Circadian rhythmicity of locomotor behavior and oviposition in female Teleogryllus commodus

Summary Locomotor activity of the Teleogryllus commodus is under circadian control, with _LL=25.3 h and _DD=23.4 h. In LD 12:12 h, running occurs either exclusively during darkness (57%), mainly in the dark phase (35%), or with substantial activity peaks in both phases (8%). For oviposition, _LL>24 h and _DD<24 h; in LD 12:12 h, 80% of the studied deposited their eggs mainly during the light phase and 20% primarily during darkness. In the discussion, a temporal correlation between stridulation, spermatophore formation, and locomotion, and oviposition is established, which serves to make an encounter and mating between the sexes as likely as possible.Dedicated to Prof. Dr. M. Gersch on the occasion of his 70th birthday     

The effect of mating on female sexual behavior of Teleogryllus commodus Walker

Summary Virgin Teleogryllus commodus females show rhythmic locomotor activity in light-dark (LD) and constant light (LL) conditions. A taped 3-h calling song stimulates them into further walking, and they lay few eggs. Successful mating suppresses or reduces circadian-controlled walking, but in LL-conditions the free-run still persists. Mated females no longer respond to the 3-h calling song. The number of eggs laid within 24–72 h after insemination increases, and the three effects of mating occur independently of one another. The possible physiological basis of these changes and their ecological and behavioral significance under field conditions are discussed.     

The effect of female mating status on male offspring traits

In haplodiploid insects, males develop from unfertilized eggs; consequently, unmated females can reproduce. In a patchy, highly structured population, where brothers compete for mates and the reproductive return through sons is lower, females should minimize the number of male offspring. Consequently, unmated females are likely to have a reduced fitness compared to mated females. Here, we tested the oviposition behaviour of the haplodiploid beetle Coccotrypes dactyliperda. In this species, the unmated female can mate with her son to produce daughters. We predicted that unmated females could increase their fitness by (1) producing only few and small sons sufficient for mother–son mating and (2) dispersing to a patch occupied by conspecific females in order to increase their or their sons’ chance of mating. We demonstrate that (1) unmated females are common (23 % of all females), (2) they oviposit more frequently than mated females in occupied patches, (3) unmated females oviposit more eggs than mated females—this is in spite of the trade-offs, evident in this study, between the number of sons and the number of the mother’s future offspring after mating, (4) unmated females have a higher proportion of dispersing sons, and (5) sons of unmated females are smaller than sons of mated females. We conclude that the incidence of unmated females in the structured populations of C. dactyliperda is explained by plasticity in their oviposition behaviour. We discuss conditions where a high incidence of unmated females can persist as a successful strategy in structured populations.     

Fighting success and attractiveness as predictors of male mating success in the black field cricket, Teleogryllus commodus: the effectiveness of no-choice tests

Females are generally assumed to prefer larger, more dominant males. However, a growing number of studies that control for male-male competition have shown no correlation between dominance and attractiveness. Aggressive males can interfere with female mate preference either by physically coercing females into mating or by driving submissive males away and restricting mate choice. The most common method of assessing female mate choice is by using simultaneous two-choice tests. These control for male-male interactions, but usually interfere with physical and chemical cues involved in mate selection or alter male behaviour. They are therefore unsuitable for many study species, especially insects. Another method is the no-choice test that measures a females latency to mating when placed with a single male as an indication of male attractiveness. No-choice tests control for male-male aggression while allowing full contact between pairs (they allow actual mating to be directly observed rather than to occur based on a correlated behaviour). So far, however, no study has confirmed that males that entice females to mate sooner actually enjoy increased longer-term mating success. As such, the accuracy of no-choice tests as a method of examining mate choice remains untested. Here, we used no-choice tests on the black field cricket, Teleogryllus commodus, to show that (1) females did not prefer males that won fights (dominant males), and (2) latency to mating predicts actual mating success. We have clearly demonstrated the usefulness of no-choice tests and, considering the advantages of this method, they should be more often considered for a wider variety of taxa.Communicated by D. Gwynne     

Growth rate and the cost of calling activity in male carpenter frogs,Rana virgatipes

Summary Energy stress during the breeding season and relationships between calling activity and growth were investigated in male carpenter frogs, Rana virgatipes. This species has a prolonged breeding season of up to three months in Southern New Jersey. Monthly collections made in 1985 revealed that both dry mass and percent body lipid decreased throughout the breeding season but sharply increased at the end of the breeding season. Observations of free-living males showed that small males were more likely to gain mass than large males during the breeding season. All males gained mass at higher rates after the breeding season. A simultaneous record of calling activity and mass change was obtained for 42 males. Males called on 95% of nights, indicating that they rarely ceased their reproductive activities. Small males tended to have low calling efforts and high growth rates. When the effect of initial mass was removed, growth rate was negatively correlated with calling effort among small males. This is the first demonstration of a direct tradeoff between a reproductive activity and growth in an anuran.     

The effect of perceived female parasite load on post-copulatory male choice in a sex-role-reversed pipefish

The last several decades of research in behavioral ecology have resulted in a deeper appreciation of post-mating processes and sexual conflict in sexual selection. One of the most controversial aspects of sexual selection is cryptic mate choice. Here, we take advantage of male pregnancy in a sex-role-reversed pipefish (Syngnathus typhle) to quantify cryptic choice based on perceived parasite load and other sources of variance in female fitness. Studies have shown that S. typhle males preferentially mate with females with lower parasite loads and that a male’s perception of female parasite load can be altered by tattooing females. We manipulated the apparent parasite load of females in controlled mating experiments to test the hypothesis that post-copulatory sexual selection is dependent on a male’s perception of female parasite load in pipefish. Our results provided no evidence for cryptic male choice based on perceived female parasite load. However, we found evidence that eggs from larger females were more likely to result in viable offspring than eggs from smaller females and that the first female to mate with a male transferred more eggs per copulation on average. Overall, our results show that potential for post-copulatory sexual selection does exist in pipefish, but the male’s perception of female parasite load does not play a major role in this process.     

Audience effect alters male but not female mating preferences

Males often face strong mating competition by neighboring males in their social environment. A recent study by Plath et al. (Anim Behav 75:21–29, 2008a) has demonstrated that the visual presence of a male competitor (i.e., an audience male) affects the expression of male mating preferences in a poeciliid fish (Poecilia mexicana) with a weaker expression of mating preferences when an audience male observed the focal male. This may be a tactic to reduce sperm competition, since surrounding males likely share intrinsic preferences for female traits or copy mate choice decisions. Here, we examined the hypothesis that a same-sex audience would affect female mate preferences less than male mating preferences. Our hypothesis was based on the assumptions that (1) competition for mates in a fashion that would be comparable in strength to sperm competition or overt male–male aggression is absent among Poecilia females, and (2) P. mexicana females typically form female-biased shoals, such that almost any female mate choice in nature occurs in front of a female audience. Poecilia females (P. mexicana, surface and cave form, and the closely related gynogenetic Poecilia formosa) were given a choice between a large and a small male, and the tests were repeated while a conspecific, a heterospecific, or no audience female (control) was presented. Females spent more time in the neutral zone and, thus, less time near the males during the second part of a trial when an audience was presented, but—consistent with predictions—females showed only slightly weaker expression of mate preferences during the second part of the tests. This decline was not specific to the treatment involving an audience and was significantly weaker than the effect seen in the male sex.     

No male agonistic experience effect on pre-copulatory mate choice in female earwigs

Mating with dominant males may confer considerable benefits, but also incur significant costs, hence intrasexual competitiveness is a likely target of mate choice. In addition to established modes of mate assessment, females may use cues or signals associated with agonistic experience effects to assess the relative competiveness of males. Experience effects, where the outcome of a fight increases the likelihood of a similar outcome in subsequent fights, may result from an animal’s altered state after conflict, but can also arise from strategic rival use of information perceived about this altered state. While females may similarly use this information in mate choice decisions, this potential consequence of male–male conflict has largely been neglected. Here, we investigate the effects of experience on subsequent agonistic performance in the earwig Euborellia brunneri by imposing winning or losing experiences on males and rematching them with naïve, size-matched rivals. We reveal a strong loser effect in subsequent fights, with nearly all previous “losers” losing against new rivals. In contrast, we found no equivalent winner effect, with previous “winners” exhibiting no increased likelihood of winning. We subsequently test whether the effects of male agonistic experience extend to pre-copulatory female mate choice. We show that females, when allowed to choose between naïve males and “winners” or “losers”, do not discriminate between males based on their recent agonistic experience. Therefore, while fighting history can play an important role in male–male interactions, females may not attend to this information.     

Sequential female choice and the previous male effect in sticklebacks

Summary Female choice, identified as a major force in sexual selection theory, has recently been demonstrated in a number of species. These tests concentrated on simultaneous choice situations although females have to compare males sequentially in most territorial species, which is the more demanding task. Here it is shown that female three-spined sticklebacks, Gasterosteus aculeatus L., rate sequentially presented males according to their brightness. With increasing costs of sampling the females become less choosy. Furthermore, a male's attractiveness has a significant effect on the female's rating of the next male; a given male is rated higher when preceded by a duller male than by a brighter one and vice versa. Female sticklebacks use a stochastic decision rule in sequential mate choice that is attuned to the attractiveness of the present and previously encountered male. This demonstration of a previous male effect not only indicates an efficient mechanism for finding the best of a number of males but also extends the applicability of sexual selection theory.Offprint requests to: T.C.M. Bakker     

The eye and some effects of light on locomotor activity in Nephrops norvegicus

The compound eye of Nephrops norvegicus (L.) is of the superposition type, well-adapted to the low levels of light prevailing at the sea bed during the activity periods of the species. Only the proximal retinal shielding pigment responds to light, the distal retinal shielding pigment being in the dark-adapted position at all times. The response of the proximal pigment appears to vary seasonally. Field observations compared light intensity at the sea bed with the numbers of N. norvegicus caught by trawl at various times of day in the Irish Sea in summer and winter. Laboratory experiments were combined with these field data to indicate that light is an important modulator of locomotor activity in this species.     

The effect of male coloration on female mate choice in closely related Lake Victoria cichlids (Haplochromis nyererei complex)

We studied the effect of male coloration on interspecific female mate choice in two closely related species of haplochromine cichlids from Lake Victoria. The species differ primarily in male coloration. Males of one species are red, those of the other are blue. We recorded the behavioral responses of females to males of both species in paired male trials under white light and under monochromatic light, under which the interspecific differences in coloration were masked. Females of both species exhibited species-assortative mate choice when colour differences were visible, but chose non-assortatively when colour differences were masked by light conditions. Neither male behaviour nor overall female response frequencies differed between light treatments. That female preferences could be altered by manipulating the perceived colour pattern implies that the colour itself is used in interspecific mate choice, rather than other characters. Hence, male coloration in haplochromine cichlids does underlie sexual selection by direct mate choice, involving the capacity for individual assessment of potential mates by the female. Females of both species responded more frequently to blue males under monochromatic light. Blue males were larger and displayed more than red males. This implies a hierarchy of choice criteria. Females may use male display rates, size, or both when colour is unavailable. Where available, colour has gained dominance over other criteria. This may explain rapid speciation by sexual selection on male coloration, as proposed in a recent mathematical model. Received: 11 April 1997 / Accepted after revision: 27 July 1997     

The effect of social interactions on calling energetics in the gray treefrog (Hyla versicolor)

Summary The vocal behavior of Hyla versicolor was studied in the field by means of behavioral observations and playback experiments, and these data were coupled with measurements of oxygen consumption in calling frogs to estimate the effect of social interactions on calling energetics. Male gray treefrogs have intense calls (median peak SPL=109 dB, fast RMS SPL=100 dB at 50 cm). At an air temperature of 23° C, males produced an average of 1,200–1,300 calls/h for 2–4 h per night. Calling rates and call durations differed among individuals, but were relatively constant for each male during periods of sustained calling. Males in dense choruses gave calls about twice as long as isolated males, but produced calls at about half the rate. Consequently, total calling effort and estimated aerobic costs were largely independent of chorus density. Playbacks of recorded calls to males in the field elicited increases in call duration and decreases in calling rate, regardless of the rate or duration of the stimulus. Males gave longer calls in response to long calls or to stimuli presented at high rates, but they did not precisely match either stimulus rate or duration. Calling effort and estimated oxygen consumption changed only slightly during stimulus playbacks. These results indicate that male-male competition elicits pro-found changes in the vocal behavior of calling males, but these changes have little effect on energy expenditure. We estimated that most calling males had metabolic rates of about 1.7–1.8 ml O₂/(g\h), or about 280 J/h for an average size (8.6 g) male at 20° C. Although changes in call duration and calling rate did not affect aerobic costs of calling, males producing long calls at slow rates called for fewer hours per night than males producing shorter calls at higher rates. This suggests that calling time may be limited by the rate at which muscle glycogen reserves are depleted.     

Utilization of energy substrates during calling activity in tropical frogs

Calling activity in frogs is energetically demanding to males because they usually perform at or near their physiological capacities. Metabolic fuel for muscle contractions during bouts of aerobic calling activity comes from carbohydrates and lipids that are stored in the trunk muscles. I monitored nightly calling performance in males of seven tropical frog species from two families, Hylidae and Leptodactylidae, and compared levels of glycogen and lipid in the trunk muscles from males collected before and after a three-hour period of calling activity. Trunk muscles from late-evening males in five species had up to 63% less glycogen than the trunk muscles from early-evening males; relatively little depletion was observed in two other species. Overall, glycogen reserves and rates of depletion were highest in species with very high calling rates. It was not possible to measure changes in the relatively large stores of lipid in the trunk muscles after only 3 h of calling. Nevertheless, intramuscular lipid stores probably provide a greater percentage of the energy needed for sound production than glycogen stores, and are largest in species with high calling rates. Received: 7 January 1997 / Accepted after revision: 20 July 1997     

Experimental manipulation of mate choice by male katydids: the effect of female encounter rate

Summary This study tests the general prediction that discrimination among potential mates increases with the availability of potential mates. Specifically, we conducted two experiments that examined mate choice by male zaprochiline katydids in relation to their prior encounter rate with females. The probability of mate acceptance or rejection was measured for males given either frequent or no contact with females in the laboratory (experiment 1) and males taken directly from natural areas of either high or low female abundance (experiment 2). In both experiments, males with low female encounter rates were more likely to mate than males with high female encounter rates. In both cases, the decreased mating probability of males in the high encounter treatment resulted from their tendency to reject lighter (and less fecund) females. Despite the presumed advantage to males of selecting heavier females, field data indicate that, unlike females, males do not aggregate in rich food patches. Possible explanations for this finding are discussed. Offprint requests to: T.E. Shelly at the present address     

The role of male harassment on female fitness for the dengue vector mosquito Aedes aegypti

Sexual harassment studies in insects suggest that females can incur several kinds of costs from male harassment and mating. Here, we examined direct and indirect costs of male harassment on components of female fitness in the predominantly monandrous mosquito Aedes aegypti. To disentangle the costs of harassment versus the costs of mating, we held females at a low or high density with males whose claspers were modified to prevent insemination and compared these to females held with normal males and to those held with females or alone. A reduced longevity was observed when females were held under high-density conditions with males or females, regardless if male claspers had been modified. There was no consistent effect of harassment on female fecundity. Net reproductive rate (R ₀) was higher in females held at low density with normal males compared to females held with males in the other treatments, even though only a small number of females showed direct evidence of remating. Indirect costs and benefits that were not due to harassment alone were observed. Daughters of females held with normal males at high density had reduced longevity compared to daughters from females held without conspecifics. However, their fitness (R ₀) was higher compared to females in all other treatments. Overall, our results indicate that A. aegypti females do not suffer a fitness cost from harassment of males when kept at moderate densities, and they suggest the potential for benefits obtained from ejaculate components.     

Effects of spermatophores on male and female monarch butterfly reproductive success

Summary I present the results of experiments designed to measure the effects of spermatophores produced by male monarch butterflies on male and female reproductive success. There was wide variation in the number of matings by captive males, suggesting the potential for strong sexual selection on males. Male lifespan was not affected by total number of matings, nor did it differ between males that were allowed to mate and those not exposed to females. Two effects of spermatophores on female behavior or fecundity are reported; (1) Females that received large spermatophores delayed remating longer than those receiving small ones. (2) Females allowed to mate several times laid more eggs than singly-mated females. The relative importance of these effects is discussed in relation to monarch mating patterns.     

Environmental influence on the locomotor activity rhythm of the sand-shore amphipod Talorchestia deshayesi

The precision and persistence of the nocturnal, surface locomotor activity rhythm of the sand-beach amphipod Talorchestia deshayesi is described. The rhythm is expressed as a circadian activity period with no evidence of a circa-tidal component associated with the time of high tide. The rhythm is light-sensitive and entrainment occurs in response to changes in the time of an experimentally simulated dusk transition. Locomotor activity is initiated at the end of the dusk transition with cessation always occurring prior to dawn. The point of activity initiation is taken to be the position of a synchronizing cue controlling entrainment. The cue appears to be an absolute irradiance level of approximately 1.0 to 2.0×10^-4 W m^-2     

Independent effects of male and female density on sexual harassment, female fitness, and male competition for mates in the western mosquitofish Gambusia affinis

Operational sex ratio (the ratio of sexually active males to fertilizable females) has a major influence on male competition for mates and male–female interactions. The contributions of male and female density per se to mating system dynamics, however, are rarely examined, and the fitness consequences are often inferred rather than quantified. Male mosquitofish (Gambusia affinis) compete aggressively and frequently harass females for copulations, a behavior thought to reduce female fitness. Female fitness can also be reduced by increases in female density, which may affect food availability, cannibalism rates, and chemical interactions between females. I manipulated male and female densities of G. affinis to measure their effects on male–male aggression, male harassment toward females, and female fitness. I found that males chased rivals more often and attempted fewer copulations when female density decreased, but surprisingly male density had no significant effect on the frequency of these male behaviors. In contrast, males’ agonistic displays toward other males increased with male density, but display behavior was unaffected by female density. These results suggest that male and female density do not always contribute equally or at all to the patterns of behavior we observe. Female fitness declined as female density increased, the opposite pattern expected if male harassment is costly to females. This suggests that a strong, negative effect of female density overwhelmed any potential costs of male harassment. Sources of female density dependence and the consequences of changes in male and female density to patterns of male behavior are discussed.