Methods for obtaining neonates of known age from the Virginia opossum (Didelphis marsupialis virginiana).

Postlactational estrus occurred in the opossum 6-17 da (mean 10.08 +/- 3.2da) after sucklings were removed from the pouch 1-60 da postpartum. This estrus occurred somewhat earlier in females whose young were removed later than 24 hr postpartum, rather than within the first 24 hr. Thirteen litters (37% conception) resulted from 35 initial attempts at breeding during postlactational estrus. Three of 5 females conceived when litters were removed twice in succession. The tendency forindividual females to bear large or small litters was sustained regardless of conventional or postlactational breeding. Continual rebreeding of the opossum after removal of nursing young may increase the yield of known age neonates for experimental purposes.     

The unique lungworms (Nematoda: Metastrongyloidea) of the opossum (Didelphis marsupialis linnaeus)

Summary Prestwoodia delicata (Travassos, 1946) Anderson, 1978, Heterostrongylus heterostrongylus Travassos, 1925 and Didelphostrongylus hayesi Prestwood, 1976 are redescribed on the basis of new collections of specimens from Didelphis marsupialis from North and South America. The three genera are unique to the opossum. Prestwoodia from the nasal sinuses is most similar to Troglostrongylus of Felidae. Heterostrongylus and Didelphostrongylus are similar in size and certain other features such as their six prominent lips and reduced bursae. The dorsal ray in the former, however, consists of a large, rounded lobe whereas in the latter, it is divided into two long branches. Didelphostrongylus is found under the pleura whereas Heterostrongylus is found in the bronchi. ac]19790102     

The extensor assembly in two species of opossum,Philander opossum and Didelphis marsupialis

In considering primate and hominoid phylogeny, the fundamental position assigned to opossums is explained partially by the characteristic morphology of their hands and feet. One of the main functional features of the human hand is the ability to make a stabilized arch of the finger. Because the extensor assembly plays a key role in establishing an arched finger, the extensor systems of the digits of both the hands and feet were studied in two species of opossum, Philander opossum and Didelphis marsupialis. In the foot, two extensor tendons join in each toe to form one tendinous plate, which inserts onto the base of the second phalanx. Lumbricals join this plate along the tibial side, and interosseus insertions are found, although a true interosseus wing is lacking. At the proximal interphalangeal level, a terminal tendon takes its origin from this tendinous plate. This terminal tendon is oval in cross-section and contains elastic structures. Oblique bands arise from this terminal tendon and run proximally along the proximal interphalangeal joint inserting onto the base of the first phalanx. There are elastic structures in the flexor tendon on the dorsal side near its site of insertion. In the hand, the main extensor tendons are arranged differently and the interossei contribute substantially to the extensor assembly. Otherwise, the extensor assembly of the hands and feet are quite similar. The function of the so-called paratendinous intravaginal flexors is discussed as are evolutionary aspects of the extensor assembly.     

Site selection by intestinal helminths of the Virginia opossum (Didelphis virginiana)

Digestive tract helminths of the Virginia opossum (Didelphis virginiana) were examined for site specificity and interspecific interactions. Thirty opossums were live-trapped at 2 localities in Georgia, killed, and their digestive tracts removed and divided into the following sections; esophagus, stomach, small intestine (20 equal sections), cecum, and large intestine (5 equal sections). Helminths present in each section were identified and counted. Three trematode, 1 cestode, 2 acanthocephala, and 6 nematode species were found. Two parasites (the acanthocephalan Centrorhynchus spinosus and the nematode Viannaia hamata) are new state records for Georgia and this is the first report of C. spinosus from an opossum. There was considerable overlap between the spatial distributions of many of the helminth species found in the small intestine though most species had different modal locations. Helminth species locations were unaffected by host sex or trapping locality. There was no evidence that the presence, absence, or intensity of any helminth species affected the location or intensity of other helminth species in the digestive tract.     

Helminths of the Virginia opossum Didelphis virginiana (Mammalia: Didelphidae) in Mexico

The goal of this study was to provide further information about helminth parasites of Virginia opossum Didelphis virginiana Kerr, 1792 from Mexico. During routine faunal investigations between 1958 and 2001, 101 opossum were necropsied. Nineteen taxa of helminths were collected, representing 13 genera from hosts in 27 localities from Mexico. There are 58 new locality records, with 6 species recorded in Mexico for the first time: Brachylaima virginiana Dickerson, 1930; Cruzia americana Mapleston, 1930; Didelphonema longispiculata (Hill, 1939); Didelphostrongylus hayesi Prestwood, 1976; Viannaia didelphis Travassos, 1914; and Viannaia viannai Travassos, 1914. This increases the number of helminth taxa previously known for this host in Mexico to 28.     

Transcriptomic analysis of skin pigmentation variation in the Virginia opossum (Didelphis virginiana)

Skin pigmentation and coat pigmentation are two of the best‐studied examples of traits under natural selection given their quantifiable fitness interactions with the environment (e.g., camouflage) and signalling with other organisms (e.g., warning coloration). Previous morphological studies have found that skin pigmentation variation in the Virginia opossum (Didelphis virginiana) is associated with variation in precipitation and temperatures across its distribution range following Gloger's rule (lighter pigmentation in temperate environments). To investigate the molecular mechanism associated with skin pigmentation variation, we used RNA‐Seq and quantified gene expression of wild opossums from tropical and temperate populations. Using differential expression analysis and a co‐expression network approach, we found that expression variation in genes with melanocytic and immune functions is significantly associated with the degree of skin pigmentation variation and may be underlying this phenotypic difference. We also found evidence suggesting that the Wnt/β‐catenin signalling pathway might be regulating the depigmentation observed in temperate populations. Based on our study results, we present several alternative hypotheses that may explain Gloger's rule pattern of skin pigmentation variation in opossum, including changes in pathogen diversity supporting a pathogen‐resistant hypothesis, thermal stress associated with temperate environments, and pleiotropic and epistatic interactions between melanocytic and immune genes.     

Parasitological aspects of Schistosoma haematobium (Iran) infection in the American opossum (Didelphis marsupialis L.)

Parasitological studies on 25 American opossums (Didelphis marsupialis) exposed to 1000 cercariae each of S. haematobium (Iran) have indicated a host-parasite situation and general parasitological conditions which show this marsupial to be a satisfactory host for experimental schistosomiasis. The return of schistosomes in relation to cercarial exposure was not excessively high, but there were egg deposits in the major visceral organs. Varied macroscopic pathology due to egg deposits in different organs was demonstrated as well as a potential for urinary bladder involvement, including tumor formation. Even though the precise nature of tumor pathology is not yet known, availability of the host, a good host-parasite compatability, and a low death rate in infected hosts favor this mammal as a model for experimental schistosomiasis haematobia.     

Isolation of 21 polymorphic microsatellite markers for the Virginia opossum (Didelphis virginiana)

Twenty-one polymorphic microsatellite markers were developed for the Virginia opossum (Didelphis virginiana). The number of alleles ranged from two to 13 and observed heterozygosities ranged from 0.464 to 0.964. Significant heterozygote deficiencies were observed at three loci and null alleles were detected at five loci. Evidence for gametic disequilibrium was observed between three sets of paired loci after a sequential Bonferroni correction was applied. These markers will enable us to investigate the mating tactics, movement behaviour and social structure of Virginia opossum populations inhabiting fragmented agricultural landscapes.