Intraspecific Variation In Number Research Articles

Isolation and characterization of 5S rDNA sequences in catfishes genome (Heptapteridae and Pseudopimelodidae): perspectives for rDNA studies in fish by C0t method.

Sequences of 5S ribosomal RNA (rRNA) are extensively used in fish cytogenomic studies, once they have a flexible organization at the chromosomal level, showing inter- and intra-specific variation in number and position in karyotypes. Sequences from the genome of Imparfinis schubarti (Heptapteridae) were isolated, aiming to understand the organization of 5S rDNA families in the fish genome. The isolation of 5S rDNA from the genome of I. schubarti was carried out by reassociation kinetics (C0t) and PCR amplification. The obtained sequences were cloned for the construction of a micro-library. The obtained clones were sequenced and hybridized in I. schubarti and Microglanis cottoides (Pseudopimelodidae) for chromosome mapping. An analysis of the sequence alignments with other fish groups was accomplished. Both methods were effective when using 5S rDNA for hybridization in I. schubarti genome. However, the C0t method enabled the use of a complete 5S rRNA gene, which was also successful in the hybridization of M. cottoides. Nevertheless, this gene was obtained only partially by PCR. The hybridization results and sequence analyses showed that intact 5S regions are more appropriate for the probe operation, due to conserved structure and motifs. This study contributes to a better understanding of the organization of multigene families in catfish's genomes.

Physical mapping of 5S and 18S-5.8S-26S RNA gene families in polyploid series of Cenchrus ciliaris Linnaeus, 1771 (Poaceae)

The Buffelgrass (Cenchrus ciliaris L., Poaceae) is one of the most important pasturage grasses due to its high productivity and good forage qualities. This species possess a high adaptability to bioclimatic constraints of arid zones and may be used for the restoration of degraded arid ecosystems. Tunisian populations present three ploidy levels (4x, 5x and 6x) with a basic chromosome number x=9. This study reported for the first time the distribution of the ribosomal genes (rRNA) for pentaploid and hexaploid cytotypes of Cenchrus ciliaris. Molecular cytogenetic study using double fluorescence in situ hybridization has shown that the two rDNA families, 5S and 18S-5.8S-26S (18S), displayed intraspecific variation in number of loci among different ploidy levels. Each ploidy level was characterized by specific number of both 5S and 18S rDNA loci (two loci in tetraploid, five in pentaploid and six in hexaploid level). For three studied cytotypes (4x, 5x and 6x) all 5S rDNA loci were localized on the subcentromeric region of chromosomes, while 18S loci were situated on the telomeric region of short chromosome arms. Data of the FISH experiments show proportional increase of ribosomal loci number during polyploidization processes.

Cytogenetic analysis of Hieracium transylvanicum (Asteraceae)

Abstract Hieracium transylvanicum is a relic species which occurs in refugial areas of south-eastern Europe. The structure of its karyotype, including determination of morphometric features of somatic metaphase chromosomes as well as the number and distribution of ribosomal DNA loci, was attempted using both classical chromosome staining and the FISH method with 25S rDNA and 5S rDNA probes. The cytotypes under study were collected from eight sites and did not vary significantly in terms of their karyotype organisation. All 11 specimens had the same chromosome number, 2n=2x=18, and 9 similar chromosomal types, whose total length ranged from 4.62 to 2.64 μm. The karyotype of the species is highly symmetrical. Two chromosomal types, 3 and 6, have a 45S rDNA locus in distal parts of their short arms. In addition, the short arm of type 6 has interstitial 5S rDNA sequences. No intraspecific variation in number and chromosomal distribution of ribosomal DNA loci was observed. The very uniform structure of the kar...

Variation in the Female Frenulum in Tortricidae (Lepidoptera). Part 2. Olethreutinae

This paper, treating the tortricid subfamily Olethreutinae, represents the second in a proposed three-part series examining variation in the number of bristles in the frenulum of female tortricid moths. Based on an examination of 6,333 individuals of 1,464 species representing 188 genera of Olethreutinae, the number of bristles in the female frenulum varies from one to six, and it is sometimes asymmetrical on the same specimen (7.5% of individuals examined). A three-bristled frenulum is the most common condition in Microcorsini, Endotheniini, Bactrini, Gatesclarkeanini, Olethreutini, Enarmoniini, and Eucosmini, with varying degrees of intraspecific variation in number within each tribe. However, in both Eucosmini and Enarmoniini several genera have a predominantly or exclusively two-bristled frenulum (e.g., Gypsonoma Meyrick, Herpystis Meyrick, and Rhopalovalva Kuznetsov in Eucosmini; Hystrichophora Walsingham, Neoanathamna Kawabe, and Pseudacroclita Oku in Enarmoniini). In Grapholitini, two- and three-bristled frenula occur in nearly equal frequency, suggesting that this character may be of some phylogenetic significance, but an overall pattern is not immediately obvious. In contrast to the situation in Chlidanotinae, where the distribution of the two- and three-bristled frenulum corroborates previously proposed phylogenetic hypotheses, we conclude that variation in the number of bristles in the frenulum in Olethreutinae is not phylogenetically informative at higher levels (e.g., tribes, subtribes) owing to the high degree of intrageneric and intraspecific variation. However, the number of bristles may be of phylogenetic significance at the generic level, particularly in Eucosmini and Grapholitini.

Effect of Flower Clumping on Defense of Artificial Flowers by Aggressive Stingless Bees

Certain species of stingless bees are highly aggressive and defend floral food sources, especially when the flowers occur in locally dense patches. An experiment with two bee species, Trigona silverstriana and Trigoona corvina, exploiting a large number of artificial baits, tested the effect of grouping the baits on the success of aggressive defense. Spacing or clumping the baits made no difference in the numbers of the dominant bee species (T. silvestriana) visting the experimental site. However, the numbers of the rival bee species (T. corr'ina) were reduced dramatically when the baits were clumped, because of more effective distribution of defending T. silv estriana bees. STINGLESS BEES, common in the tropics, are social insects which exhibit broad overlap in the floral resources they exploit (Johnson 1974; see Leppik 1955, Wille 1963, Bawa 1975 for examples). There is evidence that many of these bee species are food limited (Hubbell and Johnson 1977) and that intraspecific and interspecific competition for food routinely occurs (Johnson 1974, 1980; Johnson and Hubbell 1974). The variety in foraging behavior and worker communication in these bee species (Hubbell and Johnson 1978, Lindauer and Kerr 1960, Kerr and Esch 1965) suggests that coexistence may depend on partitioning according to differences in timing, persistence, renewal rate, and spatial dispersion of their food resources. Such partitioning can even be accomplished on the variability that occurs among individual plants of the same species. In spite of general synchrony of flowering in populations of tropical trees (Janzen 1967; Daubenmire 1972; Frankie, Baker, and Opler 1974), trees exhibit considerable intraspecific variation in number of flowers offered on a given day, timing of flower opening, nectar or pollen reward, and spatial dispersion (Bawa 1975, Carpenter 1976, Eldridge 1976, Hedgegart 1976, Hubbell 1979). Johnson and Hubbell (1975) hypothesized that permits coexistence between the stingless bee species Trigona fuscipennis and T. fulviveintris. They found T. fuscipennis to be a highdensity specialist that forages in groups and visits only the densest clumps of flowers. Trigona fulviventris, on the other hand, is a low-density specialist that frequently forages alone on more-dispersed flowers. Density specialization with group foraging by the high-density specialist has subsequently been found in desert ants (Davidson 1977), a circumstance which suggests that it may be a common feature of foraging in eusocial insects that communicate the location of food sources. An assumption of the model for density specialization is that species adapted for exploiting the high-density resources control access to these resources. In stingless bees such control is exerted by groups of bees aggressively sequestering high-density resources. Johnson and Hubbell (1975) argued that the suitability of aggressive group foraging for highdensity spatially aggregated food sources was not only that such food sources provided sufficient food returns for all defending bees, but also that such food sources could be effectively guarded against rival

Morphological characters of taxonomical importance in Cryptoniscina (Isopoda Epicaridea) A scanning electron microscopic study of Cryptoniscus Larvae

Abstract By means of scanning electron microscopy, several morphological characters have been investigated in a large number of cryptoniscus larvae, representing all the 7 families of the Cryptoniscina. However, with the present subdivision of the taxon, features characterizing the entire superfamily or the different species were easier to settle than those of the generic or family levels. The number and arrangement of setae on the two proximal antennular segments, the number of segments of the antennal peduncle and flagellum, as well as their setation, and the number and position of setae on the different segments of the pleopods, are all characters of the super-family. Presence or absence of posterior teeth on the antennular plate is a family character, with the exception of Cabiropsidae, while the number of these teeth generally can be used at the generic level. However, in one genus, Cyproniscus, they even showed an intraspecific variation in number. Apart from the Hemioniscidae, the presence or absen...

Chromosome patterns and Robertsonian polymorphism in Blarina brevicauda (Say) (Mammalia: Insectivora)

A sample of 21 Blarina brevicauda, (Say) from seven localities in the Province of Ontario shows an intraspecific chromosomal polymorphism according to the rule of Robertson; 16 specimens have a homozygous karyotype, 2N = 50, composed of 48 acrocentric autosomes of regularly decreasing lengths and metacentric sex chromosomes, a large X. and a very small Y. Five specimens have a heterozygous karyotype, 2N = 49, showing one large submetacentric autosome arisen by centric fusion of two acrocentrics. The homozygous chromosomal complement, 2N = 48, has so far not been observed, but must exist in the population. It is impossible to determine exactly which are the chromosomes corresponding to the new submetacentric. The fundamental number, which is not affected by robertsonian mechanisms, is 52. The simplicity of the chromosomal set of B. brevicauda is discussed.The acrocentric nature of the autosomes allows for the possibility of a more extensive polymorphism, but this requires an analysis of numerous animals from several points of the distribution area of B. brevicauda. The exploration of intra-specific variation in number or morphology of chromosomes will require the analysis of considerably larger samples than has been customary in the study of mammalian karyotypes.