Older males are often reported to have higher mating success than younger males. To the extent that male quality and survival are positively correlated, this observation raises the possibility that females use male signals to assess age and thus quality. I tested this hypothesis in the fall field cricket, Gryllus pennsylvanicus, a species in which females are known to prefer older males, and males call to attract females. Tests were both longitudinal (males recorded early and late in life) and cross-sectional (males recorded once, each at different ages). I measured a variety of temporal and spectral calling song parameters and tested the predictions that: 1) calling song changes with age, and 2) variation in calling song correlates with variation in age. I found significant changes with increased age: calls showed decreased pulse period, decreased pulse duration, decreased pulse peak frequency, more pulses per chirp and increased pulse period variability. Although pulse period and pulse duration were negatively correlated with male age in bivariate correlations, canonical correlation failed to detect any significant relationship between male age and any linear combination of song parameters. I also measured a number of male body size traits and found that the majority of information in male song appears to be related to body size. I discuss the results in relation to the auditory sensitivity of G. pennsylvanicus, and suggest a simple mechanism that explains both female preference for older males and female discrimination against heterospecific males.
Sexual conflict over mating rate has selected for male adaptations to induce females to mate. These inducements can be either coercive or enticing, and there is a growing realization that males of a given species may employ both tactics simultaneously to acquire mating success. Insects in the genus Cyphoderris Uhler, 1864 (Orthoptera: Haglidae) have a unique breeding system in which females feed on the fleshy hind wings of males during copulation, but as mating proceeds males use a specialized abdominal pinching organ known as a gin trap to hold the female until she copulates with him. Previous research has demonstrated the coercive nature of the gin trap, but evidence for a beneficial effect of hind-wing feeding is lacking. Here we tested whether hind-wing feeding provides material benefits to females by manipulating females’ access to nutrition-food restricted or ad lib food-and then providing females with four opportunities to mate over 8 days. As predicted, food-restricted females were more likely to feed on male hind wings, did more hind-wing damage, and were more likely to copulate with males than females provided ad lib food. We discuss these results in the context of the evolution of polyandry and sexual conflict
Background: An increasing number of factors have been shown to affect female mating behaviour, and thus to affect the strength and/or direction of selection that females exert on males. One of these factors is female social experience (including mating history). Question: How does female social experience affect the strength and direction of selection on four male traits - age, body size, weaponry size, and body condition? Methods: I used multivariate selection analysis to estimate the linear and non-linear selection gradients exerted by female field crickets (Gryllus pennsylvanicus) with different social backgrounds. Females were either virgins with no experience of conspecifics as adults or experienced females from a large, mixed-sex population. I assessed relative fitness through mating success (mated or not) and calculated selection gradients for the four male traits. Results: Experienced females exerted significant positive directional selection on male weaponry size and favoured older males. However, linear variation in these traits did not affect the probability of an inexperienced female mating. I also detected correlational selection by inexperienced females, who preferred combinations of age and body size (old/large and young/small).
Both resource-holding potential (RHP) and experience in aggressive contests are known to affect future aggressive behaviour. However, few studies have examined the effects of mating experience on agonistic behaviour, despite the fact that dominant males usually acquire more matings. We investigated the effect of mating experience on male aggressive behaviour including the relationship between RHP and fighting success in the fall field cricket, Gryllus pennsylvanicus. We formed pairs of size- and age-matched males that varied in RHP (relative weapon size) and conducted two experiments. In the first, we varied male mating experience by allowing one male in a pair to either be (a) ’mated’: court, be mounted and copulate with a virgin female or (b) ’experienced’: court, be mounted, but prevented from copulating. The second experiment varied postcopulatory experience where the male was allowed (’contact’) or prevented from (’no-contact’) continued contact with his recent mate. Following treatment, experimental males engaged in an aggressive contest with the na < ve size- and age-matched male. In our first experiment, we found that mated and experienced males were equally likely to escalate contests to combat with a na < ve opponent, but mated males were less likely than experienced males to win. There was no effect of mating on the relationship between RHP and fighting success. In our second experiment, we found no effect of maintaining contact with the female on the tendency to escalate or the probability of winning. As in the first experiment, males with relatively larger heads again won more fights and this relationship was unaffected by male experience. These results suggest that mating is itself detrimental to male success in aggressive contests, but that this effect is not sufficient to eliminate the effect of RHP on fighting success.
During mating, the female Carolina ground cricket (Eunemobius carolinus (Scudder, 1877)) chews specialized spurs on the male’s hind tibia for access to his hemolymph. One potential benefit to spur chewing includes nutritional acquisition from male hemolymph. A method for testing this hypothesis is to manipulate food quality or quantity, with the prediction that mating rate will increase as food quality or quantity decreases. We manipulated diet quality in adult females and provided them with four consecutive mating opportunities. We measured four aspects of mating behaviour (mating rate, latency to copulate, copulation duration, and spur chewing duration) and three of female fitness (egg number, egg-laying rate, and life span). Females of the two diet treatments did not differ significantly in any of the measured mating behaviours, although females fed a low-quality diet lived longer. Male life span did not correlate with any measured variable, although males that experienced more matings and longer total times of copulation and spur chewing lost more mass. These results suggest that spur chewing may be costly for males, although we detected no evidence that this behaviour was a benefit to the female or represented a form of male coercion.
Intrinsic factors such as female age and mating status have been found to affect female choosiness. However, as these factors are often confounded in the wild because mated females are usually older individuals, the relative influence of these two factors on female behaviour is unclear. Using a fully factorial design, we tested the relative effects of age and mating status of female field crickets (Gryllus pennsylvanicus Burmeister, 1838) on both (i) the probability that she would mate and (ii) her latency to mate. We found that virgin females were both more likely to mate and copulated more quickly than mated females, but female age had no significant effect on either the probability of mating or the latency to copulate. These results clearly show that mating status is more important in determining female mating behaviour than age. We suggest that previous work which showed an age effect on female choosiness in virgins alone might be of reduced relevance if most females do not remain unmated for long
Scientific literature often touts the many advantages of large body size, but seldom addresses the value of small body size. Yet selection for large size must be counterbalanced by selection for small size, otherwise, all animals would be large. In this paper, we demonstrate female-biased size dimorphism and a strong copulatory advantage for small males in a Jerusalem cricket (JC) (Stenopelmatus) from central California. We selectively paired male and female JCs of diverse body sizes and recorded their ability to copulate. All copulations were successful for males smaller or equal in size to females. In contrast, when the male was 6.1 mm longer than the female, copulation had only a 50% chance of occurring successfully. In general, as the difference between male and female body length increased (i.e., as males became longer than their mates), the probability of successful copulation decreased. These patterns of mating resulted in net selection for small male size and large female size. We also detected positive linear direct selection on male hind leg length, which may explain why male JCs have longer legs than females. The copulatory disadvantage of large males derives from the odd mating behavior of this group, in which males must contort and precisely align their bodies to couple. We believe that this is the first example of small-male advantage based solely on the physical aspects of copulation. In this species, small, not large, males have a copulatory advantage.
Sexually selected traits are thought to impose survival costs on showy males. Recent empirical work found a negative relationship between male display and survival in a field cricket species (Orthoptera, Gryllidae, Gryllinae) where there is no evidence of a mating bias toward older males. In most species, however, male survival and ornamentation are positively correlated, and older males often have a mating success advantage over younger males. These findings suggest that male quality and survival are positively correlated, but more tests of this hypothesis are needed. We measured the condition dependence of male survival and calling effort in another grylline, Gryllus pennsylvanicus, where older males have previously been shown to have greater mating success. We varied condition by manipulating diet, and measured male life span and calling effort to assess the relative condition dependence of these traits. High- and medium-condition males survived longer than low-condition males, and high-condition males called more than medium- and low-condition males. Differences in calling effort among the condition treatments were not apparent early in life, but emerged as males aged. We discuss possible explanations for the differences between our study and contrasting results such as the previous grylline work.
Sexually selected male weaponry is widespread in nature. Despite being model systems for the study of male aggression in Western science and for cricket fights in Chinese culture, field crickets (Orthoptera, Gryllidae, Gryllinae) are not known to possess sexually dimorphic weaponry. In a wild population of the fall field cricket, Gryllus pennsylvanicus, we report sexual dimorphism in head size as well as the size of mouthparts, both of which are used when aggressive contests between males escalate to physical combat. Male G. pennsylvanicus have larger heads, maxillae and mandibles than females when controlling for pronotum length. We conducted two experiments to test the hypothesis that relatively larger weaponry conveys an advantage to males in aggressive contests. Pairs of males were selected for differences in head size and consequently were different in the size of maxillae and mandibles. In the first experiment, males were closely matched for body size (pronotum length), and in the second, they were matched for body mass. Males with proportionately larger weaponry won more fights and increasing differences in weaponry size between males increased the fighting success of the male with the larger weaponry. This was particularly true when contests escalated to grappling, the most intense level of aggression. However, neither contest duration nor intensity was related to weaponry size as predicted by models of contest settlement. These results are the first evidence that the size of the head capsule and mouthparts are under positive selection via male-male competition in field crickets, and validate 800-year-old Chinese traditional knowledge
Atlantic salmon (Salmo salar) was once native to Lake Ontario, however, its numbers rapidly declined following colonisation by Europeans and the species was extirpated by 1896. Government agencies surrounding Lake Ontario are currently undertaking a variety of studies to assess the feasibility of reintroducing Atlantic salmon. We released hatchery-reared adult Atlantic salmon into a Lake Ontario tributary to examine spawning interactions between this species and fall-spawning exotic salmonids found in the same stream. Chinook salmon, coho salmon and brown trout were observed interacting with spawning Atlantic salmon in nearly one-quarter of our observation bouts, with chinook salmon interacting most frequently. Whereas a previous investigation found that chinook salmon caused elevated agonistic behaviour and general activity by spawning Atlantic salmon, the present study found that interspecific courtship was the most common form of exotic interaction with spawning Atlantic salmon. In particular, we observed precocial male Chinook salmon courting female Atlantic salmon and defending the female against approach by male Atlantic salmon. We discuss the potential implications of these interactions on the Lake Ontario Atlantic salmon reintroduction programme
Chorus tenure is the number of nights that a male anuran spends attending choruses, and dominant tenure is the number of nights that a male adopts a dominant (i.e. territorial) mating tactic. While male bullfrogs that have longer tenure (chorus tenure and dominant tenure) acquire more mates, tenure is believed to be energetically costly, During the summer of 1998, we tested the hypothesis that tenure of bullfrogs is energy constrained, by conducting a feeding experiment to manipulate energetic condition, and by measuring each male’s body condition on every night of his chorus tenure. The energetic constraint hypothesis did not adequately predict variation in male chorus tenure. However, male bullfrogs with longer dominant tenures, other things being equal, were in better initial condition, poorer final condition and lost condition more slowly than males with shorter dominant tenures. Feeding had no significant effect on either chorus tenure or dominant tenure. We found evidence that direct selection through endurance rivalry favoured traits in male bullfrogs that increased tenure. (C) 2001 The Association for the Study of Animal Behaviour