Morphometric variation among populations of Ambrysus mormon Montandon (Heteroptera : Naucoridae)

Morphometric variation with respect to 15 mensural characters was assessed for adult specimens from 13 populations of Ambrysus mormon Montandon in the United States. This provides a context from which to assess the degree of divergence of an isolated population (Ash Warm Springs, Nevada), which poss esses discrete-state characteristics that differ markedly from those of oth er populations of the species. A multivariate analysis of variance revealed that interpopulational differences were dependent on sex, a finding corrob orated by the univariate perspective provided by Bonferroni's sequential ad justment that additionally identified lengths of body, protibia, and protar sus as contributing to the interaction between population and sex. Moreover , all pairwise comparisons of the 13 populations were significant for males as well as for females (F-tests from discriminant function analysis). Inde ed, the pattern of morphometric variation among populations was similar in males and females but was not a consequence of differentiation by geographi c distance (Mantel analyses). Interindividual variation primarily was due t o differences in size, as the first axis from principal components analysis accounted for 92.2% of the total variation. Three additional axes represen ted shape, and each accounted for at least 10% for the remaining variation among individuals. The population from Ash Warm Springs differed markedly ( larger protarsus relative to meso- and metatarsi, and smaller pro-, meso-, and metatarsi relative to body length and synthlipsis) from the other popul ations, suggesting the need for systematic revision of its subspecific affi liation. In contrast, populations of A. m. heidemanni Montandon and A. m, m inor La Rivers were similar to the other populations of the nominate subspe cies, suggesting their subspecific recognition is questionable. The distinc tiveness of the population from Ash Warm Springs as an isolated remnant of the historically connected pluvial White River intimates that it may be a t axon in the process of specific differentiation.