Inga Species Research Articles

New Synthesis—Back to the Future: New Approaches and Directions in Chemical Studies of Coevolution

Published online: 9 June 2011# Springer Science+Business Media, LLC 2011The concept of an arms race between herbivores and plants, associatedwith increases in diversity of plant secondary compounds, has longprovided an appealing theoretical framework for evolutionary biologistspondering adaptive radiations, and has been a stimulus for studies ofchemical ecology. While publications on coevolution are steadilyincreasing in ecology and evolutionary biology, such studies havestagnated in chemical ecology, even though modern chemical techniqueshavemadeiteasiertoexaminecoevolutionarypredictionsforphytochem-icaldiversification.Anexampleofwhatcanbeaccomplishedisillustratedby Kursar et al. (2009), who documented considerable divergence ineffective antiherbivore defenses of the tropical plant genus Inga,indicating that an arms race between plants and herbivores caused rapid,divergent trait evolution. Interestingly, closely related Inga species thatoccur together in tropical forests al so have distinct defensive profilesdriven by tritrophic interactions. Thus, diffuse multitrophic coevolution-ary interactions, mediated in part by plant chemistry, help structurediverse communities, allowing for high alpha diversity for Inga.ThestudyofInga and related studies on Quercus, Piper,andBurserautilize modern approaches to natural history, ecology, phylogenetics, andchemistry, and indicate that the time is ripe for chemical ecologists toreturn to coevolution as a unifying research theme. For natural productschemistry, synthesis and complex mixture analysis have improveddramatically (Hoye and Sizova 2009) with advances in MS sources,including electrospray ionization, matrix-assisted laser desorptionionization, and atmospheric pressure chemical ionization. Theseapproaches permit rapid elucidation of a broad array of compounds ina taxon of interest, which is necessary for testing causes andconsequences of increases of chemical diversity. Such input fromchemists can synergize with advances in molecular ecology. Forexample, new sequencing technologies present the opportunity togenerate high resolution population genomic data that can be used totest the hypothesis that host plant affiliations are associated with distinctchemical profiles and population genetic differentiation.How will these new technologies contribute to understandingchemical mediation of coevolution? The answer includes a long list oftheoretical advances, but here I provide two examples of excitingresearch directions.First, a major problem with any approach to studying insect-plantcoevolution is that there is a bias t owards examining individual plantcompounds and their effects on the physiology of herbivores and theirpredators. Redundancy in plant defenses has long been appreciated, andcommon effects such as synergy obfuscate results from traditionalmechanistictestsofcoevolutionaryhypotheses.Forexample,innumerouscoevolutionary studies, the failure to demonstrate negative correlations inperformance on hosts with different defensive compounds or todemonstrate defensive efficacies of secondary metabolites could easilybe due to the fact that compounds do not function in isolation. It is quitepossible that phytochemical synergy is the rule rather than the exception,even for putatively induced defenses, and we need new initiatives ofchemicalecologicalresearchthataimtotestfordefensiveefficacyofsuitesof compounds or cross-host tradeoffs for different synergistic mixtures.Second, any new approach to studying coevolution must acknowl-edgethatplantsandparasitesinteractwithincomplexfoodwebs.Thus,itmakes sense to examine the phylogenetic histories and ecologicalinteractions of both the hosts and the parasites of focal herbivores.Forister and Feldman (2011) take this approach when they present theconcept of a “phylogenetic cascade,” in which diversification at onetrophic level affects two or more other levels, resulting in a sharedevolutionary history across a food chain. Classic coevolutionaryhypotheses are a subset of the phylogenetic cascades framework, andchemistry can play a major role in these interactions, as evidenced fromnumerous ecological studies that demonstrate strong indirect trophiceffects of variation in plant chemistry. If future research on chemicalmediationofcoevolutionisconsideredwithinsynergisticorphylogeneticcascades contexts, by utilizing the latest technological advances, ourunderstanding of diversity of animals, plants, and secondary metabolitesshould improve dramatically.

Synchronous phenology of hawkmoths (Sphingidae) and Inga species (Fabaceae–Mimosoideae): implications for the restoration of the Atlantic forest of northeastern Brazil

Biotic and abiotic factors such as resource availability and rainfall may exert influence on the life cycle of several organisms. In this study, we investigated correlations between the phenology of hawkmoths, flowering phenology of Inga Mill. species (Fabaceae–Mimosoideae–Ingeae) and rainfall in one of the largest remnants of Atlantic forest in northeastern Brazil (Coimbra forest with ca. 3500 ha). We carried out monthly hawkmoth inventories and phenological observations of the five most abundant Inga species in Coimbra forest from October 2005 to August 2007. Altogether 39 hawkmoth individuals were collected with light trap or butterfly net, which were ascribed to nine genera and 14 species. With the present study Pachygonidia caliginosa Boisduval (Bombycoidea–Sphingidae–Dilophonotina) is registered for the second time in Brazil, since the species had been previously collected only in the Amazon. The tribe Dilophonotina was the most represented with five species. Animals with short proboscises (14.7–35.0 mm) represented over 69.7% of the sample. Most individuals were collected during the months of low rainfall, the same period of the highest flower abundance of five Inga species. The flowering of Inga vera, I. striata and I. ingoides was positively correlated with hawkmoth abundance. The synchrony of the activity period of these animals in adult phase with certain nectar sources, and the relationship between morphological parameters of hawkmoths and Inga flowers suggest a narrow pollination mutualistic relationship at the study site. Considering the hotspot status of the Atlantic forest due to high fragmentation and habitat loss, as well as the previous local extinction of hawkmoth species in smaller fragments of the studied landscape, our results are relevant for restoration plans not only for the Brazilian Atlantic forest, but for neotropical forests in general, where Inga is native.

Is extrafloral nectar production induced by herbivores or ants in a tropical facultative ant–plant mutualism?

Many plants use induced defenses to reduce the costs of antiherbivore defense. These plants invest energy in growth when herbivores are absent but shunt energy to defense when herbivores are present. In contrast, constitutive defenses are expressed continuously regardless of herbivore presence. Induction has been widely documented in temperate plants but has not been reported from tropical plants. Most tropical plants have higher, more constant herbivore pressure than temperate plants. In this situation, it is hypothesized that constitutive defenses rather than induced defense would be favored. Using natural herbivores of four species of Inga saplings on Barro Colorado Island, Panama, herbivore presence was crossed with ant presence to determine their effects on extrafloral nectar production. Analysis of nectar samples revealed that Inga species do not induce nectar production in response to herbivores. This result is not due to an inability of the plants to respond, as the plants in this study increased nectar production in response to light and ant presence. Contrary to most induction experiments with temperate ecosystem plants, these results demonstrate that tropical plants do not induce one type of defense, and they suggest that the most adaptive defense strategies are different for the two ecosystems.

The evolution of antiherbivore defenses and their contribution to species coexistence in the tropical tree genusInga

Plants and their herbivores constitute more than half of the organisms in tropical forests. Therefore, a better understanding of the evolution of plant defenses against their herbivores may be central for our understanding of tropical biodiversity. Here, we address the evolution of antiherbivore defenses and their possible contribution to coexistence in the Neotropical tree genus Inga (Fabaceae). Inga has >300 species, has radiated recently, and is frequently one of the most diverse and abundant genera at a given site. For 37 species from Panama and Peru we characterized developmental, ant, and chemical defenses against herbivores. We found extensive variation in defenses, but little evidence of phylogenetic signal. Furthermore, in a multivariate analysis, developmental, ant, and chemical defenses varied independently (were orthogonal) and appear to have evolved independently of each other. Our results are consistent with strong selection for divergent defensive traits, presumably mediated by herbivores. In an analysis of community assembly, we found that Inga species co-occurring as neighbors are more different in antiherbivore defenses than random, suggesting that possessing a rare defense phenotype increases fitness. These results imply that interactions with herbivores may be an important axis of niche differentiation that permits the coexistence of many species of Inga within a single site. Interactions between plants and their herbivores likely play a key role in the generation and maintenance of the conspicuously high plant diversity in the tropics.

Soil type affects seedling shade response at low light for two Inga species from Costa Rica

Distributions of many humid tropical tree species are associated with specific soil types. This specificity most likely results from processes at the seedling stage, but light rather than nutrient levels is generally considered the dominant limitation for seedling growth in the tropical forest understory. If nutrients are limiting and allocation to belowground resources differs, seedling growth responses to shade should also differ. Here we tested the effects of soil type and light environment on the seedling growth of two canopy tree species in the genus Inga with different soil-type and light-environment affinities as adults. Inga alba is a shade-tolerant soil generalist and I. oestediana is a light-demanding soil specialist. We used four native soils and three light levels (1 and 5% of full sun in shade houses and the forest understory). All growth variables were greatest in 5% full sun, with highest growth rates for the light-demanding soil-type specialist. Soil type significantly affected growth parameters, even at the lower light levels. The specialist grew best on the soils with the most soil phosphorus where adult trees typically occur. Leaf tissue nitrogen:phosphorus ratios suggest increased phosphorus limitation in the low phosphorus soils and with increased light level. Light and soil interacted to significantly affect seedling biomass allocation, growth, and net assimilation rates, indicating that the seedling shade responses were affected by soil type. Seedlings growing on high nutrient soil allocated less to roots and more to photosynthetic tissue. Adult distributions of these two Inga species may be a result of the different growth rates of seedlings in response to the interactive effects of light and soil.

Lutein epoxide cycle, light harvesting and photoprotection in species of the tropical tree genusInga

Dynamics and possible function of the lutein epoxide (Lx) cycle, that is, the reversible conversion of Lx to lutein (L) in the light-harvesting antennae, were investigated in leaves of tropical tree species. Photosynthetic pigments were quantified in nine Inga species and species from three other genera. In Inga, Lx levels were high in shade leaves (mostly above 20 mmol mol(-1) chlorophyll) and low in sun leaves. In Virola surinamensis, both sun and shade leaves exhibited very high Lx contents (about 60 mmol mol(-1) chlorophyll). In Inga marginata grown under high irradiance, Lx slowly accumulated within several days upon transfer to deep shade. When shade leaves of I. marginata were briefly exposed to the sunlight, both violaxanthin and Lx were quickly de-epoxidized. Subsequently, overnight recovery occurred only for violaxanthin, not for Lx. In such leaves, containing reduced levels of Lx and increased levels of L, chlorophyll fluorescence induction showed significantly slower reduction of the photosystem II electron acceptor, Q(A), and faster formation as well as a higher level of non-photochemical quenching. The results indicate that slow Lx accumulation in Inga leaves may improve light harvesting under limiting light, while quick de-epoxidation of Lx to L in response to excess light may enhance photoprotection.

Divergence and diversity in the defensive ecology of Inga at two Neotropical sites

Summary 1. Tropical plants express multiple defensive traits that enable them to resist, deter or escape herbivores. In this study, we approached plant defensive adaptations by focusing on variation and interaction between sets of plant defensive strategies from a community perspective. 2. We compared two sites: the aseasonal Amazonian forest of Yasuni, Ecuador, and the seasonal forest of Barro Colorado National Monument (BCNM), Panama. We suggest that differences in ant abundance between these sites influence the divergence, local assembly and interaction of chemical and indirect ant-mediated defences in 18 tree species of the genus Inga (Fabaceae: Mimosoideae). 3. Relative ant abundance and visitation to extra floral nectaries were significantly higher at Yasuni than at BCNM. Correspondingly, Yasuni Ingas had low leaf extract bioactivity compared with BCNM Ingas , suggesting that Yasuni Ingas rely more on indirect ant defences, while BCNM Ingas rely more on chemical defences. 4. Yasuni Inga s varied widely in their ant visitation and extract bioactivity, and the strategies were negatively correlated in a trade-off like pattern. In comparison, BCNM Ingas had a positive correlation and little variation in their ant visitation, suggesting that their defence ecology was driven by environmental characteristics other than ants. 5. An experiment planting the same Inga species at both sites supported the prediction of higher herbivore pressure at Yasuni than at BCNM. However, leaf damage to naturally occurring Ingas was similar between sites, suggesting that the adaptations at the two sites were equally effective. Damage levels were also similar among species with contrasting defensive strategies, suggesting that ant and chemical strategies were also equally effective at a single site. 6. Synthesis . While tropical forests are thought to be a cradle of specialized interactions that promote diversification and allow the coexistence of a large number of species, the observed divergence in the defence ecology of Inga between these two sites suggests that general community characteristics can also promote diversity by favouring local and geographical diversity in defensive solutions.

Biology and occurrence of Inga Busk species (Lepidoptera: Oecophoridae) on Cerrado host plants

We sampled Inga Busk species caterpillars weekly in the cerrado on 15 plants of Diospyros burchellii Hern. (Ebenaceae) from January 2002 to December 2003, on 30 plants of Caryocar brasiliense (Caryocaraceae) from July 2003 to June 2004, and since 1991 on several other plant species. In total we found 15 species of Inga on cerrado host plants. Nine species were very rare, with only one to five adults reared. The other six species occurred throughout the year, with higher abundance during the dry season, from May to July, coinciding with overall peaks of caterpillar abundance in the cerrado. Caterpillars of the genus Inga build shelters by tying and lining two mature or old leaves with silk and frass, where they rest and develop (a common habit found in Oecophorinae). The final instar builds a special envelope inside the leaf shelter, where it will complete the larval stage and pupate. The species are very difficult to distinguish in the immature stages. External features were useful in identifying only four species: I. haemataula (Meyrick), I. phaecrossa (Meyrick), I. ancorata (Walsingham), and I. corystes (Meyrick). These four species are polyphagous and have wide geographical distributions. In this paper we provide information on the natural history and host plants of six Inga species common on cerrado host plants, for which there are no reports in the literature.

FOOD QUALITY, COMPETITION, AND PARASITISM INFLUENCE FEEDING PREFERENCE IN A NEOTROPICAL LEPIDOPTERAN

We surveyed Lepidoptera found on 11 species of Inga (Fabaceae:Mimosoideae) co-existing on Barro Colorado Island, Panama, to evaluate factors influencing diet choice. Of the 47 species of caterpillars (747 individuals) recorded, each fed on a distinct set of Inga. In the field, 96% of the individuals were found on young leaves. Growth rates of caterpillars that were fed leaves in the laboratory were 60% higher on young leaves compared to mature leaves. When caterpillars were fed leaves of nonhost Inga, they grew more slowly. These data provide support for a link between preference and performance. However, among hosts on which larvae normally occurred, faster growth rates were not associated with greater host electivity (the proportion of larvae found on each host species in the field, corrected for host abundance). Growth rates on normal hosts were positively correlated with leaf expansion rates of the host, and fast expansion was associated with leaves with higher nutritional content. Detailed studies on a gelechiid leaf roller, the species with the largest diet breadth, allowed us to assess the importance of factors other than growth that could influence diet electivity. This species showed a 1.7-fold difference in growth rate among Inga hosts and faster growth on species with fast-expanding leaves. However, there was no correlation between caterpillar growth rate and abundance on different host species. Instead, abundance of the gelechiid on each Inga species was significantly correlated with the temporal predictability of food (synchrony of leaf flushing) and was negatively correlated with competition (amount of leaf area removed by species other than the gelechiid). Although rates of parasitism were high (23-43%), there were no differences among hosts. Parasitism was also not related to measures of escape, such as growth rates of caterpillars, leaf expansion rates, and synchrony of leaf production. Together, food availability, parasitism, and competition explained 84% of the variation in host preference by the gelechiid. We suggest that these ecological interactions may be particularly important in determining diet choice initially and that preferences may be reinforced by subsequent divergence in host chemistry and/or the herbivore's ability to tolerate the secondary metabolites.

Divergence in Structure and Activity of Phenolic Defenses in Young Leaves of Two Co-Occurring Inga Species

The leaves of tropical forest trees are most likely to suffer herbivore damage during the period of expansion. Herbivore selection on young leaves has given rise to a variety of leaf developmental strategies and age-specific chemical defense modes. We are studying correlations between leaf developmental types and chemical defenses in the Neotropical genus Inga. We have characterized defense metabolites in Inga goldmanii and Inga umbellifera, two species that co-occur in the lowland moist forest of Panama. These congeners have markedly different young-leaf developmental phenotypes but suffer approximately equal rates of herbivory. Bioassays of whole and fractionated leaf extracts using larvae of Heliothis virescens show that I. goldmanii chemical defenses are nearly three times more inhibitory than those of I. umbellifera. In both species, most of the inhibitory activity resides in complex mixtures of monomeric and polymeric flavan-3-ols. This group comprises >30% of young leaf dry weight in both I. goldmanii and I. umbellifera. The species' phenolic chemistry differs markedly, however, both in the structure of the monomeric units and in the distribution of polymer sizes. The differences in chemical structure have pronounced effects on their bioactivities, with I. goldmanii flavans being twice as inhibitory to H. virescens larvae as I. umbellifera flavans, and more than three times more efficient at protein binding. Given the extraordinarily high polyphenol concentrations that are found in the young leaves of these species, protein precipitation could be an important mechanism of growth inhibition. Nevertheless, our data show that another mode of phenolic action, possibly oxidative stress, occurs simultaneously.

Characterization of slow-growing root nodule bacteria from Inga oerstediana in organic coffee agroecosystems in Chiapas, Mexico

The leguminous tree genus Inga is thought to be critical for providing N to certified organic coffee shrubs that commonly grow beneath its shade in the state of Chiapas, Mexico. Organic certification prohibits use of synthetic N fertilizers, necessitating understanding of the Inga–rhizobia symbiosis. The objectives of this study were to: (1) establish a collection of isolates from Inga sp. nodules found on organic coffee farms in Chiapas, Mexico; (2) use phenotypic and genotypic approaches to characterize these isolates, and (3) examine cross-inoculation patterns of strains isolated from Inga sp. with other Inga species and N 2-fixing trees. Eighty-three strains were isolated from root nodules of Inga oerstediana, Inga pavoniana and an unknown species of Inga. Aside from isolates of I. pavoniana, Inga isolates demonstrate characteristics consistent with Bradyrhizobium. Dendrograms generated using phylogenetic and phenotypic traits showed strains to exhibit significant diversity, even among strains originating from the same farm. Strains isolated from I. pavoniana were 95% similar, and displayed strikingly different characteristics from strains isolated from other species. Cross-inoculation experiments used three Inga strains (cowpea miscellany CB756, and isolates from I. oerstediana and I. sp.) as inoculants with I. edulis, I. fuellii, Acacia mangium, Acacia koa, Vigna unguculata and Gliricidia sepium. All three strains formed nodules containing leghaemoglobin with V. unguculata, while isolates from I. oerstediana, Inga sp. and cowpea miscellany formed nodules with I. feulli and I. edulis, but not with A. mangium and G. sepium. A. koa formed nodules containing leghaemoglobin when inoculated by cowpea miscellany strain CB756 and the strain from Inga sp., but nodules formed with the strain isolated from I. oerstediana did not contain leghaemoglobin. One and two-way ANOVA results showed that no mean biomass of inoculated seedlings was significantly greater than the −N control for each of A. koa, G. sepium, A. mangium ( p < 0.001), supporting our hypothesis that inoculation with non- Inga strains would have no effect on biomass production. We suggest that great spatial variation exists among Inga isolates from organic coffee farms in the Chiapas highland region, both between and within farms, and that more research is needed to identify reasons for the genetic distribution and function of Inga symbionts.

Coffee yields and soil nutrients under the shades of Inga sp. vs. multiple species in Chiapas, Mexico

For many decades, simplification of traditionally shaded coffee-production systems has been an idealised model for increasing yields. In Mexico, coffee producers have been interested in replacing diverse natural shade with Inga species monocultures due to this practice having the supposed advantages of producing higher coffee yields than diverse shade. However, the effect of different shade systems on yields is little known. The purpose of this study was to evaluate the effect of two types of shaded-coffee systems on coffee yields and soil nutrient content; the first shade system is mainly dominated by Inga latibracteata Harms and the other composed of species-rich natural vegetation. The investigation took place in producer plots in the Francisco I. Madero Community, Municipality of Jitotol, Chiapas, Mexico. Collected data included species richness, shade-tree density, number of strata, tree diameter, tree height, shade-cover percentage, direct and diffused light, coffee yields, soil-nutrient concentrations (N, P, K, Ca and Mg), soil-organic matter and pH. Evaluated shade type did not have an effect on grain yield or soil nutrients. The perceived advantage of the Inga shade system is reduced weed emergence, saving farmers one annual weed-clearing. There was no significant correlation between total N and organic matter. The presence of fewer products and services in comparison to the multiple shade system was thought to be an additional disadvantage to the Inga dominated system. Organic matter in the multiple shade system correlated positively with total N. Due to its complex structure and diversity, the multiple shade system could be certified as shade or bird-friendly coffee.

Chemotaxonomic significance of hydroxylated pipecolic acids in Central American Inga (Fabaceae: Mimosoideae: Ingeae)

Hydroxylated pipecolic acid derivatives of 47 species of Inga were analyzed primarily from herbarium leaf samples supplemented by field collections. Inga species are noted for their morphological variability, which has resulted in considerable taxonomic confusion. Pipecolic acid chemistry appears to be a relatively stable character within species, and the large number of pipecolic acid derivatives translates to greater intraspecific diversity in chemical patterns (18 distinct hydroxypipecolic acid patterns) than previously found in related genera. This chemical diversity makes pipecolic acids particularly useful in solving taxonomic problems in this genus; problems such as identification of distinct species with convergent morphology and identification of mislabeled herbarium specimens. Chemistry provides data independent of morphology with which to assess recent changes in nomenclature (some of which are supported, others not) and may also be useful in the assessment of hybridization and in delimitation of proper species boundaries. At present our chemical knowledge is too fragmentary to allow strong statements regarding relationships above the species level, but there is a trend for taxa traditionally grouped on morphological criteria to share similar chemistries.

Tree architecture and secondary tropical rain forest development: A case study in Araracuara, Colombian Amazonia

Summary Four successional forests, the oldest 30 years old, and a mature forest on the low terrace of the Caqueta river (Colombian Amazonia), were analysed architecturally. The architecture of these secondary forests was largely determined by species of Vismia , Miconia and Inga reaching their maximal crown expansion during the first 30 years of secondary forest development. Forest profiles were drawn to scale, indicating the development phase of every tree (Dbh > 5 cm). Three development phases were distinguished according to crown architecture, i.e. potential trees, trees of the present and trees of the past. These development phases were used to determine the dynamics of the species within the secondary forest A first approximation of the secondary forest development in Araracuara is as follows: 1. Within seven years a set of trees of the present (Vismia glaziovii and Miconia minutiflora) develop a low ( 2. Between seven and eleven years Vismia japurensis and Vismia macrophylla develop a higher (10–15 m) canopy of trees of the present making survival of the previous set of the present impossible. Again potential trees of other species are present, some of them emerging. 3. Around 20 years Miconia poeppigii, Miconia myriantha, Jacaranda copaia and several Inga species form a still higher (c. 20 m) canopy of trees of the present, making survival of the Vismia set almost impossible. Most potential trees in this development phase are lower than the trees of the present, some are still emerging, i.e. Cecropia spp. A lower (ca. 10m) set of the present is formed by several Miconia species already present from the initiation of the succession ( Miconia prasina, Miconia pilgeriana, Miconia punctata, Miconia splendens ) and Piper arboreum 4. Around 30 years the canopy of Miconia and Inga species starts to degenerate. Potential trees grow into the gaps. 5. In the mature forest the formation of gaps by trees of the past is the most important factor in the regeneration From every tree species encountered in the transects documented by profiles, the basic branching pattern, i.e. architectural model (sensu HALLE et al. 1978), was determined. For every transect an architectural spectrum was made. These spectra show the numbers of individuals and species having the same architectural models. By approximation, the results are broadly in agreement with earlier research from French Guyana. Young secondary forests have many individuals with Rauh's model, together with many individuals with Roux's model, and few individuals with Troll's and Massart's model, and certainly few species with those models. In mature forest there is a large number and great variety of Troll's model, Massart's model and often Aubrevilles model, and still quite a number of individulas with Rauh's model. Roux's model is found in the understorey of the mature forest

Some New Chromosome Counts in the Genus Inga (Leguminosae : Mimosoideae)

Inga Mill. is a neotropical leguminous genus comprising c. 300 species. The modern interpretation of the genus is due to the work of Bentham (1875), who produced the only monograph of the genus. It is defined within the Leguminosae: Mimosoideae: Ingeae by its simply pinnate leaves with foliar nectaries between each pair of leaflets, numerous stamens united in the lower half into a staminal tube, and indehiscent legume containing fleshy seeds surrounded by a sweet fleshy sarcotesta. Inga is confined mainly to the American Tropics, with some penetration into temperate areas both north and south (Le6n 1966). The species are trees varying in height from 3 to 40 m, and have been used in a variety of ways, for instance as fuelwood, and shade for cultivated crops such as coffee and cocoa (Le6n 1966). The purpose of this study was to obtain chromosome counts for the Inga species growing in the Science Support Unit, Royal Botanic Gardens, Kew, in collaboration with Dr T. D. Pennington who is preparing a taxonomic revision of the genus.

Floral and Extrafloral Nectars of Costa Rican Inga Trees: A Comparison of their Constituents and Composition

Two types of nectaries occur in the neotropical genus Inga (Fabaceae: Mimosoideae). Floral nectar is ingested by visitors to flowers and foliar nectar is utilized by a variety of insects. Although their flowers are similar in appearance and morphology, different Inga species exhibit different floral behaviors and have different primary pollinators. The floral nectars of the eight species analyzed are, however, similar in proportions of various sugars. Freshly secreted floral nectars are sucrose-dominant, though over time the sucrose is hydrolyzed and nectars become hexose-rich. In some species, this change corresponds to a shift in the pollinator fauna. Amino acid constituents of floral nectars differ among Inga spp., but are constant within a species. Extrafloral nectars are hexose-dominant and have substantially greater sugar concentrations than floral nectars. Extrafloral nectars of different species differ in array of amino acids present, but amino acids in floral and extrafloral nectar of a given species are similar, but not identical. Differences in composition of the two types of nectar produced by a given Inga species may result from natural selection by mutualists utilizing the nectar as well as non-evolutionary influences of the abiotic and biotic environment.

SOME ASPECTS OF WOOD-ANATOMICAL RESEARCH IN THE GENUS INGA (MIMOSACEAE) FROM THE GUIANAS AND ESPECIALLY SURINAME

A key is offered to the wood of 35 out of 38 Inga species known from Suriname and the other Guianas. The wood structure indicates that the sections Leptinga, Diadema, Bourgonia and Euinga sensu Bentham are taxonomically sound. Section Pseudinga is unnatural and should be subdivided. The author is in favour of keeping the sections Leptinga and Diadema apart.