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The Great American Biotic Interchange (GABI) was greatly influenced by the completion of the Isthmus of Panama and impacted the composition of modern faunal assemblages in the Americas. However, the contribution of preceding events has been comparatively less explored, even though early immigrants in the fossil records are evidence for waif dispersals. The cricetid rodents of the subfamily Sigmodontinae are a classic example of a species-rich South American radiation resulting from an early episode of North American invasion. Here, we provide a temporal and spatial framework to address key aspects of the historical biogeography and diversification of this diverse mammal group by using mitochondrial and nuclear DNA datasets coupled with methods of divergence time estimation, ancestral area reconstruction and comparative phylogenetics. Relaxed-clock time estimates indicate that divergence of the Sigmodontinae began in the middle-late Miocene (ca. 12-9 Ma). Dispersal-vicariance analyses point to the arrival of a single lineage of northern invaders with a widespread ancestral distribution and imply that the initial differentiation between Central and South America gave rise to the most basal groups within the subfamily. These two major clades diversified in the late Miocene followed by the radiation of main tribes until the early Pliocene. Within the Oryzomyalia, tribes diverged initially in eastern South America whereas multiple dispersals into the Andes promoted further diversification of the majority of modern genera. A comparatively uniform background tempo of diversification explains the species richness of sigmodontines across most nodes, except for two akodontine genera with recent increases in diversification rates. The bridging of the Central American seaway and episodes of low sea levels likely facilitated the invasion of South America long before the onset of the post-Isthmian phase of the GABI.

The spiny rats, genus Proechimys, have the highest species richness within the Echimyidae family, as well as species with high genetic variability. The genus distribution includes tropical South America and Central America south to Honduras. In this study, we evaluate the phylogeographic histories of Proechimys guyannensis and P. cuvieri using cytochrome b, in a densely sampled area in northeastern Amazon where both species are found in sympatry in different environments. For each species, Bayesian and Maximum Likelihood phylogenetic analysis were congruent and recovered similar clades in the studied area. Bayesian phylogenetic analysis using a relaxed molecular clock showed that these clusters of haplotypes diversified during Pleistocene for both species. Apparently, the large rivers of the region did not act as barriers, as some clades include specimens collected from opposite banks of Oiapoque, Araguari and Jari rivers. Bayesian skyline plot analysis showed recent demographic expansion in both species. The Pleistocene climatic changes in concert with the geologic changes in the Amazon fan probably acted as drivers in the diversification that we detected in these two spiny rats. Proechimys cuvieri and P. guyannensis show genetic structure in the eastern part of the Guiana region. Greater genetic distances observed in P. guyannensis, associated with highly structured groups, suggest that more detailed studies of systematics and ecology should be directed to this species.

Species boundaries are difficult to establish in groups with very similar morphology. As an alternative, it has been suggested to integrate multiple sources of data to clarify taxonomic problems in taxa where cryptic speciation processes have been reported. This is the case of the harvest mouse Reithrodontomys mexicanus, which has a problematic taxonomy history as it is considered a complex species. Here, we evaluate the cryptic diversity of R. mexicanus using an integrative taxonomy approach in order to detect candidate lineages at the species level. The molecular analysis used one mitochondrial (cytb) and two nuclear (Fgb‐I7 and IRBP) genes. Species hypotheses were suggested based on three molecular delimitation methods (mPTP, bGMYC, and STACEY) and cytb genetic distance values. Skull and environmental space differences between the delimited species were also tested to complement the discrimination of candidate species. Based on the consensus across the delimitation methods and genetic distance values, four species were proposed, which were mostly supported by morphometric and ecological data: R. mexicanus clade I, R. mexicanus clade IIA, R. mexicanus clade IIIA, and R. mexicanus clade IIIB. In addition, the evolutionary relationships between the species that comprise the R. mexicanus group were discussed from a phylogenetic approach. Our findings present important taxonomic implications for Reithrodontomys, as the number of known species for this genus increases. Furthermore, we highlight the importance of the use of multiple sources of data in systematic studies to establish robust delimitations between species considered taxonomically complex. We evaluate the cryptic diversity of Reithrodontomys mexicanus using an integrative taxonomy approach in order to detect candidate lineages at the species level. Our results suggest at least four candidate species supported by molecular, morphometric, and ecological data, which has important implications for the current taxonomy of the genus.

The phylogeography of Sumichrast’s harvest mouse (Reithrodontomys sumichrasti) was examined through maximum‐likelihood and parsimony analyses of 1,130 bp of mitochondrial Cytochromebsequence data from 43 individuals. The phylogeography of this Middle American highland forest‐dwelling species was compared to that previously published for the codistributed Aztec deer mouse complex (Peromyscus aztecus/Peromyscus hylocetescomplex) in order to test competing hypotheses of concerted versus independent responses of codistributed forms to past climatic fluctuations. Qualitatively, there were strong similarities in the phylogeographic patterns of the two groups, yet there were also areas of incongruence. Likelihood‐ratio tests (Kishino‐Hasegawa‐Templeton and parametric bootstrap tests) indicated that this incongruence is significant and cannot be attributed simply to uncertainty in phylogenetic estimation, thereby falsifying the concerted‐response hypothesis. Conversely, tree‐reconciliation analysis of the area relationships inferred for each group separately indicated that there has been a significant history of covicariance between the two groups, falsifying the independent‐response hypothesis. It appears that codistributed taxa in the geologically complex highlands of Mesoamerica share more common biogeographical history than can be accounted for by the independent‐response hypothesis yet have not responded to past climatic fluctuations in the lock‐step fashion predicted by the concerted‐response hypothesis.

Specimens of the Peromyscus boylii species group occurring in the montane regions of Michoacán, México, historically have been assigned to P. levipes. However, previous studies have shown that some specimens from eastern Michoacán possessed mitochondrial DNA haplotypes and karyotypes that were distinct from P. levipes and other members of the P. boylii species group. Phylogenetic analyses (parsimony and likelihood) of additional DNA sequences obtained from the mitochondrial cytochrome-b gene indicated that specimens from central and eastern Michoacán and western Morelos formed a monophyletic clade that was sister to a clade containing representatives of P. beatae. Estimations of genetic divergence for members of these 2 sister clades exceeded 5% and were greater than most pairwise comparisons reported for other members of the P. boylii species group. Collectively, there are no discernable morphological differences between those specimens and other cryptic species in the P. boylii species group. Together, these results indicated that specimens from the Sierra Madre del Sur region of Michoacán, Morelos, and likely throughout the Neovolcanic Axis of the Estado de México represent an undescribed species of Peromyscus for which we propose the name Peromyscus kilpatricki.

The spiny rats, genus Proechimys, have the highest species richness within the Echimyidae family, as well as species with high genetic variability. The genus distribution includes tropical South America and Central America south to Honduras. In this study, we evaluate the phylogeographic histories of Proechimys guyannensis and P. cuvieri using cytochrome b, in a densely sampled area in northeastern Amazon where both species are found in sympatry in different environments. For each species, Bayesian and Maximum Likelihood phylogenetic analysis were congruent and recovered similar clades in the studied area. Bayesian phylogenetic analysis using a relaxed molecular clock showed that these clusters of haplotypes diversified during Pleistocene for both species. Apparently, the large rivers of the region did not act as barriers, as some clades include specimens collected from opposite banks of Oiapoque, Araguari and Jari rivers. Bayesian skyline plot analysis showed recent demographic expansion in both species. The Pleistocene climatic changes in concert with the geologic changes in the Amazon fan probably acted as drivers in the diversification that we detected in these two spiny rats. Proechimys cuvieri and P. guyannensis show genetic structure in the eastern part of the Guiana region. Greater genetic distances observed in P. guyannensis, associated with highly structured groups, suggest that more detailed studies of systematics and ecology should be directed to this species.

As a periodic assessment of the mammal collection resource, the Systematic Collections Committee (SCC) of the American Society of Mammalogists undertakes decadal surveys of the collections held in the Western Hemisphere. The SCC surveyed 429 collections and compiled a directory of 395 active collections containing 5,275,155 catalogued specimens. Over the past decade, 43 collections have been lost or transferred and 38 new or unsurveyed collections were added. Growth in number of total specimens, expansion of genomic resource collections, and substantial gains in digitization and web accessibility were documented, as well as slight shifts in proportional representation of taxonomic groups owing to increasingly balanced geographic representation of collections relative to previous surveys. While we find the overall health of Western Hemisphere collections to be adequate in some areas, gaps in spatial and temporal coverage and clear threats to long-term growth and vitality of these resources have also been identified. Major expansion of the collective mammal collection resource along with a recommitment to appropriate levels of funding will be required to meet the challenges ahead for mammalogists and other users, and to ensure samples are broad and varied enough that unanticipated future needs can be powerfully addressed.

Reithrodontomys mexicanus (Saussure, 1860) is a cricetid rodent commonly called the Mexican harvest mouse and is one of 24 recognized species in the genus. It has grooved upper incisors distinctive of Reithrodontomys, and a medium to relatively large size, with tail longer than head and body; dorsal pelage varies from brown to cinnamon orange. It is distributed from Mexico to Nicaragua and in the northwestern region of South America. It occupies different habitats including humid pine-oak forests, cloud forests, and deciduous forests at elevations from about 1,000 to 3,800 m. R. mexicanus is listed as “Least Concern” by the International Union for Conservation of Nature and Natural Resources, although information about population size throughout its distribution range is unknown.

Handleyomys chapmani (Chapman's Handley's mouse) is a Mexican endemic rodent inhabiting humid montane forest of the Sierra Madre Oriental (SMO), the Oaxacan Highlands (OH), and the Sierra Madre del Sur (SMS). The systematic status of populations currently classified as H. chapmani has been problematic and to date evolutionary relationships among populations remain unresolved. In this study we use sequences from the mitochondrial cytochrome-b gene (1,143 base pairs [bp]) and intron 7 of the beta fibrinogen gene (621 bp) to reconstruct a phylogeny, estimate divergence times, and assess patterns of sequence variation over geography among samples of H. chapmani. This species was recovered as 2 monophyletic clades corresponding to the SMO-OH and SMS mountain ranges. Moreover, H. saturatior, the purported sister taxon to H. chapmani, was consistently recovered as the sister lineage to the SMO-OH clade, rendering H. chapmani paraphyletic. The geographic distribution of the 2 H. chapmani clades and of H. saturatior strongly correlate with the geographic extent of the SMO-OH, SMS, and the Trans-Isthmian Highlands (highlands east of the Isthmus of Tehuantepec through Central America) mountain ranges. Divergence times associate their isolation to late Pleistocene climatic changes that likely were reinforced by barriers such as the Isthmus of Tehuantepec, the Tehuacán–Cuicatlán Valley, and the Central Valleys of Oaxaca. The fact that populations of H. chapmani represent 2 independent evolutionary lineages results in a substantial reduction in the distributional range for both entities. Therefore, the conservation status of H. chapmani should be re-evaluated. Handleyomys chapmani (ratón de Handley de Chapman) es un roedor endémico de México con distribución en la Sierra Madre Oriental (SMO), Sierra Norte de Oaxaca (OH) y Sierra Madre del Sur (SMS). El estatus taxonómico de las poblaciones actualmente clasificadas como H. chapmani ha sido problemático y hasta la fecha, las relaciones evolutivas entre dichas poblaciones continúan sin resolverse. En este estudio, usamos secuencias del gen mitocondrial citocromo b (1143pb) y del intron 7 del gen beta fibrina (621pb) para estimar una filogenia del grupo, tiempos de divergencia y analizar los patrones de variación genética entre poblaciones de H. chapmani en un sentido geográfico. H. chapmani fue recuperado en 2 clados monofiléticos correspondientes a los sistemas montañosos de la SMO-OH y SMS. Además, H. saturatior (ratón de Handley de bosque nublado), reconocido como el grupo hermano de H. chapmani, fue consistentemente recuperado como el linaje hermano al clado de las SMO-OH; revelando a H. chapmani como un taxón parafilético. La distribución geográfica de los 2 clados en H. chapmani y H. saturatior muestra una fuerte correlación con la extensión geográfica de la SMO-OH, la SMS y las Tierras Altas Trans-Istmicas (TIH; tierras altas al este del Istmo de Tehuantepec en Chiapas y América Central). Los tiempos de divergencia asocian el aislamiento de éstas entidades con cambios climáticos del Pleistoceno superior, que posiblemente fue reforzado por barreras geográficas como el Istmo de Tehuantepec, el Valle Tehuacán-Cuicatlán y los Valles Centrales de Oaxaca. El hecho de que las poblaciones de H. chapmani constituyan 2 entidades evolutivas, tiene como consecuencia la reducción significativa del rango de distribución de estos 2 linajes. Por lo tanto, el estatus de conservación de H. chapmani debe ser reevaluado.

The Systematic Collections Committee of the American Society of Mammalogists advises curators and other personnel affiliated with natural history collections in matters relating to administration, curation, and accreditation of mammal specimens and their associated data. The Systematic Collections Committee also maintains a list of curatorial standards for managing a collection-accreditation program under the auspices of the American Society of Mammalogists. To date, the Systematic Collections Committee has provided guidance for the more traditional specimen collections (skin, skeletal, fluid, etc.) and specimen data management. Given the rapidly expanding role of genetic resources in biological research, the Systematic Collections Committee herein presents a series of formal guidelines and standards designed to assist collections professionals in the current best practices for curation and maintenance of collections of genetic resources, to ensure long-term integrity of the archived material, and to address personnel safety and guidelines for researchers and curatorial staff. These guidelines and standards are intended to provide constructive guidance and a mechanism of accreditation for collections that vary in scale and infrastructure.