Marcelo Weksler

Myotis armiensis was recently described from specimens collected in the mountain ranges of Costa Rica, Panama, and Ecuador. During a systematic revision of Neotropical Myotis , we identified additional specimens from Venezuela and Colombia. Using an integrative approach that combined morphological traits, cytochrome b sequences, and ecological niche modeling, we assessed the geographic variation of M. armiensis . Our findings indicate that this species can be structured into two allopatric populations: one in the Talamanca Cordillera of Central America, and another restricted to the South American Andes and Cordillera de La Costa in Venezuela. These populations are reciprocally monophyletic, exhibiting genetic distances greater than 3% and notable morphometric variation. The diversification of this taxon likely occurred during the Pleistocene, possibly driven by environmental fluctuations associated with glacial cycles. It is possible that M. armiensis comprises two recently diverged lineages, but future studies incorporating broader datasets are needed to properly assess the taxonomic status of these populations.

Natural history collections serve as crucial infrastructure for both basic and applied scientific research, providing temporal and spatial specimen data needed to understand biodiversity, environmental change, and emerging pathogens. This study surveyed mammal collections across South America to assess the scope and quality of this infrastructure. A detailed questionnaire was distributed to curators and collection managers from May 2021 to February 2022, gathering information on institutional characteristics, collection size, taxonomic and geographical scope, preservation methods, genetic resource availability, percentage digitization, financial support, and challenges such as funding limitations. Our survey identified 141 collections; more than twice the number reported by the American Society of Mammalogists in 2018. South American collections house ∼746 000 catalogued specimens, including 452 primary type specimens, representing only a modest proportion of the vast mammalian diversity of South America. Collections are geographically concentrated in Argentina, Brazil, Colombia, and Peru, with a significant gap in the Guianas region and a decline in responses from Venezuela. The survey highlights four major challenges facing South American collections: staffing shortages, minimal cryogenic infrastructure, incomplete digitization, and sustainability issues. This initiative aims to raise awareness of collections in South America, plan for strategic growth, and strengthen research capacity to address pressing global issues, such as climate change, zoonotic disease transmission, and long-term conservation strategies.

The diversification of Neotropical sigmodontine rodents represents one of the most remarkable evolutionary events among mammals, encompassing numerous endemic, rare, and endangered genera and species. One of the most emblematic examples is Microakodontomys transitorius Hershkovitz 1993, originally described from a single specimen based on morphological traits, and considered a “transitional” taxon between the tribes Akodontini and Oryzomyini, due to its unique combination of characters. However, the lack of additional specimens and its morphological resemblance to small species of Oligoryzomys led to its taxonomic synonymization with that genus. Here, we report new karyological, morphological, and natural history information on this taxon, and present results of total evidence phylogenetic analyses of the tribe Oryzomyini. Cytogenetic analyses revealed two distinct karyotypes: a female with 2n = 38, FNa = 46, and a male with a mosaic 2n = 36–37, FNa = 44–45. Phylogenetic analyses integrating morphological, mitochondrial (cytochrome b), and nuclear (IRBP) data support the placement of M. transitorius within the Oryzomyini, but distinct from Oligoryzomys, and as a sister taxon to Lundomys molitor. We redescribe the taxon, discuss its phylogenetic relationships, and the implications of its diversification within the Cerrado biome.