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Blood parasite infection in mice from cloud forest and nearby disturbed habitats Jesse A. Blumenstock Department of Biological Sciences, University of Pittsburgh ABSTRACT Conversion of habitat by humans is pervasive, increasing, and the root of serious environmental problems. This study was performed to find differences in blood parasite infections of host mice in neotropical cloud forest versus nearby disturbed habitat. In Monteverde, Costa Rica, mice were trapped and examined for blood parasite species richness and abundance in primary forest and disturbed areas near houses. Twenty-eight mice were captured: 15 from the forest and 13 from the disturbed habitats. Eighty-six percent of these mice were of the species Peromyscus nudipes There was no significant difference of parasite species richness between mice from the forest habitat (mean = 2.818 1.25; N = 11) and disturbed habitat (mean = 3.25 0.75; N = 12)(Mann-Whitney U = 54.5; P > 0.05) or of parasite abundance between the forest habitat (mean = 8.36 5.12; N = 11) and disturbed habitat (mean = 10.33 5.02; N = 12) (Mann-Whitney U = 57.0; P > 0.05). Transference between the habitats may be frequent, causing similarities in parasite infection rates and types between the populations. Peromyscus nudipes is a weedy species and possibly does not discern between the different areas, resulting in this transference. RESUMEN La conversin del habitat por los seres humanos sigue en aumento y es la raz de problemas ambientales serios. Este estudio fue realizado para encontrar diferencias en las infe cciones de parsitos de la sangre en ratones del bosque neotropical nuboso comprado con habitats degradados aledanos. En Monteverde, Costa Rica, atrap ratones y examin la riqueza de las especies de parsitos de la sa ngre y su abundancia en bo sque primario y las reas degradados cerca de las casas. Veintiocho ratones fueron capturados, 15 del bosque y 13 de los habitates degradados. Ochenta y seis por ciento de estos ratones pertenecieron a la especie Peromyscus nudipes No hubo una diferencia significativa de la riqueza de las especies de pa rsitos encontrados entre los ratones del habitat del bosque (promedio = 2.818 el 1.25; N = 11) y habitat degradado (promedio = 3.25 0.75; N = 12) (Mann-Whitney U = 54.5; P > 0.05), o de la abundancia del parsito entre el habitat del bosque (promedio = 8.36 5.12; N = 11) y habitat degradado (promedio = 10.33 5.02; N = 12) (Mann-Whitney U = 57.0; P > 0.05). La transferencia entre los habitates puede ser frecuente, lo que puede estar causando las semejanzas encontrados en los ndices de infeccin de los parsitos entre las poblaciones. Peromyscus nudipes es una especie oportunista y posiblemente no discierne entre las diversas reas, da ndo por resultado esta transferencia. INTRODUCTION Transformation of land by human use represents the most significant human modification of the planet. Human impact on Earths ecosystems includes intensive row-crop farming, urban development, and various other destructive prac tices resulting in a n early 30% increase in atmospheric CO2 since the Industrial Revolution (Vitous ek et al. 1997). According to some estimates, approximately 50% of the potential cl osed-canopy forest on earth has already been cleared and converted to other uses. During the 1990s, secondar y forest reclaimed just one hectare for every six or seven deforested. Therefor e, we are cutting forest at a much faster rate than it is growing back (Wright 2005). Climate change, loss of biodiversity, and changes in community composition are among the most notable effects of human land use (Vito usek et al. 1997). As a result of continuing population growth and growing consumption, the few large, undisturbed areas remaining are threatened. This is especially true in devel oping countries in the Tropi cs, where the rate of human population growth and biodiversity are the highest. Inst ead, many species will go extinct and a mosaic of persisting, disturbed habitats will contain the majority of remaining tropical diversity. These disturbed patches are rarely studied, yet the re sponse of biodiversity to this 1
fragmentation will determine its future. According to a study of avifauna in southern Costa Rica, social interactions drastically change in open habitats, negatively affecting some species and favoring other, more generalist species (Daily 2001). These generali st species may be nonnative and may only invade a habitat and increa se in density if a disturbance occurs and conditions change. The species that most often suffer when environments are transformed for human use are forest specialist species, which ar e very sensitive to change in their habitat. Rate and frequency of infection and tr ansmission of pathogens, depend on several parameters of the host population, their habitat, and th e nature of the pathogen. Factors of the host population that affect pathoge n transmission include populati on density and migration. In a more dense population, susceptible individuals may be in clos er contact with infected individuals. A high rate of migr ation in a population affects transmission because it potentially puts more individuals that are sus ceptible to infection into contact with infected individuals. The qualities of a pathogen that affect its transmission are things such as its virulence, its method of transmission, and its host specificity. If a pathogen is a host genera list, there may be one or more reservoir species on which the pathogen has le ss impact than it does on the definitive host species. In this case, the reservoir host can tran sfer the infection to more affected species and thus contact between species may affect the spread of disease (McCallum and Dobson 2002). One habitat factor that affects pathogen transmissi on is variability in the external environment of a host, such as habitat disturbance. This could stress the host population, increasing the susceptibility of a host to infection, allowing parasite transmission re gardless of whether the change has any direct effects on parasite deve lopment and survival (Morgan et al. 2004). Based on recent data, (Pederson 1998, Rothman 1999, Lippert 2001, Hayes and Laval 1989) predominantly one species of mouse, Peromyscus mexicanus, exists in the Monteverde area in Habitat Zone Three (Hayes and Laval 19 89). The specific subspecies that exists in Montverde is the P. mexicanus nudipes sometimes considered its own species as P. nudipes. P. nudipes is a small, omnivorous, weedy species that exists in many differe nt habitats. This rodent community was not always dominated by one species. In a trapping study conducted to compare population ecology of P. nudipes from 1979 to 1981, in plots in Monteverde habitat zone three, several other species of rodents we re trapped with moderate to high frequency. In fact, individuals of the species Herteromys desmarestianus were determined to be equal or greater in abundance than P. nudipes in this study (Anderson 1982) This weedy species has since invaded the forest habitat, increased in density, and potentially linked disturbed habitat and forest. This could have passed parasites from one habitat to the other, causing widespread effects from an unspecified change in community structure from the past. To examine whether land changes from forest to open, human use areas have an effect on the prevalence of blood parasites in rodents, I compared the sp ecies richness and abundance of parasites found in blood samples fr om rodents captured in forest to rodents captured in close proximity to forest. In a past experiment by Roelands and Taft (1999), several identified parasites were found to occur in the mouse populations of Monteverde. Trypanosoma Plasmodium and Microfilarial stages of parasites were found in varying abundances in several rodent species in secondary and primary forests. The study suggests that both the abundance and species richness of endo-pa rasites in rodents are hi gher in hosts found in sec ondary forest than in primary forest sampled in this study (Roela nds and Taft 1999). I hypothesized that my study would demonstrate similar trends between pa rasite levels and population habitats when comparing primary forest and habitats that have been deforested for many years. This comparison of forest habitat to transformed ar eas should show a higher abundance and frequency 2
of infected individuals in disturbed habitats be cause the conditions in a disturbed habitat should increase the rate of paras ite infection according to pat hogen transmission parameters. I also compared host weight and length in each habitat to parasite abundance and species richness to determine whether size is related to parasite infection rate If small mice were observed to have a higher paras ite richness or abundance, then it could be assumed that the young were more susceptible to para site infection and that highly infected individuals were not healthy enough to spend energy on growing to full size. METHODS Study Sites This study was conducted around the Estacin Biolgi ca de Monteverde, in Monteverde, Costa Rica. I trapped rodents over seven nights in two ha bitats: forest and in close proximity to houses. Both habitats were in Lower Montane Wet Fore st (Holdridge 1967), in the Monteverde habitat zone three (Hayes and Laval 1989), and between 1520 m and 1600 m. The forest study site was along the Sendero Principal trail, beginning approxim ately 150m into the forest with traps placed along the sides of the trail every ten meters. The house study traps we re placed surrounding the Estacin Biolgica de Montever de, nearby cabins, and a house approximately 150m down the road, all within ten meters of a human habitation. Rodent Trapping Seventeen Sherman live traps were used to capture rodents in each of the two habitat types. The traps were baited with one tablespoon of a mixt ure of peanut butter and oatmeal before each trapping night. The following morning each trap was checked. Captured rodents were identified to species and sex and measurements of weight, head to vent length, and hind foot length were taken. Rodents were marked to prevent repetitio n of data through recaptures by cutting a small amount of hair off the upper part of the back. A blood sample was collected from each individual by lancing the bottom of the back foot behind the pad. The resulting droplet of blood was pressed against a glass slide. Identifying and Counting Blood Parasites At the end of each collection day, the slides with blood were fixed with 100% methanol (MeOH) for 2-5 minutes (Gardner 1996). They were then stained with a soluti on of 5% Geimsa stain diluted with Wright buffer for 20 to 30 minut es, face down on a shallow plate, propped up on other slides. Twelve of the co llected samples were initially ob served with a microscope under oil immersion 1000x magnification to identify severa l categories of morphospecies. The nine morphospecies identified (Appendix) were then used in the analysis of each of the blood samples under oil immersion 1000x magnification. If a new morphospecies was found during sample analysis, it was added to the list of possible mo rphospecies. Ten random fields of view were observed in each slide for the presence and abundance of the nine morphospecies. RESULTS Over seven nights of trapping, 30 mice were captu red. Two of these were recaptures. Twentyfour of the mice were P. nudipes and four individuals trapped were Scotinomys teguina Sixteen captures were made in the forest site, with one known recapture. Out of these 16 captures from 3
0 0.5 1 1.5 2 2.5 3 3.5 4 Forest Site House SitesParasite Morphospecies Richness (a) 0 2 4 6 8 10 12 14 Forest site House sitesParasite Morphospecies Abundance (b) Figure 1. Comparisons of means between sample s from a forest study site and multiple house study sites of (a) Parasite Morphospecies Richne ss and (b) Parasite Morphospecies Abundance in mouse hosts. In both comparisons, the average value from the house sites was higher than the average value from the forest site. However, this difference was not significant in (a) the comparison of the means of parasite morphos pecies richness (Mann-Whitney U = 54.5; P > 0.05), or in (b) the comparison of the means of parasite morphospecies abundance (MannWhitney U = 57.0; P > 0.05) (SE bars included). 4
the forest site, 13 were P. nudipes and three were S. teguina. In the four different house sites, 14 mice were trapped, with one known recapture. Thirteen of the house site captures were P. nudipes while one was S. teguina No captured rodents showed a ny outwardly apparent signs of illness or infection. No significant difference wa s observed between the mean parasite morphospecies richness in blood samples from the forest habitat (2.818 1.25; N = 11) and the mean parasite morphospecies richness in the blood sa mples from the house habitats (3.25 0.75; N = 12) (Figure 1a) (Mann-Whitney U = 54.5; P > 0.05). No significant difference was seen between the mean parasite abundance in blood samples from the forest habitat (8.36 5.12; N = 11) and the mean parasite abundance in the blood samples from the house habitats (10.33 5.02; N = 12) (Figure 1b) (Mann-Whitney U = 57.0; P > 0.05). There were no clear tr ends regarding which parasites were found in each habitat or in each host species (Appendix B). Regressions comparing morphospecies richne ss in blood samples to host weight showed no significant relationships in the forest site (R2 = 0.003; p-value = 0.87; n = 11) or in the house sites (R2 = 0.001; p-value = 0.92; n = 12). Regressi ons comparing morphospecies richness in blood samples to host head to vent length showed no significant relationships in the forest site (R2 = 0.0001; p-value = 0.98; n = 11 ) or in the house sites (R2 = 0.002; p-value = 0.90; n = 12). Regressions comparing parasite abundance in blood samples to host weight showed no significant relationships in the forest site (R2 = 0.094; p-value = 0.36; n = 11) or in the house sites (R2 = 0.008; p-value = 0.79; n = 12). Regressi ons comparing parasite abundance in blood samples to host head to vent length showed no significant differences in the forest site (R2 = 0.059; p-value = 0.47; n = 11) or in the house sites (R2 = 0.028; p-value = 0.60; n = 12). DISCUSSION The lack of relationship between parasite infection (as morphospecies richness or as morphospecies abundance) to host size (as weight or as head to vent length) leads to several conclusions. As smaller mice were not observe d to have a higher parasite morphospecies richness or abundance, it cannot be assumed th at the young were more susceptible to parasite infection. Instead, all individuals are apparently being exposed to parasites. Another conclusion that can be drawn from these results is that infection does not seem to be keeping mice from growing to full size. My data on mouse length and weight are very similar to average literature values for adult size (Reid 1997). All mice al so showed no outwardly apparent signs of infection, yet all were infected with at least one morphospecies of parasite. Parasite infection, therefore, may not have signifi cant effects on mouse health. Individuals in both habitats are equally infected by parasites. This could result from three different mechanisms. First, there may be contact between some individuals living in the two different habitats. Many of the parasites that infect mice, including many of those parasites infecting my samples (suggested by morphospeci es appearance), are vector-borne. Another possibility is that vectors of the parasites may be able to travel between habitats, infecting individuals in both areas (Morgan et al. 2004). The final way that individuals in both habitats could have equal exposure to parasite infection, is that the mice may see both habitat types as one and range over both disturbed areas and forest without discern. The species has a relatively small average home range of approximately 0.10 h ectares. However, if the species has a high 5
density, as it has been shown to have in this lo cation, then it is possible that an infection by a parasite could easily spread through a con tinuous population spanning the transition from a forest area to a disturbed area (Anderson 1982). There is further evidence that P. nudipes does not discern between habitats and has actually benefited from the destruction of forest habitat. The population ecology study of P. nudipes conducted from 1979 to 1981 demonstrated a significantly diverse community of small rodents (Anderson 1982). In the past six years, however, several studies conducted in the same areas have found P. nudipes to make up a much larger subset of the small rodent population (Pederson 1998, Rothman 1999, Lippert 2001). On e study collected 69 mice, of which, 95.7% were P. nudipes (Pederson 1998). It seems apparent that something has happened in the recent past f acilitating a change in the rodent species richness of the area and allowing P. nudipes to become the dominant species. A possible explanation is that a threshold has be en reached where sufficient habitat clearing in the past created a community change where othe r species that were dominant could no longer survive and the weedy P. nudipes species took over. This coul d be an example of what Nee and May (1992) found in their study on habitat destruction and competition. As habitat loss increases, a formerly inferior competitor may increase in numbers relative to a superior competitor. This will occur if the inferior speci es is a weedy generalist-type species and has a higher rate of colonization than the competitor (Nee and May 1992). Another study suggested that the compe titive force could be a pathogen, preventing multiple host species to coexist in the same patch (McCallum and Dobson 2002). Therefore, a possible explanation of the recent dominance of P. nudipes could be that the species may not be as affected by the parasites as other species are. It is possible that when the forest was cleared, the habitat change caused the other small rodent species fitness to be more negatively affected than the fitness of P. nudipes, causing them to be outcompeted. The loss of competing species, since 1982, may have resulted in easier parasite transmission be tween the dense, monodominat host community. This hypothesis, however, must be tested by future studies. One such study could test the idea that currently, P. nudipes does not discern between the habitats, by trapping along a continuous stretch from one habitat to the other. Individuals could be marked specifically to observe movement between the hab itats. If available, genetic data could be collected from collected mice to further analy ze similarity between individuals the habitats. With current deforestation claiming two pe rcent of forests worldwide each year, problems associated with the loss of biodiversity and changing community dynamics as a result of habitat destruction will likely worsen (Ter bourgh 1992). The microscopic world is often less studied, yet it can have immense impacts on an eco system. Microorganisms often act as an obscure keystone species (Dobson 1997), potentially determining the community structure. Future conservation efforts must take into acco unt the possibility of microorganisms affecting the outcome of altering land use. Processes, such as destruction of ha bitat can lead to the degradation of biodiversity and, perhaps a mo re selfish concern, effects on human health. ACKNOWLEDGEMENTS I would like to thank the Estacin Bioglgica de Monteverde for the use of the forest and surrounding land for my mouse collections and for the use of the laboratory. I woul d also like to thank Alan and Karen Masters for the use of their property for mouse collection and for their support thro ughout the process of this study, without which, I would have been completely lost at times. I would like to thank Ruth Salas for her hours of lab guidance even though she had her own students to help. Finally I would like to thank Tom McFarland and Cam Pennington for their 6
unbelievable amounts of assistance and guidance throughout the entire course of this project, at all hours, no matter how ridiculous my requests. LITERATURE CITED Anderson, S.D. 1982. Compara tive population ecology of Peromyscus mexicanus in a Costa Rican wet forest. University of Southern California. Los Angeles, Califonia. Daily, G.C., P.R. Ehrlich, and G. A. Snch ez-Azofeifa. 2001. Countryside biogeography: Use of human-dominated habitats by the av ifauna of southern Costa Rica. Ecological Applications 11 : 1-13. Dobson, A. 1997. Infectious disease and the conservation of biodiversity. In: Principles of Conservation Biology, 2nd Ed. Meffe, G. and C. R. Corroll, ed. Sinauer Press, MA, pp. 256-257 Gardner, S.L. 1996. Field Parasitology Techniques for Use with Mammals. In: Measuring and Monitoring Biological Diversity: Standard Methods for Mammals D.E. Wilson, et al., ed. Smithsonian Institution Press, Washington, DC, pp. 291-298 Hayes, M. and R. Laval. The mammals of Monteverde: An a nnotated check list to the mammals of Monteverde Tropical Science Center, San Jos, Costa Rica, 1989. Holdridge, L.R. 1967. Life Zone Ecology. Tropi cal Science Center, San Jos, Costa Rica. Lippert, L.I. Amblyopinus beetles and their relationship to parasites of Mexican Deer Mice ( Peromyscus mexicanus ). EAP Spring 2001. McCallum, H. and A. Dobson. 2002. Disease, habitat fragmentation and conservation. Biological Sciences 269 : 2041-2049. Morgan, E.R., E.J. Milner-Gulland, P.R. To rgerson, and G.F. Medley. 2004. Ruminating on complexity: macroparasites of wildlife and livestock. TRENDS in Ecology and Evolution 19 : 181-187. Nee, S. and R.M. May. 1992. Dynamics of Meta populations: habitat destruction and competition coexistence. Journal of Animal Ecology 61 : 37-40. Pederson, A. 1998. Edge effects on Blood Parasite Abundance in Peromyscus nudipes CIEE Spring 1998. Reid, F.A. 1997. Mexican Deer Mouse. Field Guide to the Mammals of Central American and Southeast Mexico Oxford University Press, New York, NY, pp. 232-233. Roelands, J. and R. Taft. 1999. The hidden world in rodents: incidence of blood-borne parasites in mice and rats in Monteverde, Costa Rica. EAP Fall 1999. Rothman, A.W. 1999. Effects of climate change and elevation on small rodent communities in Monteverde, Costa Rica. CIEE Spring 1999. Terbourgh, J. 1992. Diversity and the Tropical Rain Forest Scientific American Library, New York, NY. Vitousek P. M., H. A. Mooney, J. Lubche nco, and J.M. Melillo. 1997. Human Dominance of Earths Ecosystems. Science 277 : 494-499. Wright, S.J. 2005. Tropical forests in a changing environment. TRENDS in Ecology and Evolution 20 : 553-560. 7
Appendix A Photo examples of nine parasite morphospecies QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Cluster (Ruptured Schizont stage of Plamodium ) QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Trypanosome Possible Hepatozoon QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. 8
QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Rods QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Microfilarial parasite QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Gametophyte stage (Possible Plasmodium ) 9
QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Ribbons QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Infected Red Blood Cell (Possibly Plasmodium, Babesia, or Grahamella ) Flagellate QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. 10
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Blumenstock, Jesse A.
Infeccin de hemoparsitos en los ratones del bosque nuboso y cerca de los hbitats perturbados
Blood parasite infection in mice from cloud forest and nearby disturbed habitats
Conversion of habitat by humans is pervasive, increasing, and the root of serious environmental problems. This study was performed to find differences in blood parasite infections of host mice in neotropical cloud forest versus nearby disturbed habitat. In Monteverde, Costa Rica, mice were trapped and examined for blood parasite species richness and abundance in primary forest and disturbed areas near houses. Twenty-eight mice were captured: 15 from the forest and 13 from the disturbed habitats. Eighty-six percent of these mice were of the species Peromyscus nudipes. There was no significant difference of parasite species richness between mice from the forest habitat (mean = 2.818 1.25; N = 11) and disturbed habitat (mean = 3.25 0.75; N = 12)(Mann-Whitney U = 54.5; P > 0.05) or of parasite abundance between the forest habitat (mean = 8.36 5.12; N = 11) and disturbed habitat (mean = 10.33 5.02; N = 12) (Mann-Whitney U = 57.0; P > 0.05). Transference between the habitats may be frequent, causing similarities in parasite infection rates and types between the populations. Peromyscus nudipes is a weedy species and possibly does not discern between the different areas, resulting in this transference.
Este estudio se realiz para encontrar diferencias en las infecciones de hemoparsitos en la sangre de los ratones hospederos en los bosques nubosos neotropicales versus el hbitat perturbado cercano.
Text in English.
Environmental impact analysis
Anlisis de impacto ambiental
Tropical Ecology 2006
Ecologa Tropical 2006
t Monteverde Institute : Tropical Ecology