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VIDEO PLAYBACK EXPERIMENTS TESTING THE FUNCTION OF CLAW WAVING IN THE SAND FIDDLER CRAB

Like many territory advertisement signals, the claw waving display of fiddler crabs (genus Uca) is commonly thought to have the dual function of simultaneously repelling males and attracting females. I have found, however, that male sand fiddler crabs (U. pugilator) wave significantly more in the presence of females than males, suggesting that their waves are primarily directed to females. Here I use laboratory video playback experiments to ask whether male and female U. pugilator are both responsive to the display. Males and females were presented with video of an example of either a waving or a feeding male conspecific, or no video, and their behavior was measured in seven behavioral categories that were then collapsed into three principal components. Analysis of variance of females' principal component scores revealed significant differences in their behavior in the presence of waving male video compared with feeding male video or no video, demonstrating that females attend to the display. Male behavior, however, was not significantly different between the three treatments, which is inconsistent with the hypothesis that claw waving serves to repel or threaten other males. These results, together with my recent work on male signaling behavior, suggests that the claw waving display of U. pugilator is a signal primarily directed to females and attended to by females, and thus is not an example of a dual function signal.

Quantitative genetics of ultrasonic advertisement signalling in the lesser waxmoth Achroia grisella (Lepidoptera: pyralidae).

Males of the lesser waxmoth Achroia grisella (Lepidoptera: Pyralidae) produce ultrasonic advertisement signals attractive to females within several metres. Previous studies showed that females prefer male signals that are louder, delivered at a faster rate, and have a greater asynchrony between pulses produced by the right and left wings. These three signal characters vary considerably within populations but are repeatable within individuals. Breeding experiments employing half-sib designs were conducted on both collectively and individually reared moths to determine genetic variance within and covariance among these signal characters. Heritabilities of all signal characters were significant among collectively reared moths. Heritabilities for signal rate and right-left wing asynchrony interval were not significant, however, among individually reared moths, suggesting the presence of significant nonadditive genetic variance or common environmental variation. Development time was also significantly heritable, but only under individual rearing. The only significant genetic correlation was between signal rate and length of the right-left wing asynchrony and this was negative. Our findings on heritability of signal characters are consistent with a coevolutionary sexual selection mechanism, but the absence of signal x development genetic correlation fails to support specifically a good-genes mechanism. The variation in heritability among conditions suggests that environmental variance may be high, and may render selection on signal characters by female choice ineffective. Thus, additive genetic variance for these characters may be maintained in the presence of directional female choice.

Quantitative genetics of ultrasonic advertisement signalling in the lesser waxmoth Achroia grisella (Lepidoptera: Pyralidae)

Males of the lesser waxmoth Achroia grisella (Lepidoptera: Pyralidae) produce ultrasonic advertisement signals attractive to females within several metres. Previous studies showed that females prefer male signals that are louder, delivered at a faster rate, and have a greater asynchrony between pulses produced by the right and left wings. These three signal characters vary considerably within populations but are repeatable within individuals. Breeding experiments employing half-sib designs were conducted on both collectively and individually reared moths to determine genetic variance within and covariance among these signal characters. Heritabilities of all signal characters were significant among collectively reared moths. Heritabilities for signal rate and right–left wing asynchrony interval were not significant, however, among individually reared moths, suggesting the presence of significant nonadditive genetic variance or common environmental variation. Development time was also significantly heritable, but only under individual rearing. The only significant genetic correlation was between signal rate and length of the right–left wing asynchrony and this was negative. Our findings on heritability of signal characters are consistent with a coevolutionary sexual selection mechanism, but the absence of signal × development genetic correlation fails to support specifically a good-genes mechanism. The variation in heritability among conditions suggests that environmental variance may be high, and may render selection on signal characters by female choice ineffective. Thus, additive genetic variance for these characters may be maintained in the presence of directional female choice.

Energetically costly behaviour and the evolution of resting metabolic rate in insects

1. A general hypothesis is presented to explain interspecific differences in size‐independent resting metabolic rate. This hypothesis is based on a presumed trade‐off between a low resting metabolism and adaptations of metabolism during activity. 2. With such a trade‐off, selection to reduce resting metabolism is less intense in active species than in species where resting metabolism constitutes a large proportion of the daily metabolic costs. Those animals that spend more energy on activity should therefore have a higher resting metabolic rate than animals that spend less energy on activity. 3. A literature review reveals that flying insects have higher resting metabolic rates than species that use energetically less demanding types of locomotion. 4. Insects producing acoustic advertisement signals can be shown to have higher mass‐independent resting metabolic rates than closely related species without this energetically demanding behaviour. 5. Literature data on vertebrate resting metabolic rates are also consistent with the presented hypothesis: the more energy animals spend on activity, the higher the mass‐independent resting metabolic rate.

Bushcricket song structure and predation by the acoustically orienting parasitoid fly Therobia leonidei (Diptera: Tachinidae: Ormiini)

Males of most bushcricket species produce acoustic advertisement signals to attract females for mating. These signals can also increase conspicuousness to predators. In the genus Poecilimon (Orthoptera: Phaneropterinae) males are attacked by the parasitoid fly Therobia leonidei (Diptera: Tachinidae: Ormiini) which locates males by their calls. In Greece T.leonidei parasitizes several Poecilimon species with different song structures: we examined whether host choice is related to song structure by comparing parasitism rates in two closely related Poecilimon species. One of these species produces monosyllabic songs, the songs of the other species being polysyllabic. The tachinid fly parasitized the polysyllabic species to a greater extent. We demonstrate in a field-experiment that this preference for the polysyllabic species does not depend on local adaptations of the fly. The most probable explanation for the preference of the fly for the polysyllabic singing species seems to be better detection of longer songs. This result is discussed in the context of male song evolution.

Partitioning the Components of Sexual Selection: Attractiveness and Agonistic Behaviour in Male Wax Moths, Achroia grisella (Lepidoptera: Pyralidae)

AbstractTwo components of sexual selection in the lesser wax moth, Achroia grisella, are clearly defined: females choose males based on characters of their ultrasonic advertisement signals, and males display agonistic behaviour patterns in contests over signalling stations. We conducted a series of laboratory trials to determine whether successes in these two sexual selection arenas were related. Our trials showed that winners in contests over signalling stations were characterized by earlier initiation of both signalling and aggression. These characteristics may indicate higher levels of ‘motivation,’ but it is unclear whether this level is a fixed trait. There was no relationship, however, between any measure of a male's attractiveness to females and his success in winning competition trials. Thus, inter‐ and intra‐sexual selection may be acting on different, uncorrelated traits in A. grisella.

When are good genes good? Variable outcomes of female choice in wax moths

Female lesser wax moths (Achroia grisella) choose males based on characters of their ultrasonic advertisement signals. Because a female's opportunity to obtain increased somatic benefits by mating with a particular male is limited, we investigated whether females obtain genetic benefits for their offspring via mate choice. Controlled breeding experiments conducted under favourable food and temperature conditions showed that developmental characters are heritable, that sire attractiveness and offspring survivorship are unrelated, but that females mating with attractive signallers produce offspring who mature faster than the offspring of females mating with non-attractive signallers. However, under some unfavourable food or temperature conditions, it is the offspring of females mating with non-attractive males who mature faster; these offspring are heavier as well. Thus, the relationship between male attractiveness and offspring development is not environmentally robust, and support for a good genes model of mate choice in A. grisella is dependent on conditions. These findings suggest genotype–environment interactions and emphasize the necessity of testing sexual selection models under a range of natural environments.

Variation and repeatability of ultrasonic sexual advertisement signals inAchroia grisella (Lepidoptera: Pyralidae)

MaleAchroia grisella (Lepidoptera: Pyralidae) produce ultrasonic advertisement signals for pair formation. The signals are generated by wing-fanning and consist of pairs of approximately 100-µs pulses of 70- to 130-kHz sound. In a previous study, playback experiments showed that femaleA. grisella preferred signals whose pulses were louder, longer, and delivered at a higher rate and included longer silent (asynchrony) intervals within pairs. To understand the variation and repeatability of these signal characters, acoustic signals of 18A. grisella males were recorded twice daily on the first 4 days and the seventh day after adult eclosion. ANOVA and MANOVA revealed significant among-individual and among-age variation for all signal characters. Peak amplitude, average amplitude, rate, and pulse length peaked 2–3 days after eclosion and then decreased. Asynchrony interval, however, continued to increase as males aged. Repeatabilities of peak amplitude, average amplitude, rate, and asynchrony interval were all relatively high (>0.5).

Acoustic Behavior of Males of the Rio Grande Leopard Frog (Rana berlandieri): An Experimental Analysis Through Field Playback Trials

Calling by resident males of Rana berlandieri was evoked when they were presented with three types of prerecorded natural sounds at intensities above 80 dB, peak SPL. Playback of conspecific mating trills, and of the mating call of the sympatric species, Bufo vaUiceps, resulted in vigorous chuckle-calling; while playback of a conspecific chuckle call evoked both chuckle calls and mating trills. It is concluded that the mating trill of R. berlandieri is an advertisement signal which functions to announce occupied space to nearby males; and that the chuckle call is a territorial signal which is evoked by calls of an intruding male. The efficacy of the mating call of B. valliceps in evoking chuckle-calling is believed to rest in the similarity of its carrier frequency and pulse rate to those in the mating trill of R. berlandieri.