Microsatellite markers for two stifftail ducks: the white‐headed duck,Oxyura leucocephala,and the ruddy duck,O. jamaicensis

Hybridization with a close relative, the North American ruddy duck (Oxyura jamaicensis), is a major problem for the conservation of the endangered white‐headed duck (Oxyura leucocephala). We report the development of 11 microsatellite markers that can facilitate the identification of hybrids as well as the study of the population structure of both species across their distributions. These markers were tested in 63 white‐headed ducks and 50 ruddy ducks and show a larger diversity in the latter species.     

The Influence of Water Stress on the Photosynthesis of a Simulated Sward of Perennial Ryegrass

The rate of canopy photosynthesis, single leaf photosynthesis,leaf resistance to gaseous exchange, and leaf water potentialof simulated swards of perennial ryegrass (Lolium perenne cv.S24) in a controlled environment, were determined during a periodof increasing water stress and recovery from that stress. Canopyphotosynthesis did not decline immediately water was withheldbut continued at an undiminished rate for several days; thereafterit fell rapidly, particularly at first. As water stress increasedsuccessive relationships between canopy photosynthesis and irradiancebecame more curved, indicating that the effect of water stressincreased with increasing irradiance. After the swards werere-watered canopy photosynthesis rose, most rapidly during thefirst 24 h. In general, the pattern of change of leaf waterpotential was similar to that of canopy photosynthesis, althougha more detailed examination of this relationship showed it tobe hysteresial; in particular, the fall in leaf water potentialpreceded that of canopy photosynthesis. Single leaf photosynthesisappeared to be the main agent through which water stress influencedcanopy photosynthesis although in the more severely stressedswards (leaf water potentials of about—15 bars) some leaftissue died and so limited the recovery of canopy photosynthesis.The leaf resistance to gaseous diffusion increased with increasingwater stress, as did the CO₂ compensation point, thereby influencingsingle-leaf photosynthesis and through it canopy photosynthesis.