Evolutionary responses to environmental heterogeneity in central american echinoid larvae: plastic versus constant phenotypes

Do changes in food resources lead to evolutionary changes in phenotypic plasticity or in different constant phenotypes? I addressed this question by studying plasticity of larval feeding arms for “geminate species pairs” in three echinoid genera. These closely related species were geographically isolated when the Panamanian Isthmus raised 2.8–3.1 million years ago, creating two different food level environments: high but variable food levels in the eastern Pacific versus chronically low food levels in the western Caribbean. I reared larvae of geminate species in different replicated food environments for 10 days postfertilization, collected morphological measurements of individual arm and body lengths, and calculated degrees of plasticity of relative arm length for each species. In contrast to previous studies with temperate echinoids, there was no significant plasticity of arm length in either the Pacific or Caribbean species considered here. Caribbean species, however, had significantly longer relative arm lengths than Pacific species, regardless of food levels. These results suggest that historical changes in food levels have led to the evolution of constant rather than plastic differences between Pacific and Caribbean echinoids. The evolution of plasticity may be limited by the timing of reproduction or by egg size in this system.     

Nutrient content of incident rainfall,throughfall and stemflow in a Nigerian secondary lowland rainforest

Abstract. Nutrient content of rainfall, throughfall and stemflow was studied over one year in the open and under the crowns of three tree species in a secondary rain forest at Ile‐Ife, Nigeria. Throughfall and stemflow comprised 78.8 % and 5.2 % respectively; 16.0 % of the incident rainfall was intercepted by the forest canopy. The concentrations of various nutrient elements in throughfall and stemflow were higher than those of incident rainfall. In throughfall and stemflow potassium concentration was highest and that of ammonium nitrogen was the lowest. Only calcium and sodium concentrations showed significant monthly variation in incident rainfall. Ca, Mg, K. Cu and P showed significant monthly variation in throughfall and stemflow. The concentrations of the elements were highest during the heavy‐rain months (May‐September). High concentrations of some of the elements were recorded also in November, the last rain month and the beginning of the dry season. The concentration of these elements in stemflow and throughfall was affected by tree species. The highest quantity of each element was deposited in the forest via throughfall followed by incident precipitation and the lowest via stemflow. The tree species affected the quantities of these elements by the volume of their stemflow and throughfall and the concentration of the various elements herein. Total nutrient concentration was much higher than available (dissolved) nutrient concentration. This was very pronounced with micronutrients.     

Allelopathic potential of Zilla spinosa on growth of associate flowering plants and some rhizosphere fungi

Zilla spinosa plant part extracts exhibited significantly different inhibitory effect on the seed germination and seedling growth of its associate species. Shoot extract reduced the percentage germination and seedling length of different test species more than root extract. Except of Z. coccineum, seedling growth was more sensitive than seed germination. Shoot/root ratio of all test species increased significantly with increase in extract concentration. Mycelia growth of the two rhizosphere fungal species was more significantly reduced by Z. spinosa shoot extract than root extract. The effects of the different extracts on total protein and total carbohydrate contents of the two test species were comparable. Non-significant increase was recorded at low concentration of both shoot and root extract. However, with the rise of extract concentration, highly significant reduction in the content of these metabolites was recorded. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evidence for positive density-dependent effects in recovering Diadema antillarum populations

Recovering populations may experience positive density-dependent feedbacks that contribute to population increases. Diadema antillarum, a keystone herbivore on Caribbean coral reefs, suffered a well-documented mass mortality in 1983-84. High densities of adults of this long-spined urchin could provide effective refuge from predation for juveniles under a spine canopy, as has been suggested for other urchin species. We evaluated the effect of adult density on juvenile persistence of D. antillarum experimentally, and examined size-frequency distributions of recovering local populations for evidence of positively density-dependent juvenile persistence at St. Croix, U.S. Virgin Islands. Juvenile persistence was significantly higher in high adult density treatments, and bimodal population size distributions also suggest potential positive effects of adult density on juveniles. This positive feedback could accelerate the recovery of this important coral reef grazer.     

Postmetamorphic Growth and Metabolism of Long-Spined Black Sea Urchin (Diadema antillarum) Reared in the Laboratory

Postmetamorphic growth and metabolism measurements were obtained on two cohorts of laboratory-reared Diadema antillarum. The cohorts grew linearly from less than 1 mm to over 43 mm. Daily growth averaged 0.097 and 0.11 mm d^?1, respectively, for the two cohorts, and was found to differ significantly. Urchin metabolism was examined by a series of simultaneous measurements of oxygen consumption and ammonium excretion over 16 days on starved juveniles ranging 16.5 to 18.3 mm. Metabolic activity under conditions of starvation was used as a test of the viability of urchins reared in the laboratory with cultured food resources. Catabolic activity differed from the first week of starvation compared to the second. Metabolic response included: (1) a 2.2-fold increase in oxygen consumption rate; (2) 50% decline in ammonium excretion rate; and (3) a 5.1-fold increase in oxygen to nitrogen ratio. These measurements are consistent with a shift from almost pure protein catabolism during the first seven days of starvation to a lipid : protein catabolic ratio of 1 : 1 after the first week. Growth and metabolism experiments of this type are seen as a first step towards optimizing laboratory culture techniques of this species.     

The African cherry (Prunus Africana): From hoe-handles to the international Herb Market

I studied the uses of the African cherry (Prunus africana) by four ethnic groups who live near the Kilum-Ijim Forest Preserve on Mount Oku, Cameroon. Prunus africana is valued for its timber, which is used for tool handles and for fuel, and it is an important wildlife food. However, its greatest value is for traditional medicines. Healers use the bark and leaves to treat more than 30 human ailments and several animal diseases and it is the most important plant used in their practices. This study is the first to document this importance, particularly for animal medicines. I also examined the growing worldwide herbal use to treat benign prostatic hyperplasia. Market demand has caused resource depletion and an erosion of traditional resource protection practices. Preservation of the species will depend on sustainable harvesting methods and on cultivation.

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La Cerise Africaine (Prunus Africana): Du Manche De Houe Au Marche International D’herbes

Résumé  J’ai etudié I’emploi de la cerise africaine (Prunus africana) par quatre groupes ethniques residant prés de la préserve forestiére Kilum-Ijim surle Mont Oku, au Cameroun. Prunus africana est prisé pour son bois, qui est utilisé pour fabriquer des manches d’outils, et comme combustible. C’est également un aliment important pour la faune sauvage. Pourtant, sa plus grande valeur est dans la medecine traditionnelle. Les guerisseurs en utilisent l’écorce et les feuilles pour trailer plus de 30 maladies humaines et plusieurs maladies animates; c’est la plante la plus importante utilisée dans leurs cures. Cette étude est la premiére á documenter cette importance, particuliérement dans le domaine des médicaments pour les animaux. J’ai aussi examiné son usage mondial croissant comme traitement de I’hypertrophie bénigne de la prostate. La demande économique a causé une dépletion des ressources et une érosion des pratiques traditionnelles de protection des ressources. La préservation de cette espéce exigera des méthodes de moisson soutenables ainsi que la cultivation.