Ecological distribution of Stephanodiscus niagarae Ehrenberg in central Mexico and niche modeling for its last glacial maximum habitat suitability in the Nearctic realm

Properties of the subduction system in Mexico

A hypothesis of historical area relationships for Mexico, Central, and South America was investigated by a cladistic biogographic analysis using 10 taxon cladograms of the herpetofauna of Mexico. A hypothesis is presented based on previous narrative biogeographic scenarios and compared with the general area cladograms (GACs) obtained using reconciled trees of COMPONENT 2.0 and Brooks Parsimony Analysis (BPA). For tree reconciliation, 1 000 trees were saved after the analysis. BPA yielded 18 GACs (CI = 0.805, RI= 0.549). The GAC derived from tree reconciliation is more or less pectinate and has only 3 groups of 2 areas each. These groups consist of the Chihuahuan and Sonoran deserts as sister areas on the one hand (DCHI, DSON), and the Sierra Madre Oriental and Occidental as sister areas on the other (SMOR, SMOC). This latter clade is sister to the Chihuahuan and Sonoran desert clade. The third group has the Transvolcanic Belt and Sierra Madre del Sur as sister areas (TVA, SMEX). The GAC obtained by BPA showed 4 main groups of areas: the fi rst is comprised of the Pacifi c coast of Mexico and the Balsas Depression (PCBAL), the Sierra Madre del Sur (SMEX), and the Transvolcanic Belt (TVA); the second group includes the Sierra Madre Oriental (SMOR), Sierra Madre Occidental (SMOC), Sonoran (DSON) and Chihuahuan deserts (DCHI); the third comprised the Highlands of Chiapas and Guatemala (CHIG), the Eastern Lowlands, on the Atlantic coast (ELL) and the Semiarid Lands of Tamaulipas-Texas (TAMS); the fourth group contains the Western Lowlands, in the Pacifi c coast (WLL) and northern South America (SA); the Talamanca Ridge (TALA) is isolated at the base of the 3 fi rst groups. The GAC from narrative biogeography contains 3 groups: the fi rst has areas of northern Mexico (DSON, DCHI, TAMPS), the second has areas from central Mexico (PCBAL, SMOR, SMOC, TVA), and third has areas from southern Mexico and Central America (SMEX, CHIG, TALA, WLL, ELL, SA). In general, the GAC from the BPA analysis shared more groups with the hypothesis of narrative biogeography; when compared to the GAC obtained via reconciled trees; however, all the GACs obtained are topologically distinct. Accounting for the lack of congruence between the narrative biogeography GAC, reconciled tree analysis and BPA, is challenging due to several factors: 1), erroneous interpretation of vicariant events when constructing the narrative area cladogram; 2), lack of congruence among patterns of speciation and endemism for the taxa used in this analysis; 3), the region under study is a geologically complex zone and the history of the inhabiting biota is equally complex; 4), there are many widespread species present in this region, and may obscure the relationship among the areas of endemism; 5), the patterns of endemicity are poorly-defi ned and -studied in Mexico and Central America; 6), the incorrect selection of the areas of endemism used in this study. Despite these issues the results presented here are evidence of the multi-dimensional complexity of historical biogeographical processes in the region.

Red dendrocronológica del pino de altura (Pinus hartwegii Lindl.) para estudios dendroclimáticos en el noreste y centro de México

SUMMARY Prediction of ground motion in central Mexico is of great consequence not only for Mexico City but also for several other cities in the region. However, the geometry and velocity distribution of the geological structures in central Mexico is unknown. In this paper, the velocity structure in central Mexico is investigated using seismic noise records from three different arrays, one permanent and two temporary. Distances between stations span 3–300 km. Seismic noise is analysed using time domain cross-correlation to estimate the Green's function between stations. Only the fundamental mode of Rayleigh waves is recovered in the cross-correlation of vertical component records, between 5 and 10 s period. At smaller periods, we obtain no correlation, even between closely spaced stations. This suggests that the heterogeneity of the Trans-Mexican Volcanic Belt (TMVB) hampers the propagation of Rayleigh waves smaller than 9 km. We observe a large velocity contrast between the Guerrero terrain and the TMVB. This velocity contrast, measured here for the first time at this scale, explains the appearance of regional amplification in central Mexico and the origin of the diffracted waves behind the long duration of ground motion observed in Mexico City. In the large scale, average Rayleigh wave group velocity at 5 s period is about 2.5 km s−1 in the TMVB and larger than 3.6 km s−1 outside it. Significant lateral heterogeneity is evident. In the stations of the dense Meso-American Subduction Experiment array we analysed, we observe in addition a significant increase in velocity from north to south in the central portion of the TMVB. Our results are part of ongoing studies with the final objective of building a model of TMVB that may be used to simulate ground motion in central Mexico from subduction zone earthquakes.

Distribution of hydrous minerals in the subduction system beneath Mexico

The genus Sceloporus represents a diverse and ecologically significant group of lizards within the Mexican herpetofauna, particularly in the Trans-Mexican Volcanic Belt (TMVB), a region of exceptional endemism increasingly threatened by anthropogenic pressures. In this study, we conducted a comprehensive spatial vulnerability assessment of 17 species of Sceloporus that are present in the TMVB, integrating ecological niche modelling (ENM), habitat fragmentation metrics, land-use exposure and protected area overlap. Binary distribution maps were generated from the ensemble models optimised with biomod2. For each species, we calculated the habitat area, number of habitat patches and mean patch size, synthesising these values into a composite vulnerability index. Land-use pressures were quantified through spatial overlaying of urban, agricultural and pasture-land layers, followed by principal component analysis (PCA) and k-means clustering to generate a multivariate anthropogenic pressure zonation. Species distributions were also compared against those of state and federal protected areas. ​​The 17-species analysis revealed noteworthy variation in spatial dimensions and fragmentation of habitat, exhibiting high spatial vulnerability and high exposure to anthropogenic pressure. Furthermore, our results revealed that the predicted habitats of all 17 species overlap with highly transformed urban landscapes. A bivariate risk assessment identified S. megalepidurus as the only species with both high pressure and high vulnerability, while the species S. anahuacus, S. albiventris and S. minor, currently listed as “least concern” or “not evaluated” by the IUCN, showed alarming risk signals when spatially explicit metrics were incorporated. Our integrative framework underscores the need to revisit conservation assessments by incorporating habitat quality, fragmentation and exposure to land-use pressures, not just geographic range.

Phylogenomic insights into the diversification of salamanders in the Isthmura bellii group across the Mexican highlands

Data from NASA’s TRMM satellite and NOAA’s GOES satellites were used to survey the orographic organization of cloud precipitation in central and southern Mexico during the monsoon with two main objectives: 1) to investigate large-scale forcing versus local landform controls, and 2) to compare the results with previous work in the Himalayas. At large scales, the modes of spatial variability of cloudiness were estimated using the empirical orthogonal function (EOF) analysis of GOES brightness temperatures. Terrain modulation of synoptic-scale high-frequency variability (3–5- and 6–9-day cycles normally associated with the propagation of easterly waves) was found to cause higher dispersion in the EOF spectrum, with the first mode explaining less than 30% of the spatial variability in central and southern Mexico as opposed to 50% and higher in the Himalayas. A detailed analysis of the first three EOFs for 1999, an average La Niña year with above average rainfall, and for 2001, a weak La Niña year with below average rainfall, shows that landform (mountain peaks and land–ocean contrast) and large-scale circulation (moisture convergence) alternate as the key controls of regional hydrometeorology in dry and wet years, or as active and break (midsummer drought) phases of the monsoon, respectively. The diurnal cycle is the dominant time scale of variability in 2001, as it is during the midsummer drought in all years. Strong variability at time scales beyond two weeks is only present during the active phases of the monsoon. At the river basin scale, the data show increased cloudiness over the mountain ranges during the afternoon, which moves over the low-lying regions at the foot of the major orographic barriers [the Sierra Madre Occidental (SMO)/Sierra Madre del Sur (SMS) and Trans-Mexican Volcanic Belt (TMVB)], specifically the Balsas and the Rio de Santiago basins at nighttime and in the early morning. At the ridge–valley scale (∼100–200 km), robust day–night (ridge–valley) asymmetries suggest strong local controls on cloud and precipitation, with convective activity along the coastal region of the SMO and topographically forced convection at the foothills of headwater ridges in the Altiplano and the SMS. These day–night spatial shifts in cloudiness and precipitation are similar to those found in the Himalayas at the same spatial scales.

AimOur aims were to determine the pattern of genetic variation in the endemic shrub Nolina parviflora, and to evaluate the influence of the geological history of the Trans‐Mexican Volcanic Belt (TMVB) and nearby mountainous regions on plant population divergence.LocationTrans‐Mexican Volcanic Belt, Sierra Madre Occidental, Sierra Madre Oriental and Sierra Madre del Sur mountain ranges in Mexico.MethodsTwenty‐eight populations (210 individuals) were sequenced for one nuclear (rpb2) and two chloroplast (trnL–F and psbA–trnH) DNA markers. Intraspecific phylogenetic relationships among haplotypes were reconstructed, and molecular dating, population genetic analyses and group testing were performed on the data. Isolation‐by‐distance analysis was conducted for the populations spanning the distribution of the species.ResultsTwenty‐four chloroplast marker haplotypes and 36 rpb2 haplotypes were recovered from the populations sampled. The combined marker phylogeny indicates the presence of two well‐supported clades within the N. parviflora populations. Clade 1 includes populations from Jalisco and Zacatecas and Clade 2 comprises the remaining populations. We found an east–west geographical pattern of chloroplast DNA (cpDNA) haplotype distribution, indicating a lack of gene flow between these two regions. Divergence time estimates indicate an Oligocene to mid‐Miocene divergence between Nolina and Dasylirion. Divergence estimates for Clade 1 are from the mid‐Miocene to early Pleistocene, and for Clade 2 from the early Miocene to mid‐Pliocene. Values of cpDNA GST (0.702) indicate a strong population structure and differentiation. A spatial analysis of molecular variance indicates 11 groups among the sampled populations and detects various well‐supported geographical barriers.Main conclusionsDivergence time estimates suggest a correlation between the time of divergence between distinct N. parviflora populations and periods of uplift in the TMVB. We infer that the orogeny of this mountain range played an important role in driving the diversification of plant populations in central Mexico by creating topographical barriers that limited gene flow.

Palaeolimnological records of climate change in México — Frustrating past, promising future?

The Tehuacán-Cuicatlán Valley, located at the southeast of the state of Puebla and the northeast of the state of Oaxaca in Central Mexico, south of the Trans-Mexican Volcanic Belt (TMVB), is of particular interest for understanding the evolutionary dynamics of arid and semi-arid environments, being one of the main reservoirs of biological diversity for the arid zones of North America, including the highest diversity of Agavaceae worldwide and high levels of endemism. Studying in detail the phylogeography, environmental history and population genetics of representative species will hopefully shed light on the evolutionary and ecological dynamics that generated the tremendous biodiversity and endemism of this important region in Mexico. We sequenced three non-coding regions of chloroplast genome of Agave kerchovei, a representative species of the Tehuacán Valley, generating 2,188 bp from 128 individuals sampled from eight populations throughout the species range. We used this data set to (i) characterize the levels of genetic diversity and genetic structure in A. kerchovei; (ii) predict the distribution of A. kerchovei for the present day, and to reconstruct the past geographical history of the species by constructing ecological niche models (ENM); and (iii) compare the levels of diversity in this species with those estimated for the widely distributed Agave lechuguilla. Agave kerchovei has high levels of total chloroplast genetic variation (Hd = 0.718), especially considering that it is a species with a very restricted distribution. However, intrapopulation diversity is low (zero in some populations), and genetic structure is high (FST = 0.928, GST = 0.824), which can be expected for endemic species with isolated populations. Our data suggest that Pleistocene glacial cycles have played an important role in the distribution of A. kerchovei, where the climatic variability of the region – likely associated with its topographic complexity – had a significant effect on the levels of genetic diversity and population dynamics, while the potential distribution of the species seems to be stable since the middle Holocene (6 kya). We conclude that in A. kerchovei there is a core group of populations in the Tehuacán Valley, and peripheric populations that appear to be evolving independently and thus the species is fundamentally an endemic species from the Tehuacán Valley while the populations outside the Valley appear to be in the process of incipient speciation.

Lycianthes moziniana (Solanaceae: Capsiceae) is a perennial herb with edible fruits that is endemic to Mexico. Three varieties are recognized, all known in the Mexican Transition Zone. Lycianthes moziniana var. margaretiana grows in the Sierra Madre Oriental, whereas L. moziniana var. moziniana is common along the Trans-Mexican Volcanic Belt and in the Sierra Madre Occidental. Lycianthes moziniana var. oaxacana is found exclusively in the Sierra Madre del Sur. The Mexican Transition Zone is a complex geological, climatic and biogeographical area, the result of tectonic and volcanic activity that has promoted genetic divergence and speciation. We determined the genetic variation and structure of L. moziniana. Using phylogeographical approaches, we described the demographic history and evolutionary processes leading its divergence. The intergenic spacers rpl32-trnL and ycf1 were sequenced for 133 individuals pertaining to 15 populations. The genealogical relationships were analysed using haplotype networks. Finally, based on ecological niche models, we inferred the palaeodistribution of L. moziniana during the Pleistocene. The genetic differences and the haplogroups matched the three described varieties. Geological and climatic events of the Mexican Transition Zone facilitated these results. The Trans-Mexican Volcanic Belt isolated the populations of the Sierra Madre Oriental and the Sierra Madre del Sur, while allowing the migration to the Sierra Madre Occidental, during the middle Holocene.

Mexico is a major center of evolutionary radiation for the genus Quercus, with oak species occurring across different habitat types and showing a wide variation in morphology and growth form. Despite representing about 20% of Mexican species, scrub oaks have received little attention and even basic aspects of their taxonomy and geographic distribution remain unresolved. In this study, we analyzed the morphological and climatic niche differentiation of scrub oak populations forming a complex constituted by six named species, Quercus cordifolia, Quercus frutex, Quercus intricata, Quercus microphylla, Quercus repanda, Quercus striatula and a distinct morphotype of Q. striatula identified during field and herbarium work (hereafter named Q. striatula II). Samples were obtained from 35 sites covering the geographic distribution of the complex in northern and central Mexico. Morphological differentiation was analyzed through geometric morphometrics of leaf shape and quantification of trichome traits. Our results indicated the presence of two main morphological groups with geographic concordance. The first was formed by Q. frutex, Q. microphylla, Q. repanda and Q. striatula, distributed in the Trans-Mexican Volcanic Belt, the Sierra Madre Occidental and a little portion of the south of the Mexican Altiplano (MA). The second group consists of Q. cordifola, Q. intricata and Q. striatula II, found in the Sierra Madre Oriental and the MA. Therefore, our evidence supports the distinctness of the Q. striatula II morphotype, indicating the need for a taxonomic revision. Within the two groups, morphological differentiation among taxa varied from very clear to low or inexistent (i.e. Q. microphylla-Q. striatula and Q. cordifolia-Q. striatula II) but niche comparisons revealed significant niche differentiation in all pairwise comparisons, highlighting the relevance of integrative approaches for the taxonomic resolution of complicated groups such as the one studied here.

The Costa de Nayarit in western Mexico is a classic modern example of the progradation of a coastline in a wave-dominated depositional environment. Throughout the Pleistocene, sediments have been brought to the Costa De Nayarit via three major river systems, the Rio Grande de Santiago, the Rio San Pedro and the Rio Acaponeta. These river systems obtain their sediments from two distinctly different volcanic provinces within central Mexico, the Sierra Madre Occidental (SMO), a volcanic province characterized by its predominance of felsic volcanism (rhyolites) and pyroclastic flows (welded ash flow tuff and ignimbrite), and the Trans-Mexican Volcanic Belt (TMVB), which is characterized by its predominance of mafic and intermediate volcanism (basalts and andesites). Petrographic studies of sediment samples collected from these river systems and the modern beaches of the Costa de Nayarit along with Scanning Electron Microscope (SEM) and electron Microprobe chemical analyses, provide insight into the provenance of sediments from each river system as well as to where the sediments on the modern beaches are originating. Progradation in a wave-dominated depositional environment results from the construction and successive accretion of shoreface successions (beach ridges) to the coastline. Studying sediment samples from the shoreface succession (beach ridges) constructed during the current Holocene sea-level highstand along the Costa de Nayarit determined that they are made up of a mixture of sediments sourced from longshore transportation of Rio Grande de Santiago/Rio San Pedro (RGS/RSP) paleo-river sediment and onshore transportation of reworked sediment from the drowned RGS/RSP paleo-river delta constructed on the continental shelf during the previous sea-level lowstand in the Pleistocene. The study also determined that sediments of the southern shoreface successions (beach ridges) were more influenced by longshore transportation of RGS/RSP paleo-river sediments than the northern shoreface successions (beach ridges), which were more influenced by sediments being reworked from the continental shelf and transported onshore.

The genus Polianthes (Agavaceae) is endemic to Mexico and is important at the scientific, economical, and cultural level since prehispanic times. Habitat destruction is one of the main factors affecting populations of Polianthes species, yet little is known about the geographic distribution of this genus, and thus its vulnerability to habitat change. We compared three different approaches to measure the Polianthes species area of distribution to assess the risk of species extinction applying the MER (Method of Evaluation of Risk extinction of wild species for Mexico): area of occupancy, extent of occurrence, and ecological modeling. We also found the richness areas of distribution of this genus. We compared the species distributions with Terrestrial Protected Regions (TPR) and Natural Protected Areas (NPA). Although the three methods used to calculate the species area of distribution agree about the highly restricted nature of Polianthes species. The area of occupancy sub-estimate the species distribution, while the extent of occurrence over-estimate it for species with disjoint distribution. Thus, we recommend the use of ecological modeling to improve the assessment of the current species distribution area to apply the MER. Most Polianthes species are distributed in the Sierra Madre Occidental and Transvolcanic Belt. Three species do not occur in any of the NPA or TPR, one species has suitable habitat in three TPR but has not been recorded there, and one species, P. palustris, is likely extinct.