The methylation status of DNA derived from potato plants recovered from slow growth

The in vitro conservation of potato using tissue culture medium supplemented with the growth retardant mannitol causes morphological changes in the propagated material. These culture conditions seem to have an affect on the DNA extracted from the regenerated plants, when it is digested by the methylation sensitive restriction enzymes Hpa II/Msp I and Eco RII/Bst NI, compared to the control material. In most of these plants, there appears to be preferential methylation of nuclear domains that contain Eco RII/Bst NI recognition sites in contrast to those that contain Hpa II/Msp I sites. The refractory nature of the isolated DNA to these restriction enzymes was attributed to hypermethylation of genomic DNA and the ribosomal RNA genes. These findings indicate that methylation of DNA sequences may be an adaptive response to conditions of high osmotic stress. The importance of these results for the conservation of potato germplasm and international exchange is discussed.     

Evolutionary epistemology as an overlapping,interlevel theory

I examine the branch of evolutionary epistemology which tries to account for the character of cognitive mechanisms in animals and humans by extending the biological theory of evolution to the neurophysiological substrates of cognition. Like Plotkin, I construe this branch as a struggling science, and attempt to characterize the sort of theory one might expect to find this truly interdisciplinary endeavor, an endeavor which encompasses not only evolutionary biology, cognitive psychology, and developmental neuroscience, but also and especially, the computational modeling of artificial life programming; I suggest that extending Schaffner's notion of interlevel theories to include both horizontal and vertical levels of abstraction best fits the theories currently being developed in cognitive science. Finally, I support this claim with examples drawn from computational modeling data using the genetic algorithm.     

3. Genetic conservation in seed banks

The safest and most economical and convenient way of preserving the genetic resources of the majority of crop plants is by long-term seed storage. The technology is well developed, but recent research resulting from a greater understanding of behaviour at very low water potentials is leading to further improvements     

The application of reproductive technology to endangered species breeding programmes

Captive breeding plays an increasingly important role in species conservation, but special problems are encountered in achieving the ideal of a demographically stable but genetically diverse population. Breeding programmes involving co-operation among a number of centres are now being developed which will overcome some of these difficulties by identifying individual animals, genetic lineages or age cohorts from which to breed. Application of techniques such as artificial insemination, embryo transfer and semen collection and storage, as well as the monitoring of reproductive status will contribute to the success of such programmes. The usefulness of these procedures for various population problems is discussed and criteria for their appropriate implementation within breeding programmes is outlined.     

Population differentiation and evolution in the common guillemot Uria aalge

Common (Uria aalge) and Brünnich's guillemots (U. Iomvia) are colonial seabirds that nest in temperate to arctic oceans throughout the Northern hemisphere. They are very similar in the characteristics of ecology, demography and life history that are thought to determine the extent of differentiation among populations, yet geographic variation in morphology is notably greater in common guillemots. Despite evidence of strong natal philopatry, previous analyses of allozymes and the mitochondrial cytochrome b gene revealed little genetic differentiation among North Atlantic colonies of Brünnich's guillemots. To determine if the more extensive morphological variability in common guillemots reflects greater genetic variability, we sequenced part of the cytochrome b gene for 160 common guillemots from 10 colonies distributed throughout the Northern hemisphere. Genotype frequencies and phylogenetic relationships among genotypes both indicated that Atlantic and Pacific populations are genetically distinct. Genetic divergence among genotypes suggested that differentiation of these populations has resulted from separation by Pleistocene glaciers and the Bering Landbridge, as well as by currently unsuitable breeding habitat in the Arctic Ocean. Cytochrome b genotype frequencies also differed among Atlantic colonies, and appeared to define a cline similar to that described for morphological characters. Analyses of sequence variation suggested that this variation probably results from secondary contact between two refugial populations from the Pleistocene glaciations, rather than from isolation by distance or selection. In contrast, the Atlantic population of Brünnich's guillemots appears to have arisen through recent expansion of a single homogeneous refugial population.     

GENETIC CONSTRAINTS ON MACROEVOLUTION: THE EVOLUTION OF HOST AFFILIATION IN THE LEAF BEETLE GENUS OPHRAELLA

We hypothesize that the evolution of an ecologically important character, the host associations of specialized phytophagous insects, has been influenced by limitations on genetic variation. Using as a historical framework a phylogenetic reconstruction of the history of host associations in the beetle genus Ophraella (Chrysomelidae), we have employed quantitative-genetic methods to screen four species for genetic variation in larval survival, oviposition (in one species only), and feeding responses to their congeners' host plants, in the Asteraceae. We here report results of studies of one species and evaluate the results from all four. Analysis of half-sib/full-sib families and of progenies of wild females of O. notulata, a specialist on Iva (Ambrosiinae), provided evidence of genetic variation in larval consumption of five of six test plants and in adult consumption of four of six. Larval mortality was complete on five plants; only on Ambrosia, a close relative of the natural host, was there appreciable, and genetically variable, survival. Oviposition on Ambrosia showed marginally significant evidence of genetic variation; a more distantly related plant elicited no oviposition at all. In compiling results from four Ophraella species, reported in this and two other papers, we found no evidence of genetic variation in 18 of 39 tests of feeding responses and 14 of 16 tests of larval survival on congeners' hosts. This result is consistent with the hypothesis that absence or paucity of genetic variation may constrain or at least bias the evolution of host associations. The lower incidence of genetic variation in survival than in feeding behavior may imply, according to recent models, that avoidance is a more common evolutionary response to novel plants than adaptation. The usually great disparity between mean performance on congeners' hosts and the species' natural hosts, and an almost complete lack of evidence for negative genetic correlations, argue against the likelihood that speciation has occurred by sympatric host shift. The presence versus apparent absence of genetic variation in consumption was correlated with the propinquity of relationship between the beetle species tested and the species that normally feeds on the test plant, suggesting that the history of host shifts in Ophraella has been guided in part by restrictions on genetic variation. It was also correlated with the propinquity of relationship between a test plant and the beetle's natural host. The contributions of plant relationships and insect relationships, themselves correlated in part, to the pattern of genetic variation, are not readily distinguishable, but together accord with phylogenetic evidence that these and other phytophagous insects adapt most readily to related plants. In this instance, therefore, the macroevolution of an ecologically important character appears to have been influenced by genetic constraints. We hypothesize that absence of the structural prerequisites for genetic variation in complex characters may affect genetic variation and the trajectory of evolution.     

Mitochondria transfer into mouse ova by microinjection

A method for mitochondria isolation and interspecific transfer of mitochondria was developed in mice. Mitochondria were isolated from Mus spretus liver samples for microinjection into fertilized ova obtained from superovulated M. musculus domesticus females. Electron microscopic observations of mitochondria preparations used for microinjection demonstrated intact mitochondrial vesicles with little microsomal contamination. Species-specific nested PCR primers complementary to sequence differences in the mitochondrial DNA D-loop region revealed high rates of successful transfer of foreign mitochondria after isolation and injection into zygotes cultured through the blastocyst stage of embryonic development. Of 217 zygotes, 67 survived mitochondria injection and 23 out of 37 zygotes developed were at the blastocyst-stage of embryonic development after 4.5 days of in vitro culture. All 23 of these blastocysts contained detectable levels of foreign mitochondria. These results represent an initial step in developing a model system to study mitochondrial dynamics and development of therapeutic strategies for human metabolic diseases affected by aberrations in mitochondrial function or mutation     

Genetic variability in the European minnow,Phoxinus phoxinus (L.)

An electrophoretic study of genetic variation at 11 loci was performedfor a population of European minnows, Phoxinus phoxinus (L.). Ten loci, EST-1 ^*, EST-2 ^* EST-3 ^*,GPD-1 ^*,GPD-2 ^*,GPI-1 ^*,GPI-2 ^*,MPI ^*,6PGD ^* and PGM ^* were polymorphic. IDH ^*wasmonomorphic. The mean number of heterozygotic loci over all 176 fish was 3.05 ± 0.104(SE). Observed mean heterozygosity was 0.28±0.058(SE) and expected mean heterozygosity was 0.27±0.054(SE). EST-2 ^*, EST-3 ^* andPGM ^* were not in Hardy-Weinberg equilibrium. Length,condition, parasite numbers or male breeding characters, i.e. red colorationand tubercles, were not influenced by single enzyme loci.     

Effects of asexual reproduction on the neighborhood area of cyclical parthenogens

The habitat occupied by a subpopulation and withinwhich there is random mating is known as itsneighborhood area. Neighborhood area is dependenton dispersal rates and organisms with low rates ofdispersal are expected to have small neighborhoodareas. In the absence of evolutionary forces,neighborhood areas under sexual reproduction will beconstant in size as long as dispersal patterns do notchange. This scenario differs when reproduction is bycyclical parthenogenesis since recombination anddispersal may occur in different generations. Ingeneral, dispersal distances increase with the numberof parthenogenetic generations. We show that cyclicalparthenogenesis increases neighborhood area which,concomitantly, decreases the potential for geneticsubdivision. It is noteworthy, however, that theincrease in neighborhood area is a decreasing functionof the number of parthenogenetic generations.This mechanism may have important implications for thepopulation structure of planktonic rotifers living ina horizontally undifferentiated habitat. In suchhabitats organisms are effectively unrestricted intheir lateral movements. Because rotifers typicallyhave low dispersal rates spatial geneticdiscontinuities may develop that divide the populationinto genetically distinct subpopulations. Counteringthis tendency is the increased neighborhood areaproduced by dispersal during the parthenogeneticphase. Thus cyclical parthenogenesis in organismslike rotifers may have important and previouslyunreported effects on the population's geneticstructure.