Meeting Abstract

21.2  Monday, Jan. 4  Why are there silent catfishes: shifts in pectoral fin function and changes in pectoral spine morphology KAATZ, I.M.*; RICE, A.N.; STEWART, D.J.; LOBEL, P.S.; no current affiliation; Bioacoustics Program, Cornell University, NY; SUNY College of Environmental Science and Forestry, NY; Boston University, MA ingridmkaatz1@yahoo.com

The evolutionary selection pressures and constraints responsible for the loss of sound signal communication in fishes are poorly understood. Pectoral spine stridulation is common in catfishes. Spines are part of predator defense or social display in known vocal species. Several catfish clades have secondarily lost the ability to produce sounds. We test the hypothesis that change in functional attributes of the pectoral fin and in particular the spine can lead to loss of sound production. We compared the length of the spine across 38 catfish families (993 species) from the literature and found it statistically significantly longer in vocal families. Spines of families with vocal species also had increased ossification and serration. Microscopy (scanning electron and dissecting) of the surface morphology of the dorsal process where bony vocal ridges are located identified four ridge types at the base of the spine that were absent in silent taxa (124 species, 21 families). We compared locking and swimming behavior, spine strength, dorsal process dimensions and microscopic surface structure for six species of doradoid catfishes. Silent species used fins for hovering not spine locking, while vocal species used spines as weapons in defense and locking. Silent species had atrophied spines and processes while vocal species had well developed spines and processes with “vocal ridges”. Thus, there appears to be an integral trade-off in the evolutionary design of pectoral spines. We further evaluate the functional shift hypothesis by identifying other suites of ecological and behavioral traits possibly associated with silent vs. vocal catfishes.