Low host specificity of herbivorous insects in a tropical forest.

Institute of Entomology, Czech Academy of Sciences and Biological Faculty, University of South Bohemia, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic.
Nature (Impact Factor: 38.6). 05/2002; 416(6883):841-4. DOI: 10.1038/416841a
Source: PubMed

ABSTRACT Two decades of research have not established whether tropical insect herbivores are dominated by specialists or generalists. This impedes our understanding of species coexistence in diverse rainforest communities. Host specificity and species richness of tropical insects are also key parameters in mapping global patterns of biodiversity. Here we analyse data for over 900 herbivorous species feeding on 51 plant species in New Guinea and show that most herbivorous species feed on several closely related plant species. Because species-rich genera are dominant in tropical floras, monophagous herbivores are probably rare in tropical forests. Furthermore, even between phylogenetically distant hosts, herbivore communities typically shared a third of their species. These results do not support the classical view that the coexistence of herbivorous species in the tropics is a consequence of finely divided plant resources; non-equilibrium models of tropical diversity should instead be considered. Low host specificity of tropical herbivores reduces global estimates of arthropod diversity from 31 million (ref. 1) to 4 6 million species. This finding agrees with estimates based on taxonomic collections, reconciling an order of magnitude discrepancy between extrapolations of global diversity based on ecological samples of tropical communities with those based on sampling regional faunas.

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    ABSTRACT: The Hymenodicteae-Naucleeae clade is a predominantly Paleotropical group with 220 species in 28 genera. The phylogenetic relationships and generic limits within Naucleeae have previously been assessed using combined molecular-morphological data, however the status of some genera remains questionable. The evolutionary relationships within Hymenodictyeae have never been investigated before. We performed phylogenetic analyses of the Hymenodictyeae-Naucleeae clade using nuclear [nrETS; nrITS] and chloroplast [ndhF; rbcL; rps16; trnT-F] data and a large sampling of both tribes. Our study supports the monophyly of the tribes, all subtribes of Naucleeae (Adininae, Breoniinae, Cephalanthinae, Corynantheinae, Mitragyninae, Naucleinae, and Uncariinae), and the Hymenodictyeae genera Hymenodictyon and Paracorynanthe. In Naucleeae, the monotypic genera Adinauclea, Metadina, and Pertusadina are nested within Adina, Mitragyna within Fleroya, Ludekia, Myrmeconauclea, and Ochreinauclea within Neonauclea, and Burttdavya and Sarcocephalus within Nauclea. Corynanthe and Pausinystalia are mutually paraphyletic. We provisionally maintain the current generic status of Neonauclea and its allied genera, pending further study. In sum, we recognize 17 genera in Naucleeae: Adina s. l. The sister tribes Hymenodictyeae sensu Razafimandimbison and Bremer (2006) and Naucleeae sensu Razafimandimbison and Bremer (2001, 2002) are positioned as an early branch in the mostly Neotropical subfamily Cinchonoideae of the family Rubiaceae (Andersson and Antonelli 2005; Manns and Bremer 2010; Manns et al. 2012). This group has been circumscribed to include 220 species in 28 genera. Hymenodictyeae includes two genera, Hymenodictyon Wall. with 24 species and Paracorynanthe Capuron with two species (Razafimandimbison and Bremer 2006). The tribe is restricted to the Paleotropics with the highest species diversity found in Madagascar. Hymenodictyeae species are typically medium-sized to tall trees, and often grow on rocky sub-strates; however, Hymenodictyon epiphyticum Razafim. & B. Bremer is an epiphyte, and Hymenodictyon biafranum Hiern and Hymenodictyon flaccidum Wall. are facultative epiphytes. The members of the tribe can easily be distinguished from those of Naucleeae by their spiciform to racemose inflores-cences and lenticellate capsular fruits (Razafimandimbison and Bremer 2006). Hymenodictyeae is additionally character-ized by its stipules bearing large, deciduous colleters on the margins, valvate corolla aestivation, and elongate, bilaterally flattened, and accrescent placentae. The generic status of Hymenodictyon and Paracorynanthe has never been questioned, but their monophyly and sister-group relationship have yet to be tested using molecular data. Naucleeae includes 26 genera and 194 species (Govaerts et al. 2013) of trees, shrubs, and lianas mostly distributed in the Paleotropics, with a few species in the Neotropics and North America (Ridsdale 1975, 1978a, 1978b; 1989; Razafimandimbison and Bremer 2002). The tribe is a well-defined monophyletic group that can easily be recognized by its spherical inflorescences; an additional synapomorphy for the tribe is epigynous floral nectaries, deeply embedded in the hypanthia (see Razafimandimbison and Bremer (2001, 2002) and Verellen et al. (2007) for more information on the morphological characters in the tribe). Naucleeae has received much attention over the last 40 yr, and is known to have problematic intratribal classifications (e.g. Bremer et al. 1995; Razafimandimbison and Bremer 2001, 2002; Razafimandimbison et al. 2005; Ridsdale 1975, 1978a; Wikströ m et al. 2010). The broad circumscription of Naucleeae, established by Razafimandimbison and Bremer (2002), subdivided the tribe in seven subtribes: Adininae, Breoniinae, Cephalanthinae, Corynantheinae, Mitragyninae, Naucleinae, and Uncariinae. However, the monophyly of Adininae and Cephalanthinae has been questioned, because the subtribes were not supported as monophyletic in their analyses and the inter-subtribal rela-tionships were poorly supported. Razafimandimbison and Bremer (2002) proposed new generic limits within Naucleeae based on their combined molecular-morphological tree. In that study, genera that contain more than one species are maintained as a genus if they 1) are monophyletic, 2) maxi-mize nomenclatural stability, and 3) are easy to recognize in the field, criteria as outlined by Backlund and Bremer (1998). For the assessment of the monotypic genera in Naucleeae, Razafimandimbison and Bremer (2002) utilized the following three criteria: 1) not nested within a well-defined genus, 2) with at least two autoapomorphic characters, and 3) with relationships to other genera that are strongly supported. Razafimandimbison and Bremer (2002) accepted a total of 24 genera based on their combined molecular-morphological tree. However, the monophyly of Corynanthe Welw., Neonauclea Merr., and Pausinystalia Pierre ex Beille, based on molecular data alone remains questionable, as the genera were shown to be non-monophyletic in the combined molecular (nrITS/rbcL/trnT-F) tree in Razafimandimbison and Bremer (2002). For example, Ludekia Ridsdale and Myrmeconauclea Merr., represented each by one species in their analyses, were nested within Neonauclea Merr, and the African genera Corynanthe and Pausinystalia, both sensu Stoffelen et al. (1996),
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