Relationship between floral tube length and nectar robbing in Duranta erecta L. (Verbenaceae)

Although nectar robbing is a common phenomenon in plant species with tubular flowers or flowers with nectar spurs, the potential effect of this illegitimate interaction on plant reproductive success has not received the deserved attention. In the present study, we analysed the functional relationship between flower morphology and nectar robbing, and examined the reproductive consequences of the interaction in a population of Duranta erecta (Verbenaceae) on the island of Cuba. The results show that nectar robbing is conducted by the carpenter bees Xylocopa cubaecola and affects up to 44% of flowers in the studied population. However, not all the flowers have the same probability of being robbed. The chance of flowers being robbed increases with flower length and flower diameter. Moreover, nectar robbing significantly decreases the chance that flowers will set fruit. Also, the impact of nectar robbing on the probability of flowers to set fruits is dependent on the plant. We suggest that nectar robbing may represent an opposite selective force that balances the selection for longer corollas often imposed by pollinators specializing in visiting tubular flowers. Such a relationship with nectar robbers would have obvious implications for the evolution of tubular or closed flowers. This preliminary finding deserves further research in light of the ecological and evolutionary consequences of nectar robbing in tubular flowers.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 392–398.     

Spatial eigenfunction analyses in stream networks: do watercourse and overland distances produce different results?

1. The use of spatial variables is a common procedure in ecological studies. The technique is based on the definition of a connectivity/distance matrix that conceptually defines the dispersal of organisms. The shortest distance between two points is a straight line. Despite the fact that a straight line may not represent the easiest dispersal path for many kinds of organisms, straight‐line distances are often used to detect patterns. We argue that other types of connectivity/distance matrices will better represent dispersal paths, such as the watercourse distance for aquatic organisms (e.g. fish, shrimps). 2. We used empirical and simulated community data to evaluate the usefulness of spatial variables generated from watercourse and overland (straight‐line) distances. 3. Spatial variables based on watercourse distances captured patterns that straight‐line distances did not, and provided better representations of the spatial patterns generated by dispersal along a dendritic network.     

Impact of habitat fragmentation on the genetics of populations in dendritic landscapes

1. The effect of habitat fragmentation on freshwater species has been addressed using brown trout Salmo trutta L. as a model species with a dendritic population structure. 2. Microsatellite loci were employed as molecular markers. Levels of gene flow and population subdivision were determined in more than 1200 brown trout individuals inhabiting four south European rivers with contrasting patterns of fragmentation, defined by the presence of barriers. 3. The genetic units in the four rivers were restricted by artificial barriers, and gene flow among samples within each river was associated with the level of fragmentation of the river. 4. Loss of genetic diversity and dislocation of the dendritic model have been detected in fragmented rivers. These results emphasise the importance of mitigating the impact of dams by constructing passages to restore gene flow along the river, for fish and other migratory species, as well as the need for caution in relation to stocking in isolated areas to avoid problems of inbreeding.     

A revised classification of subtribe Helianthinae (Asteraceae: Heliantheae) II. Derived lineages

Sequence data for internal transcribed spacer (ITS) and partial external transcribed spacer (ETS) regions were combined in a phylogenetic analysis with previously obtained plastid DNA restriction site data to provide a comprehensive molecular phylogenetic hypothesis for derived members of subtribe Helianthinae. Analyses of the two molecular datasets provided conflicting evidence on relationships among some groups, supporting the hypothesis that hybridization has played a significant role in the divergence of the subtribe. A revised generic‐level classification is presented that divides the approximately 350 species of the subtribe among 21 genera. The paraphyletic Viguiera is narrowed to embrace only the type species, V. dentata. Four newly described genera, Dendroviguiera, Gonzalezia, Heiseria and Sidneya, are composed of species formerly included in Viguiera. Aldama is expanded to include 118 species extending from southwestern North America and Mexico to South America. This requires 116 new combinations, including 58 that were recently transferred into Rhysolepis, which is a synonym of Aldama, based on molecular phylogenetic results. One species of Viguiera is transferred to Tithonia, and two combinations in Hymenostephium are validated. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 167 , 311–331.     

Factors influencing egg parasitism in sub‐social insects: insights from the treehopper Alchisme grossa (Hemiptera,Auchenorrhyncha, Membracidae)

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Karyosystematic study of Potentilla L. subgen. Potentilla (Rosaceae) in the Iberian Peninsula

Chromosome numbers in 80 populations belonging to 18 species of Potentilla L. subgen. Potentilla from the Iberian Peninsula and two of P. maura, a North African endemic taxon, have been counted. The basic number of chromosomes is always x = 7 and these chromosomes are small (between 1 and 2 μm). For three species, the number of chromosomes is reported for the first time and, for another six, this number has been established in Iberian representatives. Moreover, new ploidy levels have been obtained for P. hispanica and P. crantzii with regard to their entire distribution area, and in P. cinerea and P. neumanniana for the Iberian Peninsula. Some taxonomic, phylogenetic and phytogeographic comments are made for several species or groups of species from the West Mediterranean region. In 13 species only one ploidy level has been found, but six species have several ploidy levels. Seven ploidy levels occur in the investigated taxa. The frequency of each ploidy level represented within Iberian Potentilla is analysed and the data are compared with those available for taxa from the rest of the distribution area of the genus.     

Effects of different thermal treatments during embryonic development on the artificial incubation efficiency of crayfish (Austropotamobius pallipes Lereboullet) eggs. Control of the embryogenetic duration and implications for commercial production

Summary

The development and improvement of artificial incubation techniques for freshwater crayfish eggs and their incorporation into the working schedule of breeding centres is of great interest for commercial production. Factors such as the water circulation system, flow rate, thermal treatment, etc., could strongly influence the success of the process. The present study attempts to test the possible influence of one of these variables, the thermal regime, on both the duration of embryonic development and the efficiency rates obtained in the artificial incubation of white-clawed crayfish (Austropotamobius pallipes) eggs. Four different thermal treatments were tested (three of them included a period at low temperature: 4°-5°C). Survival rates to juvenile stage 2 were similar in the four cases, ranging between 66.7 and 72.7%. We conclude that water cooling (an expensive management procedure) is not necessary in astacid breeding centres provided that egg development takes place at moderately low temperatures (8°-10°C) with a subsequent increase of up to 15°C from the eyed stage. However, the inclusion of periods at low temperature (4°-5°C) allows the staggered production of juvenile batches throughout a 3-week period without adverse effects on efficiency rates. This could be useful to breeding centres in meeting seasonal market requirements. In our study, egg and juvenile losses (mortality rate: 15–20%) were concentrated during the last phases of embryogenesis, particularly from the eyed stage to juvenile stage 2, during which they amounted to more than 90% of the overall mortality which took place during the artificial incubation process.     

Plant species variation in bottom‐up effects across three trophic levels: a test of traits and mechanisms

1. An increasing number of studies have addressed the mechanisms by which plant inter‐specific variation influence interactions at higher trophic levels, but little is known about the underlying plant traits driving these dynamics. 2. Here we investigated the effects of host plant species on herbivore‐parasitoid interactions and the underlying traits driving such effects. For this, we measured the abundance of seed‐eating bruchids and their parasitoids across seven sympatric populations of the bean species Phaseolus coccineus and Phaseolus vulgaris in Central Mexico. To investigate the mechanisms underlying differences between bean species in bruchid‐parasitoid interactions, we carried out two laboratory experiments to test whether bruchid and parasitoid performance differed between plant species. We also measured seed size and phenolic compounds to investigate if seed traits mediate bruchid‐parasitoid interactions by influencing herbivore susceptibility or resistance to parasitoids. 3. Field surveys revealed that the rate of parasitoid recruitment to bruchids was significantly higher on P. vulgaris than on P. coccineus. Subsequent laboratory bioassays indicated that bruchids developed more slowly and exhibited lower fitness on P. vulgaris seeds than on P. coccineus seeds. Accordingly, we found that bean species differed in seed size, with P. vulgaris having smaller (less nutritious) seeds, which explains why bruchid development was slower on this plant species. 4. These results provide a mechanism for why bruchids exhibited higher parasitism rates on seeds of P. vulgaris in the field which could be due to Slow‐Growth/High‐Mortality effects, a smaller physical refuge provided by the seed, or both factors. The roles of these mechanisms remain inconclusive without further study.