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Being areas of biotic overlap located between biogeographic regions, transition zones function as natural laboratories. The present study explores the phylogenetic history of the dung beetle subfamily Scarabaeinae, in order to present an evolutionary scenario that allows inference of the biogeographic history of the Mexican Transition Zone (MTZ) and integration of the distributional patterns of its biota. The species sampling included 94 New World taxa (93 species of Scarabaeinae and one species of Aphodiinae). The phylogenetic relationships of the main clades recovered in our study were supported with PP values 0.95. Based on the BAYAREALIKE model to reconstruct the ancestral distributional patterns of Scarabaeinae, we inferred a complex scenario with 19 dispersal events, 15 vicariance events, and three extinctions. We suggest that the Ancient Neotropical and Tropical Paleoamerican patterns represent the most likely ancestral distributional patterns for the Scarabaeinae of the MTZ, which probably settle there during the Eocene-Oligocene. The rest of the Scarabaeinae distributional patterns were assembled in subsequent periods. The results suggest that the MTZ had two separate formation stages: a Paleo-MTZ (Eocene-Miocene) and a current MTZ (Pliocene-Anthropocene). We conclude that the evolutionary history as well as the dispersal-vicariance scenario for the Scarabaeinae of the MTZ fits the out of the tropics model.

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The Onthophagus mexicanus species group includes at least 18 species: O. anewtoni Howden and Génier, O. arnetti Howden and Cartwright, O. browni Howden, O. cartwrighti Howden, O. championi Bates, O. concinnus Castelnau, O. cynomysi Brown, O. eulophus Bates, O. guatemalensis Bates, O. hecate (Panzer), O. mcclevei Howden and Génier, O. medorensis Brown, O. mexicanus Bates, O. orpheus (Panzer), O. polyphemi Hubbard, O. pseudoguatemalensis sp. n., O. totonacus sp. n. and O. velutinus Howden and Cartwright. Onthophagus pseudoguatemalensis sp. n. and O. totonacus sp. n. are described from Mexico (Jalisco and Veracruz, respectively). Onthophagus cartwrighti, O. championi, O. eulophus and O. guatemalensis are redescribed, while lectotypes are designated herein for O. championi and O. eulophus. The distribution of O. cartwrighti is clarified; a new country record is provided for O. championi (Honduras); new state records are reported for O. championi (Oaxaca and Veracruz, Mexico) and O. guatemalensis (Oaxaca, Mexico). The accurate distribution of O. eulophus remains unknown since its original description. Updated distribution maps are included for all the species within the group. An updated determination key to species of the O. mexicanus species group is provided. The rarity of O. eulophus and O. totonacus in the entomological collections is thought to be a consequence of their trophic habits; both species are suggested to be inquilines of rodent nests or burrows.

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In this study, we take the Onthophagus chevrolati species group, likely a monophyletic species group as an example to analyze the processes that led to the biogeographic integration of the Holarctic fauna in the mountains of the Mexican Transition Zone to test our biogeographic hypotheses. We propose a change from the status of subspecies to species for O. oaxacanus Zunino Halffter, 1988 new status; O. howdeni Zunino Halffter, 1988 new status; O. jaliscensis Zunino Halffter, 1988 new status; O. longecarinatus Zunino Halffter, 1988 new status; O. omiltemius Bates, 1889 revised status; and O. retusus Harold, 1869 revised status. Consequently, the O. chevrolati group of species is currently made up of 47 species belonging to four species lines: O. vespertilio, O. hippopotamus, O. cyanellus and O. chevrolati. The diversification of the Onthophagus chevrolati species group in this region resulted from three hypothetical stages of evolution. In the first, the penetration and expansion of the ancestor of the O. chevrolati species group occurred before the Miocene and the Trans-Mexican Volcanic Belt arose. During the second stage, the O. hippopotamus species line expanded and evolved, integrating with the paleogeographic changes and the formation of the Trans-Mexican Volcanic Belt, as a consequence of volcanism during the Miocene-Pliocene. In the third and most recent stage, the O. chevrolati species line used the existing mountain systems and interglacial climate fluctuations of the Pleistocene to expand and diversify. Thus, the mountains of the Mexican Transition Zone are not simply periglacial refugia. The entomofauna of Holarctic origin present in the region evolved while the Earth's geological processes were underway.

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Two new species of the genus Ateuchus Weber are described from the region of Los Chimalapas, Oaxaca, Mexico: A. benitojuarezisp. n. and A. colossussp. n. A diagnosis for distinguishing these new species from the other species of this genus in North America is included. This paper is illustrated with pictures of the dorsal habitus and the male genitalia of the new species. The evolutionary relationships of the species are discussed, as well as their distribution and ecology. It is considered that the species of the genus Ateuchus present in North and Central America correspond to the Typical Neotropical and Mountain Mesoamerican distribution patterns.

ResumenDescribimos dos especies nuevas del género Ateuchus Weber, de la región de Los Chimalapas, Oaxaca, México: A. benitojuarezisp. n. y A. colossussp. n. Incluimos diagnosis para distinguir a estas especies nuevas del resto de especies del género presentes en Norteamérica. Presentamos ilustraciones del hábito dorsal y la genitalia masculina de las nuevas especies. Discutimos las relaciones evolutivas de las especies, así como también su distribución y ecología. Consideramos que las especies del género Ateuchus corresponden con los patrones de distribución Neotropical Típico y Mesoamericano de Montaña.

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Insect diversity patterns of high mountain ecosystems remain poorly studied in the tropics. Sampling dung beetles of the subfamilies Aphodiinae, Scarabaeinae, and Geotrupinae was carried out at four volcanoes in the Trans-Mexican Volcanic Belt (TMVB) in the Mexican transition zone at 2,700 and 3,400 MASL, and on the windward and leeward sides. Sampling units represented a forest-shrubland-pasture (FSP) mosaic typical of this mountain region. A total of 3,430 individuals of 29 dung beetle species were collected. Diversity, abundance and compositional similarity (CS) displayed a high variability at all scales; elevation, cardinal direction, or FSP mosaics did not show any patterns of higher or lower values of those measures. The four mountains were different regarding dispersion patterns and taxonomic groups, both for species and individuals. Onthophagus chevrolati dominated all four mountains with an overall relative abundance of 63%. CS was not related to distance among mountains, but when O. chevrolati was excluded from the analysis, CS values based on species abundance decreased with increasing distance. Speciation, dispersion, and environmental instability are suggested as the main drivers of high mountain diversity patterns, acting together at different spatial and temporal scales. Three species new to science were collected (>10% of all species sampled). These discoveries may indicate that speciation rate is high among these volcanoes-a hypothesis that is also supported by the elevated number of collected species with a restricted montane distribution. Dispersion is an important factor in driving species composition, although naturally limited between high mountains; horizontal colonization events at different time scales may best explain the observed species composition in the TMVB, complemented by vertical colonization events to a lesser extent. Environmental instability may be the main factor causing the high variability of diversity and abundance patterns found during sampling. Together, we interpret these results as indicating that species richness and composition in the high mountains of the TMVB may be driven by biogeographical history while variability in diversity is determined by ecological factors. We argue that current conservation strategies do not focus sufficiently on protecting high mountain fauna, and that there is a need for developing and applying new conservation concepts that take into account the high spatial and temporal variability of this system.

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Phanaeus bravoensissp. n. is described from the coniferous-oak forests in the state of Guerrero, and P. huicholsp. n. from coniferous-oak forests and cloud forests in Jalisco and Nayarit. The new species are closely related to P. halffterorum and P. zoque respectively. Morphological trait combination, geographic distribution, and trophic habits show important differences among the studied species. A distribution map and an updated key to separate the species are included.

ResumenDescribimos a Phanaeus bravoensissp. n. proveniente de los bosques de coníferas y encino del estado de Guerrero, y a P. huicholsp. n. de los bosques de coníferas y encino y bosques de niebla de Jalisco y Nayarit. Las nuevas especies están cercanamente relacionadas con P. halffterorum y P. zoque, respectivamente. Las combinaciones de caracteres morfológicos, áreas de distribución geográfica y los hábitos alimenticios muestran diferencias importantes entre las especies estudiadas. Incluimos un mapa de distribución y una clave actualizada para separar a las especies.

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The Mexican transition zone (MTZ) is the complex area where the Neotropical and Nearctic biotas overlap, including south-western United States, Mexico and a large part of Central America extending to the Nicaraguan lowlands. In a strict sense, it corresponds to the mountain highlands of Mexico, Guatemala, Honduras, El Salvador and Nicaragua. We review Halffter's theory explaining the biotic evolution of the MTZ, including the description and discussion of the distributional patterns and cenocrons recognized within it. Distributional patterns are generalizations that help analyse and compare distributions of different taxa. Cenocrons correspond to sets of taxa that share the same biogeographic history, constituting identifiable subsets within the transitional biota by their common biotic origin and evolutionary history. The heuristic value of distributional patterns and cenocrons lies in their application to formulate hypotheses on biotic assembly in the geographical-ecological space, to analyse the ecological response to anthropic impact, to analyse altitudinal patterns and to undertake time-slicing in cladistic biogeography. Three case studies are analysed with some detail: the Neotropical genus Canthon and the tribe Phanaeini and the Holarctic/Nearctic subfamily Geotrupinae. The Paleoamerican and Mexican Plateau cenocrons define the approximate boundaries of the MTZ, whereas the Mountain Mesoamerican, Nearctic and Typical Neotropical cenocrons correspond to the more conventional boundaries of the Nearctic and Neotropical regions. The biotic assembly of the MTZ is summarized into five stages: in the Jurassic-Cretaceous, the Paleoamerican cenocron (later diversified into five varieties) extended in Mexico; in the Late Cretaceous-Palaeocene, the Mexican Plateau cenocron dispersed from South America; in the Oligocene-Miocene, the Mountain Mesoamerican cenocron dispersed from the Central American Nucleus; in the Miocene-Pliocene, the Nearctic cenocron dispersed from northern North America; and in the Pleistocene, the Typical Neotropical cenocron dispersed from South America. Finally, we review the impact of Halffter's MTZ, with particular reference to dispersal, track, cladistic biogeographic, endemicity and phylogeographic analyses, as well as biogeographic regionalization.

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The beetle Omorgus suberosus (F.) is a facultative predator of eggs of the olive ridley turtle Lepidochelys olivacea (Eschscholtz). Laboratory and field investigations were conducted in order to characterize volatile attractants of O. suberosus and to explore the potential for application of these volatiles in a selective mass trapping method. Headspace sorptive extraction (HSSE) coupled to thermo-desorption gas chromatography-mass spectrometry (TD-GC-MS) analysis of the volatile constituents from beetles or turtle nests revealed 24 potential compounds. However, electroantennographic (EAG) measurements revealed antennal sensitivity only to indole, linoleic acid, trimethylamine, dimethyl sulphide, dimethyl disulphide and ammonia. Behavioural tests showed that these compounds are highly attractive to O. suberosus. Field trapping experiments revealed that indole and ammonia were more attractive than the other volatile compounds and showed similar attractiveness to that produced by conventional baits (chicken feathers). The use of a combined bait of indole and NH3 would therefore be the most effective trap design. The data presented are the first to demonstrate effective massive capture of O. suberosus using an attractant-based trapping method. These findings have potential for the development of an efficient mass trapping method for control of this beetle as part of efforts towards conservation of L. olivacea at La Escobilla in Oaxaca, Mexico.

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Recent intensive samplings carried out across the mountainous regions of El Pinal (Puebla, Mexico) have provided new insights into the main environmental factors that affect the geographic distribution of the scarabaeinae beetles of the Trans-Mexican Volcanic Belt above 2500 m a.s.l. This study is part of an ongoing project investigating the diversity and biogeography of copro-necrophagous beetles (Scarabaeinae, Aphodiinae, Geotrupinae and Silphidae) in the easternmost areas of the Trans-Mexican Volcanic Belt. Previous experience allows us to propose a series of predictions that we expect will provide possible explanations for current distribution patterns observed in Scarabaeinae and other groups of insects found in the Trans-Mexican Volcanic Belt. This mountain range has a primarily biogeographic importance, limiting the Mexican High Plateau in the South and connecting the western and eastern Sierra Madre mountain chains, which are considered the most important routes for dispersal of mountain fauna of northern origin. The taxonomic and biogeographic study of the species collected so far in El Pinal (including Onthophagus clavijeroisp. n. and Onthophagus martinpieraisp. n. described here), along with their possible relationships with other known species, allows us to answer the preliminary assumptions proposed.

ResumenCon base en capturas intensivas realizadas en la montaña de El Pinal (estado de Puebla, México) se plantea un análisis de los factores que intervienen en la distribución geográfica de la fauna de montaña (en este caso Scarabaeinae) por encima de los 2500 m de altitud, en el Sistema Volcánico Transversal (SVT), principal cordillera dispuesta en sentido latitudinal de México y de toda América. Este artículo es parte de una serie de trabajos coordinados para estudiar los escarabajos coprófagos y necrófagos de la parte oriental del SVT.La experiencia generada nos permite plantear una serie de premisas (Introducción) que se espera cumpla la distribución de la fauna de Scarabaeinae y de otros grupos en el SVT, cordillera de primera importancia biogeográfica, pues limita por el sur el Altiplano Mexicano (una península de Norte América) y une las dos principales cordilleras que se desarrollan N-S: las Sierras Madres Occidental y Oriental, las más importantes vías de penetración de la fauna de montaña de origen septentrional. Un análisis de las afinidades taxonómicas y biogeográficas de las colectas de Scarabaeinae en El Pinal (incluyendo dos especies nuevas de Onthophagus que se describen) nos permite dar respuesta en la Discusión a las premisas planteadas en la Introducción.