Costly parasite resistance: a genotype-dependent handicap in sand lizards?
Male sand lizards (Lacerta agilis) with a specific restriction fragment length polymorphism fragment in their major histocompatibility complex (MHC) genotype ('O-males') are more resistant to ectoparasites (a tick, Ixodes ricinus) than are males that lack this fragment ('NO-males'). However, emerging evidence suggests that such adaptive immune responses are costly, here manifested by reduced body condition and a compromised defence against secondary infections by haemoprotid parasites that use the ticks as vectors. Subsequent to tick encounter, O-males suffer from a higher leucocyte-erythrocyte ratio, and higher haemoprotid parasitaemia, in particular in relation to vector encounter rate. Furthermore, O-males (i.e. successful tick defenders) with more haemoprotid parasites remaining in their blood stream were in better body condition, whereas this did not apply in NO-males, demonstrating that the adaptive immunoreaction can--in the short term--be energetically even more costly than being moderately parasitized. In agreement with Zahavian handicap theory, O-males had a (marginally) higher reproductive success than males that lacked this fragment.
Olsson
Mats
M
Department of Zoology, The University of Gothenburg, Animal Ecology, PO Box 463, 413 90 Gothenburg, Sweden. molsson@uow.edu.au
Wapstra
Erik
E
Madsen
Thomas
T
Ujvari
Beata
B
Rugfelt
Carl
C
D000818:Animals; D006233:Persons with Disabilities; D004912:Erythrocytes / Q000378:metabolism; D005838:Genotype; D006790:Host-Parasite Interactions / Q000502:physiology*; D007962:Leukocytes / Q000378:metabolism; D008116:Lizards / Q000235:genetics / Q000469:parasitology / Q000502:physiology; D008285:Major Histocompatibility Complex / Q000235:genetics*; D008297:Male; D008954:Models, Biological; D012150:Polymorphism, Restriction Fragment Length; D013984:Tick Infestations / Q000276:immunology* / Q000469:parasitology / Q000662:veterinary; D013987:Ticks / Q000472:pathogenicity