Microsatellite DNA analysis of northern pike (Esox lucius L.) populations: insights into the genetic structure and demographic history of a genetically depauperate species

The northern pike Esox lucius L. is a freshwater fish exhibiting pronounced population subdivision and low genetic variability. However, there is limited knowledge on phylogeographical patterns within the species, and it is not known whether the low genetic variability reflects primarily current low effective population sizes or historical bottlenecks. We analysed six microsatellite loci in ten populations from Europe and North America. Genetic variation was low, with the average number of alleles within populations ranging from 2.3 to 4.0 per locus. Genetic differentiation among populations was high (overall θ_ST = 0.51; overall ρ_ST = 0.50). Multidimensional scaling analysis of genetic distances between populations and spatial analysis of molecular variance suggested a single phylogeographical race within the sampled populations from northern Europe, whereas North American and southern European populations were highly distinct. A population from Ireland was monomorphic at all loci, presumably reflecting founder events associated with introduction of the species to the island in the sixteenth century. Bayesian analysis of demographic parameters showed differences in θ (a product of effective population size and mutation rate) among populations from large and small water bodies, but the relative differences in θ were smaller than expected, which could reflect population subdivision within the larger water bodies. Finally, the analyses showed drastic population declines on a time scale of several thousand years within European populations, which we ascribe to either glacial bottlenecks or postglacial founder events.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 91–101.     

SEM study of surface structures of the spathe in Cryptocoryne and Lagenandra (Araceae: Aroideae: Cryptocoryneae)

SEM studies of the spathe structures in the two closely related genera Cryptocoryne and Lagenandra show differences between the inner and outer surfaces, as well as in cell structures in the various parts of the spathe. The cell structure reveals patterns mat makes it possible to depict homologous structures of the spathe, even though the spathes of the two genera look different. The basal part of the kettle has a mucilage covering of the cells, interpreted as a hitherto unnoticed food source. The cells of the inner surface of the kettle and tube have downward pointing trichomes. On the second day of flowering these collapse and sink into the cell lumen, which is suggested to create a unique lattice-like structure that enables the insects to climb out of the kettle and tube. The cell structure of the flap shows that it is a prolongation and continuation of the spathe tube margin.     

Xylem function of arid-land shrubs from California, USA: an ecological and evolutionary analysis

Xylem traits were examined among 22 arid-land shrub species, including measures of vessel dimensions and pit area. These structural measures were compared with the xylem functional traits of transport efficiency and safety from cavitation. The influence of evolution on trait relationships was examined using phylogenetic independent contrasts (PICs). A trade-off between xylem safety and efficiency was supported by a negative correlation between vessel dimensions and cavitation resistance. Pit area was correlated with cavitation resistance when cross species data were examined, but PICs suggest that these traits have evolved independently of one another. Differences in cavitation resistance that are not explained by pit area may be related to differences in pit membrane properties or the prevalence of tracheids, the latter of which may alter pit area through the addition of vessel-to-tracheid pits or through changes in xylem conduit connectivity. Some trait relationships were robust regardless of species ecology or evolutionary history. These trait relationships are likely to be the most valuable in predictive models that seek to examine anatomical and functional trait relationships among extant and fossil woods and include the relationship among hydraulic conductivity and vessel diameter, between vessel diameter and vessel length, and between hydraulic conductivity and wood density.     

Restoring lakes by using artificial plant beds: habitat selection of zooplankton in a clear and a turbid shallow lake

1. Return of large‐bodied zooplankton populations is of key importance for creating a shift from a turbid to a clear‐water state in shallow lakes after a nutrient loading reduction. In temperate lakes, recovery is promoted by submerged macrophytes which function as a daytime refuge for large zooplankton. However, recovery of macrophytes is often delayed and use of artificial plant beds (APB) has been suggested as a tool to enhance zooplankton refuges, thereby reinforcing the shift to a clear‐water state and, eventually, colonisation of natural plants. 2. To further evaluate the potential of APB in lake restoration, we followed the day–night habitat choices of zooplankton throughout summer in a clear and a turbid lake. Observations were made in the pelagic and littoral zones and in APB in the littoral representing three different plant densities (coverage 0%, 40% and 80%). 3. In the clear lake, the zooplankton (primarily Daphnia) were mainly found in the pelagic area in spring, but from mid‐May they were particularly abundant in the APB and almost exclusively so in mid‐June and July, where they appeared in extremely high densities during day (up to 2600 ind. L⁻¹). During night Daphnia densities were overall more equally distributed between the five habitats. Ceriodaphnia was proportionally more abundant in the APB during most of the season. Cyclopoids were more abundant in the high APB during day but were equally distributed between the five habitats during night. 4. In the turbid lake, however, no clear aggregation was observed in the APB for either of the pelagic genera (Daphnia and Bosmina). This may reflect a higher refuge effect in the open water due to the higher turbidity, reduced ability to orient to plant beds and a significantly higher fish density (mainly of roach, Rutilus rutilus, and perch, Perca fluviatilis) in the plant beds than in the clear lake. Chydorus was found in much higher proportions among the plants, while cyclopoids, particularly the pelagic Cyclops vicinus, dominated in the pelagic during day and in the pelagic and high density plants during night. 5. Our results suggest that water clarity is decisive for the habitat choice of large‐bodied zooplankton and that introduction of APB as a restoration measure to enhance zooplankton survival is only a useful tool when water clarity increases following loading reduction. Our results indicate that dense APB will be the most efficient.     

Are altitudinal limits of equatorial stream insects reflected in their respiratory performance?

1. We measured respiration of the larvae of aquatic insects from streams in the Ecuadorian Andes in relation to oxygen saturation at 5, 8, 11, 14 and 17 °C. Polycentropus (Polycentropodidae), Lachlania (Oligoneuriidae), Anchytarsus (Ptilodactylidae) and Anacroneuria (Perlidae) represented genera absent from the highest altitudes, reaching 2720, 2930, 3120, 3450 m a.s.l., respectively, while Claudioperla (Gripopterygidae) and Anomalocosmoecus (Limnephilidae) occurred only above 2900 m a.s.l. Our purpose was to determine whether natural altitudinal limits were reflected in physiological critical points on respiration versus oxygen curves and by the effect of temperature on the ability to oxy‐regulate. 2. For all six genera, respiration was affected by oxygen saturation and temperature. Respiration (mg O₂ g⁻¹ AFDM h⁻¹) at 70% oxygen saturation (Michaelis–Menten fitted) varied from 2.6 to 7.6 between genera at 17 °C, and from 1.3 to 2.5 at 5 °C. Q₁₀ values for this temperature interval ranged 1.5–2.9 (mean 2.3). The two “high‐altitude” genera had higher respiration rates at low temperature and oxygen saturation, and their respiration rate saturated at lower temperatures, than three of the four “low‐altitude” genera. 3. The oxy‐regulatory capacity (critical points and initial decrease in respiration versus oxygen regressions) varied among genera and was affected by temperature. Lachlania, Claudioperla and Anomalocosmoecus had a higher ability to oxy‐regulate at low than at high temperatures, Anacroneuria was not clearly affected by temperature, while Polycentropus and Anchytarsus had a greater oxy‐regulatory capacity at high than at low temperature. These results indicate that the ability to oxy‐regulate is related to the temperature (altitude) at which species naturally occur. 4. Upper altitudinal limits of the six genera were not reflected in their respiratory performance, because all genera had critical minima of temperature and oxygen saturation much lower than those occurring at the limits of their natural distribution. So, the altitudinal limit could not be attributed to absolute short‐term physiological tolerance of low temperature and oxygen concentration. 5. Multiple regressions (based on respiration experiments and previously obtained relationships between water temperature, oxygen saturation and altitude) were used to predict how respiration rates should vary with altitude. At the upper limit of the four “low‐altitude” genera, respiration rates were 50–68% of those predicted at the centre of the range. With an arbitrary increase of 400 m above the actual limit, the effect of temperature would be a 13% decrease, and that of oxygen a 2% decrease, in respiration rate of Polycentropus, Lachlania and Anacroneuria, while respiration in Anchytarsus would be reduced by 5% by both factors. 6. It seems that, while the immediate decrease in respiration with increased altitude is caused mainly by a decrease in temperature, the long‐term survival of a species at given altitudes might be more affected by oxygen saturation. Further quantitative and long‐term studies on survival and recruitment in populations and communities are needed to determine the importance of temperature and oxygen for altitudinal limits of aquatic insects.     

Invertebrate herbivory on the submerged macrophyte Potamogeton perfoliatus in a Danish stream

• 1 Invertebrate herbivory on the submerged macrophyte Potamogeton perfoliatus was studied in a Danish lowland stream during the main growth seasons of summer 1991 and 1992. Young apical leaves escaped consumption probably because of their location and dense packing, but herbivory loss increased linearly with age and exposure time of older leaves. Nitrogen content was relatively high in both young (4.61% DW) and old leaves (3.65% DW) but a food preference experiment showed that young leaves were preferred by the main herbivore, the trichopteran Anabolia nervosa.
• 2 The percentage of standing plant biomass lost to herbivory (the apparent loss) between sampling periods increased from early May to a mid-June maximum (24.8% in 1991, 4.2% in 1992), and subsequently declined to zero within a month. The averages for the growth seasons were 10.5% in 1991 and 2.0% in 1992. Yet, the proportions of annual plant production harvested by herbivores were low and almost the same (1.3 and 1.8%) because consumption was low when plant production peaked in late summer. Consumption was almost the same early in the two years, but plant growth dynamics differed markedly and was the main factor determining apparent herbivory loss.
• 3 Despite heavy damage early in the summer, P. Perfoliatus contributed a minor fraction (1–5%) of the trichopteran diet. This fraction appeared to be restricted by the low macrophyte biomass during early summer.
• 4 The results emphasize that apparent herbivory loss does not estimate the harvested proportion of plant production, and that plant growth dynamics should be analysed to attain precise estimates of herbivory rates.