Intraspecific sexual isolation in Drosophila.

Intraspecific sexual isolation was examined among wild strains of Drosophila malerkotliana, D. parabipectinata and D. pseudoananassae by multiple-choice method in Elens-Wattiaux mating chamber. In D. pseudoananassae, mating between two strains tested was random and isolation estimate was close to one. In one out of 6 crosses, involving geographic strains of D. malerkotliana, there was significant deviation from randomness and isolation estimate remained low which shows non-random (preferential or positive assortative) mating. In D. parabipectinata, the deviation from randomness was statistically significant due to higher number of homogamic matings in three crosses involving wild strains derived from geographically distant places and isolation estimate remained low in these crosses. The results provide evidence for incipient sexual isolation within D. malerkotliana and D. parabipectinata as a result of genetic divergence.     

The Ribosomes of Drosophila. III. RNA and Protein Homology between D. MELANOGASTER and D. VIRILIS

The extent of interspecific homology between D. melanogaster and D. virilis for ribosomal RNA and ribosomal protein was examined using the techniques of two-dimensional gel electrophoresis, and RNA-DNA filter hybridization. Only 2 of the 71 ribosomal proteins resolved were found to be species specific, while comparisons of soluble larval hemolymph protein patterns showed little similarity. Depending on the technique employed, the sequence homology for 18S + 28S ribosomal RNA was found to be between 83–94%, and sequence homology for 5S rRNA was judged to be complete.     

Intraspecific DNA divergence in Drosophila: a study on parthenogenetic D. mercatorum

Drosophila mercatorum is a species that can give rise to totally homozygous parthenogenetic strains. Using the technique of DNA-DNA hybridization, we have assessed the overall single-copy DNA differences among three independently derived strains that represent three independent genomes. Among strains, the average difference between homoduplex and heteroduplex median melting temperatures is 1.3 degrees C. This represents greater than or equal to 1.3% base-pair mismatch. Normalized percent of reassociation indicates further genetic differences, probably reflecting insertion/deletion differences and/or regions of the genome that are highly variable. This overall intraspecific genetic variation is higher than generally is thought to exist but is consistent with growing evidence of extensive DNA diversity within species of invertebrates. High intraspecific DNA variation may be correlated with rapid phyletic rates of evolution. Because of this high level of variation, the technique of DNA-DNA hybridization may be used to study intraspecific variation in invertebrates but is limited in its usefulness for higher systematic studies.      

The Chloroplast and Cytoplasmic Ribosomes of Euglena: II. Characterization of Ribosomal Proteins

Cytoplasmic and chloroplast ribosomal proteins were isolated from Euglena gracilis and analyzed on polyacrylamide gels. Cytoplasmic ribosomes appear to contain 75 to 100 proteins ranging in molecular weight from 10,200 to 104,000, while chloroplast ribosomes appear to contain 35 to 42 proteins with molecular weights ranging from 9,700 to 57,900. This indicates that the cytoplasmic ribosomes are similar in composition to other eucaryotic ribosomes, while chloroplast ribosomes have a protein composition similar to the 70S procaryotic ribosome. The kinetics of light-induced labeling of cytoplasmic ribosomal proteins during chloroplast development has been determined, and the results are compared with the kinetics of ribosomal RNA synthesis.     

Intraspecific Variation in Developmental Characters: The Origin of Evolutionary Novelties

Evolutionary developmental biology is inevitably a comparativesubject. However, the taxonomic level at which comparisons canbe made varies widely, and this greatly affects the kind ofinformation that can be gained from the comparison. Broadlyspeaking, high-level comparisons (e.g., between phyla) are moreinformative about phylogenetic pattern and homology, while low-levelcomparisons (e.g., between congeneric species) are more informativeabout evolutionary mechanisms, including speciation. However,so far evolutionary developmental biology has had a relativelyminor input into the traditional territory of population genetics,namely comparisons within species—both within and betweengeographic populations. Yet this area is crucial, as all evolutionarynovelties ultimately arise from intraspecific variation. Here,I address this issue, focusing on the question of how earlyin development novelties arise. To shed light on this question,I discuss two examples of developmental polymorphism withinspecies involving two of the main body axes: anteroposteriorsegmentation in centipedes and left–right asymmetry (chirality)in gastropods.     

Levels of Intraspecific Variation Within the Catarrhine Skeleton

The amount of phenotypic variation between conspecifics is largely a result of the opposing forces of constraint and plasticity. Because selection is the product of competition between individuals of the same species, understanding the interactions between these forces is vital to understanding evolution. We investigated levels of intraspecific variation in the catarrhine skeleton using a morphometric analysis of 245 crania and 189 appendicular postcranial skeletons. We identified regions of interest from the literature and made comparisons of intraspecific variation between the appendicular postcranium and cranium, the forelimb and hind limb, the diaphyses and epiphyses of long bones, and the diaphyses of the proximal and distal segments of the limbs. We confirmed that variation is significantly higher in the appendicular postcranium than in the cranium, in the forelimb compared to the hind limb, and in the diaphyses compared to the epiphyses. Further, we found that this pattern was repeated in 12 species spanning the infraorder, suggesting a characteristic of catarrhines in general. The relatively low level of variation in the cranium suggests that constraint is more widespread in this region compared to the appendicular postcranium, which is more plastic, especially in the diaphyses of the forelimb. In contrast to previous studies, we found the diaphyses of the distal segment to be more variable than the diaphyses of the proximal segment. The results from this study, which show regional differences in intraspecific variation, will aid the interpretation of evolutionary and plastic influences on morphological variation and inform decisions about which skeletal regions are suitable for answering specific evolutionary questions.     

Intraspecific Morphological Variation Among Populations of Pratylenchus brachyurus and P. coffeae

Three populations of Pratylenchus coffeae and two of P. brachyurus, each originating from a single female, were maintained on Citrus spp. or Solanum nigrum L. for several years under greenhouse conditions. Nematodes were extracted from roots, and adult female specimens were killed, fixed, and mounted in glycerine for microscopic study. Variables measured were distance between vulva and anus and lengths of the stylet, posterior uterine sac, and tail. The mean data and coefficients of variability suggest that styler length had the least variability, and length of posterior uterine sac the most. When males and distinct spermathecae are not evident in P. coffeae populations, the species can he distinguished from P. brachyurus by a shorter mean stylet length, longer mean posterior uterine sac length, and much longer distance between the vulva and anus.     

Specificity of Mammalian Transferase II Binding to Ribosomes

Transferase II from rat liver binds specifically at the ribosome receptor site. Sulphydryl groups on both ribosome and enzyme must be in the reduced state before binding is feasible.     

Intraspecific Variation of Ribosomal Gene Redundancy in ZEA MAYS

Ribosomal genes in eukaryotes are highly redundant. Considerable variation in the level of redundancy among species, especially in higher plants, has been reported; but except for deletion and duplication mutants, it is generally accepted that intraspecific variability in redundancy level is small. We have examined the level of redundancy in several lines of maize by DNA-rRNA saturation hybridization. The amount of nuclear DNA which hybridizes with rRNA in the ten lines examined varied from 0.24% to 0.50%. The number of rRNA genes per diploid genome thus ranges from 1.12 x 10⁴ to 2.32 x 10⁴. Results also indicate that the level of redundancy is genetically transmitted.