Life History of Brachyrhaphis parismina: Variation Within and Among Populations
Poeciliids provide a model system for comparative studies of life-history variation because of the relatively large number of species and the diversity of environments they occupy. Brachyrhaphis parismina is a narrow-bodied poeciliid that occupies rivers and streams in the eastern lowlands of Costa Rica. Detailed life-history information on species in the narrow-bodied clade of the genus Brachyrhaphis is lacking compared to the many studies on the round-bodied species of the genus. We test for variation in life history among five populations of Brachyrhaphis parismina, and for patterns of allometry associated with the reproductive value hypothesis among individuals. Life-history traits exhibited little variation among populations in contrast to variation observed among populations of round-bodied congeners. Furthermore, within locations females exhibit isometric patterns of reproductive allocation with female body size, thus life history varies little over a female's lifetime. This pattern is inconsistent with that expected from the reproductive value hypothesis. Variation among and within populations in this species may be constrained by the high flow environment they occupy.Abstract
Map of major drainages of Costa Rica showing collection locations. Numbers correspond to location numbers in the text and Table 1.
Variation in life-history traits among collection locations. (A) Means ± 1 SE of female standard length (open circles), male standard length (closed circles), and minimum observed female standard length (open triangles) by location. (B) Mean ± 1 SE reproductive allotment (clutch mass in mg) from the ANCOVA that included female somatic mass and stage of embryonic development as covariates. (C) Mean ± 1 SE offspring size (mass of single embryo in mg) from the ANCOVA that included female somatic mass and stage of embryonic development as covariates. (D) Mean ± 1 SE clutch size (number of embryos) from the ANCOVA that included female dry somatic mass as a covariate. All variables are plotted on the original (untransformed) scale.
Best fit lines from the RMA regression for each of the five collection locations for the relationship between (A) reproductive allotment and female somatic mass, (B) clutch size and female somatic mass, and (C) offspring size and female somatic mass. Lines that stretch across the entire range of female somatic mass represent the isometric line (i.e., slope = 1). Allometry is observed when the slope departs significantly from one as in panel C. All variables were natural log transformed.
Slopes and 95% confidence intervals from the RMA regressions for reproductive allotment on female somatic mass (closed circles), clutch size (number of offspring) on female somatic mass (open circles), and offspring size on female somatic mass (closed triangles). Reproductive allotment and clutch size are isometric with female somatic mass as evidenced by the overlap of their 95% confidence intervals with a slope of 1. Offspring size shows a hypoallometric relationship with female somatic mass as evidenced by the slope between 0 and 1.
Contributor Notes
Associate Editor: J. F. Schaefer.