Nancy Casna - Academia.edu (original) (raw)

Papers by Nancy Casna

Journal of Biological Chemistry, Nov 1, 1986

Molecular genetics makes it possible to measure basic but long elusive parameters of the breeding... more Molecular genetics makes it possible to measure basic but long elusive parameters of the breeding biology of the Brown-headed Cowbird (Molothrus ater). We examined cowbird fecundity and host selection behavior using a combination of molecular genetic techniques to link female cowbirds to the eggs they lay, radio-telemetry techniques to track female cowbirds’ daily movements, and geographic information systems (GIS) to integrate these genetic and spatial data. Our study site lay within a forested 1300.ha landscape in New York composed primarily of mature forest with adjacent old fields. We found that female cowbirds used their home ranges as principal egg-laying areas. Individual females used characteristic individual home ranges throughout the breeding season, and they returned to the same home range every breeding season. Over one-half (54%) of females laid all their eggs in host nests inside or close to their home range. Proximity to a female’s home range was the only significant ecological or biological feature affecting a cowbird’s host selection. Neither host species identity, nest height, adult mass, egg size, incubation period, nor host taxonomic classification predicted which nests would be parasitized. Eggs laid outside the home range were frequently found in multiply-parasitized nests located along common flyways or in conspicuous sites that a cowbird could discover opportunistically. We also found that female cowbirds avoided laying more than one egg in a particular host nest, even though multiple parasitism characterized over one-third of parasitized nests in the study. Finally, we estimated that effective cowbird fecundity lies between a minimum of 1.72 eggs per female and an upper bound of 8.16 eggs per female. Effective cowbird fecundity is defined as the actual number of cowbird eggs laid in appropriate host nests and not ejected; it is lower than raw fecundity or the physiological egg production capacity of cowbirds. We suggest that the female cowbird’s use of home range is a critical element in its breeding behavior, enabling cowbirds to use a known-host selection strategy. Experienced female cowbirds selectively parasitize the host pairs that nested in their home ranges in previous breeding seasons and were most successful. The three elements of cowbird breeding behavior reported here challenge the stereotype of the Brownheaded Cowbird as an r-selected species that produces a large number of young and invests no parental care. Instead, these results suggest that cowbirds lay fewer eggs in host nests than has been speculated and that they do invest parental care. Two examples of parental care we discuss are observing a host’s parental behavior and nest success before parasitizing it, and laying each egg in a different host nest, even though that requires females to search longer and to find a larger number of host nests. Current cowbird trapping programs should be evaluated for their effect on age structure of cowbird populations and resulting parasitism patterns. Yearling females may be associated with higher rates of multiple parasitism and higher rates of parasitism on more conspicuous hosts. Conspicuous hosts such as the Black-capped (Vireo atricapillus) and Least Bell’s (Vireo bellii pusillus) vireos are probably most at risk from cowbird populations with disproportionately high numbers of immigrant yearling female cowbirds such as those created by trapping programs. Key Words; Brown-headed Cowbird, DNA fingerprinting, fecundity, GIS, home range, management, Molothrus ater, telemetry. To evaluate whether Brown-headed Cowbirds ism patterns at the population level rather than (Molothrus ater) pose a threat to particular speat the individual level, focusing on features that ties or communities, conservation biologists generally make host nests more conspicuous to need to measure basic parameters that have long cowbirds, such as proximity to forest edge (e.g., been invisible. Fundamental reproductive traits Brittingham and Temple 1983); nest height such as the average laying rate per female, perabove the ground, with low nests being more centage of breeding females in a population, use exposed in some sites (Hahn and Hatfield in of a breeding territory, and the number of eggs press) and more camouflaged in other sites laid per nest are readily determined in non-par(Martin 1993); differences in host density (e.g., asitic birds, but are still not well established for Clark and Robertson 1979); and breeding bethe Brown-headed Cowbird. These reproductive havior that makes a host’ s nest more susceptible traits require measurement at the individual levto parasitism, such as the nest singing of the el, and in brood parasites this is a feat that was endangered Least Bell’ s Vireo (Vireo bellii pusnot possible until the recent advent of molecular illus; Kus this volume) and Black-capped Vireo genetic techniques. (Vireo atricupillus; e.g. Graber 1961). Without genetic information, previous…

Journal of Raptor Research, 1994

Primates, 1996

... DA GUST, TP GORDON, Emory University W. E GERGITS, NJ CASNA, Therion Corporation KG GOULD, an... more ... DA GUST, TP GORDON, Emory University W. E GERGITS, NJ CASNA, Therion Corporation KG GOULD, and HM MCCLURE, Emory University ... Subsequent semen evaluation revealed an absence of sperm in the semen of the alpha male, but revealed a sperm count within ...

Journal of Heredity, Nov 1, 1995

Proceedings of the National Academy of Sciences, 1986

We have developed a method for distinguishing fragments of DNA that contain single-base mismatche... more We have developed a method for distinguishing fragments of DNA that contain single-base mismatches from their perfectly paired homologues. Single-stranded regions within a duplex fragment are accessible to 1-cyclohexyl-3-(2-[4-(4-methyl)morpholinyl]ethyl)carbodiimide, which reacts with unpaired guanidylate and thymidylate residues in DNA. Intact linear duplex DNA molecules do not react with carbodiimide, whereas DNA molecules containing single-base mismatches react quantitatively. After carbodiimide reaction, the DNA molecules are electrophoresed in high-percentage polyacrylamide gels so that modified and unmodified fragments can be resolved. Application of this technique should make it possible to locate and purify DNA fragments that exhibit sequence differences from those that do not; these might be used to signal phenotypic variation as well as to diagnose inherited disease.

Gene, 1982

We have designed a method for inserting foreign DNA segments into bacteriophage T4. A plasmid con... more We have designed a method for inserting foreign DNA segments into bacteriophage T4. A plasmid containing T4 DNA is opened within the T4 sequence and the foreign DNA is inserted in vitro. Recombination in vivo, between T4 and the doubly chimeric plasmid, results in insertion of the foreign DNA into the'genome of viable T4 phage. We have demonstrated the method by inserting a 203-bp DNA fragment from the lactose operon of Escherichia coli, into the dispensable region of the rIIB gene of T4. With minor modifications, the method should make possible the cloning of very large DNAs into any one of a large number of sites on the T4 chromosome.

Gene, 1985

The amino-terminal portion of the T4 rIIB gene has been fused to the coding sequence of a truncat... more The amino-terminal portion of the T4 rIIB gene has been fused to the coding sequence of a truncated ZacZ gene from Escherichiu co& giving rise to a fusion protein with fi-galactosidase activity. The 3 192-bp rIIB-ZacZ gene fusion was transferred into phage T4, and enzymatically active protein was produced after phage infection. T4 may be a useful expression vector in special circumstances, in particular for proteins whose accumulation in E. cob is limited by sensitivity to proteases.

Molecular Ecology, 1994

Kin structure among founders can have a significant effect on subsequent population structure. He... more Kin structure among founders can have a significant effect on subsequent population structure. Here we use the correlation between DNA profile similarity and relatedness calculated from pedigrees to test hypotheses regarding kin structure among founders to the captive Guam rail (Rallus owstoni) population. Five different pedigrees were generated under the following hypotheses: (i) founders are unrelated; (ii) founders are unrelated except for same-nest chicks; (iii) founders from the same major site are siblings; (iv) founders from the same local site are siblings; and (v) founders are related as defined by a UPGMA cluster analysis of DNA similarity data. Relatedness values from pedigrees 1, 2 and 5 had the highest correlation with DNA similarity but the correlation between relatedness and similarity were not significantly different among pedigrees. Pedigree 5 resulted in the highest correlation overall when using only relatedness values that changed as a result of different founder hypotheses. Thus, founders were assigned relatedness based on pedigree 5 because it had the highest correlations with DNA similarity, was the most conservative approach, and incorporated all field data. The analyses indicated that estimating relatedness using DNA profiles remains problematic, therefore we compared mean kinship, a measure of genetic importance, with mean DNA profile similarity to determine if genetic importance among individuals could be determined via use of DNA profiles alone. The significant correlation suggests this method may provide more information about population structure than was previously thought. Thus, DNA profiles can provide a reasonable explanation for founder relatedness and mean DNA profile similarity may be helpful in determining relative genetic importance of individuals when detailed pedigrees are absent.

Understanding the nature of DNA sequence differences among individuals is important to the unders... more Understanding the nature of DNA sequence differences among individuals is important to the understanding of fundamental questions in biology. To analyze such differences in complex genomes new approaches must be developed. He report two new techniques which aid in this effort. First, we have developed a modification of the Phenol Emulsion Reassociation Technique (PERT) that allows hybridization of long (20 kb and longer) single copy heteroduplex DNA fragments from human genomic DNAs. Secondly, by using a differential methylase protection technique we have shown that double methylase resistant heteroduplex DNA molecules can be size fractionated away from reannealed single methylase resistant homoduplex DNA molecules. These methods will be useful in obtaining DNA from chromosomal subregions linked to the inheritance of a specific trait or condition as described in the preceding paper (1) and could also be used to create a map of the chromosomal subregion which includes the gene for th...