The architecture of the aquatic environment and its influence on the growth and development of tadpoles (Xenopus laevis)

Abstract

Many ecological factors are known to influence anuran growth and development. However, little is known about the influence of the shape of the aquatic environment. We investigated how the size of the air-water interface (surface area), water depth, and partitioning the aquatic space independently affect the growth and development of tadpoles of Xenopus laevis. To do this, we used a series of pyramidal frustra and partitioned aquaria. In our experimental containers, as the surface area decreased the dissolved oxygen concentration decreased and the tadpoles' air-breathing rates increased. As the depth of the water increased, the dissolved oxygen concentration decreased and the tadpoles' air-breathing rates increased. When the aquatic space was vertically partitioned to form a maze with corridors either 2 cm or 4 cm wide, the tadpoles avoided the narrow spaces between the partitions. Neither varying the surface area, nor vertically partitioning the aquatic space, significantly affected the growth or development of the tadpoles. However, the tadpoles raised in the shallower containers grew significantly slower than the tadpoles raised in the deeper containers. Tadpoles raised in shallow water behaved differently than those raised in deeper water. Shallow water appeared to prevent the tadpoles from ascending normally to break the surface tension of the water and properly air-breathe. Instead, the tadpoles in the shallow containers often floated at the surface, rather than in their normal position in the water column. Our study suggests that shallow water, independent of other variables such as water volume or dissolved oxygen concentration, may detrimentally impact air-breathing tadpoles, since shallow water appears to physically impede the animals' ability to air-breathe.