Sources of fish in the ephemeral western iishana region of the Cuvelai–Etosha Basin in Angola and Namibia

The triangle between the Kavango and Kunene rivers is drained by the Cuvelai, an ephemeral and deltaic drainage system covering more than 100 000 km². In good rainfall years, the area becomes populated by fish communities dominated by five species migrating southward towards the endorheic Etosha Pan, the basin’s terminal sump. When water dries up, fish subsequently die-off and their sudden appearance in rainy years has captivated scientists for decades. The current study was prompted by hitherto untapped indigenous knowledge through narratives of opportunistic fish harvesting of migrating fish at temporary connections between the Kunene River and the Cuvelai- Etosha Basin. A reconnaissance fish survey in 2017 was complemented by digital satellite images and elevation data analyses. Results support the presence of at least three major ephemeral fish migration routes. The dominant fish genera migrating upstream in Kunene tributaries comprise Enteromius, Oreochromis and Clarias, all eurytopic and known to undertake upstream, lateral and downstream migrations on floodplains. Although other notable fish refugia in the Cuvelai–Etosha Basin are yet to be identified, there is a necessity for the protection and management of these migration routes in tandem with studies on the nature and extent of this inter-basin fish migration under climate change and variability.     

Tertiary structures for the extracellular domains of the epithelial polyimmunoglobulin receptor (secretory component) derived by primary structure comparisons with immunoglobulins

The amino acid sequences of the rabbit receptor and human secretory component (SC) domains have been compared with those of immunoglobin (Ig) domains. Accessible and inaccessible sites of tryptic cleavage in bovine SC have been located by sequence homology. Computerized secondary structure prediction and three dimensional model building have been carried out. The resulting tertiary structures are extremely Ig-like consisting of two superposed beta-pleated sheets. All carbohydrate sites lie at external positions as do tryptic cleavage sites. Potential sites for tryptic hydrolysis that are not cleaved lie at buried or partially buried positions. 6. Inter-beta-sheet contact between domains appears to be highly unlikely so that the quaternary structure is largely determined by longitudinal contacts.     

Regulation of rat liver phosphoenolpyruvate carboxykinase (GTP) messenger ribonucleic acid activity by N6, O2'-dibutyryladenosine 3',5'-phosphate

N6,O2'-Dibutyryladenosine 3',5'-phosphate (Bt2cAMP) induces the synthesis of the gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.32), in rat liver by increasing the activity of messenger ribonucleic acid (mRNA) coding for this enzyme (mRNAPEPCK) more than 20-fold (from less than 0.01% to greater than 0.20% of total mRNA activity) as determined by using in vitro translation systems which measure only active mRNAPEPCK. The increase in mRNAPEPCK activity could result from increased synthesis, increased processing, or decreased inactivation rates. Actinomycin D and cordycepin inhibit mRNAPEPCK induction by 89% and 70%, respectively, a result that indicates a requirement for ongoing RNA synthesis but that does not distinguish which of these steps is regulated by cAMP. We have employed a kinetic approach, not involving RNA synthesis inhibitors, to determine the half-life of mRNAPEPCK both during a period of deinduction following glucose feeding and during a subsequent induction by Bt2cAMP. An estimated half-life of 20 +/-5 min during both of these periods indicates that Bt2cAMP has no effect on the rate of inactivation of mRNAPEPCK. We conclude that Bt2cAMP effects the increase in activity of mRNAPEPCK by promoting its synthesis or processing.     

Does climate change explain the decline of a trans-Saharan Afro-Palaearctic migrant?

There is an urgent need to understand how climate change will impact on demographic parameters of vulnerable species. Migrants are regarded as particularly vulnerable to climate change; phenological mismatch has resulted in the local decline of one passerine, whilst variations in the survival of others have been related to African weather conditions. However, there have been few demographic studies on trans-Saharan non-passerine migrants, despite these showing stronger declines across Europe than passerines. We therefore analyse the effects of climate on the survival and productivity of common sandpipers Actitis hypoleucos, a declining non-passerine long-distant migrant using 28 years’ data from the Peak District, England. Adult survival rates were significantly negatively correlated with winter North Atlantic Oscillation (NAO), being lower when winters were warm and wet in western Europe and cool and dry in northwest Africa. Annual variation in the productivity of the population was positively correlated with June temperature, but not with an index of phenological mismatch. The 59% population decline appears largely to have been driven by reductions in adult survival, with local productivity poorly correlated with subsequent population change, suggesting a low degree of natal philopatry. Winter NAO was not significantly correlated with adult survival rates in a second, Scottish Borders population, studied for 12 years. Variation in climatic conditions alone does not therefore appear to be responsible for common sandpiper declines. Unlike some passerine migrants, there was no evidence for climate-driven reductions in productivity, although the apparent importance of immigration in determining local recruitment complicates the assessment of productivity effects. We suggest that further studies to diagnose common sandpiper declines should focus on changes in the condition of migratory stop-over or wintering locations. Where possible, these analyses should be repeated for other declining migrants.