Katherine E. Muma

Male traits expressed in females: direct or indirect sexual selection?

SummaryColored epaulets in female red-winged blackbirds (Agelaius phoeniceus) could be due either to direct sexual selection favoring the maintenance of this trait in females due to intrasexual competition for breeding opportunities, or to sexual selection favoring bright epaulets in males indirectly causing expression of the trait in females by genetic correlation. Older females tend to be brighter than younger females. Also, brighter females tend to breed earlier in the season than dull females. These patterns are consistent with both of the hypotheses. In a series of experiments in which males and females were presented with taxidermic mounts of dull and bright females, the plumage of these mounts had no influence on the response of either males or females. Also, the response of females was independent of their own plumage. The results of all of the experiments consistently supported the interpretation that male plumage characteristics expressed in female redwinged blackbirds have no functional value and are a consequence of genetic correlation with males. Since recent studies have also indicated that female aggression has no functional value, we speculate that this too could be due to genetic correlation with a trait favored in males.

Parasitism of Sympetrum dragonflies by Arrenurus planus mites: maintenance of resistance particular to one species.

Using field surveys and histological methods, we show that a dragonfly species (Sympetrum internum) has an effective resistance, not seen previously in other odonates, to a mite parasite (Arrenurus planus). This mite is a generalist parasite known to effectively engorge on several other odonate species. We argue that selection is likely weak, favouring counter adaptations of Arrenurus planus to Sympetrum internum, in part because other host species are available. We further argue that this pattern is possibly linked to the fact that the mode of resistance is relatively novel, and because Sympetrum internum is rare compared to another host species, Sympetrum obtrusum, at our study site. Although resistance of Sympetrum internum is quite effective against Arrenurus planus, Arrenurus planus larvae still attach to this species, but less often than they attach to Sympetrum obtrusum. Attachment to unsuitable hosts may reflect constraints operating on Arrenurus planus larvae during host discovery. Such factors influencing the evolution of resistance, when several potential host species exist, have not received much attention.

Recapture of male and female dragonflies in relation to parasitism by mites, time of season, wing length and wing cell symmetry

For aquatic mites parasitic on dragonflies, completion of their life cycle depends on their being returned to appropriate water bodies by their hosts, after completion of engorgement. We examined whether differences among hosts in timing of emergence or phenotypic attributes might affect their probability of return to an emergence pond, and hence success of mites. Parasitized males and females of the dragonfly Sympetrum obtrusum (Hagen) did not differ in overall recapture rates. Females that had wing cell symmetry and emerged early were more likely to be recaptured than females that emerged later or had wing cell asymmetry, but there were no consistent relations between these variables and parasitism by mites. No such relations between wing cell asymmetry, emergence date, and recapture likelihood were found for males. Using randomization tests, we found that mean intensities of Arrenurus planus (Marshall) mites at host emergence were the same for recaptured females and females not recaptured; however, males that were recaptured had lower mean intensities of mites at emergence than males not recaptured. Further, mature females carried more mites than mature males, and the latter had fewer mites than newly emerged males not recaptured. Biases in detachment of engorging mites do not explain the differences in parasitism between mature males and females, nor the differences in mite numbers between mature males and newly emerged males that were not recaptured. Rather, heavily parasitized males appear to disperse or die and are not recaptured, which should have implications for dispersal of mites and fitness of male hosts.

Persistence and regression of hearing in the exclusively diurnal moths, Trichodezia albovittata (Geometridae) and Lycomorpha pholus (Arctiidae)

Abstract.  1. Auditory sensitivities and ultrasound avoidance behaviour of two exclusively diurnal moths were examined to test the prediction that total isolation from the predatory effects of echolocating bats will result in the regression of these sensory systems and/or the defences they evoke.

Blood Parasites and Dominance in Captive Blackbirds

Evidence of the pathogenicity of haematozoa in wild bird populations is limited, possibly because infected birds alter their behavior to avoid the costs of being parasitized. We tested this hypothesis by examining dominance relationships relative to parasite status in captive Red-winged Blackbirds Agelaius phoeniceus, and Brownheaded Cowbirds Molothrus ater. There was some evidence that uninfected individuals tended to be dominant to infected individuals, but the pattern was variable, even within two studies involving male Red-winged Blackbirds. Dominant parasitized individuals were not consistently larger than the uninfected individuals they dominated, although other, untested asymmetries might have allowed the infected birds to overcome any cost associated with being parasitized.