Phylogeography, geometric morphometrics, and life history variation of the knife livebearer, Alfaro cultratus (Cyprinodontiformes: Poeciliidae) from Costa Rica

Authors: Justin C. Bagley, Tessa Brummer, Lacey Nay, Jerald B. Johnson

Year: 2008 (xl)

Abstract

Alfaro cultratus is a small, livebearing fish endemic to the Atlantic versant of Lower MesoAmerica (LMA) from the Río Prinzapolka, Nicaragua, to the Río Cricamola in western Panama. A. cultratus represents an important, yet untargeted focal species for ecological and evolutionary studies because its distribution spans >20 major hydrological basins and three major LMA biogeographical fish provinces (Usumacinta, San Juan, Bocas). Given the hypotheses (i) that LMA fishes colonized the area during recent times following the Pliocene completion of the Isthmus of Panama, (ii) drainage basins limit dispersal of primary and secondary LMA freshwater fishes, and (iii) that a regional basis for relationships among LMA fish faunas suggests similar processes have shaped patterns of species with similar distributions, we predict inferring ecological and genetic signatures of colonization events will be possible. Also, some natural populations of A. cultratus contain predatory fishes, while others historically do not. These aspects of biogeographical and ecological heterogeneity within the species’ range suggest potential genetic breaks (between provinces and drainages) and environmental associations (e.g., of predator regimes) with (physical, ecological) constraints on and trade-offs in phenotypic life history variation (e.g., female body size vs. offspring size and number). We present analyses of mitochondrial DNA (cytochrome b gene) phylogeography, body shape differences, and life history variation among A. cultratus throughout its range in Costa Rica. Our analyses not only test multiple biogeographical and evolutionary hypotheses, which will be discussed, but also serve as baseline information for future inquiry into these facets of biological variation within this unique species.