Identification of Fire Ants (Hymenoptera: Formicidae) from Northeastern Mexico with Morphology and Molecular Markers

RESUMEN La hormiga de fuego roja importada, Solenopsis invicta Buren, especie invasora, se ha dispersado exitosamente a muchos países desde su origen en Sudamérica, y ha alcanzado la frontera Estados Unidos-México (p. ej. Matamoros, estado de Tamaulipas, México) donde ahora coexiste con hormigas de fuego nativas, Solenopsis geminata y especies del subcomplejo Solenopsis xyloni. La identificación morfológica de las Solenopsis spp. es difícil, particularmente de las obreras más pequeñas. Examinamos la secuencia del gene mitocondrial citocromo oxidasa I (COI) como marcador para poblaciones de hormigas de fuego en varios sitios de México. Los productos de PCR de este locus rindieron secuencias únicas y patrones de restricción que permitieron distinguir entre S. invicta, S. geminata y caracterizar miembros del subcomplejo S. xyloni. Las secuencias de S. invicta fueron iguales en 99% a secuencias reportadas para especímenes de Florida y Nuevo México. Las secuencias de S. xyloni fueron iguales en 96% a las secuencias reportadas de Nuevo México. Las secuencias de S. geminata fueron similares (93% identidad) a las de Florida, y comparten un sitio de restricción Hinf I con algunas pero no todas las secuencias reportadas para Florida. Las secuencias de S. xyloni también se detectaron en hibridos de S. geminata/S. xyloni identificados por morfología; junto con otros caracteres el marcador permite su caracterización. ABSTRACT The invasive red imported fire ant, Solenopsis invicta Buren, has successfully dispersed across many countries from its South American homeland and now has reached the USMexico border (e.g., Matamoros, state of Tamaulipas, México), where it now coexists with native fire ants, Solenopsis geminata, Solenopsis xyloni, and others. The morphological identification of Solenopsis spp. workers is difficult, particularly small ones. We examined the sequence of the cytochrome oxidase I (COI) mitochondrial gene (mtDNA) as a marker for fire ants collected at several Mexican localities. PCR products from this locus yielded unique sequences and restriction patterns that allowed distinguishing between S. invicta, S. geminata, and specimens harboring S. xyloni sequences. The S. invicta sequences obtained were 99% identical to sequences reported from Florida and New Mexico specimens. The S. xyloni sequences obtained were 96% identical to New Mexico sequences. The S. geminata sequences were similar (93% identity) to those from Florida, and shared a Hinf I restriction site with some but not all Florida sequences. The S. xyloni sequences were detected in S. geminata/S. xyloni hybrids identified by morphology; along with other characters, the marker allows their characterization

A new species of Trachymyrmex (Hymenoptera, Formicidae) fungus-growing ant from the Sierra Madre Oriental of northeastern Mexico

Here we describe a new species of Trachymyrmex, T. pakawa sp. n., from the Gran Sierra Plegada range of the Sierra Madre Oriental, in the states of Coahuila and Nuevo Leon, northeastern Mexico. Trachymyrmex pakawa is a large-sized species compared to other North American Trachymyrmex. Its geographic distribution includes the piedmont of the Gran Sierra Plegada at La Estanzuela, Monterrey, as well as peripheral mountains segregated from the Sierra Madre Oriental (Cerro de las Mitras, Sierra de Zapalinamé, Cañon de San Lorenzo, Cerro de las Letras). The preferred habitats of T. pakawa include oak-pine forest at La Estanzuela, xeric oak forest at Zapalinamé and mesic Chihuahuan desert scrub with sotol (Dasylirion) at other sites. All localities are on slopes, on very rocky, shallow lithosols overlaying large boulders. This species nests under and between large boulders and rocks. It has not been observed on alluvial or better developed, deeper soils, and it is absent from sites with human activity (urban, disturbed, and landscaped areas). It is closely related to and morphologically similar to Trachymyrmex smithi. The known distribution ranges of T. pakawa and T. smithi almost overlap in Saltillo, Coahuila state. The main character that distinguishes the new species from T. smithi is longer antennal scapes in T. pakawa; also, different nesting habits (rocky slopes vs. alluvial sites or deep sand in T. smithi), and geographic distribution. Phylogenetic analysis of DNA sequences from the mitochondrial marker cytochrome c oxidase subunit I (COI) and the first intron of the F1 copy of the nuclear protein-coding gene Elongation Factor 1- α (EF1-α-F1) confirm a sister-species relationship between T. pakawa and T. smithi. Bayesian coalescent analyses indicate a divergence time of about 8.00 million years before present (95% confidence interval: 4.8–11.5 mya) between T. pakawa and T. smithi. The divergence of the lineages of T. pakawa and T. smithi could have been driven by the Pliocene-Holocene desertification of southwestern North America. This process resulted in isolated mesic refugia and forests in the Madrean ranges and piedmonts of northeastern Mexico (the current habitat of T. pakawa) while T. smithi adapted to the deeper, often sandy soils on the drier desert plains of Coahuila and Chihuahua states in Mexico, and New Mexico and Texas in the USA. Within the Nearctic species of the Trachymyrmex septentrionalis species group, T. pakawa is the species that is closest (by geographical distribution) to Neotropical species of Trachymyrmex like T. saussurei