will then be selection for sex limitation and hence sexual dimorphism. This sex limitation could break down in hybrids and reduce their fitness. Pleiotropic genetic correlations between the sexes could also affect the likelihood of mating in interpopulation encounters. Conflict can also occur between (sex-limited) loci that determine behaviour in males and those that determine behaviour in females. Reproductive isolation may occur by rapid coevolution of male trait and female mating preference. This would tend to generate assortative mating on secondary contact, hence promoting speciation. Sexual conflict resulting from sensory exploitation, polyspermy and the cost of mating could result in high levels of interpopulation mating. If females evolve resistance to make pre- and postmating manipulation, males from one population could be more successful with females from the other, because females would have evolved resistance to their own (but not to the allopatric) males. Between-locus sexual conflict could also occur as a result of conflict between males and females of different populations over the production of unfit hybrids. We develop models which show that females are in general selected to resist such matings and males to persist, and this could have a bearing on both the initial level of interpopulation matings and the likelihood that reinforcement will occur. In effect, selection on males usually acts to promote gene flow and to restrict premating isolation, whereas selection on females usually acts in the reverse direction. We review theoretical models relevant to resolution of this conflict. The winning role depends on a balance between the 'value of winning' and 'power' (relating to contest or armament costs): the winning role is likely to correlate with high value of winning and low costs. Sperm-ovum (or sperm-female tract) conflicts (and their plant parallels) are likely to obey the same principles. Males may typically have higher values of winning, but it is difficult to quantify 'power', and females may often be able to resist mating more cheaply than males can force it. We tentatively predict that sexual conflict will typically result in a higher rate of speciation in 'female-win' clades, that females will be responsible for premating isolation through reinforcement, and that 'female-win' populations will be less genetically diverse.

Alleles↗
PubMed1992

Molecular variants of human papillomavirus type 16 from four continents suggest ancient pandemic spread of the virus and its coevolution with humankind.

We have amplified by the polymerase chain reaction, cloned, and sequenced genomic segments of 118 human papillomavirus type 16 (HPV-16) isolates from 76 cervical biopsy, 14 cervical smear, 3 vulval biopsy, 2 penile biopsy, 2 anal biopsy, and 1 vaginal biopsy sample and two cell lines. The specimens were taken from patients in four countries--Singapore, Brazil, Tanzania, and Germany. The sequence of a 364-bp fragment of the long control region of the virus revealed 38 variants, most of which differed by one or several point mutations. Phylogenetic trees were constructed by distance matrix methods and a transformation series approach. The trees based on the long control region were supported by another set based on the complete E5 protein-coding region. Both sets had two main branches. Nearly all of the variants from Tanzania were assigned to one (African) branch, and all of the German and most of the Singaporean variants were assigned to the other (Eurasian) branch. While some German and Singaporean variants were identical, each group also contained variants that formed unique branches. In contrast to the group-internal homogeneity of the Singaporean, German, and Tanzanian variants, the Brazilian variants were clearly divided between the two branches. Exceptions to this were the seven Singaporean isolates with mutational patterns typical of the Tanzanian isolates. The data suggest that HPV-16 evolved separately for a long period in Africa and Eurasia. Representatives of both branches may have been transferred to Brazil via past colonial immigration. The comparable efficiencies of transfer of the African and the Eurasian variants to the New World suggest pandemic spread of HPV-16 in past centuries. Representatives of the African branch were possibly transferred to the Far East along old Arab and Indonesian sailing routes. Our data also support the view that HPV-16 is a well-defined virus type, since the variants show only a maximal genomic divergence of about 5%. The small amount of divergence in any one geographic location and the lack of marked divergence between the Tanzanian and Brazilian African genome variants two centuries after their likely introduction into the New World suggest a very slow rate of viral evolution. The phylogenetic tree therefore probably represents a minimum of several centuries of evolution, if not an age equal to that of the respective human races.

Base Sequence↗
PubMed2003

Phenotype matching in wild parsnip and parsnip webworms: causes and consequences.

According to the geographic mosaic theory of coevolution, selection intensity in interactions varies across a landscape, forming a selection mosaic; interaction traits match at coevolutionary hotspots where selection is reciprocal and mismatch at coldspots where reciprocity is not a factor. Chemical traits play an important role in the interaction between wild parsnip (Pastinaca sativa) and the parsnip webworm (Depressaria pastinacella). Furanocoumarins, produced as plant defenses, are detoxified by the webworms by cytochrome P450 monooxygenases; significant additive genetic variation exists for both furanocoumarin production in the plant and detoxification in the insect, making these traits available for selection. To test the hypothesis that differences in selection intensity affect the distribution of coevolutionary hotspots and coldspots in this interaction, we examined 20 populations of webworms and wild parsnips in Illinois and Wisconsin that varied in size, extent of infestation, proximity to woods (and potential vertebrate predators), and proximity to a chemically distinct alternate host plant, Heracleum lanatum (cow parsnip). Twelve of 20 populations displayed phenotype matching between plant defense and insect detoxification profiles. Of the eight mismatched populations, a logistic regression model related matching probability to two predictors: the presence of the alternate host and average content of xanthotoxin (one of the five furanocoumarins produced by P. sativa). The odds of mismatching were significantly increased by the presence of the alternate host (odds ratio = 15.4) and by increased xanthotoxin content (odds ratio = 6.053). Parsnips growing near cow parsnip displayed chemical phenotypes that were chemically intermediate between cow parsnip and parsnips growing in isolation. Rapid phenotype matching in this system is likely due in part to differential mortality every season; larvae transferred to a plant 30 m or more from the plant on which they developed tended to experience increased mortality over larvae transferred to another umbel on the same plant on which they had developed, and plant populations that mismatched in 2001 displayed a change in chemical phenotype distribution from the previous year. Trait mixing through gene flow is also a likely factor in determining mismatch frequency. Populations from which webworms were eradicated the previous year were all recolonized; in three of seven of these populations, infestation rates exceeded 90%. Our findings, consistent with the geographic mosaic theory, suggest that the presence of a chemically distinct alternate host plant can affect selection intensity in such a way as to reduce the likelihood of reciprocity in the coevolutionary interaction between wild parsnip and the parsnip webworm.

Animals↗