Allozymic variation and divergence in three species of Antirrhinum L. (Scrophulariaceae-Antirrhineae)

An allozymic study of three wild species of Antirrhinum L. A. lopesiamum Rothm., A. mollissimum Roihni. and A. microphyllum Rothm. is described. All are members of subsection Kickiella Rothm., and are narrow-range endemics of the Iberian Peninsula. The variability of the different loci, as well as the number and mobility of the alleles, differ among the three species, a demonstration of the usefulness of allozymes for the systematics of the genus. The finding of alleles unique to each species indicates high divergence among species suggesting ancient diversification, and supports the hypothesis of a geographical model of speciation. All three species show high levels of within-species variability, mainly partitioned within populations, while between populations genetic differentiation is low. Correlations between population size, sample size and genetic variability, and the usefulness of allozymic data for conservation purposes, are discussed.     

Gradual speciation in a global hotspot of plant diversity

The speciation process that underlies recent, rapid radiations of plants is controversial, and suggested mechanisms range from pollinator or ecological niche differentiation to allopatry and nonadaptive divergence. Phylogenetic approaches to locating the most appropriate speciation models have been constrained by the low levels of molecular divergence between recently diverged species, which are typical of recent, rapid radiations. In this issue of Molecular Ecology, Rymer et al. (2010) used coalescence analyses of sequence data and genome scans of Amplified Fragment Length Polymorphism (AFLP) loci to demonstrate that in a species complex in the irid genus Gladiolus, a member of the hyper diverse Cape flora of southern Africa, speciation is a gradual process. Older divergences are genetically more differentiated, and show a greater difference in flowering time and floral morphology, than taxa that diverged more recently. There is no evidence of any abrupt events. Gene flow is limited by shifts in flowering time and floral morphology; thus, by pre-zygotic rather than by post-zygotic mechanisms, these evolved together with the occupation of somewhat different habitats. This research gives the first critical insight into how the remarkable diversity in a diversity hotspot could have arisen. More importantly, it demonstrates that the speciation process in recent, rapid radiations is tractable and can be investigated with suitable genetic tools.     

Geographic variation of the Greater white-toothed shrew (Crocidura russula Hermann, 1780 Mammalia, Soricidae)

A multivariate morphometric study of the Greater white-toothed shrew ( C. russula ) throughout its Palearctic range was carried out to search for patterns of geographic variation within the species boundary. Burnaby's and multiple group principal component analysis allowed the adjustment of raw data with respect to within-sample allometric variation. Multivariate 'size-free'results show a stepped cline with the phenotypical trait reduction and shape change from the eastern to the western Maghreb. Pleistocene fossil mandibles proved to have low phenetic distances with eastern populations (Tunisia, east Algeria) and it is argued that their character set is the primitive condition. The ancestral Mid-Pleistocene shrews lived in a relatively more humid climate. Geo-climatic changes in the north African range during the Quaternary provoked phenetic variation of C. russula and, it can be argued, evolution of the modern western C.r. yebalensis. A historical process can thus be assumed as the main cause of this categorical variation, by segmentation of the species range due to geo-climatic events. Morphometric discontinuity within the C. russula Maghreb range is shown to be congruent with karyological and biochemical studies. Moroccan and Tunisian shrews differ, for example, in NFa chromosomes and electrophoretical traits. A stasipatric process should be invoked to explain categorical variation in the Maghreb range. Colonization and divergence of insular populations results in more or less differentiated geographic races. The populations of Ibiza and Pantelleria are close to the species threshold (Nei's D ≥ 0.1). The process of speciation undergone by the Greater white-toothed shrew results in a complex pattern of geographic variation, including both allopatric and non-allopatric modes.     

Recognizing species,present and past

Nobody disputes that nature is meaningfully “packaged” in some way. But debate persists over exactly how (and even whether) the boundaries dividing taxa should (can) be drawn. At one end of the scale, some zealots abstrusely deny real existence to higher taxa.¹ At the other, laborers at the taxonomic rock‐face confront genuine challenges in recognizing and delineating the species that systematists agree constitute the most fundamental unit of taxonomic analysis. 2 , 3     

Population studies of native grass-endophyte symbioses provide clues for the roles of host jumps and hybridization in driving their evolution

Fungal endophytes in the genera Epichloë and Neotyphodium, collectively termed the epichloae, have fascinated biologists for decades. These intriguing fungi, also referred to as ‘class 1 or clavicipitaceous endophytes’, spend the large majority, or even their entire life cycle, within the tissues of their cool‐season grass hosts without eliciting any symptoms of infection. While all epichloae reside within the intercellular spaces of aboveground vegetative grass tissues, the species at the symbiotic extreme are known as Neotyphodium, and the intimacy of their interaction extends to the reproductive (flowering) stage. At this point, fungal filaments (hyphae) nondestructively invade the developing ovaries of their host and are incorporated into perfectly viable, healthy seeds. Thus, these endophytes live solely within the tissues of their host plants and are transmitted maternally from generation to generation. A second life history characteristic of interest is that while all Epichloë and some Neotyphodium species are haploid, a great many of the strictly seed‐transmitted Neotyphodium spp. are interspecific hybrids. This phenomenon may be critical for the success of these symbioses over longer spans of evolutionary time and will be discussed in greater detail below. A third characteristic, and one of the primary reasons these grass endophytes have received so much attention over the last three decades, is the strong mutualistic nature these relationships often exhibit. In exchange for photosynthetically derived carbon, the endophytes protect their cool‐season grass hosts from grazing herbivores and a variety of abiotic stresses. It has been hypothesized that these three biological phenomena are related ( Schardl & Craven 2003 ), perhaps with the former two driving the third, and it is here that the recent article in Molecular Ecology entitled ‘Genetic diversity in epichloid endophytes of Hordelymus europaeus suggests repeated host jumps and interspecific hybridizations’, by Oberhofer & Leuchtmann (2012) , provides critical clues to linking these traits together. While the large majority of studies have focused on documenting the ever‐increasing list of mutualistic qualities attributed to these fungi, very few have taken an exhaustive population‐level approach to document plant and endophyte genotypes within a naturally occurring system ( Faeth et al. 2010 ; Jani et al. 2010 ; Tintjer & Rudgers 2006 ). Such information is crucial to more fully elucidate the factors shaping grass‐endophyte symbioses and those often driving these relationships to mutualistic extremes.     

The Mecyclothorax beetles (Coleoptera,Carabidae, Moriomorphini) of Tahiti,Society Islands

The 101 species of Mecyclothorax Sharp known to inhabit Tahiti Island, French Polynesia are taxonomically revised, including 28 species that are newly described: Mecyclothorax claridgeiae sp. n., Mecyclothorax jeanyvesi sp. n., Mecyclothorax poria sp. n., Mecyclothorax aano sp. n., Mecyclothorax papau sp. n., Mecyclothorax manina sp. n., Mecyclothorax everardi sp. n., Mecyclothorax ramagei sp. n., Mecyclothorax pitohitiensis sp. n., Mecyclothorax curtisi sp. n., Mecyclothorax hoeahiti sp. n., Mecyclothorax ninamu sp. n., Mecyclothorax kokone sp. n., Mecyclothorax paahonu sp. n., Mecyclothorax kayballae sp. n., Mecyclothorax ehu sp. n., Mecyclothorax papuhiti sp. n., Mecyclothorax tuea sp. n., Mecyclothorax taatitore sp. n., Mecyclothorax konemata sp. n., Mecyclothorax arboricola sp. n., Mecyclothorax rahimata sp. n., M. oaoa sp. n., Mecyclothorax maninapopoti sp. n., Mecyclothorax hunapopoti sp. n., Mecyclothorax fefemata sp. n., Mecyclothorax maninamata sp. n., and Mecyclothorax niho sp. n. Mecyclothorax muriauxioides Perrault, 1984 is newly synonymized with Mecyclothorax muriauxi Perrault, 1978. Lectotypes are designated for: Thriscothorax altiusculus Britton, 1938; Thriscothorax bryobius Britton, 1938; Mecyclothorax globosus Britton, 1948: and Mecyclothorax sabulicola Britton, 1948. Dichotomous identification keys augmented by dorsal habitus and male aedeagal photographs are provided to the various species-groups and all included species. The spermatophore of Mecyclothorax papau sp. n. is described, with the ampulla and collar found to correspond dimensionally to the length of the internal sac flagellar plate. Variation among characters of the female reproductive tract is presented for all newly described plus other representative species comprising the radiation. Taxa are assigned to species groups, modified from the classification of G.G. Perrault, based on derived character states polarized using the Australian outgroup taxon Mecyclothorax punctipennis (MacLeay). Much of the species-level diversity on this small Pacific island is partitioned allopatrically over very small distributional ranges. No species is shared between Tahiti Nui and Tahiti Iti, and nearly all species in Tahiti Nui are geographically restricted to one ridgelike massif of that volcano. Cladistically similar species are often distributed on different massifs suggesting that vicariance associated with erosional valley formation has facilitated speciation, however several instances in which sister species occupy sympatric distributions on the same ridge system demonstrate that speciation may also occur across extremely localized landscapes. Such localized differentiation is facilitated by the low vagility of these small-bodied, flightless predators whose fragmented populations can persist and diverge within spatially limited habitat patches. The intense philopatry of Tahitian Mecyclothorax spp. coupled with the highly dissected landscape has produced the geographically densest adaptive radiation on Earth. This radiation has occurred very rapidly, with species durations averaging 300,000 yr; a speciation rate similar to that observed in Hawaiian Oliarus planthoppers and Laupala crickets, and East African Rift lake cichlid fishes.     

Botany without borders: barcoding in focus

This recent meeting, held on the campus of the University of British Columbia, attracted 1200 delegates and a vast array of talks, but was notable for a remarkable showing of talks and posters on DNA barcoding in plants, spread through many sessions. The Canadian Centre for DNA Barcoding defines barcoding as ‘species identification and discovery through the analysis of short, standardized gene regions known as DNA barcodes’. This approach is somewhat controversial in animals ( Rubinoff et al., 2006 ), although it has been shown to be useful and reliable in many metazoan taxa ( Meyer & Paulay 2005 ; Hajibabaei et al., 2007 ), in which the mitochondrial cytochrome oxidase I (COI) gene is used. However, in land plants, COI evolves far too slowly to be useful, and there is no obvious single universal alternative ( Fazekas et al., 2008 ). Genes that work well in one taxon may perform poorly in other taxa. Additionally, some perfectly good plant species, reproductively isolated and morphologically and ecologically distinct, are too young to show much sequence divergence at most loci. Nevertheless, as we saw at this conference, progress has been made towards identifying genes that serve many of the functions of DNA barcodes, at least in some plant taxa.