Global threats to human water security and river biodiversity.

Protecting the world's freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the world's population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.

Population structure in the freshwater shrimp (Paratya australiensis) inferred from allozymes and mitochondrial DNA.

In 1995, an allozyme study was conducted on the genetic structure of a population of the common atyid shrimp, Paratya australiensis, in the Conondale Range, south-eastern Queensland with two subcatchments each within two river drainages sampled. The allozyme study revealed a high degree of population structure, with the data interpreted as reflecting a pattern of restricted contemporary gene flow, primarily between streams within subcatchments. High levels of differentiation occurred between all subcatchments. In this study, we analysed a partial fragment of the mitochondrial COI gene in order to further test and verify these results. The mtDNA data largely conflicted with the hypothesis of restricted gene flow indicating that contemporary dispersal was highly unlikely, even between streams within subcatchments, with many sites fixed for unique mtDNA haplotypes. Additionally, the level of divergence between the Stony Creek subcatchment and all other sampling sites indicated that it had been isolated for approximately 2-3 million years, while low levels of divergence were detected across the Conondale Range between the Kilcoy and Booloumba Creek subcatchments. The sharing of alleles at certain allozyme loci between all subcatchments is, therefore, likely to be the result of ancestral retention and possibly because of the effects of balancing selection.

A hierarchical analysis of the genetic structure of an aquatic insect Bungona (Baetidae: Ephemeroptera).

Recent studies of the genetic structure of stream-dwelling organisms have suggested that fine-scale patterns are the consequence of patchy recruitment from a small number of matings and limited in-stream dispersal. Predictions of this hypothesis were tested by spatial and temporal analysis of the genetic structure of populations of a stream mayfly (Bungona sp: Baetidae) in subtropical streams in south-eastern Queensland. Significant departures from Hardy-Weinberg proportions occurred more often than would be predicted by chance alone and no consistent pattern was observed across sites, loci or sampling times. As in previous studies, the largest differentiation was observed at the smallest spatial scale (reaches within streams) on most sampling occasions. These data provide additional support for a patchy recruitment hypothesis. Despite the fine-scale population structure, there was evidence of widespread adult dispersal across the study region, especially between streams and subcatchments within the same block of continuous dense forest.

Corticosteroids and control of nasal salt gland function in the lizard Tiliqua rugosa.

The scincid lizard Tiliqua rugosa possesses a well-developed nasal gland composed of both mucoserous and salt-secreting cells. Confusion over its secretory capacities (see H. Saint- Girons , M. Lemire , and S. D. Bradshaw, 1977, Zoomorphologie 88, 277-288) has been resolved and NaCl- and KCl-injected animals can secrete a hyperosmotic fluid with an F/P ratio of about 3.6. The concentration of Na+ in the secretion varied from a mean of 434 mmol/liter when sodium loaded to 167 mmol/liter when potassium loaded. Potassium concentrations varied from 226 to 433 mmol/liter, respectively. Na:K ratios thus vary from 1.98 with NaCl loading to 0.42 with KCl loading, demonstrating the gland's capacity to vary the nature of the secretion. Rates of fluid production did not differ significantly between NaCl- and KCl-loaded individuals and varied from 13.3 to 19.6 microliter (100 x g hr)-1. Adjacent studies on the north African agamid lizard Uromastix acanthinurus suggested that aldosterone may influence the rate and composition of the nasal gland secretions and this possibility was investigated in Tiliqua by hormone binding studies. High affinity binding for both corticosterone and aldosterone was demonstrated during the breeding season, with a Kd of 5.2 x 10(-9) and 12.9 x 10(-9) M, respectively. Binding of aldosterone to nasal gland receptors was not evident in nonbreeding animals and the binding of corticosterone was primarily nonspecific in these individuals. These data suggest that hormone receptor concentrations and affinity vary on a seasonal basis and in concert with reproductive activity.