Fruit‐quality tradeoffs generate asymmetry in plant reliance on mutualistic frugivores

Seed dispersal by animals is critical to both animal and plant ecology. Among species, fruits show a tremendous diversity of traits such as colour, scent, texture and size. Recent studies demonstrated a significant degree of variation in fruit traits within species as well. This often-overlooked variation may play a critical role in animal–plant interactions as they can inform fruit selection and be the basis for the evolution of interspecific variation. Yet data on the role of intraspecific variation on animal behaviour are rare. We combine behavioural and fruit trait data to test whether sensory ecology is driven by: (H1) intraspecific variation in fruit traits; and/or (H2) traits that are correlated with fruit quality. Our overarching hypothesis is that variation within a species will lead to differential deployment of senses across species. We collected sensory behaviour of wild red-bellied lemurs and quantified intraspecific variation in the traits of six consumed fruit species. We found support for both: the use of olfaction was significantly associated with both intraspecific variation in fruit scent and its association with sugar content. This underscores the significance of intraspecific variation in plant traits to animal sensory ecology, as well as their potential implications for fruit trait evolution.

Fruits, frugivores and the evolutionary arms race.

Aromatic pickle-mango types, locally termed as ‘Appemidi’, are extensively collected for household use and for commerce from the wild habitats even today in the central Western Ghats, India. Because of the deep cultural attachment, people have recognized several pickle-mango types from the wild habitats. However, studies on treeto-tree variation in fruit and stone traits in natural populations are not done, which is a pre-requisite for cultivar development. Unripe fruits collected from 34 wild fruiting trees in two populations, 17 from Sirsi and 17 from Siddapur localities in Central Western Ghats, India were studied for variation in fruit traits and its association traits. Fruits from Sirsi locality were significantly larger than those from Siddapur (84.27 vs. 51.26g) due to their greater green flesh mass (79.91 vs. 43.17 g). Tree-to-tree variation was highly significant and continuous in fruit length (Sirsi = 49.45–102.51 mm; Siddapur = 28.23–59.19 mm), stone length (Sirsi=26.97–55.59 mm; Siddapur=20.43–51.47mm), fruit mass (Sirsi=19.78–84.27g; Siddapur=15.50–51.26 g) and flesh mass (Sirsi=18.01– 79.91g; Siddapur=13.93–43.17g), indicating the potential for selection. The strong relationships between fruit mass and green flesh mass in aromatic pickle-mango found in this study indicated that selection for green flesh mass can be based on fruit mass. Based on five important traits preferred by growers/fruit collectors/sellers and four quantitative traits from observations, development of an ‘ideal type’ and identification of potential superior trees was attempted. These results have important implications for the domestication of pickle-mango genetic resources.

Climate change, habitat destruction, overexploitation, and invasive species have led to the loss of key species interactions and gains of novel species interactions. These interactions may have long-term consequences for ecosystem stability and function. With such drastic change, there is an urgent need to understand 1) the underlying variation and drivers of traits linked to fitness and 2) how organisms rapidly modify their behavior as a response to change through phenotypic plasticity. Although plants are mostly sessile, there is increasing evidence that plants actively respond to changes in their abiotic and biotic environment through shifts in resource allocation. In comparison to vegetative plant structures, little is known about how plants manipulate resources in their reproductive structures to directly respond to changes in species interactions. Fleshy-fruited plants require animal-mediated dispersal to disperse their seeds; thus, seed dispersers increase their overall fitness. The role of biotic interactions in shaping fruit traits has not been fully explored. With a change or loss of frugivory, we hypothesized that a plant would plastically respond to this lack of stimulus by manipulating its fruit traits. I used a combination of greenhouse and field experiments to address the following questions: 1) How does light availability and competition impact fruit traits? 2) What is the degree of intraspecific variation in fruits traits on islands with different levels of animal-mediated dispersal? 3) Do plants demonstrate plasticity in their fruit traits to changes in frugivore abundance? Using an observational approach over a season, I tracked the phenology of invasive blackberry in a mesic forest in Hawaiʻi to determine if light and native understory competition impacted blackberry reproductive output. While I found that light increased reproductive output, there was no evidence of native competition affecting reproduction; phenology was not impacted by either variable. I then conducted a comparative study in the Mariana Islands, analyzing fruit traits at multiple spatial scales on islands with and without avian seed dispersal. I found that variation in fruit traits of canopy trees was high, especially at the within-population and within-tree levels. I also found that a few species showed differences in mean fruit size in Guam, where avian frugivores are largely absent, compared to other islands with avian frugivores, suggesting a biotic factor - the lack of frugivory - may be impacting the underlying trait variation across the island. To test this idea, I conducted a greenhouse experiment in which I manipulated fruit removal rates in a wild tomato, Solanum pimpinellifolium, and measured fruit traits over time. I found that plants with no fruit removal produced significantly smaller, less seedy fruits, and this effect became stronger over time. Plants with a high rate of fruit removal had a more consistent phenotype across the study duration than those with moderate or low removal rates. This suggests that plants can exhibit frugivore-mediated plasticity by reducing resources allocated to individual fruits when frugivore visitation is reduced. This is the first experimental evidence of frugivore-mediated plasticity in morphological fruit traits and suggests plants may have strategies to optimize their resources during conditions when frugivore visitation is uncertain. This dissertation provides a framework to continue frugivore-mediated plasticity and emphasizes the importance of incorporating reproductive traits into functional trait research.

--Many ripe fruits contain chemicals that presumably protect them against attacks by frugivores that do not disperse seeds. These secondary metabolites may be generally toxic, representing an evolutionary compromise between defense from pathogens and attraction of seed dispersers (the General Toxicity hypothesis). Alternatively, they may be nontoxic to seed dispersers and simultaneously to vertebrate frugivores that do not disperse seeds (the Directed Toxicity hypothesis). To tease apart these hypotheses, we tested whether consumption of artificial fruit agar by captive Cedar Waxwings (Bombycilla cedrorum) was reduced by the presence of c•-solamargine, a glycoalkaloid common in solanaceous fruits. We recorded consumption of three artificial fruit types differing in c•solamargine concentration and a control fruit that lacked c•-solamargine. Waxwings were strongly and equally deterred by all concentrations of c•-solamargine. These concentrations, 0.1, 0.2, and 0.3% wet mass, are commonly found in some Solanum fruits. In a second trial, we addressed another hypothesis, the Nutrient-Toxin Titration hypothesis, which predicts that the deterrent effects of c•-solamargine can be overridden by highly nutritious fruit pulp. We offered waxwings three types of artificial fruits that varied in nutrient concentration but not in c•-solamargine concentration. Nutrient content had no effect on consumption when c•-solamargine was present. In summary, our results are inconsistent with both the Directed Toxicity and the Nutrient-Toxin Titration hypotheses. Received 24 June 1996, accepted 27 August 1997. BIRDS ARE PRIMARY CONSUMERS of fruits and dispersers of seeds. At one interface of this mutualistic interaction is the match between the nutritional requirements of birds and the chemical content of fruits (Martinez del Rio and Restrepo 1993). Nutrients of particular interest to researchers have been lipids, proteins, and carbohydrates (Martinez del Rio et al. 1989, Worthington 1989, Karasov and Levey 1990, Levey and Grajal 1991, Place and Stiles 1991, Witmer 1994, Afik and Karasov 1995). Largely overlooked are secondary metabolites, which promise to yield new insights for studies of fruit-frugivore interactions, as they have for studies of plant-herbivore interactions (Cipollini and Levey 1997b). For example, some secondary metabolites in ripe fruit pulp are paradoxical because they appear to deter fruit consumption-and hence seed dispersal--by seed-dispersing birds (Herrera 1982, Cipollini and Levey 1997c). How can their presence be explained in the context of mutualism? Here, we use Cedar Waxwings (Bombycilla cedrorum) to test two • E-mail: dlevey@zoo.ufl.edu 2 Present address: Department of Biology, 430 Berry College, Rome, Georgia, 30149, USA sets of hypotheses, formally proposed by Cipollini and Levey (1997c), that address the evolutionary significance of fruit secondary metabolites. The Directed Toxicity hypothesis tates that secondary metabolites in ripe fruit are to vertebrate frugivores that do not disperse seeds but are not to those that disperse seeds (Janzen 1975). This hypothesis gains credence from observations that seed-dispersing birds consume a wide range of toxic fruit (Martin et al. 1951, Kear 1968, Heiser 1969, Herrera 1982, Jordano 1987) and appear to be broadly tolerant of naturally occurring toxins (Herrera 1985). Alternatively, the General Toxicity hypothesis posits that secondary metabolites are repellent o all frugivores, regardless of how they treat seeds (Cipollini and Levey 1997c). This hypothesis is bolstered by studies concluding that variation in behavior and morphology among frugivores cannot account for variation in fruit traits (Herrera 1992, Jordano 1995, Tamboia et al. 1996). The Nutrient-Toxin Titration and Removal Rate hypotheses focus on interspecific variation among plants and the possible interactions of nutrient content, secondary chemistry, mi-

The taxonomy of Solanum melongena L., also known as brinjal eggplant, has remained difficult because previous studies to establish genetic relationships among taxa are mainly based on morphological features, which are insufficient to establish genetic affinities. In the present investigation, five highly polymorphic random amplified polymorphic DNA primers were used to describe the genetic similarity and diversity among its accessions in Nigeria. The results show a high level of polymorphism based on the banding patterns among the samples. This indicated a wide and diverse genetic base. Four distinct clusters were equally noticeable at a coefficient of 0.80 from the dendrogram generated. Generally, the grouping pattern clearly indicates that irrespective of variations in fruit traits among samples, they were still grouped together in different clusters with a high similarity coefficient value. This probably showed some genetic relatedness/closeness among the samples concerned. The study also revealed that there is no association between RAPD pattern and the geographic origin of accessions. These agreed with previously published data on the characterization of eggplant. The study disclosed that molecular methods coupled with morphological analyses could make proper classification of S. melongena and other Solanum species in Nigeria possible to achieve.   Key words: Eggplant, random amplified polymorphic DNA (RAPD), Data, polymorphism, taxonomy.

Chapter 22 - Domestication Potential of Marula (Sclerocarya birrea subsp caffra) in South Africa and Namibia: 1. Phenotypic Variation in Fruit Traits: This chapter was previously published in Leakey, R.R.B., Shackleton, S., du Plessis, P., 2005. Agroforestry Systems, 64, 25–35, with permission of Springer

Studies of tree-to-tree variation in fruit traits are a pre-requisite for cultivar development. Fruits were collected from each of 63 marula (Sclerocarya birrea) trees in Bushbuckridge, South Africa and from 55 trees from the North Central Region of Namibia. The South African trees were in farmers fields, communal land and natural woodland, at three sites: Acornhoek road, Allandale/Green Valley and Andover/Wits Rural Facility. The Namibian trees were all from farmers fields in three areas: North east, North west and West. The fruits were partitioned into skin and flesh/juice to examine the extent of the variation found in different components of marula fruits from different trees. Namibian fruits were significantly larger than those from South Africa (26.7 vs 20.1 g), due to their greater pulp mass (22.2 vs 16.2 g), especially the flesh/juice component. In South African fruits, those from farmers fields were significantly larger in all components (Fruit mass = 23.6 vs 19.3 and 18.0 g in natural woodland and communal land respectively). In Namibia, mean fruit mass did not differ significantly across sites (25.5 − 27.0 g). However, within each sample there was highly significant and continuous variation between trees in the pulp (S Africa = 7.5 − 31.3 g; Namibia = 8.3 − 36.0 g) and flesh/juice mass (S Africa = 2.2 − 7.6g; Namibia = 3.8 − 22. 6g), indicating the potential for selection of trees producing superior products. The fruits of the Namibian trees were compared with the fruits from one superior tree (‘Namibian Wonder) with a mean fruit mass of 69.9 g The percentage frequency distribution of fruit mass from trees in farmers fields in South Africa was skewed, while being bimodal in North east and North west populations from Namibia, suggesting that at these sites farmers are engaged in domestication through truncated selection of the best mother trees. It is concluded that there are trees in on-farm populations that have great potential to be propagated vegetatively as selected cultivars.

Phenotypic variations in fruits and selection potential in Sclerocarya birrea subsp. birrea

A quantitative analysis of the patterns of intra- and interspecific variance of fleshy fruit traits (length, width, pulp mass, seed mass, percent pulp mass) in eight species of southeastern Spanish vertebrate-dispersed plants, Berberis hispanica, Crataegus monogyna, Daphne laureola, Hedera helix, Juniperus communis, Juniperus phoenicea, Juniperus sabina, and Rosa canina, shows a statistically significant individual variability in the five fruit traits considered. Individual variability tended to be largest for pulp mass and seed mass (coefficient of variation of individual means between 20% and 30%) and smallest for fruit width and length and for proportion of pulp (CV of 5%-12%). Most variance in fruit traits (67%-88%) was accounted for by taxonomic affiliation, while the remainder of the variance was partitioned in roughly similar proportions among and within plants of individual species. There were some differences between fruit traits in the relative proportion of variance contributed by within and among individual variation, but all fruits traits in all species consistently exhibited a remarkably high proportion of within-individual variance, roughly comparable to the variance among individuals. The potential ecological and evolutionary implications of observed patterns of fruit variability are discussed in relation to the foraging behavior of seed-dispersing frugivores.

In vitro shoots of six pear (Pyrus communis L.) cultivars, ‘Conference’, ‘Doyenned'Hiver’, ‘Passe Crassane’, ‘Bartlett’, ‘AbbeFetel’ and ‘Butirra Precoce Morettini’ were irradiated with gamma rays (3.5 Gy). After three subcultures, microcuttings from the irradiated shoots and from additional non-irradiated microcuttings were rooted to establish plants for survey orchards. All trees were individually observed for variation in fruit traits and for productivity. Trees were selected for improved characters related to production such as early bearing and consistent productivity. Variations observed in fruit appearance concerned degree of russeting, fruit shape and size. The frequencies of the observed variations in fruit traits depended on the cultivar, ranging from 0.81% in ‘Doyenned'Hiver’ to 3.64% in ‘Passe Crassane’. Of the 97 variants selected, only two showed chimeral behavior.

Ten fruit and kernel traits were assessed in 24 fruits of each of 152Irvingia gabonensis trees in three distinct populations in west and central Africa [2 populations of non-planted trees in Cameroon: Nko'ovos II (21 trees) and Elig-Nkouma (31 trees) and 1 population of planted trees in Nigeria: Ugwuaji (100 trees)]. Strong relationships were found between fruit weight and other fruit traits (e.g. flesh weight[r2 = 0.99: P < 0.001],fruit length [r2 = 0.74–0.83:P < 0.001], fruit width[r2 = 0.77–0.88: P< 0.001]). In contrast, relationships between kernel weight and other kernel/nut traits (e.g. shell weight and nut weight) were found to be weak[r2 = 0.009–0.37, P =0.058–0.001], with the exception of nut weight at Nko'ovos II(r2 = 0.65, P < 0.001).Relations hips between fruit and kernel traits (fruit massv. kernel mass, fruit mass v. shell mass, flesh mass v. kernel mass, nut massv. fruit mass and flesh depth v.kernel mass) were found to be very weak. This indicates that domestication through the selection and vegetative propagation of multiple-trait superior phenotypes is unlikely to be able to combine good fruit characteristics and good kernel characteristics within cultivars. Consequently, domestication activities should independently focus on ideotypes representing: 'fresh fruit' traits, and 'kernel' traits, that combine high values of the different fruit and kernel characteristics respectively. Evidence from this study indicates that selection of the three trees closest to the fruit ideotype per village as the mother plants for vegetative propagation and cultivar development, should give village level gains of 1.3 – 2-fold in fruit mass, and up to 1.5-fold in taste. Similarly for the kernel ideotype, selection of the three trees with the best fit would give potential gains in kernel mass of 1.4 – 1.6-fold.

Aim To assess large‐scale geographical trends in the character of fleshy, vertebrate‐dispersed fruits.Location Europe between central Sweden and southern Spain.Methods Analyses of fruit of sixty‐three plant species from twenty‐nine families were compiled from four regional data sets. Four structural and five chemical fruit traits were analysed intraspecifically to control rigorously for phylogenetic lineage effects. Trends were examined in relation to various biological features of the considered species.Results Contents of soluble carbohydrate and lipids decreased markedly northwards. Fruit diameter and fresh mass peaked at the wettest site, while the pulp water content remained more constant throughout the gradient than any other fruit trait. Ash content, seed number and seed mass did not change, while the nitrogen content showed conflicting trends. No relation was detected between observed variation in fruit traits and fruit type, fruit colour, ripening season, plant growth form, leaf longevity, or geographical distribution of the considered plant species.Main conclusions Considerable intraspecific variability exists in vertebrate‐dispersed fruits on large geographical scales. Climate presumably affects particularly those traits related to carbon and water gain and storage. Most research on fruit–frugivore interactions has been carried out on small spatial scales and failed to find matchings between frugivore communities and the character of fleshy fruits. I suggest that explicitly addressed large‐scale surveys on the geographical variability of fruits and their disperser assemblages are needed to elucidate their spatial patterns and to determine the extent to which fleshy fruit traits are shaped by animals and/or abiotic factors.

Fruit traits have historically been interpreted as plant adaptations to their seed dispersers. On the other hand, different environmental factors, which vary spatially and temporally, can shape fruit-trait variation. The mistletoe Tristerix corymbosus has a latitudinal distribution along the South American Pacific rim that encompasses two different biomes, the matorral of central Chile and the temperate forest that extends south of the matorral. This mistletoe shows contrasting fruiting phenology (spring vs summer), fruit color (yellow vs green), and seed dispersers (birds vs marsupial) in these two biomes. We characterized geographic variation of morphological and nutritional fruit traits of T. corymbosus to evaluate which macroecological factor, biome or latitude, better explains spatial variation in these variables. For each of 22 populations, we obtained environmental data (temperature, precipitation, and canopy cover), measured fruit and seed morphology traits (size, shape, and weight), and pulp moisture and nutritional content (fiber, protein, fat, carbohydrates, ash, and caloric content). Patterns of variation for each variable were described by fitting and comparing five different simple models varying in slope, intercept or both. Fruit morphology showed a clear biome-related disruptive pattern, seed morphological traits were unrelated to either biome or latitude, whereas nutritional variables showed diverse patterns. Different environmental factors seem to affect fruit development and phenology, determining the observed fruit characteristics, with seed dispersers playing a minor role in shaping these patterns. More generally, the contrasting plant-seed disperser associations we addressed can be interpreted as the outcome of an ecological-fitting rather than of a coevolutionary process.

Aonla (Phyllanthus emblica) is widely used in the Ayurvedic and pharmaceutical industries due to the presence of medicinally important bioactive compounds. In the present study, seven commercial cultivars of P. emblica along with one wild genotype were characterized for morpho-molecular traits and antioxidant potential. Morphological evaluation was conducted using a randomized block design, while molecular analysis was carried out using random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers. Pomological traits exhibited significant variation among the evaluated cultivars. Principal component analysis explained 75.1% of the total variation in fruit traits, clustering all commercial cultivars together and separating the wild genotype into a distinct group. The commercial cultivars were superior in all fruit traits and showed higher antioxidant potential compared to the wild genotype. Molecular characterization revealed a mean polymorphic information content (PIC) value of 0.51 with 76.7% polymorphism. At the cultivar level, polymorphic loci ranged from 79.2% in cv. Kanchan to 95.2% in cv. Krishna. Shannon’s information index varied from 0.28 in the wild genotype to 0.37 in cv. NA-7, indicating considerable genetic diversity. Cluster analysis using the UPGMA method showed a minimum similarity coefficient of 0.53 between the wild genotype and cv. Kanchan. The combined pomological and molecular results confirmed substantial variability among the evaluated aonla cultivars and demonstrated the usefulness of these approaches for precise characterization of P. emblica genotypes, which can be effectively exploited in future varietal improvement programmes.