Potential Reproductive Rates Of Males Research Articles

Fecundity selection predicts Bergmann's rule in syngnathid fishes

The study of latitudinal increases in organismal body size (Bergmann's rule) predates even Darwin's evolutionary theory. While research has long concentrated on identifying general evolutionary explanations for this phenomenon, recent work suggests that different factors operating on local evolutionary timescales may be the cause of this widespread trend. Bergmann's rule explains body size variation in a diversity of warm-blooded organisms and there is increasing evidence that Bergmann's rule is also widespread in ectotherms. Bergmann's rule acts differentially in species of the Syngnathidae, a family of teleost fishes noted for extreme adaptations for male parental care. While variation in body size of polygamous Syngnathus pipefish is consistent with Bergmann's rule, body size is uncorrelated with latitude in monogamous Hippocampus seahorses. A study of populations of Syngnathus leptorhynchus along a natural latitudinal and thermal gradient indicates that increases in body size with latitude maintain the potential reproductive rate of males despite significant decreases in ambient temperatures. Polygyny is necessary in order to maximize male reproductive success in S. leptorhynchus, suggesting a possible a link between fecundity selection and Bergmann's rule in this species.

The ecological basis of unusual sex roles in reverse-dichromatic eclectus parrots

In theory, sex roles are determined by the potential reproductive rates of males and females, which are constrained by parental investment. Thus the sex that invests least in offspring typically competes most for matings and is most subject to sexual selection, whereas the caring sex is most choosy when selecting mates. Here I show that ecological variables, rather than patterns of parental investment, can be influential in determining sex roles and the direction of sexual selection. In the polyandrous eclectus parrot, Eclectus roratus , both sexes care for offspring, yet despite traditional parental care patterns, both sexes are competitive and both are subject to sexual selection. The bright red and blue females compete for scarce nest hollows and the iridescent green males for mates. Using data from an 8-year field study, I show that the major ecological variable driving this system is nest hollow quality. Females with drier hollows had higher reproductive success and more males feeding and competing to mate with them. Females with nest hollows that were prone to flooding had fewer fledglings in years with higher dry season rainfall, confirming that hollow quality was a primary determinant of reproductive success. Comparisons of females before and after they changed hollows during the study provided further evidence that these trends were due to hollow quality rather than individual female quality. Thus competition for a scarce resource can lead to high variance in female reproductive success, and promote competition for high-quality mates among males.

Costs of breeding and their effects on the direction of sexual selection

A recent life-history model has challenged the importance of the operational sex ratio and the potential reproductive rates of males and females as the factors most important for the control of sexual selection, arguing that the cost of breeding, interpreted as the probability of dying as a consequence of the current breeding attempt, is the single most important factor that best predicts a mating system. In one species of bushcricket, the mating system can be reversed by resource manipulation. Here, we examine the costs of breeding in this system. Consistent with the model, increased costs of breeding can explain female competition and increased male choosiness under resource limitation. However, this is due to differences in the time required for a breeding attempt, rather than differences in breeding mortality which did not differ between the sexes. In general, males lived longer than females and we discuss the possible reasons behind this pattern of sex-biased non-breeding mortality.

Intrasexual competition and mate choice in assassin bugs with uniparental male and female care

Paternal care has the potential to lead to female-biased operational sex ratios and sex role reversal. Whereas this issue has been repeatedly investigated in fish, we present the first study on insects. We investigated two species of assassin bug: Rhinocoris tristis, which shows male care of eggs, and Rhinocoris carmelita, which shows female care of eggs. In both species, the potential reproductive rate of males exceeded that of females. Since the population sex ratio was unbiased and there was no difference in mortality rates between the sexes, we predicted that the operational sex ratio would be skewed in favour of males in both species and thus males would be the more competitive sex. Field and laboratory observations upheld this prediction, with males competing for females in both species. In R. tristis, males also competed for ownership of eggs, whereas females discriminated between males according to ownership of eggs. However, choosiness was not restricted to females in R. tristis. Observations suggested that R. tristis males discriminated between females according to their weight: heavier females, which were likely to oviposit sooner, were guarded for longer by males in a period of postcopulatory riding. We suggest that the primary function of postcopulatory riding is to prevent females from mating with conspecifics, thus reducing the possibility of sperm competition. This behaviour might also be an important prerequisite for the evolution of male care.

Temporal and spatial opportunities for polygamy in a monogamous seahorse, Hippocampus whitei

AbstractThe sex with the higher potential reproductive rate is expected to mate polygamously unless there are temporal or spatial constraints on mate availability. We investigated whether such constraints were evident in a population of the monogamous seahorse Hippocampus whitei (family Syngnathidae). Across the whole study site, breeding was more asynchronous than expected by chance. Our findings are thus compatible with the hypothesis that asynchronous breeding may promote and/or maintain monogamy. Asynchrony per se was unlikely to explain monogamy entirely, however, as temporal opportunities for polygamy remained and the males that were nearest one another had the lowest level of asynchrony. Moreover, each animal's home range overlapped with home ranges of potential mates other than their partner, implying a lack of spatial constraints on polygamy. We suggest that H. whitei mated monogamously because the benefits of polygamy were reduced by (1) only small differences in the potential reproductive rates of males and females and/or (2) a mate familiarity effect that increased reproductive success in successive matings. Further research could investigate relationships between mating pattern and varying intersexual differences in potential reproductive rates across syngnathid species.

Sexual selection and speciation in mammals, butterflies and spiders.

Recently refined evolutionary theories propose that sexual selection and reproductive conflict could be drivers of speciation. Male and female reproductive optima invariably differ because the potential reproductive rate of males almost always exceeds that of females: females are selected to maximize mate 'quality', while males can increase fitness through mate 'quantity'. A dynamic, sexually selected conflict therefore exists in which 'competitive' males are selected to override the preference tactics evolved by 'choosy' females. The wide variation across taxa in mating systems therefore generates variance in the outcome of intrasexual conflict and the strength of sexual selection: monandry constrains reproductive heterozygosity and allows female choice to select and maintain particular (preferred) genes; polyandry promotes reproductive heterozygosity and will more likely override female choice. Two different theories predict how sexual selection might influence speciation. Traditional ideas indicate that increased sexual selection (and hence conflict) generates a greater diversity of male reproductive strategies to be counteracted by female mate preferences, thus providing elevated potentials for speciation as more evolutionary avenues of male-female interaction are created. A less intuitively obvious theory proposes that increased sexual selection and conflict constrains speciation by reducing the opportunities for female mate choice under polyandry. We use a comparative approach to test these theories by investigating whether two general measures of sexual selection and the potential for sexual conflict have influenced speciation. Sexual size dimorphism (across 480 mammalian genera, 105 butterfly genera and 148 spider genera) and degree of polyandry (measured as relative testes size in mammals (72 genera) and mating frequency in female butterflies (54 genera)) showed no associations with the variance in speciosity. Our results therefore show that speciation occurs independently of sexual selection.

Parental investment, potential reproductive rates, and mating system in the strawberry dart-poison frog, Dendrobates pumilio

We studied the effect of relative parental investment on potential reproductive rates (PRRs) to explain sex differences in selectivity and competition in the dart-poison frog Dendrobates pumilio. We recorded the reproductive behavior of this species in a Costa Rican lowland rainforest for almost 6 months. Females spent more time on parental care than males, and `time out' estimates suggest that PRRs of males are much higher than than those of females, rendering females the limiting sex in the mating process. Males defended territories that provide suitable calling sites, space for courtship and oviposition, and prevent interference by competitors. Male mating success was highly variable, from 0 to 12 matings, and was significantly correlated with calling activity and average perch height, but was independent of body size and weight. Estimates of opportunity for sexual selection and variation in male mating success are given. The mating system is polygamous: males and females mated several times with different mates. Females were more selective than males and may sample males between matings. The discrepancy in PRRs between the sexes due to differences in parental investment and the prolonged breeding season is sufficient to explain the observed mating pattern i.e., selective females, high variance in male mating success, and the considerable opportunity for sexual selection.

Male potential reproductive rate influences mate choice in a bushcricket

Male bushcrickets,Requena verticalis, provide their mates with a proteinaceous nuptial gift, which functions both as paternal investment in offspring and to ensure sperm transfer. When nutrients are limited, males have a lower potential reproductive rate than females, so the operational sex ratio becomes female biased. Males are then expected to discriminate more in their choice of mate for two reasons: (1) the relatively higher female potential reproductive rate should reduce the costs of rejecting a female; (2) multiple mating by females should increase variance in female mate quality, because of first male sperm precedence. Males are known to discriminate against old females, which are more likely to have mated previously. Our objective in this study was to partition experimentally the influences of male potential reproductive rate (manipulated by diet) and variance in female quality (estimated by age) and to assess their relative influence on the level of mate choice of male bushcrickets. The potential reproductive rate of males had a great impact on their choosiness, whereas variance in female age had no effect. These results support recent theoretical models that predict costs, rather than benefits, will primarily influence the level of mate choice.

The effect of brood cannibalism on the operational sex ratio in parental teleost fishes

The operational sex ratio (OSR), an important determinant of the intensity of sexual selection, can vary with the population sex ratio and the potential reproductive rates of males and females. In parental teleosts, different forms of brood cannibalism, filial and non-kin, could affect the potential reproductive rates of males and females, and thereby the OSR. The direction of the effect of brood cannibalism on the OSR would depend on the sex of the cannibal and the parent. No evidence has been found that brood cannibalism can affect the OSR by altering the sex ratio.

Temperature affects male and female potential reproductive rates differently in the sex-role reversed pipefish, Syngnathus typhle

The differences in potential reproductive rate between the sexes can be used to predict the operational sex ratio and the patterns and intensity of mating competition and hence sexual selection in a population. This article describes how one environmental component, temperature, affects potential reproductive rates of the two sexes in the paternally brooding, sex-role reversed pipefish (Syngnathus typhle). Males brooded embryos much longer (on average 58 days) in cold water (about 10°C) than in warmer water (35 days at about 15°C). As a consequence, the potential reproductive rate (number of eggs brooded per day) of males was significantly higher in warm water. In females, however, potential reproductive rate, i.e., number of eggs produced per day given an unlimited access to mates, was not significantly different between temperatures. In both sexes, potential reproductive rate was positively related to body size. At both temperatures, females had the potential to reproduce faster than males. As a result, the operational sex ratio will become female biased and sex-roles reversed, as is the case in this species. Since temperature differently influenced the potential reproductive rates of males and females, with the sexual difference larger at lower temperatures, more intense female-female competition is predicted at low temperatures.

Sex-Role Reversal in the Black-Chinned Tilapia, Sarotherodon Melanotheron (RÜPpel) (Cichlidae)

AbstractIn the animal kingdom most species follow standard sex roles: males compete more intensely for mates and females exert greater mate choice. Recent theory suggests that the direction of sexual selection is the outcome of sexual differences in potential reproductive rates (PRRs): the sex with the higher PRR will compete for mates and the sex with the lower PRR will be most selective. This study tests the theory experimentally by examining competition for mates and mate choice in the black-chinned tilapia, Sarotherodon melanotheron, a paternal mouth brooding cichlid. In this species, the PRR of males is lower than that of females. In laboratory competition trials, females were more aggressive: they bit, chased and initiated mouth fights more often than males. Dominant females were also much better at monopolising potential mates compared to dominant males. A second experiment confirmed that males were choosy for size, preferring large partners over small ones, while females did not discriminate for size. Therefore, the prediction of sex role reversal (competitive females and discriminating males) is confirmed.

Quantification of role reversal in relative parental investment in a bush cricket

SEXUAL differences in courtship roles are thought to depend on the ratio of sexually available females to males1–3. This 'operational sex ratio'3 should be biased towards the sex investing least in reproduction because they will have the higher potential reproductive rate4. Thus relative parental investment1,2 is thought to underlie observed courtship roles. Typically, males have the lower investment and compete for choosy females2,3,5. But role reversal can occur when males invest parentally2,3. Recent evidence supports the contentions that role reversal reflects shifts in the potential reproductive rates of males and females4and shifts in the operational sex ratio6. Cases of male investment exceeding female investment in role-reversed species have not been found. In some insects, males invest in reproduction by providing the female with nutrients used for zygote production7,8. Here I report the measurement of male and female investment in reproduction for a nutrient-provisioning bush cricket (Orthoptera: Tettigoniidae) and demonstrate that reversals in relative parental investment underlie courtship role reversals seen in this species6,9.

Sexual selection and the potential reproductive rates of males and females

PRONOUNCED sex differences in mating competition are a prominent feature of many animal breeding systems. These differences are widely attributed to sex differences in parental investment1,2which bias the ratio of sexually receptive females to males3 (the operational sex ratio), generating more intense competition between members of one sex, usually males3–5. Unfortunately, relative parental investment1 is usually impossible to measure in species where both sexes invest in their offspring6,7 and there is currently no empirical basis for predicting the pattern of mating competition in these species. In contrast, the potential rate of reproduction by males and females (measured as the maximum number of independent offspring that parents can produce per unit time) is both more directly related to the operational sex ratio and more easily estimated in natural populations7. Here we show that among species where males care for the young, the sex with the higher potential reproductive rate competes more intensely for mates than the sex with the lower potential rate of reproduction.

Sexual Selection, Natural Selection, and a Fitness Trade-Off in a Tropical Frog with Male Parental Care

Previous articleNext article No AccessNotes and CommentsSexual Selection, Natural Selection, and a Fitness Trade-Off in a Tropical Frog with Male Parental CareDaniel S. TownsendDaniel S. Townsend Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 133, Number 2Feb., 1989 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/284915 Views: 8Total views on this site Citations: 7Citations are reported from Crossref Copyright 1989 The University of ChicagoPDF download Crossref reports the following articles citing this article:Kyle Summers, James Tumulty Parental Care, Sexual Selection, and Mating Systems in Neotropical Poison Frogs, (Jan 2014): 289–320.https://doi.org/10.1016/B978-0-12-416028-6.00011-6Wei-Chun Cheng, Yi-Huey Chen, Hon-Tsen Yu, J. Dale Roberts, Yeong-Choy Kam, T. Tregenza Sequential Polygyny During Egg Attendance is Rare in a Tree Frog and Does not Increase Male Fitness, Ethology 119, no.44 (Feb 2013): 286–295.https://doi.org/10.1111/eth.12062Yi-Huey Chen, Hon-Tsen Yu, Yeong-Choy Kam The Ecology of Male Egg Attendance in an Arboreal Breeding Frog, Chirixalus eiffingeri (Anura: Rhacophoridae), from Taiwan, Zoological Science 24, no.55 (May 2007): 434–440.https://doi.org/10.2108/zsj.24.434Flora Acuña Juncá, Miguel Trefaut Rodrigues The reproductive success of Colostethus stepheni (Anura: Dendrobatidae), Studies on Neotropical Fauna and Environment 41, no.11 (Apr 2006): 9–17.https://doi.org/10.1080/01650520500309883Heike Pröhl Territorial Behavior in Dendrobatid Frogs, Journal of Herpetology 39, no.33 (Sep 2005): 354–365.https://doi.org/10.1670/162-04A.1 References, (Jan 2000): 379–462.https://doi.org/10.1016/B978-012487460-2/50013-1T. H. Glutton-Brock, A. C. J. Vincent Sexual selection and the potential reproductive rates of males and females, Nature 351, no.63216321 (May 1991): 58–60.https://doi.org/10.1038/351058a0