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1.
Peter M. Kappeler 《Behavioral ecology and sociobiology》1997,41(2):115-127
The primates of Madagascar (Lemuriformes) deviate from fundamental predictions of sexual selection theory in that polygynous
species lack sexual dimorphism, have even adult sex ratios and often live in female-dominated societies. It has been hypothesized
that intrasexual selection in these species is either reduced or primarily focused on traits related to scramble competition.
The goal of this study was to examine these hypotheses by studying the mating system of a solitary nocturnal species, Mirzacoquereli. During a 4-year field study in western Madagascar, I captured and followed 88 individually marked animals. I found that
adult males were significantly larger than females, providing the first evidence for sexual size dimorphism in lemurs. In
addition, the adult sex ratio was biased in favour of females in 3 out of 4 years. There was no significant sex difference
in canine size, however. Males showed pronounced seasonal variation in testis size with a 5-fold increase before and during
the short annual mating season. During the mating season, males had more injuries than females and more than quadrupled their
home ranges, overlapping with those of more than ten females, but also with about the same number of rivals. Only about one
social interaction per 10 h of observation was recorded, but none of them were matings. Together, these results indicate that
these solitary lemurs are clearly subject to intrasexual selection and that male-male competition is primarily, but not exclusively,
of the scramble type. In addition, they suggest that the above-mentioned idiosyncracies may be limited to group-living lemurs,
that social systems of solitary primates are more diverse than previously thought, and that the temporal distribution of receptive
females is responsible for this particular male mating strategy.
Received: 11 January 1997 / Accepted after revision: 18 April 1997 相似文献
2.
Juan C. Alonso Marina Magaña Carlos Palacín Carlos A. Martín 《Behavioral ecology and sociobiology》2010,64(10):1589-1600
We examined how mating success varied in relation to age, weight, body size, and display behavior among great bustard Otis tarda males. The estimated mating success was strongly skewed, with 45% of adult males being involved in copulation attempts and
only 9.7% actually seen copulating successfully. Unlike most birds, body size continued increasing in great bustards several
years after reaching sexual maturity. Age, weight, and display effort were all significant and independent predictors of male
mating success. The higher display effort involved performing longer full-display bouts. Older males could detach from the
male flock earlier in the season as well as on each day and spend longer seasonal and daily periods displaying as solitary
birds, which contributed to increase their mating success. In contrast, males weighing more did not invest more in display,
which suggests that they could be recognized as dominants by other males and selected by females through assessment of their
plumage sexual traits. In contrast to most other bird species, the system described for great bustards resembles that found
in some lek-mating ungulates, where social rank is a complex trait determined by both age and mass, and as in these mammals,
it suggests that sexual selection continues to favor a high male weight in this extremely sexually dimorphic species. 相似文献
3.
Sjouke A. Kingma István Szentirmai Tamás Székely Veronika Bókony Maarten Bleeker András Liker Jan Komdeur 《Behavioral ecology and sociobiology》2008,62(8):1277-1288
Melanin-based ornaments are often involved in signaling aggression and dominance, and their role in sexual selection is increasingly
recognized. We investigated the functions of a melanin-based plumage ornament (facial ‘mask’) in male Eurasian penduline tits
Remiz pendulinus in the contexts of male–male aggression, mating success, and parental care. The penduline tit is a passerine bird with a
unique mating system in which both sexes may mate with several mates in a breeding season, and one (or both) parent deserts
the clutch. Our study revealed that mask size of males is more likely an honest signal used by females in their mate choice
decisions than a trait involved in male–male competition. First, mask size increased with both age and body condition, indicating
that the mask may signal male quality. Second, males with larger masks paired more quickly and had more mates over the breeding
season than males with smaller masks. Third, we found no evidence that male mask size signals male–male aggression or dominance
during competitive encounters. The increased mating success of large-masked males, however, did not translate into higher
reproductive success, as nestling survival decreased with mask size. Therefore, we conclude that there is either no directional
selection on male mask size or males with larger masks receive indirect, long-term benefits. 相似文献
4.
Male-biased size dimorphism is usually expected to evolve in taxa with intense male–male competition for mates, and it is
hence associated with high variances in male mating success. Most species of pycnogonid sea spiders exhibit female-biased
size dimorphism, and are notable among arthropods for having exclusive male parental care of embryos. Relatively little, however,
is known about their natural history, breeding ecology, and mating systems. Here we first show that Ammothella biunguiculata, a small intertidal sea spider, exhibits male-biased size dimorphism. Moreover, we combine genetic parentage analysis with
quantitative measures of sexual selection to show that male body size does not appear to be under directional selection. Simulations
of random mating revealed that mate acquisition in this species is largely driven by chance factors, although actual paternity
success is likely non-randomly distributed. Finally, the opportunity for sexual selection (I
s), an indirect metric for the potential strength of sexual selection, in A. biunguiculata males was less than half of that estimated in a sea spider with female-biased size dimorphism, suggesting the direction of
size dimorphism may not be a reliable predictor of the intensity of sexual selection in this group. We highlight the suitability
of pycnogonids as model systems for addressing questions relating parental investment and sexual selection, as well as the
current lack of basic information on their natural history and breeding ecology. 相似文献
5.
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
6.
Female distribution affects mate searching and sexual selection in male northern water snakes (Nerodia sipedon) 总被引:2,自引:0,他引:2
Mating systems and sexual selection are assumed to be affected by the distribution of critical resources. We use observations
of 312 mating aggregations to compare mate-searching success of male northern water snakes (Nerodia sipedon) in two marshes in which differences in mating substrate availability resulted in more than fourfold differences in female
dispersion. Reproductive males had significantly larger home ranges where females were dispersed than where females were clumped.
The number of females encountered by males increased significantly with male home range size where females were dispersed,
and decreased significantly where females were clumped. Where females were clumped, males were more likely to encounter other
males when they located females. We found no evidence in either population that mate searching was energetically expensive
or that males with relatively more energy had larger home ranges. However, males with greater fat reserves at the start of
the season participated in more mating aggregations when females were dispersed, suggesting that fat reserves could affect
a male’s willingness to attempt mating or to persist in aggregations. When females were dispersed there was weak stabilizing
selection acting to maintain male body size (β=–0.14), but strong directional selection favoring larger (β=0.50) and fatter
(β=0.37) males. Over 7 years, the intensity of selection favoring larger males varied substantially (β=0.14–1.15), but that
variation was not related to variation in the operational sex ratio. We found no evidence of directional selection on either
body size (β=0.05) or fat reserves (β=0.10) of males when females were spatially clumped. Overall, the distribution of females
had a pronounced effect on male behavior, on the factors that affected male success in locating females, and probably on the
extent of sperm competition once females had been located.
Received: 23 November 1998 / Received in revised form: 9 August 1999 / Accepted: 18 August 1999 相似文献
7.
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
8.
In many salmonid species, males exhibit morphological dimorphism associated with alternative mating behaviors. ”Precocious
males” have a small body size with little or no development of sexual characters and adopt sneaking to gain access to females,
while ”migratory males” of large body size and well-developed secondary sexual characters fight. We quantified selection on
precocious male parr of masu salmon (Oncorhynchus masou) under simulated natural conditions to examine the contribution of morphology to sneaking success. In contrast to the prediction
that sneaking behavior favors small body size, we detected selection favoring relatively large body size for sneaking success.
This selection pressure was caused by the dominance hierarchy within parr and may have been facilitated by indifference of
dominant migratory males to parr. Unlike the secondary sexual characters exhibited by migratory male salmon, such as the hooked
snout and humped back, no morphological characters other than body size contributed to the reproductive success of masu salmon
parr. This non-contribution may have been responsible for the lack of development of sexual characters in precocious males.
Received: 15 November 1999 / Accepted: 20 May 2000 相似文献
9.
Socioecological theory predicts that the distribution of fertile females in space and time is the major determinant of male spacing behavior and mating strategies. Using a small nocturnal Malagasy primate, the gray mouse lemur (Microcebus murinus), we determined the spatiotemporal distribution of estrous females during the brief annual mating season to examine the predictive power of the socioecological model for male mating strategies. Mouse lemurs are particularly interesting in this respect because this polygynous species is characterized by seasonal reproduction, seasonally reversed sexual dimorphism, and relatively large testes. All resident animals in our 8-ha study area, a total of 30 adult males and 27 adult females, were individually marked and regularly recaptured to determine female reproductive status and to obtain home range data. We found that the mating season is limited to 4 weeks following female emergence from hibernation. Only 3-9 females could have synchronized estruses during a given week, indicating a moderately high male monopolization potential. However, receptive females were not spatially clumped and male ranges overlapped with those of many other rivals. Therefore, we suggest that individual powerful males may be unable to defend exclusive permanent access to receptive females because of prohibitive costs of range defense resulting from the strongly male-biased operational sex ratio and the corresponding intruder pressure. Our general conclusions are (1) that the socioecological model provides a useful heuristic framework for the study of mating systems, but that (2) it does not specify the degree of spatiotemporal clumping of receptive females at which male mating strategies switch among mate guarding, spatial exclusion of rivals, and roaming, and that (3) the operational sex ratio can have profound effects on male mating strategies as well. 相似文献
10.
R. G. Harcourt J. J. Kingston M. F. Cameron J. R. Waas M. A. Hindell 《Behavioral ecology and sociobiology》2007,61(4):643-652
For polygynous mammals with no paternal care, the number of offspring sired is often the sole measure of male reproductive
success. The potential for polygyny is highest when resources or other environmental factors such as restricted breeding sites
force females to aggregate. In these circumstances, males compete intensely for females and mating success may vary greatly
among males, further intensifying selection for those traits that confer an advantage in reproduction. Hence, determinants
of male success in competition for females are likely to be under strong sexual selection. Paternity analysis was used in
conjunction with measures of age, site fidelity, and behavior during the breeding season to assess variance in male breeding
success in Weddell seals (Leptonychotes weddellii) breeding at Turtle Rock, McMurdo Sound (77.727S, 166.85E) between 1997 and 2000. Paternity could be assigned to 177 pups
at relaxed or 80% confidence level or 111 pups at strict or 95% confidence levels. Weddell seals at Turtle Rock show a modest
degree of polygyny with the greatest number of pups sired by any individual male in a single season equalling 5 or ∼10% of
the pups born. Over four consecutive years, most (89.2%) males sired at least one pup. In a generalized linear model (GLM),
age and the age first seen at the study site as an adult were unrelated to mating success, but adult experience, either site-specific
or elsewhere in McMurdo Sound, over the reproductive life span of males explained nearly 40% of variance in total mating success
with 80% confidence and 24% of variance at 95% confidence. While learning where females are likely to be may enhance male
reproductive success, aquatic mating reduces the ability of males to monopolize females, and thereby increases equity in mating
success. 相似文献
11.
David J. Able 《Behavioral ecology and sociobiology》1999,46(6):423-428
Darwin predicted that scramble competition for access to reproductive females would result in sexual dimorphism of locomotory
structures, but direct evidence for this is extremely rare. I examined the relationship between variation in tailfin size
and mating success in a field and laboratory study of red-spotted newts, Notophthalmus viridescens. Over three breeding seasons, male tailfin size was positively correlated with variation in male amplexus frequency, and
indirectly correlated with male insemination frequency. In a laboratory study, I confirmed that males' ability to capture
females is affected by variation in tailfin size. This is the first study to show that naturally occurring variation in male
locomotory structures affects male mating success. It corroborates the prediction that scramble competition leads to sexual
selection on locomotory structures and, potentially, to dimorphism in these structures.
Received: 16 April 1999 / Received in revised form: 16 May 1999 / Accepted: 12 June 1999 相似文献
12.
Functions of the major cheliped in pagurid hermit crabs have been studied in fights for shells. The major cheliped often shows
sexual size dimorphism, suggesting that sexual selection favors the development of the male major cheliped. The function of
the major cheliped in male–male competition was examined in Pagurus nigrofascia collected from April to June 2009 on the intertidal rocky shore in southern Hokkaido, Japan (41°N, 140°E). Sexual size dimorphism
of the major cheliped was observed, and precopulatory guarding males had larger major chelipeds than solitary ones. Guarding
males used the major cheliped to deter intruders during competitive interactions. Males without a major cheliped were disadvantaged
even if they were larger than opponents and had ownership. Cheliped size affected the outcomes of contests between similar
sized males. This suggests that the male major cheliped in P. nigrofascia protects mates from competitors and, consequently, enhances male mating success. Sexual selection may favor the development
of the major cheliped in male pagurids. 相似文献
13.
Sex-specific interests over the maximization of reproductive success lead to an inter-sexual conflict over the optimal mating system in a species. Traditionally, the outcome of this inter-sexual conflict has been studied from the male perspective but it also depends on female mating strategies, such as manipulating the temporal distribution of sexual activity, advertisement, and mate choice. We used a small nocturnal primate, the gray mouse lemur (Microcebus murinus) to determine the relative importance of female mating strategies on the outcome of this conflict in a species where females are solitary during their activity period. We studied their mating behavior over three consecutive annual mating seasons and determined the genetic relationships among more than 300 study animals to quantify individual reproductive success. We found that most females were receptive asynchronously. Females did not exhibit any obvious direct mate choice, probably due to a highly male-biased operational sex ratio and the corresponding costs of choosiness. However, females exercised indirect choice for multiple matings. They mated with 1–7 males up to 11 times during their single night of receptivity. As a result, mixed paternity was common but heavier males sired more offspring, meaning that indirect female choice for superior males cannot be excluded. Females exhibited a mixed mating strategy, avoiding costly direct mate choice but still counteracting male efforts to monopolize mating, successfully increasing genetic variability among offspring. Thus, females had a major influence on the outcome of the inter-sexual conflict despite male monopolization attempts.Communicated by J. Setchell 相似文献
14.
A comprehensive understanding of sexual selection requires knowledge of the traits and mechanisms responsible for increasing a male’s paternity share (proportion of progeny sired) relative to that of other males mating with the same female. In this study we manipulated by starvation the expression of traits that might influence male paternity share in Tribolium castaneum. We then conducted experiments to examine how male starvation affects male performance during sequential episodes of sexual selection from mating to progeny production, and investigated female control over specific stages by using live vs dead females. Comparison of starved vs fed males revealed that T. castaneum females have control over spermatophore transfer during mating, as live females rejected inseminations by starved (“low quality”) males. None of the measured male copulatory behaviors (leg-rubbing frequency, asymmetry, and percent of time spent rubbing) affected the probability of successful insemination, but the last two were positively associated with male paternity share. Spermatophore positioning within the female reproductive tract was not affected by male treatment (starved/fed), by female treatment (live/dead), or by male copulatory behaviors. Starvation, however, had a dramatic effect on male reproductive physiology, decreasing both accessory gland size and total number of sperms transferred (but not sperm viability in seminal vesicles). In addition, females who mated to starved males stored fewer sperms in their spermathecae, which, together with decreased ejaculate size, may explain the reduced paternity share of starved males compared to fed males. This study elucidates some cryptic mechanisms influencing male reproductive success and aids our understanding of trait evolution through sexual selection. 相似文献
15.
R. Terry Bowyer Janet L. Rachlow Kelley M. Stewart Victor Van Ballenberghe 《Behavioral ecology and sociobiology》2011,65(12):2251-2260
Evidence of female fomentation of male–male aggression as a mechanism of mate choice is rare, especially in mammals. Female
choice of mates in polygynous species may be masked by intense male competition or by males attempting to restrict female
choice. We studied protest moans of female Alaskan moose Alces alces gigas in interior Alaska, USA, from 1987 to 1990, to determine if moans incited male–male aggression. Alaskan moose exhibit a mating
system in which one dominant male (the harem master) herds, defends, courts, and attempts to mate with females in his harem.
Protest moans were given by females only in response to courtship. We hypothesized that if protest moans were related to females
reducing harassment and exercising mate choice, females should give protest moans more frequently when courted by small males
and less often when courted by large males, and that rates of male–male aggression would be elevated following protest moans.
Harems were composed of one large male, with a mean of 4.4 females (median = 3 females); 10% of 132 harems included ≥10 females.
The temporal pattern of protest moans from late August through November was associated with, but tended to lag behind, mating
behavior. The rate of protest moans given by females decreased with increasing size of males courting them. Male–male aggression
was significantly less during periods without protest moans than during periods in which protest moans occurred. These results
indicate that female moose gave protest moans to reduce harassment by smaller males, and assure a mating opportunity with
the most dominant male. Such a subtle mechanism of indirect mate choice by females may occur in other vertebrates in which
choice is limited by a mating system in which male–male combat and male dominance over females reduces opportunities for female
choice. The importance of female choice may be undervalued in studies of sexual selection in mammals. 相似文献
16.
Palestina Guevara-Fiore Jessica Stapley Penelope J. Watt 《Behavioral ecology and sociobiology》2010,64(10):1665-1672
Males vary in the degree to which they invest in mating. Several factors can explain this variation, including differences
in males’ individual condition and the fact that males allocate their energy depending on the context they face in each mating
attempt. Particularly, female quality affects male reproductive success. Here, we studied whether male guppies (Poecilia reticulata) strategically allocated more mating effort, in terms of mating behaviour and male–male competition, when they were matched
with a receptive (R) female than a non-receptive one. In accordance with our prediction, we found that males increased their
mating behaviour when they were with a receptive female. Even though male guppies can inseminate non-receptive females, we
only found high levels of courtship between males that were with a receptive female rather than a non-receptive one. Although
there was little affect of female receptivity on male–male competition, we found that males chased and interrupted courtships
more with receptive females than with non-receptive females regardless of odour. Finally, we also studied whether the sexual
pheromone produced by receptive female guppies is a cue that males use in order to increase their mating effort. We found
that males were more attracted to a female when they perceived the sexual pheromone, but only increased their mating and aggressive
behaviours when females showed receptive behaviour. This strategic increase in mating effort could result in higher male reproductive
success because mating attempts towards receptive females are likely to be less costly and males could have a greater probability
of fertilisation. 相似文献
17.
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
18.
In mammals with solitary females, the potential for males to monopolize matings is relatively low, and scramble competition polygyny is presumed to be the predominant mating system. However, combinations of male traits and mating tactics within this type of polygyny have been described. The main aim of our study was to identify the relative importance of, and interactions among, potential determinants of contrasting male reproductive tactics, and to determine their consequences for male reproductive success in a small solitary nocturnal Malagasy primate, the gray mouse lemur (Microcebus murinus). We studied their mating behavior over three consecutive annual mating seasons. In addition, we determined the genetic relationships among more than 300 study animals to quantify the reproductive success of individual males. We found that, with a given relatively low overall monopolization potential, successful male mouse lemurs roamed extensively in search of mates, had superior finding ability and mated as early as possible. However, contest competition was important too, as temporary monopolization was also possible. Males exhibited different mating tactics, and heavier males had a higher reproductive success, although most litters had mixed paternities. Switching between tactics depended on short-term local variation in monopolization potential determined by a pronounced dynamic in fertilization probability, number of alternative mating opportunities, and the operational sex ratio. This study also revealed that the dynamics of these determinants, as well as the mutual interactions between them, necessitate a detailed knowledge of the mating behavior of a species to infer the impact of determinants of alternative mating tactics.Electronic Supplementary Material Supplementary material is available in the online version of this article at
Communicated by S. AlbertsThis revised version was published online in August 2004 with corrections to Figure 2. 相似文献
19.
We studied sexual selection in the red bishop, Euplectes orix, a colonial, polygynous weaverbird widely distributed over sub-Saharan Africa. Male reproductive success measured in terms
of the number of nests accepted by females and the number of eggs and nestlings in all the nests on a male's territory varied
considerably. The standardized variance (variance/mean2) in male reproductive success ranged from 0.505 to 1.737 in different years, indicating a high potential for sexual selection
in this species. An analysis of genetic parentage for 432 nestlings by non-radioactive, multilocus DNA fingerprinting confirmed
that male reproductive success (number of young sired on the territory) in this species can be reliably estimated by the measures
introduced above. In all 4 study years there was a strong positive correlation between male mating success and the total number
of nests that males built in their territories. The number of nests built can be partitioned into the number of weeks a male
held a territory and his nest-building performance. Both factors exert a significant positive effect on male mating success
and in combination explained between 53.3 and 86.3% of the variation in male reproductive success. Male morphological characters
were found to be of no importance. Males that established a territory in the following season built more nests and held their
territories for longer than males that did not establish a territory in the following season, suggesting that these measures
might be indicators of male condition and quality. Male nest-building performance (number of nests built per week) seems to
be unrelated to male condition or quality.
Received: 8 January 1999 / Received in revised form: 7 June 1999 / Accepted: 13 June 1999 相似文献
20.
Exaggerated male eye span influences contest outcome in stalk-eyed flies (Diopsidae) 总被引:3,自引:0,他引:3
Evolution of male weapons or status signals has been hypothesized to precede evolution of female mating preferences for those
traits. We used staged male fights among three species of Malaysian stalk-eyed flies (Diptera: Diopsidae) to determine if
elongated eye span, which is preferred by females in two sexually dimorphic species, influences contest outcome. Extreme sexual
dimorphism, with large males possessing longer eye span than females, is shared by Cyrtodiopsis whitei and C. dalmanni. In contrast, C. quinqueguttata exhibits a more ancestral condition – short, sexually monomorphic eye stalks. Videotape analysis of 20-min paired contests
revealed that males with larger eye span and body size won more fights in the dimorphic, but not monomorphic, species. To
determine if males from the dimorphic species use eye span directly to resolve contests, we competed male C. dalmanni from lines that had undergone artificial selection for 30 generations to increase or decrease eye span. We found that eye
span, independently of body size, determines contest outcome in selected-line males. Furthermore, in both dimorphic species,
the average encounter duration declined as the eye span difference between contestants increased, as expected if males use
eye span to assess opponent size. The number of encounters also increased with age in dimorphic, but not monomorphic, species.
Selected-line males did not differ from outbred males in either fight duration or number of encounters. We conclude that exaggerated
male eye stalks evolved to influence both competitive interactions and female mating preferences in these spectacular flies.
Received: 20 July 1998 / Received in revised form: 2 February 1999 / Accepted: 12 March 1999 相似文献