Evolution of polyploidy and the diversification of plant-pollinator interactions

One of the major mechanisms of plant diversification has been the evolution of polyploid populations that differ from their diploid progenitors in morphology, physiology, and environmental tolerances. Recent studies have indicated that polyploidy may also have major effects on ecological interactions with herbivores and pollinators. We evaluated pollination of sympatric diploid and tetraploid plants of the rhizomatous herb Heuchera grossulariifolia (Saxifragaceae) along the Selway and Salmon Rivers of northern Idaho, USA, during four consecutive years. Previous molecular and ecological analyses had indicated that the tetraploid populations along these two river systems are independently derived and differ from each other in multiple traits. In each region, we evaluated floral visitation rate by all insect visitors, pollination efficacy of all major visitors, and relative contribution of all major pollinators to seed set. In both regions, diploid and tetraploid plants attracted different suites of floral visitors. Most pollination was attributable to several bee species and the moth Greya politella. Lasioglossum bees preferentially visited diploid plants at Lower Salmon but not at Upper Selway, queen Bombus centralis preferentially visited tetraploids at both sites, and worker B. centralis differed between sites in their cytotype preference. Hence, diploid and autotetraploid H. grossulariifolia plants act essentially as separate ecological species and may experience partial reproductive isolation through differential visitation and pollination by their major floral visitors. Overall the results, together with recent results from other studies, suggest that the repeated evolution of polyploidy in plants may contribute importantly to the structure and diversification of ecological interactions in terrestrial communities.     

Humic substances

GOALS, SCOPE AND BACKGROUND: Changing environmental conditions and handling stress are well known to cause chronic or acute stress situations in fish with subsequent infections. These requires a therapy by means of antibiotics and chemicals. In contrast to the huge number of pathogens, only a few substances are permitted for application as therapeutics in German aquaculture. Hence, there emerges an urgent need for highly effective and residueless alternatives. MAIN FEATURES: The prophylactic stimulation and training of the defense system of fish by alternative approaches becomes increasingly necessary. One approach is the application of dissolved humic substances (HS) of natural or artificial origin. For example, there exist several reports on the positive effect of HS to fishes. These effects shall be considered in detail. Furthermore, the impact of HS on the constitution of parasites and pathogens will be displayed. The reports on this issue are diverse, if not inconsistent. We try to shed some light on these discrepancies. The last aspect covered by this review is the outdated paradigm that calcium ions act as antidotes. In the presence of HS, even the opposite effect may occur. APPROACH: To overcome old paradigms on HS and their potential interactions with fish and fish parasites, we reviewed recent international literature, as well as 'grey' literature. We also include results from own former and ongoing studies. RESULTS AND DISCUSSION: HS are able to increase the physiological condition of the individuals and to reduce adverse physiological and histological consequences caused by stress; the mechanism behind remains obscure. HS detoxify heavy metals and organic pollutants. Damages caused by several fish pathogens, such as bacteria and parasites, can be repaired more quickly in the presence of HS. Some parasites--mainly fungi--appear to be directly affected by HS. Comparing the fungicidal effects of HS from various sources, evidence is increasing that the aliphatic moiety may be the effective structures. However, further research is necessary to relate more physiological and anti-pathogenic effects to the chemical characteristics of HS. CONCLUSIONS: HS are not real alternatives to strong traditional therapeutics. However, they show different advantages in repairing secondary, stress induced damages in fish. The ecophysiological relevance of HS in either aquatic systems or aquaculture is getting conspicuously. PERSPECTIVES: The lack of therapeutic and antiparasitic substances in aquaculture requires new strategies and ways of thinking. The search for alternatives to the 'traditional' chemical therapeutics calls for the intensive research. Inevitably, this search will lead to an intensive contemplation on HS as 'health promoting substances' and/or even therapeutics. Basic research is needed to detect the functional groups of the HS responsible for the effects observed. Health promoting effects of first investigations made in vitro to affect pathogens via application of HS and several field studies with HS raises hopes for a broader utilisation of HS to reduce stress consequences in fish and fish pathogens residuelessly.     

Seventh International Congress of Ecology: Symposium on “Trace Metals in the Environment” Florenz, Juli 1998

Der VII. Internationale Kongre? für ?kologie ergab die M?glichkeit, auch einige Spezialisten aus der ?kologischen Spurenelementforschung in Florenz zusammenzubringen. Dabei zeigte sich deutlich, da? noch wesentliche Arbeit auf dem Weg zu einem generellen Verst?ndnis der Wirkung einzelner Elemente und ihrer Spezies vor uns liegt. Obwohl auf analytischem Sektor beachtliche Durchbrüche durch die Entwicklung leistungsf?higer Methoden bewerkstelligt wurden, bleiben noch wichtige Fragen zur essentiellen und/oder toxikologischen Wirkung einzelner Spurenelemente zu beantworten. Hieraus lassen sich aus den Beitr?gen der Teilnehmer des Symposiums folgende Forderungen ableiten: