Dietary shifts of sympatric buteos during a prey decline

Summary Diets of nesting Red-tailed Hawks (Buteo jamaicensis) and Ferruginous Hawks (Buteo regalis) were sampled before and after a decline in the hawks' principal prey species. Diets of pairs that shared their foraging ranges with interspecifics were contrasted with those of pairs whose home ranges did not overlap with interspecifics. Current theory predicts that diets should diverge during prey shortages and that overlap should be especially reduced in ranges shared with interspecifics. Species composition of the two hawks' diets diverged during the prey shortage, but the divergence was most pronounced in hawks that did not share foraging ranges with interspecifics. In contrast to predictions, the two species converged on similar-sized prey during the prey shortage. Available data on differences in habitat composition and prey availability at the sample sites did not explain the deviations from the predicted response. Although our findings on diet shifts differ from those of most other studies, the implications are consistent with observations of others who have studied assemblages of mammal-feeding raptors. We conclude that diet composition of the hawks we studied was not directly affected by interspecific competition and that shifts in diet overlap during prey shortages do not necessarily imply that interspecific competition is occurring.     

Ultrastructure of Volvox carteri

Summary Somatic cells of mature asexual colonies of Volvox carteri do not possess a true cell wall, but are otherwise similar in ultrastructure to Chlamydomonas. Somatic cells are embedded in multilayered fibrillar material of the colonial matrix. The reproductive cells (gonidia) of Volvox carteri lie internal to the somatic cell layer of the colony matrix in an apparently structureless portion of the colony matrix. Mature gonidia are large vacuolate cells with a central nucleus and parietal chloroplasts and mitochondria. They are non-flagellated at maturity, but each contains a pair of kinetosomes.     

Bamboo germplasm screening with nuclear restriction fragment length polymorphisms

Summary Bamboo species are difficult to identify because flowering material is seldom available and taxonomy is of necessity based on vegetative characters. To evaluate the utility of restriction fragment length polymorphism (RFLP) analysis in bamboo systematics and germplasm screening, a library of random genomic probes from a Phyllostachys nigra PstI library was constructed. Probes from the library were used to screen bamboo germplasm consisting mostly of temperate bamboos of the genus Phyllostachys. RFLP variation was abundant, and species-specific patterns were readily obtained. Chloroplast DNA showed little variation among the bamboo accessions analyzed.     

RFLP variability in peanut (Arachis hypogaea L.) cultivars and wild species

Summary RFLP variability was studied in eight U.S. peanut cultivars, representing the four market types, and in 14 wild Arachis species accessions, using random genomic clones from a PstI library. Very low levels of RFLP variability were found among the allotetraploids, which included the U.S. cultivars and Arachis monticola, a wild species. The diploid wild species were very diverse, however. RFLP patterns of the allotetraploids were more complex than the diploids, and the two constituent genomes could usually be distinguished. On the basis of RFLP band sharing, A. ipaensis, A. duranensis, and A. spegazzinii appeared most closely related to the diploid progenitor species of the allotetraploids. A dendrogram of relationships among the diploid wild species was constructed based on band sharing.     

A study of genetic variation and evolution of Phyllostachys (Bambusoideae: Poaceae) using nuclear restriction fragment length polymorphisms

Phylogenetic and taxonomic difficulties are common within the woody bamboos, due to their unique life cycle, which severely limits the availability of floral characters. To addresss some of these problems, 20 species of woody bamboos in the genus Phyllostachys were analyzed using nuclear restriction fragment length polymorphisms (RFLPs). The RFLP data were used to generate genetic distances between all pairs of taxa and to examine the degree of genetic variation within and among bamboo species. The genetic distances were also used to create dendrograms of accessions and species. These trees supported the current division of the genus into two sections and provided some information on the thorny taxonomic problems in this group. We show that RFLPs can be used for species identification and the delineation of species limits.     

Characterization and genetic mapping of a short, highly repeated, interspersed DNA sequence from rice (Oryza sativa L.).

Summary A short, highly repeated, interspersed DNA sequence from rice was characterized using a combination of techniques and genetically mapped to rice chromosomes by restriction fragment length polymorphism (RFLP) analysis. A consensus sequence (GGC)_n, where n varies from 13–16, for the repeated sequence family was deduced from sequence analysis. Southern blot analysis, restriction mapping of repeat element-containing genomic clones, and DNA sequence analysis indicated that the repeated sequence is interspersed in the rice genome, and is heterogeneous and divergent. About 200000 copies are present in the rice genome. Single copy sequences flanking the repeat element were used as RFLP markers to map individual repeat elements. Eleven such repeat elements were mapped to seven different chromosomes. The strategy for characterization of highly dispersed repeated DNA and its uses in genetic mapping, DNA fingerprinting, and evolutionary studies are discussed.     

Characterization of a unique genomic clone located 5′ upstream of the <Emphasis Type="Italic">Oshsp16.9B</Emphasis> gene on chromosome 1 in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L. cv Tainung No. 67)

Small heat-shock proteins (sHSP) are the most abundant heat stress-induced proteins in plants. In rice, there are at least seven members of class-I sHSP. A 1.6-kb DNA fragment was isolated from the EcoRI-digested rice genomic library probed with the cDNA pTS1 encoding a 16.9-kDa class-I sHSP. This fragment was composed of 365-bp tandem direct repeats (DRs) and 441-bp near perfect long terminal inverted repeats (LTIRs). The DRs contain 123-bp regions with 99% nucleotide identity to the 5' coding region of the Oshsp16.9B gene. Two putative pseudogenes were deduced from the DRs. Using the LTIR as a specific probe, Southern-blotting analysis showed that there was a single copy of this 1.6-kb DNA fragment in the rice genome. By genomic walking, we located this fragment in proximity 5'-upstream of the Oshsp16.9B gene that was mapped on chromosome 1 with other two class-I sHSP genes, Oshsp16.9A and Oshsp16.9C. By comparative analysis of the nucleotide sequences of class-I sHSP genes clustered on chromosome 1 between Tainung No. 67 and Nipponbare cultivars, we confirmed our mapping results of these genes and only the promoter region of Oshsp16.9B was different. However, we found that the expression profile of Oshsp16.9B upon different heat stresses in Nipponbare was not significantly different relative to that in Tainung No. 67.     

Molecular analysis of Arachis interspecific hybrids

Incorporation of genetic resistance against several biotic stresses that plague cultivated peanut, Arachis hypogaea (2n=4x=40), is an ideal option to develop disease resistant and ecologically safe peanut varieties. The primary gene pool of peanut contains many diploid wild species (2n=2x=20) of Arachis, which have high levels of disease and insect resistances. However, transfer of resistant genes from these species into A. hypogaea is difficult due to ploidy level differences and genomic incompatibilities. This study was conducted to monitor alien germplasm transmission, using Random Amplified Polymorphic DNA (RAPD) markers, from two diploid wild species, A. cardenasii and A. batizocoi, into A. hypogaea. Triploid interspecific hybrids were produced by crossing two A. hypogaea cultivars (NC 6 and Argentine) with the two species and by colchicine-treating vegetative meristems, fertility was restored at the hexaploid (C_o) level in the four hybrids. Hexaploids were allowed to self-pollinate for four generations, each referred to as a cycle (C₁, C₂, C_3, and C₄). At each cycle, a backcross was made with the respective A. hypogaea cultivar as the maternal parent and only lineages tracing back to a single hexaploid hybrid were used for RAPD analysis. Analysis of mapped, species-specific RAPD markers in BC₁F₁ to BC₁F₃ hybrids indicated that alien germplasm retention decreased every generation of inbreeding, especially in Argentine and in A. batizocoi crosses. A similar trend was also observed for every cycle in BC₁F₂ and BC₁F₃ families, possibly, due to the loss of alien chromosomes following selfing of hexaploids. RAPD marker analysis of 40–chromosome interspecific hybrid derivatives from the four crosses supported previous reports that reciprocal recombination and/or translocations are the predominant mechanisms for exchange of chromosomal segments. No evidence was found for preferential transfer of alien chromosomal regions to specific linkage groups. The implications for developing disease resistant peanut breeding lines are discussed in light of these findings.     

Differentiation of bermudagrass (Cynodon spp.) genotypes by AFLP analyses

 Bermudagrasses (Cynodon spp.) are major turfgrasses for home lawns, public parks, golf courses and sport fields, and are widely adapted to tropical and warmer temperate climates. Morphological and physiological characteristics are not sufficient to differentiate some bermudagrass genotypes because the differences between them are often subtle and subject to environmental influence. In this study, a DNA-typing technique, amplified fragment length polymorphism (AFLP), was used to differentiate bermudagrass genotypes and to explore their genetic relationships. Twenty seven bermudagrass cultivars and introductions, mostly from the Coastal Plain Experiment Station in Tifton, Ga., were assayed by the radioactive (³²P) and the fluorescence-labeled AFLP methods. The AFLP technique produced enough polymorphism to differentiate all 27 bermudagrass genotypes, even the closely related ones. An average of 48–74 bands in the 30–600-bp size range was detected by the ³²P-labeled AFLP method. The results indicated that most of the 14 primer combinations tested in this study could be used to distinguish bermudagrass genotypes, and that some single primer-pairs could differentiate all 27 of them. To test the reliability and reproducibility of the AFLP procedure, three DNA isolations (replications) of the 27 bermudagrass genotypes were assayed using five primer pairs. Only 0.6% of the bands were evaluated differently among the three replications. One replication of one genotype (which was most likely a planting contaminant) was grouped in an unexpected cluster using the Unweighted Pair Group Mean Average (UPGMA) method. A one- or two-band difference in scoring did not change the clustering of genotypes or the replications within genotypes. The 27 genotypes were grouped into three major clusters, many of which were in agreement with known pedigrees. Trees constructed with different primer combinations using ³²P- and fluorescence-labelling formed similar major groupings. The semi-automated fluorescence-based AFLP technique offered significant improvements on fragment sizing and data handling. It was also more accurate for detection and more efficient than the radioactive labelling method. This study shows that the AFLP technique is a reliable tool for differentiating bermudagrass genotypes and for determining genetic relationships among them. Received: 28 July 1998 / Accepted: 3 November 1998