Production of the chironomid Procladius bellus in an annual drawdown reservoir

SUMMARY. 1. In Laurel Creek Reservoir. Ontario, a small, eutrophic annual drawdown reservoir, some individuals of the chironomid Procladius bellus survive the winter drawdown.
2. With refilling of the reservoir in spring, colonization by P. bellus is continuous and there were three generations a year.
3. Production estimated by the size-frequency method was 117.12 kg (175 mg m⁻²) in 1980 and 70.14 kg (105 mg ^m-2) in 1981. Annual P:B was about 13 in both years.
4. Substantial slation-to-station variations in production occurred and overall production was lower than in shallow habitats.     

Oxygen stress and reduced growth of Lobelia dortmanna in sandy lake sediments subject to organic enrichment

1. Lobelia dortmanna is a common representative of the small isoetid plants dominating the vegetation in nutrient‐poor lakes in Europe and North America. Because of large permeable root surfaces and continuous air lacunae Lobelia exchanges the majority of O₂ and CO₂ during photosynthesis across the roots. This leads to profound diel pulses of O₂ and CO₂ in sandy sediments with low microbial O₂ consumption rates. The ready radial root loss of O₂ may, however, make Lobelia very susceptible to more reducing sediments. Therefore, we grew Lobelia for 6 months on natural and organically enriched sandy sediments to test how: (i) root oxygenation influenced degradation of organic matter and depth profiles of N and C; (ii) Lobelia and microbial O₂ consumption rates influenced pool size and depth penetration of O₂ in the sediments; and (iii) sediment enrichment influenced growth and mineral nutrition of Lobelia. 2. Naturally low‐organic sediments (0.32% DW) accumulated organic C and N during the experiment as a result of growth of Lobelia and surface micro‐algae. In contrast, surface layers of enriched sediments (0.58, 0.87 and 2.46% DW) lost organic C and N because of enhanced mineralisation rates because of oxygen availability. In deeper layers of enriched sediments no significant differences in organic C and N pools were found between plant‐covered and plant‐free sediments probably because faster organic degradation because of root oxygenation was balanced by release of organic matter from the plants and because short roots with dense Fe‐Mn coatings in the most enriched sediments constrained O₂ release. 3. Depth‐integrated O₂ pools were much higher in light than darkness, higher in plant‐covered than plant‐free sediments and higher in sandy than in organically enriched sediments. All sediments had a primary O₂ maximum 1–2 mm below the sediment surface in light because of photosynthesis of micro‐algae. Plant‐covered sediments of low organic content (0.32 and 0.58% DW) also had a secondary deep maximum (2–4 cm) because of higher O₂ release from Lobelia roots than microbial O₂ consumption. Nitrification occurred here resulting in depletion of NH and accumulation of NO. In low organic sediments, oxygen pools increased with higher plant biomass both in light and darkness. The deep O₂ and NO₃ maxima disappeared in high organic sediments of greater O₂ consumption rates and smaller O₂ release rates. 4. Lobelia was stressed by increasing O₂ consumption rate of the sediments. Plant weight and leaf number declined twofold and maximum root length declined fourfold suggesting severe problems maintaining sufficient axial O₂ transport to the root tips because of rapid radial O₂ loss. Despite markedly higher nutrient concentrations in the enriched sediments, leaf‐N declined twofold and leaf‐P declined fourfold to growth‐limiting levels. These responses can be explained by constrains on mycorrhisal activity, root metabolism and vascular transport because of O₂ depletion. Management efforts to stop the decline and ensure the recovery of the isoetid vegetation should therefore focus on improving water quality as well as sediment suitability for growth.     

Characterization of eight microsatellite loci in Grant's gazelle (Gazella granti)

Eight microsatellite loci were isolated from a genomic DNA library created from Grant's gazelle (Gazella granti). Observed and expected levels of heterozygosity were computed utilizing 20 individuals from a population in Central Kenya. Tests for Hardy–Weinberg equilibria were conducted and found that two of the eight loci deviated from equilibrium in this population. These markers were developed to analyse the genetic effects of culling and isolation on a game preserve in Kenya.     

Homozygosity at a class II MHC locus depresses female reproductive ability in European brown hares

The link between adaptive genetic variation, individual fitness and wildlife population dynamics is fundamental to the study of ecology and evolutionary biology. In this study, a Bayesian modelling approach was employed to examine whether individual variability at two major histocompatibility complex (MHC) class II loci (DQA and DRB) and eight neutral microsatellite loci explained variation in female reproductive success for wild populations of European brown hare (Lepus europaeus). We examined two aspects of reproduction: the ability to reproduce (sterility) and the number of offspring produced (fecundity). Samples were collected from eastern Austria, experiencing a sub‐continental climatic regime, and from Belgium with a more Atlantic‐influenced climate. As expected, reproductive success (both sterility and fecundity) was significantly influenced by age regardless of sampling locality. For Belgium, there was also a significant effect of DQA heterozygosity in determining whether females were able to reproduce (95% highest posterior density interval of the regression parameter [−3.64, −0.52]), but no corresponding effect was found for Austria. In neither region was reproduction significantly associated with heterozygosity at the DRB locus. DQA heterozygotes from both regions also showed a clear tendency, but not significantly so, to produce a larger number of offspring. Predictive simulations showed that, in Belgium, sub‐populations of homozygotes will have higher rates of sterile individuals and lower average offspring numbers than heterozygotes. No similar effect is predicted for Austria. The mechanism for the spatial MHC effect is likely to be connected to mate choice for increased heterozygosity or to the linkage of certain MHC alleles with lethal recessives at other loci.     

Reconstructing routes of invasion using genetic data: why,how and so what?

Detailed knowledge about the geographical pathways followed by propagules from their source to the invading populations—referred to here as routes of invasion—provides information about the history of the invasion process and the origin and genetic composition of the invading populations. The reconstruction of invasion routes is required for defining and testing different hypotheses concerning the environmental and evolutionary factors responsible for biological invasions. In practical terms, it facilitates the design of strategies for controlling or preventing invasions. Most of our knowledge about the introduction routes of invasive species is derived from historical and observational data, which are often sparse, incomplete and, sometimes, misleading. In this context, population genetics has proved a useful approach for reconstructing routes of introduction, highlighting the complexity and the often counterintuitive nature of the true story. This approach has proved particularly useful since the recent development of new model‐based methods, such as approximate Bayesian computation, making it possible to make quantitative inferences in the complex evolutionary scenarios typically encountered in invasive species. In this review, we summarize some of the fundamental aspects of routes of invasion, explain why the reconstruction of these routes is useful for addressing both practical and theoretical questions, and comment on the various reconstruction methods available. Finally, we consider the main insights obtained to date from studies of invasion routes.