An Analysis of Frequency as a Factor Contributing to the Diffusion of Variable Phenomena

Paper presented at the 13th Hispanic Linguistics Symposium, October 21-24, 2009, Universidad de Puerto Rico.This investigation examines the behavior of intervocalic dental fricative deletion in past-participle contexts versus all other instances, as well as palato-alveolar fricative devoicing to determine the effect of frequency. The evidence found reveals that lexical frequency and type frequency are relevant to explain rates of deletion in the case of intervocalic dental fricative. High frequency tokens show more deletion than less frequent ones. Past participles ending in -ado reflect the influence of high type frequency. Regarding devoicing of the palato-alveolar fricative, words that occur more frequently in contexts favoring the devoicing also devoice at a higher rate in disfavoring contexts as the phenomenon is spreading from favoring contexts to disfavoring ones. Furthermore, in the disfavoring context, low frequency words devoice at a higher rate than high frequency words. The evidence presented contributes to the growing body of studies regarding frequency effects on Spanish phonological processes

The variable effect of form and lemma frequencies on phonetic variation: evidence from /s/ realization in two varieties of Colombian Spanish

Research has shown that frequency conditions the variable realization of sounds. However, the literature has not addressed whether the frequency of the individual word forms, or form frequency, has a larger conditioning effect than the combined frequencies of the members of the paradigm to which the forms belong, or lemma frequency. Monofactorial correlation tests and monofactorial and multifactorial linear regression analyses are performed on 2,734 tokens of Spanish /s/ in sociolinguistic interviews conducted in Cali and Barranquilla, Colombia. Two findings are highlighted: (1) frequency is only significant in the variety of Spanish that has low overall rates of /s/ reduction, Cali, and (2) form frequency is more influential than lemma frequency

Variable Degrees of Constituency: Frequency Effects in the Alternation of pa vs. para in Spoken Discourse

Paper presented at the 14th Hispanic Linguistics Symposium, October 14-17, 2010, Indiana University.This study examines how repetition in discourse determines variable degrees of constituency between the preposition para 'to, for' and surrounding words, thus predicting greater reduction of para in cases where the degree of constituency is tightest. Our study contributes to the overall understanding of the role of usage in explaining reductive phonetic processes in contemporary Spanish. The findings of this corpus-based study of Caracas Spanish reveal that the frequency of the collocation is a key factor in predicting reduction of the form para. Further, frequency of use is a better explanation for the reduction of para than more traditional variables such as phonetic context. This result provides evidence to support the hypothesis that frequent combinations are accessed as autonomous units, due to their tighter degree of constituency, as in the case of I don't know in American English (Bybee and Scheibman 1999)

Going Retro: An Analysis of the Interplay between Socioeconomic Class and Age in Caracas Spanish

Paper presented at the 5th Workshop on Spanish Sociolinguistics, April 8-10, 2010, North Carolina State University.Socioeconomic class, whose definition in sociolinguistic studies often incorporates a range of variables such as education level, income, occupation, and residential area, amongst others, has been shown to be of profound importance in the patterning of sociolinguistic variation (Ash 2004, Labov 1972, Trudgill 1974). However, although education has often been argued to play a large role in the social stratification of sociolinguistic variables in the sociolinguistic literature, the influence of generational change in access to education has never been fully explored. The purpose of this study is to examine the influence of socioeconomic class and age in the patterning of linguistic behavior in the Spanish spoken in Caracas, Venezuela. To this end we examine syllable-final /ɾ/ deletion, intervocalic /ɾ/ deletion in para 'for', and intervocalic /d/ deletion. The findings of this investigation reveal that upper and middle class speakers are less likely to use vernacular variants of all three variables than the lower socioeconomic speakers in the speech community. This behavior of the upper and middle class in contrast with the working class in Caracas Spanish can in part be explained as a consequence of changes in access to education and occupation. Furthermore, as access to education increases in younger generations, a sharp rise in the use of the normative variants is reflected in the lowest socioeconomic class

Constraining uncertainties of diazotroph biogeography from <i>nifH</i> gene abundance

Marine diazotrophs fix dinitrogen gas into bioavailable nitrogen that drives the ocean nitrogen cycle; yet, efforts to infer global diazotroph distributions have been limited by a sparsity of observations. In situ measurements of nifH gene abundance (essential for nitrogen fixation) are increasingly being used to inform the biogeography of diazotrophs. However, comparing such gene abundances spatially, temporally and between diazotroph species remains difficult. We synthesize existing data on gene-to-cell and cell-to-biomass conversions for four major diazotroph groups to convert nifH gene counts to abundance- and biomass-based biogeographic "currencies." Results suggest up to two orders of magnitude uncertainty converting from nifH gene abundance to cell abundance, and up to four orders of magnitude uncertainty from nifH gene abundance to biomass. Uncertainty arises due to large taxonomic variation in cell size and presumed polyploidy, that is, variability in the number of genomes per cell. Such uncertainties hinder comparing biogeographies of different species. Additionally, numerical models need biogeographies for validation, typically in the currency of carbon biomass. Here, we show that conversion uncertainty from nifH gene abundance to biomass overwhelms biomass variability simulated in such models. These results demonstrate a basic currency problem in converting gene abundance observations to biogeographically meaningful quantities for synthesizing studies and modeling approaches. Such issues may also have relevance to other genes and organisms beyond diazotrophs. To avoid biases in interpreting gene counts as a measure of abundance, we suggest converting gene counts to a binary presence/non-detect metric to map broad biogeographical distributions more robustly.ISSN:0024-3590ISSN:1939-559

Non-cyanobacterial diazotrophs: global diversity, distribution, ecophysiology, and activity in marine waters.

Biological dinitrogen (N2) fixation supplies nitrogen to the oceans, supporting primary productivity, and is carried out by some bacteria and archaea referred to as diazotrophs. Cyanobacteria are conventionally considered to be the major contributors to marine N2 fixation, but non-cyanobacterial diazotrophs (NCDs) have been shown to be distributed throughout ocean ecosystems. However, the biogeochemical significance of marine NCDs has not been demonstrated. This review synthesizes multiple datasets, drawing from cultivation-independent molecular techniques and data from extensive oceanic expeditions, to provide a comprehensive view into the diversity, biogeography, ecophysiology, and activity of marine NCDs. A NCD nifH gene catalog was compiled containing sequences from both PCR-based and PCR-free methods, identifying taxa for future studies. NCD abundances from a novel database of NCD nifH-based abundances were colocalized with environmental data, unveiling distinct distributions and environmental drivers of individual taxa. Mechanisms that NCDs may use to fuel and regulate N2 fixation in response to oxygen and fixed nitrogen availability are discussed, based on a metabolic analysis of recently available Tara Oceans expedition data. The integration of multiple datasets provides a new perspective that enhances understanding of the biology, ecology, and biogeography of marine NCDs and provides tools and directions for future research

Non-cyanobacterial diazotrophs: global diversity, distribution, ecophysiology, and activity in marine waters

25 pages, 7 figures, 2 tables, supplementary data https://doi.org/10.1093/femsre/fuac046Biological dinitrogen (N2) fixation supplies nitrogen to the oceans, supporting primary productivity, and is carried out by some bacteria and archaea referred to as diazotrophs. Cyanobacteria are conventionally considered to be the major contributors to marine N2 fixation, but non-cyanobacterial diazotrophs (NCDs) have been shown to be distributed throughout ocean ecosystems. However, the biogeochemical significance of marine NCDs has not been demonstrated. This review synthesizes multiple datasets, drawing from cultivation-independent molecular techniques and data from extensive oceanic expeditions, to provide a comprehensive view into the diversity, biogeography, ecophysiology, and activity of marine NCDs. A NCD nifH gene catalog was compiled containing sequences from both PCR-based and PCR-free methods, identifying taxa for future studies. NCD abundances from a novel database of NCD nifH-based abundances were colocalized with environmental data, unveiling distinct distributions and environmental drivers of individual taxa. Mechanisms that NCDs may use to fuel and regulate N2 fixation in response to oxygen and fixed nitrogen availability are discussed, based on a metabolic analysis of recently available Tara Oceans expedition data. The integration of multiple datasets provides a new perspective that enhances understanding of the biology, ecology, and biogeography of marine NCDs and provides tools and directions for future researchThis work was supported by the National Science Foundation (grant number OCE-2023498 to K.A.T.-K., and OCE-2023278 to K.R.A., Stanford); the Simons Foundation (award ID 824082 to J.P.Z.); Simons Collaboration on Ocean Processes and Ecology (SCOPE, award ID 724220 to J.P.Z.); 'La Caixa' Foundation (ID 100010434, grant 105090 to F.M.C.-C.); the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie (grant 847648 to F.M.C.-C.]; and the ‘Severo Ochoa Centre of Excellence’ accreditation through the Spanish Government (grant CEX2019-000928-S to F.M.C.-C.)Peer reviewe

Multiple biotic interactions establish phytoplankton community structure across environmental gradients

AbstractThe combination of taxa and size classes of phytoplankton that coexist at any location affects the structure of the marine food web and the magnitude of carbon fluxes to the deep ocean. But what controls the patterns of this community structure across environmental gradients remains unclear. Here, we focus on the North East Pacific Transition Zone, a ~ 10° region of latitude straddling warm, nutrient‐poor subtropical and cold, nutrient‐rich subpolar gyres. Data from three cruises to the region revealed intricate patterns of phytoplankton community structure: poleward increases in the number of cell size classes; increasing biomass of picoeukaryotes and diatoms; decreases in diazotrophs and Prochlorococcus; and both increases and decreases in Synechococcus. These patterns can only be partially explained by existing theories. Using data, theory, and numerical simulations, we show that the patterns of plankton distributions across the transition zone are the result of gradients in nutrient supply rates, which control a range of complex biotic interactions. We examine how interactions such as size‐specific grazing, multiple trophic strategies, shared grazing between several phytoplankton size classes and heterotrophic bacteria, and competition for multiple resources can individually explain aspects of the observed community structure. However, it is the combination of all these interactions together that is needed to explain the bulk compositional patterns in phytoplankton across the North East Pacific Transition Zone. The synthesis of multiple mechanisms is essential for us to begin to understand the shaping of community structure over large environmental gradients.</jats:p

Multiple biotic interactions establish phytoplankton community structure across environmental gradients

Abstract: The combination of taxa and size classes of phytoplankton that coexist at any location affects the structure of the marine food web and the magnitude of carbon fluxes to the deep ocean. But what controls the patterns of this community structure across environmental gradients remains unclear. Here, we focus on the North East Pacific Transition Zone, a ~ 10° region of latitude straddling warm, nutrient‐poor subtropical and cold, nutrient‐rich subpolar gyres. Data from three cruises to the region revealed intricate patterns of phytoplankton community structure: poleward increases in the number of cell size classes; increasing biomass of picoeukaryotes and diatoms; decreases in diazotrophs and Prochlorococcus; and both increases and decreases in Synechococcus. These patterns can only be partially explained by existing theories. Using data, theory, and numerical simulations, we show that the patterns of plankton distributions across the transition zone are the result of gradients in nutrient supply rates, which control a range of complex biotic interactions. We examine how interactions such as size‐specific grazing, multiple trophic strategies, shared grazing between several phytoplankton size classes and heterotrophic bacteria, and competition for multiple resources can individually explain aspects of the observed community structure. However, it is the combination of all these interactions together that is needed to explain the bulk compositional patterns in phytoplankton across the North East Pacific Transition Zone. The synthesis of multiple mechanisms is essential for us to begin to understand the shaping of community structure over large environmental gradients