Global convergence properties in multilocus viability selection models: the additive model and the Hardy-Weinberg law

A natural coordinate system is introduced for the analysis of the global stability of the Hardy-Weinberg (HW) polymorphism under the general multilocus additive viability model. A global convergence criterion is developed and used to prove that the HW polymorphism is globally stable when each of the loci is diallelic, provided the loci are overdominant and the multilocus recombination is positive. As a corollary the multilocus Hardy-Weinberg law for neutral selection is derived.Research supported in part by NIH grants GM 39907-01, GM 10452-26 and NSF Grant DMS 86-06244Research supported in part by a US-Israel Binational Science Foundation grant 85-00021 and NIH grant GM 28016     

Ribosomal DNA non-transcribed spacer polymorphism in subterranean mole rats: genetic differentiation,environmental correlates and phylogenetic relationships

Summary An analysis is presented of genetic differentiation in the non-transcribed spacers of ribosomal DNA (NTS rDNA). Diversity, environmental correlates and the phylogenetic relationships are examined within and between species of the actively speciating subterranean mole rat, superspeciesSpalax ehrenbergi (2n=52, 54, 58, 60) in Israel. This analysis is based on a previous study of the geographic distribution of restriction fragment length polymorphisms of NTS rDNA. Here we present results indicating that NTS rDNA diversity exists mostly (66%) within populations, while 20% is between populations within species, and 14% between species. Multivariate discriminant analysis succeeded in separating 10 of the 13 populations (77%) into their correct chromosomal species, on the basis of the combination of three NTS rDNA repetypes. The phylogenetic relationships suggest that the complex involves two pairs of closely related species (2n=52–54 and 2n=58–60). NTS rDNA diversity, as well as the decrease southward in frequency of repetype C, are correlated with climatic factors of humidity and temperature. These data are discussed in terms of the evolutionary forces of migration and selection which may cause NTS rDNA differentiation. Climatic selection appears to be the major differentiating factor of NTS rDNA.     

Ethanol production from xylose by Thermoanaerobacter ethanolicus in batch and continuous culture

The fermentation of xylose by Thermoanaerobacter ethanolicus ATCC 31938 was studied in pH-controlled batch and continuous cultures. In batch culture, a dependency of growth rate, product yield, and product distribution upon xylose concentration was observed. With 27 mM xylose media, an ethanol yield of 1.3 mol ethanol/mol xylose (78% of maximum theoretical yield) was typically obtained. With the same media, xylose-limited growth in continuous culture could be achieved with a volumetric productivity of 0.50 g ethanol/liter h and a yield of 0.42 g ethanol/g xylose (1.37 mol ethanol/mol xylose). With extended operation of the chemostat, variation in xylose uptake and a decline in ethanol yield was seen. Instability with respect to fermentation performance was attributed to a selection for mutant populations with different metabolic characteristics. Ethanol production in these T. ethanolicus systems was compared with xylose-to-ethanol conversions of other organisms. Relative to the other systems, T. ethanolicus offers the advantages of a high ethanol yield at low xylose concentrations in batch culture and of a rapid growth rate. Its disadvantages include a lower ethanol yield at higher xylose concentrations in batch culture and an instability of fermentation characteristics in continuous culture.     

Hepatocystis in populations of baboons (Papio hamadryas s.l.) of Tanzania and Ethiopia

Bloodsmears from 119 yellow baboons (Papio hamadryas cynocephalus) in six groups in Mikumi National Park, Tanzania, and from 189 olive (P.h. anubis) hamadryas (P.h. hamadryas) and hybrid baboons in three groups in Awash National park, Ethiopia showed differing levels of infection with Hepatocystis simiae. 0% to 42% in the Tanzanian groups were carriers of the parasite but none of the Ethiopian baboons was positive. The remarkable absence of H. simiae in the Ethiopian baboons is believed to be related to environmental factors that exclude transmission in the absence of the Culicoides vector.     

Effects of selection criteria on yield stability in chickpea (Cicer arietinum L.)

Summary Selection in the F₃ generation for seed yield, fruiting branches/plant, effective pods/plant, and seed index (100-seed weight) was carried out in two chickpea crosses. Sixty F₅ lines (15 lines/selection criterion) along with check variety were evaluated for seed yield in three distinct environments. The effects of selection criteria on yield stability was examined using linear regression approach and genotype-grouping technique. There were no differences between selection criteria for linear yield responses of F₅ lines to different environments. Within all four selection criteria the lines showed similar linear responses. The non-linear component was relatively higher for lines selected for effective pods and seed index than lines selected for yield and fruiting branches. On the basis of mean yield and coefficient of variation across environments, the seed index was the least effective selection criterion for developing high yielding and stable lines. When the results of stability parameters and genotype-grouping technique were considered together, selection for yield and fruiting branches was highly effective for isolating stable and high yielding lines.     

The genetic structure of a primate species: Rhesus macaques and other Cercopithecine monkeys

Among rhesus macaques (Macaca mulatta)and other cercopithecine monkeys, social groups occupying adjacent home ranges (i.e., members of the same local population) exchange individuals and genes and thus exhibit marked genetic similarities. To assess the degree to which this pattern extends beyond the local population, the genetic structure of M. mulattaand six other primate species was determined using Nei’s (1973) gene-diversity analysis. The genetic similarities seen among social groups in the Dunga Gali population of M. mulatta (Melnick et al.,1984a) can be seen over the entire species range. Comparison of these results with the structures of other similarly organized primate species indicates that (1) the average social group contains most of its local population’s genetic diversity, (2) the average local population contains the majority of the genetic diversity found in the region to which it belongs, and (3) the proportion of species gene diversity found in the average regional population varies substantially between species. Genetic homogeneity within local and regional populations is probably the product of gene flow. The application of a number of analytical models of selection and gene flow strongly suggests that gene flow, genetic drift, and zoogeography offer a more parsimonious and plausible explanation for interspecific variation in regional differentiation than does stabilizing selection.     

Simultaneous modelling of distributional patterns in a guild of eastern-Australian cicadas

Summary The distributions, with respect to habitat structure, of nine species of eastern-Australian cicadas have been shown to be non-random. The most striking consequence of this non-randomness is a marked inverse relationship between habitat breadth and habitat position (terms defined in text). Eight basic models and 12 derived models were used in conjunction with a canonical space to try to account for the ways in which the species of cicadas were distributed with respect to habitat. Several models produced results that were in reasonable agreement with the observed data. The most parsimonious of these corresponds to analytical results of other workers, such as Diamond's (1975) incidence curves, occurrence sequences (Schoener and Schoener 1983), and probability functions (Adler and Wilson 1985). The distributions of cicadas can be modelled by assuming that the species occupy sites independently of one another. These species of cicadas are unlikely to engage in interspecific competition, which is consistent with independence of distributions.     

Resource utilization of sympatric and experimentally allopatric cutthroat trout and Dolly Varden charr

Summary Resource utilization by cutthroat trout (CT) and Dolly Varden charr (DV) was studied 8 years after experimental transfers from sympatry had established reproducing allopatric populations in two nearby fishless lakes. Allopatric DV significantly increased their utilization of shallow-dwelling zoobenthos, and increased their vertical distribution in comparison to that in sympatry. In contrast, allopatric CT showed little change in the proportions of major prey types utilized, and, if anything, restricted their vertical distribution in comparison to that in sympatry. The results can be explained by the hypothesis that the resource use of DV is strongly influenced by interspecific competition from CT, whereas CT largely remains unaffected by this interaction. An alternative hypothesis, that lake differences can explain the differences in resource use between sympatry and allopatry, was evaluated by comparing food resource availability and other biotic and abiotic characteristics of the three study lakes. None of these could account for the shift in resource use by DV between sympatry and allopatry, but lake differences may explain why allopatric CT showed a restricted habitat use in comparison with their sympatric donor stock. The results of this whole-lake transfer experiment are consistent with earlier reported field and laboratory studies, and suggest that the aggressive dominance of CT is the most important mechanism by which DV are displaced from littoral and near-surface habitats in sympathy with CT.     

Background selection by the peppered moth (Biston betularia Linn.): individual differences

The hypothesis that dimorphically coloured, cryptic moths select appropriate rest sites by comparing their body scales to substrate reflectance was tested using typical and melanic morphs of the peppered moth, Biston betularia (L.). Experiments designed to block the individual's inspection of its inherited colour phenotype do not support Kettlewell's contrast/conflict (self-inspection) hypothesis. Instead, tracking of marked moths over successive days revealed individual differences in rest-site selection which were not related to treatments, experience (imprinting), nor closely to a moth's inherited colour pattern. Differences between family broods indicate that some genetic bias in background selection exists. The production of artificially selected lines with consistent but opposing preferences will allow us to investigate the co-evolution of pattern and behaviour.