Currently recognized species of Ictiobinae are easily distinguished on the basis of shape characteristics such as proportions of the head and body, size and shape of the eye, length of the snout, position of the nares, size and height of the fins, and size and position of the mouth (Body Forms). Considerable shape variation also exists within species. A preliminary analysis of shape variation in Western Gulf Slope populations of Carpiodes carpio (principal component analysis of 21 arcsine-transformed body proportions, Figure: C. cyprinus PCA) supports the recognition of a distinctive form in the Rio Grande system (Suttkus and Bart 1999). Meek (1904) described C. elongatus from the Rio Grande and Gulf of Mexico drainages to the south in Mexico. Hubbs and Black (1940) relegated C. elongatus to the synonymy of C. carpio, and speculated about the distribution and zone of integradation of what they regarded as eastern and western subspecies.
Univariate comparisons of the 21 body proportions revealed significant differences within C. carpio (sensu strictu) that are not readily apparent in the PCA results. The upper Red River population differs from all other populations studied in four characters describing eye size and shape of the head. This form, isolated in upland portions of the Red River, may be a relict of a pre-glacial Plains drainage, which geological and biogeographic evidence suggests was captured by the Red River during Pleistocene times (Cross et al. 1986). For many body proportions, the Sabine River population differs from other populations on the Western Gulf Slope, clustering instead with populations in the lower Red and lower Mississippi River. This suggests the hypothesis that the Sabine River population is derived from fish dispersing westward from the lower Red/Mississippi rivers.
We have yet to gather and analyze much data on body proportions for the other two "species" of Carpiodes. However, in the course of collecting and examining specimens from different river systems, we have developed a sense of how shape and body coloration varies in different parts of the ranges of these species. It appears that the range of C. velifer comprises as many as five distinct forms: a form in upper Mississippi and Ohio river basins that is deep bodied and possess extremely long anterior dorsal fin rays; a form mostly in western tributaries of the Mississippi River that is not as deep bodied and has a shorter dorsal fin; a form in coastal drainages east of the Mississippi River from Lake Pontchartrain to the Mobile Basin; a form in Gulf drainages east of Mobile Bay; and a form on the middle to lower Atlantic slope. The range of C. cyprinus also comprises as many as five forms with distributions similar to those of the five C. velifer forms, but ranging further north: a deep and short bodied, long quilled form in the Hudson Bay drainage, upper Mississippi River, Great Lakes, and (possibly) the upper Atlantic Slope; a more slender and elongate bodied form in the Plains and prairie streams of the Midwest (the C. forbesi phenotype of Hubbs 1930); a distinct form in coastal drainages east of the Mississippi River from Lake Pontchartrain to the Mobile Basin; a form in Gulf drainages east of Mobile Bay; and a form on the lower to middle Atlantic Slope.
We are less certain about body-form diversity within species of Ictiobus. The range of I. bubalus appears to encompass two forms (Mississippi River and Eastern Gulf), however little is known about western Gulf and Mexican populations. The southern most species of Ictiobus (I. meridionalis Gunther) closely resembles I. bubalus and may be synonymous (Robert R. Miller, pers comm.). We can recognize only one form of I. cyprinellus based on body shape, but have noted considerable variabily in shape among populations. I. niger is enigmatic. For years, fisheries biologists have speculated that it is a hybrid between I. bubalus and I. cyprinellus. Its general body form is intermediate between these two species. However, that fact that its range extends westward into Mexico without one of its presumed parent species (I. cyprinellus), leaves little doubt of its validity. We have not studied any of the western populations, but understand from colleagues that the forms in the Rio Grande and possibly the isolated form in the Rio Nazas of Mexico are distinctive.
We will use modern morphometric methods to quantify differences in body morphometry and to interpret this taxonomically. Bart will oversee this part of the project, assisted by undergraduates from the Louisiana Alliance for Minority Participation (LAMP) Program ( http://www.tulane.edu/~eeob/LAMP/ ), which he coordinates. A video camera will be used to capture images of samples of 60 specimens from throughout the ranges of all of the currently recognized forms. The images will be uploaded into a PC equipped with a frame grabber board and running MorphoSys software (Meacham and Duncan 1990) for registry of 24 landmarks, selected to approximate important axes along which shape of ictiobines varies (Figure: Ictiobine Landmarks). The advantage of using this equipment is that data can be gathered and analyzed much quicker than if it were gathered manually with calipers and later entered into a computer. Considering the large number of populations to be sampled for each of the currently recognized species, the reduction of effort is substantial.
A digital camera will be used to capture images of types and specimens examined while visiting other museums. The camera images will be downloaded to a notebook computer to preview image quality and ensure images are adequate for landmark registry. Partial warp analysis and superposition analysis will be used to transform the coordinate variables into shape variables. Principal component analysis and canonical variate analysis will then be used to summarize shape variation within and among species of Carpiodes and Ictiobus. Assuming the species are diagnosable by other characters, this analysis should resolve questions about shape variability within species. Moreover, by integrating information on environments specimens are drawn from (lake vs. stream, turbid vs. clear stream, etc.), the analysis should help to resolve questions about ecophenotypic variation within species (e.g., C. forbesi and C. cyprinus, Bailey and Allum 1962)
