Mechanisms of selective attention in grasshopper choruses: who listens to whom?

In many rhythmically signaling species of acoustic insects and anurans, males form choruses at typical population densities. Recent findings that females may prefer leading calls indicate that the timing of a male's signals relative to those of neighboring choruses is an important component of mate attraction. Within a chorus, however, males cannot time their calls such that they lead all neighbors. Hence, they are expected to show selective attention toward only a subset of the group. We used field playback experiments to determine the incidence of and mechanism(s) responsible for selective attention in choruses of the territorial grasshoppers Ligurotettix coquilletti and L. planum. Our data revealed significant selective attention in both species and are inconsistent with either fixed-threshold or fixed-number mechanisms. Rather, regulation of selective attention by a sliding-threshold mechanism is supported. We discuss these results in the context of the evolution of chorus structure. Received: 24 September 1997 / Accepted after revision: 28 February 1998     

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     

Sexual selection in the zebra finch Taeniopygia guttata : condition, sex traits and immune capacity

The aim of this study was to test two hypotheses: (1) that condition-dependent secondary sexual traits reflect an individual's immune capacity and (2) that immune capacity and secondary sexual traits covary with primary sex traits, specifically ejaculate quality. We used the zebra finch Taeniopygia guttata as a study species, since the traits that females find attractive in males of this species, song rate and beak colour, are well established. A paired experimental design comprising 31 pairs of brothers was used; for each pair, one male was assigned to a control group provided with ad libitum food and no additional exercise, and the other male was assigned to an experimental group which experienced additional exercise and a reduced rate of food intake. After 11 weeks, the experimental group differed significantly from the control group in a range of variables, including body mass, haematocrit, granulocyte:lymphocyte (G:L) ratio and several primary sex traits, indicating that condition in this group was reduced. Birds in the experimental group showed a differential response to the treatment. We used the rank order in which birds could be captured by an experimenter as an index of condition. Birds easily caught were assumed to be in poorer condition than those which were more difficult to capture. Rank capture order was repeatable and was significantly correlated with the G:L ratio in the experimental group, but not in the control group. In the experimental group, rank capture order was correlated significantly with both secondary sex traits: birds in better condition had redder beaks and a higher song rate. However, beak colour and song rate did not covary significantly, suggesting that these two traits provide different types of information. Secondary sex traits did not covary with primary sex traits or any sperm features. Thus, there was no evidence for Trivers' sexual-competence hypothesis or the phenotype-linked fertility hypothesis. We used four assays of immune capacity, two general (G:L ratio and spleen mass) and two specific [antibody titres to sheep red blood cells (SRBCs) and Brucella abortus (BA)]. The G:L ratio was significantly higher in the experimental group, spleen mass (absolute and relative) did not differ between the groups, anti-SRBC antibody titres were significantly higher in the control group (contrary to expectation), and anti-BA antibody titres were close to being significantly lower in the experimental group. Within the experimental group, there was no evidence that antibody titres covaried with secondary sex traits. Although we demonstrated that beak colour and song rate were condition dependent, our experiment provided no evidence that either of these traits covaried with immune capacity or sperm features. Received: 9 February 1998 / Accepted after revision: 5 September 1998     

Sex-specific nest defense in house sparrows (Passer domesticus) varies with badge size of males

According to indicator models of sexual selection, females can benefit from choosing males with above average epigamic traits, but empirical evidence for such benefits is scarce. Here, we report results from an experiment with 29 pairs of house sparrows (Passer domesticus) where the intensity of nest defense against a mounted mustelid predator was related to the size of the black throat and breast patch (“badge”) in males. Using principal components analysis (PCA), original response variables of both sexes were reduced to two factors: “Approach” to the predator and “Distant warning”. “Approach”, the more risky behavior, increased from small- through medium- to large-badged males and decreased in their females. Since large-badged males have a higher certainty of paternity (i.e. greater benefits from defense) and may be older and more experienced (i.e. incur lower costs), the most likely explanation for male defense intensity increasing with badge size is an improving benefit/cost ratio. The resulting optimal response of their females and evolutionarily stable participation in joint parental care is illustrated by a graphical model. It shows that females would, indeed, benefit directly from choosing large-badged males. This, however, is no proof of a direct evolutionary tie between badge size and paternal behavior, as assumed by indicator models of sexual selection. It may simply represent a spurious relationship, originating from the correlation of badge size and defense with confidence of paternity. Received: 22 September 1997 / Accepted after revision: 3 November 1997     

Male asymmetry and postcopulatory sexual selection in the fly Dryomyza anilis

The significance of male asymmetry in postcopulatory sexual selection was studied in the fly Dryomyza anilis by examining whether male asymmetry is related to fertilization success. The traits measured were wing length, tibia length and the length of small and large claspers. The male claspers are situated at the tip of the abdomen, functional pair of claspers consists of a large and a small clasper on the same side of the body. These claspers are used to tap the female abdomen after sperm transfer, which has been shown to increase fertilization success for the mating male. Fertilization success was negatively related to the fluctuating asymmetry of wing length, suggesting either female preference for more symmetrical males or a relationship between male asymmetry and intrasexual selection which was reflected in mating performance. Fertilization success was also related to the length of small claspers, decreasing with increasing length of the claspers. In addition, males with asymmetrical small claspers enjoyed higher fertilization success than symmetrical ones. This study shows that fluctuating asymmetry in wing length is an important fitness trait in postcopulatory sexual selection. Since male tapping affects sperm distribution in the female's sperm storage organs, the higher fertilization success of males with asymmetrical small claspers could have a functional relationship with the asymmetrical position of female sperm storage organs. Received: 6 March 1997 / Accepted after revision: 8 November 1997     

Combining motions into complex displays: playbacks with a robotic lizard

Complex displays composed of multiple, seemingly independent, units can result from sexual selection for increasingly variable, but redundant, displays and from potentially opposing selective pressures imposed by use of the display in multiple contexts. Our playback results support the latter, multireceiver hypothesis by confirming that two aspects of the sagebrush lizard headbob display (number of headbobs and use of display-specific body postures) are independently-meaningful components that are interpreted differently by different receivers. Male receivers use species-typical body postures to distinguish between aggressive and broadcast forms of the display, whereas female receivers are more attentive to the number of headbob motions, using these to distinguish male courtship from a challenge from a female competitor. Thus, display components are likely subject to different selective pressures and the display as a whole is evolving in response to a complex selective regime. Our example differs from other complex signals that have been considered in that both display elements involve dynamic motions (turned on and off by the display producer) as opposed to static signal elements (e.g., color, size). In addition, we found evidence that display structure is highly malleable, and that lizards both produce and respond to artificial displays that violate syntactic rules identified from field observations. Finally, our experiments demonstrate that a robotic lizard can be used effectively in playback studies of visual display behavior in lizards.Electronic Supplementary Material: S1. Movie clip of the robotic lizard producing a species-typical headbob display as in Fig. 1a.     

A fungus infecting domestic flies manipulates sexual behaviour of its host

The Enomopathogenic fungus Entomophthora muscae infects and kills domestic flies Musca domestica, and rates of transmission are higher at high population densities. I tested whether features of parasitized hosts increased the likelihood of transmission of the fungus in a series of experiments. Individual flies contacting an infected conspecific had a much higher probability of becoming infected than had flies contacting a dead fly without signs of infection. Males especially were attracted to and behaved sexually towards dead, infected flies even when a choice was available between a dead, infected fly and a dead, uninfected individual. The abdomen of infected flies swelled considerably as a consequence of infection, and uninfected female flies with larger abdomens are more fecund than the average female and maybe more attractive. Experiments in which abdomens of infected and uninfected flies were cut off and glued back on other flies demonstrated that the abdomens of infected flies were highly attractive to males. When the size of the abdomen of infected and uninfected individual flies was held constant, infected dead flies were still more attractive than corpses of uninfected flies. This result suggests that features other than the size of the swollen abdomen enhanced the attractivity of infected flies. Features of infected hosts therefore increased the likelihood of transmission of the parasitic fungus.     

Religious harassment in the workplace: An examination of observer intervention

Religious harassment claims in the United States have risen sharply over the past decade. However, victims of religious harassment may not always report harassment, and true rates may be higher. Hence, actions taken by third parties present (observers) are important in combating harassment in the workplace. The purpose of this paper is to extend a previous model of observer intervention and related research by testing it empirically in the context of religious harassment and identify factors that influence observers' decision to intervene (intervention), when they intervene (level of immediacy), and how much they intervene (level of involvement). Across two studies, we find evidence that verbal harassment, ambiguity of intent, relationship to target/harasser, recurrence belief, religious commitment, pro‐social orientation, and the interactive effect of shared religion and religious commitment predict intervention. Furthermore, individuals show higher levels of involvement and immediacy in intervention when costs are low and emotional reactions are high. Implications of these findings for engaging observers in combatting harassment are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

The evolution of female copulation calls in primates: a review and a new model

Female copulation calls are mating-associated vocalizations that occur in some species of Old World monkeys and apes. We argue that copulation calls have two immediate functions: to encourage mating attempts by other males and to increase mate guarding by the consort male. We hypothesize that female copulation calls have evolved under the selective pressures of risk of infanticide and sperm competition. When male mate guarding is effective, copulation calls allow females to concentrate paternity in dominant males and benefit from their protection against the risk of infanticide. When mate guarding is ineffective, copulation calls may bring genetic benefits to females through facilitation of sperm competition. We present a quantitative model in which interspecific variation in females' promiscuity predicts their tendency to use copulation calls in conjunction with mating. The model predicts that in species with little female promiscuity, copulation calls should be rare and exhibited only in association with mating with dominant males. In species in which females are highly promiscuous, copulation calls should be frequent and unrelated to male dominance rank. The limited data available to test the model support its main predictions as well as the predicted relation between copulation calls and male dominance rank.

Parasite distribution and virulence: implications for parasite-mediated sexual selection

The Hamilton-Zuk hypothesis states that females choosing males with more developed secondary sexual traits, i.e. brighter males, achieve greater fitness if variability in brightness reflects heritable variation in resistance to parasites. However, several factors will affect the likelihood that parasites play a role in sexual selection in given species. Here, using simple models, we show that because of parasite aggregation on a few hosts, only few breeding males would suffer from reductions in brightness due to parasites. Only in cases where parasites are abundant and show low levels of aggregation among their hosts would there be sufficient variability in brightness among breeding males for female choice of bright, resistant males to evolve. In addition, sufficient parasite-induced variability in brightness among breeding males will only occur in host-parasite systems where pathology is linearly related to the number of parasites per host. The presence of males that are uninfected and bright but genetically susceptible to parasites will also influence the fitness advantages obtained by females choosing bright males. If genetic immunity against parasites is rare in the host population, females can probably only benefit from choosing bright males if parasites are common and little aggregated among males. These results greatly limit the generality of the Hamilton-Zuk hypothesis, and suggest that only a small fraction of host-parasite associations could promote the evolution of host mate choice for resistance based on brightness. Correspondence to: R. Poulin