A Story About a “Gem”: The Rivoli’s Hummingbird, Eugenes fulgens

By Luz E. Zamudio

Linked paper: Genetic and morphological differentiation among populations of the Rivoli’s Hummingbird Eugenes fulgens species complex (Aves: Trochilidae) by L.E. Zamudio-Beltrán, J.F. Ornelas, A. Malpica, and B.E. Hernández-Baños, The Auk: Ornithological Advances.

Ever since I was a child, all kinds of living forms have captured my attention. However, I have developed a particular admiration and affinity for hummingbirds, thanks to their colorful feathers, incredible physiology, and graceful behaviors. These amazing characteristics made me want to know more about them, especially about their evolutionary histories.

My journey in studying hummingbirds began during my postgraduate studies, with Dr. Blanca E. Hernández-Baños as my main advisor. We decided to focus on a particular group of hummingbirds, the “mountain gem” group, where the Rivoli’s Hummingbird, Eugenes fulgens, belongs. We were attracted to them because of their great variety in forms, habitats, and distributions.

At the beginning of this study, Eugenes fulgens was considered to be distributed from northern Mexico to Panama highlands, but some authors had argued that the southern population belonged to a separate species on the basis of differences in plumage. This hummingbird has a geographic distribution in Middle America and inhabits pine and pine-oak forests highly threatened by human activity, and we thought that if it’s really two species, this is something important to know. To assess whether this was true, we conducted a molecular study to analyze this divergence, and our results confirmed that Eugenes fulgens (formerly known as the Magnificent Hummingbird) should be split into at least two different species: Eugenes fulgens (Rivoli’s Hummingbird) and Eugenes spectabilis (Talamanca Hummingbird). Based on our findings as well as previous studies, the formal split took place in 2017.

However, we still wanted to know more about the Rivoli’s Hummingbird, because this species has a disjunct distribution and showed signs of genetic differentiation. We wondered whether isolated populations were in the early stages of speciation themselves. To find out for sure, we needed to increase our sampling in order to perform more robust analyses at population level. We accomplished this through fieldwork in Mexico as well as loans from various biological collections. Our next step was the integration of molecular data (mitochondrial and microsatellites) and morphometric data to detect and describe differences between the disjunct populations.

During this process, we invited two collaborators to join us in disentangling the evolutionary history of this hummingbird: Dr. Francisco Ornelas, who has broad experience in evolutionary studies with hummingbirds, and Ph.D. candidate Andreia Malpica. Both helped us to obtained valuable information from genetic markers.

Together, we reconstructed the phylogeographic history of Rivoli’s hummingbird, resulting in the recognition of three main lineages isolated by important geographic barriers (the Isthmus of Tehuantepec in Mexico and the Motagua-Polochic-Jocotan fault in Guatemala). The role of climatic fluctuation during the Quaternary also played a crucial role in the formation of these lineages. The populations of Rivoli’s Hummingbird on either side of the Isthmus of Tehuantepec diverged nearly 59,600 years ago, during the early Pleistocene, in the presence of gene flow. According to these estimates, the formation of the Isthmus of Tehuantepec during the Late Miocene was not the primary cause of the population divergence, but formed a permeable barrier that, in combination with strong selection, contributed to their divergence.

We hope that this study will be considered in future taxonomic revisions recognizing the populations of Rivoli’s Hummingbird in the process of speciation. Genetic and morphometric data support the conclusion that populations situated east of the Isthmus of Tehuantepec are independent from those situated to the west, previously considered by some other authors as the “viridiceps” lineage or group.

Today, our team is working on incorporating new kinds of data into our studies, including genomics, geographic information systems, and morphological traits such as coloration. This will lead us to a broader work in evolutionary biology, and we are looking forward to expanding our collaborations with researchers with the same interests.