Mexican Transvolcanic Belt Research Articles

Extinction risk assessment of the endemic terrestrial vertebrates in Mexico

An increasing number of species at risk raise concerns worldwide. While global assessments provide a comprehensive framework, national species conservation status is needed to provide specific policies. The IUCN Red List and the Mexican Norm (MER) methods were used to assign risk categories for 310 endemic species of terrestrial vertebrates at national and ecoregion levels. We used ecological niche models projected as species potential distributions, and refined species extant distributions including only remnant suitable habitat, to assess species risk assignments for Criterion A and B (IUCN Red List), and Criterion A, B, C, and D (MER). Of the total number of species, the IUCN Red List and MER report 71 and 155 species at risk, respectively. Our assessment assigned a risk category to 38 and 299 species, respectively. The discrepancies in the number of species between our proposal and the IUCN Red List and MER are striking and probably due to shortcomings of deficient information or expert opinion of species, standardization between methods, and the number and particular characteristics of criteria. Species occurring in the Mexican Transvolcanic Belt, the Great Plains and the Yucatan Peninsula ecoregions were at higher extinction risk than species occurring in the Mexican deserts, the Mexican High Plateau, the Southern Sierra Madre and the Western Sierra Madre ecoregions. Our proposal of using species potential and extant distributions models facilitates frequent species assessments, as conditions of risks fluctuate over time, and contributes to designing national and regional conservation programs of species and populations at risk.

Population Viability Analysis of Kinosternon hirtipes murrayi in Central México, with Notes on the Conservation Status of the Other Three Subspecies of the Lineage

With 6 subspecies described, the rough-footed mud turtle (Kinosternon hirtipes) has been considered a species with high morphological diversity. One subspecies, K. h. megacephalum, is already extinct. The remaining subspecies are poorly studied, with very limited information available only for K. h. murrayi (a widespread subspecies). The remaining taxa (K. h. tarascense, K. h. chapalense, K. h. magdalense, and K. h. hirtipes) are microendemic and restricted to endorheic valleys in the Mexican Transvolcanic Belt. Using baited fyke nets, hoop traps, and a seine, we surveyed for these microendemic subspecies for 3 yrs across their known distributions. With the data gathered in the field and published information, we conducted a population viability analysis (PVA) to model the minimum characteristics needed to improve population growth under 3 scenarios (optimistic, intermediate, and pessimistic). Very few K. hirtipes turtles were collected. No K. h. chapalense were located in Lake Chapala, but we did capture 4 individuals in Lake Zapotlan. Similarly, only 6 individuals of K. h. magdalense were captured. No K. h. hirtipes individuals were collected in the Valley of México. Two populations of K. h. tarascense were located in the Pátzcuaro basin: the first populations reported for that subspecies. The PVA showed that harvest on adults in populations with fewer than 200 turtles significantly compromises population persistence. However, a population size of 200 and limited or no harvest are enough to increase population size and persistence for at least 100 yrs. Assurance colonies and head-starting may be the only chance for long-term survival of some of these microendemic turtle lineages.

Precopulatory mating and postzygotic isolation between two walnut‐infesting species of Rhagoletis from Mexican highlands

AbstractPleistocene glacial and postglacial cycles producing contraction and expansion of temperate habitats have resulted in substantial diversification among several plant and animal taxa of Neararctic origin undergoing periods of isolation and secondary contact in high‐elevation areas of Mexico. One of such groups are walnut‐infesting fruit flies in the genus Rhagoletis (Diptera: Tephritidae), comprised of six recently derived species among which phylogenetic relationships have been difficult to unravel using conventional molecular methods. Here, we examined pre‐ and postzygotic isolation between two genetically similar and morphologically distinct species which are currently parapatric in central Mexico. Local adaptation driven by differences in host plant phenology between Rhagoletis zoqui Bush and Rhagoletis ramosae Hernández‐Ortíz resulted in allochronic isolation. Despite the existence of precopulatory mating isolation, there was a substantial number of hybrid matings in field cages where conspecific and heterospecific males and females were simultaneously released. The bulk of mating activity took place on host fruit. Rhagoletis zoqui females were more reluctant to mate with R. ramosae males than with males of their own species. Distinctive behavioral differences were observed between males during contests, fruit guarding, and approach to conspecifics on fruit. There was also some asymmetric postzygotic isolation, with the hybrid combination of R. zoqui males and R. ramosae females resulting in lower egg hatch than other mating combinations. Results were consistent with those of a phylogenetic study suggesting recent divergence of R. ramosae from Rhagoletis completa Cresson and R. zoqui in the Sierra Madre Oriental and the Mexican Trans Volcanic Belt.

The morphological phylogeny of the family Protoschizomidae revisited (Arachnida: Schizomida): setal characters, fossil and paraphyletic genera

Abstract The schizomid family Protoschizomidae, endemic to North America, is represented by two genera and 15 species. While most of the species are distributed in caves in the Sierra Madre Oriental system in Mexico; other species are found in caves in the Sierra Madre Occidental system. Recently, a new species of this family was described from a cave in the Mexican Trans-Volcanic Belt, representing the linking bridge between both Sierras. In the present contribution, we propose a new nomenclature of the pedipalp setae of the protoschizomids. We revise the phylogenetic status of Protoschizomidae using 137 morphological characters (including the proposed pedipalp setae) and 7 outgroup taxa using parsimony criteria. Based on our results, Protoschizomidae was recovered as monophyletic, but the monophyly of Protoschizomus Rowland, 1975 was not recovered because of the inclusion of Agastoschizomus Rowland, 1971 and the fossil Onychothelphynous bonneri Pierce, 1951. Therefore, we transfer the genus Onychothelyp...

Phylogenomics and species delimitation in the knob-scaled lizards of the genus Xenosaurus (Squamata: Xenosauridae) using ddRADseq data reveal a substantial underestimation of diversity

Middle American knob-scaled lizards of the genus Xenosaurus are a unique radiation of viviparous species that are generally characterized by a flattened body shape and a crevice-dwelling ecology. Only eight species of Xenosaurus, one of them with five subspecies (X. grandis), have been formally described. However, species limits within Xenosaurus have never been examined using molecular data, and no complete phylogeny of the genus has been published. Here, we used ddRADseq data from all of the described and potentially undescribed taxa of Xenosaurus to investigate species limits, and to obtain a phylogenetic hypothesis for the genus. We analyzed the data using a variety of phylogenetic models, and were able to reconstruct a well-resolved and generally well-supported phylogeny for this group. We found Xenosaurus to be composed of four major, allopatric clades concordant with geography. The first and second clades that branch off the tree are distributed on the Atlantic slopes of the Sierra Madre Oriental and are composed of X. mendozai, X. platyceps, and X. newmanorum, and X. tzacualtipantecus and an undescribed species from Puebla, respectively. The third clade is distributed from the Atlantic slopes of the Mexican Transvolcanic Belt in west-central Veracruz south to the Pacific slopes of the Sierra Madre del Sur in Guerrero and Oaxaca, and is composed of X. g. grandis, X. rectocollaris, X. phalaroanthereon, X. g. agrenon, X. penai, and four undescribed species from Oaxaca. The last clade is composed of the four taxa that are geographically closest to the Isthmus of Tehuantepec (X. g. arboreus, X. g. rackhami, X. g. sanmartinensis, and an undescribed species from Oaxaca). We also utilized a variety of molecular species delimitation approaches, including analyses with GMYC, PTP, BPP, and BFD∗, which suggested that species diversity in Xenosaurus is at least 30% higher than currently estimated.

Haplotype and nucleotide variation in the exon 3-VNTR of the DRD4 gene from indigenous and urban populations of Mexico.

To describe the population structure of the 48-bp variable number of tandem repeats (VNTR), located in exon 3 of the dopamine receptor D4 gene (DRD4), in 41 Tarahumara from northern Mexico, 20 Mixe from southern Mexico, and 169 people from Mexico City. Genotypes for the DRD4-VNTR were determined, from which 15 Tarahumara, eight Mixe, and 37 urban homozygous individuals were sequenced. Repeat-allele frequencies were compared with other world populations. The DRD4-VNTR variation in Mexico City appeared similar to the world mean. For the Mixe and Maya, DRD4-VNTR diversity appeared closer to South American groups whereas the Tarahumara were similar to North American groups. People from Mexico City and the Mixe exhibited attributes of a large and admixed population and an isolated population, respectively. The Tarahumara showed endogamy associated with a substructure as suggested by a preliminary regional differentiation. For the DRD4-VNTR and/or the adjacent 5'-173 bp sequence, the three populations exhibited negative Tajima's D. Two new VNTR haplotypes were discovered: one in Mexico City and another among the Tarahumara. A differentiation in the DRD4-VNTR of global relevance occurs between northern and southern populations of Mexico suggesting that the Mexican Trans-volcanic Belt has been a major frontier for human dispersion in the Americas. Ancient trespass of this barrier appears thus related to a major change in the population structure of the DRD4-VNTR. Distinctive and independent patterns of DRD4-VNTR diversity occur among the two Mexican indigenous populations by a still undefined combination of drift and selection.

Firewood extraction affects carbon pools and nutrients in remnant fragments of temperate forests at the Mexican Transvolcanic Belt

Globalmente, los fragmentos forestales representan un almacen importante de carbono, pero estos fragmentos estan bajo una fuerte presion de degradacion; principalmente, debido a la extraccion ilegal de madera para lena y carbon vegetal. El presente estudio evaluo el efecto de la extraccion de lena sobre los almacenes de carbono y la dinamica de nutrientes del suelo en bosques templados de fragmentos remanentes en el centro de Mexico. Se estudiaron cuatro sitios con diferente grado de intensidad de extraccion de lena, donde se midieron el carbono almacenado y el flujo de nutrientes durante dos anos consecutivos. El carbono en la biomasa aerea y en el suelo se redujo con el aumento de la intensidad de la extraccion. El bosque degradado (DF) presento 55 % menos contenido total de carbono que el bosque seminatural (SF). Asi mimo, la produccion de hojarasca tambien se redujo en el DF, pero la descomposicion del mantillo fue mayor en el SF. Como consecuencia, el DF presento menores entradas de carbono organico al suelo. El amonio disponible, el carbono y nitrogeno en la biomasa microbiana del suelo tambien fueron menores en el DF. La conclusion de este trabajo es que la extraccion de lena en los fragmentos forestales en Mexico reduce drasticamente las cantidades de carbono almacenado, los flujos de carbono y nutrientes por medio de la hojarasca, y por tanto, la dinamica de los nutrientes del suelo es afectada.

Floristics of the cloud forest and border vegetation in Avándaro, Valle de Bravo, Mexico state, Mexico

The cloud forest studied in this work is located at the central part of the border between the Mexican Transvolcanic Belt and the Balsas basin. The floristic list of the area includes 98 families, 245 genera and 391 species of vascular plants. The arboreal vegetation is divided into three strata, a higher (40 m) mostly constituted by oaks and Zinowiewia integerrima, a medium (20 m) by Carpinus caroliniana, Ternstroemia lineata subsp. lineata and Tilia americana, among others, and a lower one (5-15 m) by Clethra spp., Cleyera integrifolia, Cornus disciflora, Garrya laurifolia, Meliosma dentata, Oreopanax xalapensis, Parathesis melanosticta, Styrax argenteus and Symplocos citrea. Shrubby and herbaceous layers are rich because the disturbance caused by the surrounding agricultural and recreational areas. We discussed the conservation status of the cloud forest based on environmental indicators derived from the floristic results.

Enzyme activity as an indicator of soil quality changes in degraded cultivatedAcrisolsin the Mexican Trans‐volcanic Belt

AbstractSoils located at the Mexican Trans‐Volcanic Belt (MTB) have a worrying degree of degradation due to inappropriate management practices. Early indicators of soil changes are very useful to alert about negative impacts of wrong managements on these volcanic soils. The aim of this work was to evaluate the short‐term effects (4 years) of different agricultural practices on soil organic matter (SOM) quality and to validate the potential of the selected biochemical properties as optimal early indicators of soil quality in Mexican cultivatedAcrisols. During 2002–2005 four agronomic management systems: conventional (Tc); improved conventional (Ti); organic (To) and fallow (Tf) were assayed in plots located at the MTB. An uncultivated soil under grass cover (Sg) was used as reference. Soil samples were collected at 0–10 cm depth and were analysed chemically (soil organic C, total N, water‐soluble C and humic C), and biochemically (total and extra‐cellular enzyme activity). After 4 years, soil organic C, total N, water‐soluble C, and dehydrogenase activity had higher values in To, followed by Ti treatment. A similar response pattern was observed in the extra‐cellular enzyme activity. The highest total enzyme activity was found in Sg, followed by Ti and To treatments, and the lowest values appeared in Tc and Tf. To and Ti increased SOM contents of the degradedAcrisolsstudied, while Tc and Tf managements decreased the quality of these soils. The results showed that the assayed soil enzymes can be used as indicators of quality changes of these Mexican volcanic soils. Copyright © 2010 John Wiley & Sons, Ltd.

Biochemical indicators of carbon dynamic in an Acrisol cultivated under different management practices in the central Mexican highlands

Prediction of soil changes that occurs as a result of agronomic management practices is very useful, particularly when restoration of degraded soils wants to be implemented. The aim of this work was to study the short-term effect (4 years) of different agricultural practices on biochemical and microbial indicators related to soil organic matter (SOM) and to validate the sensibility of a set of biological indicators expressing C dynamic in a representative Mexican volcanic soil. Four soil management systems (2002–2005): traditional (Tt), improved (Ti), organic (To), and fallow (Tf) were assayed in experimental plots ( Acrisol) located at the Mexican Trans-volcanic Belt. An uncultivated soil under grass cover (Sg) was used as reference. The Acrisol came from weathered volcanic materials and had severe problems of erosion. Soil samples (0–10 cm depth) were analyzed for soil organic C (SOC), total N (Nt), water-soluble C (WSC), and humic C (Hm-C); and for microbial biomass (MB), soil respiration (SRv), net N mineralization (Nm), dehydrogenase activity (DHa), arginine ammonification (ARa), and extra-cellular enzyme activities (urease, protease, β-glucosidase, and acid phosphatase). Higher values of SOC, Nt, WSC, Hm-C, MB, SRv, Nm, DHa and ARa were found under To and Ti as compared to Tt and Tf managements. A similar response pattern was observed in the case of extra-cellular enzyme activities. These results suggested an interaction between the available energy-rich compounds and the biochemical energy preserved in humus–enzyme complexes. Higher levels of the biological parameters measured in To and Ti treatments were associated to a higher SOC content. These two treatments contributed to the regeneration of these degraded Acrisols, while no soil quality improvements were registered under Tt and Tf managements in the short-term. The selected biological indicators were useful to evaluate the soil quality changes of degraded Mexican cultivated Acrisols.

Woods from Miocene sediments in Panotla, Tlaxcala, Mexico

The extant regional vegetation of Panotla, Tlaxcala, Mexico, is the result of its geography, mainly due to the buildup of the Mexican Trans-volcanic Belt. Before this volcanic belt originated, palaeobotanical evidence suggests that topographic, palaeoclimatic and ecological conditions were different, allowing the establishment of an evergreen tropical forest represented by plants similar to Terminalia, Cedrela and cf. Hypodaphnys, which together suggest the presence of a warm–humid (tropical) climate in a region not higher than 900 masl. In contrast, today Panotla is located at an altitude that varies from 2100 to 2300 masl, has a temperate sub-humid climate, with annual precipitation of 1650 mm, maximum annual temperature of 24.3 °C, and its vegetation is composed of a white pine ( Pinus pseudostrobus Lindol.), oak ( Quercus spp.) and white cedar ( Cupressus benthamii Endl.). Geological and palaeobiological evidence suggests an active volcanic and tectonic scenario that influenced plant evolution by shifting climatic conditions from high temperature-humid to high temperature-dry, selecting the plant communities in the region through time, supporting the change from a tropical rain forest to a xeric vegetation.

Effect of different agricultural management systems on chemical fertility in cultivated tepetates of the Mexican transvolcanic belt

Volcanic soils in their natural state often require some amelioration to accommodate their use for agriculture. Tepetates are defined as hardened volcanic tuffs derived from geo-pedological processes; they have been partially altered by weathering. Tepetates occupy extensive areas of Mexico's Central Highlands and some of them have been adapted for agricultural use after the mechanical breaking up of this hard material. In their native condition tepetates contain only traces of C, N and available P. So, after their incorporation into agriculture production, the addition of fertilisers becomes necessary to improve soil fertility. In the present work changes in certain chemical and physico-chemical soil properties of cultivated tepetates were studied in the short-term (2002–2005) and medium-term (1986–2005) scales. Experimental plots situated in Tlalpan (State of Tlaxcala) were subjected to the following agricultural management systems: Traditional (Tt), Improved (Ti) and Organic (To). In the short term (4 years), the To management system, in which organic residues and manures were added, led to a decrease in the acidification tendency after cultivation, a recovery of initial exchangeable K + levels, and an increase in soil organic C (SOC), total nitrogen (Nt) and available P (Pa) contents in the Ap horizon. The Ti management, in which crop residues and more chemical fertilisers were added, was especially efficient in increasing the concentration of available P. After 20 years of traditional cultivation, the tepetates showed a decrease in soil pH and exchangeable Mg 2+ and K + values, leading to a decline of the base saturation. These results point to the fragility and low buffer capacity of these systems. In contrast, a tendency of SOC, Nt and Pa accumulation was observed after 20 years of cultivation, influenced by the agricultural management system applied. Tepetates adapted for agricultural use evolved into more fertile substrates over the years of cultivation.

Phylogenetic Position of Porthidium Hespere (Viperidae: Crotalinae) and Phylogeography of Arid-Adapted Hognosed Pitvipers Based on Mitochondrial DNA

Gaps in recent studies of hognosed pit vipers in the genus Porthidium have left researchers with an incomplete estimate of the evolutionary history of this group. Mitochondrial DNA sequence data from the poorly known P. hespere and additional Porthidium sequences obtained from GenBank were used to re-analyze the phylogenetic relationships of Porthidium. Using sequence data from the South American Porthidium, we also updated a previous molecular clock calibration based on the uplift of the Isthmus of Panamá, and utilized this updated calibration to evaluate the phylogeography of arid-adapted Porthidium. Results from Bayesian Markov chain Monte Carlo phylogenetic methods underscore the historical pattern of bi-directional dispersal into and out of South America within Porthidium, and place P. hespere as the sister species to P. dunni. The three species of arid-adapted Porthidium distributed across the Pacific coast of southern Mexico and northern Central America may have diverged in the late Miocene after the enlargement of the Río Balsas drainage following the formation of the Mexican Transvolcanic Belt and the volcanic uplifting across the Chiapan–Guatemalan highlands.Debido a la ausencia de algunas especies en los estudios recientes de las nauyacas nariz de cerdo del género Porthidium, los investigadores no tienen una estimación completa de la historia evolutiva de este grupo. Se utilizaron nuevas secuencias de ADN mitocondrial de la poco conocida P. hespere y otras secuencias obtenidas de GenBank para reanalizar las relaciones filogenéticas de Porthidium. Usando secuencias de Porthidium sudamericanas, también se actualizó una calibración previa del reloj molecular basada en la elevación del Istmo de Panamá, y esta calibración actualizada se utilizó para evaluar la filogeografía de las especies de Porthidium adaptadas a la aridez. Los resultados de los métodos filogenéticos Bayesianos Markov chain Monte Carlo enfatizan el patrón histórico de dispersión bidireccional hacia y desde Sudamérica en Porthidium, y ubican a P. hespere como especie hermana de P. dunni. Las tres especies de Porthidium adaptadas a la aridez de la costa Pacífica del sur de México y norte de Centroamérica podrían haber divergido en el Mioceno tardío después del ensanchamiento del drenaje del Río Balsas que siguió a la formación del Eje Neovolcánico y la elevación volcánica de las tierras altas de Chiapas y Guatemala.

Riqueza de aves del Parque Nacional Barranca del Cupatitzio, Michoacán, México

Se documenta la riqueza de aves del Parque Nacional Barranca del Cupatitzio, Michoacán, México, registrada mensualmente de agosto de 2003 a junio de 2005 mediante colecta, detección visual y auditiva y foto trampeo. La riqueza avifaunística en el parque fue de 128 especies, pertenecientes a 93 géneros, 35 familias y 12 órdenes. El estimador Jackknife de segundo orden de la riqueza de especies indica que pueden registrarse al menos 13 especies más y que se logró detectar el 90.8% de las especies posibles a ocurrir en la zona de estudio. Por su estacionalidad, 93 especies son residentes, 25 migratorias, 4 transitorias, 5 casuales y 1 introducida. El endemismo fue de 15 especies, que constituyen el 12% de las aves endémicas de México y el 51.8% de las endémicas del eje Neovolcánico. De las especies registradas, 1 se encuentra amenazada y 6 sujetas a protección especial. Se identificaron 20 especies prioritarias para su conservación considerando criterios de riesgo, endemismo y restricción de distribución.

Molecular systematics of the genus Allodontichthys (Cyprinodontiformes: Goodeidae)

Phylogenetic analyses of cytochrome c oxidasesubunit I (627bp) and mitochondrial controlregion (338bp aligned) sequences for all knownspecies of Allodontichthys wereperformed. Allodontichthys was recoveredas monophyletic, and A. hubbsi wassupported as the most primitive member of thegenus in all analyses. Combined-data analysessuggest that A. polylepis is sister to aclade comprising A. tamazulae and A. zonistius; however, a strict consensus of COIand control region cladograms results in acollapse of this node. The two species thatare broadly sympatric, A. hubbsi and A. tamazulae, are not sister taxa.Allodontichthys was found the sistergroup of a clade including Ilyodon andXenotaenia. These three genera are theonly goodeids to occupy high-gradient riversystems. Ilyodon and Allodontichthys share similar distributions;however, Allodontichthys exhibits greaterthan an order of magnitude more geneticvariation in COI than Ilyodon incomparisons of individuals from the samelocalities in the Ameca and Armeria drainagesystems. This is interpreted to mean Allodontichthys arrived in some westerndrainages significantly before Ilyodon.The Rio Coahuayana appears to be the center oforigin of the genus Allodontichthys. This river basin contains the most primitivemember of the genus, and appears to haveconnected with the Mesa Central, the center of endemism of the Goodeidae. A calibrated rateof molecular change in COI reveals Allodontichthys began diverging approximately6.2 million years ago (mya). Remainingspeciation in the group appears to haveoccurred about 2.7 to 3.3 mya. The hypothesisthat a “hard” polytomy comprising A. zonistius, A. polylepis, and A. tamazulae could be explained by speciation ofA. polylepis and A. tamazulae fromdifferent A. zonistius ancestors ispresented. Stream capture is evident but notfrequent in the history of Allodontichthys, and speciation does notclearly correlate with documented geologicactivity of the Mexican Transvolcanic Belt.

Los peromyscus (Rodentia: Muridae) en la colección de mamíferos de la Universidad Autónoma Metropolitana-Unidad Iztapalapa (UAMI)

Se examinaron 3704 ejemplares de ratones de los géneros Habromys, Osgoodomys y Peromyscus, excepto los de Tlaxcala. La mayoría de los ejemplares proceden de localidades del Eje Volcánico Transversal, aunque también se incluyen los de capturas marginales en otras regiones del país, así como los donados o que en calidad de depósito permanente se albergan en la Colección. Por lo anterior, se consignan ejemplares de las especies Habromys lophurus, Osgoodomys banderanus, Peromyscus aztecus, P. beatae, P. bullatus, P. difficilis, P. eremicus, P. furvus, P. gratus, P. guatemalensis, P. hylocetes, P. leucopus, P. levipes, P. maniculatus, P. megalops, P. melanocarpus, P. melanophrys, P. melanotis, P. mexicanus, P. ochraventer, P. perfulvus, P. simulus, P. spicilegus, P. yucatanicus y P. zarhynchus.

Ultrastructure and motility of the caudal epididymis spermatozoa from the volcano mouse (Neotomodon alstoni alstoni Merriam, 1898)

The volcano mouse Neotomodon alstoni alstoni is a genus endemic to the higher elevations of the Mexican transvolcanic belt. In the present study we examined for the first time the morphological features of the spermatozoa taken from the caudal epididymis of this species by transmission and scanning electron microscopy. Spermatozoan motility was studied in sucrose and bicarbonate solutions; vitality and morphology were observed by light microscopy. Transmission electron microscopy shows that the head of spermatozoon is asymmetric and possesses a large and curved hook. The axoneme of the spermatozoan tail is highly developed at fibers 1, 5, and 6. Absolute and relative measurements of the length of the head, the midpiece, and the rest of the tail were also obtained. N. alstoni alstoni spermatozoa were hyperactive in the presence of 290 mM sucrose and 10 and 20 nM bicarbonate solutions exhibited high motility (180–190 μm/sec), and high flagellum beating frequency (10–12 Hz). In contrast, the spermatozoa in 310 mM sucrose solution showed scarce motility (13.5 ± 3.8 μm/sec) and low beating frequency (1.5 ± 0.4 Hz). It is proposed that the volcano mouse spermatozoa possess some features very similar to other mammalian spermatozoa and that bicarbonate triggers caudal epididymal sperm motility of this species. J. Exp. Zool. 287:316–326, 2000. © 2000 Wiley-Liss, Inc.

Systematics of the Smooth-Toothed Pocket Gopher,Thomomys umbrinus, in the Mexican Transvolcanic Belt

Difficulties in the subspecific identification of more than 200 specimens of Thomomys umbrinus from the State of Tlaxcala led us to examine the systematic status of the eight subspecies recognized within the Mexican Transvolcanic Belt. We gathered representative samples of those subspecies (≥ 50) during three years of fieldwork. These were analyzed together with samples from other populations not previously assigned to subspecies, as well as voucher specimens from several collections. Thirty-seven variables, obtained from 1145 specimens, were analyzed morphometrically using univariate and multivariate statistics. Within-population variation was highly influenced by sexual dimorphism, and especially by ontogenetic variation; therefore, these two factors should be considered carefully when making systematic and taxonomic decisions. Our analysis of geographic variation determined only two recognizable subspecies of Thomomys umbrinus within the Mexican Transvolcanic Belt: Thomomys umbrinus umbrinus (Richardson, 1829) and Thomomys umbrinus pullus Hall and Villa, 1948.

Ultrastructure and motility of the caudal epididymis spermatozoa from the volcano mouse (Neotomodon alstoni alstoniMerriam, 1898)

The volcano mouse Neotomodon alstoni alstoni is a genus endemic to the higher elevations of the Mexican transvolcanic belt. In the present study we examined for the first time the morphological features of the spermatozoa taken from the caudal epididymis of this species by transmission and scanning electron microscopy. Spermatozoan motility was studied in sucrose and bicarbonate solutions; vitality and morphology were observed by light microscopy. Transmission electron microscopy shows that the head of spermatozoon is asymmetric and possesses a large and curved hook. The axoneme of the spermatozoan tail is highly developed at fibers 1, 5, and 6. Absolute and relative measurements of the length of the head, the midpiece, and the rest of the tail were also obtained. N. alstoni alstoni spermatozoa were hyperactive in the presence of 290 mM sucrose and 10 and 20 nM bicarbonate solutions exhibited high motility (180-190 microm/sec), and high flagellum beating frequency (10-12 Hz). In contrast, the spermatozoa in 310 mM sucrose solution showed scarce motility (13.5 +/- 3.8 microm/sec) and low beating frequency (1.5 +/- 0.4 Hz). It is proposed that the volcano mouse spermatozoa possess some features very similar to other mammalian spermatozoa and that bicarbonate triggers caudal epididymal sperm motility of this species. J. Exp. Zool. 287:316-326, 2000.

Plantae Alpinae Novae Mexicanae: Argemone Subalpina (Papaveraceae)

A new species ofArgemone (Papaveraceae),A. subalpina, is recognized from the subalpine glades of Sierra Pena Nevada, Nuevo Leon, Mexico. It is the first member of the poppy family to be associated with timberline vegetation in the New World. The new taxon is closely related toA. platyceras of the Mexican transvolcanic belt, but differs by retrorse cauline spines, broadly ellipsoid flower buds to 20 mm long, caudate sepal norns 3–5 mm long, and recurved fruit spines.