Cell and genome coevolution: facultative anaerobiosis, glycosomes and kinetoplastan RNA editing.
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Adaptation, Physiological↗
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Results for “Biological Coevolution”
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The coevolutionary potential of a 'generalist' parasite, the hen flea Ceratophyllus gallinae.
Hosts exert selection pressures on their parasites and it is often assumed that host-parasite coevolution with each host is less intense in a generalist parasite than for a parasite with a narrow host range. Selection pressure on the parasite, however, is rather determined by host specificity, i.e. the relative importance of each host, than simply by the range of hosts. The determination of host specificity requires an assessment of the prevalence and intensity of parasite infestation within each host's nests, as well as the local abundance of each host species. Since the hen flea, Ceratophyllus gallinae, is a rather generalist parasite of birds it could be concluded that there has been weak coevolution with each of its hosts. By reviewing the literature on the prevalence and intensity of hen flea infestations in bird nests we estimated the number of individuals produced in the nest of each host species. The comparative analysis shows (1) that the prevalence of infestation is highest in hole-nesting avian families, (2) that prevalence and intensity of infestation among bird families are highly correlated, and (3) that hole-nesting Paridae have the highest intensities of infestation and harbour the majority of the flea population. These results underline the fleas' potential for coevolution with Paridae despite their extensive host range.
Animals↗
The evolution of polyandry: patterns of genotypic variation in female mating frequency, male fertilization success and a test of the sexy-sperm hypothesis.
The sexy-sperm hypothesis predicts that females obtain indirect benefits for their offspring via polyandy, in the form of increased fertilization success for their sons. I use a quantitative genetic approach to test the sexy-sperm hypothesis using the field cricket Teleogryllus oceanicus. Previous studies of this species have shown considerable phenotypic variation in fertilization success when two or more males compete. There were high broad-sense heritabilities for both paternity and polyandry. Patterns of genotypic variance were consistent with X-linked inheritance and/or maternal effects on these traits. The genetic architecture therefore precludes the evolution of polyandry via a sexy-sperm process. Thus the positive genetic correlation between paternity in sons and polyandry in daughters predicted by the sexy-sperm hypothesis was absent. There was significant heritable variation in the investment by females in ovaries and by males in the accessory gland. Surprisingly there was a very strong genetic correlation between these two traits. The significance of this genetic correlation for the coevolution of male seminal products and polyandry is discussed.
Animals↗
Population structure of plasmid-containing strains of Streptococcus mutans, a member of the human indigenous biota.
There are suggestions that the phylogeny of Streptococcus mutans, a member of the human indigenous biota that is transmitted mostly mother to child, might parallel the evolutionary history of its human host. The relatedness and phylogeny of plasmid-containing strains of S. mutans were examined based on chromosomal DNA fingerprints (CDF), a hypervariable region (HVR) of a 5.6-kb plasmid, the rRNA gene intergenic spacer region (IGSR), serotypes, and the genotypes of mutacin I and II. Plasmid-containing strains were studied because their genetic diversity was twice as great as that of plasmid-free strains. The CDF of S. mutans from unrelated human hosts were unique, except those from Caucasians, which were essentially identical. The evolutionary history of the IGSR, with or without the serotype and mutacin characters, clearly delineated an Asian clade. Also, a continuous association with mutacin II could be reconstructed through an evolutionary lineage with the IGSR, but not for serotype e. DNA sequences from the HVR of the plasmid produced a well-resolved phylogeny that differed from the chromosomal phylogeny, indicating that the horizontal transfer of the plasmid may have occurred multiple times. The plasmid phylogeny was more congruent with serotype e than with mutacin II evolution, suggesting a possible functional correlation. Thus, the history of this three-tiered relationship between human, bacterium, and plasmid supported both coevolution and independent evolution.
Biological Evolution↗
Mites and birds: diversity, parasitism and coevolution.
Ectoparasites play important roles in the lives of birds. Among these parasites, mites offer unique potential because of their extraordinary ecological and evolutionary diversity. However, the basic biology of most mites is poorly understood, and misleading extrapolations are sometimes made from better studied systems involving lice and fleas. Most importantly, not all bird-associated mites are parasitic; indeed, recent research suggests that some might even be beneficial. Here, we summarize what is known about the diversity of bird-mite relationships, and highlight how mites provide an ideal tool for the study of host life histories, sexual selection, immunocompetence and cospeciation.
Journal Article↗
In search of a bacterial species definition.
The bacterial species concept was examined within the framework of plant and animal associated alpha-2 proteobacteria, taking into consideration the phylogenetic, taxonomic and biological approaches as well as the microbiologists' perception. The virtue of the phylogenetic approach is that it gives an evolutionary perspective of the bacterial lineage; however the methods used possess low resolution for defining species located at the terminal branches of the phylogenetic trees. The merit of the taxonomic approach is that species are defined on the basis of multiple characteristics allowing high resolution at the terminal branches of dendograms; its disadvantage is the inaccuracy in the earlier nodes. On an individual level, the qualitative biological characteristics used for the definition of species frequently reveal shortcomings because many of these properties are the result of coevolution, parallel evolution or the horizontal transfer of genes. Nevertheless, when considered together with the phylogenetic and taxonomic approaches, important uncertainties are discovered: these must be weighed if a practical definition of bacterial species is conceived. The microbiologists' perception is the criterion expressed by a group of sponsors who, based on scientific and practical grounds, propose a new bacterial species. The success of this new proposal is measured by its widespread acceptance and its permanence. A difficult problem concerned with defining bacterial species is how to distinguish if they are independent evolutionary units or if they are reticulate evolutionary units. In the first case the inherence is vertically transmitted as a result of binary fission and clonal expansion. This may be the case of some animal cell associated bacteria in which recombination appears to be precluded or exceptional. In the second case adaptive changes occurring within an individual can be horizontally transferred to many or all group members. This seems to be the condition of many intestinal and plant associated bacteria. Genetic drift and speciation in clonal bacteria will depend almost exclusively on mutation and internal genetic rearrangement processes, whereas speciation in reticulate bacteria will depend not only on these processes but in their genetic interactions with other bacterial strains. This uncertainty, which corresponds to the evolutionary process, is at the same time one of the key factors in defining a bacterial species.
Bartonella↗
Sexual conflict and sexual selection: lost in the chase.
The emergent field of evolutionary biology that studies disparities between the evolutionary interests of alleles expressed in the two sexes, or sexual conflict, promises to offer novel insights into male-female coevolution and speciation. Our theoretical understanding of basic concepts is, however, still incomplete. In a recent perspective paper, Pizzari and Snook provided a framework for understanding sexually antagonistic coevolution and for distinguishing this process from other models of male-female coevolution and suggested an experimental protocol to test for sexually antagonistic coevolution. Here, I show that the framework is flawed, primarily because it is built upon the mistaken assumption that male and female fitness can evolve independently. Further, while the empirical strategy advocated has indeed offered important insights in the past, it does not allow unambiguous discrimination between competing hypotheses.
Animals↗
Evolutionary biology of plant defenses against herbivory and their predictive implications for endocrine disruptor susceptibility in vertebrates.
Hormone disruption is a major, underappreciated component of the plant chemical arsenal, and the historical coevolution between hormone-disrupting plants and herbivores will have both increased the susceptibility of carnivores and diversified the sensitivities of herbivores to man-made endocrine disruptors. Here I review diverse evidence of the influence of plant secondary compounds on vertebrate reproduction, including human reproduction. Three of the testable hypotheses about the evolutionary responses of vertebrate herbivores to hormone-disrupting challenges from their diet are developed. Specifically, the hypotheses are that a) vertebrate herbivores will express steroid hormone receptors in the buccal cavity and/or the vomeronasal organ; b) absolute sex steroid concentrations will be lower in carnivores than in herbivores; and c) herbivore steroid receptors should be more diverse in their binding affinities than carnivore lineages. The argument developed in this review, if empirically validated by support for the specific hypotheses, suggests that a) carnivores will be more susceptible than herbivores to endocrine-disrupting compounds of anthropogenic origin entering their bodies, and b) diverse herbivore lineages will be variably susceptible to any given natural or synthetic contaminant. As screening methods for hormone-disrupting potential are compared and adopted, comparative endocrine physiology research is urgently needed to develop models that predict the broad applicability of those screening results in diverse vertebrate species.
Adaptation, Physiological↗
Evolution of host-parasite associations among species of lice and rock-wallabies: coevolution? (J. F. A. Sprent Prize lecture, August 1990).
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Animals↗
Bacterial antigenic variation, host immune response, and pathogen-host coevolution.
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Animals↗
Plant chemical defense against herbivores and pathogens: generalized defense or trade-offs?
Plants are often attacked by multiple enemies, including pathogens and herbivores. While many plant secondary metabolites show specific effects toward either pathogens or herbivores, some can affect the performance of both these groups of natural enemies and are considered to be "generalized defense compounds". We tested whether aucubin and catalpol, two iridoid glycosides present in ribwort plantain (Plantago lanceolata), confer in vivo resistance to both the generalist insect herbivore Spodoptera exigua and the biotrophic fungal pathogen Diaporthe adunca using plants from P. lanceolata lines that had been selected for high- and low-leaf iridoid glycoside concentrations for four generations. The lines differed approximately three-fold in the levels of these compounds. Plants from the high-selection line showed enhanced resistance to both S. exigua and D. adunca, as evidenced by a smaller lesion size and a lower fungal growth rate and spore production, and a lower larval growth rate and herbivory under both choice and no-choice conditions. Gravimetric analysis revealed that the iridoid glycosides acted as feeding deterrents to S. exigua, thereby reducing its food intake rate, rather than having post-ingestive toxic effects as predicted from in vitro effects of hydrolysis products. We suggest that the bitter taste of iridoid glycosides deters feeding by S. exigua, whereas the hydrolysis products formed after tissue damage following fungal infection mediate pathogen resistance. We conclude that iridoid glycosides in P. lanceolata can serve as broad-spectrum defenses and that selection for pathogen resistance could potentially result in increased resistance to generalist insect herbivores and vice versa, resulting in diffuse rather than pairwise coevolution.
Adaptation, Physiological↗
Genetic analysis of coevolution between plants and their natural enemies.
Plants exhibit a diverse array of characteristics that have been interpreted as functioning primarily as defenses against natural enemies, such as pathogens and herbivores. Recent genetic analyses of resistance provide evidence supporting this interpretation. In addition, these analyses also support a key assumption underlying models of the evolution of resistance (i.e. that resistance is costly) and suggest that the outcome of coevolution is often not explainable in terms of pairwise interactions between a plant and individual natural enemies (i.e. coevolution is often likely to be diffuse rather than pairwise).
Animals↗
Conserved arrangements of repeated DNA sequences in nontranscribed spacers of ciliate ribosomal RNA genes: evidence for molecular coevolution.
We have analyzed the nucleotide sequences of the nontranscribed spacer (NTS) and transcription initiation and termination regions of the extrachromosomal rDNAs of the ciliated protozoans Tetrahymena thermophila and Glaucoma chattoni. The sequences surrounding the sites of transcription initiation and termination are highly conserved. The only extensive homologies of the NTS regions occur in five sets of dispersed repetitive sequences. Type I, II and III repeats in the 5' NTS are strongly conserved in sequence between Tetrahymena and Glaucoma in the case of the type I and III repeats, and in location relative to the transcription initiation site in the case of type I and II repeats. We identify two new repeat types, designated IV and V, in the 3' NTS. The sequence of type IV repeats, and the location relative to the transcription termination site of type IV and V repeats, are conserved. All five types of repeats are interspersed with nonconserved DNA sequences. These results suggest that the five repeat types in the 5' and 3' NTSs are important in rRNA gene function; the sequence organization, and the differing rates of divergence between species of the repeat types, provide strong evidence for their functional selection through the process of molecular coevolution.
Animals↗
[Adaptive property of hantaviruses during their isolation from cultured VERO-E6 cells in relation to the type of the ecological host].
As a result of virological studies, 185 lung tissue specimens from 4 rodent species caught near Khabarovsk were isolated and fixed in the passages of cultured Vero-6 cells of 68 hantavirus strains. The capacity of the strains to adapt to the cells was assessed by using the adaptive index involving the mean rates of successful isolation, its duration, hantavirus antigen titer in the material used for infection. The strains of hantavirus serotypes were noted for the highest adaptive properties, which are ecologically associated with rodents of the family Mus, such as field and East-Asiatic mice. Lower adaptive capacities were established for the strains of hantavirus serotypes, which are ecologically related to rodents of the family Cricetidae, such as large and large-toothed redback voles. The differences found in the adaptive capacities of hantavirus strains cultured in Vero-E6 cells reflect the degree of specialization of some hantavirus serotypes to particular host rodent species during their long-term coevolution.
Adaptation, Biological↗
Coevolution of Danaid butterflies with their host plants.
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Animals↗
Sexually antagonistic coevolution of a postmating-prezygotic reproductive character in desert Drosophila.
Rapid divergence in postmating-prezygotic characters suggests that selection may be responsible for generating reproductive barriers between closely related species. Theoretical models indicate that this rapid divergence could be generated by a series of male adaptations and female counteradaptations by means of sexual selection or conflict, but empirical tests of particular mechanisms are generally lacking. Moreover, although a male--female genotypic interaction in mediating sperm competition attests to an active role of females, molecular or morphological evidence of the female's participation in the coevolutionary process is critically needed. Here we show that postmating-prezygotic variation among populations of cactophilic desert Drosophila reflects divergent coevolutionary trajectories between the sexes. We explicitly test the female's role in intersexual interactions by quantifying differences in a specific postmating-prezygotic reproductive character, the insemination reaction mass, in two species, Drosophila mojavensis and Drosophila arizonae. A series of interpopulation crosses confirmed that population divergence was propelled by male--female interactions, a prerequisite if the selective forces derive from sexual conflicts. An association between the reaction mass and remating and oviposition behavior argues that divergence has been propelled by sexually antagonistic coevolution, and potentially has important implications for speciation.
Animals↗
Maximum-likelihood divergence date estimates based on rRNA gene sequences suggest two scenarios of Trypanosoma cruzi intraspecific evolution.
The phylogenetic relationships of Trypanosoma cruzi strains were inferred using maximum-likelihood from complete 18S rDNA sequences and D7-24Salpha rDNA regions from 20 representative strains of T. cruzi. For this we sequenced the 18S rDNA of 14 strains and the D7-24Salpha rDNA of four strains and aligned them to previously published sequences. Phylogenies inferred from these data sets identified four groups, named Riboclades 1, 2, 3, and 4, and a basal dichotomy that separated Riboclade 1 from Riboclades 2, 3, and 4. Substitution models and other parameters were optimized by hierarchical likelihood tests, and our analysis of the 18S rDNA molecular clock by the likelihood ratio test suggests that a taxa subset encompassing all 2,150 positions in the alignment supports rate constancy among lineages. The present analysis supports the notion that divergence dates of T. cruzi Riboclades can be estimated from 18S rDNA sequences and therefore, we present alternative evolutionary scenarios based on two different views of T. cruzi intraspecific divergence. The first assumes a faster evolutionary rate, which suggests that the divergence between T. cruzi I and II and the extant strains occurred in the Tertiary period (37-18 MYA). The other, which supports the hypothesis that the divergence between T. cruzi I and II occurred in the Cretaceous period (144-65 MYA) and the divergence of the extant strains occurred in the Tertiary period of the Cenozoic era (65-1.8 MYA), is consistent with our previously proposed hypothesis of divergence by geographical isolation and mammalian host coevolution.
Animals↗
Replicated population divergence caused by localized coevolution? A test of three hypotheses in the red crossbill-lodgepole pine system.
Several lines of evidence support the hypothesis that local populations of red crossbills (Loxia curvirostra complex) enter into a predator-prey arms race with lodgepole pine (Pinus contorta latifolia) in the absence of competing pine squirrels (Tamiasciurus hudsonicus). Nevertheless, the alternative hypotheses that neutral evolution or factors other than squirrels have caused crossbill population differentiation have not been thoroughly tested. We compared crossbill and pine cone morphology between island populations where squirrels are absent or present, and mainland sites where squirrels are present, in order to distinguish among these hypotheses. All comparisons supported an effect of squirrel absence, not island status, on crossbill and cone morphology. Hence our results provide further evidence that strong localized coevolutionary interactions in a geographic mosaic have driven adaptive population differentiation. In addition, vocal differentiation of crossbills was related to the absence of squirrels, but not to island status. As morphological and vocal differentiation is correlated with reproductive isolation in crossbills, the geographic mosaic of coevolution also seems to promote ecological speciation.
Adaptation, Physiological↗