An expressed sequence tag (EST) library from developing fruits of an Hawaiian endemic mint (Stenogyne rugosa, Lamiaceae): characterization and microsatellite markers

Background  

The endemic Hawaiian mints represent a major island radiation that likely originated from hybridization between two North American polyploid lineages. In contrast with the extensive morphological and ecological diversity among taxa, ribosomal DNA sequence variation has been found to be remarkably low. In the past few years, expressed sequence tag (EST) projects on plant species have generated a vast amount of publicly available sequence data that can be mined for simple sequence repeats (SSRs). However, these EST projects have largely focused on crop or otherwise economically important plants, and so far only few studies have been published on the use of intragenic SSRs in natural plant populations. We constructed an EST library from developing fleshy nutlets of Stenogyne rugosa principally to identify genetic markers for the Hawaiian endemic mints.     

Cladogenesis and reticulation in the Hawaiian endemic mints (Lamiaceae)

The Hawaiian endemic mints, which comprise 58 species of dry‐fruited Haplostachys and fleshy‐fruited Phyllostegia and Stenogyne, represent a major island radiation that likely originated from polyploid hybrid ancestors in the temperate North American Stachys lineage. In contrast with considerable morphological and ecological diversity among taxa, sequence variation in the nrDNA 5S non‐transcribed spacer was found to be remarkably low, which when analyzed using standard parsimony resulted in a lack of phylogenetic resolution among accessions of insect‐pollinated Phyllostegia and bird‐pollinated Stenogyne. However, many within‐individual nucleotide polymorphisms were observed, and under the assumption that they could contain phylogenetic information, these ambiguities were recoded as new character states. Substantially more phylogenetic structure was obtained with these data, including the resolution of most Stenogyne species into a monophyletic group with an apparent recent origin on O’ahu (3.0 My) or the Maui Nui island complex (2.2 My). Subsequent diversification appears to have involved multiple inter‐island dispersal events. Intergeneric placements for a few morphotypes, seemingly misplaced within either Phyllostegia or Stenogyne, may indicate reticulation as one polymorphism‐generating force. For a finer scale exploration of hybridization, preliminary AFLP fragment data were examined among putative hybrids of Stenogyne microphylla and S. rugosa from Mauna Kea, Hawai’i, that had been identified based on morphology. Cladistic analysis (corroborated by multivariate correspondence analysis) showed the morphologically intermediate individuals to group in a strongly supported monophyletic clade with S. microphylla. Therefore, reticulation could be both historic and active in Stenogyne, and perhaps a force of general importance in the evolution of the Hawaiian mints. The relatively greater extent of lineage‐sorted polymorphisms in Stenogyne may indicate selective differentiation from other fleshy‐fruited taxa, perhaps through the agency of highly specialized bird pollinators that restricted gene flow with other Hawaiian mint morphotypes.     

Pollination systems in Pogonieae (Orchidaceae: Vanilloideae): A hypothesis of evolution among reward and rewardless flowers

The tribe Pogonieae of Vanilloideae (Orchidaceae) consists of six genera, including Pogoniopsis, a myco-heterotrophic taxon with morphological characteristics distinct from the remaining of the tribe. A hypothesis about the phylogeny of the tribe was inferred, involving all currently recognized genera, based on isolated and combined sequence data of 5.8S, 18S and 26S (nrDNA) regions using parsimony and Bayesian analyses. Phylogenetic analyses show that inclusion of Pogoniopsis turns the tribe Pogonieae paraphyletic. All analyses reveal that Pogoniopsis is closely related to members of Epidendroideae. The pantropical Vanilla is monophyletic if Dictyophyllaria is assumed as synonym of Vanilla. Members of Pogonieae are pollinated by several groups of solitary and social bees, two pollination systems being recognized: reward-producing and deceptive. The molecular phylogeny suggests that ancestrals related to Pogonieae gave rise to two evolutionary lines: a tropical one with reward production of flowers, and a predominantly temperate regions invading line with deceptive flowers. Reward-producing flowers characterize the South and Central American clade (=Cleistes), while deceptive pollination is prominent in the clade that includes North American-Asiatic taxa plus the Amazonian genus Duckeella.     

Phylogeny and radiation of pollination systems in DISA (Orchidaceae)

We studied the patterns of adaptive radiation in Disa, a large orchid genus in southern Africa. A cladogram for 27 species was constructed using 44 morphological characters. Pollination systems were then mapped onto the phylogeny in order to analyze pathways of floral evolution. Shifts from one pollination system to another have been a major feature of the evolutionary diversification of Disa. Unlike many plant genera that are pollinated mainly by a single group of insects, radiation in Disa has encompassed nearly all major groups of pollinating insects; in all, 19 different specialized pollination systems have been found in the 27 species included in this analysis. Another striking pattern is the repeated evolution of broadly similar pollination systems in unrelated clades. For example, butterfly-pollinated flowers have evolved twice; showy deceptive flowers pollinated by carpenter bees, twice; long-spurred flowers pollinated by long-tongued flies, four times; night-scented flowers pollinated by moths, three times; and self-pollination, three times. This suggests that a few dominant pollinator species in a region may be sufficient to generate diversification in plants through repeated floral shifts that never retrace the same pathways.     

Interspecific hybrid ancestry of a plant adaptive radiation: allopolyploidy of the Hawaiian silversword alliance (Asteraceae) inferred from floral homeotic gene duplications.

The polyploid Hawaiian silversword alliance (Asteraceae), a spectacular example of adaptive radiation in plants, was shown previously to have descended from North American tarweeds of the Madia/Raillardiopsis group, a primarily diploid assemblage. The origin of the polyploid condition in the silversword alliance was not resolved in earlier biosystematic, cytogenetic, and molecular studies, apart from the determination that polyploidy in modern species of Madia/Raillardiopsis arose independent of that of the Hawaiian group. We determined that two floral homeotic genes, ASAP3/TM6 and ASAP1, are found in duplicate copies within members of the Hawaiian silversword alliance and appear to have arisen as a result of interspecific hybridization between two North American tarweed species. Our molecular phylogenetic analyses of the ASAP3/TM6 loci suggest that the interspecific hybridization event in the ancestry of the Hawaiian silversword alliance involved members of lineages that include Raillardiopsis muirii (and perhaps Madia nutans) and Raillardiopsis scabrida. The ASAP1 analysis also indicates that the two species of Raillardiopsis are among the closest North American relatives of the Hawaiian silversword alliance. Previous biosystematic evidence demonstrates the potential for allopolyploid formation between members of the two North American tarweed lineages; a vigorous hybrid between R. muirii and R. scabrida has been produced that formed viable, mostly tetraporate (diploid) pollen, in keeping with observed meiotic failure. Various genetic consequences of allopolyploidy may help to explain the phenomenal evolutionary diversification of the silversword alliance.     

Pollination of Cyphomandra endopogon var. endopogon (Solanaceae) by Eufriesea spp. (Euglossini) in French Guiana

The pollination systems of two closely related genera.Cyphomandra andSolanum, differ in rewards offered and pollinator activity. I suggest that the anther differences which define these two genera have evolved in response to the different pollination systems. Male euglossine bees of the genusEufriesea were observed to pollinate the flowers ofCyphomandra endopogon var.endopogon while gathering aromatic compounds from the anther connectives. Samples of the compound collected from the flowers and the bees were tentatively identified as ocimene, a terpene.     

Radiation of pollination systems in the Iridaceae of sub-Saharan Africa

BACKGROUND: Seventeen distinct pollination systems are known for genera of sub-Saharan African Iridaceae and recurrent shifts in pollination system have evolved in those with ten or more species. Pollination by long-tongued anthophorine bees foraging for nectar and coincidentally acquiring pollen on some part of their bodies is the inferred ancestral pollination strategy for most genera of the large subfamilies Iridoideae and Crocoideae and may be ancestral for the latter. Derived strategies include pollination by long-proboscid flies, large butterflies, night-flying hovering and settling moths, hopliine beetles and sunbirds. Bee pollination is diverse, with active pollen collection by female bees occurring in several genera, vibratile systems in a few and non-volatile oil as a reward in one species. Long-proboscid fly pollination, which is apparently restricted to southern Africa, includes four separate syndromes using different sets of flies and plant species in different parts of the subcontinent. Small numbers of species use bibionid flies, short-proboscid flies or wasps for their pollination; only about 2 % of species use multiple pollinators and can be described as generalists. SCOPE: Using pollination observations for 375 species and based on repeated patterns of floral attractants and rewards, we infer pollination mechanisms for an additional 610 species. Matching pollination system to phylogeny or what is known about species relationships based on shared derived features, we infer repeated shifts in pollination system in some genera, as frequently as one shift for every five or six species of southern African Babiana or Gladiolus. Specialized systems using pollinators of one pollination group, or even a single pollinator species are the rule in the family. Shifts in pollination system are more frequent in genera of Crocoideae that have bilaterally symmetric flowers and a perianth tube, features that promote adaptive radiation by facilitating precise shifts in pollen placement, in conjunction with changes in flower colour, scent and tube length. CONCLUSIONS: Diversity of pollination systems explains in part the huge species diversity of Iridaceae in sub-Saharan Africa, and permits species packing locally. Pollination shifts are, however, seen as playing a secondary role in speciation by promoting reproductive isolation in peripheral, ecologically distinct populations in areas of diverse topography, climate and soils. Pollination of Iridaceae in Eurasia and the New World, where the family is also well represented, is poorly studied but appears less diverse, although pollination by both pollen- and oil-collecting bees is frequent and bird pollination rare.     

Area and the rapid radiation of Hawaiian Bidens (Asteraceae)

Aim To estimate the rate of adaptive radiation of endemic Hawaiian Bidens and to compare their diversification rates with those of other plants in Hawaii and elsewhere with rapid rates of radiation. Location Hawaii. Methods Fifty‐nine samples representing all 19 Hawaiian species, six Hawaiian subspecies, two Hawaiian hybrids and an additional two Central American and two African Bidens species had their DNA extracted, amplified by polymerase chain reaction and sequenced for four chloroplast and two nuclear loci, resulting in a total of approximately 5400 base pairs per individual. Internal transcribed spacer sequences for additional outgroup taxa, including 13 non‐Hawaiian Bidens, were obtained from GenBank. Phylogenetic relationships were assessed by maximum likelihood and Bayesian inference. The age of the most recent common ancestor and diversification rates of Hawaiian Bidens were estimated using the methods of previously published studies to allow for direct comparison with other studies. Calculations were made on a per‐unit‐area basis. Results We estimate the age of the Hawaiian clade to be 1.3–3.1 million years old, with an estimated diversification rate of 0.3–2.3 species/million years and 4.8 × 10^?5 to 1.3 × 10^?4 species Myr^?1 km^?2. Bidens species are found in Europe, Africa, Asia and North and South America, but the Hawaiian species have greater diversity of growth form, floral morphology, dispersal mode and habitat type than observed in the rest of the genus world‐wide. Despite this diversity, we found little genetic differentiation among the Hawaiian species. This is similar to the results from other molecular studies on Hawaiian plant taxa, including others with great morphological variability (e.g. silverswords, lobeliads and mints). Main conclusions On a per‐unit‐area basis, Hawaiian Bidens have among the highest rates of speciation for plant radiations documented to date. The rapid diversification within such a small area was probably facilitated by the habitat diversity of the Hawaiian Islands and the adaptive loss of dispersal potential. Our findings point to the need to consider the spatial context of diversification – specifically, the relative scale of habitable area, environmental heterogeneity and dispersal ability – to understand the rate and extent of adaptive radiation.     

SEQUENTIAL RADIATIONS AND PATTERNS OF SPECIATION IN THE HAWAIIAN CRICKET GENUS LAUPALA INFERRED FROM DNA SEQUENCES

The tremendous diversity of endemic Hawaiian crickets is thought to have originated primarily through intraisland radiations, in contrast to an interisland mode of diversification in the native Hawaiian Drosophila. The Hawaiian cricket genus Laupala (family Gryllidae) is one of several native genera of flightless crickets found in rain-forest habitat across the Hawaiian archipelago. I examined the phylogenetic relationships among mitochondrial DNA (mtDNA) sequences sampled from 17 species of Laupala, including the 12S ribosomal RNA (rRNA), transfer RNA (RNA)^val and 16S rRNA regions. The distribution of mtDNA variants suggests that species within Laupala are endemic to single islands. The phylogenetic estimate produced from both maximum likelihood and maximum parsimony supports the hypothesis that speciation in Laupala occurred mainly within islands. The inferred biogeographical history suggests that diversification in Laupala began on Kauai, the oldest rain-forested Hawaiian island. Subsequently, colonization to younger islands in the archipelago resulted in a radiation of considerable phylogenetic diversity. Phylogenetic patterns in mtDNA are not congruent with prior systematic or taxonomic hypotheses. Hypotheses that may explain the conflict between the phylogenetic patterns of mtDNA variation and the species taxonomy are discussed.     

The pollination ecology of Pedicularis rex subsp. lipkyana and P. rex subsp. rex (Orobanchaceae) from Sichuan, southwestern China

Pedicularis is one of few genera for which pollination ecology has been studied extensively. Although over half of the species of Pedicularis are found in the mountains of southwestern China, pollination ecology has been studied there on a few species only. The present paper reports pollination ecology of Pedicularis rex subsp. lipskyana and P. rex subsp. rex from Sichuan, southwestern China. The two subspecies are nectariferous, with sugar content 28% in P. rex lipskyana and 22% in P. rex, respectively. The flowers of the two subspecies are adapted to pollination by bumblebee workers. Bumblebees are the primary and effective pollinators although honeybees were also observed pollinating P. rex subsp. lipskyana at one studied population. Usually bumblebees entered the corolla tube from the right side in an upright or a nearly half-inverted position to imbibe nectar located at the base of the corolla tube. The stigma usually contacts the side region of the thorax and abdomen or occasionally directly contacted pollen loads, leading to pollination of flowers. Much less commonly, bumblebees foraged on flowers of P. rex subsp. rex in an inverted position for pollen, which pollinated flowers sternotribically. We suggest that pollination mechanism is closely associated with floral morphology. Some important differences were found from a previous study on P. rex in floral morphology and the primary pollination mechanism.     

苦苣苔科镜像花的多样性及演化

泛热带分布的苦苣苔科(Gesneriaceae)在我国南方具有极高的物种丰富度与特有率,花部特征变化丰富,是研究物种形成与适应演化的代表类群。镜像花(mirror-image flowers)是极为特化的传粉系统,在苦苣苔科中出现了较多的不同类型,可能与苦苣苔科物种多样性形成与维持有关。该研究总结与分析了苦苣苔科镜像花的类型多样性以及系统分布与适应演化等,讨论了镜像花对苦苣苔科物种形成与维持的积极意义。结果表明:镜像花仅分布在亚洲和非洲的苦苣苔亚科(Didymocarpoideae)的7个属,在历史上就至少发生了5次独立起源。长冠苣苔属(Rhabdothamnopsis)、南洋苣苔属(Henckelia)及长蒴苣苔属(Didymocarpus)镜像花的花柱与可育雄蕊分别向左、右两侧偏转,形成互补镜像花;蛛毛苣苔属(Paraboea)、喜鹊苣苔属(Ornithoboea)、非洲堇属(Saintpaulia)镜像花缺乏与花柱对应侧偏的可育雄蕊(非互补镜像花);而海角苣苔属(Streptocarpus)直立堇兰亚属(subg.Streptocarpella Engler)则同时出现了互补、非互补镜像花。不同于其他被子植物(离瓣花、缺乏花冠筒),苦苣苔科中的镜像花大多伴随着明显的花冠筒、内藏的雄蕊、合生的花药,以非互补镜像花为主;传粉者以小型的无垫蜂(Amegilla spp.)和熊蜂(Bombus spp.)为主。这些特殊的花部综合征与特化的传粉机制,提高了传粉精确性,可能促进了传粉隔离与物种适应辐射。今后的一个研究重点应通过分子系统发育方法,进一步揭示苦苣苔亚科互补与非互补镜像花的进化顺序及其在物种分化与长距离扩散过程中的可能作用。     

Natural history, biogeography, and endangerment of Hawaiian dry forest trees

We describe the floristic composition of Hawaiian dry forest trees and identify natural history characteristics and biogeographic variables that are associated with risk of endangerment. Hawaiian dry forests are comprised of 109 tree species in 29 families, with 90% of all species endemic, 10% indigenous, and 37% single-island endemics. Forty-five percent of Hawaiian dry forest taxa are at risk of endangerment. Dry forest taxa at risk have a significantly larger range size compared to taxa from other Hawaiian forest types. Dispersal mechanism was a significant predictor of a species occurrence in dry forest compared to other forest types based on logistic regressions clustered by lineage. Among dry forest taxa, hermaphroditic breeding systems, autochorous dispersal mechanisms, conspicuous flowers, and dry fruit were all more likely to be at risk of endangerment. When analyses were clustered by lineage using logistic regressions, only dispersal mechanism and flower size were significant predictors of risk and taxa with autochorous dispersal and conspicuous flowers were more likely to be at risk. The Big Island, Maui, Oahu, and Kauai all have remarkably similar numbers of dry forest taxa (63–65 species) and dry forest taxa at risk of endangerment. However, Big Island and Kauai have the highest number and percentage of single-island endemics. These results demonstrate patterns of endangerment specific to Hawaiian dry forests, the high levels of endangerment in this forest type, and the importance of prioritizing conservation in dry forest regions.     

The origin and number of introductions of the Hawaiian endemic Silene species (Caryophyllaceae)

The Hawaiian endemic Silene are a small group of woody or semiwoody representatives from a large, predominantly herbaceous, species-rich genus. We here investigated the origin and number of introductions of the endemic Hawaiian Silene based on phylogenetic relationships inferred from DNA sequences from both the plastid (the rps16 intron) and the nuclear (ribosomal internal transcribed sequences, ITS, and intron 23 of the RPB2 gene) genomes. Silene antirrhina, a widespread weedy American annual, is strongly supported as sister to a monophyletic group consisting of the Hawaiian Silene, indicating a single colonization event. There are no obvious morphological similarities between S. antirrhina and any of the species of Hawaiian Silene. Our results suggest an American origin for the Hawaiian endemics because that would require only a single trans-ocean dispersal. Two of the Hawaiian endemics (S. struthioloides and S. hawaiiensis) that form a subclade in the analyses have evolved woodiness after introduction to the Hawaiian Islands. Our results contribute to other recent results based on molecular phylogenetics that emphasize the American continent as a source area for the Hawaiian flora and support a striking morphological radiation and evolution of woodiness from a single introduction to the archipelago.     

Molecular phylogenetics of Houstonia (Rubiaceae): descending aneuploidy and breeding system evolution in the radiation of the lineage across North America

Nuclear and chloroplast DNA sequence variation was used to infer evolutionary relationships within and among members of Houstonia (Rubiaceae) and other closely related genera in North America. Sequences from the internal transcribed spacer (ITS) of the nrDNA and a cpDNA intron in the trnL gene were used to reconstruct phylogenetic relationships of 30 species of Houstonia and closely related genera. The data suggest that the North American species of Houstonia are not monophyletic, but belong to the same lineage as Stenaria. The radiation of this lineage has been accompanied by changes in the basic chromosome number of the major clades through descending aneuploidy. This loss of chromosomes was also associated with northward colonization of North America. However, other characters, such as an annual versus perennial habit, heterostylous and homostylous breeding systems, and the evolution of self fertilization, seem to be labile throughout the lineage, originating multiple times throughout the evolutionary history of the lineage.     

The molecular evolution of the alcohol dehydrogenase locus and the phylogeny of Hawaiian Drosophila.

DNA sequences in the alcohol dehydrogenase genes of flies representing the major groups of Hawaiian Drosophila are used to clarify the relationships of these groups, among themselves and with mainland Drosophila. The topology of the tree derived from these sequences agrees with karyotypic and morphological data but disagrees, in part, with the results of an earlier study that used immunological comparisons between variants of a larval hemolymph protein. A time scale, derived from a comparison of closely related Hawaiian Drosophila species, provides divergence-time estimates that are substantially more recent than those obtained from the immunological studies, although they are still within the bounds set by fossil and biogeographical evidence. The two major lineages of Hawaiian Drosophila, the scaptomyzoids and the drosophiloids, are shown to be widely separated from one another. The scaptomyzoids appear to have diverged early in the history of the subgenus Drosophila, greater than 25 Mya. While hundreds of scaptomyzoid species are found in the Hawaiian archipelago, many fewer are found elsewhere around the world, suggesting that they could have originated outside Hawaii. The drosophiloid lineage is strictly endemic to Hawaii and originated little more than 10 Mya, according to the alcohol dehydrogenase molecular clock. Thus, Drosophila apparently inhabited the Hawaiian archipelago (greater than or equal to 5 Myr before the emergence of the oldest existing high island, Kauai, 5 Mya.     

Hawaiian angiosperm radiations of North American origin

Background

Putative phytogeographical links between America (especially North America) and the Hawaiian Islands have figured prominently in disagreement and debate about the origin of Pacific floras and the efficacy of long-distance (oversea) plant dispersal, given the obstacles to explaining such major disjunctions by vicariance.

Scope

Review of past efforts, and of progress over the last 20 years, toward understanding relationships of Hawaiian angiosperms allows for a historically informed re-evaluation of the American (New World) contribution to Hawaiian diversity and evolutionary activity of American lineages in an insular setting.

Conclusions

Temperate and boreal North America is a much more important source of Hawaiian flora than suggested by most 20th century authorities on Pacific plant life, such as Fosberg and Skottsberg. Early views of evolution as too slow to account for divergence of highly distinctive endemics within the Hawaiian geological time frame evidently impeded biogeographical understanding, as did lack of appreciation for the importance of rare, often biotically mediated dispersal events and ecological opportunity in island ecosystems. Molecular phylogenetic evidence for North American ancestry of Hawaiian plant radiations, such as the silversword alliance, mints, sanicles, violets, schiedeas and spurges, underlines the potential of long-distance dispersal to shape floras, in accordance with hypotheses championed by Carlquist. Characteristics important to colonization of the islands, such as dispersibility by birds and ancestral hybridization or polyploidy, and ecological opportunities associated with ‘sky islands’ of temperate or boreal climate in the tropical Hawaiian archipelago may have been key to extensive diversification of endemic lineages of North American origin that are among the most species-rich clades of Hawaiian plants. Evident youth of flowering-plant lineages from North America is highly consistent with recent geological evidence for lack of high-elevation settings in the Hawaiian chain immediately prior to formation of the oldest, modern high-elevation island, Kaua‘i.     

New adapiform primate of Old World affinities from the Devil's Graveyard Formation of Texas

Most adapiform primates from North America are members of an endemic radiation of notharctines. North American notharctines flourished during the Early and early Middle Eocene, with only two genera persisting into the late Middle Eocene. Here we describe a new genus of adapiform primate from the Devil’s Graveyard Formation of Texas. Mescalerolemur horneri, gen. et sp. nov., is known only from the late Middle Eocene (Uintan) Purple Bench locality. Phylogenetic analyses reveal that Mescalerolemur is more closely related to Eurasian and African adapiforms than to North American notharctines. In this respect, M. horneri is similar to its sister taxon Mahgarita stevensi from the late Duchesnean of the Devil’s Graveyard Formation. The presence of both genera in the Big Bend region of Texas after notharctines had become locally extinct provides further evidence of faunal interchange between North America and East Asia during the middle Eocene. The fact that Mescalerolemur and Mahgarita are both unknown outside of Texas also supports prior hypotheses that low-latitude faunal assemblages in North America demonstrate increased endemism by the late middle Eocene.     

IS FLORAL SPECIALIZATION AN EVOLUTIONARY DEAD‐END? POLLINATION SYSTEM TRANSITIONS IN RUELLIA (ACANTHACEAE)

Pollination systems frequently reflect adaptations to particular groups of pollinators. Such systems are indicative of evolutionary specialization and have been important in angiosperm diversification. We studied the evolution of pollination systems in the large genus Ruellia. Phylogenetic analyses, morphological ordinations, ancestral state reconstructions, and a character mapping simulation were conducted to reveal key patterns in the direction and lability of floral characters associated with pollination. We found significant floral morphological differences among species that were generally associated with different groups of floral visitors. Floral evolution has been highly labile and also directional. Some specialized systems such as hawkmoth or bat pollination are likely evolutionary dead-ends. In contrast, specialized pollination by hummingbirds is clearly not a dead-end. We found evidence for multiple reverse transitions from presumed ancestral hummingbird pollination to more derived bee or insect pollination. These repeated origins of insect pollination from hummingbird-pollinated ancestors have not evolved without historical baggage. Flowers of insect-pollinated species derived from hummingbird-pollinated ancestors are morphologically more similar to hummingbird flowers than they are to other more distantly related insect-pollinated flowers. Finally, some pollinator switches were concomitant with changes in floral morphology that are associated with those pollinators. These observations are consistent with the hypothesis that some transitions have been adaptive in the evolution of Ruellia.     

Pollination ecology of four epiphytic orchids of New Zealand

BACKGROUND AND AIMS: In New Zealand epiphytic orchids are represented by four genera and eight species. The genera Earina (three species) and Winika (one species) are the most conspicuous and widespread. These are likely to be some of the southernmost distributed genera of epiphytic orchids in the world. METHODS: To identify the pollination strategies that have evolved in these orchids, hand-pollination treatments were done and floral visitors were observed in several wild populations at two areas of southern North Island (approx. 40 degrees S). Pollen:ovule ratio and osmophores were also studied and the total carbohydrate content of the nectar produced by each species was measured. KEY RESULTS: Earina autumnalis and Earina mucronata are self-compatible, whereas Earina aestivalis and Winika cunninghamii appear to be partially self-incompatible. All four orchids are incapable of autonomous selfing and therefore completely dependent on pollinators to set fruits. Floral visitors observed in the genus Earina belong to Diptera, Coleoptera and Hymenoptera and to Diptera and Hymenoptera in W. cunninghamii. CONCLUSIONS: Contrary to many epiphytic orchids in the tropics, the orchid-pollinator relationship in these orchids is unspecialized and flowers are visited by a wide range of insects. Putative pollinators are flies of the families Bibionidae, Calliphoridae, Syrphidae and Tachinidae. All four orchids display anthecological adaptations to a myophilous pollination system such as simple flowers, well-exposed reproductive structures, easily accessed nectar and high pollen : ovule ratios.     

Anagenetic evolution in island plants

Aim  Plants in islands have often evolved through adaptive radiation, providing the classical model of evolution of closely related species each with strikingly different morphological and ecological features and with low levels of genetic divergence. We emphasize the importance of an alternative (anagenetic) model of evolution, whereby a single island endemic evolves from a progenitor and slowly builds up genetic variation through time.
Location  Continental and oceanic islands.
Methods  We surveyed 2640 endemic angiosperm species in 13 island systems of the world, both oceanic and continental, for anagenetic and cladogenetic patterns of speciation. Genetic data were evaluated from a progenitor and derivative species pair in Ullung Island, Korea, and Japan.
Results  We show that the anagenetic model of evolution is much more important in oceanic islands than previously believed, accounting for levels of endemic specific diversity from 7% in the Hawaiian Islands to 88% in Ullung Island, Korea, with a mean for all islands of 25%. Examination of an anagenetically derived endemic species in Ullung Island reveals genetic (amplified fragment length polymorphism) variation equal or nearly equal to that of its continental progenitor.
Main conclusions  We hypothesize that, during anagenetic speciation, initial founder populations proliferate, and then accumulate genetic variation slowly through time by mutation and recombination in a relatively uniform environment, with drift and/or selection yielding genetic and morphological divergence sufficient for the recognition of new species. Low-elevation islands with low habitat heterogeneity are highly correlated with high levels of anagenetic evolution, allowing prediction of levels of the two models of evolution from these data alone. Both anagenetic and adaptive radiation models of speciation are needed to explain the observed levels of specific and genetic diversity in oceanic islands.