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PubMed1988

Evolution of a bacteria/plasmid association.

Associations between bacteria and their accessory elements (viruses, plasmids and transposons) range from antagonistic to mutualistic. A number of previous studies have demonstrated that plasmid carriage reduces bacterial fitness in the absence of selection for specific functions such as antibiotic resistance. Many studies have demonstrated increased fitness of evolving microbial populations in laboratory environments, but we are aware of only one study in which fitness gains were partitioned between a plasmid and its host. Here, we examine the evolution of an association between a plasmid and its bacterial host. Carriage of the non-conjugative plasmid pACYC184 initially reduced the fitness of Escherichia coli B in the absence of antibiotic. We then cultured plasmid-bearing bacteria for 500 generations in the presence of antibiotic. The fitness of each combination of host and plasmid, with and without the culture history, was determined by competing it against a baseline strain. The results indicate adaptation by the host genome, but no plasmid adaptation. We also competed the evolved host, transformed with the baseline plasmid, against its isogenic plasmid-free counterpart. The plasmid now increased the fitness of its host.

Adaptation, Physiological↗
PubMed2002

The functional CD8 T cell response to HIV becomes type-specific in progressive disease.

High levels of HIV-specific CD8 T cells are demonstrable throughout HIV disease using laboratory assays that measure responses to consensus epitopes. In acute infection, the dynamics of the antiviral CD8 T cell response correlate well with the decline in viremia. However in chronic infection, although responses are detected against a broader spectrum of epitopes, virus-specific CD8 T cells are apparently unable to control viral replication. To investigate whether CD8 T cells responding to consensus epitopes may have lost their in vivo relevance in the chronic phase because of viral evolution driven by immune pressure, we compared the CD8 T cell response to CD4 T cell targets infected with either lab-adapted HIV(IIIB) or the patient's own virus. The magnitude of the IFN-gamma response declined with disease progression, especially to autologous virus. T cell receptor (TCR) clonotypes of HIV(IIIB) and autologous virus-responding cells were determined by sequencing TCR beta chain variable (TCRBV) genes. In two of three asymptomatic donors, the dominant clonotypes overlapped, whereas in five symptomatic patients, the TCR clonotypes responding to HIV(IIIB) virus were completely different from those responding to autologous virus. Moreover, in cytolytic assays, T cell lines derived from IFN-gamma(+) cells responding to lab-adapted or autologous virus cross-recognized target cells infected with either virus in asymptomatic subjects with shared TCR clonotypes but not in progressors with differing clonotypes. Therefore, in advanced-stage patients, viral-specific CD8 T cells recognizing consensus epitopes persist from an earlier response but no longer effectively recognize autologous virus.

CD8-Positive T-Lymphocytes↗
PubMed1999

Population structure, speciation, and introgression in the Anopheles gambiae complex.

We review here what is known about the population structure and evolutionary dynamics of members of the Anopheles gambiae complex with emphasis on the situation in West Africa. First, the importance of the 2nd chromosome inversion polymorphism is demonstrated especially in adaptation to levels of aridity, a major environmental variable in Africa. This affects the distribution of karyotypes on both a macro- and micro-geographic scale as well as temporally. Such differentiation leads to karyotypes being differentially effective transmitters of malaria and differentially susceptible to indoor residual spraying of insecticides. Second, we review the evidence that cryptic taxa, especially in An. gambiae s.s., exist. This observation stems from both karyotype studies and molecular studies. It is abundantly clear that West African populations of An. gambiae s.s. are often not panmictic units, with premating factors evidently acting to maintain distinct genetic forms. Third, we review phylogenetic studies that have revealed the presence of introgression between the two most important vectors, An. gambiae and An. arabiensis. This is most evident for the 2nd chromosome inversions. This interpretation of phylogenetic data is consistent with a direct laboratory study indicating inversions in this chromosome are stably maintained in back-crossed populations. All of this information has led to the view that members of the An. gambiae complex are highly variable with an abundance of adaptive genetic variation. This presents a significant challenge to vector control programs designed to reduce malaria in sub-Saharan Africa.

Africa, Western↗
PubMed1998

Manipulation of a mollusc by a trophically transmitted parasite: convergent evolution or phylogenetic inheritance?

We investigated the influence of infection by the trematode Curtuteria australis on the burrowing behaviour of its intermediate host, the bivalve Austrovenus stutchburyi. Laboratory experiments and field observations revealed that cockles, unable to bury completely or even partially under the sediment, have a reduced foot length compared with buried individuals. The ability to bury proved to be highly repeatable in field experiments: cockles found at the surface and transplanted to an experimental area did not bury themselves, and cockles found buried stayed buried when relocated. All metacercariae of C. australis were found strictly in the foot and for each of 3 samples collected in different sites, there was a negative and significant relationship between the relative length of the foot and the parasite load. A predation test conducted under natural conditions indicated that cockles with the stunted foot and the altered behaviour are significantly more susceptible to predation by aquatic birds than other cockles. Given that the definitive host of C. australis is an oystercatcher, we first discuss our results in the context of transmission strategy. Comparisons with other studies on more or less related trematode species parasitic in bivalves and evolving under similar constraints for their transmission, shed light on the origin of this adaptation in C. australis.

Animals↗
PubMed2005

The evolution of parental care.

Our understanding of parental care behavior can be significantly advanced through the application of Williams's Principle, which states that reproduction has not only a benefit but also a cost to lifetime fitness. My laboratory has formalized Williams's Principle into the relative value theorem and found that its application to fishes, the taxa with the most diverse patterns of parental care, can help to explain which sex provides care and how much. In fishes, it is often the male that provides parental care, not because the male obtains greater benefits from this care, but probably because he pays fewer costs. Fish dynamically adjust their investment into parental care according to the number of offspring in their brood, past investment, genetic relatedness, and alternative mating opportunities, all of which affect the value of current offspring relative to potential future offspring. These results may also help us understand the joy and the challenges of parental care in humans.

Adaptation, Physiological↗
PubMed2004

The property 'instinct'.

Evolutionary theory and empirical studies suggest that many animals, including humans, have a genetic predisposition to acquire and retain property. This is hardly surprising because survival is closely bound up with the acquisition of things: food, shelter, tools and territory. But the root of these general urges may also run to quite specific and detailed rules about property acquisition, retention and disposition. The great variation in property-related behaviours across species may mask some important commonalities grounded in adaptive utility. Experiments and observations in the field and laboratory suggest that the legal rules of temporal priority and possession are grounded in what were evolutionarily stable strategies in the ancestral environment. Moreover, the preferences that humans exhibit in disposing of their property on their deaths, both by dispositions made in wills and by the laws of intestacy, tend to advance reproductive success as a result of inclusive fitness pay-offs.

Animals↗
PubMed2026

Genetic mutations driving ciprofloxacin resistance in laboratory-evolved Salmonella Typhimurium.

Ciprofloxacin resistance in Salmonella Typhimurium is a significant public health concern, and the mechanisms by which the resistance evolves are poorly defined. Here, by serial passaging under antibiotic selection, we isolated ciprofloxacin-resistant S. Typhimurium mutants and subjected them to whole-genome sequencing to reveal the major mutations associated with resistance. The Low CipR mutant acquired four chromosomal mutations in ramR, icdA, lipB, and gyrA, and the High CipR mutant gained additional mutations in gyrB, yaiC, and corA. Functional characterization determined that mutations in ramR resulted in efflux pump upregulation, while disruptions in the TCA cycle caused by mutations in icdA and lipB led to metabolic alterations. These changes indirectly enhanced resistance by increasing the expression of the global regulator MarA and reducing OmpF-dependent membrane permeability. Despite the observation of the G105A substitution in GyrA, enzymatic assays confirmed the failure to support resistance to ciprofloxacin, possibly because the structural alteration remained minimal. GyrB488-489dup was associated with maintained supercoiling under ciprofloxacin and enhanced fluoroquinolone resistance, suggesting a major role in resistance evolution. Other mutations in yaiC impaired biofilm and, in corA, intracellular accumulation of magnesium, possibly stabilizing the bacterial cell envelope under antibiotic pressure. The findings provide novel explanations for the multifaceted mechanisms leading to ciprofloxacin resistance in Salmonella and suggest targets to combat antimicrobial resistance.IMPORTANCEAntibiotic resistance in Salmonella Typhimurium is an increasing public health concern, yet the genetic changes that allow bacteria to become resistant are not fully understood. In this study, we evolved ciprofloxacin-resistant Salmonella in the laboratory and identified the mutations that arise during resistance development. We found that resistance does not result from a single change but from multiple adaptations affecting drug efflux, metabolism, and the antibiotic target. Some mutations increased the activity of pumps that remove antibiotics from the cell, while others altered bacterial metabolism and reduced membrane permeability, making it harder for the drug to enter. A duplication in the DNA gyrase subunit GyrB played a particularly important role in maintaining DNA function under antibiotic stress. Together, these results reveal how diverse genetic changes cooperate to generate ciprofloxacin resistance and provide insights that may help guide strategies to combat drug-resistant Salmonella infections.

DNA gyrase↗
PubMed2000

Pinniped diving response mechanism and evolution: a window on the paradigm of comparative biochemistry and physiology.

Starting even before the end of World War II, the discipline of comparative physiology and biochemistry experienced a period of unprecedented growth and development that pioneers in this field thought would never end. However, by the mid-1970s many of the major mechanistic problems in the field were pretty well understood in principle, and by the mid-1980s workers in the field widely recognized that the discipline was at the point of diminishing returns. One response to this was disillusionment, which turned out to be premature because the field was already absorbing molecular biology tools which has now caused a kind of renaissance in mechanistic physiology studies. The second major response to the sense of disillusionment led to a search for new approaches, and out of this endeavor the newly rejuvenated field of evolutionary physiology arose, and this research area too is now in a growth phase. These general patterns of growth and development in our discipline as a whole are particularly clearly evident in the field of aquatic mammals and birds. Between the 1930s and the 1970s, studies of diving physiology and biochemistry made great progress in mechanistically explaining the basic diving response of aquatic mammals and birds. Key components of the diving response (apnea, bradycardia, peripheral vasoconstriction, redistribution of cardiac output) were found in essentially all species analyzed and were generally taken to be biological adaptations. By the mid-1970s, this approach to unraveling the diving response had run 'out of steam' and was in conceptual stasis. The breakthrough which gave renewal to the field at this time was the development of microprocessor based monitoring of diving animals in their natural environments, which led to a flurry of studies mostly confirming the essential outlines of the diving response based upon laboratory studies and firmly placing it into a proper biological context, underlining its plasticity and species specificities. Now as we begin a new millenium, despite ever more detailed field monitoring of physiology, behavior and ecology, studies aimed at improving understanding of physiological mechanisms in diving are again approaching a point of diminishing returns. To avoid another conceptual stasis, what seems required are new initiatives which may arise from two differing approaches. The first is purely experimental, relying on magnetic resonance imaging (MRI) and spectroscopy (MRS) to expand the framework of the original 'diving response' concept. The second, evolutionary study of the diving response, is synthetic, linked to both field and laboratory studies. To date the evolution of the diving response has only been analyzed in pinnipeds and from these studies two kinds of patterns have emerged. (1) Some physiological and biochemical characters, required and used in diving animals, are highly conserved not only in pinnipeds but in all vertebrates; these traits are necessarily similar in all pinnipeds and include diving apnea, bradycardia, tissue specific hypoperfusion, and hypometabolism of hypoperfused tissues. (2) Another group of functionally linked characters are more malleable and include (i) spleen mass, (ii) blood volume, and (iii) hemoglobin (Hb) pool size. Increases in any of these traits (or in a morphological character, body size) improve diving capacity. Assuming that conserved physiological function means conserved sequences in specific genes and their products (and that evolving function requires changes in such sequences), it is possible to rationalize both the above trait categories in pinniped phylogeny. However, it is more difficult for molecular evolution theory to explain how complex regulatory systems like those involved in bradycardia and peripheral vasoconstriction remain the same through phylogenetic time than it is to explain physiological change driven by directional natural selection.

Animals↗
PubMed2000

Predisposed to adapt? Clade-level differences in characters affecting swimming performance in damselflies.

Previous studies have shown that two or three lineages of Enallagma damselflies, which historically co-existed with fish, recently invaded and adapted to living with large dragonfly predators in fishless waters. In adapting to live with these new predators, lineages shifted behaviorally to using swimming as an evasive tactic against attacking predators, evolved morphological features that made them faster swimmers, and evolved biochemical features to increase refueling strenuous activities like swimming. However, these habitat shifts have occurred in only one of the two primary clades within the genus in North America. Here, I show that clade-level differences exist among species in the ancestral, fish-lake habitat that should make habitat shifts easier to accomplish in the clade in which they have occurred. Specifically, fish-lake species in the clade in which habitat shifts occurred have much higher propensities to swim in the laboratory, swim faster when they do swim, and have higher mass-specific activities for arginine kinase than do species in the other primary clade, in which no extant species are found in fishless waters. These results are discussed in the context of the dynamics of founder events and the potential implications for community structure.

Adaptation, Physiological↗
PubMed1993

Chemical and behavioral studies of femoral gland secretions in iguanid lizards.

Comparative studies on the chemistry and behavioral significance of femoral gland secretions in desert iguanas (Dipsosaurus dorsalis) and green iguanas (Iguana iguana) are reviewed. Field and laboratory studies suggest that femoral gland secretions function in conspecific recognition and range marking. In desert iguanas, secretions are of low volatility and may be detected initially using long-range ultraviolet visual cues. In contrast, green iguana secretions contain a diversity of volatile lipids and appear to be localized by chemoreception. Interspecific differences in femoral gland chemistry may reflect adaptations to the diverse climatic conditions of arid desert and tropical forest environments.

Animal Communication↗
PubMed2001

Physiological bases of genetic differences in cannibalism behavior of the confused flour beetle Tribolium confusum.

Physiological causes of genetic differences in cannibalism were examined to gain a better understanding of constraints on behavior evolution. Cannibalism has complex population level consequences in Tribolium confusum, including dramatic effects on population size. Laboratory strains with low and high cannibalism rates, obtained through inbreeding, have maintained distinct levels of cannibalism for over two decades even in the absence of artificial selection to maintain the differences. Why strains differ in their cannibalism rates was examined by measuring: (1) the nutritional benefit from cannibalism in both nutritionally good and poor environments, and (2) the possibility that eggs are an important source of water. How strains achieve differences in cannibalism was examined by testing for differences between strains in their ability to find eggs and in their tendency to eat eggs. Beetles from both strains survive equally well in a nutritionally good environment, but they accomplish this in different ways. The low cannibalism strain has high survivorship with and without cannibalism. The high cannibalism strain has low survivorship when not fed eggs and survivorship equivalent to the low cannibalism strain when fed eggs, suggesting it compensates for poor nutritional adaptation by eating eggs. The strains also differ in feeding behavior; beetles from the high cannibalism strain have a higher appetite for eggs. Beetles from the two strains did not differ in locomotor activity, search efficiency, or need for water. The observed behavioral and nutritional differences may contribute to the maintenance of different levels of cannibalism.

Animals↗
PubMed2003

Environment-dependent inbreeding depression in a hermaphroditic freshwater snail.

Inbreeding depression was simultaneously studied under contrasted environments, laboratory and natural conditions, using individuals originating from 14 families of the freshwater snail Physa acuta. Both survival and growth of juveniles showed inbreeding depression under laboratory conditions. The same fitness components were monitored with mature snails either kept under laboratory conditions or released at a natural site and analysed using capture-mark-recapture models. Genetic composition of both samples was similar. Inbreeding depression on survival was highest in the laboratory while strong outbreeding depression was revealed in the field. Thus inbreeding depression may not be always higher under natural conditions, at the opposite of what is commonly assumed. We suggest that inbreeding depression is dependent on metabolic requirements imposed by the environment. Other evidences showing that inbreeding depression is environment-dependent are reviewed. We conclude that genetic models should include both genetic and environmental variance in inbreeding depression for studying mating system evolution.

Adaptation, Physiological↗
PubMed2003

Diverse Mesorhizobium plurifarium populations native to Mexican soils.

Forty-six Mesorhizobium strains associated with the leguminous plants Leucaena leucocephala and Sesbania herbacea in an uncultivated Mexican field were characterized using a polyphasic approach. The strains were identified as Mesorhizobium plurifarium based upon the close relationships with the reference strains for this species in PCR-based restriction fragment length polymorphism analyses, sequencing of 16S rRNA genes, multilocus enzyme electrophoresis, and DNA-DNA hybridization. Although the strains isolated from both plants formed the same group in multilocus enzyme electrophoresis and cross-nodulations were observed in the laboratory, different electrophoretic types were obtained from the two plants grown in natural soils, indicating the existence of a preferable association between the plants and the rhizobia. The M. plurifarium strains from Mexico and the reference strains from Africa and Brazil formed different phenotypic clusters in a numerical taxonomy. The Mexican strains did not grow at 37 degrees C and were sensitive to salty-alkaline conditions, while the reference strains from Africa and Brazil grew at 42 degrees C and were more resistant to salty-alkaline conditions. These results demonstrate that both the plants and environmental factors affected the evolution of rhizobia and that the Mexican strains had adapted to the neutral soils and the cool climate where they were isolated.

Adaptation, Biological↗
PubMed1978

Evolutionary adaptation of membranes to temperature.

The "fluidity" of brain synaptosomal membrane preparations of arctic and hot-springs fish species, two temperature water fish species acclimated to different seasonal temperatures, and two mammals was estimated using the fluorescence polarization technique. At all measurement temperatures, the fluidity decreased in the order: arctic sculpin, 5 degrees-acclimated goldfish, 25 degrees-acclimated goldfish, desert pupfish, and rat. This correlated with increasing adaptation or body (i.e., cellular) temperatures of 0 degrees, 5 degrees, 25 degrees, 34 degrees, and 37 degrees and suggested a partial compensation of membrane fluidity for environmental temperature that occurs over the evolutionary time period as well as during laboratory (seasonal) acclimation. Evolutionary adaptation of relatively stenothermal species to constant thermal environments resulted in a more complete compensation than laboratory (seasonal) acclimation. Each compensation is accompanied by differences in the saturation of membrane phosphoglycerides. At increased cellular temperatures the proportion of saturated fatty acids increased and the unsaturation index decreased; the correlation between these indices and the measured expression of membrane dynamic structure was highly significant. It is concluded that the homeoviscous compensation of synaptic membrane function is an important component of temperature adaptation.

Adaptation, Physiological↗
PubMed1990

Evolution of spatial cognition: sex-specific patterns of spatial behavior predict hippocampal size.

In a study of two congeneric rodent species, sex differences in hippocampal size were predicted by sex-specific patterns of spatial cognition. Hippocampal size is known to correlate positively with maze performance in laboratory mouse strains and with selective pressure for spatial memory among passerine bird species. In polygamous vole species (Rodentia: Microtus), males range more widely than females in the field and perform better on laboratory measures of spatial ability; both of these differences are absent in monogamous vole species. Ten females and males were taken from natural populations of two vole species, the polygamous meadow vole, M. pennsylvanicus, and the monogamous pine vole, M. pinetorum. Only in the polygamous species do males have larger hippocampi relative to the entire brain than do females. Two-way analysis of variance shows that the ratio of hippocampal volume to brain volume is differently related to sex in these two species. To our knowledge, no previous studies of hippocampal size have linked both evolutionary and psychometric data to hippocampal dimensions. Our controlled comparison suggests that evolution can produce adaptive sex differences in behavior and its neural substrate.

Animals↗
PubMed2005

A within-species warning function for an aposematic signal.

Aposematic, or warning, signals are generally interspecific in form: one species advertises noxiousness to a predator or parasite species. In a study of the pipevine swallowtail butterfly (Battus philenor), we show that a pattern of colouration in the caterpillars that is considered to be aposematic in the context of attack by natural enemies also deters oviposition by conspecific females. In field and laboratory assays, females avoided oviposition on plants bearing live conspecific larvae. Females avoided oviposition on plants bearing artificially constructed models identical to larvae in shape, size and colour pattern. Finally, oviposition on plants harbouring a model bearing the larval colour pattern was reduced relative to plants bearing a leaf-green model, suggesting that the larval colour pattern was essential for avoidance. We discuss how intraspecific and interspecific processes might interact in the evolution of an aposematic signal.

Adaptation, Biological↗
PubMed2006

The pea aphid, Acyrthosiphon pisum: an emerging genomic model system for ecological, developmental and evolutionary studies.

Aphids display an abundance of adaptations that are not easily studied in existing model systems. Here we review the biology of a new genomic model system, the pea aphid, Acyrthosiphon pisum. We then discuss several phenomena that are particularly accessible to study in the pea aphid: the developmental genetic basis of polyphenisms, aphid-bacterial symbioses, the genetics of adaptation and mechanisms of virus transmission. The pea aphid can be maintained in the laboratory and natural populations can be studied in the field. These properties allow controlled experiments to be performed on problems of direct relevance to natural aphid populations. Combined with new genomic approaches, the pea aphid is poised to become an important model system for understanding the molecular and developmental basis of many ecologically and evolutionarily relevant problems.

Adaptation, Biological↗
PubMed2003

Evolutionary adaptation of a mammalian species to an environment severely depleted of iodide.

Lack of dietary iodine is associated with thyroid insufficiency and its dire consequences including cretinism, yet territories severely deficient in iodine are home to many species of wild animals. The premise of our work is that an adaptation must be in place in order to allow these animals to thrive. We collected phyllotine rodents of the genus Auliscomys from the Altiplanic region of North Chile, an area historically associated with goitre and other manifestations of iodine deficiency disorders. The iodide concentration in the stream water in this locality, at <1 micro g l(-1) would undoubtedly result in widespread thyroidal insufficiency in humans and domestic livestock. The animals we collected, identified as Auliscomys boliviensis, showed no evidence of thyroidal insufficiency. There was no enlargement of the thyroid glands; the serum concentrations of thyroid hormone (measured as T4) and thyroid-stimulating hormone were comparable to laboratory rats. Serum iodide concentration was about 40% of that measured in laboratory rats. We conclude that these animals have established a specialised adaptive mechanism, most probably at the level of the Na(+)/I(-) symporter, that acts to enhance the uptake of dietary iodide into the gut and again from the serum into the follicular cells of the thyroid gland.

Adaptation, Physiological↗