Tlacuatzin canescens (J. A. Allen, 1893)

Russell A. Mittermeier & Don E. Wilson, 2015, Didelphidae, Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona: Lynx Edicions, pp. 129-186 : 147

26.

Tlacuatzin

Tlacuatzin canescens

French: Opossum cendré / German: Graue Zwergbeutelratte / Spanish: Ticuachin

Other common names: Gray Mouse Opossum, Grayish Mouse Opossum

Taxonomy. Didelphis (Micoureus) canescens J. A. Allen, 1893 ,

“ Santo Domingo de Guzman , Isthmus of Tehuantepec , [Oaxaca], Mexico ”

Recent opossum classifications consider this species to be monotypic, with the subspecies representing synonyms. Two of the subspecies fall within the range of the nominal subspecies, but their validity needs to be properly assessed. Four species recognized.

Subspecies and Distribution.

T:c.canescens].A.Allen,1893—WMexico,fromSSonoratoOaxaca,andintheYucatanPeninsula;possiblyalsoinNWGuatemala.

T.c.insularisMerriam,1898—IslasMarias,Nayarit,Mexico.

T.c.oaxacaeMerriam,1897—knownonlyfromthetypelocality,“CityofOaxaca,”vicinityofOaxacadeJuarez,probablynearslopesoftheCerroSanFelipe,Oaxaca,Mexico.

T: c. sinaloaeJ. A. Allen, 1898 — known only from the type locality, Tatamales, Sinaloa, Mexico.

Descriptive notes. Head-body 11-16 cm, tail 10.5-16.7 cm; weight 30-70 g. The Tlacuatzin has pale gray or grayish-brown dorsal fur, which continues on head and mid-rostral region where it becomes progressively paler. There is no mid-rostral stripe. Dark eye-rings around black eyes do not reach ears or nose. Tail length is about the same as head-body length, and tail has fur on its proximal one-tenth (10-15 mm) or less. Naked part oftail is grayish, sometimesslightly paler ventrally or with a whitish tip. Ventral fur is whitish, creamy or buffy, extending to legs, and throat gland is absent. Fur varies from soft, short, dense, and crisp to quite long and slightly woolly. Feet are gray or yellow-white, and carpal tubercles are present in adult males. Ears are broad, relatively rounded, naked, and blackish. Postpartum molt has been recorded. Female Tlacuatzins lack a pouch and have nine or eleven mammae, with four or five on each side, and a medial mamma. The Tlacuatzin is unique in being the only small opossum with a 2n = 22 karyotype. Itis unique also because all autosomes are acrocentric, the Xchromosome is a small acrocentric and the Y-chromosome is a very small and biarmed. There is no sexual dimorphism in its skull size and shape.

Habitat. Tropical and semi-deciduous dry forests along the Pacific coast of Mexico from sea level to elevations of 2100 m (most of the region is below 1000 m). The Tlacuatzin occurs in evergreen and deciduous forests, scrublands, savanna-like grasslands, secondary forests, and cultivated areas such as croplands and orchards, generally characterized by dry-wet seasonality with rainfall concentrated in July-October.

Food and Feeding. Diet of the Tlacuatzin is mainly invertebrates, particularly arthropods such as Hemiptera, Orthoptera, Lepidoptera, and Coleoptera. It also eats vertebrates such as geckos and bird eggs (one specimen was spotted foraging inside birds’ nests). It also feeds on blooming flowers of Stenocereus queretaroensis , an endemic cactus, and fruits of wild fig trees.

Breeding. Tlacuatzins make nests in a great variety of locations. Apart from the usual locations such as tree hollows, under rocks, fallen logs, trees, and shrubs, they also build nests in cacti and abandoned hanging birds’ nests, such as those built by banded wrens (Thryothorus pleurostictus), white-bellied wrens (Uropsila leucogastra), and orioles (Icterus sp.). Nests are always located above the ground at heights varying from 70 cm to 5 m. Nests are very similar to those of other species of opossums; they are spherical, built with leaves and stems, and lined with grasses and “hairy” plant fibers of Ceiba pentandra (Malvaceae) and similar species. Breeding of Tlacuatzins occurs all year long. Females with young or lactating have been captured in July-December and juveniles in February-September. Reported litter sizes are 8-14 young, with an average of eleven young. Mating behavior of the Tlacuatzin has been observed in the wild. The male approached the female and engaged in nose-to-nose contact at entrance to her nest, which contained her offspring. Both adults hissed loudly for c.3 minutes, and then they left the nest entrance for a nearby branch c.1-8 m above the ground. Both grabbed the branch with their tails and hung suspended from it while the male grabbed the female around her shoulders with his forelimbs, bit her on her neck, and grabbed her hindlegs with his hindlimbs. Three intromissions occurred, lasting c.2 minutes each. Shortly after the last penetration, the female bit the male, both hissed, and they fell onto the ground. They separated and climbed back up the tree. The female returned to her nest and her offspring, and the male groomed his genital area.

Activity patterns. Tlacuatzins are reported to be nocturnal, but no precise information on activity patterns is available. Some individuals were caught by hand while foraging at night in Maria Madre Island, but observations of a pair mating in the wild were made at 18:30 h before sunset.

Movements, Home range and Social organization. Tlacuatzins are probably scansorial or arboreal because they mate and nest in trees. Nests are always located above the ground, and Tlacuatzins are more frequently captured in traps set above the ground (76-6-85-7% of the time in two different studies). Densities were 40-450 ind/km? in Chamela-Cuixmala Biosphere Reserve in Jalisco and 67-800 ind/km?® in different location in Colima. Average distances traveled in two different sites were 33-2 m and 35-2 m.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Tlacuatzin has a wide distribution, presumably a large population, and occurs in a number of protected areas. Nevertheless, its primary habitat of deciduous forest is being deforested. Although as a whole the Tlacuatzin does not seem at risk,it has been suggested that island populations, particularly of the subspecies insularis, might be at greater risk because they are now rare and might have been affected by introduction of the Roof Rat (Rattus rattus).

Bibliography. Armstrong & Jones (1971), Astua (2010), Ceballos (1990), Engstrom & Gardner (1988), Her shkovitz (1992a), Ibarra-Cerdena et al. (2007), Kennedy et al. (2013), Svartman (2009), Valtierra-Azotla & Garcia (1998), Voss & Jansa (2003, 2009), Wilson (1991), Zarza et al. (2003).

Figures

65. Pygmy Opossum (Chacodelphys formosa), 66. Agricola’s Opossum (Cryptonanus agricola), 67. Chacoan Mouse Opossum (Cryptonanus chacoensis), 68. Guaiba Mouse Opossum (Cryptonanus guahybae), 69. Unduavi Mouse Opossum (Cryptonanus unduaviensis), 70. . Emilie’s. 9 Opossum.. Gracilinanus. (null), 71. Aceramarca Opossum (Gracilinanus aceramarcae), 72. Agile Opossum (Gracilinanus agilis), 73. Wood Sprite Opossum (Gracilinanus dryas), 74. Northern Gracile Opossum (Gracilinanus marica), 75. Brazilian Gracile Opossum (Gracilinanus microtarsus)

Subspecies and Distribution. T:c.canescens].A.Allen,1893—WMexico,fromSSonoratoOaxaca,andintheYucatanPeninsula;possiblyalsoinNWGuatemala. T.c.insularisMerriam,1898—IslasMarias,Nayarit,Mexico. T.c.oaxacaeMerriam,1897—knownonlyfromthetypelocality,“CityofOaxaca,”vicinityofOaxacadeJuarez,probablynearslopesoftheCerroSanFelipe,Oaxaca,Mexico. T: c. sinaloaeJ. A. Allen, 1898 — known only from the type locality, Tatamales, Sinaloa, Mexico.