Accelerated body size evolution in upland environments is correlated with recent speciation in South American freshwater fishes.

Speciation rates vary greatly among taxa and regions and are shaped by both biotic and abiotic factors. However, the relative importance and interactions of these factors are not well understood. Here we investigate the potential drivers of speciation rates in South American freshwater fishes, the most diverse continental vertebrate fauna, by examining the roles of multiple biotic and abiotic factors. We integrate a dataset on species geographic distribution, phylogenetic, morphological, climatic, and habitat data. We find that Late Neogene-Quaternary speciation events are strongly associated with body-size evolution, particularly in lineages with small body sizes that inhabit higher elevations near the continental periphery. Conversely, the effects of temperature, area, and diversity-dependence, often thought to facilitate speciation, are negligible. By evaluating multiple factors simultaneously, we demonstrate that habitat characteristics associated with elevation, as well as body size evolution, correlate with rapid speciation in South American freshwater fishes. Our study emphasizes the importance of integrative approaches that consider the interplay of biotic and abiotic factors in generating macroecological patterns of species diversity.

Effect of Productivity on Community Size Explains the Latitudinal Diversity Gradient of South American Small Mammals.

AbstractAlthough many studies have shown that species richness increases from high to low latitudes (the latitudinal diversity gradient), the mechanisms responsible for generating and maintaining higher species richness in the tropics remain intensely debated. Here we investigate how the effects of temperature on speciation rates (kinetic effects) and the effects of productivity on community size (chemical effects) explain the latitudinal diversity gradient of South American small mammals. We implemented Bayesian models that integrate processes from the neutral and metabolic theories, comparing model predictions with empirical richness patterns. The neutral-metabolic model predicted the latitudinal richness gradient in South American small mammals. We found evidence that the effects of productivity on community size are more important for explaining differences in species richness than the effects of temperature on speciation rates. These results suggest that differences in species richness along latitudinal gradients are regulated primarily by the chemical effects of productivity on speciation-extinction dynamics.

The scale-dependent effect of environmental filters on species turnover and nestedness in an estuarine benthic community.

Environmental filtering is a major mechanism structuring ecological communities. However, it is still not clear how different abiotic drivers composing the environmental filter interact with each other to determine local species assemblage and create spatial patterns in species distribution. Here, we evaluated the effects of two strong and uncorrelated environmental variables (salinity and sediment properties) on the ß-diversity of an estuarine macrobenthic community while accounting for spatial effects. Our results show that the benthic community composition has a strong spatial structure along the estuary, which can be greatly explained by salinity and sediment variation. Salinity is most associated with species replacement (turnover), whereas sediment is more important for species loss (nestedness). However, the effects of sediment variation on nestedness are mainly detected at a smaller spatial scale (estuarine sectors), whereas the effects of salinity on species turnover are stronger as spatial scale increases (entire estuary). Our findings suggest that environmental filters can drive both turnover and nestedness components of ß-diversity, but that their relative importance depends on the spatial scale of investigation. Although abiotic drivers associated with detrimental effects (sediment) usually result in nestedness, larger spatial scales encompass abiotic drivers associated with different suitable conditions (salinity), increasing the relative importance of the replacement component of species ß-diversity.

Description of the imago of Neocapritermes utiariti (Isoptera: Termitidae: Termitinae).

The neotropical termite genus Neocapritermes Holmgren (1912) was revised by Krishna & Araujo (1968), who recognized 14 valid species. Two additional species were described by Constantino (1991), and another one by Bandeira & Cancello (1992). However, the imago of most species of Neocapritermes remain unknown. In this paper we describe for the first time the imago of Neocapritermes utiariti based on specimens from the State of Rondônia, Brazil. The examined material will be deposited in the Invertebrate Collection of the Instituto Nacional de Pesquisas da Amazônia, in Manaus, Amazonas, Brazil (INPA). Comparisons with other imagoes of Neocapritermes were made based on descriptions and figures from Krishna & Araújo (1968). The measurements were taken with an ocular micrometer following Roonwal's (1970) system of morphometric characters.

Prezygotic resource-allocation dynamics and reproductive trade-offs in Calymperaceae (Bryophyta).

PREMISE OF THE STUDY: Resource allocation is difficult to characterize in plants because of the challenges of quantifying gametes and propagules. We surveyed six sympatric, unisexual species in the family Calymperaceae (Bryophyta) to test for trade-offs in prezygotic sexual and asexual expression and density-dependent survivorship of female gametangia. METHODS: We tallied gametangial and asexual propagule output for 1820 shoots from 17 populations of six species at monthly intervals during one year (2010-2011) in a central Amazonian forest. Generalized linear mixed models were used to test for trade-offs in sexual and asexual expression and density-dependent senescence probability of gametangia. Precipitation and microsite variables were also included in the model. KEY RESULTS: For all species, sexual and asexual expression were positively correlated with mean monthly precipitation. Asexually expressing shoots produced significantly fewer gametangia than nonexpressing ones, and the probability of senescence increased with shoot density. Archegonium density per shoot was also consistently lower than the modeled optimum to maximize the number of receptive archegonia. CONCLUSIONS: Trade-offs among reproductive strategies and positive density-dependent senescence of female gametangia suggest that prezygotic sexual and asexual expression come at a tangible investment. However, the apparently inefficient resource-allocation dynamics in the production of female gametangia makes the possible advantages of squandering such investments unclear. One possibility is that the study populations, like those of many dioicous mosses, are skewed toward expressing females with low sporophyte production, which would suggest that asexual reproduction predominates and upstages efficient resource allocation in prezygotic investment.