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L R Hilburn

Publications and source records attributed to L R Hilburn.

18 recordsLinked to original sources
PubMed1995

Cytosystematics of five North American Amblyomma (Acarina: Ixodidae) species.

The karyotypes of 5 species of Amblyomma ticks found in North America were examined for the presence and location of constitutive heterochromatin (C-bands). All specimens examined had 20 autosomes and an XX:XO sex-determining system, with the X being the largest element in the karyotype. Except as noted in text, the autosomes of all species were acrocentric and heterochromatin was restricted to the centromeric region. The third largest autosome in 4 of the 5 species displayed a consistent band of heterochromatin just below the centromere; Amblyomma imitator displayed heterochromatin on the third largest pair of autosomes but in the form of an entire heterochromatic short arm. It is hypothesized that the third largest autosome could be the location of the nucleolar organizer region. Unique features of the C-banded karyotype that characterize and differentiate each species are presented. Similarity in the C-banding pattern exists between Amblyomma americanum and Amblyomma maculatum (the C-band in the X chromosome) and Amblyomma cajennense and A. imitator (the extreme subacrocentric X chromosome). The placement of Amblyomma inornatum remains difficult and cannot be clearly determined based on the placement of heterochromatin.

Animals↗
PubMed1993

Implications of selection and hybridization studies on the mode of inheritance of photoperiodically induced developmental diapause in laboratory strains of the lone star tick (Acari: Ixodidae).

Selection of lone star ticks, Amblyomma americanum (L.), that were reared in the laboratory under short-day photoperiods of 10:14 (L:D) h resulted in third generation (F3) diapause versus F3 nondiapause strain replete nymphs having significantly different mean molting times (days from detachment to ecdysis) of 100.9 versus 54.7 d, respectively; whereas, the F7 unselected laboratory control strain had an even smaller, significantly different mean molting time of 49.5 d. Two hybrid crosses of F2 nondiapause male with F2 diapause female ticks and F2 nondiapause female with F2 diapause male ticks yielded intermediate replete nymphal mean molting times of 62.0 and 68.9 d, respectively. All strains retained the ability to develop rapidly under long-day photoperiodic conditions of 14:10 (L:D) h, although F3 nondiapause strain ticks also exhibited reduced fitness, especially when exposed to the long-day stimuli. Analyses of molting times used as phenotypic values indicate that this diapause trait is incompletely dominant, and these and other observations indicate that inheritance of photoperiodically induced prolonged replete nymphal molting times is polygenic in this species.

Animals↗
PubMed1992

Test for assortative mating between Boophilus microplus and Boophilus annulatus (Acari: Ixodidae).

The closely related cattle ticks, Boophilus microplus (Canestrini) and B. annulatus (Say), were tested for possible assortative mating under conditions designed to mimic those in the field. Patterns in the numbers of the four possible types of matings were generally indicative of a preference for conspecific mates in both species. There were significantly more conspecific and fewer interspecific matings than would be predicted from the observed frequencies of males and females among the two species had they mated at random.

Animals↗
PubMed1991

Non-random mating between Boophilus microplus and hybrids of B. microplus females and B. annulatus males, and its possible effect on sterile male hybrid control releases.

When Boophilus microplus and Type-II hybrids (B. microplus females X B. annulatus males) were released simultaneously onto bovine hosts, mating between the two forms appeared not to be at random. There were more contypic and fewer intertypic matings than predicted under an assumption of panmixia. An examination of the patterns of matings revealed that more of the matings on the first two days of detachment were between the two sexes of B. microplus. Engorged females dropping on the last four days of maximum female detachment were predominantly hybrids mated to both B. microplus and hybrid males. The non-random mating pattern does not appear to be caused by assortative mating between B. microplus and Type-II hybrids, but because the B. microplus were competent to mate two days before the hybrids and the B. microplus males compete for males of both types better than the Type-II males.

Animals↗
PubMed1991

Reduction in egg viability resulting from infestations on cattle of hybridized Boophilus ticks and B. microplus (Acari: Ixodidae) at various ratios.

The competitiveness of hybridized Boophilus males, which are 100% sterile, was compared to B. microplus (Canestrini). Hybrid larvae used in the study were the offspring derived by cross-mating B. annulatus (Say) males with B. microplus females. Cattle were infested with a total of 2,500 larvae at ratios of 5:1 and 10:1 (hybrid to pure strain). The reduction in egg hatch resulting from the hybrid males was 68 and 77.5% at the 5:1 and 10:1 ratios, respectively. Both treatment ratios produced egg sterility that were lower than expected, assuming purely random mating, suggesting that hybrid ticks were not as competitive as B. microplus males. At the 5:1 treatment level, genotypic determinations based on isoenzyme analysis indicated that mate pairings involving hybrid males occurred 20-40% less frequently than expected, whereas matings involving pure-strain B. microplus males occurred twice as frequently as expected. At the 10:1 treatment level, mate pairings involving hybrid males occurred 10-20% less frequently than expected, whereas pairings involving pure strain B. microplus occurred 2-4 times more frequently than expected. The results indicated that in a sterile hybrid male program, it would be necessary to increase the ratios of hybrids by approximately 2-fold over the 5:1 or 10:1 ratios to achieve the 80-90% sterility expected, because of the decreased competitiveness of hybrid males.

Animals↗
PubMed1990

Cytosystematics of five North American Dermacentor (Acari: Ixodidae) species.

The karyotypes of five species of Dermacentor ticks found in North America were examined for the presence and location of constitutive heterochromatin (C-bands) and the location of the nucleolar organizing regions (NORs). All specimens examined had 20 autosomes and an XX:XO sex-determining system; the X was the largest element in the karyotype. Except as noted, the autosomes of all species were acrocentric, and heterochromatin was restricted to the centromeric region. The one-host species D. nitens and D. albipictus were distinguished from the three-host species by a lack of additional bands of heterochromatin and by having a subtelocentric X chromosome. However, some individuals of D. albipictus were observed to have acrocentric X chromosomes. D. nitens differed from D. albipictus in having two subtelocentric autosomal pairs (pairs 1 and 8). A single pair of NORs was noted for the one-host species; however, heterochromatin was not associated with the NORs. Among the three-host species, D. occidentalis showed a band of heterochromatin proximal to the centromere in autosomal pairs 1 and 8, and D. andersoni had similar bands in autosomal pairs 1, 3, 7, and 9. D. variabilis displayed heterochromatic bands in autosomal pairs 3, 7, and 9. All three-host species displayed a single pair of NORs, which was associated with the band of heterochromatin on pair 9. Indications of some genetic incompatibility between the two recognized forms of D. albipictus are discussed.

Animals↗
PubMed1989

Comparison of the isozyme phenotypes of the morphologically similar ticks Amblyomma cajennense and A. imitator (Acari: Ixodidae) from south Texas.

A survey of Amblyomma Koch tick populations in southern Texas revealed that A. imitator Kohls was restricted to the two most southern counties, but that A. cajennense (Fabricius) ranged at least as far north as Kingsville, Tex. Females of the two species could be distinguished by the presence of chitinous tubercles on the festoons of A. cajennense and the presence of projections over both sides of the apron of the genital aperture in A. imitator. Males were distinguished by size, ornamentation, and the elongate ventral scutes of A. imitator. In addition, six enzymes, AATA, ACONA, IDH2, LDH, MPI, and PEP, were diagnostic for the two species and two others, aGPD and ACONC, had high diagnostic values. Resulting interspecific divergence was significant, I = 0.582. Genetic variability was higher in A. imitator (h = 0.092) than in A. cajennense (h = 0.057), but neither species exhibited marked interpopulation divergence (I = 0.991 in A. imitator, I = 0.994 in A. cajennense).

Animals↗
PubMed1989

Differential staining of tick chromosomes: techniques for C-banding and silver-staining and karyology of Rhipicephalus sanguineus (Latreille).

A new karyotypic procedure is described for tick chromosomes along with modifications of accepted techniques for C-banding and silver-staining. The staining procedures produce patterns with staining limited to the centromeric regions and the nucleolar organizer regions (NORs). The possible reasons for the concordant patterns are discussed based on the staining characteristics of the 2 techniques. The karyotype of Rhipicephalus sanguineus possesses 20 acrocentric autosomes with a single pair of NORs located proximal to the centromere on the largest autosomal pair. The sex-determining system is XX:XO with the X chromosome being the largest chromosome in the complement and subtelocentric.

Animals↗
PubMed1987

Expression, inheritance, and linkage relationships among eight enzyme genes in Dermacentor albipictus (Packard) (Acarina: Ixodidae).

Starch gel electrophoresis was used to examine the inheritance, expression, and linkage relationships among eight enzyme genes in the winter tick, Dermacentor albipictus. A fructose-specific hexokinase (FHK), adenylate kinase (ADK), and two forms of aconitase (ACON-A, ACON-C) appeared to have monomeric quaternary structures. A glycylleucine peptidase (PEP), isocitrate dehydrogenase (IDH), and anodally migrating malate dehydrogenase (MDH-A) were apparently dimers. The quaternary structure of glucose phosphate isomerase (GPI) could not be determined because of the similarity in relative mobility of the two available electromorphs. The genes for GPI, FHK, and ADK are located on the X chromosome in the following order: Adk - 37.4 - Gpi - 24.6 - Fhk, with Adk - Fhk being 46.5 map units apart. The remaining five genes were autosomally inherited. Of the 10 possible paired combinations of these genes, only the data for two pairs, Idh-Mdh (44.5% recombinants) and Acon-A--Acon-C (46.4% recombinants), suggested statistically significant linkage.

Animals↗
PubMed1986

Electrophoretically detectable protein variation in natural populations of the lone star tick, Amblyomma americanum (Acari: Ixodidae).

Nine populations of Amblyomma americanum (L.) were examined electrophoretically for variation of 21 enzymes. Only three enzymes were not polymorphic and the average heterozygosity per individual (h) for the species was 0.085 with a range of 0.077 to 0.110, comparing well with values in other arthropods. The average Nei identity value for pairwise comparisons among the nine populations was high, 0.994 +/- 0.004 (I +/- SD). These high identity values and the absence of geographic structuring of the protein variation suggest that this species is genetically homogeneous. Normal levels of genic variability within and a lack of divergence between populations were not predicted by models developed to describe these genetic characteristics on the basis of the heterogeneities encountered by parasites in their environment. An analysis of data from several different species of ticks suggests host mobility and abundance, as well as tick abundance and selectivity in choosing a host, are important parameters in determining genetic variation in these ectoparasites.

Animals↗
PubMed1986

Are tick populations really less variable and should they be?

Empirical evidence from electrophoretic examinations of Metastriate ticks does not support the prediction that these ectoparasites necessarily have low levels of genetic variability within populations and large interpopulation differences. In part, the failure of the theory to produce a parsimonious prediction seems to stem from the use of an inappropriate model based on spatial environmental heterogeneity. The experimental data are better explained in terms of host mobility, tick population size, and the degree of host specificity of the tick.

Animals↗
PubMed1986

Genetic similarity and variability between natural populations and laboratory colonies of North American Boophilus (Acari: Ixodidae).

Four natural populations and 4 laboratory colonies of Boophilus microplus (Canestrini) and a laboratory colony of Boophilus annulatus (Say) were subjected to electrophoretic analysis to determine levels of genetic similarity and genetic variability. Populations of B. microplus exhibited high genetic similarity (I = 0.984 +/- 0.012) indicating that all populations share a relatively undifferentiated gene pool. Host vagility is proposed as an important mechanism promoting gene flow in ectoparasites. Levels of genetic variability for B. microplus (h = 0.092 +/- 0.008; P = 0.330 +/- 0.050) were within levels reported for other arthropods. The average genetic identity of 0.716 +/- 0.013 between B. microplus and B. annulatus is of a level characteristic of sibling species. Diagnostic isozymes between laboratory colonies will facilitate identification of these morphologically similar species.

Alleles↗
PubMed1985

Biochemical differentiation between species of ticks (Acari: Ixodidae).

An electrophoretic analysis of nine species of ticks representing three genera of the family Ixodidae was performed. Within the genus Ambylomma, the species are completely distinguished using ACPH and PEP-1. The phenotype of A. americanum is ACPH1-00 and PEP-1(1-00) or PEP-1(0-92); A. maculatum has phenotype ACPH0-92 and no expression of PEP-1; A. cajennense has phenotype ACPH1-04 and PEP-1(0-98); while the phenotype of A. inoratum is ACPH1-02 and PEP0-98. Among the Dermacentor, peptidase phenotypes completely distinguish the species. The species D. albipictus has phenotypes PEP-1(0-94) or PEP-1(0-88) and PEP-2(0-98); D. andersoni has phenotype PEP-1(1-00) and PEP-2(1-00); D. variabilis has phenotype PEP-1(0-94) and no expression of PEP-2; and D. nitens has phenotypes PEP-1(1-06) or PEP-1(0-98) and no expression of PEP-2. The final species, R. sanguineus can be distinguished from all the other species by its having the unique allele ACPH0-98.

Alleles↗
PubMedDate not supplied

Genetic analysis of abnormal male sexual development in Aedes aegypti and Ae. mascarensis backcross progeny.

When male hybrids of Aedes aegypti females and A. mascarensis males were backcrossed to A. aegypti females, 32.8 percent of the male progeny exhibited abnormal sexual development, including failure of the terminalia to rotate, a split sternite of the eighth abdominal segment with partially duplicated telomeres, or feminization that gives rise to sterile intersexes. Observations made on three morphological marker loci and five isozyme loci with characteristic electromorphs in the two parental species suggested that when the sex-determining M locus is derived from A. mascarensis and the chromosome regions including s, LDH, and lDH2 on chromosome 2 and blt and 6PGD on chromosome 3 are homozygous for genes from A. aegypti, the frequency of abnormal sexual development is increased. An even greater percentage of males suffer aberrant development if recombination also occurs between the M and re locus of chromosome 1. The data suggest that genes on chromosome 2 control normal development of the male terminalia, genes on chromosome 3 control sexual differentiation, and the entire process is controlled by genes on chromosome 1 that are linked to, but not identical with, the M locus.

Aedes↗
PubMedDate not supplied

Linkage relationships among four enzyme loci in the predatory, treehole mosquito.

Estimates are reported for the linkage distances between the isozyme loci for hydroxybutyrate dehydrogenase (HbDH), phosphoglucomutase (PGM), phosphoglucose isomerase (PGI), and esterase 8 (Est 8) in the predatory, treehole mosquito, Toxorhynchites rutilus rutilus. Measured linkage distances suggest that these four loci form a single autosomal linkage group approximately 47.4 linkage units in length. The estimates were measured with error because of small family sizes and, perhaps, because of different rates of recombination between males and females or the presence of a paracentric inversion associated with this linkage group. The four loci are tentatively placed in the following order: Est 8--HbDH--PGM--PGI.

Animals↗
PubMedDate not supplied

Linkage relationships among 12 enzyme loci in cattle fever ticks of the genus Boophilus.

Electrophoretic variation at 12 enzyme loci in cattle fever ticks were examined for mode of inheritance and linkage relationships. All variants exhibited codominant Mendelian inheritance, and PGI and GOT were sex-linked. Four pairs of enzyme loci were linked (PGI and GOT, ACON-A and alpha GPD, MDH-1 and LDH, and EST-3 and EST-4). Four additional enzyme loci (ACON-C, MDH-2, PEP, and PP) did not show linkage to any other locus tested, giving eight presumptive linkage groups that have enzyme markers in the genus Boophilus.

Animals↗
PubMedDate not supplied

Homology within the X chromosomes of Boophilus microplus (Canestrini) and B. annulatus (Say).

Chromosome banding patterns of the X chromosomes of Boophilus annulatus (Say) and B. microplus (Canestrini) indicate considerable homology between the two species. All bands of the small X chromosome of B. microplus are represented in the large X chromosome of B. annulatus with the exception of one medially located dark band. A large region of material proximal to the centromere and a small segment located at the telomere of the large X chromosome of B. annulatus are not represented in the small X chromosome of B. microplus. Meiotic abnormalities and the potential differentiation/evolution of the two X chromosomes are discussed. The extensive homology between the two species supports the genic data and linkage analyses previously published for these species.

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