Phaseolus Lunatus) Has No Apparent Effect on Bruchid Beetle Performance
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CORE Metadata, citation and similar papers at core.ac.uk Provided by RERO DOC Digital Library J Chem Ecol (2014) 40:468–475 DOI 10.1007/s10886-014-0434-0 Variation in Cyanogenic Glycosides Across Populations of Wild Lima Beans (Phaseolus lunatus) Has No Apparent Effect on Bruchid Beetle Performance J. Gwen Shlichta & Gaetan Glauser & Betty Benrey Received: 15 January 2014 /Revised: 4 April 2014 /Accepted: 15 April 2014 /Published online: 27 May 2014 # Springer Science+Business Media New York 2014 Abstract Cyanogenic glycosides (CNGs) act as feeding or Introduction oviposition deterrents and are toxic after enzymatic hydroly- sis, thus negatively affecting herbivore performance. While A variety of chemical defense compounds are part of a plant’s most studies on CNGs focus on leaf herbivores, here we arsenal against herbivores. These antiherbivory chemicals or examined seeds from natural populations of Phaseolus secondary metabolites include terpenoids, phenolics, and lunatus in Mexico. The predominant CNGs, linamarin and nitrogen-containing compounds such as cyanogenic glyco- lotaustralin, were quantified for each population by using sides (CNGs). Cyanogenic plants are found throughout the ultra-high pressure liquid chromatography-mass spectrometry. plant kingdom (Jones 1988; Seigler 1998), and currently over We also examined whether there was a correlation between 2500 plant species are known to release toxic hydrogen cya- the concentration of CNGs and the performance of the nide from cyanide-containing secondary metabolites Mexican bean beetle, Zabrotes subfasciatus, on seeds from (Zagrobelny et al. 2004). Cyanogenic glycosides are stored each population. The concentrations of CNGs in the seeds in vacuoles as inactive glycosylated precursors, i.e., O-β- were relatively high compared to the leaves and were signif- glycosides of α-hydroxynitriles (cyanohydrins) (Gleadow icantly variable among populations. Surprisingly, this had and Woodrow 2002; Vetter 2000). Tissue disruption results little effect on the performance of the bruchid beetles. in cyanogenesis, a process in which the CNGs are cleaved by Zabrotes subfasciatus can tolerate high concentrations of β-glucosidases followed by hydrolysis through the action of CNGs, most likely because of the limited β-glucosidase ac- α-hydroxynitrile lyases (Selmar et al. 1989). Hydrogen cya- tivity in the seeds. Seed herbivory does not appear to nide (HCN), a compound that is toxic to many herbivores liberate hydrogen cyanide due to the low water content (Ballhorn et al. 2007; Zagrobelny et al. 2004), is released. in the seed. This study illustrates the importance of Non-adapted herbivores avoid CNGs (Gleadow and quantifying the natural variation and activity of toxic Woodrow 2002; Jones 1988; Nahrstedt 1988), and CNGs compounds in order to make relevant biological infer- can act as feeding deterrents or inhibitors (Ballhorn et al. ences about their role in defense against herbivores. 2010), as well as oviposition deterrents (Ballhorn and Lieberei 2006; Ballhorn et al. 2007). Furthermore, CNGs can slow down the development of insect herbivores, thereby Keywords Cyanogenic glycosides . Linamarin . Plant-insect increasing their risk of predation or parasitism, and thus indi- interaction . Plant defense . Zabrotes subfasciatus . Phaseolus rectly defending the plants (Benrey and Denno 1997). lunatus The actual effectiveness of cyanogenic glycosides as a defense mechanism is variable (Gleadow and Woodrow 2002; Puustinen and Mutikainen 2001; Vetter 2000), and in Electronic supplementary material The online version of this article some cases CNGs have minimal or no effect on herbivores (doi:10.1007/s10886-014-0434-0) contains supplementary material, which is available to authorized users. (Ferreira et al. 1997). Specialist herbivores can resist the negative effects of CNGs by several metabolic or behavioral : : * J. G. Shlichta G. Glauser B. Benrey ( ) mechanisms. For example, the Sara Longwing butterfly, Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland Heliconius sara, feeds on the cyanogenic leaves of the passion e-mail: [email protected] vine, Passiflora auriculata, but prevents the release of cyanide J Chem Ecol (2014) 40:468–475 469 by metabolizing the CNGs. In fact, the nitrogen that is re- It is thought to have evolved in Central America, and initially it leased is utilized in the insect’s primary metabolism (Engler used the wild ancestors of Phaseolus lunatus and P. vulgaris as et al. 2000). Other species are able to sequester the toxins and its hosts (Gonzalez-Rodriguez et al. 2002). Zabrotes use them as a defense against predators. The larvae of the subfasciatus has a relatively broad host range within the genus Mexican fritillary, Euptoieta hegesia, sequesters CNGs and is Phaseolus and may not be specifically adapted to CNG- therefore distasteful to Anolis lizards (Schappert and Shore containing lima beans. Hence, this insect appears ideally suited 1999). For some specialists, CNGs may even act as feeding or to test the effects of variation in CNG concentration among lima oviposition stimulants (Calatayud and Le Ru 1996;Honda bean populations on seed-feeding herbivores. et al. 1997). For instance, larvae of the southern armyworm, For our study we sampled seeds from natural populations of Spodoptera eridania that are fed a diet containing CNGs have Phaseolus lunatus along the western coast of Oaxaca, Mexico. similar or improved growth compared to controls (Brattsten The dominating CNGs, linamarin and lotaustralin, were quan- et al. 1983). Calatayud and Le Ru (1996) found that the tified for each population using liquid chromatography coupled cassava mealybug, Phenacoc cuemanihot, is attracted to the to mass spectrometry (LC/MS). We further measured the β- CNGs of cassava plants. glucosidase activity of the beans in order to assess the HCN- Natural plant populations may vary in CNG concentration capacity, i.e., the release of HCN by the beans when consumed (Aikman et al. 1996;Buhrmesteretal.2000; Gleadow and by beetles. Lastly, we quantified the performance of Woodrow 2000a, b). For example, significant quantitative Z. subfasciatus on beans from each population by measuring variation in the CNG prunasin was found in two natural mass, development time, and survival of emerging adult beetles. populations of the Australian Eucalyptus tree, Eucalyptus Our specific objectives were: 1) to characterize wild lima bean polyanthemos, with levels in one population ranging from populations for variation in cyanogenic glycosides; 2) to assess zero to as much as 2.07 mg CN/g dry weight, while levels in the performance of bruchid beetles on seeds from each popula- the other population were between 0.17 to 1.98 mg CN/g dry tion; and 3) to test whether differences in the concentration of weight (Goodger et al. 2002). More extreme variation was CNGs among populations correlate with bruchid performance. found in elderberry, Sambucus canadensis L, in which some populations were essentially acyanogenic, while other popu- lations showed high variation in the concentration of CNGs among individuals (Buhrmester et al. 2000). This variability Methods and Materials on the plant side adds another layer of complexity and needs to be considered in efforts to understand the role of these Seed Collection Seed pods were collected from 12 sites in the compounds in defending plants against herbivory. state of Oaxaca, Mexico from December to February 2010– The vast majority of studies of CNGs have focused on leaf 2011. These sites included 10 populations along the coast herbivores. As a consequence, there is little information de- from 597 km north to 50 km south of Puerto Escondido, and scribing the variation in the concentrations of CNGs in seeds, two populations 586–702 km east of Puerto Escondido (see or the effects of variation on seed-feeding herbivores. Table 1, and Online resource 1). Samples were taken from 5 to Cyanogenic glycoside concentrations in the fruiting structures 10 plants per site, except when less than 10 plants were of plants are important in the context of plant domestication, particularly in cases where fruits and seeds serve as food for Table 1 GPS coordinates and altitude for each site where beans were humans and/or livestock. Just as for other defensive chemicals, collected CNGs levels can be expected to be lower in domesticated plants Population Latitude Longitude Altitude (meters) as a result of selective breeding (Poulton 1990). Phaseolus lunatus, the wild lima bean, appears to be unique HHI N16 46.626 W99 29.712 80 in that it is the only Phaseolus species reported to contain INK N15 43.469 W96 39.188 35 CNGs (Jones 1988;Poulton1990;Vetter2000). Previous stud- ITC N17 00.675 W100 06.171 25 ies have focused on CNGs in leaves of P. lunatus,andonlyfew KM N15 57.742 W97 20.503 65 have investigated their presence in seeds (Frehner et al. 1990). MAD N17 21.158 W101 03.368 35 None of these studies has specifically examined the effect of MAR N16 35.732 W98 46.102 55 CNGs on seed-feeding herbivores. The goal of the current study PET N17 26.118 W101 11.647 7 was to examine the potential role of CNGs in the seeds of lima SMA N16 47.541 W99 22.688 91 bean as a defense against a seed-feeding herbivore. The bruchid UMA N15 55.330 W97 09.132 17 beetle Zabrotes subfasciatus Boheman (Coleoptera: WAS N18 35.938 W98 33.142 1238 Chrysomelidae) attacks the seed of several Phaseolus species, YAU N18 55.191 W99 02.397 1236 including the cyanogenic P. lunatus, and it is one of the most YEL N16 15.071 W97 48.169 240 important pests of stored beans worldwide (Benrey et al. 1998). 470 J Chem Ecol (2014) 40:468–475 available. Pods were shelled and subsamples of seeds were not feasible to use these techniques for Z. subfasciatus because separated for chemical extraction and analysis. the beetle larvae are very small (about 2 mm) and feed within the seed over a long period of time (about 35 d).