Volcano rabbit
The volcano rabbit , also known as the teporingo or zacatuche, is a species of small rabbit that lives in pine and alder forests on volcanic slopes in Mexico. It is the only species in the genus Romerolagus and is considered to be the most primitive species among the rabbits and hares. It has small, rounded ears, short legs, a large forehead, and short, thick fur. It is one of the world's smallest rabbits, lives in groups consisting of between two and five members, and makes burrows and runways among bunchgrasses. Up to three young are produced per litter, born in nests formed from shallow depressions in the ground lined with fur and plant matter.
Uniquely among the rabbits, the volcano rabbit emits high-pitched sounds to warn other rabbits of danger, a habit common in the related pikas. It is awake and most active in the early morning and evening. Populations have been estimated as approximately 7,000 adult individuals over their entire range. Human developments surrounding the volcano rabbit's habitat—including overgrazing, hunting, and burning of the species' preferred scrublands—have caused significant declines in population, even in protected parks. Both the IUCN and the Mexican government consider the volcano rabbit an endangered species. It is listed on Appendix I of the CITES treaty, which is intended to restrict trade of the animal.
Taxonomy and etymology
Romerolagus diazi was first described by the head of the Mexican Geographical and Exploring Commission, Fernando Ferrari-Pérez, in 1893 as a member of the hares, using the scientific name Lepus diazi and common name conejo del Volcán. The species name diazi honors the Mexican cartographer Agustín Díaz, who published the work where the species was first described. The type specimen was collected on the northeastern slopes of Ixtaccíhuatl, a volcano near San Martín Texmelucan, in the Mexican state of Puebla. It was separately described as the Popocatepetl rabbit, Romerolagus nelsoni, in 1896 by American zoologist Clinton Hart Merriam in an account that did not refer to the earlier work of Ferrari-Pérez. Merriam noted a type specimen that was collected on Popocatépetl at an altitude of by Edward William Nelson, an American naturalist for whom Merriam named the species. Merriam noted several characteristics that differed significantly from any member of the hares, such as its anatomy and means of locomotion, and gave it the genus name Romerolagus in honor of Matías Romero, Mexican ambassador in the United States and a supporter of the United States Biological Survey in Mexico. American zoologist Gerrit Smith Miller Jr. noted the discrepancy between the two descriptions and, after consulting with Nelson and Ferrari-Pérez in 1911, clarified the nomenclature of the species by using the name Romerolagus diazi, a new combination, and making Romerolagus nelsoni and Lepus diazi synonyms of the new name. From this point up until the 1950s, the authority of the species was attributed to Díaz alone; biologist Paulino Rojas Mendoza argued in 1952 that the correct name under International Code of Zoological Nomenclature rules would credit Ferrari-Pérez as well. Since then, the scientific name and authority of the volcano rabbit has been Romerolagus diazi.The volcano rabbit is named for its preferred habitat: the slopes of volcanoes. One Nahuatl name, zacatochtle, refers to the rabbit's relationship with subalpine tussock grass in the genus Festuca. The name comes from the combination of zacatl and tochtle, and has been modified to the currently-used epithet zacatuche. Another common name, teporingo, likely derives from Classical Nahuatl, combining tepētl, olīn and the suffix -co referring to location. Several accounts of the species find no obvious etymology for this name, and tentatively ascribe it to a corruption of another name in Nahuatl.
Phylogeny
No subspecies of the volcano rabbit are recognized, and it is the only species within its genus. No fossils of the volcano rabbit are known, but analysis of its morphology and genetic records indicate it is the most morphologically primitive living leporid. The species has high genetic diversity and is separated into five haplogroups across its distribution; these groups appear to have some level of gene flow between them due to the short distance between populations. It was in 1929 placed in the subfamily Paleolaginae by Lee R. Dice, alongside Pentalagus, Pronolagus, and the extinct Alilepus and Palaeolagus. The following cladogram is based on mitochondrial genome analysis of the volcano rabbit, the European rabbit, the snowshoe hare, and the black-tailed jackrabbit, as well as a broader phylogenetic tree produced by biologist Leandro Iraçabal Nunes and colleagues:Characteristics
The volcano rabbit is one of the smallest rabbits in the world, having an adult weight that ranges from and a total length of. Its ears are small and rounded, measuring less than in length, and the hind feet are short, measuring. It has a vestigial tail which is only visible in young rabbits and becomes hidden under the skin in adulthood. Three pairs of mammary glands are present in female rabbits. The volcano rabbit has dense, short fur. Its fur is yellowish brown across all of its body, and is softer on the rabbit's underside. Each hair is black at the base and tip and antimony yellow in the middle. This fur color changes only near the nose, eyes, and at the base of the ears, where it appears more buff. The dark coloration of the volcano rabbit's fur blends in with the volcanic soils in its habitat. This adaptation may help it evade predators. Its coat does not change color from one season to the next. However, it does undergo molting in four stages over the course of the year. First, hair is lost, then melanin disappears, then melanin is deposited at the site of hair loss, after which hair regrows. The volcano rabbit strongly resembles pikas, closely related mountain-dwelling lagomorphs, though Marcus Ward Lyon Jr., a naturalist credited with the complete classification of the rabbit and hare genera, notes it as being closest in appearance to the Amami rabbit.The skull of the volcano rabbit has small triangle-shaped projections from the brow ridge towards the back of the head. It has a long palate, and a distinctly separated interparietal bone. Like other leporids, it has a dental formula of, indicating that it has two pairs of upper and one pair of lower incisors, no canines, three upper and two lower premolars on each side, and three upper and lower molars on either side of the jaw. The cheekbones are wide, larger towards the back of the head, and the auditory bullae are large compared to those of other leporids, larger than the foramen magnum. The clavicle is complete and connects directly to the sternum, which is on average smaller than that of other rabbits and hares. The central part of the sternum is segmented into three parts, which are articulated with six pairs of the ribs. The rabbit's navicular bone is short and does not extend below the metatarsal bones. It has a strong curve to its pelvis. The rabbit's morphological features, specifically the arrangement of its teeth, resembles those of several extinct leporids from the Tertiary period, including Nekrolagus, which lived during the Pliocene. The hip bones of the volcano rabbit are more similar to another extinct species, Limnolagus, aside from being thinner and more pronounced towards the front and bottom part of the spine.
Distribution and habitat
Volcano rabbits are endemic to an area of only just southeast of Mexico City, in alpine scrublands surrounding four volcanoes. The largest of these volcanic regions is within the Iztaccíhuatl–Popocatépetl National Park, with other areas including the Chichinautzin and Pelado volcanoes. The highly vegetated Altzomoni peak within the park is noted as being able to sustain a notably large volcano rabbit population compared to other regions. Historically, the volcano rabbit likely occupied larger areas within the Trans-Mexican Volcanic Belt and the Sierra Chichinautzin mountain range. The range of the volcano rabbit has since been fragmented into 16 individual patches across these volcanoes due to human disturbance. Volcano rabbits are commonly found at altitudes between, but can occur anywhere from.The local climate in the volcano rabbit's habitat is temperate and subhumid, with a mean annual temperature of. Annual rainfall averages about. The soil consists mostly of andosols and lithosols, and the vegetation includes varieties from the Nearctic and Neotropical realms, with plants coming from both coniferous forest and tropical communities. This vegetation diversity is attributed to the Trans-Mexican Volcanic Belt acting as a barrier between these realms. The plants Festuca tolucensis and Pinus hartwegii are abundant in volcano rabbit habitats. The species prefers habitats with tall, dense vegetation from a variety of bunch grasses referred to as zacatón, such as Muhlenbergia macroura and Festuca amplissima. Volcano rabbits show strong preferences for thickly vegetated pine, alder, and mixed pine-alder forest habitats. Human activity in the area has had a great impact upon the volcano rabbit's habitat, which highways, farming have fragmented, afforestation, and unsound fire and grazing practices. A study on the effects of climate change upon volcano rabbit populations concluded that fluctuations in climate affected rabbits more on the edge of their habitable range.
The volcano rabbit was once considered to live on the volcano Nevado de Toluca, and a specimen was collected there in 1975 by mammalogist Ticul Álvarez. Research conducted by Jurgen Hoth and colleagues in 1987 found no records of the species there, and noted that it had not been seen in at least 15 years, according to local accounts. There was a sighting of a single rabbit in the region in August 2003, but it was declared extinct within this portion of its range in 2018. Populations exist elsewhere within the Trans-Mexican Volcanic Belt and in captivity. By 2019, the International Union for Conservation of Nature no longer mentioned the Nevado de Toluca as a current or potential site for the distribution of this species.