Diversification and secondary contact in the magpie‐jays ( Calocitta ) throughout the pacific lowlands of Mesoamerica

Diversity and biogeography of South American mud turtles elucidated by multilocus DNA sequencing (Testudines: Kinosternidae)

Kinosternon is the most speciose genus of extant turtles, with 22 currently recognized species, distributed across large parts of the Americas. Most species have small distributions, but K. leucostomum and K. scorpioides range from Mexico to South America. Previous studies have found discordance between mitochondrial and nuclear phylogenies in some kinosternid groups, with the current taxonomy following the nuclear-based results. Herein, based on extended molecular, geographic, and taxonomic sampling, we explore the phylogeographic structure and taxonomic limits for K. leucostomum and the K. scorpioides group and present a fossil-calibrated nuclear time tree for Kinosternon. Our results reveal contrasting differentiation patterns for the K. scorpioides group and K. leucostomum, despite overlapping distributions. Kinosternon leucostomum shows only shallow geographic divergence, whereas the K. scorpioides group is polyphyletic with up to 10 distinct taxa, some of them undescribed. We support the elevation of K. s. albogulare and K. s. cruentatum to species level. Given the deep divergence within the genus Kinosternon, we propose the recognition of three subgenera, Kinosternon, Cryptochelys and Thyrosternum, and the abandonment of the group-based classification, at least for the K. leucostomum and K. scorpioides groups. Our results show an initial split in Kinosternon that gave rise to two main radiations, one Nearctic and one mainly Neotropical. Most speciation events in Kinosternon occurred during the Quaternary and we hypothesize that they were mediated by both climatic and geological events. Additionally, our data imply that at least three South American colonizations occurred, two in the K. leucostomum group, and one in the K. scorpioides group. Additionally, we hypothesize that discordance between mitochondrial and nuclear phylogenetic signal is due to mitochondrial capture from an extinct kinosternine lineage.

Temporal stability of the hybrid zone between Calocitta magpie-jays revealed through comparison of museum specimens and iNaturalist photos

Hybrid zones are natural experiments for the study of avian evolution. Hybrid zones can be dynamic, moving as species adjust to new climates and habitats, with unknown implications for species and speciation. There are relatively few studies that have comparable modern and historic sampling to assess change in hybrid zone location and width over time, and those studies have generally found mixed results, with many hybrid zones showing change over time, but others showing stability. The white-throated magpie-jay (Calocitta formosa) and black-throated magpie-jay (Calocitta colliei) occur along the western coast of Mexico and Central America. The two species differ markedly in throat color and tail length, and prior observation suggests a narrow hybrid zone in southern Jalisco where individuals have mixed throat color. This study aims to assess the existence and temporal stability of this putative hybrid zone by comparing throat color between georeferenced historical museum specimens and modern photos from iNaturalist with precise locality information. Our results confirm the existence of a narrow hybrid zone in Jalisco, with modern throat scores gradually increasing from the parental ends of the cline toward the cline center in a sigmoidal curve characteristic of hybrid zones. Our temporal comparison suggests that the hybrid zone has not shifted its position between historical (pre-1973) and modern (post-2005) time periods-a surprising result given the grand scale of habitat change to the western Mexican lowlands during this time. An anomalous pocket of white-throated individuals in the northern range of the black-throated magpie-jay hints at the possibility of prehistorical long-distance introduction. Future genomic data will help disentangle the evolutionary history of these lineages and better characterize how secondary contact is affecting both the DNA and the phenotype of these species.