Limits...
Historical mammal extinction on Christmas Island (Indian Ocean) correlates with introduced infectious disease.

Wyatt KB, Campos PF, Gilbert MT, Kolokotronis SO, Hynes WH, DeSalle R, Ball SJ, Daszak P, MacPhee RD, Greenwood AD - PLoS ONE (2008)

Bottom Line: In the case of mammals, however, there are still no well-corroborated instances of such diseases having caused or significantly contributed to the complete collapse of species.Hybridization between endemic and black rats was also previously hypothesized, but we found no evidence of this in examined specimens, and conclude that hybridization cannot account for the disappearance of the endemic species.This is the first molecular evidence for a pathogen emerging in a naïve mammal species immediately prior to its final collapse.

View Article: PubMed Central - PubMed

Affiliation: Biological Sciences Department, Old Dominion University, Norfolk, VA, USA.

ABSTRACT
It is now widely accepted that novel infectious disease can be a leading cause of serious population decline and even outright extinction in some invertebrate and vertebrate groups (e.g., amphibians). In the case of mammals, however, there are still no well-corroborated instances of such diseases having caused or significantly contributed to the complete collapse of species. A case in point is the extinction of the endemic Christmas Island rat (Rattus macleari): although it has been argued that its disappearance ca. AD 1900 may have been partly or wholly caused by a pathogenic trypanosome carried by fleas hosted on recently-introduced black rats (Rattus rattus), no decisive evidence for this scenario has ever been adduced. Using ancient DNA methods on samples from museum specimens of these rodents collected during the extinction window (AD 1888-1908), we were able to resolve unambiguously sequence evidence of murid trypanosomes in both endemic and invasive rats. Importantly, endemic rats collected prior to the introduction of black rats were devoid of trypanosome signal. Hybridization between endemic and black rats was also previously hypothesized, but we found no evidence of this in examined specimens, and conclude that hybridization cannot account for the disappearance of the endemic species. This is the first molecular evidence for a pathogen emerging in a naïve mammal species immediately prior to its final collapse.

Show MeSH

Related in: MedlinePlus

Phylogenetic relationships among trypanosome sequences bases on 18S rDNA sequences.Scale bars denote substitutions per site along branches. Blue-colored sequences are the trypanosome sequences obtained in this study.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2572834&req=5

pone-0003602-g003: Phylogenetic relationships among trypanosome sequences bases on 18S rDNA sequences.Scale bars denote substitutions per site along branches. Blue-colored sequences are the trypanosome sequences obtained in this study.

Mentions: Two primer pairs (TrypA and TrypB) targeting the kinetoplastid 18S rDNA region (Table 1) were used to investigate whether trypanosomal DNA was present in any of the specimens. All 21 samples were tested, including three examples of R. nativitatis, which were collected prior to the introduction of black rats to Christmas Island. Although it was not expected that all specimens would return a positive signal for trypanosomes, since even highly infectious pathogens rarely exhibit 100% successful infection rates, we did expect OMNH 18846 to test positive because this was one of the animals Durham reported as displaying firm evidence of trypanosome infection [7]. In the event, six of the rats, including OMNH 18846, yielded trypanosome sequences. Five displayed unambiguous (100%) matches to published sequences for Trypanosoma lewisi, a known murine-infecting trypanosome; the remaining sample displayed a 3 bp deletion in the fragment amplified and thus could not be unambiguously characterized (Table 3). Unsurprisingly, as there were no differences between the GenBank sequence and those recovered from Christmas Island rats (except for the one instance of a 3 bp deletion), phylogenetic analysis unequivocally grouped them within T. lewisi (FIG. 3). Several of the infected rats were independently retested in two separate laboratories: for three samples our results were fully validated, but for three others validation must be regarded as tentative because only one (rather than both) laboratories reported a single replicate positive result—an effective illustration of the difficulties in working with less than single-copy pathogenic DNA from archival samples [14] (Table 1). Although a free-living kinetoplastid, Bodo saliens, was detected among the clones, this environmental contaminant could be easily distinguished from obligate parasitic trypanosomes at the sequence level. All morphologically defined subgroups (R. rattus, alleged hybrid, and R. macleari) contained T. lewisi DNA, confirming all three were susceptible to the infection.


Historical mammal extinction on Christmas Island (Indian Ocean) correlates with introduced infectious disease.

Wyatt KB, Campos PF, Gilbert MT, Kolokotronis SO, Hynes WH, DeSalle R, Ball SJ, Daszak P, MacPhee RD, Greenwood AD - PLoS ONE (2008)

Phylogenetic relationships among trypanosome sequences bases on 18S rDNA sequences.Scale bars denote substitutions per site along branches. Blue-colored sequences are the trypanosome sequences obtained in this study.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2572834&req=5

pone-0003602-g003: Phylogenetic relationships among trypanosome sequences bases on 18S rDNA sequences.Scale bars denote substitutions per site along branches. Blue-colored sequences are the trypanosome sequences obtained in this study.
Mentions: Two primer pairs (TrypA and TrypB) targeting the kinetoplastid 18S rDNA region (Table 1) were used to investigate whether trypanosomal DNA was present in any of the specimens. All 21 samples were tested, including three examples of R. nativitatis, which were collected prior to the introduction of black rats to Christmas Island. Although it was not expected that all specimens would return a positive signal for trypanosomes, since even highly infectious pathogens rarely exhibit 100% successful infection rates, we did expect OMNH 18846 to test positive because this was one of the animals Durham reported as displaying firm evidence of trypanosome infection [7]. In the event, six of the rats, including OMNH 18846, yielded trypanosome sequences. Five displayed unambiguous (100%) matches to published sequences for Trypanosoma lewisi, a known murine-infecting trypanosome; the remaining sample displayed a 3 bp deletion in the fragment amplified and thus could not be unambiguously characterized (Table 3). Unsurprisingly, as there were no differences between the GenBank sequence and those recovered from Christmas Island rats (except for the one instance of a 3 bp deletion), phylogenetic analysis unequivocally grouped them within T. lewisi (FIG. 3). Several of the infected rats were independently retested in two separate laboratories: for three samples our results were fully validated, but for three others validation must be regarded as tentative because only one (rather than both) laboratories reported a single replicate positive result—an effective illustration of the difficulties in working with less than single-copy pathogenic DNA from archival samples [14] (Table 1). Although a free-living kinetoplastid, Bodo saliens, was detected among the clones, this environmental contaminant could be easily distinguished from obligate parasitic trypanosomes at the sequence level. All morphologically defined subgroups (R. rattus, alleged hybrid, and R. macleari) contained T. lewisi DNA, confirming all three were susceptible to the infection.

Bottom Line: In the case of mammals, however, there are still no well-corroborated instances of such diseases having caused or significantly contributed to the complete collapse of species.Hybridization between endemic and black rats was also previously hypothesized, but we found no evidence of this in examined specimens, and conclude that hybridization cannot account for the disappearance of the endemic species.This is the first molecular evidence for a pathogen emerging in a naïve mammal species immediately prior to its final collapse.

View Article: PubMed Central - PubMed

Affiliation: Biological Sciences Department, Old Dominion University, Norfolk, VA, USA.

ABSTRACT
It is now widely accepted that novel infectious disease can be a leading cause of serious population decline and even outright extinction in some invertebrate and vertebrate groups (e.g., amphibians). In the case of mammals, however, there are still no well-corroborated instances of such diseases having caused or significantly contributed to the complete collapse of species. A case in point is the extinction of the endemic Christmas Island rat (Rattus macleari): although it has been argued that its disappearance ca. AD 1900 may have been partly or wholly caused by a pathogenic trypanosome carried by fleas hosted on recently-introduced black rats (Rattus rattus), no decisive evidence for this scenario has ever been adduced. Using ancient DNA methods on samples from museum specimens of these rodents collected during the extinction window (AD 1888-1908), we were able to resolve unambiguously sequence evidence of murid trypanosomes in both endemic and invasive rats. Importantly, endemic rats collected prior to the introduction of black rats were devoid of trypanosome signal. Hybridization between endemic and black rats was also previously hypothesized, but we found no evidence of this in examined specimens, and conclude that hybridization cannot account for the disappearance of the endemic species. This is the first molecular evidence for a pathogen emerging in a naïve mammal species immediately prior to its final collapse.

Show MeSH
Related in: MedlinePlus