Interference at several temporal and spatial scales between two chestnut insects

Detection of interspecific competition between insects is often sensitive to scaling. We give an example of scale-dependent interference between the weevil Curculio elephas and the moth Cydia splendana, which both have larvae that develop in the fruits of chestnut Castanea sativa. Measures at three scales were considered: chestnut, husk (with one to three fertile fruits) and tree. Data come from observations in the field over 14 years, complemented by experiments done directly in trees. Data on individual chestnut fruits revealed a marked statistical interference between the two insects. Experiments demonstrated that presence of a moth larva in a fruit usually inhibits weevil egg-laying. Conversely, weevil presence does not strongly modify moth larval behavior. Cases of double infestation often correspond to fruits first attacked by the weevil. With measures on husks, interference between the two insects was observed only in some trees; its intensity was always weaker than in the chestnuts themselves. At the scale of entire trees, rates of infestation by each insect are not correlated. Interference in chestnut fruits is interpreted by assuming that the weevil female either is sensitive to a repellent molecule originating from a moth larva or its frass, or can detect moth larval sounds. Mechanisms governing infestation rates from data per tree are discussed in relation to those found at fruit scale and to plant-insect interactions. The need to estimate available resources both from quantitative and qualitative points of view is emphasized.     

Laboratory evaluation of Turkish entomopathogenic nematodes for suppression of the chestnut pests,Curculio elephas (Coleoptera: Curculionidae) and Cydia splendana (Lepidoptera: Tortricidae)

The lepidopteran, Cydia splendana, and the coleopteran, Curculio elephas, are the most serious pests of chestnut fruit in Turkey. We evaluated the biological control potential of three Turkish entomopathogenic nematode species, Steinernema feltiae, S. weiseri and Heterorhabditis bacteriophora, against the last instar larvae of C. splendana and C. elephas, both of which occur in the soil from fall (October–November) until mid-summer (August). The optimal temperature for infection, time to death of the hosts, and reproductive potential of the nematodes were determined at 10, 15, 20 and 25°C for both pest species. Cydia splendana was more susceptible to nematode infection than C. elephas. Temperature had a significant effect on the infectivity and development of entomopathogenic nematodes. The cold-adapted S. weiseri and S. feltiae were the most virulent species at 10 and 15°C, whereas the warm-adapted H. bacteriophora was the most effective at 20 and 25°C. In soil pot experiments conducted at 15°C, S. weiseri was the most virulent species against C. elephas and C. splendana. However, our data show that C. elephas larvae had a lower and C. splendana larvae had a higher susceptibility to the nematode species tested. Accordingly, we recommend that future efforts of using entomopathogenic nematodes, especially S. weiseri, be directed against C. splendana and that there be a continued effort to find more virulent nematode isolates against larvae of C. elephas.     

Resource limitation in natural populations of phytophagous insects. A long-term study case with the chestnut weevil

The chestnut weevil, Curculio elephas (Gyll.), is a non-outbreaking species whose populations and food resources, the European chestnut, Castanea sativa, can be precisely defined. Thirteen and 17 generations of this insect were studied in two isolated sites. Field observations and experiments allowed us to estimate the absolute abundance, availability and use of chestnuts for weevil oviposition, and the number of weevil females emerging per site. Unavailable chestnuts were defined as the fruits either infested first by the chestnut moth (Cydia splendana) larvae (because of competition between the two species) or those avoided by chestnut weevil females when selecting their egg-laying sites, independently of chestnut moth presence. From a third to a half of the chestnuts were not available on the average for weevil infestation. Only one-fourth, on the average, of those available for oviposition were actually used by chestnut weevil females. Regardless of year and site, the number of available chestnuts per weevil female was higher than that of weevil-infested fruits per female, considering global food resources independently of their temporal variation in quality. However, realized fecundity of weevil females was positively correlated with the mean number of available chestnuts per female. We concluded that food resources can be limiting without being fully exploited by females because of temporal variation in chestnut quality.     

Effects of defoliation by horse chestnut leafminer (<Emphasis Type="Italic">Cameraria ohridella</Emphasis>) on reproduction in<Emphasis Type="Italic"> Aesculus hippocastanum</Emphasis>

In large parts of Europe horse chestnut trees ( Aesculus hippocastanum) suffer from severe defoliation by an alien invasive species, the specialist leaf mining moth Cameraria ohridella (Lepidoptera; Gracillariidae). Heavily infested trees have a drastically shortened period for photosynthesis. We quantified the effect of moth infestation on reproduction of horse chestnut trees in two different cities in central Europe, Bern and Munich. C. ohridella negatively affected seed and fruit weight of A. hippocastanum at both locations. In Munich, seed weight of heavily damaged trees was reduced by almost half. However, the number of seeds per fruit, the number of fruits per inflorescence, and the number of inflorescences per tree did not change due to herbivory. We conclude that C. ohridella mining affects seed quality but not seed quantity. The reduced seed weight may severely impair growth and survival of horse chestnut seedlings and thus may endanger the long-term persistence of A. hippocastanum in its endemic forests in south-east Europe.     

Spread and population structure of <Emphasis Type="Italic">Cryphonectria parasitica</Emphasis> in a young chestnut orchard in Slovakia

The chestnut blight pathogen Cryphonectria parasitica was studied in a chestnut collection composed of both seedlings and grafts derived from selected Castanea sativa and C. sativa × C. crenata trees located in south-east Slovakia, near village Príbelce on an area of approximately 3.5 ha. The study was conducted during eight years (2003–2010). During this period 133 trees were infected, which represents 59.82% of chestnut trees of all chestnut accessions. Based on the phenotype of the fungus culture and the type of cankers in the field, all isolates were determined to be virulent. No hypovirulent strains were found. No vegetative compatibility (vc) type diversity was observed. More than 130 isolates were analyzed for vc and all were in single vc type, which was identical with EU 12. All isolates assayed for mating type were MAT-1. No perithecia were observed. No significant differences were found between the proportion of cankered and dead cankered trees in seedlings and grafts of hybrid origin (C. sativa × C. crenata) and of C. sativa origin. However, particular seedlings and grafts of hybrid origin seemed to exhibit certain resistance to chestnut blight.     

Comparative efficacy of gypsy moth (Lepidoptera: Erebidae) entomopathogens on transgenic blight‐tolerant and wild‐type American,Chinese, and hybrid chestnuts (Fagales: Fagaceae)

American chestnut (Castanea dentata [Marsh.] Borkh.) was once the dominant hardwood species in Eastern North America before an exotic fungal pathogen, Cryphonectria parasitica (Murrill) Barr, functionally eliminated it across its range. One promising approach toward restoring American chestnut to natural forests is development of blight‐tolerant trees using genetic transformation. However, transformation and related processes can result in unexpected and unintended phenotypic changes, potentially altering ecological interactions. To assess unintended tritrophic impacts of transgenic American chestnut on plant–herbivore interactions, gypsy moth (Lymantria dispar L.) caterpillars were fed leaf disks excised from two transgenic events, Darling 54 and Darling 58, and four control American chestnut lines. Leaf disks were previously treated with an LD₅₀ dose of either the species‐specific Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) or the generalist pathogen Bacillus thuringiensis subsp. kurstaki (Btk). Mortality was quantified and compared to water blank controls. Tree genotype had a strong effect on the efficacies of both pathogens. Larval mortality from Btk‐treated foliage from only one transgenic event, Darling 54, differed from its isogenic progenitor, Ellis 1, but was similar to an unrelated wild‐type American chestnut control. LdMNPV efficacy was unaffected by genetic transformation. Results suggest that although genetic modification of trees may affect interactions with other nontarget organisms, this may be due to insertion effects, and variation among different genotypes (whether transgenic or wild‐type) imparts a greater change in response than transgene presence.     

Effect of Chestnut Ink Disease on Photosynthetic Performance

In order to evaluate the evolutionary impact of chestnut ink disease, infected trees (cv. Judia), were compared with non‐infected trees, in three separate months: July, September and October. The aim of this work is to analyse the effects of the infection using parameters related to plant water relations, gas exchange and biometric data of leaves and fruits. In this period, temperatures decreased from 31 to 16°C contrarily to precipitation, which increased from 18 to 178 mm, respectively. In consequence, leaf water potential changed between ?1.6 and ?1.0 MPa while in infected plants the values maintained around ?1.2 MPa over the referred period. Nevertheless, at the gas exchanges level, differences in stomatal conductance, transpiration and photosynthesis were only detected in October. Concerning photosynthesis rate, the infected plants showed, in relation to September, a reduction around 35% whereas in non‐infected plants the decline was 25%. Alterations in the chlorophyll contents were also observed between September and October. In infected plants reduction on total amount of chlorophyll was from 18.6 to 13.4 mg/W_f, while in non‐infected plants values were only decayed from 15.1 to 13.1 mg/W_f. In relation to chlorophyll a/chlorophyll b ratio, plants infected by the oomycete preserved values in the level of 2.6, whereas in healthy plants values changed from 2.5 to 2.3. Leaves and fruits from infected chestnut trees were 13 and 20% smaller, respectively than those from non‐infected. Fruits from infected plants also had less starch but more crude protein.     

Identification and characterisation of traditional chestnut varieties of southern Spain using morphological and simple sequence repeat (SSRs) markers

The maintenance of plant genetic resources requires the identification of places and agroforestry systems that support high levels of genetic diversity. The aim of this work was to clarify the number and names of chestnut ( Castanea sativa ) cultivars in the south of Spain. Accordingly, 100 grafted chestnut trees corresponding to 34 traditional names were evaluated using 10 qualitative morphological traits and seven simple sequence repeat (SSRs) markers. We identified 38 varieties, 12 in the Huelva region and 26 in Malaga, and synonymies and homonymies were discussed. This work demonstrated that the joint use of morphological traits and SSR markers is an efficient method to evaluate the agrobiodiversity of chestnut in this region. It was also stated that chestnut production in the south of Spain is a traditional system using varieties developed ' in situ '. This constitutes a genuine system of on-farm conservation, which is now threatened. Consequently, adopting strategies for its safeguarding are urgently recommended.     

Forest Management and Plant Species Diversity in Chestnut Stands of Three Mediterranean Areas

Over many centuries, chestnut fruits had an important role as food, while chestnut wood was used for local purposes. Today sweet chestnut stands are very common around the western Mediterranean Basin, and it is necessary to analyze the dynamic of plant species diversity in different chestnut stand types (groves and coppices) to guide management strategies that will allow the conservation of biodiversity. Our objective was to analyze consequences on plant species diversity of various management strategies in chestnut stands of three Mediterranean areas, Salamanca (Spain), the Cévennes (France), and Etna volcano (Italy). We found that plant species diversity is different according to management types; it is higher in groves than in coppice stands. We also demonstrated that Castanea sativa cultivated groves were characterized by small heliophillous therophytes. C. sativa abandoned groves, mixed C. sativa–Quercus pyrenaica coppice stands, Q. pyrenaica coppice stands, and young C. sativa coppice stands were characterized by hemicryptophytes with anemochorous dispersal mode and chamaephytes. Medium and old C. sativa coppice stands (that differ by the shoot age) were characterized by phanerophytes with zoochorous dispersal mode. Human perturbations maintain a quite high level of species diversity. In contrast, the abandonment of chestnut stands leads to homogeneous vegetation with decreasing diversity. One solution could be to maintain a landscape mosaic constituted of diverse chestnut stands modified by human activities (groves, cultivated or abandoned, and coppice stands). This could enhance regional plant diversity.     

Learning to find fruit in Ceratitis capitata flies

Wild Mediterranean fruit fly females, Ceratitis capitata (Wiedemann), from an essentially monophagous population on the island of Hawaii were exposed to natural mock orange (Murraya paniculata) or sweet orange (Citrus sinensis) host fruit hung from branches of potted trees for 3-day periods in field enclosures. Subsequently, when flies were released individually onto potted trees harboring one or the other (or a mixture) of these fruit types, a higher proportion visited the type of fruit with which they were familiar (and visitors found familiar fruit faster) compared with the fruit type with which they were unfamiliar. Moreover, fruit-finding flies of this monophagous population attempted oviposition exclusively in the familiar fruit type, and thus appeared to be just as capable of learning to accept fruit for oviposition as wild flies from a previously-tested polyphagous population on the island of Maui. Additional tests were conducted in which flies were exposed to natural or colored-wax-covered mock oranges or sweet oranges and tested for response to colored-wax-covered natural or artificial fruit. Results suggested that fruit size was the principal character learned and used in finding mock orange or sweet orange fruit, while fruit color and odor appeared to be of little or no importance in this regard.

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Résumé Des femelles sauvages d'une population essentiellement monophage de C. capitata Wiedemann, provenant de l'île de Hawaï, ont été mises en présence pendant des périodes de 3 jours dans des enceintes dans la nature à des fruits de Murraya paniculata et de Citrus sinensis suspendus à des branches d'arbres empotés. Quand les mouches ont été libérées individuellement sur les arbres empotés portant l'un ou l'autre de ces fruits (ou leur mélange), une plus forte proportion a visité le fruit avec lequel elles étaient familiarisées (et l'ont trouvé plus vite) que le fruit avec lequel elles ne n'étaient pas. De plus, les femelles découvrant des fruits de cette population monophage ne tentèrent de pondre que dans le type de fruit avec lequel elle étaient familiarisées. Elles se montrèrent aussi capables que les mouches d'une population polyphage de l'île de Maui d'apprendre à accepter de nouveaux fruits pour pondre. Des expériences complémentaires ont été réalisées dans lesquelles les mouches étaient mises en présence de fruits de M. paniculata ou de C. sinensis naturels ou couverts de cire colorée ou encore de fruits artificiels. Les résultats suggèrent que la taille du fruit est le principal critère d'apprentissage utilisé pour trouver M. paniculata ou C. sinensis, la couleur et l'odeur du fruit étant apparus comme de moindre importance ou sans effet.

     

Intra-tree foraging behavior of Ceratitis capitata flies in relation to host fruit density and quality

We examined the intra-tree foraging behavior of individually-released, wild-population Mediterranean fruit flies (medflies), Ceratitis capitata (Wiedemann), on field-caged host trees bearing each of three different densities (0, 3, or 12 per tree) of non-infested host fruit (kumquat) or each of two levels of fruit quality (12 non-infested fruit or 12 fruit infested with eggs and covered with host marking pheromone). With increasing density of non-infested fruit, medflies tended to remain longer in trees, visit more fruit before leaving, oviposit more often, accept a proportionately smaller number of fruit visited, and emigrate sooner after the last egg was laid (i.e. have a shorter Giving-Up-Time). Medflies spent much less time, oviposited much less often, and exhibited a longer Giving-Up-Time on trees harboring pheromone-marked fruit than non-infested fruit. Variation in temperature within the range at which experiments were conducted (25–36°C) had little detectable influence on foraging behavior. We compare our findings with published findings on the intra-tree foraging behavior of another tephritid fly, Rhagoletis pomonella (Walsh), and with current foraging behavior theory. We discuss implications of our findings with respect to medfly management strategies, particularly fruit stripping in eradication programs and use of synthetic marking pheromone for control.

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Résumé Nous avons étudié le comportement de prospection dans un arbre, de femelles d'une population sauvage de C. capitata, libérées individuellement à l'intérieur de cages contenant des Eriobotrya japonica (kumquat), portant chacun 3 densités différentes de fruits no contaminés (0, 3, 12 par arbre) et chacun 2 niveaux de qualité de fruits: 12 fruits non infestés ou 12 fruits contaminés par des oeufs et recouverts de phéromone de marquage de l'hôte. C. capitata avait terndance à rester plus longtemps dans les arbres, à visiter plus de fruits avant le quitter, à pondre plus souvent, à accepter proportionnellement un nombre plus réduit de fruits déjà visités, à émigrer plus tôt après la ponte du dernier oeuf (c'est-à-dire à présenter un temps d'abandon plus bref), quand la densité des fruits non contaminés augmentait. C. capitata a dépensé beaucoup moins de temps, pondu beaucoup moins souvent, et présenté un temps d'abandon plus long sur les arbres portant des fruits marqués par la phéromone que sur ceux ayant des fruits non contaminés. Les variations de température dans la gamme de cells où les observations ont eu lieu (23–36°C) n'ont eu qu'une faible influence décelable sur le comportement de prospection. Nous avons comparé nos résultats avec ceux publiés sur la prospection à l'intérieur de l'arbre par une autre téphritide (Rhagoletis pomonella) et avec la théorie dominante sur le comportement de prospection. Nous discutons les conséquences de nos résultats sur les stratégies de lutte contre C. capitata, en particulier l'élimination des fruits dans les plans d'erradication et l'utilisation de phéromone synthétique de marquage.

     

Spatial analysis of nuclear and mitochondrial RFLP genotypes in populations of the chestnut blight fungus, Cryphonectria parasitica

Spatial structure of both nuclear and mitochondrial RFLPs were studied in several populations of the chestnut blight fungus, Cryphonectria parasitica, using a variety of spatial autocorrelation tests designed to detect nonrandom patterns. Fungal individuals were sampled from cankers on infected chestnut trees, and the location of each tree was mapped. Single-locus nuclear RFLPs, nuclear fingerprints, and mitochondrial DNA haplotypes were determined for each individual. Individuals with the same DNA fingerprint genotypes occurred closer together than would be expected at random in four of the five plots, while mitochondrial DNA haplotypes were aggregated in all five plots. Genetic distances between individuals, expressed as one minus the proportion of shared restriction fragment size classes for fingerprints and mitochondrial haplotypes, were significantly correlated with Euclidean distances between individuals in four of the five populations, but these correlations were very weak (r < 0.18). The same DNA fingerprint and single-copy nuclear RFLP alleles occurred on the same trees or immediately neighbouring trees more often than would be expected at random. Most of the aggregation for all three genetic markers occurred among individuals within the same cluster of chestnut stems or on neighbouring trees. Lack of spatial autocorrelation in one population was probably due to sampling on a larger scale that was too coarse to detect any patterns. Significant aggregation of genotypes in C. parasitica is most likely caused by some degree of restricted dispersal within populations. The implications of restricted dispersal are discussed in relation to the breeding system and isolation by distance in populations of. C. parasitica.     

Genetic variation of horse chestnut and red horse chestnut and trees susceptibility to Erysiphe flexuosa and Cameraria ohridella

Trees of Aesculus sp. are often present in European landscapes. Common horse chestnut and red horse chestnut are seriously damaged by the fungus Erysiphe flexuosa as well as the pest Cameraria ohridella. Both pathogen and pest have spread throughout Europe. A genetic background of trees resistance still remains unknown. The present study was undertaken to estimate genetic variation of A. hippocastanum and A.×carnea grown in urban greens and their susceptibility to powdery mildew and horse chestnut leafminer. According to obtained results both species were infected by E. flexuosa in a similar degree but there were significant differences in susceptibility of particular trees (ANOVA). C. ohridella damaged only A. hippocastanum. The correlation between age of trees and degree of infestation by pathogen and pest was not observed. The significant genetic variability between two Aesculus species was revealed by the analysis of molecular variance (AMOVA) where both the intra- and the inter-species variation were found to be significant. It was shown that 73.0% of the genetic variance was contributed by the differentiation between A. hippocastanum and A.×carnea, whereas 27.0% was partitioned within species. The medium level of genetic diversity of Aesculus spp. was determined using SRAP and RAPD analyses. The mean value of genetic similarity was equal to 0.55 for common horse chestnut and 0.98 for red horse chestnut. Among 40 polymorphic SRAP and RAPD markers 17 were associated with degree of leaf damage caused by C. ohridella.     

Spatial patterns and infestation processes in the horse chestnut leafminer Cameraria ohridella: a tale of two cities

Spatial patterns of the horse chestnut leafminer Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae) population density was analysed in the cities of Bern and Brussels in order to explore its spatial population dynamics. The surveys were carried out in Bern in 1998 and 2000 and in Brussels in 2001 to assess population density in relation to local characteristics. In Brussels, population density was also measured using pheromone traps distributed over the city and collected twice per moth generation. A quantitative relationship was found between local population density (measured by pheromone traps and survey observations) and the amount of leaves left on the ground the previous fall. Several other factors were related to observed infestation levels: the occurrence of the pathogen Guignardia aesculi was inversely related to infestation by C. ohridella in Bern in 1998 and 2000, the number of horse chestnut trees within 800 m distance was positively related to infestation level in Bern in 2000, and the proportion of green areas within 100 m and the number of other horse chestnut trees within 2000 m were positively related to infestation levels in the 2001 Brussels survey. The pattern of infestation levels as a function of distance to potential population reservoirs suggested that C. ohridella re‐invades areas where overwintering leaves have been cleaned from refuge areas such as parks or urban forests. Our results indicate that the removal of leaves is a feasible first aid control measure to reduce moth population densities. However, leaf removal may not reduce moth densities when done improperly. In places where proper leaf removal is not feasible, other control measures are needed.     

Fruit size in a tropical tree species: variation,preference by birds,and heritability

Ocotea tenera (Lauraceae), an understory bird-dispersed tree, produces single-seeded fruits that vary in diameter from 1.4 to 2.4 cm. Much of the variation within a population at Monteverde, Costa Rica occurred within individual trees. The relative size of fruits produced by different trees remained generally constant over an 11-year period despite slight differences between years in the average size of fruits produced by a given tree.Fruit-eating birds could thus express their preferences for particular fruit size characteristics by choosing among trees that have distinct distributions of fruit diameters, and between individually variable fruits within trees. In a field study of individually marked fruits, birds removed 46.2% of fruits; the rest of the fruits were destroyed by invertebrate (25.3%) and vertebrate (4.3%) pulp-feeders or aborted by the plant after remaining ripe but uneaten for as long as 100 days (24.2%). The four major avian seed dispersers of O. tenera each have gape widths exceeding all but the largest fruits. Birds preferred plants with greater-than-average-sized fruits; within trees, they favored larger fruits, apparently because net pulp mass increases with fruit diameter. Fruits that ripened early in the season were more likely to be removed and were removed more quickly than late-ripening fruits.Based on mother-offspring regressions of mean fruit size, the phenotypic variation in fruit diameter in O. tenera is highly heritable, indicating the potential for an evolutionary response to selection by birds. Nonetheless, directional selection on fruit size or shape is likely to be inconsistent, constrained by genetic correlations, and weak compared to selection on traits like fecundity or phenology.     

Genetic characterisation of traditional chestnut varieties in Italy using microsatellites (simple sequence repeats) markers

European chestnut (Castanea sativa) is an important multipurpose tree that has been cultivated for wood and fruit in the Mediterranean basin since ancient times. Cultivation of traditional chestnut varieties has a long tradition in Italy, where cultivars have been selected over centuries as a function of the best nut traits. In this study, 94 grafted chestnuts corresponding to 26 representative cultivars from Italy were evaluated by seven simple sequence repeat (SSR) markers to establish whether they corresponded to varieties in the narrow sense. The results allowed 20 genotypes to be identified that corresponded to the same number of clones. In total, 52 alleles were identified, eight of which were exclusive. Cases of homonymies and synonymies were detected. Moreover, our results highlighted a considerable genetic uniformity among ‘Marrone-type’ cultivars and, on the contrary, a high genetic diversity among the evaluated cultivars demonstrating that this is a valuable germplasm and an important genetic resource to be preserved.     

Round and large: morphological and genetic consequences of artificial selection on the gourd tree Crescentia cujete by the Maya of the Yucatan Peninsula, Mexico

Background and Aims

Artificial selection, the main driving force of domestication, depends on human perception of intraspecific variation and operates through management practices that drive morphological and genetic divergences with respect to wild populations. This study analysed the recognition of varieties of Crescentia cujete by Maya people in relation to preferred plant characters and documents ongoing processes of artificial selection influencing differential chloroplast DNA haplotype distribution in sympatric wild and home-garden populations.

Methods

Fifty-three home gardens in seven villages (93 trees) and two putative wild populations (43 trees) were sampled. Through semi-structured interviews we documented the nomenclature of varieties, their distinctive characters, provenance, frequency and management. Phenotypic divergence of fruits was assessed with morphometric analyses. Genetic analyses were performed through five cpDNA microsatellites.

Key Results

The Maya recognize two generic (wild/domesticated) and two specific domesticated (white/green) varieties of Crescentia cujete. In home gardens, most trees (68 %) were from domesticated varieties while some wild individuals (32 %) were tolerated. Cultivation involves mainly vegetative propagation (76 %). Domesticated fruits were significantly rounder, larger and with thicker pericarp than wild fruits. Haplotype A was dominant in home gardens (76 %) but absent in wild populations. Haplotypes B–F were found common in the wild but at low frequency (24 %) in home gardens.

Conclusions

The gourd tree is managed through clonal and sexual propagules, fruit form and size being the main targets of artificial selection. Domesticated varieties belong to a lineage preserved by vegetative propagation but propagation by seeds and tolerance of spontaneous trees favour gene flow from wild populations. Five mutational steps between haplotypes A and D suggest that domesticated germplasm has been introduced to the region. The close relationship between Maya nomenclature and artificial selection has maintained the morphological and haplotypic identity (probably for centuries) of domesticated Crescentia despite gene flow from wild populations.     

Tracing coco de mer's reproductive history: Pollen and nutrient limitations reduce fecundity

Habitat degradation can reduce or even prevent the reproduction of previously abundant plant species. To develop appropriate management strategies, we need to understand the reasons for reduced recruitment in degraded ecosystems. The dioecious coco de mer palm (Lodoicea maldivica) produces by far the largest seeds of any plant. It is a keystone species in an ancient palm forest that occurs only on two small islands in the Seychelles, yet contemporary rates of seed production are low, especially in fragmented populations. We developed a method to infer the recent reproductive history of female trees from morphological evidence present on their inflorescences. We then applied this method to investigate the effects of habitat disturbance and soil nutrient conditions on flower and fruit production. The 57 female trees in our sample showed a 19.5‐fold variation in flower production among individuals over a seven‐year period. Only 77.2% of trees bore developing fruits (or had recently shed fruits), with the number per tree ranging from zero to 43. Flower production was positively correlated with concentrations of available soil nitrogen and potassium and did not differ significantly between closed and degraded habitat. Fruiting success was positively correlated with pollen availability, as measured by numbers and distance of neighboring male trees. Fruit set was lower in degraded habitat than in closed forest, while the proportion of abnormal fruits that failed to develop was higher in degraded habitat. Seed size recorded for a large sample of seeds collected by forest wardens varied widely, with fresh weights ranging from 1 to 18 kg. Synthesis: Shortages of both nutrients and pollen appear to limit seed production of Lodoicea in its natural habitat, with these factors affecting different stages of the reproductive process. Flower production varies widely amongst trees, while seed production is especially low in degraded habitat. The size of seeds is also very variable. We discuss the implications of these findings for managing this ecologically and economically important species.