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PubMed2005

Genetic coadaptation of the amylase gene system in Drosophila melanogaster: evidence for the selective advantage of the lowest AMY activity and of its epistatic genetic background.

In natural populations of Drosophila melanogaster, an amylase isozyme with the lowest alpha-amylase activity (AMY(1,1)) is predominant. To evaluate the selective significance of AMY(1,1) and its regulatory factor(s), we examined selection experiments in laboratory populations on two distinct food environments. After 300 generations, AMY(1,1) became predominant (89%) in a glucose (a product of AMY)-rich environment, while an isozyme with higher alpha-amylase activity, AMY(1,6), became predominant (83%) in a starch (substrate)-rich environment. We found that the identical alleles of the amylase (Amy) gene, which encodes each of AMY(1,1) and AMY(1,6), were shared between the two populations in the different food environments, employing the nucleotide sequencing of the duplicated Amy genes. Nevertheless, AMY(1,6) homozygotes selected in the starch-rich environment had a twofold higher AMY enzyme activity than those selected in the glucose-rich environment, suggesting a coadaptation of the coding region and its regulatory factor(s) on the genetic background. Such a difference in AMY enzyme activity was not detected between AMY(1,1) homozygotes, suggesting that the effect of the genetic background is epistatic. Our results indicate that natural selection is working on the Amy gene system as a whole for flies to adapt to the various food environments of local populations.

Adaptation, Physiological↗
PubMed1977

Genic similarity of American and European species of the lobster Homarus.

European lobsters (Homarus gammarus) from the Norway coast and from the Irish Sea are examined for electrophoretically detectable genetic variation in seventeen functionally different proteins. Forty-one loci encoding these proteins are homologous with loci studied in a previous survey of eight populations of H. americanus. Progeny hatched from ovigerous Norway females show variation in three enzymes, but Mendelian inheritance is confirmed only for triosephosphate isomerase and for one of the phosphoglucose isomerases. Complex PGI phenotypes are described. The average amounts of genetic variability in European and American lobster populations appear to be equivalent. More than one allele is detected at 20% of the loci, the average number of alleles detected per locus is 1.2 and the average proportion of loci heterozygous per individual is 4.0%. While much less genically variable than other invertebrates, Homarus is not atypical when compared with eleven decapod species that average 5.8% heterozygosity. This is consistent with hypotheses relating genetic variability to adaptive strategy. At thirty loci H. gammarus is monomorphic for the common H. americanus allele. Two acid phosphatase systems are fixed or nearly fixed for alternative alleles in the two species while the remaining polymorphic loci show various degrees of interspecific divergence. Unique H. gammarus alleles are detected at five loci but only contribute significantly to species differences at the Acph-5, Me, and Pgi-4 loci. Acph-1, Est-2, Pgi-3, and Pgm-1 are polymorphic for the same alleles in both species, but again, with various differences in allelic frequencies. In sum, average genetic identity and average genetic distance are: I = 0.896 +/- 0.007 and D = 0.110 +/- 0.007, respectively. Compared to the values for conspecific population comparisons, I = 0.994 +/- 0.001 and D - 0.006 +/- 0.001, it is clear that a small but significant amount of genetic divergence separates the European and American lobster. Based on the premise that protein differences between existing species reflect the amount of time since they shared a common ancestor, it can be speculated that the European and American lobsters were isolated during the Pleistocene. The apparent weakness of reproductive isolating barriers suggests that these populations have evolved allopatrically. Finally, quantification of species' genetic differences, together with recent successes in interspecific laboratory matings, implicates species hybridization as a potentially important breeding practice in lobster aquaculture.

Animals↗
PubMed2006

Temporal evolution of 2-dimensional direction signals used to guide eye movements.

The smooth pursuit system must integrate many local motion measurements into a coherent estimate of target velocity. Several laboratories have studied this integration process using eye movements elicited by targets, such as tilted bars, containing conflicts between local motion signals measured along contours [one dimensional (1D)] and those measured at the bar's endpoints, or terminators [two dimensional (2D)]. The general finding is that 1D signals dominate early responses, whereas later components of the behavior are determined by 2D signals. We studied the dynamics of the integration process in macaque monkeys by systematically varying the relative proportions of 1D and 2D signals and the retinal eccentricities at which they appeared. Predictably, longer bars produced greater and longer-lasting contour-induced deviations. The evolution of the 2D response occurred over a period of 50-400 ms, depending on the relative proportions of 1D and 2D signals. As contours were displaced from the fovea the deviation decreased but much less so for early (1st 40 ms) than for late (subsequent 40 ms) pursuit initiation. These bottom-up effects could be overcome to a limited extent by the top-down influence of predictability. Finally, we observed that when animals were free to track any part of the bar, they spontaneously made short-latency saccades to the terminators on most trials, especially when the bars were tilted. This suggests an increased saliency of moving terminators, particularly when discrepancies exist among local motion signals.

Adaptation, Ocular↗
PubMed2003

Antioxidant defenses in killifish (Fundulus heteroclitus) exposed to contaminated sediments and model prooxidants: short-term and heritable responses.

A population of killifish (Fundulus heteroclitus) inhabiting a Superfund site on the Elizabeth River (VA, USA) is tolerant of the acute toxicity of the sediments from the site; previous work suggests that this tolerance is based both on genetic adaptation and physiological acclimation. In this study, larval first- and second-generation (F1 and F2) offspring of Elizabeth River killifish were more resistant to the toxicity of t-butyl hydroperoxide (a model prooxidant) than were King's Creek (reference site) offspring, indicating a heritable tolerance of exposure to oxidative stress. In laboratory experiments designed to elucidate the mechanistic basis for this increased tolerance, we exposed laboratory-raised F1 and F2 offspring from Elizabeth River and King's Creek killifish to Elizabeth River sediments, menadione, or t-butyl hydroperoxide, and measured the following antioxidant parameters: total oxyradical scavenging capacity (TOSC); glutathione content (total and disulfide); activities of glutathione reductase (GR); glutathione peroxidase (GPx); and glutamate cysteine ligase (GCL) activities and protein levels of copper-zinc superoxide dismutase (CuZnSOD); and protein levels of manganese superoxide dismutase (MnSOD). Exposure to Elizabeth River sediments lead to consistent increases in total glutathione concentrations, GR activities, and MnSOD protein levels, and in some cases increased GPx and GCL activities, in both populations. In addition, Elizabeth River offspring (larvae) showed higher basal TOSC values, glutathione concentrations, and MnSOD protein levels. These data suggest that upregulated antioxidant defenses play a role in both short-term (physiological) and heritable (multigenerational/evolutionary) tolerance of the toxicity of these Superfund sediments. The responses of specific antioxidant parameters, including sex-specific responses in the cases of glutathione concentrations and GR activity, are also discussed.

Acclimatization↗
PubMed1992

The population biology and evolutionary significance of Ty elements in Saccharomyces cerevisiae.

The basic structure and properties of Ty elements are considered with special reference to their role as agents of evolutionary change. Ty elements may generate genetic variation for fitness by their action as mutagens, as well as by providing regions of portable homology for recombination. The mutational spectra generated by Ty1 transposition events may, due to their target specificity and gene regulatory capabilities, possess a higher frequency of adaptively favorable mutations than spectra resulting from other types of mutational processes. Laboratory strains contain between 25-35 elements, and in both these and industrial strains the insertions appear quite stable. In contrast, a wide variation in Ty number is seen in wild isolates, with a lower average number/genome. Factors which may determine Ty copy number in populations include transposition rates (dependent on Ty copy number and mating type), and stabilization of Ty elements in the genome as well as selection for and against Ty insertions in the genome. Although the average effect of Ty transpositions are deleterious, populations initiated with a single clone containing a single Ty element steadily accumulated Ty elements over 1,000 generations. Direct evidence that Ty transposition events can be selectively favored is provided by experiments in which populations containing large amounts of variability for Ty1 copy number were maintained for approximately 100 generations in a homogeneous environment. At their termination, the frequency of clones containing 0 Ty elements had decreased to approximately 0.0, and the populations had became dominated by a small number of clones containing > 0 Ty elements. No such reduction in variability was observed in populations maintained in a structured environment, though changes in Ty number were observed. The implications of genetic (mating type and ploidy) changes and environmental fluctuations for the long-term persistence of Ty elements within the S. cerevisiae species group are discussed.

Biological Evolution↗
PubMed2026

Spatiotemporal patterns of Rift Valley fever virus in Africa: a retrospective genomic epidemiology and phylodynamic modelling study.

BACKGROUND: Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic pathogen causing outbreaks in humans and ruminants across Africa and the Arabian Peninsula. Originally restricted to the Great Rift Valley, RVFV has expanded geographically, prompting its classification by WHO as a pathogen of pandemic potential. We investigated the evolutionary and spatial dynamics of RVFV across Africa. METHODS: We used genomic data generated at the International Livestock Research Institute Nairobi genomic laboratory (BioProject PRJNA1106221) and combined with publicly available datasets retrieved from the National Center for Biotechnology (NCBI) GenBank nucleotide database. In retrieving RVFV genome sequences from the NCBI GenBank, we applied the search terms "Rift Valley fever virus segment L AND 6404[SLEN]", "Rift Valley fever virus segment M AND 3885[SLEN]", and "Rift Valley fever virus segment S AND 1520:1690[SLEN]" for L (Large), M (Medium), and S (Small) segments, respectively. For sequences without additional spatiotemporal information, we searched PubMed to extract the associated sequence metadata. We performed molecular clock analysis, phylogenetic inference, phylodynamic modelling (continuous phylogeographic reconstruction), and landscape phylogeography on the three RVFV genome segments (L, M, and S). We aimed to assess evolutionary rates, dispersal patterns, and environmental drivers. Focus was placed on lineage C, the most widely distributed variant. FINDINGS: The global dataset used in this study consisted of large (n=236), medium (n=237), and small (n=247), which were further filtered to exclude potential reassortants and vaccine strains. Genome sequences retrieved from NCBI GenBank database comprised large (n=180), medium (n=184), and small (n=202). The genome sequences from retrospective human and livestock isolates comprised large (n=56), medium (n=53), and small (n=45) collected in Burundi (2018), Kenya (2007, 2018, 2019, 2021, and 2022), and Rwanda (2018 and 2022). Our dataset revealed that RVFV exhibited low overall genetic diversity. Lineage C, however, showed evidence of active evolution, with substitution rates ranging from 3·58 × 10-4 to 9·76 × 10-4 substitutions per site per year. This lineage probably originated in Zimbabwe in the mid-1970s and has since expanded across eastern and southern Africa. Phylogeographic reconstructions revealed rapid spread, with diffusion coefficients exceeding 50 000 km2 per year. INTERPRETATION: Lineage C appears capable of establishing endemic transmission in new regions, with ongoing diversification observed during interepidemic periods. These observations reinforce the value of continuous genomic surveillance, particularly during cryptic transmission phases when adaptive mutations might emerge. Although further evidence is needed, observed trends in climate variability and land-use change point to the potential benefit of targeted surveillance in settings that could be at increased risk, including urban centres and wetlands. FUNDING: This work was supported by the German Federal Ministry for Economic Cooperation and Development, the Rockefeller Foundation, and the Africa Centres for Disease Control and Prevention.

Rift Valley fever virus↗
PubMed2001

Lack of response to artificial selection on the slope of reaction norms for seasonal polyphenism in the butterfly Bicyclus anynana.

The tropical butterfly Bicyclus anynana shows adaptive phenotypic plasticity in response to wet-dry seasonality. The wet season form (WSF) has a conspicuous wing pattern with large eyespots, whereas the dry season form (DSF) lacks eyespots and therefore has a more cryptic appearance. Temperature is the main factor controlling this difference: rearing larvae at a low (<19 degrees C) temperature in the laboratory results in the DSF, whereas rearing at a high (>23 degrees C) temperature induces the WSF. We applied truncation selection in opposite directions in successive generations reared at two alternating temperatures (18.5 degrees C and 23.5 degrees C) to increase (for two High Plasticity (HP) lines), and decrease (for two Low Plasticity (LP) lines) wing pattern plasticity. Plasticity was assessed by partitioning full-sib families over four rearing temperatures (18.5 degrees C, 20.5 degrees C, 21.5 degrees C and 23.5 degrees C). Several wing pattern elements were measured for which the first principal component (PC1) provides a useful summary. The slopes of reaction norms for PC1 were significantly steeper in the HP lines than in the LP lines; however, the selection lines did not always differ significantly from the unselected stock. The results of crosses between the replicates of the selection lines gave no indication for effects of inbreeding. We argue that high, positive genetic correlations across temperatures retard a response to selection in opposite directions in different environments. This is discussed with respect to potential evolutionary constraints in natural populations in these butterflies.

Adaptation, Biological↗
PubMed1993

Fetal experience revealed by rats: psychobiological insights.

Psychobiological studies of fetal ontogenesis in non-human species, particularly in laboratory rat, now have much to offer students of human development. Psychobiological approaches are 'ecologically' oriented which, for fetal research, implies consideration of the adaptive significance of behavior within the uterine habitat. Consistent with this orientation is a concern for the sensory capabilities of the fetus, especially in relation to the specific forms and levels of stimulation that occur within the uterine milieu. We describe recent advances in these areas, and the impressive range of fetal responses to naturally-occurring (often mother-induced) forms of sensory stimulation. To the psychobiologist, sensory-evoked responses of all kinds constitute the fetus' experience and much has been learned about the roles of such experience in regulating the rate, direction, and form of development. Indeed, experience can be considered a significant, if not neglected, mechanism of development. Finally, we briefly survey some contemporary analyses of the interrelations between developmental and evolutionary processes. We use onset of sensory function (which occurs in a stereotyped sequence in every vertebrate species for which there are data) as a developmental phenotype. Phylogenetic considerations of sensory development are discussed. By identifying and clarifying some of the intellectual questions that guide perinatal research with non-human species, we hope to improve the appreciation of novel insights and interpretive strategies that derive from different approaches. This is bound to enhance the study of human development and to improve the design and use of animal models.

Animals↗
PubMed2001

Genomic characterization of Helicobacter hepaticus: ordered cosmid library and comparative sequence analysis.

Helicobacter hepaticus is an important pathogen in laboratory mice and induces the development of liver tumors and gastrointestinal disease in susceptible strains of mice. In this study, a miniset of 36 cosmid clones from a genomic library of H. hepaticus was ordered and grouped into four large contigs representing approximately 1 Mb of the H. hepaticus genome using PCR, DNA sequencing, Southern and dot-blot hybridization and pulsed-field gel electrophoresis. From the 200-300 terminal nucleotide sequences of 38 cosmid clones, 56 coding regions were predicted, of which 51 were found to have orthologs in the public databases and five appeared to be unique to H. hepaticus. Of these 51 genes, 36 have orthologs in Helicobacter pylori and 25 display the highest sequence similarity to H. pylori. However, chromosomal positions of these genes are not conserved between these two helicobacters. In addition, 10 H. hepaticus genes had the highest sequence similarity to orthologs in Campylobacter jejuni. The GC content in a randomly selected 21-kb H. hepaticus genomic sequence was 35.8%, which approximates the average between H. pylori (39%) and C. jejuni (30.6%). These results demonstrate that: (1) H. hepaticus is more closely related to H. pylori than C. jejuni; (2) significant genomic alterations exist between H. hepaticus and H. pylori, including gene organization, protein sequences and GC content, probably in part due to specific adaptation to distinct ecological niches.

Animals↗
PubMed2006

Phenotypic plasticity and experimental evolution.

Natural or artificial selection that favors higher values of a particular trait within a given population should engender an evolutionary response that increases the mean value of the trait. For this prediction to hold, the phenotypic variance of the trait must be caused in part by additive effects of alleles segregating in the population, and also the trait must not be too strongly genetically correlated with other traits that are under selection. Another prediction, rarely discussed in the literature, is that directional selection should favor alleles that increase phenotypic plasticity in the direction of selection, where phenotypic plasticity is defined as the ability of one genotype to produce more than one phenotype when exposed to different environments. This prediction has received relatively little empirical attention. Nonetheless, many laboratory experiments impose selection regimes that could allow for the evolution of enhanced plasticity (e.g. desiccation trials with Drosophila that last for several hours or days). We review one example that involved culturing of Drosophila on lemon for multiple generations and then tested for enhanced plasticity of detoxifying enzymes. We also review an example with vertebrates that involves selective breeding for high voluntary activity levels in house mice, targeting wheel-running behavior on days 5+6 of a 6-day wheel exposure. This selection regime allows for the possibility of wheel running itself or subordinate traits that support such running to increase in plasticity over days 1-4 of wheel access. Indeed, some traits, such as the concentration of the glucose transporter GLUT4 in gastrocnemius muscle, do show enhanced plasticity in the selected lines over a 5-6 day period. In several experiments we have housed mice from both the Selected (S) and Control (C) lines with or without wheel access for several weeks to test for differences in plasticity (training effects). A variety of patterns were observed, including no training effects in either S or C mice, similar changes in both the S and C lines, greater changes in the S lines but in the same direction in the C lines, and even opposite directions of change in the S and C lines. For some of the traits that show a greater training effect in the S lines, but in the same direction as in C lines, the greater effect can be explained statistically by the greater wheel running exhibited by S lines ('more pain, more gain'). For others, however, the differences seem to reflect inherently greater plasticity in the S lines (i.e. for a given amount of stimulus, such as wheel running/day, individuals in the S lines show a greater response as compared with individuals in the C lines). We suggest that any selection experiment in which the selective event is more than instantaneous should explore whether plasticity in the appropriate (adaptive) direction has increased as a component of the response to selection.

Adaptation, Physiological↗
PubMed1987

Adaptation of Drosophila melanogaster populations to high mutation pressure: evolutionary adjustment of mutation rates.

Evolutionary aspects of high mutation pressure were studied in laboratory populations of Drosophila melanogaster that have irradiation histories up to 600 generations. Dose-response regressions for the x-ray induction of various types of mutation were obtained from six of these populations. The sensitivity of these irradiated populations relative to an unirradiated control population was characterized by dose reduction factors. Sensitivity decreased stepwise with the stepwise increase in irradiation levels to which the populations had been exposed every generation (0 R, 2 kR, 4 kR, 8 kR; 1 R = 0.258 mC/kg) but remained the same over hundreds of generations when the irradiation levels were constant. Resistance is controlled by single genetic factors. Additional factors evolved in subpopulations exposed to increased irradiation levels, and different factors evolved in populations that were kept separate from the beginning of their irradiation histories. Two of three factors persisted in subpopulations no longer irradiated, but one factor disappeared; this last one behaved like a transposon. Factors of relative radio-resistance are stage specific (immature oocytes) and some of them are assumed to modify or control mutation-rate genes. The resistance factors enable populations to achieve an equilibrium between the amounts of environmental mutagens and intrinsic mutation rates.

Adaptation, Physiological↗
PubMed2006

Testing three models on the adaptive significance of protandric simultaneous hermaphroditism in a marine shrimp.

Protandric simultaneous hermaphroditism, as reported for shrimps in the genus Lysmata, is a sexual system in which individuals invariably reproduce as males first and later in life as simultaneous hermaphrodites. I tested three models (i.e., sex-dependent energetic costs, sex-dependent mortality rates and sex-dependent time commitments) in an attempt to explain the adaptive value of protandric simultaneous hermaphroditism in the shrimp L. wurdemanni. Specific assumptions and predictions of each model were evaluated using manipulative experiments. In the laboratory, males grew faster than simultaneous hermaphrodites of the same size and age, an indication that the female function incurs higher energetic costs of reproduction than the male function. Also, large SHPs were more successful in monopolizing food than small males. The sex-dependent growth rate and size-dependent resource holding power agree with predictions of the sex-dependent energetic cost model. The time that simultaneous hermaphrodites required for replenishing their sperm reservoirs after mating as males was much shorter (2 days) than the time required to brood one clutch of embryos (11 days). Also, small simultaneous hermaphrodites experienced heavier mortality due to predatory fishes than large ones. The sex-dependent reproductive time commitment and size-dependent mortality agree with predictions of the sex-dependent time commitment model. Conversely, I found no evidence that the sex-dependent mortality model explains protandric simultaneous hermaphroditism in the studied species. In contrast to model predictions, mortality due to predatory fishes suffered by simultaneous hermaphrodites was not greater than that suffered by males of the same body size. In L. wurdemanni, the relationship between sex-specific investment and reproductive success seems to change during ontogeny in a way that is consistent with an adaptive adjustment of sex allocation to improve age-specific reproductive success.

Adaptation, Physiological↗
PubMed2000

Calorie restriction and aging: a life-history analysis.

The disposable soma theory suggests that aging occurs because natural selection favors a strategy in which fewer resources are invested in somatic maintenance than are necessary for indefinite survival. However, laboratory rodents on calorie-restricted diets have extended life spans and retarded aging. One hypothesis is that this is an adaptive response involving a shift of resources during short periods of famine away from reproduction and toward increased somatic maintenance. The potential benefit is that the animal gains an increased chance of survival with a reduced intrinsic rate of senescence, thereby permitting reproductive value to be preserved for when the famine is over. We describe a mathematical life-history model of dynamic resource allocation that tests this idea. Senescence is modeled as a change in state that depends on the resources allocated to maintenance. Individuals are assumed to allocate the available resources to maximize the total number of descendants. The model shows that the evolutionary hypothesis is plausible and identifies two factors, both likely to exist, that favor this conclusion. These factors are that survival of juveniles is reduced during periods of famine and that the organism needs to pay an energetic "overhead" before any litter of offspring can be produced. If neither of these conditions holds, there is no evolutionary advantage to be gained from switching extra resources to maintenance. The model provides a basis to evaluate whether the life-extending effects of calorie-restriction might apply in other species, including humans.

Adaptation, Physiological↗
PubMed2001

How many species of cichlid fishes are there in African lakes?

The endemic cichlid fishes of Lakes Malawi, Tanganyika and Victoria are textbook examples of explosive speciation and adaptive radiation, and their study promises to yield important insights into these processes. Accurate estimates of species richness of lineages in these lakes, and elsewhere, will be a necessary prerequisite for a thorough comparative analysis of the intrinsic and extrinsic factors influencing rates of diversification. This review presents recent findings on the discoveries of new species and species flocks and critically appraises the relevant evidence on species richness from recent studies of polymorphism and assortative mating, generally using behavioural and molecular methods. Within the haplochromines, the most species-rich lineage, there are few reported cases of postzygotic isolation, and these are generally among allopatric taxa that are likely to have diverged a relatively long time in the past. However, many taxa, including many which occur sympatrically and do not interbreed in nature, produce viable, fertile hybrids. Prezygotic barriers are more important, and persist in laboratory conditions in which environmental factors have been controlled, indicating the primary importance of direct mate preferences. Studies to date indicate that estimates of alpha (within-site) diversity appear to be robust. Although within-species colour polymorphisms are common, these have been taken into account in previous estimates of species richness. However, overall estimates of species richness in Lakes Malawi and Victoria are heavily dependent on the assignation of species status to allopatric populations differing in male colour. Appropriate methods for testing the specific status of allopatric cichlid taxa are reviewed and preliminary results presented.

Africa↗
PubMed2006

Analysis of the near full length genomes of HIV-1 subtypes B, F and BF recombinant from a cohort of 14 patients in São Paulo, Brazil.

The human immune deficiency virus (HIV) exhibits strikingly tremendous amount of genetic variability. Such feature is critically important for the virus to adapt to environmental changes by escaping the host immune system and by escaping candidate vaccine. Therefore, understanding of such diversity is fundamental for the design of successful drugs or vaccine, which is urgently needed to bring the HIV/AIDS epidemic under control. In this study, we investigated the magnitude of diversity of the HIV-1 near full-length genomes from patients previously assigned as infected with non-recombinant HIV-1 subtypes B and F1 variants based on small portion of viral genome. HIV-1 proviral DNA was extracted from 14 samples previously classified in our laboratory as six subtypes B and eight subtypes F on the basis of small amplicon sequencing. Reamplifications of DNA from these samples were carried out by an overlapping PCR followed by direct sequencing. The data were phylogenetically inferred. Sequence analysis revealed that two out of six partially identified subtype B and six out of eight partially identified subtype F were in fact BF recombinants throughout their full genomes. Two pairs BF recombinants had identical genomic recombination structure and distinct from the Argentinean CRF 12_BF strains, probably represents a novel circulating recombinant forms in Brazil. Our data provided new genetic material of some of the HIV-1 subtypes currently circulating in the country and points to the widespread of BF recombinants which are expected to change the epidemic nature by approaching the level of subtype B in Brazil.

Adult↗
PubMed2000

Vegetative and reproductive innovations of early land plants: implications for a unified phylogeny.

As the oldest extant lineages of land plants, bryophytes provide a living laboratory in which to evaluate morphological adaptations associated with early land existence. In this paper we examine reproductive and structural innovations in the gametophyte and sporophyte generations of hornworts, liverworts, mosses and basal pteridophytes. Reproductive features relating to spermatogenesis and the architecture of motile male gametes are overviewed and evaluated from an evolutionary perspective. Phylogenetic analyses of a data set derived from spermatogenesis and one derived from comprehensive morphogenetic data are compared with a molecular analysis of nuclear and mitochondrial small subunit rDNA sequences. Although relatively small because of a reliance on water for sexual reproduction, gametophytes of bryophytes are the most elaborate of those produced by any land plant. Phenotypic variability in gametophytic habit ranges from leafy to thalloid forms with the greatest diversity exhibited by hepatics. Appendages, including leaves, slime papillae and hairs, predominate in liverworts and mosses, while hornwort gametophytes are strictly thalloid with no organized external structures. Internalization of reproductive and vegetative structures within mucilage-filled spaces is an adaptive strategy exhibited by hornworts. The formative stages of gametangial development are similar in the three bryophyte groups, with the exception that in mosses apical growth is intercalated into early organogenesis, a feature echoed in moss sporophyte ontogeny. A monosporangiate, unbranched sporophyte typifies bryophytes, but developmental and structural innovations suggest the three bryophyte groups diverged prior to elaboration of this generation. Sporophyte morphogenesis in hornworts involves non-synchronized sporogenesis and the continued elongation of the single sporangium, features unique among archegoniates. In hepatics, elongation of the sporophyte seta and archegoniophore is rapid and requires instantaneous wall expandability and hydrostatic support. Unicellular, spiralled elaters and capsule dehiscence through the formation of four regular valves are autapomorphies of liverworts. Sporophytic sophistications in the moss clade include conducting tissue, stomata, an assimilative layer and an elaborate peristome for extended spore dispersal. Characters such as stomata and conducting cells that are shared among sporophvtes of mosses, hornworts and pteridophytes are interpreted as parallelisms and not homologies. Our phylogenetic analysis of three different data sets is the most comprehensive to date and points to a single phylogenetic solution for the evolution of basal embryophytes. Hornworts are supported as the earliest divergent embryophyte clade with a moss/liverwort clade sister to tracheophytes. Among pteridophytes, lycophytes are monophyletic and an assemblage containing ferns, Equisetum and psilophytes is sister to seed plants. Congruence between morphological and molecular hypotheses indicates that these data sets are tracking the same phylogenetic signal and reinforces our phylogenetic conclusions. It appears that total evidence approaches are valuable in resolving ancient radiations such as those characterizing the evolution of early embryophytes. More information on land plant phylogeny can be found at: http: //www.science.siu.edu/ landplants/index.html.

Biological Evolution↗
PubMed1977

Adaptation at specific loci. I. Natural selection on phosphoglucose isomerase of Colias butterflies: Biochemical and population aspects.

Electrophoretic variants of phosphoglucose isomerase (PGI) in Colias butterflies have been studied from field and laboratory viewpoints. The transmission pattern is that of a dimeric enzyme controlled by one structural gene locus. Populations usually harbor four to six allelic mobility classes. These mobility classes are shared among species complexes, though their frequencies differ widely. Preliminary Ferguson plot analysis of the variants has been carried out. Purified preparations of Colias PGI alleles are more effective in standardizing Ferguson plots than heterologous proteins, such as ferritin. Variation of Ferguson plot parameters is not an infallible guide to electrophoretically "cryptic alleles," as one putative case proved to be due to nonallele-specific effects. S, M, and F mobility classes in two Colias semispecies show the same retardation coefficients in Ferguson plots. Adults early in the flight periods of their nonoverlapping generations show genotype frequencies in Hardy-Weinberg equilibrium, but heterozygote excess develops as the insects age. Simple directional selection and large-scale population mixing are unlikely to be causes of this, although several other selection modes remain possible. Identical-by-descent lines of the four frequent-to-common alleles in C. eurytheme have been set up in culture, and enzyme has been purified from these for study of functional properties. Major differenecs in heat stability and in various kinetic parameters are found among the ten possible genotypes. In some cases, heterosis for kinetic parameters is seen; in other cases, opposing trends in kinetic function and heat stability create potential for net heterosis in function. Possible interpretations of these results in an adaptive metabolic context are discussed, and directions for further work are stated.

Animals↗
PubMed2003

Genetic architecture of differences between populations of cowpea weevil (Callosobruchus maculatus) evolved in the same environment.

We investigated the genetic architecture underlying differentiation in fitness-related traits between two pairs of populations of the seed beetle Callosobruchus maculatus (Coleoptera: Bruchidae). These populations had geographically distant (> 2000 km) origins but evolved in a uniform laboratory environment for 120 generations. For each pair of populations (Nigeria x Yemen and Cameroon x Uganda) we estimated the means of five fitness-related characters and a measure of fitness (net reproductive rate R0) in each of the parental populations and 12 types of hybrids (two F1 and two F2 lines and eight backcrosses). Models containing up to nine composite genetic parameters were fitted to the means of the 14 lines. The patterns of line means for all traits in the Nigeria x Yemen cross and for four traits (larval survival, developmental rate, female body weight, and fecundity) in the Cameroon x Uganda cross were best explained by models including additive, dominance, and maternal effects, but excluding epistasis. We did not find any evidence for outbreeding depression for any trait. An epistatic component of divergence was detected for egg hatching success and R0 in the Cameroon x Uganda cross, but its sign was opposite to that expected under outbreeding depression, that is, additive x additive epistasis had a positive effect on the performance of F2 hybrids. All traits except fecundity showed a pattern of heterosis. A large difference of egg-hatching success between the two reciprocal F1 lines in that cross was best explained as fertilization incompatibility between Cameroon females and sperm carrying Uganda genes. The results suggest that these populations have not converged to the same life-history phenotype and genetic architecture, despite 120 generations of uniform natural selection. However, the absence of outbreeding depression implies that they did not evolve toward different adaptive peaks.

Animals↗