Monday Mammal #9: Marsh Rice Rat

Many of this week's Monday Mammal, the Marsh Rice Rat (Oryzomys palustris), have likely perished recently as oil from the spill off of the Louisiana coastline has been recently been penetrating the coastal salt marshes.  Fortunately, these little rodents aren't limited to these coastal marshes (unlike some species), and should (as a species, at least) persist beyond the recent disaster.

Figure 1:  "Oryzomys palustris - lower image is silvery subspecies O. p. argentatus of Florida Keys

Credit: painting by Ron Klinger from Kays and Wilson's Mammals of North America,
© Princeton University Press (2002)"  [Source]

This rather broad ranging American native was first described in 1837 from a specimen taken in the north of their range in Salem Co. New Jersey.  They are semi-aquatic, mostly nocturnal omnivores and are found primarily in coastal (salt water) and interior (fresh water) marshes.  Like many (most?) other species, their distribution hasn't always been restricted to their current range.  Despite being endemic to the south eastern U.S. their ancestors likely trace back to central and South America.

These rats belong to the subfamily Sigmodontinae, the South American rats and mice. While there is one other species of Oryzomys that makes it up into North America -- the Coues's Rice Rat (O. couesi) which occurs in southern Texas -- the other species in the genus Oryzomys all appear to occur further south.

Oh, and here's one of those random facts you just don't find in species accounts any more -- just in case you were wondering how different these rats are from their domestic cousins. Unlike domestic rats, Marsh Rice Rats have 27 pairs of autosomal chromosomes plus two sex chromosomes for a grand total of 56 chromosomes...

[Source]

Hmm... this could make for a nice little pop quiz!  Do you know how many chromosomes do we humans have?