A preliminary faunistic study of soil nematodes from different land uses in Tropical Deciduous Forest in the Costa Chica of Guerrero, Mexico

Tropical Deciduous Forest (TDF) is an important biome threatened globally by climate change and human encroachment. Changes in diversity and abundance of soil nematodes can serve as indicators of soil disturbance due to human activities. Our objective was to present a first inventory of the generic biodiversity of soil nematodes in seven TDF sites subjected to different current or decade-old land uses, located near Copala in the Costa Chica region of Guerrero, Mexico. TDF landscapes are especially heterogeneous in many soil and microclimate parameters, while subsistence agriculture systems in this biome are highly diverse and present great challenges for sampling design with replication. We therefore chose to focus on characterizing the soil nematode fauna, as a first step before undertaking detailed analyses of all potentially relevant biotic and abiotic factors. Genus-level diversity ranged from 12 to 18 taxa for the sampled land uses, or 27 total taxa for all samples combined. Statistical tests for data analysis without replication revealed significant differences in nematode diversity, trophic structure, and abundance between land uses. Four sites, left as fallows for ten years after prior human uses, were statistically different from each other as well as from a forest site undisturbed for at least twenty years. Despite the methodological limitations inherent in this initial study, we hypothesize that some effects on nematode communities may persist for more than a decade after the anthropogenic impacts of subsistence farming in TDF. Thus, future nematode surveys in the TDF biome should not only analyze the current properties of sampling sites, but also document data related to factors from past human use activities. Example factors, suggested by the pattern of nematode abundance from the seven sites in our study, include past levels of trampling by human traffic and grazing, as well as estimates of past amounts of plant debris deposition accumulated by harvesting or weeding.El Bosque Tropical Caducifolio (BTC) es un importante bioma amenazado por el cambio climático y la invasión humana. Los nematodos del suelo pueden ser indicadores de la perturbación del suelo debido a las actividades humanas. Nuestro objetivo fue presentar un primer inventario sobre la biodiversidad de los nematodos en siete sitios sometidos actualmente a diferentes usos del suelo, o con usos anteriores no perturbados durante diez años. Estos sitios están localizados en el BTC cerca de Copala en la región de la Costa Chica de Guerrero, México. Los paisajes del BTC son especialmente heterogéneos en muchos parámetros de suelo y microclima, mientras que los sistemas agrícolas de subsistencia en este bioma son muy diversos y presentan grandes desafíos para el muestreo con replicación. Debido a esto decidimos observar la fauna de nematodos del suelo como un primer paso antes de empezar el análisis de todos los parámetros abióticos potencialmente relevantes. La diversidad a nivel de género osciló entre 12 y 18 taxones para los usos del suelo muestreados, o 27 taxones en total. Las pruebas estadísticas para el análisis de datos sin replicación revelaron diferencias significativas entre los usos del suelo en la diversidad de nematodos, la estructura trófica y la abundancia. Cuatro sitios dejados en descanso por una década después de varios usos fueron estadísticamente diferentes entre sí y con el sitio forestal no perturbado por veinte años. A pesar de las limitaciones metodológicas inherentes a este estudio inicial, planteamos la hipótesis de que, en el BTC, algunos efectos en las comunidades de nematodos pueden persistir durante más de una década después de los impactos antropogénicos de la agricultura de subsistencia. Por lo tanto, las futuras encuestas de nematodos de los ecosistemas derivados de un BTC no solo deberían analizar las propiedades actuales de los sitios de muestreo, sino también documentar los datos relacionados con factores de las actividades humanas en el pasado. Entre estos factores, sugeridos por los resultados de nuestro estudio, se deben incluir niveles ​​de pisoteo humano y pastoreo, así como estimaciones de cantidades de deposición de desechos vegetales acumuladas por cosecha o deshierbe

Microsporidia-nematode associations in methane seeps reveal basal fungal parasitism in the deep sea

The deep sea is Earth's largest habitat but little is known about the nature of deep-sea parasitism. In contrast to a few characterized cases of bacterial and protistan parasites, the existence and biological significance of deep-sea parasitic fungi is yet to be understood. Here we report the discovery of a fungus-related parasitic microsporidium, Nematocenator marisprofundi n. gen. n. sp. that infects benthic nematodes at methane seeps on the Pacific Ocean floor. This infection is species-specific and has been temporally and spatially stable over 2 years of sampling, indicating an ecologically consistent host-parasite interaction. A high distribution of spores in the reproductive tracts of infected males and females and their absence from host nematodes' intestines suggests a sexual transmission strategy in contrast to the fecal-oral transmission of most microsporidia. N. marisprofundi targets the host's body wall muscles causing cell lysis, and in severe infection even muscle filament degradation. Phylogenetic analyses placed N. marisprofundi in a novel and basal clade not closely related to any described microsporidia clade, suggesting either that microsporidia-nematode parasitism occurred early in microsporidia evolution or that host specialization occurred late in an ancient deep-sea microsporidian lineage. Our findings reveal that methane seeps support complex ecosystems involving interkingdom interactions between bacteria, nematodes, and parasitic fungi and that microsporidia parasitism exists also in the deep-sea biosphere

The role of habitat heterogeneity in structuring the community of intertidal free-living marine nematodes

The role of habitat complexity has been widely neglected in the study of meiofaunal community patterns. We studied the intertidal nematode community of a structurally complex macrotidal beach exhibiting contrasting microhabitats (sandbars and runnels) to understand the influence of environmental gradients and habitat heterogeneity in the community structure. We tested whether topographical complexity affected (1) the zonation pattern in terms of abundance and diversity, and (2) local diversity by promoting compartmentalization into distinct faunal groups. Our analyses revealed three major faunal assemblages along the exposure gradient associated to differences in mean grain size and chlorophyll a. Diversity patterns involved a mid-intertidal peak, consistent with the intermediate disturbance hypothesis, and another peak at the limit with the subtidal region, consistent with the transition zone. These results highlight the predominance of environmental gradients in establishing intertidal zonation. However, microhabitats differed in environmental conditions and possessed significantly distinct nematofaunal communities. Runnels featured higher levels of taxonomic and functional diversity, many unique genera, and the community differed from the assemblage at the limit to the subtidal, stressing their role as distinct microhabitats. The nematofauna of the structurally complex beach was more diverse than the one from a homogeneous beach nearby, supporting the hypothesis that structural heterogeneity promotes diversity by compartmentalization and highlighting the importance of microhabitats in the assessment of biodiversity. Contrary to previous predictions, our results indicate potentially high regional marine nematode diversity in the Upper Gulf of California

Radopholus musicola n. sp., a new pathogenic species from Australia (Nematoda: Pratylenchidae)

Radopholus musicola n. sp. is described from Musa acuminata cv. Williams at Berrimah Research Station, Darwin, Northern Territory, Australia. The new species is distinguished from other species by female lateral lines with deep folds on the outer edge and by males with a uniquely long thin tail (73.6-92.8 μm) having a pointed terminus. Radopholus musicola n. sp. is most similar to R. similis and R. bridgei but males further differ from R. similis by a smaller stylet (8.8-12 vs 12-17 μm) and from R. bridgei by well-developed separated stylet knobs vs tiny or obscure knobs. The rate of reproduction of R. musicola n. sp. is much greater at higher temperatures (>31.5°C) than that of R. similis, and some banana cultivars resistant to R. similis are less resistant to R. musicola n. sp. The relevance of previous sequence-based (rDNA) analysis for distinguishing R. musicola n. sp. from R. similis and R. bridgei is discussed