Life history and location data for Alfaro cultratus in 20 localities

Predation is known to have a significant effect on life history diversification in a variety of species. However, physical constraints of body shape and size can sometimes limit life history divergence. We test this idea in the Costa Rican livebearing fish Alfaro cultratus. Individuals in this species have a narrow body and keeled ventral surface, and females do not develop a distended abdomen when pregnant like other livebearing fishes. Here, we describe the life history of A. cultratus from 20 different populations across both high-predation and low-predation environments. We found significantly lower reproductive allotment in females from high-predation environments than in females from low-predation environments, but no significant difference in female or male size at maturity, number of offspring produced by females, or size of offspring. We found that A. cultratus exhibit isometric patterns of allocation for clutch dry mass in relation to female dry mass in high-predation and low-predation environments. Our results suggest that body shape constraints in this species limit the life history divergence we typically see between populations from high-predation and low-predation environments in other species.

Methods
We collected these fish over 3 different years (2006, 2007, and 2019) from Costa Rica using a mesh seine. We euthanized the fish using MS-222 and then preserved them in 70% ethanol prior to dissection. We separated males and females and then we dissected the females on the left lateral side. We removed embryos and stomachs. We measured the length of the females (prior to dissection), staged the embryos according to the Haynes classification method (Haynes, J. L. (1995). Standardized Classification of Poeciliid Development for Life-History Studies. Copeia 1, 147–154.), and measured the dry mass of the females as well as the dry mass of the embryos for each female. We also calculated the average size for an embryo in each brood by dividing the dry mass of the embryos by the number of embryos in each brood. Information for an individual fish and the population it originates from is found in a single row. We looked at the length of males and females within the population to decide where the size at maturity was for each population. More details on methods can be found in our manuscript as well as in Johnson and Belk 2001 (Johnson, J. B., and Belk, M. C. (2001). Predation environment predicts divergent life-history phenotypes among populations of the livebearing fish Brachyrhaphis rhabdophora. Oecologia 126, 142–149. doi:10.1007/s004420000504.) We analyzed each life history trait in a linear model looking for the effects of predation. We incorporated covariates into the model. When analyzing number of offspring, we included female dry mass as a covariate. When analyzing offspring size and reproductive allotment, we used female dry mass and developmental stage of embryos as covariates. We did not include any covariates for male or female size at maturity. Brood dry mass was our measure of reproductive allotment. In addition, we log transformed reproductive allotment and number of offspring in the analysis to satisfy assumptions of the linear model.