THE ENERGETIC CONSEQUENCES OF PARASITISM - EFFECTS OF A DEVELOPING INFECTION OF TRICHOSTRONGYLUS-TENUIS (NEMATODA) ON RED GROUSE (LAGOPUS-LAGOPUS-SCOTICUS) ENERGY-BALANCE, BODY-WEIGHT AND CONDITION

The timing of the energetic consequences of a developing, single-dose infection of Trichostrongylus tenuis larvae was investigated in captiv e red grouse Lagopus lagopus scoticus. At 12 days post-infection (p.i. ), infected birds had a resting metabolic rate 16 % greater than contr ols and thenceforth lost weight at a faster rate than controls. At 16 days p.i. infected birds consumed 38 % less energy and excreted 33 % l ess energy than controls. The estimated total daily energy expenditure and energy expended on activity for infected birds at 16 days p.i. we re 36 % and 83 % lower, respectively, than for controls. Infected bird s lost condition from 16 days p.i. onwards. The period of energy imbal ance at 12-16 days p.i. coincided with development of late 4th-stage l arvae into adult worms and the onset of patency. After this, the effec ts on energy balance diminished. Synchronous development of previously arrested T. tenuis larvae in wild birds in spring probably has simila r effects to those reported here and places grouse under conditions of energy imbalance. The observed effects on energy balance provide a po ssible mechanism by which the parasite can reduce fecundity and surviv al of infected grouse.