FIGURE 4.

Phenotypic plasticity in the onset of air breathing in two sister-species of labyrinth fishes. (A) In response to decreasing levels of aquatic oxygen, the three-spot gourami (Trichopodus trichopterus) delays the onset of air breathing. (B) In contrast, the Siamese fighting fish (Betta splendens) accelerates the onset of air breathing as larvae during varying degrees of hypoxic exposure (Data from Mendez-Sanchez and Burggren (2014)). Larvae of both species thus show developmental phenotypic plasticity, even though the responses to the same stressor (hypoxia) are in opposite directions.