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1.
Summary In order to understand the causes of sexual dimorphism, mate choice and size-related fecundity were studied in two pipefish species, Syngnathus typhle and Nerophis ophidion. Sexual dimorphism is more pronounced in N. ophidion; females are larger, have sexual colourings, and are more active during courtship. In S. typhle the sexes are alike in all these respects. Males brood their offspring in both species. In N. ophidion fecundity was positively correlated with both body size and the amount of sexual colouring in females. In males no correlation between body size and fecundity, or between body size and embryo size existed. Predictably, in mate choice experiments with equal-sized females, males chose females with more extensive sexual colourings. We explain sexual dimorphism in this species as a consequence of both natural selection (fecundity increases with size in females but not in males) and sexual selection (males prefer larger females). We argue that sexual size dimorphism did not evolve by selection minimizing overlap in food niches between the sexes, because food production is high in the Zostera beds where the fishes live, and no size dimorphism was found in the sympatrically occurring S. typhle. Furthermore, in N. ophidion dimorphism is not greater in a particular mouth character than in overall body size. In S. typhle egg size and the average number of eggs transferred per spawning were positively correlated with female body size. Apparently more energy per offspring was provided by larger males than by smaller males, and larger males also carried more offspring. As predicted, large mates were preferred by both sexes in mate choice experiments. This is explicable in terms of both natural selection (fecundity increases with size in both sexes) and sexual selection (both sexes prefer large mates). As a consequence of selection acting in the same direction in both sexes, sexual dimorphism is absent in S. typhle. 相似文献
2.
Sex ratios,mating behavior and sexual size dimorphism of the northern water snake,Nerodia sipedon 总被引:4,自引:0,他引:4
Patrick J. Weatherhead Frances E. Barry Gregory P. Brown Mark R. L. Forbes 《Behavioral ecology and sociobiology》1995,36(5):301-311
Competition among males to mate is generally associated with male-biased size dimorphism. In this study we examine mating behavior in the northern water snake (Nerodia sipedon), a species in which males are much smaller than females despite substantial competition among males to mate. Competition among males was a consequence of a male-biased operational sex ratio due to slightly higher female mortality from a birth sex ratio of 1 : 1, and, in 1 year, more synchronous and longer mating activity by males. Approximately one-third of both males and females appeared not to mate in a given year. Larger males were generally more likely to attempt mating, but size did not explain the variance in the number of aggregations in which individual males participated. Within aggregations, males that were successful at achieving intromission were larger than unsuccessful males in 1 of 2 years. Variation in condition (mass relative to length) and relative tail length were not generally useful predictors of either mating effort or success in males. Because large size was often advantageous to males, sexual size dimorphism appeared not to be a consequence of sexual selection favoring smaller males. Because sexual dimorphism was evident at birth, and both males and females matured sexually at about 4 years, sexual dimorphism was not simply a consequence of one sex growing at the maximum rate for longer. Female fecundity increased with size, and sex differences in size-fecundity relations may underly the pattern of sexual size dimorphism. However, because multiple mating by females is common, sperm competition is likely to be important in determining male reproductive success. Therefore, allocation of energy to sperm rather than growth may also prove to be an important influence on male growth rates and sexual size dimorphism. 相似文献
3.
The aim of this study was to investigate reproductive strategies and their consequences in gray mouse lemurs (Microcebus murinus), small solitary nocturnal primates endemic to Madagascar. Previous reports of sexual dimorphism in favor of males and females,
respectively, a high potential for sperm competition and pheromonal suppression of mating activity among captive males, led
us to investigate mechanisms of intrasexual competition in a wild population. Based on 3 years of mark-recapture data, we
demonstrate that sexual dimorphism in this species fluctuated annually as a result of independent changes in male and female
body mass. Male body mass increased significantly prior to the short annual mating season. Because their testes increased
by 100% in the same period and because their canines are not larger than those of females, we suggest that large male size
may be advantageous in searching for estrous females and in enabling them to sustain periods of short-term torpor. In contrast
to reports from captive colonies, we found no evidence for two morphologically distinct classes of males. Finally, we also
show that most adult males are active throughout the cool dry season that precedes the mating season, whereas most adult females
hibernate for several months. This is in contrast to other solitary hibernating mammals, where males typically emerge 1–2
weeks before females. Thus, this first extended field study of M.␣murinus clarified previous conflicting reports on sexual dimorphism and male reproductive strategies in this primitive primate by
showing that their apparent deviation from predictions of sexual selection theory is brought about by specific environmental
conditions which result in sex-specific life history tactics not previously described for mammals. A general conclusion is
that sexual selection can operate more strongly on males without resulting in sexual dimorphism because of independent selection
on the same traits in females.
Received: 6 July 1997 / Accepted after revision: 28 March 1998 相似文献
4.
Sexual size dimorphism, in which one sex is larger than the other, occurs when body size has differential effects on the fitness
of males and females. Mammals and birds usually have male-biased size dimorphism, probably because of strong sexual competition
among males. Invertebrates usually have female-biased size dimorphism, perhaps because their inflexible exoskeletons limit
ovary size, leading to a strong correlation between female body size and fecundity. In this paper, we test whether an additional
factor, the type of parental care provided, affects the degree of sexual size dimorphism. Among wasps and bees, there is a
contrast between provisioning taxa, in which females must gather and transport heavy loads of provisions to nests they have
constructed, and non-provisioning taxa, in which females lay eggs but do not construct nests or transport provisions. Males
have no role in parental care in either case. An analysis of British wasps and bees shows that provisioning taxa have significantly
more female-biased size dimorphism than non-provisioning taxa. This is true for simple cross‑species comparisons and after
controlling for phylogeny. Our data imply that the demands of carrying provision loads are at least part of the explanation
for this pattern. Thus, sexual size dimorphism is greatest in pompilid wasps, which carry the heaviest prey items. Bees, which
transport minute pollen grains, exhibit the least dimorphism. We also find that cavity‑nesting species, in which nest construction
costs may be minimized, exhibit reduced dimorphism, but this was not significant after controlling for phylogeny. 相似文献
5.
Sexual selection is often characterized by polygynous breeding systems, size dimorphism, and skewed operational sex ratios.
Koalas are sexually dimorphic in multiple domains, yet are absent from the literature on sexual selection and the structure
of their mating system is unclear. We provide the first documentation of the strength of sexual selection in koalas by using
microsatellite markers to identify sires. We combine the genetic data with morphological data in order to assess the role
of body size in regulating reproductive output. During our 4-year study, 37% of males were identified as possible sires. Males
were significantly larger than females, with sires heavier than non-sires. Male body mass correlated with annual reproductive
output, with Crow’s Index of Opportunity for Selection revealing that variation in male reproductive success was threefold
higher than that of females. Since it appears that male koalas rarely engage in physical confrontations over access to females,
size dimorphism could be based upon non-agonistic competition and/or female mate choice. We propose that size dimorphism in
koalas evolved as a consequence of endurance rivalry promoting vocal sexual advertisements that attract females. We suggest
that female choice is a key mediator of male reproductive output. 相似文献
6.
Alan G. McElligott Martin P. Gammell Hilda C. Harty Dean R. Paini Desmond T. Murphy James T. Walsh Thomas J. Hayden 《Behavioral ecology and sociobiology》2001,49(4):266-272
Sexual size dimorphism may evolve as a result of both natural and sexual selection. In polygynous mammals, the main factor resulting in the evolution of large body size in males is the advantage conferred during competition for mates. In this study, we examined whether sexual selection acts on body size in mature fallow bucks (Dama dama) by examining how the following traits are inter-related: age, body (skeletal) size, body mass, prerut dominance rank, rut dominance rank and mating success. This is the first study to examine how all these factors are together related to the mating success of a large sexually dimorphic and polygynous mammal. We found that male mating success was directly related to body size, but not to body mass. However body mass was related to prerut dominance rank which was in turn strongly related to rut dominance rank, and thus there was an indirect relationship between mating success and body mass. Rut dominance rank was the variable most strongly related to mating success. Mating success among mature males was unrelated to age. We conclude that larger mature fallow bucks have advantages over other males when competing for matings, and sexual selection therefore continues to act on sexual size dimorphism in this species. Heavier fallow bucks also have advantages, but these are mediated through the dominance ranks attained by males before the rut. 相似文献
7.
While factors affecting body growth have been extensively studied, very little is known about the factors likely to affect the sexual size dimorphism (SSD) in polygynous mammals. Based on the carcass mass of 24420 male and female moose recorded in 14 Norwegian populations, we examine three hypotheses to explain geographical variation in SSD. First, SSD is expected to decrease when the relative density of animals (for a given habitat quality) increases, because resource limitation at high population densities is assumed to affect body growth of males more than females. Second, because males are selected to invest in growth more than females, environmental seasonality and related improvement of the forage quality during the short and intense growing season are expected to increase SSD. Third, by decreasing the proportion of adult males in the population, resulting in start of rutting earlier in life, hunting may decrease the SSD by increasing the reproductive cost of young males. We found that males grew faster and for a longer time of their life than did females and thus were heavier (-24%) when they reached adulthood. Sexual size dimorphism was independent of density but was higher in areas with short growing seasons. The low SSD in populations with largely adult female-biased sex ratios (males per female) shows that male body growth decreases with a decreasing proportion of adult males in the population. Our results indicate that geographical variation in moose SSD is influenced by divergent responses in the sexes to ecological factors affecting body growth. 相似文献
8.
Field studies demonstrate that natural populations of a group of water striders (Heteroptera: Gerridae) that share a common
mating system are characterized by weak assortative mating by size and by large sizes of mating males and females relative
to single individuals. This study presents an experimental assessment of the components of mating that may contribute to these
mating patterns. The effects of male and female body size on each of three components of mating were studied in three water
strider species in the laboratory. Large females of all three species mated more frequently, copulated for longer and were
guarded longer than small females. Large males mated more frequently than small males in all three species, and also guarded
females for longer in the two species where the average of mate guarding was long. However, we found an antagonistic effect
of male size on copulation duration: small males copulated for longer than large males in all three species. We show that
the combined effects of these size biases mimic the mating patterns found in the wild, e.g. weak and variable assortative
mating, and stronger and less variable size ratios of mating versus non-mating females relative to males. We suggest that
the antagonistic effects of male size on copulation and guarding duration may be a key source of interpopulational variation
in assortative mating and sexual selection on male size. Further, neither spatial or temporal covariation in size, nor mechanical
constraints, caused the assortative mating observed here in this group of water striders. Some combination of male and female
choice (either active or passive forms) of large mates and male-male exploitation competition for mates play potentially important
roles in producing population level assortative mating in water striders.
Received: 17 March 1995/Accepted after revision: 28 October 1995 相似文献
9.
A test of male mating and hunting success in the kestrel: the advantages of smallness? 总被引:2,自引:0,他引:2
H. Hakkarainen E. Huhta Katriina Lahti Päivi Lundvall Tapio Mappes Pasi Tolonen Jürgen Wiehn 《Behavioral ecology and sociobiology》1996,39(6):375-380
We tested female choice for male wing and tarsus length and body mass in the kestrel (Falco tinnunculus), a species in which males average about 10% smaller than females. We also studied how male characters are related to their
hunting success. In the laboratory, females preferred lighter males with shorter tarsi as mates, if the difference in those
characters between competing males was larger than average. Lighter and shorter-winged males seemed to be better hunters than
heavier and longer-winged males. Field observations in a year in which voles were scarce suggested that shorter-winged males
were also better food providers in courtship feeding than longer-winged males,although in good vole years such a relationship
was not found. We argue that females may prefer to pair with smaller males, because they have higher flight performance and
better hunting success than heavier males. By doing so, females may gain direct breeding advantages. We conclude that both
female choosiness and the hunting efficiency of males well contribute to reversed sexual size dimorphism (RSD, females larger
than males) in the kestrel.
Received: 18 July 1995/Accepted after revision: 17 August 1996 相似文献
10.
Effect of size and sex on buoyancy in the oyster toadfish 总被引:1,自引:0,他引:1
In 1991 we examined the developmental consequences of swimbladder growth and sexual dimorphism on specific gravity (SG) and percent buoyancy (%B) in the oyster toadfish (Opsanus tau Linnaeus collected in the York River, Virginia) and tested the hypothesis that large ovaries compensate for the buoyancy conferred by a smaller swimbladder in females. Weight in water (Ww) increased as a linear function of weight in air (Wa) for both sexes, and there were no sexual differences between regressions. SG and %B did not change with Wa, indicating proportional growth of body and swimbladder. SG averaged 1.049±0.002 and %B 3.183±0.160. Removal of the gonads had no significant effect on Ww, SG or %B, indicating that the larger ovaries did not compensate for buoyancy associated with a smaller swimbladder. In fact testis and ovary SG did not differ significantly from values for intact fish. However, gonad composition changed with development: testis SG and % fat decreased with gonosomatic index, whereas overy SG and % fat increased, but % water decreased. Removal of the swimbladder significantly increased SG to 1.083 and %B to 6. Swimbladder volume increased linearly with Wa and was significantly larger in males; adjusted means were 11.40±0.83 and 8.94±0.83 ml for males and females, respectively. Variability in bladder volumes contributed to the absence of sexual differences in SG and may be permissible because negative buoyancy imparts minimal selective advantage for precise volume and buoyancy control. The absence of a relationship between fish buoyancy and sexual dimorphism in bladder size supports evidence that sexual dimorphism in the swim-bladder relates to its function in sound production. 相似文献
11.
Observations have been made on the locomotory behaviour and swimming performances of the Norway lobster, Nephrops norvegicus (L.), fitted with an acoustic transmitter ventrally under the cephalothorax. The walking behaviour of adult males (44 mm carapace length) appeared to be unaffected, but the tag caused significant reductions in certain measures of tail-flip swimming performance such as swimming speed and endurance. Flume-tank experiments in low water currents suggested that the transmitter would increase hydrodynamic drag during swimming by 9 to 32%, depending on lobster size. Given the weight and dimensions of the acoustic transmitters currently available, it is considered advisable to confine acoustic tracking studies to relatively large N. norvegicus.Correspondence to: C. J. Chapman 相似文献
12.
Parental investment, potential reproductive rates, and mating system in the strawberry dart-poison frog, Dendrobates pumilio 总被引:1,自引:0,他引:1
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.
Received: 9 June 1998 / Received in revised form: 27 March 1999 / Accepted: 3 April 1999 相似文献
13.
Summary Over five hundred adult longhorn milkweed beetles, Tetraopes tetraophthalmus, were individually marked and their copulatory success followed for one month in a pasture of Asclepias syriaca in northern Indiana, USA. Migration of beetles from the field site was greatest from areas of low population density. Dispersal was significantly greater for males experiencing low copulatory success; a similar but nonsignificant trend was observed for females. Large males, which displayed greater site tenacity than small males, copulated more frequently than small males because of their ability to displace small males from females. Both large and small males demonstrated a preference for large females in laboratory tests. Male preference in combination with aggressive displacement of small males results in size-assortative mating which was much stronger under conditions of high population density. It contributes to variance in male reproductive success since female size is known to be correlated with fecundity and offspring viability. Variance in copulatory success is similar for males and females, suggesting that both sexes experience similar intensities of sexual selection with respect to this component of reproductive success. Futhermore, comparison of this with other studies suggests that the intensity of sexual selection among males is positively correlated with the variance in body size which appears to be under both stabilizing and directional sexual selection in males but not in females. 相似文献
14.
Francesco Ferretti Alessia Costa Marcello Corazza Venusta Pietrocini Gloria Cesaretti Sandro Lovari 《Behavioral ecology and sociobiology》2014,68(8):1335-1344
Availability of food resources and individual characteristics can influence foraging behaviour, which can differ between males and females, leading to different patterns of food/habitat selection. In dimorphic species, females are usually more selective in food choice, show greater bite rates and spend more time foraging than males. We evaluated sexual differences in foraging behaviour in Apennine chamois Rupicapra pyrenaica ornata, during the warm season, before the rut. Both sexes selected nutritious vegetation patches and spent a comparable amount of time feeding. However, males had a significantly greater feeding intensity (bite rate) and a lower search effort for feeding (step rate), as well as they spent more time lying down than females. Females selected foraging sites closer to refuge areas than males. In chamois, sexual size dimorphism is seasonal, being negligible in winter–spring, but increasing to 30–40 % in autumn. Our results suggest that males enhance their energy and mass gain by increasing their food intake rate during the warm season, to face the costs of the mating season (November). Conversely, females seem to prioritize a fine-scale selection of vegetation and the protection of offspring. A great food intake rate of males in the warm season could have developed as a behavioural adaptation leading herbivores to the evolutionary transition from year-round monomorphism to permanent dimorphism, through seasonal dimorphism. 相似文献
15.
Male velvet swimming crabs [Necora puber (L.)] were observed to engage in long and vigorous agonistic interactions to gain possession of a sexually receptive female. The role of agonistic behaviour in male mate competition in this species was examined by investigating the effect of the perceived presence of sexually receptive females on interactions between males. Exposing male crabs to water conditioned by sexually receptive females resulted in prolonged interactions, with a greater incidence of potentially injurious behaviour than interactions between control crabs, exposed only to sea water. Maleconditioned water also resulted in more offensive behaviour, but these interactions were of shorter duration and not significantly different from sea water controls. Agonistic superiority was strongly correlated with contestant relative size when males were exposed to male-conditioned water or sea water, but not when exposed to female-conditioned water. Overall, the results conformed with the general predictions of game theoretic models in relation to the influence of resource value on agonistic behaviour. Crabs were more persistent and probably incurred greater fitness costs in the perceived presence of a sexually receptive female, when interactions may have been resolved on the basis of factors more closely related to actual fighting ability than the relative body sizes of contestants. 相似文献
16.
Sexual dimorphism, reproductive strategy, and human activities determine resource use by brown bears
Despite significant sexual dimorphism and differing reproductive strategies in carnivores, sexual segregation is rarely studied and is often overlooked in the management of wild populations. Potential nutritional constraints imposed by sexual dimorphism and differing reproductive strategies between the sexes have important implications, particularly when combined with differential effects of human activities on sex and age classes. We examined the effects of sexual dimorphism, reproductive strategies, and human activities (bear-viewing and hunting) on resource use by different sex and age classes of brown bears (Ursus arctos). Sexual segregation of habitat use and effects of experimental bear-viewing were quantified at a single site in south-central Alaska, U.S.A., by capturing, collaring, and observing brown bears at a salt marsh and salmon stream. Effects of salmon capture rate, availability of alternative salmon runs, harvest pressure, and numbers of annual visitors on sex and age class use were examined from data collected or previously published from 13 other sites. Bear-viewing sites on salmon streams where salmon capture rates were low (<4 salmon/hour) resulted in low use by adult males (<10% of all bears), except for sites with falls. However, maximum male use of viewing areas also depended on the availability of alternative salmon streams and harvest pressure. Use of habitats by females with dependent young was significantly related to the prevalence of adult males at the site. Thus, both sexual dimorphism and differing reproductive strategies led to sexual segregation in habitat use by bears. As a result of infanticide, females with young appear to prioritize avoidance of male bears over avoidance of humans when choosing habitats, in contrast to responses documented in herbivores. Because carnivores often exhibit both sexual dimorphism and infanticide, selection for sexual segregation is likely to be high. In these cases, the nutritional demands of large adult males, balanced with responses to human activity, drive dynamic temporal and spatial distributions of individuals in the population. 相似文献
17.
Flexible traits can be crucial in helping animals meet the challenges of a highly variable environment. We examined whether coral reef fishes systematically alter their swimming behaviour in response to temporal changes in hydrodynamic conditions. Exploiting site-based differences in wave energy impinging on reef habitats over calm and rough weather, we found many reef fishes changed their swimming behaviour alongside increases in wave-driven water motion. Most fishes tended to orient their bodies parallel to oncoming wave-driven flow and recruited additional stabilising fins during rough weather; such changes in swimming behaviour aid stability and minimise drag. However, not all species displayed such flexibility, with fishes possessing highly tapered pectoral fins and high levels of swimming performance continuing to successfully navigate reef habitats without significantly altering their swimming behaviour. We highlight how labile behaviours augment the morphology and performance of species to underpin their occupation of habitats subject to variable environmental conditions. 相似文献
18.
Jennifer D. Cooper Peter M. Waser Eric C. Hellgren Timothy M. Gabor J. A. DeWoody 《Behavioral ecology and sociobiology》2011,65(4):775-785
Sexual dimorphism is common in polygynous species, and there is clear evidence that both intra-sexual competition and female
preferences can drive the evolution of large body size in males. In contrast, sexual monomorphism is often argued to reflect
a relaxation of male mate competition or an intensification of resource competition among females. Alternatively, it might
imply opportunities for females to circumvent or counteract male mate competition in a polygynandrous mating system. We test
the prediction that sexual monorphism is associated with polygynandry in the collared peccary (Pecari tajacu, Tayassuidae), a social ungulate closely related to the old-world suids. The genetic mating system in the Tayassuidae is
unknown, but its sexual monomorphism presents a striking contrast to the strong size dimorphism found in most Suidae, so that
a departure from the polygynous system common in Suidae would be noteworthy. We characterized genetic relationships among
adults within herds in three geographically distinct populations, assigned parents to 75 offspring, and tested for skew in
individual reproductive success. Parentage assignment data indicated that multiple males sire offspring within a herd, and
in the population for which genetic data were most complete, 19% of parentage assignments were potentially sired by extra-herd
males. Some litters have multiple sires, and neither males nor females monopolized reproduction, even in small herds. This
result supports our prediction and suggests that sexual monomorphism may either select for or be an evolutionary consequence
of a promiscuous mating system. 相似文献
19.
Mating systems evolve with sexual size dimorphism (SSD) in many animals. Mating systems with males larger than females occur when males compete for female access or guard territories, while mating systems with group mating tend to occur in species where females are the same size or larger than males. In addition to variation in SSD with mating system, sperm competition varies among mating systems in predictable patterns. We examined the evolution of mating systems with SSD and testes mass in 111 North American Cyprinidae fishes using phylogenetic comparative methods. Our results demonstrate that the evolution of mating systems in Cyprinidae fishes is from ancestral taxa that are group spawners with females the same size or larger than males to pair spawning systems where males tend to be larger than females. We used an additive model to predict male and female body size from testes mass and mating system. Only mating system varied predictably with SSD. Our results for analyses of hyperallometry (Rensch’s rule) were that individual species of Cyprinidae can have hyperallometry for SSD, but the pattern is not present across all taxa. 相似文献
20.
Black spots and female association preferences in a sexual/asexual mating complex (Poecilia, Poeciliidae, Teleostei) 总被引:1,自引:0,他引:1
Michael Tobler Martin Plath Heike Burmeister Ingo Schlupp 《Behavioral ecology and sociobiology》2006,60(2):159-165
We investigated whether female association preferences for males are influenced by black spot disease (BSD), a parasite induced change of the host phenotype. We compared three different species of fish: a gynogenetic hybrid species, Poecilia formosa (amazon molly) and two sexual species (Poecilia latipinna and Poecilia mexicana), which were involved in the natural hybridisation leading to the amazon molly. Contrary to their sexual relatives, asexual amazon mollies significantly avoided images of males infected with black spot disease. We propose that amazon molly females have direct fitness benefits from choosing healthy males. The adaptive significance of the preference for BSD-uninfected males in the asexual amazon molly is yet unclear but may involve avoidance of predation or parasite infection as well as increased sperm availability. 相似文献