Laurence Humeau

Distyly and heteromorphic incompatibility in oceanic island species ofErythroxylum (Erythroxylaceae)

Surveys of oceanic island floras have shown that heterostyly is usually absent in such regions, probably because this floral polymorphism is often associated with a self-incompatibility system. In this context we describe the floral biology of three species ofErythroxylum on La Réunion island and examine the compatibility relationships of one of these species,E. laurifolium. All three species are distylous but differ in relative stigma-anther separation in the different morphs. In general, short-styled flowers have greater stigma-anther separation than long-styled flowers, which are often homostylous in appearance. This lack of stigma-anther separation in long-styled flowers is due to style twisting which improves reciprocity at the high organ level. The reduced stigma-anther separation does not appear to be associated with the evolution of selfing asErythroxylum laurifolium shows heteromorphic self-incompatibility. The presence of heteromorphic incompatibility in a group of species that have colonized an oceanic island is discussed.

Sapromyiophily in the native orchid, Bulbophyllum variegatum , on Réunion (Mascarene Archipelago, Indian Ocean)

Orchid species are well known for their highly specialized pollinator interactions. To better understand the reproductive biology of the tropical epiphytic orchid Bulbophyllum variegatum on Reunion, we investigated the floral morphology, breeding system, pollinator diversity, floral scent profile and fruiting success of about 30 individuals in three natural populations during two consecutive flowering seasons. Controlled hand-pollination experiments in two populations showed that the species is self-compatible, but requires pollinator service to achieve reproduction. Videotape pollinator observations were conducted during two flowering seasons for 56 h and revealed that B. variegatum is pollinated by a single species of fly from the Platystomatidae. This fly seems to be attracted by the unpleasant scent produced by the flowers, and does not receive any reward after achieving pollination. In addition, no egg-laying behaviour was observed. Bulbophyllum variegatum thus exhibits a typical sapromyiophilous pollination syndrome which constitutes the first proven case of sapromyiophily within the genus Bulbophyllum on the Mascarene Archipelago. Hand pollinations further showed that fruit set was not significantly higher for flowers that received outcross pollen than for those that were self-crossed (53% and 44% respectively). Fruit sets under natural conditions were significantly different among populations, ranging from 0.5% to 24.3%. This low fruit production is likely due to infrequent pollinator visits, particularly in disturbed forests where the pollinator has never been observed.

Evidence for Isolation-by-Habitat among Populations of an Epiphytic Orchid Species on a Small Oceanic Island

Identifying factors that promote population differentiation is of interest for understanding the early stages of speciation. Gene flow among populations inhabiting different environments can be reduced by geographical distance (isolation-by-distance) or by divergent selection resulting from local adaptation (isolation-by-ecology). Few studies have investigated the influence of these factors in small oceanic islands where the influence of geographic distance is expected to be null but where habitat diversity could have a strong effect on population differentiation. In this study, we tested for the spatial divergence of phenotypes (floral morphology and floral scent) and genotypes (microsatellites) among ten populations of Jumellea rossii, an epiphytic orchid endemic to Réunion growing in three different habitats. We found a significant genetic differentiation between populations that is structured by habitat heterogeneity rather than by geographic distance between populations. These results suggest that ecological factors might reduce gene flow among populations located in different habitats. This pattern of isolation-by-habitat may be the result of both isolation-by-ecology by habitat filtering and asynchrony in flowering phenology. Furthermore, data on floral morphology match these findings, with multivariate analysis grouping populations by habitat type but could be only due to phenotypic plasticity. Indeed floral scent compounds were not significantly different between populations indicating that specific plant-pollinator mutualism does not seem to play a major role in the population differentiation of J. rossii. In conclusion, the results from our study emphasize the importance of habitat diversity of small oceanic islands as a factor of population differentiation.

Orchid-bird interactions: a case study from Angraecum (Vandeae, Angraecinae) and Zosterops (white-eyes, Zosteropidae) on Reunion Island

Although angraecoid orchids are famous for their spectacular flowers, pollinated by hawkmoths in Madagascar, two species of Angraecum endemic to the Mascarenes (sect. Hadrangis ) have atypical unscented and short-spurred flowers that are pollinated by birds. We focused on the pollination and reproductive success of Angraecum bracteosum Balf.f. & S.Moore, a member of sect. Hadrangis . We investigated the breeding system by performing a set of hand-pollination ex- periments and by observing natural pollinators using video-captures. Pollinator efficiency (pollen removal and deposition) and reproductive success (fruit set) were quantified once a week in two natural island populations during three consecutive flowering seasons (2003–2005). The orchid is self-compatible but requires pollinator services to achieve reproduction. The two white-eye song-bird species (Zosteropidae) that occur on Reunion, Zosterops borbonicus Boddaert and Zosterops oliva- Ceus L., were recorded as pollinators. However, while pollination events were rare and occasional following flower visits by Z. borbonicus , foraging of Z. oliveaceus resulted in a high frequency of successful pollinations. White-eyes typically perched on inflorescences, and probed most of the ‘‘fresh-looking’’ flowers for nectar. This study documents a probable case of bird-pollination specialization within Angraecum section Hadrangis , and sheds light on the role played by pollina- tors during the radiation of section Hadrangis in the Mascarene Archipelago.

Variation in the breeding system of two sympatricDombeya species on La Réunion island

The high frequency of dioecy on oceanic islands has attracted a great deal of attention in plant evolution. In this study we quantify variation in the breeding system of two sympatricDombeya species on La Réunion island. BothDombeya species are cryptically dioecious, each sex retaining non-functional morphological structures of the other sex. One species is strictly dioecious, whilst the other shows leaky dioecy, with 8/13 males producing fruit during two years of study. Males that set fruit did so following outcrossing but not after self-pollination despite the growth of self-pollen tubes in the style. This suggests the occurrence of a late-acting self-incompatibility system. Several morphologically intermediate individuals are recognized and suggested to be a result of interspecific hybridization. These purported hybrids are hermaphrodite and self-compatible, consistent with a complementary breakdown in dioecy and self-compatibility.

Flower size dimorphism in diclinous plants native to La Reunion Island

Abstract.Although many diclinous plants have a flower size dimorphism, the causes and ecological correlates of dimorphism in flower size remain poorly understood. In this paper we quantify the frequency and distribution of flower size dimorphism in the native flora of La Réunion Island. The frequency of flower size dimorphism is lower than in a previous global study suggesting that the dimorphism may limit colonisation success. Flower size dimorphism is significantly more frequent in endemic taxa compared to indigenous taxa, a trend that is particularly evident at the species level, due to the large number of species with male flowers bigger than female flowers and is more common in species-rich lineages. These results suggest that flower size dimorphism may be associated with species divergence. The direction of dimorphism varies between dioecious and monoecious species, suggesting that the mechanisms acting on flower size variation differ in species with these different sexual systems.

Micropropagation of Psiadia arguta through cotyledonary axillary bud culture

A micropropagation protocol for Psiadia arguta, an endangered endemic plant from Mauritius is described using 15-day old in vitro seedling explants without the radicle. MS basal medium supplemented with TDZ (0.5–1 mg/l) proved to be the most effective medium for the induction of cotyledonary axillary buds as compared to MS medium containing NAA (0.5 mg/l) or both NAA (0.5 mg/l) and TDZ (0.5–1 mg/l). In fact, after transfer to hormone free MS medium, microshoots were obtained only from seedling explants cultured on media containing only TDZ. Regenerated shoots elongated and rooted when cultured on MS8900 containing IBA (0–1 mg/l). Hormone-free MS8900 was the best medium for rooting and development of plantlets for acclimatization.

Vertebrate pollination of the endemic Trochetia granulata (Malvaceae) on Reunion

The pollination ecology and breeding system of Trochetia granulata (Malvaceae), an endemic tree species from Reunion were studied. In 2010-2011, compatibility studies were conducted on a total of 154 flowers from 35 different individuals using three different hand pollination treatments: (a) autofertility, (b) self-pollination and (c) cross-pollination. During the period, we also studied the pollination ecology of T. granulata. During 48 h of video recordings, we tracked flower visits to T. granulata in six different sites and studied the behaviour of the visitors. The results from the hand-cross experiments show that T. granulata is self-compatible (60.8% fruit set) but cannot produce fruit (5.4% fruit set) without the visit of a pollen vector. During surveys, four different visitors were reported: the introduced honey bee (Apis mellifera), two endemic species of white-eye (Zosterops borbonicus borbonicus and Z. olivaceus) and the endemic Reunion day gecko (Phelsuma borbonica). This study documented a new case of vertebrate-pollination by lizard and birds in an insular context. These interactions might be linked to several uncommon floral traits of Trochetia species.

Dombeya formosa (Malvaceae s. l.): A New Species Endemic to La Reunion (Indian Ocean) Based on Morphological and Molecular Evidence

Abstract Dombeya formosa (Malvaceae s. l. or Dombeyaceae), a new species endemic to La Réunion, is described and illustrated. The species is distinguishable by its ovate leaves with round or slightly cordate bases, round to lightly acute apices and glabrescent abaxial surfaces, subulate and persistent stipules, umbellate inflorescences, and acute apices of floral bracts. Dombeya formosa is morphologically close to Dombeya punctata Cav. but differs from it in having ovate leaves and acute apices on floral bracts. Dombeya formosa is also morphologically similar to D. ficulnea Baill. but can be distinguished from it by its persistent and subulate stipules as well as the glabrescent adaxial surface of its leaves. Our study, focusing on 16 quantitative floral characters, demonstrates that there is a clear morphological distinction between D. formosa, D. punctata, and D. ficulnea. In comparison to the other two species, Dombeya formosa possesses smaller flowers and additionally shows cryptic dioecy along with flower-size dimorphism between sexes. Amongst the Mascarene Dombeyoideae, it is the only species distributed up to an altitude of 2,100 m. The phylogenetic position of Dombeya formosa is consistent with the morphological features and locates the species within the clade endemic to La Réunion characterized by umbellate inflorescences.

A genetic diversity study of endangered Psiadia species endemic from Mauritius Island using PCR markers

The genus Psiadia Jacq. represents the most important indigenous genus, by the number of species present, in the Mascarene archipelago (Mauritius, Reunion, Rodrigues), and is a typical example of adaptive radiation in oceanic islands. The Mauritius species are used in traditional pharmacopoeia for their expectorant properties, and most of them are heavily threatened. Molecular genetic relationships between representatives of eight endangered endemic Psiadia species from Mauritius, conserved in Le Mondrain Reserve, and P. dentata (Cass.) DC, endemic from Reunion island, were studied. The absence of length variations of the 5s rDNA non-transcribed spacer demonstrated the recent common origin of all the species surveyed. RAPD analysis revealed a relatively high intra-specific variability in accordance with the outcrossing mode of reproduction of Psiadia species. Moreover, RAPD analysis showed the existence of four major phenetic groups: (A) P. arguta (Pers.) Voigt, P. dentata, (B) P. penninervia D. C., P. terebinthina A.J. Scott, P. lithospermifolia (Lam.) Cordem, (C) P. viscosa (Lam.) A.J. Scott, P. canescens A.J. Scott, P. cataractae A.J. Scott, and (D) P. pollicina A.J. Scott. These groups were consistent with the chemical composition of the essential oils of the species as well as with their floral characteristics, based on literature. A molecular germplasm database for Psiadia species was established, which will allow further characterisation of new samples being introduced in Le Mondrain Reserve for conservation purpose.