The diversity of ant–plant interactions in the rainforest understorey tree, Ryparosa (Achariaceae): food bodies, domatia, prostomata, and hemipteran trophobionts

Ant–plant relationships, with variability in both intimacy and the trophic structure of associations, are described for the Austro-Malesian rainforest tree genus Ryparosa (Achariaceae). The range of associations involves opportunistic interactions between plants and foraging ants, mediated by food bodies, and tighter associations in which ant colonies, tending hemipteran trophobionts, reside permanently in plant structures with different degrees of adaptation to house ants. Our study provides strong baseline data to suggest that Ryparosa could become a new model system for examining the evolutionary radiation of ant-related traits. To define the diversity of ant–plant associations in Ryparosa , we first present a review of ant-plant terminology and an outline of its use in this study. Field studies of ant interactions with food bodies in myrmecotrophic R. kurrangii from Australia and the association between myrmecoxenic R. fasciculata and two Cladomyrma plant-ant species on the Malay Peninsula provide detailed examples of ant–plant interactions. An examination of herbarium material revealed a diverse range of ant–plant associations in other Ryparosa taxa. All 27 species had evidence of food body production, seven species had evidence of stem inhabitation by ants, five species had specialized stem domatia, and the domatia of R. amplifolia featured prostomata. Variation in the specificity of Ryparosa ant–plant interactions is discussed in relation to known ant partners and other ant–plant associations.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 353–371.     

An asymmetrical relationship between an arboreal ponerine ant and a trash-basket epiphyte (Araceae)

The relationship between ants and Philodendron insigne , a trash-basket epiphyte abundant along streams, was studied in French Guiana. Only a few (3%) of the young plants sheltered ants, whereas 90% of the mature individuals did. The most frequent associate was Odontomachus hastatus (Fabricius), an arboreal ponerine ant, and its nests were almost entirely (94.4%) located in P .  insigne root clusters. Experimental choice tests conducted on O .  hastatus workers confirmed their preference for P .  insigne . We propose that the interactions between P .  insigne and ants may be intermediate between non-obligatory, reward-based interactions and obligatory, specific ant–myrmecophyte interactions because (1) almost all mature P. insigne individuals are associated with ants; (2) O. hastatus is the most frequent when diverse ants nest in its root clusters; (3) ants colonize mature P .  insigne , but rarely young individuals; (4) ants, particularly O .  hastatus , protect the foliage of their host; and (5) at least one ant species, O .  hastatus , prefers P .  insigne over other host plants. The latter relationship is asymmetrical because P .  insigne is inhabited by diverse ants whereas O .  hastatus nests almost exclusively in P .  insigne .  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 341–346.     

Defensive ant,aphid and caterpillar mimicry in plants?

Here we describe three apparently novel types of visual insect mimicry in plants. In the first type, plants of Xanthium trumarium L. have dark spots and flecks that resemble ants (Formicidae) in size and shape in the epidermis of stems, branches and petioles, and plants of Arisarum vulgare Targ.-Tozz. have them on petioles and inflorescence stems. In the second type, the dark anthers of Paspalum paspaloides (Michaux) Scribner (= P. distichum ) are the size, shape and colour of aphids (Homoptera; Aphidoidea) and they sway in the wind like swivelling aphids. Similarly, the stems of Alcea setosa (Boiss.) Alef. are covered with dark flecks that look like aphids. Finally, immature pods of three wild annual legumes ( Lathyrus ochrus (L.) DC.; Pisum fulvum Sm.; Vicia peregrina L.) have conspicuous reddish spots, arranged along the pods, that appears to mimic lepidopteran caterpillars. In one of the species ( V . peregrina ) two different mimicking morphs were found. We propose that these morphological traits may serve as herbivore repellent cues and are part of the defence system of the plants.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 393–398.     

The relationship of Sophora sect. Edwardsia (Fabaceae) to Sophora tomentosa, the type species of the genus Sophora, observed from DNA sequence data and morphological characters

Sophora tomentosa , the type species of the genus Sophora , is shown by phylogenetic analyses of rbc L and ITS sequence data to be sister to Sophora sect. Edwardsia . S. tomentosa and most of the species from sect. Edwardsia share hypogeal germination, exstipulate leaves, and terete filaments. These species have buoyant seeds, and are distributed by ocean currents throughout the pantropics ( S. tomentosa ) and around southern temperate oceanic islands (sect. Edwardsia ). S. tomentosa differs from the species of sect. Edwardsia by its frutescent growth habit, terminal elongate inflorescence and smooth-walled legume. S. macrocarpa is unusual in sect. Edwardsia as its leaves have stipules, the filaments are winged, and the legume is smooth-walled.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 439–446.     

Pirate ants (Polyergus breviceps) and sympatric hosts (Formica occulta and Formica sp. cf. argentea): host specificity and coevolutionary dynamics

The pace and trajectory of coevolutionary arms races between parasites and their hosts are strongly influenced by the number of interacting species. In environments where a parasite has access to more than one host species, the parasite population may become divided in preference for a particular host. In the present study, we show that individual colonies of the pirate ant Polyergus breviceps differ in host preference during raiding, with each colony specializing on only one of two available Formica host species. Moreover, through genetic analyses, we show that the two hosts differ in their colony genetic structure. Formica occulta colonies were monogynous, whereas Formica  sp. cf. argentea colonies were polygynous and polydomous (colonies occupy multiple nest sites). This difference has important implications for coevolutionary dynamics in this system because raids against individual nests of polydomous colonies have less impact on overall host colony fitness than do attacks on intact colonies. We also used primers that we designed for four microsatellite loci isolated from P. breviceps to verify that colonies of this species, like other pirate ants, are comprised of simple families headed by one singly mated queen.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 565–572.     

Astragalus neo-assadianus (Fabaceae), a new species in sect. Alopecuroidei from Iran

Astragalus neo-assadianus (Fabaceae), a new species endemic to Iran, is described and illustrated. This species belongs to A. sect . Alopecuroidei and is distinct and interesting among the Iranian species. It is confined to the north-eastern part of Iran (Khorasan Province) and only known from a single collection close to the Turkmenistan frontier.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 197–200.     

Molecular differentiation between coexisting species of Taraxacum sect. Erythrosperma (Asteraceae) from populations in south-east and west Germany

The present study focuses on the genetic differentiation between six coexisting species of Taraxacum sect. Erythrosperma . Twenty-six individuals of T. rubicundum , T. brachyglossum , T. tortilobum , T. lacistophyllum , T. parnassicum and T. scanicum were sampled at 14 locations in south-east (Bavaria) and west Germany (Eifel). Using random amplified polymorphic DNA (RAPD) analysis 139 fragments were amplified. Nineteen of these were found to be species specific. The level of polymorphic bands within the different Taraxacum species varied between 0% and 15.8%. An analysis of molecular variance (AMOVA) revealed strong differentiation between the investigated species: 14.3% of the molecular variance were found within the species, while 85.7% of the genetic variability was observed between the species. However, a geographical differentiation between the different regions could not be observed. All analysed species were clearly separated from each other in a cluster analysis using the neighbour joining technique. The observed strong genetic differentiation between the Taraxacum species clearly supports the agamospecies concept of Taraxacum sect. Erythrosperma , which is at present mainly based on morphological and cytological criteria  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 109–117.     

A new species of Centaurea (sect. Phalolepis, Compositae: Cardueae) from eastern Peloponnisos, Greece

A new species of Centaurea L. , Centaurea leonidia Kalpoutz. & Constantin. , from two localities west and south-west of the town of Leonidio in eastern Peloponnisos, Greece, is described and illustrated. It belongs to C . sect. Phalolepis , and taxonomically its closest relatives are C. heldreichii Halácsy , a very localized species from south-west Sterea Ellas (Greece) and, surprisingly, C. niederi Heldr., which belongs to sect. Acrolophus. The new species is currently known from two populations of less than 100 individuals each, growing on almost inaccessible cliffs close to the convent of Agios Nikolaos Sintzas (St. Nicolas of Sintza) and the slopes of Poundes summit. Several other Greek endemic species are found in the same areas. Centaurea leonidia is scientifically important as it belongs to a small group of taxa, which, although they are members of sect. Phalolepis , have close allies in sect. Acrolophus. The chromosome number of C. leonidia , 2 n  = 18, counted in root tips, is also reported and illustrated.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 375–383.     

Interspecific variation in the defensive responses of ant mutualists to plant volatiles

In ant–plant mutualist systems, ants patrol their host plants and search for herbivores. Such patrolling can be inefficient, however, because herbivore activity is spatio-temporally unpredictable. It has been proposed that rapid and efficient systems of communication between ants and plants, such as volatile compounds released following herbivory, both elicit defensive responses and direct workers to sites of herbivore activity. We performed bioassays in which we challenged colonies of two Amazonian plant-ants, Azteca sp. and Pheidole minutula , with extracts of leaf tissue from (1) their respective host-plant species ( Tococa bullifera and Maieta guianensis , both Melastomataceae), (2) sympatric ant-plants from the Melastomataceae, and (3) two sympatric but non-myrmecophytic Melastomataceae. We found that ants of both species responded dramatically to host-plant extracts, and that these responses are greater than those to sympatric myrmecophytes. Azteca sp. also responded to non-myrmecophytes with an intensity similar to that of sympatric ant-plants. By contrast, the response of P. minutula to any non-myrmecophytic extracts was limited. These differences may be driven in part by interspecific differences in nesting behaviour; although P. minutula only nests in host plants, Azteca sp. will establish carton satellite nests on nearby plants. We hypothesize that Azteca sp. must therefore recognize and defend a wider array of species than P. minutula .  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 241–249.     

Sophora sect. Edwardsia (Fabaceae): further evidence from nrDNA sequence data of a recent and rapid radiation around the Southern Oceans

Phylogenetic relationships are inferred from nuclear ribosomal internal transcribed spacer sequences for species belonging to Sophora sect. Edwardsia from South America, New Zealand, Lord Howe Island, Hawai'i, La Réunion, Easter Island, and Raivavae Island (French Polynesia). Results support the monophyly of sect. Edwardsia , but relationships among the species from this section are poorly resolved due to most species having identical sequences. The origin of Sophora sect. Edwardsia is discussed, as competing hypotheses have proposed the group originated in South America from a North American ancestor, or in the north-west Pacific. We suggest sect. Edwardsia may have arisen in the north-west Pacific from a Eurasian ancestor.  © The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 140 , 435–441.     

Stem diversity, cauline domatia, and the evolution of ant-plant associations in Piper sect. Macrostachys (Piperaceae)

Plants possess a variety of structures that harbor ant nests, and the morphology of these domatia determines the nature of ant-plant mutualisms in a given plant species. In this study, we report on the differences in anatomy between myrmecophytes of Piper, which are regularly excavated by an obligate ant mutualist (Pheidole bicornis) and nonmyrmecophytes of Piper, which consistently have solid stems. Stems of excavated plant species lacked outward evidence of modification; however, striking anatomical differences were apparent between hollow-stemmed species before excavation and the remainder of the solid-stemmed species studied. Prior to excavation by ants, stems of myrmecophytes were characterized by strongly heterogeneous piths in which a large, central area had relatively large cells lacking intracellular crystals with a periphery of smaller cells containing numerous crystals. The domatium excavated by the ants was restricted to the large-celled region. This is the first report of the absence of crystals in ant-excavated portions of stems of myrmecophytes. Cauline domatia became lined with 3-8 cell layers of suberized wound tissue, which may have an impact on nutrient absorption by Piper myrmecophytes.     

Revision of the Micromeria (Labiatae) in tropical to southern Africa and on the Arabian Peninsula

The material of Micromeria s.s. ( M. sect. Micromeria ) from tropical to southern Africa and the Arabian Peninsula is revised. The endemic Ethiopian M. unguentaria Schweinf. is retained as a species, while the other African and Arabian material of Micromeria is included in M. imbricata (Forssk.) C. Chr. M. imbricata is divided into the following three varieties: var. imbricata , which is very polymorphic, widespread in the African highlands, and also occurs in Arabia; var. rhodesiaca (Elly Walther & K.H. Walther) Ryding, which occurs in the highlands of Malawi, Mozambique and Zimbabwe; and var. villosa (Elly Walther & K.H. Walther) Ryding, which occurs in montane to alpine areas of Ethiopia and East Africa. Discontinuities in the variation within var. imbricata , observed at some localities, are suggested to be a result of partial autogamy. Problems with delimitation between M. imbricata , the East Asiatic M. biflora (Buch.-Ham. ex D.Don) Benth. and some Mediterranean species are discussed.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 427–446.     

A new annual species of Bellium (Asteraceae) from the Balearic Islands

A new species, Bellium artrutxensis (Asteraceae: Astereae), is described from the therophytic pastures of southern Minorca (Balearic Islands). The analysis of nuclear ribosomal internal transcribed spacer (ITS) sequences showed that the new taxon was closely related to Bellium bellidioides , but differed with regard to the annual lifespan, the absence of epigeal stolons, and the presence of a patent eglandular indumentum on the leaves. The new taxon shows morphological features that are well suited for the colonization of dry environments with a marked summer drought, and may be of adaptive significance. The new species is diploid (2 n  = 18) and shows up to two accessory chromosomes in root tissues. B chromosomes have not been reported previously in other species of Bellium .  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 65–77.     

Diversity and specificity of Caribbean sponge–zoanthid symbioses: a foundation for understanding the adaptive significance of symbioses and generating hypotheses about higher-order systematics

The diversity and specificity of symbiotic associations may be useful in revealing the underlying ecology of symbioses and evolutionary relationships of symbiotic species. Symbioses between coral reef sponges and zoanthids are widespread and common in the greater Caribbean region, although the diversity and specificity of the species involved have only been explored at a few sites and the adaptive significance has only been examined for three combinations. We identified extensive diversity among sponges that associate with zoanthids by compiling sponge–zoanthid species associations from field surveys, the literature, and museum collections, and examined the patterns of specificity at multiple levels of sponge and zoanthid taxonomy. The results obtained indicate that facultative sponges are highly specific to the species of their partners whereas obligate zoanthids are not. The patterns of specificity among sponges and zoanthids suggest that many of these associations are not likely to be parasitic. Sponges harbouring photosynthetic endosymbionts associate at a disproportionately high frequency with zoanthids that harbour photosynthetic endosymbionts. Zoanthids embed in the surfaces of sponges to various degrees, resulting in a range of intimacy that negatively correlates with the number of hosts and polyp volume of zoanthids. Dendrograms based on the similarity among associations are largely consistent with current hypotheses of sponge higher-order systematics, but inconsistent with the current hypotheses of zoanthid systematics, and they highlight the potential utility of ecological characters in systematic analyses.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 695–711.     

Ant-fed plants: comparison between three geophytic myrmecophytes

In their association with myrmecophytes (i.e. plants that shelter a limited number of ant species in hollow structures), ants sometimes provide only poor biotic protection for their host plants, but may supply them with nutrients (myrmecotrophy). We studied three geophytic myrmecophytes growing in the understorey of Guianian rain forests. Allomerus ants build spongy-looking galleries rich in detritus and insect debris over the stems of their host plants [ Cordia nodosa Lamark (Boraginaceae) and Hirtella physophora Martius & Zuccharini (Chrysobalanaceae)], while Pheidole minutula Mayr colonies deposit their waste in the leaf pouches of their host plant [ Maieta guianensis Aublet (Melastomataceae)]. This waste is more nitrogen-rich than that found in the Allomerus galleries, themselves containing more nitrogen than the plant leaves. Using stable isotope analysis we noted a significant difference in δ¹⁵N between ant-occupied and unoccupied plants only for Maieta , for which 80% of the host plant nitrogen is derived from Pheidole waste. Experiments on all three plants using a ¹⁵N-supplemented solution of NH₄Cl confirmed these results, with an increase in this isotope noted between control and experimental plants only for Maieta . The internal surfaces of Maieta leaf pouches bear protuberances whose likely role is to absorb nutrients from the Pheidole waste. The alternative hypothesis, that these protuberances play a role in provisioning ants, was rejected after comparing their structure with those of extrafloral nectaries and food bodies in a histological study.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 433–439.