By Paul Carter (22 Feb 2022). Revised 22 March 2022 to match the open access report lodged on Zenodo as:
CARTER, Paul. (2022). Alston’s Woolly Mouse Opossum, Marmosa alstoni (Didelphimorphia, Didelphidae), in Boquete, Panama. Zenodo. https://doi.org/10.5281/zenodo.6374907
SUMMARY
On 17 Feb 2022 at 9:00 PM I photographed Marmosa alstoni (Didelphimorphia, Didelphidae) in the Boquete area, Panama. Mammal Diversity Database (2022 v1.8) treat M. alstoni as endemic to Costa Rica, following the recent review of the M. alstoni complex by Voss et al. (2021). Following the taxonomy in Voss et al (2021) and their review of previous records in Panama it appears that this record in Boquete is the first photographic record of M. alstoni in Panama; and possibly the first confirmed record in Panama.
TAXONOMY AND THE ALSTONI GROUP IN PANAMA
Voss et al. (2021) split Marmosa adleri and Marmosa nicaraguae from M. alstoni and note that the Alstoni Group in Marmosa “is almost certainly more diverse than the three species recognized”. Voss et al. (2021, Fig 3 and Table 4) show a morphological comparison of the three species. Some external morphological features of the three species, as described by Voss et al. (2021), include the following:
– M. alstoni: long, fluffy-furred tail base; >50% of the naked part of the tail is white; the average body weight of M. alstoni is 137 g.
– M. nicaraguae (on few specimens): a furry tail base that is short and not fluffy, the fur is appressed, not forming a conspicuously fluffy segment (as show in Voss et al., 2021 Figs 3 and 7b); the dorsal pelage is uniformly grayish brown from crown to rump (based on the single fully adult skin at hand); “dorsal surfaces of the hind feet and the forefeet are covered with short, pale hairs and lack any darker markings”. – M. adleri: has a short furry tail base; the unfurred (scaly) part of the tail is almost completely dark, sometimes with a short white tip; smaller than the other two species; the average body weight of M. adleri is 58 g (significantly smaller than M. alstoni).
Distribution accounts prior to the splits in 2021
Reid (2009, p48), prior to recent splits, showed the distribution in Central America of Alston’s Mouse Opossum (Micoureus alstoni, since revised to Marmosa alstoni) as being from Central Belize to Western Panama. The distribution in Panama was shown as limited to the northwestern end of Bocas del Toro state; this area located about 65 km north-northwest of Boquete. Eisenberg (1989, p33) also showed a record of M. alstoni in Bocas del Toro state. The range of M. alstoni in Mammal Diversity Database (2021 v1.7) comprised Belize, Guatemala, Honduras, Nicaragua, Costa Rica, Panama, and Colombia.
Lambert et al (2011) described a record of M. alstoni from the canal area of central Panama; that record was about 17 km west of Gamboa. It was trapped at an elevation of 90 m, weighed 150 g, had a 3 cm long furry tail base and the underbelly had a yellowish tint. Voss et al. (2021, p10) noted that “unfortunately, no tissue sample was obtained, and no photographs were taken (T.D. Lambert, personal commun.)” and “suspect that Lambert et al.’s mouse opossum may have belonged to the M. phaea complex (sensu Voss et al., 2020), some examples of which are strikingly similar to M. alstoni in size and caudal pelage (see above); however, no specimen assignable to the M. phaea complex has previously been reported from Panama”.
Distribution accounts since the splits in 2021
Voss et al. (2021 Fig 2) do not show any records of M. alstoni in Panama but do describe records of M. adleri in Bocas del Toro state. Mammal Diversity Database (2022 v1.8) now list M. alstoni as endemic to Costa Rica and M. adleri endemic to Panama whilst M. nicaraguae occurs in both Nicaragua and Costa Rica.
iNaturalist (2022 Feb) does not treat M. adleri or M. nicaraguae at species level; they describe M. alstoni as occurring from Belize to Colombia. They do not yet refer to the work by Voss et al. (2021) or any reference after 2016. This article therefore follows the taxonomy and distribution data detailed by Voss et al. (2021) and Mammal Diversity Database (2022) and not that in iNaturalist (2022).
Voss et al. (2021) and iNaturalist (2022) show that the nearest confirmed records of M. alstoni and M. nicaraguae to this Boquete record are in Costa Rica; these records are about 150 km to the northwest of Boquete. This Boquete record is about 300 km west of Lambert et al.’s Marmosa record.
LOCATION AND DESCRIPTION
This photographic record was at 8.842275°N 82.481269°W (accuracy 20 m) and 1667 m elevation (per Google Earth). It was at least 6 m above ground in a flowering tree in secondary vegetation about 70 m off the sealed Alto Chiquero-Bajo Mono road and about 20 m from a few farm huts at the bridge. It was photographed from the rough track between the sealed road and the Lost Waterfalls trailhead bridge. Reid (2009) describes M. alstoni as occurring at elevations up to 1600 m and Voss et al. (2021) refers to records up to 1750 m. This record in Boquete therefore appears to be at the higher limits of the known elevation range.
This description is based on photographs (Figs 1-3) that show characteristic features; and on visual size impression (it was not trapped or measured). The initial size impression was that of a four-eyed opossum and noticeably larger than other mouse opossums in the region. The images clearly show that the terminal 60-65% of the naked section of the tail is distinctly white or unpigmented. The base of the tail is distinctly thickly furred or fluffy; as described by Voss et al (2021 Fig 3) for M. alstoni. Fur on the tops of the forefeet and hind feet is dark brown. Dorsal fur is greyish-brown becoming darker brown towards the rear and tail collar. Ventral parts are dull creamy-buff. The eye-ring appears to be dark brown and does not continue to the base of ear.
ACKNOWLEDGEMENTS
Thanks to Robert Voss for comments on identification and to Fiona Reid for comments on earlier distribution records.
REFERENCES
Eisenberg JF (1989). Mammals of the Neotropics, Volume 1: The Northern Neotropics: Panama, Colombia, Venezuela, Guyana, Suriname, French Guiana (Mammals of Neotropics); pp32-33. The University of Chicago Press.
iNaturalist (2022). Marmosa alstoni. https://www.inaturalist.org/taxa/42598-Marmosa-alstoni. Accessed 2022 March 10.
Lambert TD, Halsey MK, Dittel JW, Mangan SA, Delfosse E, Adler GH, Schnitzer SA (2011). First record of Alston’s woolly mouse opossum (Micoureus alstoni) from the canal area of central Panama. Mammalia 75:107–109. DOI 10.1515/MAMM.2010.076.
Mammal Diversity Database (2021). Mammal Diversity Database (2021). Mammal Diversity Database (Version 1.7) [Data set]. Zenodo.
Mammal Diversity Database (2022). Mammal Diversity Database (2022 Feb). Mammal Diversity Database (Version 1.8) [Data set]. Zenodo.
Reid F (2009). A Field Guide to the Mammals of Central America and Southeast Mexico. Second Edition; p47-48 and Plate 2. Oxford University Press.
Voss RS, Giarla TC, Jansa SA (2021 Dec 8). A revision of the didelphid marsupial genus Marmosa. Part 4, species of the Alstoni Group (subgenus Micoureus). American Museum Novitates 3983:31pp.
