Mexican Transition Zone Research Articles

Geographical patterns and determinants of species richness in Mexico across selected families of vascular plants: implications for conservation

Mexico is considered a megadiverse country containing more than 10% of the world's biodiversity. The distribution of this species richness and endemism is different among the different Mexican states. We examined the species richness patterns of 13 families of vascular plants (including ferns, gymnosperms and angiosperms) in Mexico using political divisions (states) as units of analysis. We analysed the species richness values (absolute richness, endemic richness and restrictive richness) of these plant families using stepwise multiple regression analysis, assessing their relationship with a set of 10 environmental variables (expressed as heterogeneity coefficients). A combined cluster analysis with multidimensional scaling analysis (MDS) and an analysis of similarities were also undertaken to define the spatial–geographical patterns. Additionally, we proposed a methodological strategy to determine which states of Mexico have priorities for conservation. Our results suggested that the three species richness values used were significantly predicted by environmental factors, especially by climatic heterogeneity. Notwithstanding that a linear pattern was recognized, the Mexican states were gathered in four groups, which were confirmed by the MDS and the cluster analysis: (1) the Yucatan Peninsula, (2) arid Mexico, (3) the Mexican Transition Zone and (4) the megadiverse states. We proposed that 12 Mexican states include all the environmental conditions and are candidates for developing conservation programmes: (1) Quintana Roo, Tabasco and Yucatán, (2) Baja California, Chihuahua and Sinaloa, (3) Guerrero, Jalisco and Nuevo León and (4) Chiapas, Oaxaca and Veracruz.

Biogeografía de la Zona de Transición Mexicana con base en un análisis de árboles reconciliados

We analyzed the relationships of the areas of endemism of the Mexican Transition Zone through 3 hypotheses of regionalization. We used a reconciled trees method based on the phylogenies of 10 genera of beetles, gymnosperms, lizards and snakes. Seven general area cladograms were generated using assumptions 0 and 1 and the Nelson and majority consensus. They showed 2 groups of areas, 1 with Neotropical affinities and the other with Nearctic affinities. The Sierra Madre del Sur resulted as the sister area of the Trans-Mexican Volcanic Belt. Other constant patterns were the area that involves Tamaulipas and Texas as sister area of the Chihuahuan and Sonoran deserts, and the highlands of Chiapas and Guatemala were always recovered as the sister area of the Talamanca ridge. Our results suggest that the most important vicariant events within the Mexican Transition Zone are the Trans-Mexican Volcanic Belt, which divides the majority of the endemism areas with Neartic affinities (north to this) from those endemism areas of Neotropical affinities (south to this) and the Tehuantepec Isthmus; which together with the Nicaraguan depression isolates Nuclear Central America. Other patterns appear in either regionalization proposal, but not within the 3, and require future studies in order to find well supported explanations. Even though our results have appeared in previous hypotheses, there are worth due to the fact that we include phylogenetic information of different taxa, we employed reconciled trees, an insufficiently used method, and we searched for congruence between results using 3 regionalization proposals.

The classic theory of Mexican Transition Zone revisited: the distributional congruence patterns of Passalidae (Coleoptera)

We incorporated new data to re-evaluate the biogeographical patterns in the Mexican Transition Zone (MTZ) through the recognition of congruence in the geographic distributions of Mexican passalids (Coleoptera : Passalidae). We used three different approaches to parsimony analysis of endemicity (PAE): (1) the use of specific distribution data; (2) the application of a null model of significant co-occurrence to the specific distribution data; and (3) the use of predicted potential distributions through ecological niche modelling. Overall, these approaches sharpened the delimitation of distributions in three general zones. General zone (GZone) 1 includes species of restricted distribution in the state of Chiapas; the grid cells that make up this zone lie mainly in the Chiapas biogeographical province. GZone 2 includes species of restricted distribution located mainly in the states of Veracruz, Puebla, Hidalgo and Queretaro; the grid cells of this zone lie mainly in the Sierra Madre Oriental province. GZone 3 includes species with restricted distribution occurring mainly in the states of Guerrero and Oaxaca; the grid cells of this zone lie mainly in the Sierra Madre del Sur biogeographical province. The patterns of distributional congruence found in this study revealed three important distributional zones for the passalid species within the MTZ highly coincident with patterns proposed by Halffter.

Distribution patterns of the American species of the freshwater genus Eucyclops (Copepoda: Cyclopoida)

Based on the superposition of 19 individual tracks of American species of the freshwater copepod genus Eucyclops, two generalized tracks were found. The Western Amazonian track (southern Peru, eastern Brazil, and central Colombia) corresponding to the Amazonian subregion and the South American Transition Zone, and the Mesoamerican-Northwestern South American track (central Colombia, Central America, and northeastern Mexico) corresponding to the Neotropical region, the Mexican Transition Zone, and the Nearctic region. One node was found in Colombia, an area where both generalized tracks intersect. The distributional patterns of Eucyclops apparently involve two cenocrons: one Holarctic, and another Paleotropical. The Western Amazonian generalized track can be correlated with the existence of rivers that function either as barriers or dispersal passageways, the uplift of the Andes, and the presence of the Miocene “Pebas lake/wetland system.” The Mesoamerican-Northwestern South American generalized track can be associated with climate changes resulting from the uplift of North American mountain ranges, the presence of marine barriers (Isthmus of Tehuantepec and Panama) and the uplift of mountains in southern Mexico and Central America. The closing of the marine barrier represented by the Isthmus of Panama seems to have been a key event in the northward and southward dispersal of Eucyclops in the Americas.

How dung beetles respond to a human‐modified variegated landscape in Mexican cloud forest: a study of biodiversity integrating ecological and biogeographical perspectives

AbstractAim To analyse how the dung beetles (Scarabaeinae) respond to a modified, variegated landscape, taking into account the biogeographical peculiarities of the Mexican Transition Zone.Location This study covers cloud forest (CF) of the Sierra Norte de Puebla mountain range and part of the Sierra Madre Oriental mountain range (Mexico).Methods We applied proportional sampling based on the landscape variegation model with Scarabaeinae as the indicator group, and using two approaches: structural units (vegetation type) and spatial units (windows). We used two measures – richness and Shannon diversity – and applied multiplicative diversity partitioning to obtain independent alpha and beta diversities for the landscape, windows and vegetation types. We grouped species by biogeographical distribution pattern for the biogeographical analysis and by whether they were originally from CF.Results The transformation of CF into secondary forest, pastures and other types of vegetation increases the Scarabaeinae diversity of the landscape, in vegetation types and windows. This increase is the result of species arriving from the tropical lowlands. However, the original dung beetle community of the CF dominates at different scales in the number of species, abundance and biomass. With increasing habitat modification, beta diversity increases in the windows, and species with the Tropical Palaeoamerican distribution pattern increase in abundance in vegetation types and windows.Main conclusions The variegated character of the landscape explains well the distribution and diversity of this dung beetle community. The peculiar characteristics of the Mexican Transition Zone have an effect owing to the overlap of fauna with different biogeographical origins. The conversion of fragmented landscapes to variegated landscapes could be a conservation goal in human‐modified mountain landscapes. Sampling proportional to the area of different types of vegetation and the use of windows offer an alternative experimental design in variegated landscapes.

Phylogeography of Middle American gophersnakes: mixed responses to biogeographical barriers across the Mexican Transition Zone

Aim We used inferences of phylogeographical structure and estimates of divergence times for three species of gophersnakes (Colubridae: Pituophis) distributed across the Mexican Transition Zone (MTZ) to evaluate the postulated association of three Neogene geological events (marine seaway inundation of the Isthmus of Tehuantepec, formation of the Transvolcanic Belt across central Mexico, and secondary uplifting of the Sierra Madre Occidental) and of Pleistocene climate change with inter- and intraspecific diversification. Location Mexico, Guatemala, and the western United States. Methods We combined range-wide sampling (67 individuals representing three putative species distributed across northern Middle America and western North America) and phylogenetic analyses of 1637 base pairs of mitochondrial DNA to estimate genealogical relationships and divergence times. The hypothesized concordance of inferred gene trees with geological histories was assessed using topology tests. Results We identified three major lineages of Middle American gophersnakes, and strong phylogeographical structure within each lineage. Gene trees were statistically congruent with hypothesized geological histories for two of the three postulated geological events. Estimated divergence dates and the geographical distribution of genetic variation further support mixed responses to these geological events. Considerable phylogeographical structure appears to have been generated during the Pleistocene. Main conclusions Phylogenetic and phylogeographical structure in gophersnakes distributed across northern Middle America and western North America highlights the influence of both Neogene vicariance events and Pleistocene climate change in shaping genetic diversity in this region. Despite the presence of two major geographical barriers in southern Mexico, extreme geological and environmental heterogeneity in this area may have differentially structured genetic diversity in highland taxa. To the north, co-distributed taxa may display a more predictable pattern of diversification across the warm desert regions. Future studies should incorporate nuclear data to disentangle inferred lineage boundaries and further elucidate patterns of mitochondrial introgression.

Fundamental biogeographic patterns across the Mexican Transition Zone: an evolutionary approach

Transition zones, located at the boundaries between biogeographic regions, represent events of biotic hybridization, promoted by historical and ecological changes. They deserve special attention, because they represent areas of intense biotic interaction. In its more general sense, the Mexican Transition Zone is a complex and varied area where Neotropical and Nearctic biotas overlap, from southwestern USA to Mexico and part of Central America, extending south to the Nicaraguan lowlands. In recent years, panbiogeographic analyses have led to restriction of the Mexican Transition Zone to the montane areas of Mexico and to recognize five smaller biotic components within it. A cladistic biogeographic analysis challenged the hypothesis that this transition zone is biogeographically divided along a north‐south axis at the Transmexican Volcanic Belt, as the two major clades found divided Mexico in an east‐west axis. This implies that early Tertiary geological events leading to the convergence of Neotropical and Nearctic elements may be younger (Miocene) than those that led to the east‐west pattern (Paleocene). The Mexican Transition Zone consists of five biogeographic provinces: Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur, and Chiapas. Within this transition zone, at least four cenocrons have been identified: Paleoamerican, Nearctic, Montane Mesoamerican, and Tropical Mesoamerican. Future studies should continue refining the identification of cenocrons and the reconstruction of a geobiotic scenario, as well as integrating ecological biogeographic studies, to allow a more complete understanding of the patterns and processes that have caused the biotic complexity of this transition zone.

Track analysis of the Mexican species of Buprestidae (Coleoptera): testing the complex nature of the Mexican Transition Zone

AbstractAim We analysed the geographical distributions of species of Buprestidae (Coleoptera) in Mexico by means of a panbiogeographical analysis, in order to identify their main distributional patterns and test the complex nature of the Mexican Transition Zone, located between the Nearctic and Neotropical regions.Location Mexico.Methods The geographical distributions of 228 species belonging to 33 genera of Buprestidae were analysed. Localities of the buprestid species were represented on maps and their individual tracks were drawn. Based on a comparison of the individual tracks, generalized tracks were detected and mapped. Nodes were identified as the areas where generalized tracks converged.Results Thirteen generalized tracks were obtained: one was restricted to the Mexican Transition Zone and five to the Neotropical region (Antillean and Mesoamerican dominions), a further two occurred in both the Nearctic region (Continental Nearctic dominion) and the Mexican Transition Zone, and a further five in both the Neotropical region (Mesoamerican dominion) and the Mexican Transition Zone. Seven nodes were identified at the intersections of the generalized tracks – in the Mesoamerican dominion (Mexican Pacific Coast, Mexican Gulf and Chiapas biogeographical provinces) and the Mexican Transition Zone (Trans‐Mexican Volcanic Belt, Balsas Basin and Sierra Madre Oriental biogeographical provinces).Main conclusions We conclude that the geographical distribution of Buprestidae is mainly Neotropical, corresponding to the Mesoamerican dominion and the Antillean dominion of the Neotropical region, and the Mexican Transition Zone. Most of the generalized tracks and nodes correspond to the Mexican Transition Zone, thus confirming its complex nature. We suggest that the nodes we have identified could be particularly important areas to choose for conservation prioritization.

Complex evolution in the Neotropics: The origin and diversification of the widespread genus Leptodeira (Serpentes: Colubridae)

Lineage diversification in the Neotropics is an interesting topic in evolutionary biology but is also one of the least understood. The abiotic and biotic complexity of the region precludes generalizations that can be drawn regarding the historical evolutionary processes responsible for the diversity observed. The snake genus Leptodeira provides an excellent opportunity to investigate such processes because it spans the entire Neotropical region. In this study, we infer the phylogenetic position of Leptodeira within Dipsadinae, estimate evolutionary relationships among and within Leptodeira species, and estimate the diversification time and biogeography of the genus. Three mitochondrial gene regions were sequenced for individuals representing all the Leptodeira species and most subspecies currently recognized. Additionally, two nuclear protein-coding gene regions were sequenced for representatives of each species and several genera within the Dipsadinae. We infer that several Leptodeira species are either paraphyletic or polyphyletic as currently recognized, and that most recognized subspecies are not monophyletic lineages. Despite the taxonomic discordance with evolutionary relationships, clades appear to correspond very well to major biogeographic regions of Mexico, Central America and South America. Our results thus highlight the important role of the Miocene and Pliocene for lineage diversification in the Neotropics. Additionally, our time estimates suggest that recent intraspecific phylogeographic structure is likely the result of habitat and climatic fluctuations during the Pleistocene. Cumulatively, our inferences of lineage diversification within Leptodeira suggest a complex evolutionary scenario in the Mexican transition zone and a north to south expansion with a final colonization of the tropics in South America.

BIOGEOGRAPHICAL ANALYSIS OF SCARABAEINAE AND GEOTRUPINAE ALONG A TRANSECT IN CENTRAL MEXICO (COLEOPTERA, SCARABAEOIDEA)

Scarabaeinae and Geotrupinae (Coleoptera, Scarabaeoidea) species composition is analyzed along a 150 km long altitudinal transect that runs S-NE in the Mexican Transition zone. The transect is located in the state of Hidalgo in central-eastern Mexico. The spatial unit of analysis is the landscape. The transect crosses five different landscapes. As terms of reference for studying the geographic distribution of the species, the entomofauna distribution patterns for the Mexican Transition zone were used. The transect includes all the patterns established by Halffter for this zone. Only genera with northern origins were found in landscape of the Pachuca Sierra (mountain range). The two landscapes of the High Plateau (temperate and arid) have one genus with a northern origin (<em>Onthophagus</em>), along with species belonging to genera with Neotropical origins that evolved on the High Plateau. For the landscapes of the zacualtipán Sierra and the slope down to the Gulf–Las Huastecas region genera of Neotropical affinity dominate, and there are also some species with a tropical distribution and of northern-Old World origin. The relationship between the mountains and the phyletic lineages or genera of northern origin and of recent entry into the Mexican Transition zone is confirmed, as is that between the tropical lowlands and the Neotropical lines or genera, also recent arrivals. Taxa that arrived a long time ago, of either origin, do not exhibit this geographic-ecological dependence. The Hidalgo Transect is compared with two other, similar transects sampled in the Mexican Transition zone: the Cofre de Perote–Gulf Coast transect (Veracruz) and that of Manantlán (Jalisco). In the mountain landscapes, High Plateau and Tropical Lowlands, there were no important differences in the species composition of the groups studied. In contrast, in the Transition landscape (zacualtipán in the Hidalgo Transect) there were very notable differences. In the Cofre de Perote transect, an important functional group is missing from the treeless habitats: the roller Scarabaeinae. For the same landscape, in Manantlán, lineages with Neotropical affinities are represented by a single species which completely dominates the beetles of northern affinities. This contrasts markedly with the Hidalgo and Cofre de Perote transects where, in the Transition landscape, Neotropical taxa are well represented. It appears that, unlike the tropical lowlands where (geologically recent) penetration of Neotropical taxa is massive in all three transects, in the transition landscapes (originally covered by cloud forest) the penetration of Neotropical taxa is highly variable, and depends on the mountain range in which they are found. In the Conclusions section, we analyze how the beetle fauna with different distribution patterns have contributed to the composition of the fauna of the Hidalgo Transect and in general that of the Mexican Transition zone, resulting in a mixture (genera with northern-Old World affinity, and genera with Neotropical affinities) that give the Mexican Transition zone its unique character.

Zoogeographical affinities and the use of vertebrates in Xochicalco (Morelos, Mexico)

Xochicalco is a Mesoamerican locality that developed after the fall of Teotihuacan, and became one of the most important urban, ceremonial and military communities of its time. Chronologically, it is situated in the Epiclassic period (700–900 A.D.) and its buildings show a marked hierarchical distribution. The site is located in the current State of Morelos (Mexico), embedded in the Mexican Transition Zone between the two major American zoogeographic regions: Nearctic and Neotropic. The animal remains identified show a mixed assemblage from both regions. With the aim of exploring the relationship between the zoogeographical affinities of identified fauna and differential uses due to the hierarchical distribution of the site, the data were processed using two multivariate analyses in order to find the animals that characterize each social level. This comparison shows that some animals are common to all the social levels, suggesting easy availability, while a few others, mainly from the Neotropic area, were associated only with the elite places suggesting their quality as social markers. This approach offers an initial hypothesis about the different cultural attitudes toward the animals in a Mesoamerican locality, little studied, showing a positive relationship between the zoogeographic affinity and the social hierarchy.

Análisis panbiogeográfico de las especies mexicanas de Pselliopus Bergroth (Hemiptera: Heteroptera: Reduviidae: Harpactorinae)

Se llevó a cabo un análisis panbiogeográfico de las especies mexicanas de Pselliopus Bergroth. El género contiene 27 especies, que se distribuyen desde Canadá hasta la Argentina. México es el país con el mayor número de especies (21), seguido de los Estados Unidos de América (6) y Guatemala, El Salvador, Honduras y Brasil (2). Se obtuvo un trazo generalizado que abarca la Sierra Madre Occidental, la Sierra Madre Oriental, la Costa del Pacífico Mexicano, el Golfo de México, la Cuenca del Balsas, el Eje Volcánico Transmexicano, la Sierra Madre del Sur y Chiapas. Se concluye que las especies de Pselliopus se distribuyen principalmente en la Zona de Transición Mexicana (ZTM) y la región Neotropical, y pertenecen alelemento Mesoamericano Tropical.

Gymnosperms and cladistic biogeography of the Mexican Transition Zone

Distributional patterns of 81 species of three genera of Mexican gymnosperms (Ceratozamia, Dioon, Pinus) were analyzed to evaluate their contribution to the cladistic biogeography of the Mexican Transition Zone, applying Brooks Parsimony Analysis (BPA) and parsimony analysis of paralogy‐free subtrees (PAPS). BPA showed three main groups of areas: clade A is comprised of the Baja California, Great Basin, and Mojavean provinces; clade B includes the Valle de Tehuacán‐Cuicatlán, Balsas Basin, Planicie Costera del Noreste, Planicie Costera del Noroeste, Costa del Golfo de México, and Costa Pacífica provinces, located along the coasts and in the central lowlands of Mexico; and clade C includes the Appalachian, Atlantic and Gulf Coastal, Yucatán Peninsula, Caribbean, Californian, Vancouverian, Eastern Central America, Soconusco, Serranías Transístmicas, Serranías Meridionales, Sierra Madre Occidental, Altiplano, and Sierra Madre Oriental provinces, corresponding to the montane areas of the Mexican Transition Zone, Central America and some areas of the U.S.A. PAPS showed three groups of areas: clade D includes the Vancouverian, Appalachian, and Atlantic and Gulf Coastal provinces; clade E the Balsas Basin, Planicie Costera del Noreste, and Planicie Costera del Noroeste provinces; and clade F the Serranías Transístmicas, Soconusco, Serranías Meridionales, Sierra Madre Occidental, Altiplano, Sierra Madre Oriental, Baja California, Californian, Great Basin and Mojavean provinces. Comparing both analyses, three common area relationships emerge: (1) Appalachian and Atlantic and Gulf Coastal provinces, (2) Great Basin, Mojavean and Baja California provinces, and (3) Altiplano, Sierra Madre Oriental and Sierra Madre Occidental provinces. Differences between the general area cladograms can be accounted for by dispersal having a stronger influence in BPA, and the PAPS general area cladogram showing a clearer vicariant signal. The general area cladograms obtained support some area relationships not explained in previous studies, and may complement the historical distributional patterns of the biota of the Mexican Transition Zone.

Phylogenetic analysis of the subgenus Lampetis (Spinthoptera) (Coleoptera: Buprestidae) of North and Central America, and the West Indies

Phylogenetic relationships between species of Lampetis (Spinthoptera) of North and Central America and the West Indies were analysed by cladistic methods, based on 65 characters from the external morphology and male genitalia. Eleven species of different generic groups of the subtribe Dicercina were considered as outgroups, including also species of Lampetis (Lampetis) and one South American species of L. (Spinthoptera). The monophyly of Lampetis (Spinthoptera) is supported by two synapomorphies, but this subgenus appears to be more closely related to species of Psiloptera rather than to Old World species of Lampetis (Lampetis), suggesting that Lampetis (Spinthoptera) may be segregated from Lampetis as a different genus. The species of Lampetis (Spinthoptera) from North and Central America and the West Indies do not represent a monophyletic taxon, because L. (S.) tucumana (South American outgroup) is nested within them. Comparison of these results with a previous panbiogeographic analysis indicate that several generalized tracks possess species from different clades, thus suggesting an ancient radiation of this taxon in Mesoamerica and the Mexican Transition Zone.

From forest to pasture: an evaluation of the influence of environment and biogeography on the structure of beetle (Scarabaeinae) assemblages along three altitudinal gradients in the Neotropical region

The objective of this study is to evaluate the effect of environmental (associated with the expansion of cattle ranching) and biogeographical factors on the diversity of dung beetle (Scarabaeinae) assemblages along three altitudinal gradients in the Neotropical region. One gradient is located in the Mexican Transition Zone, on the Cofre de Perote mountain, the other two are in the northern Andes (the Chiles Volcano and the Río Cusiana Basin). For the three gradients, the number of species and of individuals was similar in both forest and pasture, while species composition was different between habitats. On this mountain, species turnover in pastures was characterized by the addition of new species as altitude increased. In the northern Andes, species diversity was always greater in the forest than in the pasture, and species turnover between habitats was notably influenced by species loss with increasing altitude. As such the pasture fauna of the northern Andes was an impoverished derivative of the fauna present in the forests at the same altitude characterized by species of Neotropical affinity with a limited capacity for colonizing open, sunnier habitats. The opposite occurs in the areas used by cattle on the Cofre de Perote. This habitat has its own fauna, which is mainly comprised of Holarctic and Afrotropical species adapted to the prevailing environmental conditions of areas lacking arboreal vegetation. These results suggest that the impact on beetle communities caused by human activities can differ depending on the geographic position of each mountain and, particularly, the biogeographical history of the species assemblage that lives there.

Cladistic biogeographic analysis suggests an early Caribbean diversification in Mexico

The Great American Biotic Interchange has been the predominant paradigm for explaining biotic diversification in the Nearctic/Neotropical overlap or Mexican Transition Zone, which is commonly explained by the collision of the North and South American continental plates, which began in the Oligocene and fused both landmasses. In the most far-reaching cladistic biogeographical analysis of the area to date, evidence has been found supporting the existence of a remnant Caribbean region extending from eastern Mexico to southeastern USA, a hypothesis that challenges current views of the Great American Biotic Interchange and the Mexican Transition Zone. We show herein that an older terrane, which has drifted to the present day positions of Yucatan and Cuba, may be biogeographically linked to an early 'Gondwanan' biota of the Paleocene (ca. 60 Ma). The evidence indicates an east-west biotic divide in Mexico, existing before the collision and formation of Central America. The south-north division of the country, previously recognized by several authors as associated with the Great American Biotic Interchange and the Mexican Transition Zone, is of a younger age.

Does the Trans‐mexican Volcanic Belt represent a natural biogeographical unit? An analysis of the distributional patterns of Coleoptera

AbstractAim We analysed the geographical distribution of beetle species of the families Buprestidae, Cerambycidae, Dryophthoridae, Melolonthidae, Passalidae and Staphylinidae from the Trans‐mexican Volcanic Belt (TVB) through a track analysis and a parsimony analysis of endemicity (PAE), in order to test its naturalness and determine its affinities.Location The area analysed corresponds to the TVB, which is a biogeographical province of the Mexican Transition Zone.Methods The panbiogeographical analysis was based on the comparison of the individual tracks of 299 species of Buprestidae, Cerambycidae, Dryophthoridae, Melolonthidae, Passalidae and Staphylinidae (Coleoptera). The TVB was divided into 1o × 1ogrid cells and we also included in the analysis the remaining Mexican biogeographical provinces. Parsimony analysis of endemicity with progressive character elimination (PAE‐PCE) was applied to classify areas by their shared taxa according to the most parsimonious cladograms. The nested sets of areas were represented as generalized tracks.Results Three generalized tracks were obtained: (1) grid cells 9C, 9D, 10D, 10E, Sierra Madre Oriental, Chiapas, Mexican Gulf and the Sierra Madre del Sur; (2) grid cells 3B, 3C, 4B, 4C, 5C, 6C, 7C, Sierra Madre Occidental, Sierra Madre del Sur, Balsas Basin and the Mexican Pacific Coast, and (3) grid cells 8D, 9C, 9D, 10D, 10E, Yucatán Peninsula, Chiapas, Sierra Madre Oriental and the Mexican Gulf.Main conclusions We conclude that the TVB does not represent a natural biogeographical unit because it shows different relationships with other biogeographical provinces, being clearly transitional between the Nearctic and Neotropical provinces. Some parts of the TVB are related to Neotropical provinces (Chiapas, Mexican Gulf and Mexican Pacific Coast) and others to the remaining provinces of the Mexican Transition Zone (Sierra Madre Oriental, Sierra Madre del Sur, Sierra Madre Occidental and Balsas Basin).

Track analysis of the Mexican species of Cerambycidae (Insecta, Coleoptera)

A track analysis of 221 species belonging to 68 genera of Mexican Cerambycidae was undertaken in order to identify their main distributional patterns. Based on the comparison of the individual tracks, fifteen generalized tracks were obtained: six are placed in the Neotropical region, seven are shared by the Neotropical region and the Mexican Transition Zone, one is situated in the Mexican Transition Zone, and one is shared by the Nearctic region and the Mexican Transition Zone. Eight nodes were found in the intersection of these generalized tracks, five of them located in the Neotropical region and three in the Mexican Transition Zone. Distributional patterns of Mexican Cerambycidae show two basic patterns: one mostly Neotropical, in the Mesoamerican dominion (Mexican Pacific Coast and Mexican Gulf biogeographic provinces) and another in the Mexican Transition Zone (Transmexican Volcanic Belt and Balsas Basin biogeographic provinces).

A synopsis of the fleas (Insecta: Siphonaptera) parasitizing New World species of Soricidae (Mammalia: Insectivora)

A synopsis of the 57 species and 24 genera of New World fleas parasitizing species of Soricidae is provided, with synonymical lists, and distributional and host data. Species analyzed belong to the families Ceratophyllidae (10 genera), Ctenophthalmidae (10 genera), Hystrichopsyllidae (two genera), and Leptopsyllidae (two genera). Three subspecies are elevated to species: Corrodopsylla lira, C. obtusata, and Nearctopsylla hygini. Soricid hosts include 17 species of Sorex, four species of Cryptotis, two species of Blarina, and one species of Crocidura. The species hosting the highest number of flea species is Blarina brevicauda (19 flea species), followed by Sorex cinereus (16), S. pacificus (9), S. trowbridgii (8), S. fumeus (7), S. palustris (7), and Cryptotis parva (7). Most of the flea species analyzed are polyxenous, and belong mainly to genera associated to small rodents and marginally present on Soricidae. The association with Soricidae seems to be more evident in species of Corrodopsylla, Corypsylla, Ctenophthalmus, Doratopsylla, Hystrichopsylla,and Nearctopsylla. Only Corrodopsylla lira, C. barrerai, Ctenophthalmus cryptotis, C. expansus, C. myodosus, Hystrichopsylla cryptotis, H. guatemalensis, Nearctopsylla georgiana, N. pfitzeri, and N. princei are apparently stenoxenous or monoxenous. Taxa analyzed belong to the Nearctic biotic element and are specially diversified in the Mexican Transition Zone.

Distributional patterns of freshwater taxa (fishes, crustaceans and plants) from the Mexican Transition Zone

AbstractAim To test whether distributional patterns of Neotropical freshwater taxa fit the generalized tracks already postulated for terrestrial groups occurring in the Mexican Transition Zone.Location The study units comprised 17 hydrological basins located along the Pacific coast of the Americas from Mexico to Panama, and in the Gulf of Mexico from the Papaloapan to the Grijalva–Usumacinta basin.Methods Distributional data for 22 fish species, 34 crab species of the tribe Pseudothelphusini, and 22 strictly freshwater species of angiosperms were analysed. Parsimony analysis of endemicity is based on presence/absence data of these taxa and uses the computer programs Winclada and NONA.Results Three generalized tracks were obtained: (1) Mexican North Pacific, (2) Mexican Central Pacific, and (3) Southern Mexico–Guatemala. A node resulted at the intersection of the first two tracks, coinciding with the Neovolcanic Axis in central Mexico.Main conclusions Freshwater generalized tracks with an altitudinal distribution below 1000 m, mainly including fishes and angiosperms, are close to the Tropical Mesoamerican generalized track. Generalized tracks above 1000 m, including freshwater crabs, have a stronger affinity with the Mountain Mesoamerican track. The Isthmus of Tehuantepec represents a node for the Neotropical freshwater and terrestrial biota. These results seem to indicate that common geobiotic processes have induced these patterns.