This is a combination Fish Friday and Parasaturday post. Basically, I was looking up recent news of parasites and this little gem popped up in the San Marcos Mercury:
http://smmercury.com/53183/invasive-snail-parasite-threaten-central-texas-fish-stocks/ 

An invasive snail species, Melanoides tuberculatus, from Asia is invading central Texas waterways. The species was originally adapted to warmer temperature water (above 64 degrees Fahrenheit) which had constrained its ability to spread from warm springs at the head of the Comal River to other cooler surface waters. Alas, as evolution would have it, or fortunately from the snail's point of view, the snail began to adapt to its new climate.

"In 2009, Huffman began finding snails thriving in the much colder waters of the Guadalupe River, and by 2011 they’d moved upstream as far as Gruene Crossing and downstream through Lake Dunlap and as far as one mile into Lake McQueeny. In January 2012, Huffman found hundreds of snails seemingly thriving near Dunlap Dam in water that had been between 11-13°C (51-55°F) for weeks—temperatures that should’ve killed the snails within two or three days."

I find this next part the most interesting though:
 "Because of the continuous, wild temperature swings at the confluence of the Comal and Guadalupe rivers in New Braunfels, Huffman predicted as far back as 2000 that if the snail were to ever make an evolutionary adaptation to colder temperatures, that’s where it would happen—and that prediction now seems to have been borne out." 

I also wonder how much the mild winter, hotter temperatures and drought has contributed to the invasive expansion of this snail. Shallower streams caused by drought would most likely be warmer as well, right? Huffman goes on to say that there aren't as many mature fish appearing in the Comal anymore, he attributes this to the trematode parasite carried by the snail which he doesn't name but I'm assuming is Centrocestus formosanus based on another paper he published, "Egg predation and parasite prevalence in the invasive freshwater snail, Melanoides tuberculata (Müller, 1774) in a west Texas spring system":
http://www.aquaticinvasions.net/2011/ACCEPTED/AI_2011_accepted_Ladd_Rogowski_correctedproof.pdf

The parasite actually damages the host's fitness in the following way:"Because the flatworm encysts on the gills of fish, it interferes with the fish’s ability to oxygenate the blood. With enough parasites, the effect would be like a person trying to run a race during an asthma attack. For fish, such infections would make them slow and sluggish, easy picking for predators long before the parasites killed them outright." 

The parasite has been found in west Texas springs but I don't see any evidence that is in central Texas from this paper or news article. Readers, is this parasite in our region? 

Does anyone want to build an SDM for this invasive species and its parasite, wink, wink, nudge, nudge? It could be fun!

Author

Stavana Strutz is a doctoral candidate studying disease ecology in the Parmesan lab at UT Austin.