Proceedings of the National Academy of Sciences, 2004
There is controversy concerning the role of genetic factors in species extinctions. Many authors ... more There is controversy concerning the role of genetic factors in species extinctions. Many authors have asserted that species are usually driven to extinction before genetic factors have time to impact them, but few studies have seriously addressed this issue. If this assertion is true, there will be little difference in genetic diversity between threatened and taxonomically related nonthreatened species. We compared average heterozygosities in 170 threatened taxa with those in taxonomically related nonthreatened taxa in a comprehensive metaanalysis. Heterozygosity was lower in threatened taxa in 77% of comparisons, a highly significant departure from the predictions of the no genetic impact hypothesis. Heterozygosity was on average 35% lower (median 40%) in threatened taxa than in related nonthreatened ones. These differences in heterozygosity indicate lowered evolutionary potential, compromised reproductive fitness, and elevated extinction risk in the wild. Independent evidence from stochastic computer projections has demonstrated that inbreeding depression elevates extinction risk for threatened species in natural habitats when all other threatening processes are included in the models. Thus, most taxa are not driven to extinction before genetic factors affect them adversely.
The cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae) (Bouché), is the most common flea s... more The cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae) (Bouché), is the most common flea species found on cats and dogs worldwide. We investigated the genetic identity of the cosmopolitan subspecies C. felis felis and evaluated diversity of cat fleas from Australia, Fiji, Thailand and Seychelles using mtDNA sequences from cytochrome c oxidase subunit I (cox1 ) and II (cox2 ) genes. Both cox1 and cox2 confirmed the high phylogenetic diversity and paraphyletic origin of C. felis felis. The African subspecies C. felis strongylus (Jordan) is nested within the paraphyletic C. felis felis. The south East Asian subspecies C. felis orientis (Jordan) is monophyletic and is supported by morphology. We confirm that Australian cat fleas belong to C. felis felis and show that in Australia they form two distinct phylogenetic clades, one common with fleas from Fiji. Using a barcoding approach, we recognize two putative species within C. felis (C. felis and C. orientis). Nucleotide diversity was higher in cox1 but COX2 outperformed COX1 in amino acid diversity. COX2 amino acid sequences resolve all phylogenetic clades and provide an additional phylogenetic signal. Both cox1 and cox2 resolved identical phylogeny and are suitable for population structure studies of Ctenocephalides species.
This paper describes a cat with severe localised infections with Cryptococcus neoformans/gattii s... more This paper describes a cat with severe localised infections with Cryptococcus neoformans/gattii species complex and Mycobacterium avium affecting the subcutis and underlying fascia and bone of the right pelvic limb. The simultaneous isolation of both pathogens in this patient was unexpected and posed unique issues concerning both diagnosis and clinical management. The aetiopathogenesis of this infection is discussed in relation to aspects of diagnosis and therapy.
Inbreeding and loss of genetic diversity are predicted to decrease the resistance of species to d... more Inbreeding and loss of genetic diversity are predicted to decrease the resistance of species to disease. However, this issue is controversial and there is limited rigorous scientific evidence available. To test whether inbreeding and loss of genetic diversity affect a host's resistance to disease, Drosophila melanogaster populations with different levels of inbreeding and genetic diversity were exposed separately to (a) thuringiensin, an insecticidal toxin produced by some strains of Bacillus thuringiensis, and (b) live Serratia marcescens bacteria. Inbreeding and loss of genetic diversity significantly reduced resistance of D. melanogaster to both the thuringiensin toxin and live Serratia marcescens. For both, the best fitting relationships between resistance and inbreeding were curvilinear. As expected, there was wide variation among replicate inbred populations in disease resistance. Lowered resistances to both the toxin and the pathogen in inbred populations were due to specific resistance alleles, rather than generalized inbreeding effects, as correlations between resistance and population fitness were low or negative. Wildlife managers should strive to minimise inbreeding and loss of genetic diversity within threatened populations and to minimise exposure of inbred populations to disease.
Immigration into small isolated captive and wild populations is recommended to alleviate inbreedi... more Immigration into small isolated captive and wild populations is recommended to alleviate inbreeding depression. The effects on reproductive fitness of introducing one immigrant into 10 small partially inbred captive populations of D. rnelunogaster were evaluated. The relative reproductive fitness of the immigrant populations (0.628) was approximately double that of the isolated populations (0.294) and about halfway between the isolated populations and the outbred base population ( 1 .OO). Every replicate population increased in fitness following the introduction of an immigrant. The improvements in reproductive fitness shown by the immigrant populations were not due to F, hybrid vigor, as the experimental populations underwent three generations of random mating prior to the fitness tests. These results indicate substantial benefits can be gained by the translocation of as few as a single animal between small, partially inbred populations. 0 1992 Wiley-Liss, Inc.
Immigration into small isolated captive and wild populations is recommended to alleviate inbreedi... more Immigration into small isolated captive and wild populations is recommended to alleviate inbreeding depression. The effects on reproductive fitness of introducing one immigrant into 10 small partially inbred captive populations of D. rnelunogaster were evaluated. The relative reproductive fitness of the immigrant populations (0.628) was approximately double that of the isolated populations (0.294) and about halfway between the isolated populations and the outbred base population ( 1 .OO). Every replicate population increased in fitness following the introduction of an immigrant. The improvements in reproductive fitness shown by the immigrant populations were not due to F, hybrid vigor, as the experimental populations underwent three generations of random mating prior to the fitness tests. These results indicate substantial benefits can be gained by the translocation of as few as a single animal between small, partially inbred populations. 0 1992 Wiley-Liss, Inc.
Proceedings of the National Academy of Sciences, 2004
There is controversy concerning the role of genetic factors in species extinctions. Many authors ... more There is controversy concerning the role of genetic factors in species extinctions. Many authors have asserted that species are usually driven to extinction before genetic factors have time to impact them, but few studies have seriously addressed this issue. If this assertion is true, there will be little difference in genetic diversity between threatened and taxonomically related nonthreatened species. We compared average heterozygosities in 170 threatened taxa with those in taxonomically related nonthreatened taxa in a comprehensive metaanalysis. Heterozygosity was lower in threatened taxa in 77% of comparisons, a highly significant departure from the predictions of the no genetic impact hypothesis. Heterozygosity was on average 35% lower (median 40%) in threatened taxa than in related nonthreatened ones. These differences in heterozygosity indicate lowered evolutionary potential, compromised reproductive fitness, and elevated extinction risk in the wild. Independent evidence from stochastic computer projections has demonstrated that inbreeding depression elevates extinction risk for threatened species in natural habitats when all other threatening processes are included in the models. Thus, most taxa are not driven to extinction before genetic factors affect them adversely.
The cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae) (Bouché), is the most common flea s... more The cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae) (Bouché), is the most common flea species found on cats and dogs worldwide. We investigated the genetic identity of the cosmopolitan subspecies C. felis felis and evaluated diversity of cat fleas from Australia, Fiji, Thailand and Seychelles using mtDNA sequences from cytochrome c oxidase subunit I (cox1 ) and II (cox2 ) genes. Both cox1 and cox2 confirmed the high phylogenetic diversity and paraphyletic origin of C. felis felis. The African subspecies C. felis strongylus (Jordan) is nested within the paraphyletic C. felis felis. The south East Asian subspecies C. felis orientis (Jordan) is monophyletic and is supported by morphology. We confirm that Australian cat fleas belong to C. felis felis and show that in Australia they form two distinct phylogenetic clades, one common with fleas from Fiji. Using a barcoding approach, we recognize two putative species within C. felis (C. felis and C. orientis). Nucleotide diversity was higher in cox1 but COX2 outperformed COX1 in amino acid diversity. COX2 amino acid sequences resolve all phylogenetic clades and provide an additional phylogenetic signal. Both cox1 and cox2 resolved identical phylogeny and are suitable for population structure studies of Ctenocephalides species.
This paper describes a cat with severe localised infections with Cryptococcus neoformans/gattii s... more This paper describes a cat with severe localised infections with Cryptococcus neoformans/gattii species complex and Mycobacterium avium affecting the subcutis and underlying fascia and bone of the right pelvic limb. The simultaneous isolation of both pathogens in this patient was unexpected and posed unique issues concerning both diagnosis and clinical management. The aetiopathogenesis of this infection is discussed in relation to aspects of diagnosis and therapy.
Inbreeding and loss of genetic diversity are predicted to decrease the resistance of species to d... more Inbreeding and loss of genetic diversity are predicted to decrease the resistance of species to disease. However, this issue is controversial and there is limited rigorous scientific evidence available. To test whether inbreeding and loss of genetic diversity affect a host's resistance to disease, Drosophila melanogaster populations with different levels of inbreeding and genetic diversity were exposed separately to (a) thuringiensin, an insecticidal toxin produced by some strains of Bacillus thuringiensis, and (b) live Serratia marcescens bacteria. Inbreeding and loss of genetic diversity significantly reduced resistance of D. melanogaster to both the thuringiensin toxin and live Serratia marcescens. For both, the best fitting relationships between resistance and inbreeding were curvilinear. As expected, there was wide variation among replicate inbred populations in disease resistance. Lowered resistances to both the toxin and the pathogen in inbred populations were due to specific resistance alleles, rather than generalized inbreeding effects, as correlations between resistance and population fitness were low or negative. Wildlife managers should strive to minimise inbreeding and loss of genetic diversity within threatened populations and to minimise exposure of inbred populations to disease.
Immigration into small isolated captive and wild populations is recommended to alleviate inbreedi... more Immigration into small isolated captive and wild populations is recommended to alleviate inbreeding depression. The effects on reproductive fitness of introducing one immigrant into 10 small partially inbred captive populations of D. rnelunogaster were evaluated. The relative reproductive fitness of the immigrant populations (0.628) was approximately double that of the isolated populations (0.294) and about halfway between the isolated populations and the outbred base population ( 1 .OO). Every replicate population increased in fitness following the introduction of an immigrant. The improvements in reproductive fitness shown by the immigrant populations were not due to F, hybrid vigor, as the experimental populations underwent three generations of random mating prior to the fitness tests. These results indicate substantial benefits can be gained by the translocation of as few as a single animal between small, partially inbred populations. 0 1992 Wiley-Liss, Inc.
Immigration into small isolated captive and wild populations is recommended to alleviate inbreedi... more Immigration into small isolated captive and wild populations is recommended to alleviate inbreeding depression. The effects on reproductive fitness of introducing one immigrant into 10 small partially inbred captive populations of D. rnelunogaster were evaluated. The relative reproductive fitness of the immigrant populations (0.628) was approximately double that of the isolated populations (0.294) and about halfway between the isolated populations and the outbred base population ( 1 .OO). Every replicate population increased in fitness following the introduction of an immigrant. The improvements in reproductive fitness shown by the immigrant populations were not due to F, hybrid vigor, as the experimental populations underwent three generations of random mating prior to the fitness tests. These results indicate substantial benefits can be gained by the translocation of as few as a single animal between small, partially inbred populations. 0 1992 Wiley-Liss, Inc.
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Papers by Derek Spielman