RESUMO
Understanding the effects of predators and resources on primary producers has been a major focus of interest in ecology. Within this context, the trophic cascade concept especially concerning the pelagic zone of lakes has been the focus of the majority of these studies. However, littoral food webs could be especially interesting because base trophic levels may be strongly regulated by consumers and prone to be light limited. In this study, the availability of nutrients and light and the presence of an omnivorous fish (Hyphessobrycon bifasciatus) were manipulated in enclosures placed in a humic coastal lagoon (Cabiúnas Lagoon, Macaé - RJ) to evaluate the individual and interactive effects of resource availability (nutrients and light) and food web configuration on the biomass and stoichiometry of periphyton and benthic grazers. Our findings suggest that light and nutrients interact to determine periphyton biomass and stoichiometry, which propagates to the consumer level. We observed a positive effect of the availability of nutrients on periphytic biomass and grazers' biomass, as well as a reduction of periphytic Câ¶Nâ¶P ratios and an increase of grazers' N and P content. Low light availability constrained the propagation of nutrient effects on periphyton biomass and induced higher periphytic Câ¶Nâ¶P ratios. The effects of fish presence strongly interacted with resource availability. In general, a positive effect of fish presence was observed for the total biomass of periphyton and grazer's biomass, especially with high resource availability, but the opposite was found for periphytic autotrophic biomass. Fish also had a significant effect on periphyton stoichiometry, but no effect was observed on grazers' stoichiometric ratios. In summary, we observed that the indirect effect of fish predation on periphyton biomass might be dependent on multiple resources and periphyton nutrient stoichiometric variation can affect consumers' stoichiometry.
Assuntos
Biomassa , Carbono/metabolismo , Cadeia Alimentar , Nitrogênio/metabolismo , Fósforo/metabolismo , Animais , Processos Autotróficos/efeitos da radiação , Clorofila/metabolismo , Clorofila A , Luz , Caramujos/fisiologia , Caramujos/efeitos da radiação , ÁguaRESUMO
The three brown banded land snail genus Humboldtiana (Pulmonata: Humboldtianidae) comprises 50 species of insular distribution from southern Texas to central México; its low vagility and dispersal potential are reflected in high levels of endemism and highly restricted distributions. A current scheme of classification recognizes six subgenera: Polyomphala, Oreades, Gymnopallax, Clydonacme, Aglotrochus, and Humboldtiana (the latter containing three species groups). In the present work, mitochondrial 16S rDNA and partial ITS region and ribosomal large subunit (5.8S+ITS-2+28S) sequences from 26 recognized species and 2 populations of unknown identity were studied to assess phylogenetic relationships of Humboldtiana species using parsimony and Bayesian analysis, and AU test was used to compare the different phylogenetic hypotheses. The same four major clades were recovered by both methods (buffoniana, queretaroana, montezumae and fortis), although none of them support the current scheme of classification, with the only exception being the subgenus Gymnopallax included in the clade buffoniana. The results suggest that speciation patterns observed in the genus Humboldtiana could be explained as a morphostatic radiation.
Assuntos
Filogenia , Caramujos/classificação , Caramujos/genética , Animais , Demografia , Feminino , Marcadores Genéticos , Variação Genética , México , RNA Ribossômico 16S/análise , RNA Ribossômico 28S/análise , Subunidades Ribossômicas Maiores/genética , Caramujos/anatomia & histologia , Caramujos/efeitos da radiaçãoRESUMO
The amount of solar radiation absorbed by an organism is a function of the intensity of the radiation and the area of the organism exposed to the source of the radiation. Since the prosobranch gastropod Echinolittorina peruviana is longer than it is wide, its areas of the lateral sides are approximately twice as large as the areas of the frontal and dorsal faces. We quantified the orientation of the intertidal prosobranch E. peruviana with respect to the position of the sun and solar heat gain in the different orientations. In the field, 80.9% of the E. peruviana monitored on sunny summer days tended to face the sun frontally or dorsally while only 19.1% faced the sun with the larger lateral sides. On overcast summer or on winter days, this trend was not observed. We then show that the body temperature of individuals increases more rapidly and reaches higher equilibriums when the lateral sides are facing the sun than when they face the sun with either of the smaller frontal or dorsal sides. These results therefore show that the orientation behavior of E. peruviana is thermoregulatory and that it permits the organisms to maintain lower temperatures on hot summer days.
Assuntos
Regulação da Temperatura Corporal/fisiologia , Caramujos/fisiologia , Animais , Comportamento Animal/efeitos da radiação , Chile , Locomoção , Caramujos/efeitos da radiação , Luz SolarRESUMO
The dominant lethal effects of gamma radiation of 60Co in the snail Biomphalaria glabrata were studied. Three groups of 13 wild-type snails were irradiated with single doses of 2.5; 10 and 20 Gy. Crossings were carried out at intervals of 7, 17, 23, 30 and 36 days after irradiation. The dominant lethal effect was observed only at the first crossing occurring 7 days after irradiation with 2.5 Gy. With 10 and 20 Gy, the induction of lethal mutations was detected at 7, 17 and 23 days after irradiation; a dose-response effect was observed. The effect was stronger 7 days after irradiation, decreasing in the succeeding crossings up to 30 days. Cell-killing effects on germ cells were detected in the crossings at 23 days and 30 days after irradiation with 20 Gy. After 36 days, frequencies of malformations resumed background levels; crossing rates partially recovered. These results show that gamma radiation affected all the stages of spermatogenesis. Germ cells at later phases were more sensitive to the mutagenic effect of radiation and the cell killing effects were observed on the youngest cells. This response was similar to the highly homogeneous pattern observed in widely different species and allowed us to estimate some parameters of spermatogenesis in B. glabrata.