I would be very surprised to find that there are no cool (note not cold) water species in Southern Souther American countries like Paraguay and Argentina.
erm, dont shoot me for this, just what i heard.
plecs can live in cooler water. my thermometer broke ages ago and the only fish that lived were my plecs....
and apparently thats because they can survive the water change to colder.
i read that common plecos can survive down to 55 degrees F but anything below that they drop dead. ive also read alot of reports from around the world about people putting pleco(s) in their ponds and emptying their ponds a year later to clean them and they discover that their 2" cute plecos turned into 15" monsters! i considered putting a pleco in my pond (they are $35+ here in oz for a tiny common) and i bought one and put it in a growout tank and fed it algae wafers, and come home one day and find it dead! now their seems to be a price rise (now around $45, sailfin $90). after buying all these cichlids which are supposedly becoming illegal, i might get me another pleco, and put it in with my guppies (nothing seems to die in there)
many loricariids including certain chaetosoma, ancistrus, delturus, etc. are fine for the cold water aquarium. I assumed by plecs you meant ancistrinae.