Microgeographic body size variation in a high elevation Andean anole (Anolis mariarum; Squamata, Polychrotidae)

ABSTRACT

Intra-specific body size variation is common and often is assumed to be adaptive. Studies of body size variation among sites should include or consider environmental and ecological variables in their designs. Additionally, reciprocal transplant or common garden studies will support which variables are really contributing to the observed body size variation. This study analyzed the microgeographic body size variation in Anolis mariarum, a small lizard endemic to Antioquia, Colombia. Parameters such as body size, shape, and lepidosis variation were quantified in 217 adult A. mariarum, belonging to six populations separated by less than 80km. Results showed that significant body size variation was not related to differences among sites in mean annual temperature, but covaried with mean annual precipitation, with the largest individuals occurring in dryer sites. Mark-recapture data obtained from 115 individuals from both the wettest and dryest sites from October 2004 to April 2005 showed that growth rates were higher at the latter. Eight males from each site were captured at the end of the mark- recapture study and reared for two months under identical conditions in a common garden study. Individuals from both sites grew faster when reared in the laboratory with food provided ad libitum. Although growth rates of males from the two populations did not differ significantly in the laboratory, males from the dryest site still maintained a significantly larger asymptotic body size in their growth trajectories. Multivariate analyses also demonstrated that both males and females from the six populations differed in terms of body shape and lepidosis. However, only female body size was found to covary significantly with an environmental gradient (precipitation). A. mariarum does not conform to Bergmann’s rule, but the relationship found between mean body size and asympotic growth with mean annual precipitation at these sites needs further analysis. Generally, studies of intra-specific body size variation should consider a number of additional phenotypic traits to provide stronger baseline information on the degree of overall divergence among populations, including those likely to be selectively neutral, before interpreting results of analyses on the body size differences. Rev. Biol. Trop. 57 (4): 1253-1262. Epub 2009 December 01.

RESUMEN

Se reporta diferencias en el tamaño corporal entre individuos adultos de seis poblaciones de Anolis mariarum (Squamata: Polychrotidae), separadas por una distancia de hasta 80km. Esta variación no se relacionó con las diferencias en las temperaturas promedio anuales que existen entre los sitios analizados, pero sí covarió con la precipitación promedio anual, con los individuos de mayor talla habitando los sitios más secos. Datos de marca- recaptura del sitio más seco y más húmedo, mostraron que los individuos del sitio más seco tienen mayores tasas de crecimiento corporal. Bajo condiciones de laboratorio con alimento ad libitum, machos de ambos sitios crecieron más rápido que en condiciones naturales. Aunque las tasas de crecimiento de machos de las dos poblaciones no difirieron significativamente en el laboratorio, los machos del sitio más seco mantuvieron tamaños corporales asintóticos en sus trayectorias de crecimiento que fueron significativamente mayores. Análisis multivariados mostraron que tanto los machos como las hembras de las seis poblaciones difieren en la forma corporal y en lepiodosis, pero la única variable que covarió de manera significativa con un gradiente ambiental fue el tamaño corporal con la precipitación. Estudios de variación intraespecífica en el tamaño corporal deben considerar otras características fenotípicas adicionales para obtener una línea base sobre el grado de divergencia entre poblaciones, incluso aquellas que se consideran neutrales.