The effects of gregarine parasites on longevity, weight loss, fecundity and developmental time in the field crickets Gryllus veletis and G.pennsylvanicus

ABSTRACT. 1. Gregarines, debilitating gut parasites, significantly reduced longevity and increased weight loss in the field cricket Gryllus pennsylvanicus Burmeiser when adults were kept on suboptimal diets, but in G.pennsylvanicus and G.veletis (Alexander and Bigelow) fed ad libitum , weight change, longevity, and fecundity were not significantly different in infected and control individuals.
2. Adults harbouring gregarines at eclosion took significantly longer to develop from the second and third instars than did uninfected adults.
3. Longevity of nymphs kept in the laboratory without food was decreased in infected individuals compared with uninfected ones, but not significantly so.
4. The evolutionary and ecological implications of nonlethal parasites are discussed.     

Aerobic performance does not affect social rank in female Red Jungle Fowl

1. Exercise capacity ultimately constrains behaviour, and therefore may influence social interactions. The hypothesis was tested that individual differences in maximal rates of oxygen consumption ( V· _O2max) – a primary determinant of sustainable exercise capacity – affect dominance hierarchies in experimental all-female flocks of the highly social Red Jungle Fowl ( Gallus gallus ). It was also examined whether social rank could in turn influence V· _O2max (which is quite plastic in most vertebrates), and whether these relationships were influenced by a common and relatively benign parasite, the intestinal nematode Ascaridia galli .
2. Substantial between-individual variation was found in V· _O2max that was significantly repeatable over time, but there was no indication that V· _O2max was affected by A. galli infection. Stable social hierarchies were quickly established in 26 of 28 experimental flocks (each contained three females previously isolated from each other). Infection status affected social rank, but there was no consistent pattern between rank and infection.
3. No indication was found that individual differences in V· _O2max either predicted the social rank in newly formed flocks, or were affected by social status in established flocks.     

Parasites and mate choice in red jungle fowl

Captive flocks of red jungle fowl (Gallus gallus) experimentallyinfected with the intestinal nematode Ascaridia galli were usedto test Hamilton and Zuk's (1982) hypothesis that parasitesadversely affect male secondary sex characters and that femalesprefer unparasitized over parasitized males. Infected chicksgrew more slowly than uninfected controls, with the effect particularlypronounced on comb length rather than tarsus length or bodyweight. At sexual maturity, infected roosters had duller combsand eyes, shorter combs and tail feathers, and paler hacklefeathers than control roosters. In experimental mate choicetests, females preferred unparasitized over parasitized roostersby about 2: 1, and an analysis of covariance revealed that thehens were using the traits on which the two groups differedto make their mate choice decisions. Finally, in a test of anextension of the Hamilton and Zuk hypothesis, control and infectedmales were not distinguishable based on non sexually-selectedcharacters such as bill size, suggesting that parasites havea disproportionately larger effect on ornamental traits.     

Acoustically-orienting parasitoids in calling and silent males of the field cricket Teleogryllus oceanicus

Abstract.

• 1 On three Hawaiian Islands, the introduced Australasian field cricket Teleogryllus oceanicus Le Guillou (Orthoptera: Gryllidae) was found to be attacked by the phonotactic parasitoid tachinid fly, Ormia ochracea Bigot.
• 2 Noncalling males occurred with callers in all locations, but silent males were more heavily parasitized than callers.
• 3 Body size was unrelated to both calling status and the likelihood of harbouring parasitoid larvae.
• 4 An experiment examining the likelihood of calling in the laboratory by males collected as silent or calling individuals showed no difference between the two classes of males, after accounting for parasitoid levels; males harbouring larvae were less likely to call.

     

Seasonal and individual variation in gregarine parasite levels in the field crickets Gryllus veletis and G.pennsylvanicus

ABSTRACT. 1. Gregarines, debilitating protozoan gut parasites, were monitored in two species of field cricket, Gryllus veletis (Alexander and Bigelow) and G.pennsylvanicus Burmeister, in northern Michigan in 1983 and 1984.
2. Gregarines were found in 31–51% of G.veletis individuals and 50–70% of G.pennsylvanicus.
3. Males were more heavily infected than females in G. veleris , but G.pennsylvanicus males and females had nearly equal infection levels; this disparity resulted in an overall lower infection rate for G. veletis.
4. Both species had fewer gregarines in 1983 than in 1984, possibly due to the adverse effect of drier conditions in 1983 on development of parasite cysts in the soil.
5. Levels of infection were not constant throughout the breeding season for either cricket species.
6. Body size was not correlated with parasite load in either G. veletis or G.pennsylvanicus.
7. Adult age was unrelated to gregarine level in G. veferis , whereas G.pennsylvanicus showed a positive correlation between adult age and parasite load during two non-consecutive weeks of the breeding season.     

Measuring individual variation in colour: a comparison of two techniques

Objective and reliable assessment of animal colouration is of great value to workers in the biological sciences. We present the results of a comparison between two colour measurement techniques: Munsell colour standard matching and spectroradiometry. As part of ongoing research on sexual selection in red jungle fowl ( Gallus gallus ), eather and comb colour of 49 roosters was measured using both techniques. Previous research showed that hens use variation in feather and comb colour in mate choice, and we allowed hens to choose between paired roosters. Colour matching and spectroradiometry scores were generally correlated, but spectroradiometry was more sensitive in detecting variation and also provided a better estimate of the role of secondary sexual characters in male mating success.