Courtship Role Reversal Research Articles

Size matters: Antagonistic effects of body size on courtship and digging in a wolf spider with non-traditional sex roles

Body size, nuptial gift characteristics and courtship behaviour, among other traits, can reflect the quality of a potential mate and, thus, might be under sexual selection. To maximize their mating success, individuals can show behavioural plasticity in sexual context. Allocosa senex is a burrow-digging wolf spider that exhibits reversal in courtship roles and in sexual size-dimorphism expected for spiders. Males construct the mating refuge and females prefer males that build longer burrows, which are considered as nuptial gifts because they are delivered to them after mating. This study aims to determine whether male body size and female reproductive status influence burrow dimensions, courtship displays, female preferences and cannibalism rate in A. senex. For that purpose, we allowed males to construct burrows and performed sexual trials under laboratory conditions. Larger males were more courted by females, and in turn, they expressed more vibratory behaviours during courtship. However, and contrary to our expectations, smaller males constructed longer burrows. We suggest that males of A. senex exhibit size-dependent behavioural plasticity, and when they are smaller, they invest more in burrow construction to compensate their lower opportunities of courting intensively as larger males. In addition, females courted differentially according to their reproductive status, overriding male preferences for virgin females. This study opens several doors to future research regarding mutual choice in A. senex and the traits assessed by males and females during courtship, as well as about the influence of intrinsic and extrinsic factors shaping reproductive decision-making in this and other wandering spider species.

Seasonal sex role changes in the blenniid Petroscirtes breviceps, a nest brooder with paternal care

The plasticity of the sex roles in the blenniid fish Petroscirtes breviceps, a nest brooder with exclusive paternal care, was studied throughout an 8 month breeding season. Males performed most courtships early and late in the breeding season, whereas females performed most in the middle of the season. These results indicated that the sex of individuals initiating courtship changed seasonally, with courtship role reversal in the middle of the season. Intrasexual aggression in both sexes occurred much more frequently in mid‐season than in the early and late seasons. Males frequently fought when available nest sites were limited, regardless of the presence of females, suggesting that males competed for nests in order to qualify to mate (resource competition). In contrast, courting females fought only in mid‐season, when females’ relative success in entering nests decreased, indicating that females competed for limited mating opportunities (mating competition). The reversed courtship roles and female mating competition in mid‐season suggested that the sex roles in P. breviceps changed seasonally from the conventional roles to reversed roles and back again during one breeding season. This study provides the first empirical evidence of multiple changes in the sex roles of animals within a breeding season.

The nutritional contribution of males affects the feeding behavior and spatial distribution of females in a bruchid beetle, Bruchidius dorsalis

The relationship between the quality/quantity of male investment and the feeding behavior of females was investigated in a bruchid weevil, Bruchidius dorsalis (Fahraeus), whose males donate nutrition via seminal fluid to females. Experiments on the effect of feeding regimes of both sexes on the mating frequency of females showed that females mated at a higher frequency if given low-quality food or poor male investment. On the other hand, the experiment that examined the effect of male investment quality on female feeding behavior showed that females receiving the high-quality investment exhibited feeding behavior less often. These results suggest that male investment and feeding behavior play the same role for B. dorsalis females. These experiments also showed that there are sex-related asymmetries in mating and feeding behaviors: females mated more often but males fed more often. Moreover, a field census suggested that only males visited non-host flowers to feed on the pollen and nectar during the non-flowering period of the host plants; females always stayed on the host plants irrespective of the flowering phenology. These results suggest that in B. dorsalis courtship role reversal and sex-specific feeding modes are fairly fixed and obligatory, and that male investment, derived from sexual selection, could affect the feeding behavior and spatial distribution of both sexes, which may have far-reaching impact in various ecological contexts.

Courtship role reversal and deceptive signals in the long-tailed dance fly, Rhamphomyia longicauda

We examined the function of secondary sexual characters in the role-reversed, lekking behaviour of female long-tailed dance flies, Rhamphomyia longicauda Loew (Empididae), to test the hypothesis that the degree of abdominal distention is an honest female signal about the state of egg development. Female Rhamphomyia cannot hunt for prey and they receive all of their protein from males by exchanging copulations for nuptial prey gifts. Females compete for male gifts within leks that are organized for a brief period each evening before dark. Before hovering within leks, females swallow air, inflating expandable pouches on the pleural margins of the abdomen. The result is a large saucer-like abdomen which is further exaggerated by wrapping scaled pro-, meso- and metathoracic legs along its pleural margins. Male preference for an enlarged abdomen was confirmed by suspending plastic models of varying size from monofilament lines and recording which models attracted the most males. There was a positive relationship between egg development and abdominal distention in a related species,R.sociabilis (Williston), which lacks inflatable abdominal pouches. Multiple regression showed that inR.longicauda , abdominal inflation completely masks the state of egg development. We conclude that femaleR.longicauda deceive mate-seeking males with the unreliable message that eggs are nearing maturation in order to obtain a protein meal in exchange for copulation. Males that fail to identify a female bearing mature eggs risk near-certain cuckoldry and an increased probability that the female will die before oviposition.

Ejaculate expenditure by malebush crickets decreases with sperm competition intensity

Male bushcrickets transfer a spermatophore at mating that consists of a sperm-containing ampulla and a sperm-free mass, the spermatophylax, that is consumed by the female during insemination. The costs of spermatophore production for males and benefits of consumption for females result in reversals in courtship roles in nutrient limited populations that increase both the risk and intensity of sperm competition. Here we show that under conditions characteristic of courtship role reversal, male expenditure on the spermatophore is dependent on female size. When mating with small females, males increase the amount of spermatophylax material and sperm, as expected from the increased sperm competition risk associated with courtship role reversal. However, males reduce the amount of spermatophylax material and sperm transferred to larger females. Since larger females have a higher mating success when competing for nurturant males, the intensity of sperm competition covaries with female size. Reduced ejaculate expenditure under increased sperm competition intensity is in accord with theoretical expectation.

Reproductive energetics of the role reversing bushcricket, Kawanaphila nartee (Orthoptera: Tettigoniidae: Zaprochilinae)

AbstractTheory predicts that sexual differences in reproductive strategies arise because of differences in the magnitude of investment made by males and females in reproduction. In some bushcrickets, the typical sex role of competitive male and choosy female is reversed when populations are subject to nutrient stress. Here I present an energetic analysis of reproduction for the role reversing bushcricket, Kawanaphila nartee, that supports the contention that this sex role reversal is a consequence of reversal in the pattern of relative reproductive investment. When fed ad libitum, males spent 16% of their daily energy reserves on the spermatophore compared with 26% spent on calling to attract a mate. Females spent 29% of their daily energy reserves in producing and laying eggs. However, when allowed only limited access to food, female expenditure in eggs was reduced to 23% of daily reserves while male expenditure remained unchanged. After accounting for the incorporation of male nutrients into eggs, female energy expenditure in reproduction exceeded male expenditure when animals were fed ad libitum, but male expenditure exceeded female expenditure when diet was limited. This role reversal in relative energy expenditure that is associated with courtship role reversal supports classical and contemporary theories on the control of sexual selection.

Courtship role reversal in bush crickets: another role for parasites?

Courtship role reversal in bush crickets: another role for parasites?

Food Quality Controls Sexual Selection in Mormon Crickets by Altering Male Mating Investment

Populations of several katydid species (Orthoptera: Tettigoniidae) show large differences in mating system; in some species males compete and females choose mates, whereas in others these courtship roles are reversed. Male katydids feed their mates during mating with a large, nutritious spermatophore. I hypothesized that courtship role reversal and increased sexual selection on females was a result of limitation in nutritious food items causing a decrease in the number of males available for mating (and thus in the spermatophore meals available). This hypothesis was tested by varying diet in field cages of Mormon crickets, Anabrus simplex. Results showed that, in contrast to a diet supplemented with proteinaceous food items, a poor diet resulted in: (1) a decrease in the number of sexually active males, (2) an increase in sexual selection for female body size, and (3) a reversal in the typical courtship roles. The experiment ruled out alternative explanations for variation in the mating system of this species,such as differences in population density and age. The conclusion from this study is that increased sexual selection on females due to such a change in diet is a result of an increase in the relative importance of male parental investment.

Testing Parental Investment and the Control of Sexual Selection in Katydids: The Operational Sex Ratio

Theory predicts that relative parental investment by the sexes controls the ratio of the numbers of fertilizable females and sexually active males (the operational sex ratio, OSR) and thus sexual selection and sexual differences. This paper tests the hypothesis that variation in parental investment controls the numbers of males and females available for mating. In katydids, males and females invest parentally by providing material investment to eggs, with the male donation derived from spermatophore materials eaten by the female. Previous work with katydids in nature has shown intraspecific variation in sexual selection acting on females; only certain populations show a courtship role reversal in which females compete for access to males. These observations led to the hypothesis that the availability of food in nature determines the frequency of spermatophore production and thus the number of males available for mating. In the present study, male and female katydids were maintained on diets that differed in food quality. Both sexes were given daily access to sexually receptive members of the opposite sex. As predicted, males on a low-quality diet mated less frequently than males on a high-quality diet. The opposite trend was observed for females: females on a low-quality diet increased mating frequency, apparently to obtain additional spermatophore nutrients. These data suggest that male parental investment in the spermatophore increases in its relative importance when diet is low in quality. The effects of diet on mating frequency result in different estimates of the OSR, which accord with observations in nature: for the high-quality diet, there are fewer fertilizable females than sexually active males; similar conditions in nature would be predicted to result in a male-to-male competitive (polygynous) mating system. For the low-quality diet, there were slightly fewer fertilizable females, indicating that such a diet may result in competition among females.

SEXUAL SELECTION AND SEXUAL DIFFERENCES IN MORMON CRICKETS (ORTHOPTERA: TETTIGONIIDAE, ANABRUS SIMPLEX).

Darwin (1871) suggested that differences in the intensity of sexual selection on the sexes was a cause of secondary sexual differences. He proposed that behavioral and morphological traits possessed by males had evolved in the context of sexual competition, because fertilizable females are typically in short supply. Emlen and Oring (1977) pointed to several factors that are expected to change the ratio of fertilizable females to sexually active males (the operational sex ratio) and thus, the intensity of sexual selection on the sexes; theoretically both the investment of the sexes in offspring (parental investment; Trivers, 1972) and certain features of the social and physical environment are important. Parental investment theory (Trivers, 1972) predicts that females in species where males invest most in individual offspring should exhibit typically masculine traits by competing for access to sexually active males and males should exhibit typically feminine traits by being selective of mates. In vertebrate species where males provide the majority of parental care there is good evidence for a role-reversal in courtship behavior (Wittenberger, 1979; Petrie, 1983). In insects, paternal care of eggs and offspring is rare (Smith, 1980) but males of several groups supply their mates with nutritious prey items or glandular products (Thornhill, 1976a). These male efforts represent mating effort, as they apparently function in acquiring copulations (Alexander and Borgia, 1979). They are, however, nonpromiscuous mating efforts, potentially able to limit female reproduction (Thormhill, 1976b; Gwynne, 1984a) and thus are expected to influence the evolution of sexual differences in a similar way to male parental investment (Gwynne, 1984b). Males of many katydids (Orthoptera: Tettigoniidae) feed their mates with a large spermatophore which enhances female reproduction (Gwynne, 1984a). Mormon cricket males (Anabrus simplex Haldeman) produce a large spermatophore (Gillette, 1904), investing some fifth of their body weight in a single mating. I reported a reversal in the typical courtship roles for this species; females competed for access to singing males and males discriminated among females by selecting heavier individuals as mates (Gwynne, 1981). Here I show that this courtship rolereversal is found at certain sites but not at others. I examine sexual selection and its consequences at different sites by (1) testing the prediction that sexual selection on females, as estimated by variance in mating success, should be greater at sites where sexual competition among females is observed, (2) detailing the differences in courtship behavior between sites that have apparently resulted from differences in sexual selection, (3) testing the prediction that female body size should be greater at role-reversed sites as a consequence of intersexual selection for larger females, and (4) describing possible environmental differences between sites that have caused interpopulation variation in sexual differences.

Role reversal in courtship in the stomatopod Pseudosquilla ciliata (Crustacea)

The first known case of precopulatory role reversal in a crustacean is reported here in the stomatopod Pseudosquilla ciliata. Females of this species initiate courtship through visual displays and a vigorous sexual chase. Males enter courtship with restraint and appear to exercise choice by copulating selectively with females larger than themselves. This singular reversal in courtship roles occurs in the absence of paternal care, female guarding, or other male investment strategies typically invoked to explain such behaviour. Males, however, face certain risks in breeding, including the threat of aggression from the female, and the loss of a considerable part of their reproductive investment through sperm competition. By mating with larger, more fecund females, males reduce the potential loss from sperm competition, but increase the risk of injury from the female. This combination of factors should promote caution in males along with a preference for larger females.