Microclimate effects on cyphellae density in Sticta lichens Aide Casillas Department of Earth and Environmental Sciences, Northeastern University ABSTRACT The genus Sticta is a dominant lichen in tropical montane rainforest environments that is unique in possessing cyphellae, i.e. depressed pores involved in gas exchange, on the undersides of thalli. Microclimatic parameters such as relative humidity, canopy density and temperature were measured in relation to cyphellae density and colony size of S. filix in the Monteverde Cloud Forest. Significant correlations were found relating canopy density to cyphellae density (R2 = 0.200, p = 0.0007, n = 54), (R2 = 0.213, p = 0.0016, n = 44), colony size to temperature (R2 = 0.239, p = 0.0002, n = 54), (R2 = 0.592, p =. <0.0001, n = 20), as well as colony size to humidity (R2 = 0.301, p = <0.0001, n = 54), (R2 = 0.567, p = 0.0092, n = 20), (R2 = 0.272, p = 0.0016, n = 34) . Significant differences were shown between nonreproductive individuals of edge and interior microhabitats and temperature (t = -9.024, DF = 42, p = <0. 0001). Further analyses showed significant differences between non-reproductive and reproductive individuals and temperature (U = 67.50, p= 0.0472, n = 34) as well as canopy density (U = 67.00, p = 0.0452, n = 34); as well as a significant difference between interior and edge individuals and canopy size (U = 217.00, p = 0.0276, n = 54). RESUMEN El gnero Sticta es un liquen dominante en los ambientes tr opicales de pluviselva de montane que es extraordinario en pos eer cifelas, es decir poros deprimidos imp licaron en el cambio de gas, en las caras inferiores de talos. Los parmetros de microclimatic humedad tal como relativa, la densidad de dosel y temperatura fueron medidas en la relacin a la densidad del cyphellae y el tamao de la colonia de S. filix en el Bosque de Nube de Monteverde. Las correlaciones substanciales fueron encontradas relacionando la densidad de dosel a la densidad del cifelas (R2 = 0.200, P = 0.0007, N = 54), (R2 = 0.213, P =. 0016, N = 44), el tamao de la colonia a la temperatura (R2 = 0.239, P =. 0002, N = 54), (R2 = 0.592, P =. <0001, N = 20), as como el tamao de la colonia a la humedad (R2 = 0.301, P = <.0001, N = 54), (R2 = 0.567, P =. 0092, N = 20), (R2 = 0.272, P = 0.0016, N = 34). Las diferencias substanciales fueron mostradas entre individuos no-reproductores de la orilla y microhabitats y de la temperatura interior (T = -9.024, DF = 42, P = <0.0001). Analice an ms las diferencias signifi cativas mostradas entre individuos y temperatura noreproductores y reproductores (U = 67,50, P = 0. 0472, N = 34) as como la densidad de dosel (U = 67,00, P = 0.0452, N = 34); as como una diferencia significativa entre individuos de interior y orilla y tamao de dosel (U = 217,00, P = 0.0276, N = 54). INTRODUCTION The genus Sticta is a tropical foliose lichen found in montane rainforest communities. It is one of the most common lichens to inhabi t such environments; as such it plays an important role in its community by representi ng a large portion of the epiphytic biomass 1
(Lange et al. 2004). Its â€œsp ecialized depressed poresâ€ known as cyphellae characterize Sticta , making it unique among lichens as bei ng the only genus to possess cyphellae (Brodo et al. 2001). These hydrophobic â€œlittle volcanoesâ€ are located on the abaxial thallus and function much as stomata do in plan ts as they â€œallow for gas exchange with the environmentâ€ (Umaa and Sipman 2002). However, unlike stomata, cyphellae may not have the ability to close, potentially making Sticta increasingly vulnerable to harsh or desiccating microclimatic conditions. Sticta is interesting because of its unusual relationship w ith different symbionts, which determine the shape of its thallus. Ge neral lichen ecology explains that the same lichen can take different mor phologies (color, size, and thal lus shape) dependent upon its environmental location (Purvis 2000). This is partly due to environmental conditions determining which photobiont is present in lichens (Purvis 2000). Sticta is a lichen whose fungi, an ascomycete, is known to a ssociate with both cyanobacteria and green algae, sometimes in the same thallus body (Brodo et al. 2001). Sticta is unusual among lichens in being more abundant in cool, moist microhabitats. Contrary to most lichens, which pref er open environments of abundant sun exposure, Sticta occupies wet, interior forests an d low light environments (Galloway 1991). A study done by Lange tested the phys iology (respiratory a nd photosynthetic CO2 exchange and H2O relations) on Lobariaceae species as compared to the microclimatic conditions of a lower montane tropical forest in Panama. His results showed that although for most lichens, suprasaturati on results in reduced photosynthesis, Stictaâ€™s tolerance for hydration was much higher than other lichens and photosynthesis was not lowered as much. Also, low light conditi ons limit carbon fixation in most lichens, but Sticta is less affected than other genera, agai n showing its tolerance for conditions that characterize montane forest in teriors (Rundel et al. 1979). This investigation focuses on the particular foliose species Sticta filix. This cephellate lichen is most often restricted to higher elevations with relatively high precipitation (Rundel et al. 1979). Although S. filix is tolerant of varying light levels, it is most abundant in dark forest interiors (Runde l et al. 1979). At forest edges where light levels are higher, S. filix is less abundant (R undel et al. 1979). Despite the abundance a nd distinctiveness of Sticta , there exists little published research pertaining to the ecology of Sticta in tropical rainforest habitats. To help fill that gap, this study reports on the ecology and morphology of S. filix in Monteverde, Costa Rica. The focus of this study is to examine the morphological correlates of Sticta microhabitats in order to e xplore the possible reasons for Stictaâ€™s unusual microhabitat preference. Although possible photobionts may be responsible for structure and function of Sticta , this investigation focuses primarily on ab iotic influences by testing factors such as temperature, humidity and canopy dens ity on cyphellae densit y, thallus size and reproductive states of S. filix. The purpose of this investigatio n is to test the effects of microclimatic conditions on cyphellae densit y, compare the conditions of microclimates in which reproductive and non-reproductive i ndividuals are located, and to measure the effects of microclimatic conditions on the sizes of S. filix colonies. I propose that Sticta prefers cool habitat areas because it has cyphellae and that cyphellae density may be important in determining tolerance to moist, cool conditions but may also decrease tolerance to dry, hot climates. I also propose that cyphellae adapt Sticta to the low light, high humidity conditions of forest inte riors, but because they may 2
not be able to close, cyphellae make Sticta poorly adapted to high light, high temperature conditions on the edge. Further, I proposet hat if cyphellae canâ€™t be regulated by being opened and closed, they have to be regul ated in their density. I hypothesize that cyphellae density should dec line in open areas with hi gher sun exposure and drier atmospheres and increase in wetter, cool er areas. I also hypothesize that Sticta will increase size and reproductive growth in areas that are wetter and cooler. METHODS Field data were collected between the 24th of October and the 11th of November, 2006. A total of fifty-four Sticta filix samples were collected from the lower montane wet forest life zone of the Monteverde Cloud Forest. At an elevation of 1500m, Monteverde receives 2.5 m of rain each year and another 0.67 5 m of precipitation per year in the form of mist (Haber et al 2002). Samples were ra ndomly collected from sites located in forest interior and forest edge from bark of eith er living trees, or rott ing logs. Thirty-four S. filix samples were collected from the closed canopy forest interior. Twenty S. filix samples were collected from forest edge environments along roads, trails and light gaps within and bordering the Montev erde Cloud forest. Relative humidity and temperature were measured electronically. Humidity was reported as a percentage and temperature was reported in C. Canopy density was measured with a spherical densiometer to measure percent canopy cover for each sampled site. A gridded transparent sheet and a dissecting microscope were used to estimate concentrations of cyphellae present per cm2 for each S. filix sample. Several lobes of different thalli were collected and measured for cyphellae density to ensure an accurate assessment for each of the fifty-four S. filix samples. A minimum of three measurements was recorded for each lobe. Also noted was the reproductive state of each S. filix . The size of each S. filix colony on its natural substrate was measured. Measurements were recorded in millimeters. A minimum of two diameter measurements was recorded and then averaged for each collected sample of S. filix . RESULTS Microclimatic conditions in forest edge environments as compared to forest interior environments differed minimally in average te mperature and relative humidity (Table 1). The average temperature differed only by 1.22 C from forest edge habitats to forest interior, with forest edge environments be ing warmer. The average percentage humidity varied only by 2.3 percent, with edge envi ronments being less humid than interior. Canopy density from forest interior environments to forest edge varied by 48.4 percent. The average diameter of interior indivi duals was 163.03 mm, while edge individuals averaged 127.05 mm. The average cyphellae density of edge i ndividuals was 17.06 cm2 while interior individuals averaged 50.75. Results also show that an increase of a mere 1.22C from forest interior to forest edge corresponds to a significant decrease of an 3
average 36.25mm in diameter per S. filix colony. Also shown was that a 2.31% decrease in humidity can have the same eff ects on colony size in edge populations. Simple linear regression analyses were run on data sets of all populations (n = 54 to represent the entire general sample si ze, n = 20 representative of edge sample population, n = 34 representative of interior sample populati on, n = 10 representative of reproductive sample population, n = 44 repres entative of non-reproductive sample size ) against each microclimate parameter (temperature per C, percentage humidity, percentage canopy density). There was a significant rela tionship between cyphellae density and canopy density (R2 = .200, p = .0007, n = 54). Regression analyses of nonreproductive populations showed a significant relationship between cyphellae density and canopy density (R2 = .213, p = .0016, n = 44), but no other microclimate parameters. Regression analyses showed no relationship between cyphellae density and temperature or humidity for the total population (n = 54). Regression analyses showed no relationships between cyphellae density and microclimatic parameters for the populations of interior individuals, edge individuals, or reproductive i ndividuals (n = 34, n = 20, n = 10, respectively). Further simple linear regressions were r un on all data sets to compare size of S. filix colonies against each microclimate parame ter. Analyses showed no relationship between colony size of S. filix and percentage canopy density when for the total population (n = 54). However, significant rela tionships were shown between colony size of S. filix and temperature (R2 = .239, p = .0002, n = 54) and percent humidity (R2 = .301, p = <. 0001, n = 54). Among edge individual s, significant relationships were shown between colony size and temperature (R2 = .592, p = <. 0001, n = 20) and between colony size and humidity (R2 = .567, p = .0092, n = 20). No significant results were shown when comparing colony size and canopy density in edge individuals. Regression analyses of microclimate and colony size in interior sa mple population proved significant results only between colony size and percent humidity (R2 = .272, p = .0016, n = 34) and no other microclimate parameters (temperature or canopy density). Unpaired t-Tests were run to test the average microclimate conditions on edge versus interior populat ions of non-reproductive S. filix individuals. Significant differences were found for temperature (t = 5.654, DF = 42, p = <. 0001) and canopy density (t = -9.024, DF = 42, p = <. 0001) but no significant differences were found for humidity (t = -1.865, p = .0691, DF = 42). Mann-Whitney U tests were run on all data to test microclimate parameters on populations of reproductive and non-reproductive individuals. All tests show no significant differences in the total population (n = 54). Within interior environments, there were significant differences between re productive and non-reproductive individuals and temperature (U = 67.50, p = .0472, n = 34), canopy density (U = 67.00, p = .0452, n = 34), but not humidity (U = 101. 000, p = .4727, n = 34). An additional Mann-Whitney U test showed a significant difference in co lony size after compari ng interior and edge individuals of the total popul ation (U = 217.00, p = .0276, n = 54). 4
DISCUSSION The results showed that the abiotic conditi ons of the edge and the interior were significantly different, as were the mi crohabitats of the reproductive and nonreproductive individuals in the forest (Table 1). Canopy density of the edge environments was approximately half than that of the interi or. In response to habitat differences such as this, Sticta exhibits changes in its morphology. Analyses show that higher canopy densities are significantly correlated with higher cyphellae densities in S. filix when compared to the general sample population, as a 48.4% decrease in canopy density from forest interior to forest edge corresponds with a 33.69% decrease in cyphellae density. Also, interior populations of S. filix have higher cyphellae densities under denser canopies, which suggest that S. filix adapts its cyphellae density to microclimate conditions, and that optimal conditions for growth are in forest interiors. These results suggest cephellate morphology of S. filix may be an adaptation to the low light conditions of its preferred habitat. Within interior populations alone, higher humidity correspond to a larger colony size of S. filix . Such microclimate effects on colony size of edge populations of S . filix need to be studied in more detail to allow for specific causation of such effects. Further, reproductive states appear to be significantly correlated with interior habitat ecologies. Of the S. filix samples collected, there wa s a higher number of nonreproductive individuals than reproductive i ndividuals, with non-reproductive samples representing 44 of the 54 total collections. While growth may be greatest in forest interiors, reproduction is possibl e only in particular microha bitats where temperature is elevated. Results of Mann-Whitney U tests show that reproductive individuals within interior forest populations of S. filix exist only at higher warmer interior temperatures. Interestingly enough, a difference of less than one C (.95C) in average temperature within interior populations of S. filix made the difference between the presence or absence of reproductive bodies on the upper thalli. More research on reproductive ecology of S. filix must be done in order to determine causation. Because of Stictaâ€™s specificity to its environm ents, it exhibits morphological adaptations, which lend it advantages over othe r lichen species. This may explain its obvious dominance in such environments. Th e effects of humidity, temperature and light levels on morphology, including cyphellae density and colony size, in this investigation may provide insight into Lange (2004) ear lier studies of successful physiological performance in S. filix . Lange determined that optimal thallus water content for photosynthetic production in S. filix is measured at 200% ( tha llus water content, in % dry weight). However, saturation does not occur in S. filix until 400% (thallus WC, in % dry weight). Lange went on to prove that the absolute level of CO2 uptake is significant at both optimal and saturated thallus wa ter contents. (Rundle et al. 1979). Stictaâ€™s extraordinary tolerance for high thallus water content is reason for its environmental conditions to not inhibit net photosynthesis production. Perhaps a reduced colony size is a consequence of lowered photos ynthetic ability. However, fu rther research would need to be done for this to be determined. 5
Why would Sticta adapt to have more cyphellae in environmental conditions of lower light? Perhaps this has to do with carbon fixation. Cyphellae regulate gas exchange with the environment, thus, observati ons of their higher c oncentrations in light limiting environments may suggest this as an ad vantage to facilitate fitness. A study by Lange (2004) partially supports this hypothesis. When m easuring suprasaturation in Sticta , he observed that where as low light environments usually limit carbon fixation lichens, Sticta showed a significantly less depression as compared to other lichen species in the same environment. Additionally, observations of possible dual photobionts were noted in some interior S.filix collected samples. This may poten tially explain some of the trends statistical results show. Further research must be done to assess the extent of which photobionts affect physio logy and morphology of S. filix in environments of tropical montane rainforests. This investigation addr esses the immense need for current research on basic morphologic adaptations and habitat ecologies of tropical montane rainforest lichens. Further, the sensitivity of S.filix to its specific preferred microclimatic conditions may render it susceptible to global climate cha nge. Likewise, immediate research should be conducted to further determine the importance of such effects. ACKNOWLEDGMENTS I would like to thank Karen and Alan Masters for their continual support and encouragement throughout this most wonderfu lly exigent experience. I would also like to express my sincere thanks Camryn Pennington and Tom McFarland for lending me their endless patience and help on relatively ev ery aspect of this program. I would also like to thank Tania for her guidance throughout this course. I would like to express a special thank you to all of my compaeros, my friends, all of whom I wish much success towards their future scientific careers and endeavors. Lastly, I would like to thank La Estacin Biologa, for without which I woul d have not had the opportunity for such a satisfying learning experience. LITERATURE CITED Brodo, I., Sharnoff, S. and Sharnoff, S. 2001. Lichens of North America. Yale University Press, New Haven, Connecticut, page 671. Galloway, D. 2005. Notes on the Holotype of Sticta damaeconris (= Sticta weigelii ). The Lichenologist. 38 (1):89-92. Galloway, D. 1991. Tropical Lichens: Their Sy stematics, Conservation, and Ecology. The Systematics Association, Vol. 43. Clarendon Press, New York. Pp. 128-130. Green, T., Horstmann, J., Bonnett, H., Wilkin s, A., Silvester, W. 1980. Nitrogen 6
Fixation by Members of the Stictaceae (Lichens) of New Zealand. New Phytologist. Vol. 84 ( 2):348-349. Lange, O., Bdel, B., Meyer, A., Zellner, H. and Zotz, G. 2004. Lichen Carbon Gain under Tropical Conditions: Water Relations and CO2 Exchange of Lobariaceae species of a Lower Montane Rainforest in Panama. The Lichenlogist. 36 (5): 329-342. Purvis, W. 2000. Lichens. Smithsonian Inst itution Press, Washington D.C. page 61. Rundel, P., Bratt, G., Lange, O. 1979. Habitat Ecology and Physiological Response of Sticta filix and Pseudocyphellaria delisei from Tasmania. The Lichenologist. 82(2):171180. Umaa, L., Sipman, H. 2002. Lquenes de Costa Ri ca. Instituto Nacional de Bioversidad, Santo Domingo de Heredia, Costa Rica. Pp. 100 . TABLES TABLE 1. The average microclimatic conditions of edge and interior sites where S. filix was found, and morphological conditions of the S. filix individuals Sample size Temperature (C) Humidity (%) Canopy Density (%) Cyphellae Density (cm2) Avg.erage thallus diameter (mm) Number of individuals with reproductive bodies Edge 20 22.25 63.40 47.47 17.06 127.05 0.00 Interior 34 21.03 65.71 95.87 50.75 163.30 10.00 7
FIGURES QuickTime and a TIFF (LZW) decompressor are needed to see this picture. FIGURE 1. Scanning electron microg raph of a cyphella in Sticta (Avalon.unomaha.edu/lichens/Bio%204350%20PDF/vegetative%Morpholog y%2011.pdf) 8
0 20 40 60 80 100 120 140 160 180 200 0102030405060708090100 percent canopy density 0 20 40 60 80 100 120 140 160 180 200 02 04 06 08 01 0 0 percent canopy density FIGURE 2. Effects of canopy density on cyphellae density in general sample population of S. filix (R2 = .200, p = .0007, n = 54) in Monteverde Cloud Forest FIGURE 3. Effects of canopy density on cyphellae density of non-reproductive population S. filix (R2 = .213, p = .0016, n = 44) in Monteverde Cloud Forest 0 10 20 30 40 50 60 70 80 0100200300400500600 average diameter S. filix colony (mm) 0 10 20 30 40 50 60 70 80 0100200300400500600700800900 average diameter of S. filix colony ( m FIGURE 4. Effects of humidity on colony size of S. filix from interior populations of the Monteverde Cloud forest (R2= 272, p = .0016, n = 34) FIGURE 5. Effects of humidity on S. filix colony size of edge populations (R2= .567, p = .0092, n = 20) in the Monteverde Cloud Forest 9
0 5 10 15 20 25 30 0100200300400500600700800900 average diameter of S. filix colony ( m 0 10 20 30 40 50 60 70 80 0100200300400500600700800900 average colony size of S. filix 10 FIGURE 6. Effects of temperature on edge populations (R2= .592, p = <. 0001, n = 20) of S. filix in the Monteverde Cloud Forest FIGURE 7. Effects of humidity on colony size of S. filix in the Monteverde Cloud Forest (R2= .301, p = <. 001, n =54) 0 5 10 15 20 25 30 0100200300400500600700800900 average diameter of S. filix colony (mm) FIGURE 8. Effects of temperature on colony size of S. filix in the Monteverde Cloud Forest (R2= .239, p = .0002, n =54)
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Efectos del microclima en la densidad de cifelas en lquenes Sticta
Microclimate effects on cyphellae density in Sticta lichens
The genus Sticta is a dominant lichen in tropical montane rainforest environments that is unique in possessing cyphellae, i.e. depressed pores involved in gas exchange, on the undersides of thalli. Microclimatic parameters such as relative humidity, canopy density and temperature were measured in relation to cyphellae density and colony size of S. filix in the Monteverde Cloud Forest. Significant correlations were found relating canopy density to cyphellae density (R2 = 0.200, p = 0.0007, n = 54), (R2 = 0.213, p = 0.0016, n = 44), colony size to temperature (R2 = 0.239, p = 0.0002, n = 54), (R2 = 0.592, p =. <0.0001, n = 20), as well as colony size to humidity (R2 = 0.301, p = <0.0001, n = 54), (R2 = 0.567, p = 0.0092, n = 20), (R2 = 0.272, p = 0.0016, n = 34) Significant differences were shown between non-reproductive individuals of edge and interior microhabitats and temperature (t = -9.024, DF = 42, p = <0. 0001). Further analyses showed significant differences between non-reproductive and reproductive individuals and temperature (U = 67.50, p= 0.0472, n = 34) as well as canopy density (U = 67.00, p = 0.0452, n = 34); as well as a significant difference between interior and edge individuals and canopy size (U = 217.00, p = 0.0276, n = 54).
El gnero Sticta es un liquen dominante en los ambientes del bosque montano tropical que es nico en poseer cifelas, es decir poros deprimidos involucrados en el intercambio de gases, en las caras inferiores de los talos. Los parmetros micro climticos, tales como la humedad relativa, la densidad del dosel y la temperatura fueron medidos en relacin a la densidad de la cifela y el tamao de la colonia de S. filix en el Bosque Nuboso de Monteverde.
Text in English.
Tropical Ecology 2006
Ecologa Tropical 2006
t Monteverde Institute : Tropical Ecology