Geographic variation in cranial morphology of the Water Opossum Chironectes minimus (Didelphimorphia, Didelphidae)

Abstract

The Water Opossum, Chironectes minimus (Didelphimorphia, Didelphidae), is the only semi-aquatic marsupial and can be easily identified for its uniquely patterned water resistant pelage and webbed hind-feet. The species is distributed along the Neotropical region (from Southern Mexico to Northwestern Argentina) and is currently divided on four subspecies (C. m. argyrodytes, C. m. panamensis, C. m. minimus, C. m. paraguensis), based on its geographical distribution. We evaluated the geographic variation in Chironectes minimus, using traditional and geometric morphometrics techniques to capture the size and shape of the skull to identify differences between the populations that could relate to existing subpsecies or populations that would merit particular taxonomic attention. We took 13 skull measurements, and digitized 37, 18, and 23 2D landmarks on the dorsal and lateral view of the cranium and on the lateral view of the mandible, respectively. The sample consisted on 135 individuals from 66 localities. Analyses of both datasets showed that the Southern South America and Northern Central America animals differ from the other populations. Geometric morphometrics shows on the three views that the Amazon animals differ from the others probably due to existing geographical barriers. These morphological differences among populations of the Water Opossum support the need for a proper phylogenetic assessment of these populations, in order to clarify their taxonomic status.

Estimating the potential distribution and conservation priorities of Chironectes minimus (Zimmermann, 1780) (Didelphimorphia: Didelphidae)

“…Similar cases were documented for wide-ranging Didelphidae species: the genus Didelphis, the Black-eared opossums (D. marsupialis; Cerqueira 1985) and White-eared opossums (D. albiventris; Cerqueira and Lemos 2000), and the Lutrine Opossum, Lutreolina crassicaudata (Martínez-Lanfranco et al 2014). From this perspective, our study suggests that the current taxonomic status of these populations needs to be adequately assessed using tools that could reveal their distinctiveness (Damasceno and Astúa 2016). Independently of the current taxonomic classification, a possible loss of one of these disjunct groups would be irreversible.…”

“…On the other hand, it is important to note that our models showed that there is a disjunction in the distribution of water opossum, observed in the population of southeastern of Brazil (C. m. paraguanensis [Marshall 1978;Damasceno and Astúa 2016]). This disjunct distribution could represent ecological niche differences among subspecies, which could simultaneously affect the performance of our models (see Rojas-Soto et al 2008;2009;Mota-Vargas and Rojas-Soto 2016).…”

“…This disjunct distribution could represent ecological niche differences among subspecies, which could simultaneously affect the performance of our models (see Rojas-Soto et al 2008;2009;Mota-Vargas and Rojas-Soto 2016). It is reasonable to suggest that there are climatic and geographic factors acting (or that acted) as geographic barriers that contribute to the isolation of some populations (see Damasceno and Astúa 2016). Similar cases were documented for wide-ranging Didelphidae species: the genus Didelphis, the Black-eared opossums (D. marsupialis; Cerqueira 1985) and White-eared opossums (D. albiventris; Cerqueira and Lemos 2000), and the Lutrine Opossum, Lutreolina crassicaudata (Martínez-Lanfranco et al 2014).…”

“…The water opossum or Yapok, Chironectes minimus (Zimmerman 1780), is the only Neotropical semi-aquatic marsupial (Bressiani and Graipel 2008;Acosta and Azurduy 2009;Galliez et al 2009). It belongs to a monotypic genus, which includes four subspecies (Stein and Patton 2007;Damasceno and Astúa 2016). The species is characterized by a silvery gray dorsal pelage with four black transverse patches connected by a narrow midline.…”

Mammalian Diversity and Matses Ethnomammalogy in Amazonian Peru Part 3: Marsupials (Didelphimorphia)

“…Although central Amazonia (including the Yavarí-Ucayali interfluve) falls outside the mapped geographic range of Chironectes minimus in most standard references (e.g., Stein and Patton, 2008), recent observations and gene-sequencing results (Ardente et al, 2013;Brandão et al, 2015;Oliveira et al, 2016; suggest that the water opossum is continuously distributed from Central America to southeastern Brazil. Despite geographic variation in craniodental morphology reported by Damasceno and Astúa (2016) and Cerqueira and Weber (2017), this species seems to be genetically undifferentiated across most, if not all, of cis-Andean South America, and it shows minimal genetic divergence even across the Andes . Therefore, the "subspecies" of C. minimus currently recognized by authors (Gardner, 2005;Stein and Patton, 2008) are unlikely to represent valid taxa.…”