Central-eastern Mexico Research Articles

Hydroclimate modulation of central-eastern Mexico by the North Atlantic subtropical high since the little ice age

We reconstructed the hydroclimate of central-eastern Mexico over the last 700 common era (CE) based on inferences from multi-proxies from a stalagmite (K-Inc) collected at Karmidas cave, eastern México. Projections on hydroclimate variability in Mexico raise concerns about possible future occurrences of severe droughts and seasonal water balance fluctuations related to increased global temperatures caused by anthropogenic climate change (Murray-Tortarolo, 2021). The eastern region influences the production and supply of food to Mexico. Simulations of past climates, validated by paleoclimate records, yield valuable perspectives on climate change and enhance our understanding of future projections. However, the paucity of paleoclimatic records hinders understanding past hydroclimatic variations and their climatic mechanisms in eastern Mexico. Our record covers the Little Ice Age (LIA) through the Historical Interval (HI), a crucial period for understanding the climate repercussions spanning the transition from Earth's climatic history to the post-industrial era. The reduced intensity of the North Atlantic Subtropical High (NASH) during the LIA enabled a prominent negative phase of NAO-like variability from 1600 CE until the end of LIA. Consequently, preferent meridional airflow within the continent fosters the encounter of moisture-laden intrusions with the increased frequency of cold surges as the occurrence of frontal rain in eastern Mexico, impairing the amount effect on the K-Inc δ18O record. However, after the artificial opening of the cave in 1910 CE, the δ18O records of K-Inc began to exhibit a ∼20-year oscillatory periodicity. In this context, the trace elements of K-Inc help elucidate the climatic conditions that governed the precipitation regime during the investigated period. The visual alignment between the zonal sea surface temperature (SST) variability in the eastern equatorial Pacific (EEP) and the trace elements (Sr/Ca and Ba/Ca) of K-Inc reveals their relationship. Warm zonal SST in the EEP appears to be associated with changes in the length of the winter and summer seasons in eastern Mexico during the LIA. In contrast, over the HI, the trace elements of K-Inc show an anti-phase response to Warm zonal SST in the EEP, denoting wetter climate conditions at the vicinities of Karmidas Cave. This configuration led to questioning the influence of SST zonal variability in the EEP during the HI, which was probably masked by more relevant climate forcing. Our findings enabled us to draw climate scenarios by addressing the main climate drivers in our records.

Ecological stress memory in wood architecture of two Neotropical hickory species from central-eastern Mexico

BackgroundDrought periods are major evolutionary triggers of wood anatomical adaptive variation in Lower Tropical Montane Cloud Forests tree species. We tested the influence of historical drought events on the effects of ecological stress memory on latewood width and xylem vessel traits in two relict hickory species (Carya palmeri and Carya myristiciformis) from central-eastern Mexico. We hypothesized that latewood width would decrease during historical drought years, establishing correlations between growth and water stress conditions, and that moisture deficit during past tree growth between successive drought events, would impact on wood anatomical features. We analyzed latewood anatomical traits that developed during historical drought and pre- and post-drought years in both species.ResultsWe found that repeated periods of hydric stress left climatic signatures for annual latewood growth and xylem vessel traits that are essential for hydric adaptation in tropical montane hickory species.ConclusionsOur results demonstrate the existence of cause‒effect relationships in wood anatomical architecture and highlight the ecological stress memory linked with historical drought events. Thus, combined time-series analysis of latewood width and xylem vessel traits is a powerful tool for understanding the ecological behavior of hickory species.

Environmental controls on the microfacies distribution and spectral gamma ray response of the uppermost Jurassic–Lowermost cretaceous succession (Pimienta–Lower Tamaulipas Formations) in central-eastern Mexico

Organic-rich sediments of the Pimienta Formation were deposited in the Tampico-Misantla Basin during the Late Jurassic–Earliest Cretaceous. A sedimentological, spectrometric, microfacies and geochemical analysis was performed on a stratigraphic section recording the Pimienta–Lower Tamaulipas formational transition, to gain an understanding of the depositional conditions, and to decipher the main factors that control the gamma ray signal. This latter was achieved by comparison with other records. The studied succession spans from the upper part of the lower Berriasian Calpionella Zone to the lower part of the lower Valanginian Calpionellites Zone. Moreover, the microfacies data indicate it was accumulated in an outer ramp to basinal setting influenced by high energy events and the input of grains transported from shallower areas. Oxygen levels increased during the lastest Berriasian–early Valanginian. The organic matter preserved in these sediments has a mixed marine-terrestrial origin and is immature to early mature. Several records across the basin show that from the lower part of the Pimienta Formation to the lower part of the Tamaulipas Formation sediments change from radiolarian-rich microfacies with the highest Total Organic Carbon (TOC) content and Standard Gamma Ray (SGR) values to calpionellid-rich microfacies with the lowest TOC and SGR values. This shift is interpreted as controlled by the evolution of environmental conditions from eutrophic/oxygen-depleted to oligotrophic-partially oxygenated, which caused a progressive decrease in the organic matter burial and enrichment of authigenic U.

Seasonal and elevational variation in thermal ecology of the crevice-dwelling knob-scaled lizard Xenosaurus fractus from central-eastern Mexico

There is strong covariation between the thermal physiology of ectothermic animals and their thermal environment. Spatial and temporal differences in the thermal environment across a species' range may result in changes in thermal preferences between populations of that species. Alternatively, thermoregulatory-based microhabitat selection can allow individuals to maintain similar body temperatures across a broad thermal gradient. Which strategy a species adopts is often dependent on taxon-specific levels of physiological conservatism or ecological context. Identifying which strategies species use in response to spatial and temporal variation in environmental temperatures requires empirical evidence, which then can support predictions as to how a species might respond to a changing climate. Here we present findings of our analyses of the thermal quality, thermoregulatory accuracy and efficiency for the lizard, Xenosaurus fractus, across an elevation-thermal gradient and over the temporal thermal variation associated with seasonal changes. Xenosaurus fractus is a strict crevice-dweller, a habitat that can buffer this lizard from extreme temperatures and is a thermal conformer (body temperatures reflect air and substrate temperatures). We found populations of this species differed in their thermal preferences along an elevation gradient and between seasons. Specifically, we found that habitat thermal quality, thermoregulatory accuracy and efficiency (all measures of how well the lizards' body temperatures compared to their preferred body temperatures) varied along thermal gradients and with season. Our findings indicate that this species has adapted to local conditions and shows seasonal flexibility in those spatial adaptations. Along with their strict crevice-dwelling habitat, these adaptations may provide some protection against a warming climate.

Accumulation of organic-rich sediments associated with Aptian–Albian oceanic anoxic events in central-eastern Mexico

Oceanographic and climate conditions during the early Aptian OAE 1a and the late Aptian–early Albian OAE 1b are reported from an organic-rich succession deposited in the central portion of the Mexican Interior Basin, based on the analysis and integration of geochemical data (δ13Ccarb, total organic and inorganic carbon contents, Rock-Eval parameters and major and trace elements concentrations). The carbon isotope record of the studied section displays trends that correlate with segments C2 to C13. The OAE 1a interval is clearly isotopically defined (segments C3–C6) and includes sediments moderately enriched in organic matter. Although the OAE 1b sub-events are not expressed in the isotope record, the Jacob, Kilian and Paquier events may correspond to distinctive organic-rich levels occurring through C10–C12 segments. Evidence indicates that sediments enriched in organic matter through the section were accumulated under oxygen-depleted and high nutrient conditions. Anoxic-eutrophic conditions induced by a high input of continental-derived nutrients (including biolimiting Fe and P) associated to intense chemical weathering under warm and humid conditions took place during the deposition of the Selli and Paquier levels. Enhanced P recycling and regional upwelling reinforced eutrophic conditions during OAE 1a.

Climate predictors and climate change projections for avian haemosporidian prevalence in Mexico.

Long-term, inter-annual and seasonal variation in temperature and precipitation influence the distribution and prevalence of intraerythrocytic haemosporidian parasites. We characterized the climatic niche behind the prevalence of the three main haemosporidian genera (Haemoproteus, Plasmodium and Leucocytozoon) in central-eastern Mexico, to understand their main climate drivers. Then, we projected the influence of climate change over prevalence distribution in the region. Using the MaxEnt modelling algorithm, we assessed the relative contribution of bioclimatic predictor variables to identify those most influential to haemosporidian prevalence in different avian communities within the region. Two contrasting climate change scenarios for 2070 were used to create distribution models to explain spatial turnover in prevalence caused by climate change. We assigned our study sites into polygonal operational climatic units (OCUs) and used the general haemosporidian prevalence for each OCU to indirectly measure environmental suitability for these parasites. A high statistical association between global prevalence and the bioclimatic variables ‘mean diurnal temperature range’ and ‘annual temperature range’ was found. Climate change projections for 2070 showed a significant modification of the current distribution of suitable climate areas for haemosporidians in the study region.

Accumulation of Organic-Rich Sediments Associated with Aptian–Albian Oceanic Anoxic Events in Central-Eastern Mexico

Accumulation of Organic-Rich Sediments Associated with Aptian–Albian Oceanic Anoxic Events in Central-Eastern Mexico

Historical biogeography and comparative phylogeography of the Mexican genusBakerantha(Bromeliaceae): insights into evolution and diversification

AbstractWe studied the rupicolous and dioecious species of Bakerantha (Bromeliaceae) that grow as narrow endemics in central-eastern Mexico. We aimed to describe the spatio-temporal framework in which Bakerantha and its species originated using a phylogeographic and population genetics approach. We carried out population genetics analyses on 29 populations of the five Bakerantha spp., using plastid and nuclear DNA sequences. The data were used to analyse their diversity, genetic structure and demography, to carry out molecular dating and to reconstruction their ancestral area. Our analyses revealed that speciation in Bakerantha began in the Late Pliocene, associated with vicariance resulting from the rise of the Trans-Mexican Volcanic Belt, a barrier that isolated the Bakerantha spp. to its north and south, and subsequent dispersal events in the Sierra Madre Oriental. Genetic data suggest that the species have achieved a high degree of genetic differentiation and variation, but most of them lack intraspecific structure, even though species have remained stable over the time due their life history traits.

Paleoenvironmental changes and biotic response to Aptian–Albian episodes of accelerated global change: Evidence from the western margin of the proto-North Atlantic (central-eastern Mexico)

The Aptian–Albian interval represents a time of distinctive atmospheric and oceanic changes. A major perturbation of the carbon cycle induced by intense volcanic activity produced episodes of environmental change affecting the abundance and evolution of marine plankton. Several studies based on pelagic and hemipelagic sections have used biostratigraphic events and carbon isotope stratigraphy tools to identify biotic responses to environmental perturbations. Few studies have included Aptian–Albian planktic microfossil communities and paleoenvironmental changes in Mexico, a region that was part of the western proto-North Atlantic margin. The aim of this study is to interpret paleoenvironmental and paleoceanographic conditions through a microfacies analysis of a carbonated succession of the Tamaulipas Formation from central-eastern Mexico (Tampico-Misantla Basin), within a temporal framework based on planktic foraminiferal and colomiellids biostratigraphy.The studied section, 92 m thick, consists of a continuous pelagic succession. Facies contain abundant planktic microfossils and span the stratigraphic interval between the Globigerinelloides blowi and Ticinella praeticinensis Zones. The Aptian/Albian Boundary in the studied section was established on the highest occurrence (HO) of planktic foraminifera such as Paraticinella rohri and the presence of Microhedbergella spp., followed by the lowest occurrence (LO) of colomiellids such as Colomiella recta.Detailed quantification of microfossil assemblages reveals variations in abundance of planktic foraminifera, radiolarians, praecolomiellids, colomiellids, dinocyst and echinoderm fragments. These variations related to fabric characterization and bioturbation indexes allow us to infer fluctuations in ancient trophic conditions in the water column, which might be associated with episodes of global environmental change such as Oceanic Anoxic Events.

New Records of Odonata from Central Eastern Mexico

New Records of Odonata from Central Eastern Mexico

Mid-late Cenomanian larger benthic foraminifers from the El Abra Formation, Valles-San Luis Potosí Platform, central-eastern Mexico: Taxonomy, biostratigraphy and paleoenvironmental implications

espanolThe Valles-San Luis Potosi Platform is part of an extensive carbonate platform system that rimmed the ancestral Gulf of Mexico during the middle (Albian) through Upper Cretaceous. The El Abra Formation consists of a shallow-water deposit; it contains a benthic foraminiferal assemblage that includes 18 species, which are described and illustrated in this paper. The studied successions from the upper part of the El Abra Formation were dated as mid-late Cenomanian. On the basis of these findings, two zones are proposed Pseudolituonella reicheli Assemblage Zone and Nezzazatinella picardi Interval Zone. The first Assemblage Zone is characterized by an abundant benthic foraminiferal association. It is overlain by the Nezzazatinella picardi Interval Zone where the species richness of the fora-miniferal assemblage is reduced and later disappears. The benthic foraminiferal demise is coincident with major sea-level changes and an increase in siliciclastic input from the hemipelagic deposit of the Soyatal Formation, which contains abundant pithonellids and r and r-k strategist planktic foraminifera (Whiteinella archaeo-cretacea Partial Range Zone). Two stratigraphically correlative facies have been recognized in the El Abra Formation: the Taninul and the El Abra Facies. A warm, shallow-water, open marine platform deposit (Taninul Facies) is inferred. It includes peloidal-foraminiferal packstone, packstone-grainstone, and packstone- wackestone. A restricted environment (El Abra Facies) can be deduced from the abundant miliolids and ostreids. The texture is a wackestone-packstone. Another microfacies (Soyatal Formation) consists of wackestone-packstone with an acme of pithonellids and the occurrence of r and r-k strategist planktic foraminifers deposited during the platform drowning. EnglishLa Plataforma Valles-San Luis Potosi es parte de un sistema de plataformas extenso que se encontraba bordeando el antiguo Golfo de Mexico en el Albiano hasta el Cretacico Superior. La caliza El Abra es un deposito de aguas poco profundas; esta contiene un conjunto de foraminiferos bentonicos que incluye 18 especies, que se describen e ilustran en este documento. Las sucesiones estudiadas de la parte superior de la Formacion de El Abra fueron datadas como del Cenomaniano medio- tardio; se proponen dos zonas (Zona de Conjunto Pseudolituonella reicheli y Zona de Intervalo Nezzazatinella picardi). La primera Zona de Conjunto se caracteriza por una asociacion abundante de foraminiferos bentonicos. Esta sobreyacida por la Zona de Intervalo Nezzazatinella picardi donde se reduce la riqueza de especies de las asociaciones de foraminiferos y luego desaparece. La desaparicion de foraminiferos bentonicos es coincidente con grandes cambios de nivel del mar y un aumento en el aporte de sedimentos desde el deposito hemipelagico de la Formacion Soyatal que contiene abundantes pithonelidos y foraminiferos planctonicos de estrategia r y r-k (Zona de Alcance Parcial (Whiteinella archaeocretacea)). Dos facies estratigraficamente correlacionables han sidoreconocidas en la Formacion El Abra: la Facies Taninul y la Facies El Abra. Se infiere un deposito de plataforma marina abierta de aguas calidas someras (Facies Taninul). Esta incluye un packstone peloidal con foraminiferos, packstone y packstone-wackestone. Un ambiente restringido (Facies El Abra) puede deducirse por los abundantes miliolidos y ostreidos. La textura de la roca es un wackestone-packstone. Otra microfacies consiste de un wackestone-packstone con un auge de pithonelidos y la presencia de foraminiferos de estrategia r y r-k depositados durante la inundacion de la plataforma (Formacion Soyatal).

Paleoenvironmental conditions across the Jurassic–Cretaceous boundary in central-eastern Mexico

The Padni section of central-eastern Mexico is characterized by pelagic, organic-rich carbonates and shales dated in this study by calpionellid biostratigraphy to the late Tithonian-late Berriasian time interval. Microfacies, pyrite framboid size, spectrometric gamma-ray and mineralogical data are herein integrated in order to reconstruct the paleoenvironmental change during the Jurassic-Cretaceous boundary. Deposits of the late Tithonian–early Berriasian are characterized by laminated, organic-rich facies with abundant radiolarian, tiny pyrite framboids and low Th/U ratios. They are linked to upwelling in a semi-restricted basin, high marine productivity and anoxic bottom waters. The early incursions of Tethyan oceanic waters into the proto-Gulf of Mexico occurred during late Tithonian as attested the appearance of calpionellids. Short and intermittent accumulations of saccocomids during early Berriasian suggest episodes of sporadic connection between the Tethys, the proto-Atlantic and the Pacific ocean during sea-level rise events. A full and stable connection between the Tethys and proto-Gulf of Mexico was established until the late Berriasian. This event is supported by the presence of open marine and bioturbated facies with a framboid population typical of dysoxic conditions, higher Th/U ratios and a decreasing pattern of the total organic carbon content. In addition to highlighting the replenishment of the oxygen supply to the basin, this facies also points to a younger age for the finalization of the Yucatán Block rotation and the end of the Gulf of Mexico opening. Deposition of the studied section occurred mostly during a Tithonian–Berriasian arid phase reported in other Tethyan and Atlantic regions. The similarity between the discrete segments of the standard gamma-ray curve defined in the studied outcrop and those reported from subsurface implies their regional continuity allowing their use for correlation purposes.

Progressive, episodic deformation in the Mexican Fold–Thrust Belt (central Mexico): evidence from isotopic dating of folds and faults

We used illite Ar/Ar dating to obtain absolute ages of folds and shear zones formed within the Mexican Fold–Thrust Belt (MFTB). The methodology takes advantage of illite dating in folded, clay-bearing layers and the ability to obtain accurate ages from small-size fractions of illite using encapsulated Ar analysis. We applied our approach to a cross-section that involves folded Aptian–Cenomanian shale-bentonitic layers interbedded with carbonates of the Zimapán (ZB) and Tampico–Misantla (TMB) Cretaceous basins in central-eastern Mexico. Basinal carbonates were buried by syn-tectonic turbidites and inverted during the formation of the MFTB in the Late Cretaceous. Results from folds and shear zones record different pulses of deformation within this thin-skinned orogenic wedge.Mineralogical compositions, variations in illite polytypes, illite crystallite size (CS), and Ar/Ar ages were obtained from several size fractions in limbs and hinges of the folds and in the shear zones. 1Md-illite polytype (with CS of 6–9 nm) dominates in two folds in the TMB while 2M1-illlite (with CS of 14–30 nm) dominates in the third fold, in the ZB, and in the fold/shear zone. From west (higher grade) to east (lower grade): Ar retention ages indicate shearing occurred at ~84 Ma in the westernmost shear zone, folding at ~82 Ma in the ZB with subsequent localized shearing at ~77 Ma, and Ar total gas ages constrain the time of folding at ~64 Ma on the west side of the TMB and ~44 Ma on the eastern edge. These results are consistent with the age and distribution of syn-tectonic turbidites and indicate episodic progression of deformation from west to east.

Chemical and physical defense traits in two sexual forms of Opuntia robusta in Central Eastern Mexico.

Sexually dimorphic plants provide an excellent opportunity for examining the differences in the extent of their defense against herbivores because they exhibit sex-related differences in reproductive investment. Such differences enable comparison of the sex with high reproduction expenses with the sex that expends less. The more costly sex is usually also better defended against herbivores. Generally, females are considered more valuable than hermaphrodites in terms of fitness; however, hermaphrodites are more valuable if they can produce seed by autonomous selfing, provided that the inbreeding depression is low and pollen is limited. We studied a gynodioecious population of Opuntia robusta from Central-Eastern Mexico, which has been reported to be trioecious, dioecious, or hermaphrodite, and addressed the following questions: 1) Is the hermaphrodite's reproductive output higher than the female's, and are hermaphrodites thus better defended? 2) Are plant tissues differentially defended? 3) Do trade-offs exist among different physical defense traits? and 4) among physical and chemical defense traits? We found that 1) hermaphrodites had a higher seed output and more spines per areola than females and that their spines contained less moisture. Non-reproductive hermaphrodite cladodes contained more total phenolic compounds (TPCs) than female ones. In addition, 2) hermaphrodite reproductive cladodes bore more spines than female cladodes, and 3) and 4) we found a negative relationship between spine number per areola and areola number per cladode and a positive relationship between spine number per areola per plant and TPC concentration per plant. Non-reproductive hermaphrodite cladodes contained a higher concentration of TPCs than female cladodes, and parental cladodes contained fewer TPCs than both reproductive and empty cladodes.

Variability of the radial profile of sap velocity in Pinus patula from contrasting stands within the seasonal cloud forest zone of Veracruz, Mexico

Characterizing the variability of the radial profiles of sap velocity (vs) is a critical step to improve upscaling point measurements of vs to whole-tree sap flow. One promising approach is the use of a probability distribution function (pdf) to model radial profiles of vs, because shape parameters could potentially be generalized to trees of the same species based on the premise that the shape remain consistent regardless of the tree size and age, and over time, even though the magnitude of vs may vary with environmental conditions. The objective of this study was to characterize and assess the variability of the radial profile and to examine the validity of the premises underlying this approach by applying it to Pinus patula, one of the most widely planted tree species in the uplands of central-eastern Mexico. We measured vs with the Heat Ratio method at various sapwood depths in 18 P. patula trees with a dbh between 7.3 and 59.7cm and age between of 10 and 34 years, over a period of 1.5 years. Trees were growing in two stands: a mature forest stand and a young plantation. By fitting the Beta-pdf to hourly radial profiles of vs, we derived a lumped shape parameter (ρ) to denote the radial position relative to sapwood depth with average vs and a scaling parameter (cs). The typical radial profile was unimodal, asymmetrical and with peak vs generally within the outermost 20–33% of the sapwood depth. However, tree-to-tree variability in ρ was considerable among trees within the same stand and also across stands. Long-term and day-to-day variation of ρ was marginal. The hourly dynamics of the radial profile, characterized by cs, can be explained by a linear combination of incoming shortwave radiation, vapor pressure deficit, the hour of day and their interaction (r2=0.74). An independent field evaluation confirmed that a radial profile of fixed shape can be effectively used to estimate whole-tree sap flow with relatively low bias (4–26% underestimation) relative to cut-tree water uptake, particularly for trees for which vs observations covered at least 60% of the sapwood depth. Our findings emphasize the importance of conducting multiple vs point measurements covering most of the sapwood depth for accurate characterization of the radial profile, and demonstrate the utility of fitting a pdf to point vs measurements in order to assess the variability of vs radial profiles as well as to compute sap flow at the whole-tree level.

Runoff generation in a steep, tropical montane cloud forest catchment on permeable volcanic substrate

Most studies to date in the humid tropics have described a similar pattern of rapid translation of rainfall to runoff via overland flow and shallow subsurface stormflow. However, study sites have been few overall, and one particular system has received very little attention so far: tropical montane cloud forests (TMCF) on volcanic substrate. While TMCFs provide critical ecosystem services, our understanding of runoff generation processes in these environments is limited. Here, we present a study aimed at identifying the dominant water sources and pathways and mean residence times of soil water and streamflow for a first‐order, TMCF catchment on volcanic substrate in central eastern Mexico. During a 6‐week wetting‐up cycle in the 2009 wet season, total rainfall was 1200 mm and storm event runoff ratios increased progressively from 11 to 54%. With the increasing antecedent wetness conditions, our isotope and chemical‐based hydrograph separation analysis showed increases of pre‐event water contributions to the storm hydrograph, from 35 to 99%. Stable isotope‐based mean residence times estimates showed that soil water aged only vertically through the soil profile from 5 weeks at 30 cm depth to 6 months at 120 cm depth. A preliminary estimate of 3 years was obtained for base flow residence time. These findings all suggest that shallow lateral pathways are not the controlling processes in this tropical forest catchment; rather, the high permeability of soils and substrate lead to vertical rainfall percolation and recharge of deeper layers, and rainfall‐runoff responses appeared to be dominated by groundwater discharge from within the hillslope.

Heterozygote excess through life history stages inCestrum miradorenseFrancey (Solanaceae), an endemic shrub in a fragmented cloud forest habitat

Comparisons of genetic diversity and population genetic structure among different life history stages provide important information on the effect of the different forces and micro-evolutionary processes that mould diversity and genetic structure after fragmentation. Here we assessed genetic diversity and population genetic structure using 32 allozymic loci in adults, seeds, seedlings and juveniles of eight populations of the micro-endemic shrub Cestrum miradorense in a highly fragmented cloud forest in central-eastern Mexico. We expected that due to its long history or rarity, this species may have endured the negative effects of fragmentation and would show moderate to high levels of genetic diversity. High genetic diversity (H(e) = 0.445 ± 0.03), heterozygote excess (F(IT) = -0.478 ± 0.034, F(IS) = -0.578 ± 0.023) and low population differentiation (F(ST) = 0.064 ± 0.011) were found. Seeds had higher genetic diversity (H(e) = 0.467 ± 0.05) than the later stages (overall mean for adults, seedlings and juveniles H(e) = 0.438 ± 0.08). High gene flow was observed despite the fact that the fragmentation process began more than 100 years ago. We conclude that the high genetic diversity was the result of natural selection, which favours heterozygote excess in all stages, coupled with a combination of a reproductive system and seed/pollen dispersal mechanisms that favour gene flow.

Lower Tithonian Microconchiate Simoceratins from Eastern Mexico: Taxonomy, Biostratigraphy, and Palaeobiogeography

The precise record of simoceratins sampled bed-by-bed is first reported from Mexico (Mazatepec area in Puebla, central-eastern Mexico), as well as the existence of lappeted peristomes in these ammonites. Both Pseudovolanoceras aesinense and the subspecies Pseudovolanoceras aesinense chignahuapense are shown to occur among Mexican simoceratins. The European species and the Mexican subspecies share the same stratigraphic range in the studied sections, yet they differ in ephebic sculpture. Ecological adaptation to neritic seas corresponding to eastern Mexico areas is interpreted, forcing phenotypic deviation with geographic significance, i.e., subspeciation. The new subspecies would indicate stratigraphic horizons within the Semiformiceras semiforme/Haploceras verruciferum Chronozone in the Mediterranean Tethys. A revision of contemporaneous simoceratins in the Americas is founded on a comparative analysis with respect to the European species P. aesinense.

Water balances of old-growth and regenerating montane cloud forests in central Veracruz, Mexico

► We compare the catchment water budgets of old-growth and regenerating cloud forests. ► Water use was higher in the mature forest mainly because of greater water canopy storage capacity. ► Streamflow was greater in the regenerating forest due to lower rainfall interception. ► Storm runoff was low in both forest attributed to the high permeability of the soils. ► We conclude that 20 years of forest growth is sufficient to restore the original hydrology. This paper compares the water budgets of two adjacent micro-catchments covered by mature (MAT) and 20-year-old secondary (SEC) lower montane cloud forests, respectively, in central Veracruz, Mexico over a 2-year period. Rainfall ( P ) and streamflow ( Q ) were measured continuously, whereas dry canopy evaporation (transpiration E t ), wet canopy evaporation (rainfall interception I ), and cloud water interception ( CWI ) were quantified using a combination of field measurements and modeling. Mean annual P was 3467 mm, of which typically 80% fell during the wet season (May–October). Fog interception occurred exclusively during the dry season (November–April), and was ⩽2% of annual P for both forests. Rainfall interception loss was dominated by post-event evaporation of intercepted water rather than by within-event evaporation. Therefore, the higher overall I (i.e. including CWI ) by the MAT (16% of P vs. 8% for the SEC) reflects a higher canopy storage capacity, related in turn to higher leaf area index and greater epiphyte biomass. Annual E t totals derived from sapflow measurements were nearly equal for the MAT and SEC (∼790 mm each). Total annual water yield calculated as P minus ( E t + I ) was somewhat higher for the SEC (2441 mm) than for the MAT (2077 mm), and mainly reflects the difference in I . Mean annual Q was also higher for the SEC (1527 mm) than for the MAT (1338 mm), and consisted mostly of baseflow (∼90%). Baseflow recession rates were nearly equal between the two forests, as were stormflow coefficients (4% and 5% for MAT and SEC, respectively). The very low runoff response to rainfall is attributed to the high infiltration and water retention capacities of the volcanic soils throughout the ∼2 m deep profile. The water budget results indicate that ∼875 and 700 mm year −1 leave the SEC and MAT as deep groundwater leakage, which is considered plausible given the fractured geology in the study area. It is concluded that 20 years of natural regeneration following cloud forest disturbance in central-eastern Mexico is capable of producing near-original hydrological behavior.

Post-Laramide and pre-Basin and Range deformation and implications for Paleogene (55–25 Ma) volcanism in central Mexico: A geological basis for a volcano-tectonic stress model

At central-eastern Mexico, in the Mesa Central province, there are several ranges that were formed after the K/T Laramide compression but before the Basin and Range peak extensional episodes at middle–late Oligocene. Two important volcano-tectonic events happened during this time interval, 1) uplift of crustal blocks exhuming the Triassic–Jurassic metamorphic sequence and formation of basins that were filled with red beds and volcanic sequences, and 2) normal faulting and tilting to the NE of these blocks and fanglomerate filling of graben and half-graben structures. The first event, from late Paleocene to early Eocene, was related to NNE and NNW oriented dextral strike-slip faults. These faults were combined with NW–SE en echelon faulting in these blocks through which plutonism and volcanism occurred. The second event lasted from early Oligocene to early Miocene and coincided with Basin and Range extension. Intense volcanic activity occurred synchronously with the newly-formed or reactivated old fault systems, producing thick sequences of silicic pyroclastic rocks and large domes. Volcano-tectonic peaks occurred in three main episodes during the middle–late Oligocene in this part of Mexico, at about 32–30 Ma, 30–28 Ma, and 26–25 Ma. The objectives of this work is to summarize the volcano-tectonic events that occurred after the end of the Laramide orogeny and before the peak episodes of Basin and Range faulting and Sierra Madre Occidental Oligocene volcanism, and to discuss the influence of these events on the following Oligocene–Miocene volcano-tectonic peak episodes that formed the voluminous silicic volcanism in the Mesa Central, and hence, in the Sierra Madre Occidental. A model based upon geological observations summarizes the volcanic-tectonic evolution of this part of Mexico from the late Paleocene to the Early Miocene.