| Description |
Phenetic relationships among populations of the mud turtles of the Kinosternon scorpioides and K.. leucostomum complexes in Mexico and Central America were examined using multivariate statistical techniques. Thirty-one mensural and five qualitative characters were measured on the external surfaces of 3,062 adults of the two species complexes. The geographic ranges of the species complexes were divided by river drainage into populations for statistical analyses. Fifty-eight populations were defined for the K. scorpioides complex, and 22 for J<. leucostomum. Each complete statistical analysis included a multiple discriminant analysis, a canonical analysis, and a phenetic distance (D2 ) analysis. Six complete analyses were run, one each on males and females of: (1) j<. integrum and its closest relatives; (2) K. scorpioides; and (3) J<. leucostomum. Mensural data were standardized for size by dividing each character by carapace length; a comparison of ratio vs. regression standardization in K. leucostomum analyses revealed no statistically significant differences in the results obtained. Characters selected by the discriminant analyses and their functional significance are discussed. A highly intercorrelated character complex is described which suggests relatively high, wide carapaces tend to be associated with extensive plastrons. It is hypothesized that this character complex is a terrestrial adaptation associated with seasonal aquatic environments; a test using a multiple regression analysis of environmental variables against relative plastral area confirms the hypothesis. Females of all taxa tend to have more globular shells, more extensive plastrons, and less emarginate anal notches than males. Canonical and distance analyses suggest that K. integrum is closely related but phenetically distinct from two undescribed species from Sonora and Sinaloa, and Oaxaca, Mexico. A population from the Rio Purificacion in coastal Jalisco is phenetically distinctive, but integrum populations are otherwise relatively homogeneous. Kinosternon scorpioides consists of four phenetically distinct subspecies in Mexico and Central America: (1) K. s^ cruentatum in southern Mexico, Belize, and Guatemala; (2) K. ￡. abaxillare in the Rio Grande de Chiapas; (3) K. alboqulare in most of Central America above the Isthmus of Panama; and (4) K. s_. scorpioides on the Isthmus of Panama and northern South America. The Kinosternon leucostomum complex consists of one species, K. leucostomum, with two subspecies: (1) JK. 1_. 1 eucostomum in Atlantic drainages of southern Mexico to eastern Nicaragua; and (2) K. JL postinquinale in Atlantic and Pacific drainages from the Rio San Juan in Nicaragua, southward to northwestern South America. Lists of synonymies, diagnoses, and discussions of taxonomic history are given for each taxon. Descriptions and discussions of geographic range and natural history are given for each species. The following are proposed as logical and parsimonious distributional histories. The Kinosternon scorpioides and K. leucostomum complexes arose in northern Central America during mid-Cenozoic. A scorpioides ancestor gave rise to K. integrum which spread from south- ern Pacific Coastal Mexico to the Mexican Plateau, and then to the northern Pacific Coast. K.. scorpioides dispersed throughout the Pacific Coast of Central America, entering Atlantic drainages in eastern Mexico and Nicaragua, and entering South America at the closing of the Panamanian Isthmus. j<. leucostomum dispersed throughout Atlantic Central America and entered South America at the closing of the Isthmus of Panama. The patterns of distribution of the species complexes are generally those expected of a xeric-adapted Pacific Coast form, and a mesic-adapted Atlantic Coast form. |
