Evidence for a Correlation between Systematics and Bioactivity in New Caledonian Cunoniaceae and Its Implications for Screening and Conservation1 Yohan Pillon2,3 and Bruno Fogliani3 Abstract: It is generally assumed that there is a good correlation between sys- tematics and the secondary compounds found in plants. However because of the frequent homoplasy of chemical characters this has been difficult to test us- ing statistical methods. Here we applied two nonparametric tests on a published data set, where 50 species of New Caledonian Cunoniaceae were screened for bioactivity against several pathogenic strains. Using Moran’s I index we showed that in two of nine tests against pathogenic strains there was a significantly higher similarity than expected in bioactivities between species belonging to the same genus and a significantly higher than expected dissimilarity in bioactiv- ity between species belonging to different tribes. When considering the bioac- tivities against all pathogenic strains with Mantel tests, we also found significant correlation between bioactivity and phylogenetic distance in two of four tests. This has implications in screening and conservation. Searches for new molecules and bioactivity should preferentially be made on species spread across the tree of life. There is also a need to preserve as much phylogenetic diversity as possi- ble to make sure that the widest reservoir of natural compounds remains avail- able for future generations. Biochemistry has played an important hamed 2003, Albach et al. 2005). Some of role in plant systematics (see, e.g., Grayer these problems may also be explained by sam- et al. 1999) by providing insights into the pling issues because a single taxon may not relationships between species (Albach et al. always be representative of a higher group 2005, Petrakis et al. 2005), within families (Grayer et al. 1999) or by variation associated such as the Cunoniaceae (Bate-Smith 1977), with geography (van Heerden et al. 2005) or and between families (Grayer et al. 1999). ontogeny (C¸ irak et al. 2006). However, chemical compounds are characters Secondary compounds are economically that are often affected by homoplasy because important because they can be used as, or be similar compounds can appear independently the base for, active molecules in pharmaceu- several times in the course of evolution or tical chemistry (Young 1999, Butler 2004); might be lost secondarily (Wink and Mo- they can also be important for the produc- tion of pesticides, perfumes, and other com- pounds. It is quite possible that the tropical 1 Manuscript accepted 27 March 2008. floras being screened for new molecules today 2 Corresponding author: Laboratoire de Botanique, could provide the basis for tomorrow’s new Institut de Recherche pour le De´veloppement, BP A5, medicines (Butler 2004). Because it is now ac- 98848 Noume´a Cedex, New Caledonia (phone: (þ687) cepted that biodiversity is facing an important 26 09 28; fax: (þ687) 26 43 26; e-mail: pillon@noumea .ird.nc). crisis, the economic value of that diversity 3 Laboratoire Insulaire du Vivant et de l’Environne- may be a strong argument in favor of in- ment, Universite´ de la Nouvelle-Cale´donie, BP R4, creasing conservation efforts on wild species 98851 Noume´a Cedex, New Caledonia. (Balmford et al. 2002). If there is a significant correlation between chemical composition of Pacific Science (2009), vol. 63, no. 1:97–103 species and their relatedness, then conserva- : 2009 by University of Hawai‘i Press tion strategies should be implemented to pre- All rights reserved serve the widest spectrum of the tree of life 97 98 PACIFIC SCIENCE . January 2009 (Mace et al. 2003) to ensure that the greatest Independence of Variables diversity of molecules remains available. The correlation between biochemistry and The independence of variables needed to be systematics has generally been accepted, but assessed before further testing. Correlation there has been little supporting evidence that of activities between bark and leaf extracts it is statistically significant, probably because and ethyl acetate and methanol were tested of the homoplasy of chemical characters. by the mean of a chi-squared test. We tested Few studies are available that have investi- if species showing activity in their bark were gated a large number of taxa with multiple more likely to show activity in their leaves tests using a standard protocol. In this study for a given solvent, and similarly we tested if we conducted statistical analysis on the re- species showing antimicrobial properties with the methanol extract of their leaves or bark sults obtained by Fogliani et al. (2002a), who tested the activity of 50 species of Cunonia- were more likely to show properties with the ceae against 10 pathogenic strains, and show ethyl acetate of the same part of the plant. that there is a significant and positive correla- Correlation between activities against the dif- tion between species bioactivity and their re- ferent pathogenic strains was also assessed latedness. Specifically, we used nonparametric (for an extract with a given solvent from a given part of the plant). Chi-squared tests tests such as Moran’s I index that have proven their efficiency at revealing taxonomic pat- were only conducted on a contingency table terns (Lockwood et al. 2002). New Caledo- where all expected occurrences exceeded five. nian Cunoniaceae have been the subject of extensive taxonomic work over the past de- Test of the Correlation between Systematics and cades (Hoogland et al. 1997, Hopkins 2005, Bioactivity 2006, 2007, Hopkins et al. 2007, Pillon et al. in press), and a tribal classification (Bradford Moran’s I index was used to test if there was a et al. 2004) based on morphological (Hufford significant similarity in the bioactivity of spe- and Dickison 1992) and molecular (Bradford cies belonging to the same taxonomic group and Barnes 2001) phylogenies is available. (genus or tribe). Moran’s I index was calcu- This taxonomic scheme was used to provide lated for each test against pathogenic strains rough estimates of phylogenetic distances be- for leaf or bark extracts with ethyl acetate tween species. or methanol. Only tests where at least 10 spe- cies showed activities were included. We es- materials and methods tablished three distance classes (1, 2, and 3) between species depending on their phyloge- Data netic distance: 1, if they belong to the same Fogliani et al. (2002a) tested the bioactivity of genus; 2, if they belong to the same tribe; 3, 50 of the ca. 90 species of Cunoniaceae en- if they belong to different tribes. The Mor- demic to New Caledonia, representing six an’s I index tests whether species that are genera and four tribes following the most re- closely related phylogenetically have similar cent classification of Cunoniaceae (Bradford activity. and Barnes 2001, Bradford et al. 2004). Activ- One single test against one pathogen pro- ities against eight bacteria strains and two vides little statistical power to detect signifi- fungi were assessed. In most cases the activity cant correlation for several reasons. In most of ethyl acetate and methanol extract of leaf cases, few species showed activity against a and bark were tested. A disk containing the given pathogen, and this activity does not extract was placed in a petri dish containing follow a normal distribution. To increase the a culture of each strain. In the presence of sensitivity of the tests we used another ap- antimicrobial activities, an inhibition zone proach. We took into consideration the 10 can be observed around the disk. The diame- pathogenic strains in a single statistical test ter of this zone is used as a measure of the known as the Mantel test. Activities were cen- strength of the activity. tered and reduced (i.e., for each species we Systematics and Bioactivity . Pillon and Fogliani 99 calculated the activity of the species minus tate extract from bark against Staphylococcus the average over all species divided by the aureus and Erwinia carotovora, activity of standard deviation over all). The aim of this methanol extract from bark against Coryne- procedure was to give a similar weight to bacterium accolans and Fusarium oxysporum, each pathogenic strain. ‘‘Bioactive’’ distance and activity of methanol extract from leaves was calculated for each pair of species as the against Corynebacterium accolans and Fusarium geometric distance between their activities oxysporum. In only one case we found a sig- against all 10 pathogenic strains: nificant correlation of activity against two rXffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi microbial strains: activity of ethyl acetate 2 extract from bark against Corynebacterium BD ¼ ða À a Þ ij ik jk accolans and Staphylococcus aureus (P ¼ :006). k Therefore we assumed that the different mi- BD is the ‘‘bioactive’’ distance between spe- crobial strains could be reasonably considered as independent measures of bioactivity. cies i and j. aik and ajk are the activity of species i and j, respectively, against the patho- genic strain k. Test of the Correlation between Systematics and We used the same phylogenetic distance Bioactivity as for the Moran’s I index. The Mantel test assesses the correlation between ‘‘bioactive’’ Nine tests against pathogenic strains could be distance and phylogenetic distance. One tested with the Moran’s I index; results for thousand replicates were used to evaluate the each test and the average over the nine tests significance of the test. are displayed in Figure 1. In the case of the Both Moran’s I index and the Mantel test activity of the methanol extract from leaves were computed with the software PASSAGE against Corynebacterium accolans, the value of (Rosenberg 2002). the Moran’s I index (I ¼ 0:059) was signifi- cantly higher (P ¼ :008) than expected by chance for species belonging to the same ge- results nus. Thus activities between congeneric spe- cies were closer than expected by chance.