Body Shape Variation and Population Genetic Structure of Rhoadsia altipinna (Characidae: Rhoadsiinae) in Southwestern Ecuador
The genus Rhoadsia is endemic to western Ecuador and northern Peru and includes two described species that differ in body form, size, and the elevations at which they occur. Unfortunately, there is uncertainty about the number of species that should be recognized in the genus and the causes of the morphological variation documented within and between species. We take advantage of a survey of the fish fauna of the Santa Rosa River in southwestern Ecuador that yielded large numbers of Rhoadsia altipinna, to expand knowledge of the ecological, morphological, and genetic variation of this species. Specimens were collected at five sites at elevations between 31 and 613 m above sea level, and each site was sampled in December 2012 and July 2013. Rhoadsia altipinna was the second most abundant species in the Santa Rosa River, was one of only three species collected at all elevations, and was more common in pool mesohabitats than riffle mesohabitats. Geometric morphometric analysis of body shape variation indicated strong sexual dimorphism and allometry, with body depth increasing substantially with size. More interestingly, body depth declined with elevation in the Santa Rosa River. This intraspecific pattern of variation mirrored the interspecific divergence reported between the two recognized species. Lower elevation R. altipinna are known to be deeper bodied than high elevation R. minor. However, specimens of R. minor from the paratype series measured for comparison were still more streamlined than all Santa Rosa R. altipinna examined, including those collected at the highest elevations and juveniles. Although body shape differed significantly between Santa Rosa River R. altipinna and other populations from southwestern Ecuador, the geographic differences appeared small relative to variation attributable to sexual dimorphism and allometry. Finally, sequencing of a fragment of the cytochrome oxidase I gene for samples from the Santa Rosa River and two samples from the neighboring Guayas River drainage failed to recover a monophyletic Santa Rosa lineage. Although haplotype frequencies differed significantly between the Santa Rosa and Guayas River samples, the lack of monophyly and similarity among the haplotypes make the genetic data more consistent with divergence of geographically isolated populations within a single species than with interspecific divergence. Further analysis of morphological and genetic variation throughout the range of the genus will help elucidate its ecological and evolutionary dynamics.
(A) Preserved adult male (top), female (lower left), and juvenile (lower right) Rhoadsia altipinna from the Santa Rosa River (31 m site). Scale bar is 10 mm. (B) Digital image of male specimen of Rhoadsia showing the 16 landmarks and two linear measures used in the study. Insect pins were used to mark some landmarks.
Map of sampling sites (1–11) with some major cities indicated for reference. 1–5 Santa Rosa River sampling sites, 6 Balao Chico, 7 Río Culebras, 8 Chongón, 9 Jauneche, 10 Salapi Chico, 11 Estación Científica Río Palenque. Inset on the bottom left shows the position of the Santa Rosa River drainage in western Ecuador. Inset on the top left shows a close up of the Santa Rosa River drainage.
Collection sites in the Santa Rosa River illustrating pool (left column) and riffle (right column) mesohabitats sampled. (A) 31 m pool site, (B) 31 m riffle site, (C) 86 m pool site, (D) 86 m riffle site, (E) 189 m pool site, (F) 189 m riffle site, (G) 382 m pool site, (H) 382 m riffle site, (I) 613 m pool site, (J) 613 m riffle site. Pictures from December 2012, except for (H) taken July 2013.
(A) Principal Components Analysis (PCA) depicting body shape variation of juvenile, adult male, and adult female samples of Rhoadsia collected at the 31 m site in July 2013. Percentages next to the axes labels indicate the percent of body shape variation accounted for by each PC. Deformation grids are consensus configurations for juveniles, males, and females, as deformations of the juvenile consensus. (B) Change in the fineness ratio (SL/BD) between juveniles and adults indicating an increase in body depth with size.
Variation in the fineness ratio (SL/BD) among Santa Rosa drainage Rhoadsia. (A) Standard length vs. fineness ratio for all specimens with specimens of R. minor included for reference. (B) Mean fineness ratio of Santa Rosa samples (±standard error) plotted against sample elevation. Mean of paratype series of R. minor included for reference.
Principal Component Analysis of all specimens of Rhoadsia examined. Santa Rosa River specimens are coded as male, female, and juvenile but not by sampling site to reduce the number of symbols used. Percentages of variance in body shape explained by PC axes are listed in parentheses.
Haplotype network created with Network 4.6.1.2. Circles are proportional to haplotype frequencies, and colors depict haplotype frequencies for each population. Jauneche and Palenque are part of the Guayas River drainage and are labeled as sites 9 and 11 in Figure 1, while Santa Rosa is site 2 in the Santa Rosa River.
Contributor Notes
Associate Editor: T. Grande.