Distribution of Lateral Root Primordia in Root Tips of Musa

The distribution of lateral root primordia in the root tipsof four Musa landraces (Grande Naine, Pisang Berlin, Ngok Egomeand Yangambi Km5) grown in the field has been investigated toevaluate the range of genetic variation of lateral root initiation.In banana (Musa sp.), lateral roots are initiated in the roottip, 0.6–4 mm behind the root/cap junction and arise inseveral protoxylem-based longitudinal rows or ‘ranks’.Significant differences were observed among landraces for theposition of the most distal primordium, however the longitudinalspacing between successive primordia along the ranks was similarfor all landraces. All ranks were involved in lateral root initiation.The number of ranks also showed significant variations amonglandraces and was proportional to the stelar diameter. Hencethe density of lateral roots (roots cm^-1) was affected by stelardiameter variations. Finally, root elongation in the root tipwas landrace-specific and not necessarily exponential, unlikesuggested in previous studies. It is concluded that lateralroot initiation in Musa is not involved in the genetic variationsof root architecture in the field. A dissection of root architectureinto components which may account for these variations is proposedin relation to the improvement of root system architecture.Copyright 1999 Annals of Botany Company Lateral root initiation, root architecture, Musa, banana.     

Can a sponge feeder be a herbivore? Tylodina perversa (Gastropoda) feeding on Aplysina aerophoba (Demospongiae)

Feeding biology in mollusks has important biological, ecological and evolutionary implications because many of the characteristics we observe in mollusks arise from their co-evolution with diet organisms. We investigated the relationship between the opisthobranch Tylodina perversa and the sponges Aplysina aerophoba and Aplysina cavernicola in order to ascertain the trophic interactions between them. The opisthobranch preferred specimens of Aplysina aerophoba inhabiting shallow overdeep waters, ectosome of Aplysina aerophoba over choanosome, and showed no preference for Aplysina cavernicola . The sponge Aplysina cavernicola lacks the cyanobacteria abundant in the ectosome of Aplysina aerophoba . Our study shows that the opisthobranch Tylodina perversa actively selects for sponges or sponge zones with high concentration of cyanobacteria, i.e. only a fraction of the ingested material is of animal origin. Addition of cyanobacteria to symbiont-free sponge material induced a shift in mollusk preference. Our results cast doubt over the widely recognized qualification of Tylodina perversa as a carnivorous sponge feeder and show evidence that cyanobacteria determine the opisthobranch food selection. Whether this is an isolated example of how symbionts may determine trophic interactions between hosts and predators or it is widespread in benthic organisms remains an open question that requires further investigation.  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 429–438.     

Influence of selfing and maternal effects on life-cycle traits and dispersal ability in the herb Hypochaeris radicata (Asteraceae)

The ecological and evolutionary implications of dispersal are many. Pollination type and maternal effects may affect plant fitness traits, including life-cycle traits as well as dispersal ability. This study investigated the joint influence of pollination type and maternal effects on both life-cycle traits and dispersal ability in the herb Hypochaeris radicata . We conducted experimental crosses to obtain selfed and outcrossed progeny. Individual seeds and their pappuses were measured to determine seed terminal velocity. Seed size was also used to assess maternal effects. Selfing dramatically decreased seed set, indicating that H. radicata is self-incompatible. However, the few selfed seeds produced outperformed outcrossed seeds in seed size and flowering probability, surely as a result of an effective reallocation of resources among selfed seeds. None of the life-cycle traits was affected by seed size, the estimate of maternal effects. Selfed seeds were larger and bore a smaller pappus than outcrossed seeds. As a result, dispersal ability was lower for selfed than outcrossed seeds. Several factors, such as the low proportion of plants that produced selfed seeds, the low number of selfed seeds produced per plant, and the lack of self-fertility mechanisms might act in concert to prevent the evolution of selfing in H. radicata .  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 163–170.     

Invasion or invisibility: using genetic and distributional data to investigate the alien or indigenous status of the Atlantic populations of the peracarid isopod,Stenosoma nadejda (Rezig 1989)

The peracarid isopod, Stenosoma nadejda (Rezig 1989), until recently considered to be endemic of the Mediterranean region, was first reported in the Atlantic coast of southern Spain in 2001, and in 2006 abundant populations were discovered throughout the southwestern Portuguese coast. This fast expansion was intriguing because, as a direct brooder, this species has limited mechanisms for dispersal, such as rafting on seaweeds. Did S. nadejda recently extend its range into the Atlantic or was it overlooked in the past? We examined the patterns of genetic diversity and population differentiation accordingly by sequencing the cytochrome c oxidase subunit I mitochondrial gene from 75 individuals collected in five locations in Atlantic Iberia and one in the Mediterranean. Our results indicate that the newly discovered Atlantic populations of S. nadejda appear to be old and have long persisted on Atlantic shores rather than being a recent introduction. High levels of genetic diversity and geographic structure were uncovered in what was initially suspected to be an ‘invasive’ species. Recent changes in population dynamics may have made S. nadejda more conspicuous in the Atlantic shores, or a more comprehensive survey led to the recognition of this species where it was not expected.     

Determinants of local ant (Hymenoptera: Formicidae) species richness and activity density across Europe

1. Species richness is influenced by local habitat features and large‐scale climatic gradients. Usually, both influences are studied in isolation because of the divergent spatial scales at which they occur. Here, we compared the influence of large‐scale climate and local habitat type on European ants using a continent‐wide, standardised sampling programme. 2. We investigated species richness and activity density from pitfall traps distributed over four habitat types at 17 locations from northern Sweden to Spain and Greece. Species richness and activity density were analysed with respect to ambient energy [equilibrium evapotranspiration (EET)] and productive energy (net primary productivity). Furthermore, we compared ant richness and activity density between the four habitat types: arable land, scrubland, grassland, and forest. 3. Species richness and activity density of ants increased with equilibrium evapotranspiration (EET), explaining 30.2% of the total variation in species richness and 24.2% of activity density. Habitat type explained an additional 19.2% of the variation in species richness and 20.2% of activity density, and was not related to productivity. Species richness and activity density were highest in scrubland and significantly lower in forest and (marginally significant) in arable land. 4. The increase in EET and the decrease in forest confirms the pronounced thermophily of ants, whereas the decrease in arable land is probably caused by soil disturbance.     

Inferring evolutionary scenarios with geostatistics and geographical information systems for the viperid snakes Vipera latastei and Vipera monticola

The present study aimed to infer evolutionary scenarios for Vipera latastei and Vipera monticola in the Iberian Peninsula and the Maghreb through the identification of spatial patterns in morphological character variation and biogeographic patterns in morphological variability distribution. Ten morphological traits from 630 vipers were analysed with geostatistic and ecological niche modelling in a geographical information system. Interpolation by Kriging was used to generate surfaces of morphological variation, which were combined with spatial principal components analysis (SPCA). Putative morphological differentiated groups generated by SPCA maps were tested with discriminant function analysis (DFA). Maximum entropy modelling and nine environmental variables were used to identify factors limiting the distribution of groups and areas for their potential occurrence. Groups supported by DFA were: Western Iberia, Eastern Iberia, Rif plus Middle Atlas, Algeria, and High Atlas. Their distribution is influenced by common environmental factors such as precipitation. Areas of probable sympatry between Iberian groups matched the morphological clines observed by geostatistics tools. Geographic variation patterns in V. latastei‐monticola are probably due to vicariant separation of Iberian and African populations during the opening of the Strait of Gibraltar, and population refugia during the Quaternary glaciations with secondary contact. The taxonomic status of northern Morocco and Algerian groups should be further investigated. We conclude that geostatistics and niche‐modelling tools are adequate to infer morphological variability across wide geographic ranges of species. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 790–806.     

Seed ecology of a Mediterranean perennial herb with an exceptionally extended flowering and fruiting season

Lobularia maritima is a Mediterranean short-lived herb with a flowering and fruiting season that lasts for ten months. Previous studies have shown that recruitment in periods other than autumn of the flowering season has few demographic implications; that is contributes little to the population growth rate. Since environmental conditions in periods other than autumn would allow recruitment, we examined to what extent the seed ecology of L. maritima accounts for recruitment shortage for the greater part of the year. To this end, we studied the effects of selfing and outcrossing on seed production and germination, within- and between-year variation in seed mass and germination, seed characteristics in the soil seed bank throughout the year, and the effect of temperature as a factor controlling seed germination. Results indicate that selfing does not decrease recruitment, and thus the observed changes in visitation rate and pollinator composition throughout the year cannot account for differences in recruitment. Germinability decreases throughout the year, suggesting a possible cost in reproduction associated with extended flowering. L. maritima has a transient seed bank whose seeds also experience a decrease in their germination throughout the year. Finally, temperature affects seed germination patterns, indicating the existence of quiescence mechanisms that prevent germination in the months prior to the summer drought. Overall, the results obtained support and, at least partly, explain the recruitment patterns of L. maritima observed in the field.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 273–280.