Effect of Landscape Structure on Species Diversity

The effects of habitat fragmentation and their implications for biodiversity is a central issue in conservation biology which still lacks an overall comprehension. There is not yet a clear consensus on how to quantify fragmentation even though it is quite common to couple the effects of habitat loss with habitat fragmentation on biodiversity. Here we address the spatial patterns of species distribution in fragmented landscapes, assuming a neutral community model. To build up the fragmented landscapes, we employ the fractional Brownian motion approach, which in turn permits us to tune the amount of habitat loss and degree of clumping of the landscape independently. The coupling between the neutral community model, here simulated by means of the coalescent method, and fractal neutral landscape models enables us to address how the species–area relationship changes as the spatial patterns of a landscape is varied. The species–area relationship is one of the most fundamental laws in ecology, considered as a central tool in conservation biology, and is used to predict species loss following habitat disturbances. Our simulation results indicate that the level of clumping has a major role in shaping the species–area relationship. For instance, more compact landscapes are more sensitive to the effects of habitat loss and speciation rate. Besides, the level of clumping determines the existence and extension of the power-law regime which is expected to hold at intermediate scales. The distributions of species abundance are strongly influenced by the degree of fragmentation. We also show that the first and second commonest species have approximately self-similar spatial distributions across scales, with the fractal dimensions of the support of the first and second commonest species being very robust to changes in the spatial patterns of the landscape.     

Shorter telomeres may mark early risk of dementia: preliminary analysis of 62 participants from the nurses' health study

Background

Dementia takes decades to develop, and effective prevention will likely require early intervention. Thus, it is critical to identify biomarkers of preclinical disease, allowing targeting of high-risk subjects for preventive efforts. Since telomeres shorten with age and oxidative stress, both of which are important contributors to the onset of dementia, telomere length might be a valuable biomarker.

Methodology/Principal Findings

Among 62 participants of the Nurses'' Health Study, we conducted neurologic evaluations, including patient and caregiver interviews, physical exam, neurologic exam, and neuropsychologic testing. We also conducted magnetic resonance imaging (MRI) in a sample of 29 of these women. In these preliminary data, after adjustment for numerous health and lifestyle factors, we found that truncated telomeres in peripheral blood leukocytes segregate with preclinical dementia states, including mild cognitive impairment (MCI); the odds of MCI were 12-fold higher (odds ratio = 12.00, 95% confidence interval 1.24–116.5) for those with shorter telomere length compared to longer telomere length. In addition, decreasing telomere length was strongly related to decreasing hippocampal volume (p = 0.038).

Conclusions

These preliminary data suggest that telomere length may be a possible early marker of dementia risk, and merits further study in large, prospective investigations.     

The phylogenetic position of Allocreadiidae (Trematoda: Digenea) from partial sequences of the 18S and 28S ribosomal RNA genes

Species of Allocreadiidae are an important component of the parasite fauna of freshwater vertebrates, particularly fishes, and yet their systematic relationships with other trematodes have not been clarified. Partial sequences of the 18S and 28S ribosomal RNA genes from 3 representative species of Allocreadiidae, i.e., Crepidostomum cooperi, Bunodera mediovitellata, and Polylekithum ictaluri, and from 79 other taxa representing 78 families of trematodes obtained from GenBank, were used in a phylogenetic analysis to address the relationships of Allocreadiidae with other plagiorchiiforms/plagiorchiidans. Maximum parsimony and Bayesian analyses of combined 18S and 28S rRNA gene sequence data place 2 of the allocreadiids, Crepidostomum cooperi and Bunodera mediovitellata, in a clade with species of Callodistomidae and Gorgoderidae, which, in turn is sister to a clade containing Polylekithum ictaluri and representatives of Encyclometridae, Dicrocoelidae, and Orchipedidae, a grouping supported by high bootstrap values. These results suggest that Polylekithum ictaluri is not an allocreadiid, a conclusion that is supported by reported differences between its cercaria and that of other allocreadiids. Although details of the life cycle of callodistomids, the sister taxon to Allocreadiidae, remain unknown, the relationship of Allocreadiidae and Gorgoderidae is consistent with their larval development in bivalve, rather than gastropod, molluscs, and with their host relationships (predominantly freshwater vertebrates). The results also indicate that, whereas Allocreadiidae is not a basal taxon, it is not included within the suborder Plagiorchiata. No support was found for a direct relationship between allocreadiids and opecoelids either.     

Spatial relationships between cacti and nurse shrubs in a semi-arid environment in central Mexico

Abstract. The Zapotitlán de las Salinas valley, central Mexico, harbours a high diversity of cacti. Pattern analysis indicated that the establishment of two columnar cacti, Neobuxbaumia tetetzo and Cephalocereus hoppenstedtii, and of three small globose cacti, Coryphantapallida, Mammillaria colina andM casoi, is aggregated and associated with perennial nurse shrubs. Some nurse species, Castela tortuosa, Caesalpinia melanadenia and Eupatorium spinosarum have a higher number of cacti beneath their canopies than would be expected by chance. A replacement pattern was found between the columnar cacti and their nurses, an aspect which was not found with the globose cacti. Following the assumption that protection against excessive radiation is the main factor determining the nurse effect, the azimuth orientation of the cacti with respect to their nurses was evaluated. Only Coryphanta pallida presented a non-random distribution with a tendency towards the North and West. The difference in maximum temperature between the soil surface under the different nurse species and of open spaces, which is reached at midday, was 16 °C. No significant differences were found in beneath-canopy temperatures for the three nurse species considered. Soil nitrogen levels were significantly lower beneath the different nurse plants than in open spaces. This result suggests that soil fertility is not an important factor in the nurse-plant phenomenon in Zapotitlán.     

Environmental and anthropogenic factors associated with coastal wetland differentiation in La Mancha,Veracruz, Mexico

At least 10% of the wetlands in Mexico are situated in the State of Veracruz on the central Gulf coast. The region has been intensively used for agriculture by humans for the last thousand years and today pastureland for cattle ranching is the dominant element of the landscape. We present a study of the wetland vegetation in a series of representative and internationally significant freshwater wetlands near the coastal lagoon La Mancha in Veracruz State. We obtained eleven wetland types formed by three wetland communities dominated by trees (mangrove or swamps), eight dominated by herbaceous species which we classified as marsh, five of which were native emergent marsh, one was a non-native emergent marsh and two were floating-leaved marsh. The highest diversity values were found in the Annona swamp, followed by the Sagittaria marsh and the Rhizophora–Laguncularia–Avicennia mangrove. CCA ordination showed that water level, disturbance and species number were the major factors explaining variation along axis 1, and on axis 2 conductivity, salinity, and bulk density. Wetland size was a major factor in both axes. We examined the interplay of intrinsic and extrinsic factors that give rise to the nature and diversity of wetland types that characterize the important wetland landscapes in this part of Mexico, being disturbance by human activities an important factor that favors the appearance of diverse species combinations.     

Mouse bone marrow cytogenetic damage produced by residues of tequila

Five concentrations (50-860 mg/kg) of residues obtained after distillation and lyophilization of commercial tequila were injected into mice for evaluation of chromosome aberrations, sister-chromatid exchanges, and proliferation kinetics in mouse bone marrow cells. Appropriate positive and negative controls were included. Our results showed significant dose-related increases of chromosomal aberrations starting at 50 mg/kg and for sister-chromatid exchanges at 430 mg/kg. Cellular proliferation kinetics showed no alterations. With these data we demonstrated that the residues of tequila are genotoxic in vivo.     

Growth, metabolic rate, and digestive enzyme activity in the white shrimp Litopenaeus setiferus early postlarvae fed different diets

Growth rate, soluble-protein content, oxygen consumption, ammonia excretion, and digestive-enzyme activity were studied in Litopenaeus setiferus early postlarvae under four feeding regimens that included combinations of freshly hatched Artemia nauplii, microparticulate commercial diet, and algae. Growth and of postlarvae fed a mixed diet were significantly higher. Artificial diet used alone caused the lowest growth, lowest soluble-protein content, higher ammonia excretion, lowest O:N ratio, and higher proteolytic and amylase activities. The artificial diet stimulated proteolytic activity and ammonia excretion of postlarvae, apparently in response to some deficiency in protein composition of the diet. Based on results in growth, soluble-protein content, enzymatic activity, and metabolic substrate, we determined that partial substitution of Artemia nauplii by artificial diet, with or without addition of algae when rearing early postlarval stages, will benefit the growth and nutritional state of L. setiferus postlarvae.