Seed mass maturity in the terrestrial bromeliad Hechtia perotensis (Bromeliaceae), endemic to Mexico

Introduction: H. perotensis is a plant with a high potential for ecological restoration because it yields thousands of seeds and grows under low levels of rain, poor soils and contrasting temperatures. However, little is known of the seed mass maturity (high seed germination, low seed fresh weight and low seed moisture content) in this species. Objective: Assess seed germination in the laboratory of H. perotensis during seed development and along the floral stalk (infructescence) in two sites one in rocky location and another near a lake. The hypothesis was that there is a time after flowering in which seeds have highest germination and fresh weight and that the apical, centre and base of the infructescence are different in seed germination and fresh weight in both sites. Methods: Capsules were collected in two sites one in rocky land (Frijol Colorado, Perote, Veracruz) and another near one lake (Alchichica, Puebla), in the months of August, September and November 2016 and January 2017. A repeated measure design (RMD) was used to analyze the effects of infructescence section on seed weight, moisture content and seed germination (41, 87, 152 and 215 days after flowering). Each evaluation time comprised five replicates, each one with 15 seeds. Results: Difference in seed germination, seed weight and moisture content between sections of the infructescence was not significant. However, significant differences were found not only between first and last sample dates, buy mainly between first and second dates. Eighty-seven days after flower pollination seed moisture content was lower than 20 % and up to 80 % of seed germinated in both sites of sampling. Conclusions: In this study it was found that the moisture content of H. perotensis seed can be used as an indicator of the physiological maturity of the seed and it is also related to germination of the seed.

A Novel Microbialite-Associated Phototrophic Chloroflexi Lineage Exhibiting a Quasi-Clonal Pattern along Depth

Chloroflexales (Chloroflexi) are typical members of the anoxygenic photosynthesizing component of microbial mats and have mostly been characterized from communities associated to hot springs. Here, we report the assembly of five metagenome-assembled genomes (MAGs) of a novel lineage of Chloroflexales found in mesophilic lithifying microbial mats (microbialites) in Lake Alchichica (Mexico). Genomic and phylogenetic analyses revealed that the bins shared 92% of their genes, and these genes were nearly identical despite being assembled from samples collected along a depth gradient (1–15 m depth). We tentatively name this lineage Candidatus Lithoflexus mexicanus. Metabolic predictions based on the MAGs suggest that these chlorosome-lacking mixotrophs share features in central carbon metabolism, electron transport, and adaptations to life under oxic and anoxic conditions, with members of two related lineages, Chloroflexineae and Roseiflexineae. Contrasting with the other diverse microbialite community members, which display much lower genomic conservation along the depth gradient, Ca. L. mexicanus MAGs exhibit remarkable similarity. This might reflect a particular flexibility to acclimate to varying light conditions with depth or the capacity to occupy a very specific spatial ecological niche in microbialites from different depths. Alternatively, Ca. L. mexicanus may also have the ability to modulate its gene expression as a function of the local environmental conditions during diel cycles in microbialites along the depth gradient.

Candona alchichica (Podocopida: Candonidae), a new ostracod species from saline, tropical Lake Alchichica, Mexico

In North America, most species of the Candonidae family belong to the genus <em>Candona</em>. These species are frequently found in freshwater ecosystems and in sediment sequences, which makes them valuable tools for paleoenvironmental reconstructions. Knowledge of Mexican <em>Candona</em> species is limited, however, and scant information exists regarding their taxonomy and ecology. Here we describe <em>Candona alchichica,</em> a new ostracod species we suggest being endemic to Lake Alchichica, central Mexico. The species belongs to the <em>acuminata</em> group of species, based on the presence of 5+1 setae on the second segment of the mandibular palp. It is closely related to <em>C. patzcuaro</em>,<em> C. tahoensis</em> and <em>C. ohioensis</em>, but differs from those species in that the females have an elongated genital field, wide at the base and narrow at the end. Males have elongated hook-like prehensile palps and a particular arrangement of lobes in the hemipenis, <em>i.e</em>., the a-lobe is inclined with a digitiform basal projection, the b-lobe is distally rounded and the h-lobe is square-shaped and exceeding the length of the b-lobe. <em>Candona alchichica</em> n. sp. and <em>C. patzcuaro</em> display very similar shells in length and morphology, which can cause confusion if identification is carried out in the absence of soft parts, a common situation when dealing with carapace and valve remains in sediment cores. Detailed morphometric analyses, however, revealed a clear difference between the valves of the two taxa. <em>Candona alchichica</em> n. sp. has taller valves (p˂0.05), with concave dorsal margin, and with the anterior margin considerably narrower than posterior margin, all characteristics different from<em> C. patzcuaro.</em> Most important, in spite of their similar shape, the two species exhibit contrasting ecological preferences. <em>Candona alchichica</em> n. sp. inhabits clear, cold, saline, oligotrophic waters, whereas <em>C. patzcuaro</em> dwells in turbid, warm, fresh, eutrophic waters. In addition, we include a revision of the morphological characteristics and taxonomic position of <em>C. patzcuaro</em>, based on type material and specimens collected from the type locality (<em>i.e</em>., Lake Pátzcuaro, Michoacán). This study highlights the importance of undertaking detailed morphometric analyses of the recent ostracod fauna to provide reliable taxonomic identifications and ecological characterizations of species, which are critical for accurate paleoclimatic and paleoecological reconstructions.

Inter-annual ciliate distribution variation within the late stratification oxycline in a monomictic lake, Lake Alchichica (Mexico)

<p>noxia, and ciliates might play a very important role in the plankton community budget there. We analysed changes in the composition and biomass of the ciliate assemblage and other microbial loop components throughout the oxycline just at the end of stratification in a warm-monomictic lake, Lake Alchichica, Mexico (four samplings: 2006-2008, 2010); the results were compared with those obtained from another lake from the region, La Preciosa, sampled in 2010. Bacteria, autotrophic picoplankton (APP) and flagellates were analysed using epifluorescence microscopy. Ciliates were evaluated either in DAPI stained samples (looking for pigmented organelles and/or ingested phototrophs) or in quantitative protargol stain (QPS) permanent preparations, where they were identified at the genus or species level. The end of the stratification period in Lake Alchichica was characterized by almost uniform heterotrophic picoplankton (HPP) numbers (10⁶ cells mL^-1) throughout the water column. Meanwhile, APP showed epilimnetic and/or metalimnetic maxima of 10⁵ cells mL^-1 followed by an order of magnitude drop in the hypolimnion. A very important peak (10⁵ cells mL^-1) of the autotrophic or mixotrophic flagellate <em>Pyramimonas</em> sp. was observed repeatedly above and within the oxycline of Lake Alchichica. Ciliate biomass maxima were found around the oxycline and in the above-bottom layer. The top of the oxycline was dominated by <em>Euplotes</em> spp. and <em>Spirostomum teres</em> fine- to coarse-filter feeders (feeding upon APP, nanodiatoms and algae). Raptorial haptorids (in particular, <em>Phialina </em>sp.) were the second most important group, generally occupying the layer below euplotids, followed by <em>Holophrya</em> and <em>Prorodon</em> facultative anaerobic prostomes. Sometimes, strictly anaerobic <em>Caenomorpha</em> sp. was found to be important in the anoxic hypolimnion. Minute picoplankton feeding species (both APP and heterotrophic bacteria feeders) were important throughout the water column: in the epilimnion, vorticellids (2006-2008) or scuticociliates (2010) dominated. Typically, the scuticociliate maximum was located in the oxycline and/or above the bottom. Some microaerophilic species were isolated; thus, their identification could be carried out. However, the apparent polymorphic ciliate life cycles were not described completely, and the species composition was only estimated: two dominant species (SC 1 – <em>Cristigera</em>-like and SC 2 – <em>Cyclidim</em>-like) covered nearly the total scuticociliate biomass. Strictly anaerobic scuticociliates were not isolated but observed in the deepest layers of the lake (bacteria symbiotic <em>Isocyclidium globosum</em> and <em>Cristigera </em>sp.). Significant statistical relation within the ciliate distribution and environmental variables was not confirmed due to unique species composition in the respective years. However, general trends in the distribution of ciliates on a species level were observed. Scuticociliates, including two important tentatively identified species, did not present unambiguous ecological position, and the study of their live cycle should be the next step in investigations.</p>

Estimation of the eddy diffusivity coefficient in a warm monomictic tropical Lake

<p>We used a two-year dataset (1998-1999) of monthly temperature profiles from Lake Alchichica, Mexico to estimate values of the vertical coefficient of eddy diffusivity. This lake is located in a tropical region at high altitude and shows considerable seasonal variations (i.e., rainy and dry seasons). It has an area of 2.3 km² and a mean depth of 40.9 m. Alchichica is a warm monomictic lake, which annually becomes isothermal near the end of December or early January at the onset of the dry season and remains stratified for the rest of the year (from late March or early April to early December) during the warm-rainy season. Mathematical models of the spatial and temporal variation of passive substances in lakes and oceans require a quantitative formulation of the vertical transport. Vertical mixing is generally a function of the density profile, which, in lakes, can be directly related to the temperature profile. A widely used method to estimate the vertical diffusion coefficients in lakes from temperature data is the flux-gradient method. In the present study, we applied a simple approach to calculate the eddy diffusivity coefficient (<em>K_z</em>) based on the solution of the vertical component of the modeled temperature equation. We characterized the eddy diffusivity coefficient (<em>K_z</em>) in Lake Alchichica as a dynamic coefficient that changes during the year, between years, and with depth, ranging from 10^-10 to 10^-6 m² s^-1, whereas typical values of <em>K_z</em> in thermally stratified lakes range from 10^-9 to 10^-2 m² s^-1. As expected, we found the lowest values in the deeper regions of the lake, and that the temporal variation of temperature with depth showed a quasi-bimodal shape from one year to the next. We also found a structure of alternating peaks and troughs in the vertical <em>K_z</em>, which indicates a response to oscillating vertical mixing. We concluded that the solution of the vertical component of the temperature equation could be a useful tool to estimate the eddy diffusivity in lakes. The major advantage of this method is its simplicity. We also conclude that the differences observed in the estimations of eddy diffusivity coefficients in other lakes are attributable to the differences in local characteristics of the thermal conditions in each lake.</p>

Ostrácodos no-marinos de lagos en el altiplano este-centro de México

The ostracode fauna of the neartic-neotropical transitional zone has remained poorly known until this study. Ten ostracode species inhabit ten highland lakes (five maar lakes (phreatic/phreato-magmatic explosion origin), one volcanic-tectonic lake, three natural dams and one man-made dam) in East-central Mexico. Surface sediments from the deepest part and the littoral zone from all studied lakes were collected. Environmental variables (pH, temperature, dissolved oxygen, conductivity, TDS) were measured <em>in situ</em> and parallel water samples for chemical analysis were collected for habitat description. Widely distributed species in the study area (≥5 lakes) include <em>Cypridopsis vidua</em>, <em>Darwinula stevensoni </em>and<em> </em><em>Eucandona </em>cf.<em> patzcuaro. Limnocytherina axalapasco</em> is an endemic species and was collected in three maar lakes and in one man-made dam. Rare species included: <em>Chlamydotheca</em> <em>arcuata</em>?,<em> Fabaeformiscandona acuminata</em>?<em>, Ilyocypris</em> <em>gibba</em>?,<em> Limnocythere friabilis</em>?, <em>Potamocypris smaragdina</em>?<em> </em>and<em> Potamocypris unicaudata</em>?. Highest species richness (6 spp.) was found in the large and shallow Lake Metztitlán (2.6km², 5.5m deep), with the lake water type HCO₃^-&gt;&gt;SO₄^2-&gt;Cl^- -- Ca²⁺&gt;Na⁺&gt;Mg²⁺. The rest of studied lakes (&lt;63m, &lt;27km²) had not more than three species. For instance, only two ostracode species were collected in Lake Alchichica, which is the largest, deepest and most saline studied maar lake.