Lambir Nepenthes Colour Project

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Green or Red? Color Adaptation of Nepenthes gracilis

Chen Dexiang, Sarah Peprah and Luong Thien Tam

Contents

Abstract

The state of Sarawak has 25 known species of pitcher plants, of which Nepenthes gracilis is a common species. As there is a belief that green pitchers are associated with higher heights and red pitchers in lower heights , we hypothesize that there is a height-based distribution and that color is an adaption that increases the pitcher's ability to capture prey. Using N. gracillis as a model, we analyzed the effects of light availability, color, and height on insect yield using the General linear model test. Our results indicated that there was a height-based distribution of color but refuted the secondary hypothesis that color is an adaptive trait .


Introduction

It has been observed that coloration of pitchers range from red to green (Clarke & Lee, 2004) and this is believed to be affected by the availability of light (pers. com Webb, 2010). In addition, Aprilinayati et al. (2009) have determined that morphological aspects are highly correlated to environmental variables. However, the same study indicated that the availability of light was not significant in determining insect yield, (ANOVA: p=0.2511). We aim to explore the possible adaptive nature of color in Nepenthes gracilis by studying the relationship between insect yield, coloration, height, and light.


Question

Is there a height-based distribution of color of Nepenthes gracilis? If so, is it an adaptive trait?

The study will provides a micro-scale analysis of interactions between the abiotic and biotic sphere. The significant positive effect of color on insect yield, which is used as a representation of fitness in our study, would indicate that color as an adaptive trait rather than an established effect of light.


Methods

Study Sites: Beginning of trail to Lambir CTFS plot and the Exposed patch 500 meters from HQ. The Lambir CTFS plot was selected for its high vegetation cover, hence it was more shaded than the Exposed plot which had no vegetation cover.

Equipment: 40 falcon tubes, measuring tape, markers, tweezers, hand lens, microscope, petri dish.

Field Methods: Reference pitchers were selected and defined as green or red.(see Figure 1 in Appendix). Using a random table, 20 green pitchers and 20 red pitchers at each site were selected at each site. Only open pitchers with liquid were kept and marked to keep from repeated measurements. Height of the pitchers is defined as the perpendicular distance from the lid of the pitcher to the ground. All the liquid and contents were emptied into falcon tubes for analysis.


Statistical Analysis: R statistical platform was used to conduct general linear model test (glm) to determine if height, color, and light availability significantly affect insect yield, which is defined as insect per unit volume of liquid.

Results

There was significant interaction of color and light availability (p= 0.0428). Thus, an independent evaluations revealed that color (p=0.0250) and light availability (p=0.0218) significantly affect height distribution . Both color (p< 0.0001) and light availability (p<0.0001) have significant effects on insect yield but not height (p= 0.0573). It appears that the pitchers with the highest insect yield are the green pitchers in the exposed plots with the highest light availability.


Discussion

From this study, it is inconclusive whether coloration is an adaptive trait as the effective insect yield could not be determined solely by color as light was also a significant factor. The data showed a significant interaction between color and light thus, it was not possible to isolate color's effect from light's effect because the interaction supports the established fact that light affects color but not an increased insect yield due solely to light. If the data had demonstrated a lack of interaction of light and color, then a significant difference that associated color with greater insect yield would have showed the adaptive nature of color. However, the similar effects of light and color on insect yield strongly suggests a correlation between light and color that can only be explained as the pitcher's coloration dependence on light.


However, this study proved that there is a height based distribution of color of the pitcher plants with green pitchers in higher heights than red pitchers . The results also indicated that green pitchers in more light had the greatest insect yield and red pitchers in less light had the least insect yield, although height alone did not affect insect yield. This indicates that the optimum position of pitchers plants is in areas of greater light regardless of color and green pitchers tend to outperform red pitchers regardless of light availability.

References

Clark, C. and Ch'ien, L. (2004), Pitcher Plants of Sarawak, Natural History Publications., Borneo.

Aprilinayati, F., Caro, S., Zhao, S. (2009), Insect Yield in Carnivorous Nepenthes: Environmental and Morphological Factors.