An AFLP marker approach to lower-level systematics in Eucalyptus (Myrtaceae)

Genus Eucalyptus, with over 700 species, presents a number of systematic difficulties including taxa that hybridize or intergrade across environmental gradients. To date, no DNA marker has been found capable of resolving phylogeny below the sectional level in the major subgenera. Molecular markers are needed to support taxonomic revision, assess the extent of genetic divergence at lower taxonomic levels, and inform conservation efforts. We examined the utility of 930 amplified fragment length polymorphisms (AFLPs) for analyzing relationships among Tasmanian taxa of subgenus Symphyomyrtus section Maidenaria. Phenetic and cladistic analyses resolved species into clusters demonstrating significant genetic partitioning, largely concordant with series defined in the most recent taxonomic revision of Eucalyptus. Some departures from current taxonomy were noted, indicating possible cases of morphological convergence and character reversion. Although the resolution obtained using AFLP was greatly superior to that of single sequence markers, the data demonstrated high homoplasy and incomplete resolution of closely related species. The results of this study and others are consistent with recent speciation and reticulate evolution in Maidenaria. We conclude that a combination of phylogenetic and population genetic approaches using multiple molecular markers offers the best prospects for understanding taxonomic relationships below the sectional level in Eucalyptus.     

Pollination of a core flowering shrub species in Mediterranean phrygana: variation in pollinator diversity, abundance and effectiveness in response to fire

Fire in Mediterranean-type ecosystems produces catastrophic changes in plant-pollinator systems; the recovery of which has been studied by comparing an unburnt mature forest habitat with that of an adjacent recently burnt area (eight years post-fire). The composition, visitation profiles, and effectiveness of the taxonomically diverse pollinator assemblages found on a core nectar providing species ( Satureja thymbra : Lamiaceae) were examined in these two contrasting habitats. S. thymbra in the freshly burnt area had low nectar standing crop and relatively less diverse bee community than an unburnt area which had twice the nectar standing crop and a higher bee diversity and abundance. Both sites supported bee assemblages dominated by the non-native bumblebee Bombus terrestris . Spatio-temporal heterogeneity of nectar standing crops and microclimatic conditions were sufficient to explain the form and magnitude of the diurnal foraging profiles at each site in relation to species specific foraging and flight abilities. B. terrestris, Apis mellifera and native solitary bees were the three primary guilds visiting S. thymbra and varied in the efficiency with which they delivered conspecific pollen grains to receptive stigmas. A pollinator effectiveness index for these three guilds was calculated based on floral visitation rates and pollen delivery efficiency and reflected the actual levels of effectiveness of each guild within and across the two habitat types. There was no overall inter-community difference in pollination effectiveness as the bee assemblages in both habitats were sufficient to produce maximum fruit set in S. thymbra, though the relative contribution of each guild varied intra-communally. Pollen limitation was not found to occur in either habitat.     

Patterns of size variation in bees at a continental scale: does Bergmann's rule apply?

Body size latitudinal clines have been widley explained by the Bergmann's rule in homeothermic vertebrates. However, there is no general consensus in poikilotherms organisms in particular in insects that represent the large majority of wildlife. Among them, bees are a highly diverse pollinators group with high economic and ecological value. Nevertheless, no comprehensive studies of species assemblages at a phylogenetically larger scale have been carried out even if they could identify the traits and the ecological conditions that generate different patterns of latitudinal size variation. We aimed to test Bergmann's rule for wild bees by assessing relationships between body size and latitude at continental and community levels. We tested our hypotheses for bees showing different life history traits (i.e. sociality and nesting behaviour). We used 142 008 distribution records of 615 bee species at 50 × 50 km (CGRS) grids across the West Palearctic. We then applied generalized least squares fitted linear model (GLS) to assess the relationship between latitude and mean body size of bees, taking into account spatial autocorrelation. For all bee species grouped, mean body size increased with higher latitudes, and so followed Bergmann's rule. However, considering bee genera separately, four genera were consistent with Bergmann's rule, while three showed a converse trend, and three showed no significant cline. All life history traits used here (i.e. solitary, social and parasitic behaviour; ground and stem nesting behaviour) displayed a Bergmann's cline. In general there is a main trend for larger bees in colder habitats, which is likely to be related to their thermoregulatory abilities and partial endothermy, even if a ‘season length effect’ (i.e. shorter foraging season) is a potential driver of the converse Bergmann's cline particularly in bumblebees.     

The use of amiloride to uncouple branchial sodium and proton fluxes in the brown trout, Salmo trutta

Resting proton, ammonium and sodium fluxes in Salmo trutta were 492.6 ± 19.5 (n = 29); 122.9 ± 34.2 (n = 28) and 277.1 ± 18.5 (n = 50) μmol · kg⁻¹ · h⁻¹, respectively. The resting transepithelial potential was found to be composed of three successive potentials, the outermost averaging −7.36 ± 0.19mV, the second, −14.3 ± 1.4 mV and the third −37 ± 1.7 mV. Amiloride inhibits the proton, ammonium and sodium fluxes in a dose-dependent manner at concentrations of 0.5 mmol · 1⁻¹ and 0.1 mmol · l⁻¹, but at 0.01 mmol · l⁻¹, proton and ammonium fluxes remained at control levels whilst the sodium was reduced to 70.59 ± 7.29 μmol · kg⁻¹ · h⁻¹. The trans-epithelial potential was effected in a bi-phasic manner by 0.5 mmol · l⁻¹ amiloride. An initial hyperpolarisation of ca. 6 mV was followed by a sustained depolarisation of ca. 14 mV (towards zero) which persisted until the amiloride was washed off the gill. The initial hyperpolarisation was thought to reflect a rapid inhibition of a positive inward sodium current and the subsequent depolarisation was due to the inhibition of a positive outward current (proton) which would abolish the transepithelial potential. However, at 0.01 mmol ·  l⁻¹ only the hyperpolarisation was seen, due to the inhibition of only the inward sodium current. Acetazolamide (0.1 mmol · l⁻¹) was found to have no significant effect on the proton, ammonium and sodium fluxes. These results indicate that the proton and sodium fluxes across the gill of the freshwater trout are not tightly linked. While this suggests that the trout gill resembles the model of Ehrenburg et al. (1985) of sodium uptake in frog skin, the apical potentials measured in the pavement epithelial cell(s) are too low to account for sodium uptake unless the activity of the sodium in the cells is very low. Accepted: 8 August 1996