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1.
The operational sex ratio (OSR) may influence the intensity of competition for mates and mate choice and is therefore thought
to be a major factor predicting the intensity and direction of sexual selection. We studied the opportunity for sexual selection,
i.e., the variance in male reproductive success and the direction and intensity of sexual selection on male body mass in bank
vole (Clethrionomys glareolus) enclosure populations with experimentally manipulated sex ratios. The opportunity for sexual selection was high among male-biased
OSRs and decreased towards female-biased OSRs. Paradoxically, selection for large male body mass was strongest in female-biased
OSRs and also considerable at intermediate OSRs, whereas at male-biased OSRs, only a weak relationship between male size and
reproductive success was found. Litters in male-biased OSRs were more likely to be sired by multiple males than litters in
female-biased OSRs. Our results suggest that the intensity and direction of sexual selection in males differs among different
OSRs. Although the direction of sexual selection on male body mass was opposite than predicted, large body mass can be favored
by sexual selection. Naturally varying OSRs may therefore contribute to maintain variation in male sexually selected traits. 相似文献
2.
S. Balshine-Earn 《Behavioral ecology and sociobiology》1996,39(2):107-116
Operational sex ratio (OSR) theory predicts that sexual differences in potential reproductive rates (PRRs) create biases
in the OSR and thus determine the relative strength of sexual selection (competition and choice) operating on each sex. Although
this theory is well accepted, empirical studies that quantify it are still lacking. This paper presents such a study. I measured
the natural OSR of Galilee St. Peter’s fish (Sarotherodon galilaeus) in the field (Lake Kinneret) and examined the direction of mate choice in the laboratory. The OSR in Lake Kinneret was male
biased. Both a male-biased sex ratio and higher male reproductive rates (twice as fast as females) contributed to the skew
in the OSR, but the sexual differences in PRR were shown to be the main factor causing variation in the OSR. Females, the
sex with the lower PRR, were more selective for mates. The faster male reproductive rate may explain why females are more
selective for mates despite varying less in quality.
Received: 29 May 1995/Accepted after revision: 13 April 1996 相似文献
3.
Darryl T. Gwynne Winston J. Bailey Amanda Annells 《Behavioral ecology and sociobiology》1998,42(3):157-162
In katydids such as Kawanaphilanartee, a female bias in the operational sex ratio (OSR) results in female competition for mates and male choice of mates. Previous
work showed that the excess of sexually active females occurs when food availability is low, in part because less food increases
the propensity of females to mate as they forage for the large edible spermatophores produced by males. In this study with
K.nartee, a pollen-feeding species, we estimate natural variation in numbers of sexually active males and females by assessing male
calling activity and the propensity of females to respond to experimental calling males. We found an excess of sexually active
males at a site with many flowers and an excess of sexually active females at a site with few flowers about 900 m away. Between-site
differences in gut masses of calling males were consistent with the hypothesis that pollen availability controls OSR. Finally,
at a third site where flowers were at first scarce, we found that the initial excess in sexually active females changed to
an excess of sexually active males after a clump of grass-trees flowered. The mean gut mass of all sampled males from this
site increased after flowering. The large variation in OSR that we document for K. nartee highlights the importance of identifying the appropriate spatial and temporal scales over which OSRs are measured in studies
of factors controlling sexual selection.
Received: 13 May 1997 / Accepted after revision: 27 October 1997 相似文献
4.
Denson Kelly McLain 《Behavioral ecology and sociobiology》1992,30(5):347-356
Summary Population density affects the dynamics of mate acquisition and the opportunity for sexual selection in natural populations of the seed bug, Neacoryphus bicrucis Say (Hemiptera : Lygaeidae). The opportunity for sexual selection and the intensity of directional sexual selection on body length increased as the population density declined within a season for a population in a small, disjunct patch of host plant, Senecio anonymus. In a larger, dispersed population, both measures of selection were greater in host plant patches of low rather than high adult density when the population was sampled at peak density. Under conditions of higher density, males were more likely to share plants, larger males were less likely to monopolize patches of host plant to which females were attracted for mating, and smaller males were more likely to mate in the presence of large males. Thus, resource defense polygyny collapsed under high density, obviating the advantage of size in territory control, and resulted in scramble competition among males for mates. The population exhibited significant additive genetic variation for body length. This suggests that natural selection acting on other components of fitness favors smaller size or that the direction of sexual selection on size fluctuates between generations in response to the between-year variation in population density. Thus, strong sexual selection appears to impose a significant genetic load. 相似文献
5.
Variance in female quality, operational sex ratio and male mate choice in a bushcricket 总被引:8,自引:0,他引:8
Male bushcrickets, Kawanaphila nartee, exercise mate choice when nutrients are limited. Male mate choice is associated with a female-biased operational sex ratio
(OSR) that arises from an increased relative paternal investment under nutrient limitation. However, increased male choosiness
could be attributable to the fact that females vary more in fecundity, and consequently in mate quality, when nutrient limited.
Our objective was to experimentally partition the influences of OSR (male or female bias) and variance in mate quality (high
or low) and to assess their relative influence on the intensity of mate choice by male bushcrickets. Female quality was manipulated
by controlled feeding regimes that directly affected female fecundity. We found that males and females engaged in sexual interactions
sooner under a male-biased than a female-biased OSR. Males were more likely to reject females on their first encounter when
variance in female quality was high. However, the effect of quality variance on the total number of rejections during a 4-h
observation period was dependent on the perceived OSR. A male's prior experience of variance in female quality did not influence
male choosiness. Our observed rates of mate rejection conformed well with those predicted from recent theoretical models of
sexual differences in choosiness. In conclusion, our results show that the opportunity for selection via male mate choice
is influenced by an interaction between OSR and the variance in mate quality that arises within nutrient-limited populations
of females.
Received: 5 January 1998 / Accepted after revision: 25 October 1998 相似文献
6.
Effects of male dominance and courtship display on female choice in the ring-necked pheasant 总被引:7,自引:0,他引:7
Male traits and behaviours acting in mate choice and intrasexual competition are expected to be congruent. When studying
their evolution, this often makes it difficult to differentiate between these two components of sexual selection. Studies
are therefore needed on mate choice in conjunction with the role of displays and dominance. We present the results from two
experiments conducted to investigate the effects of male dominance and courtship displays on female choice in the ring-necked
pheasant, Phasianus colchicus, controlling for differences in morphological male traits. We found: (1) different courtship behaviours had different effects
on female choice: females were mainly attracted by the feeding courtship behaviour, while another courtship display (the lateral
display) was effective in producing the copulation-acceptance response by the females; (2) subordinate males performed the
courtship behaviour before females less frequently than dominant males, and females reinforced intrasexual selection by choosing
dominant males, and (3) subordinate males in visual contact with a dominant became less attractive to females. The results
support the idea (armament-ornament model) that female pheasants may benefit from using traits selected in male-male competition
as clues for mate choice.
Received: 23 October 1997 / Accepted after revision: 7 October 1998 相似文献
7.
Male choice and competition in Tetraopes tetraophthalmus: effects of local sex ratio variation 总被引:4,自引:0,他引:4
W. S. Lawrence 《Behavioral ecology and sociobiology》1986,18(4):289-296
Summary Male milkweed beetles (Tetraopes tetraophthalmus) are shown to exhibit choice between potential mates. Males, however, also exhibit direct competition for access to potential mates. These differences in male behavior are dependent on the local sex ratio, with males becoming increasingly choosy when the sex ratio is female-biased, and more competitive when the sex ratio is malebiased. Females show neither choice nor competition. In both the laboratory and in the field, body size is important in determining patterns of competition and choice. Larger males win most aggressive encounters, and males generally prefer large females as mates. The combination in a single sex, of competition for mates and mate choice is not predicted by classical sexual selection theory. Male choice and competition may have evolved in T. tetraophthalmus due to the combination of (1) the mating system (2) the pattern of variation in female fecundity, and (3) the spatially and temporally variable operational sex ratios. This explanation is not dependent on high heritability of body size. 相似文献
8.
Protandry, the earlier arrival of males than females to breeding areas, is widespread in birds, but its underlying mechanisms
are far from well understood. The two, not mutually exclusive most highly supported hypotheses to explain avian protandry
postulate that it has evolved from intrasexual male competition to acquire the best territories (“rank advantage” hypothesis)
and/or to maximize the number of mates (“mate opportunity” hypothesis). We studied for two consecutive years the relative
importance of both hypotheses in a population of pied flycatchers (Ficedula hypoleuca), a territorial songbird with a mixed mating strategy. We measured territory quality using a long-term dataset on nest occupation
and breeding output, and we used molecular techniques to assess male fitness across the range of social and genetic mating
options. Territory quality was unrelated to breeding date and had no influence on extra-pair paternity or social polygynous
events. However, males breeding early increased their chances of becoming socially polygynous and/or of attaining extra-pair
paternity and, as a consequence, increased their total reproductive success. These results support the “mate opportunity”
hypothesis, suggesting that sexual selection is the main mechanism driving protandry in this population. 相似文献
9.
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
10.
Anders Pape Møller 《Behavioral ecology and sociobiology》1987,21(2):119-123
Summary The importance of mate guarding by males in the monogamous swallowHirundo rustica was studied by temporarily detaining the males. Mate guarding reduced the frequency of extra-pair copulations and of sexual
chases involving female mates. Males participated in sexual chases more frequently if they had a non-fertile female. Neighbouring
males of ‘widowed’ females increased their own mate guarding presumably in response to the experimentally increased rate of
sexual chases. Neighbouring males with a fertile female increased their mate guarding more than did males with a non-fertile
female.
Addition of eggs to swallow nests in the post-fledging period of the first brood induced mate guarding by male nest owners.
These males also copulated more frequently with their mates than did control males. Neighbouring male swallows responded to
the increased mate guarding by showing sexual interest in the guarded females.
removal of eggs from swallow nests during the laying period, leaving only one egg in the nest, resulted in reduced nest attendance
by females. Male mates responded by increasing their mate guarding intensity as compared to controls, and neighbouring males
showed an increased sexual interest in these females. 相似文献
11.
J. Morales O. Gordo E. Lobato S. Ippi J. Martínez-de la Puente G. Tomás S. Merino J. Moreno 《Behavioral ecology and sociobiology》2014,68(7):1195-1204
There is increasing evidence that sexual selection operates in females and not only in males. However, the function of female signals in intrasexual competition has been little studied in species with conventional sex roles. In the Iberian populations of the pied flycatcher (Ficedula hypoleuca), some females express a white forehead patch, a trait that in other European populations, only males exhibit and has become a classical example in studies of sexual selection. Here, we investigated whether the expression of this trait plays a role in female-female competition during early breeding stages. To test this hypothesis, we simulated territorial intrusions by challenging resident females with stuffed female decoys expressing or not a forehead patch. We found that resident females directed more attacks per trial and maintained closer distances to non-patched decoys than to patched ones. Also, patched females were more likely to attack the decoy than non-patched females. Interestingly, females were more aggressive against the decoys when their mate was absent. This may indicate that females relax territory vigilance in the presence of their mate or that males interfere in the interaction between competing females. The behavior of resident males was also observed, although it was not affected by decoy’s patch expression. Our findings suggest that the forehead patch plays a role in female intrasexual competition. If the forehead patch signals fighting ability, as it does in males, we may interpret that non-patched females probably avoided repeating costly agonistic encounters with the most dominant rivals. 相似文献
12.
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
13.
S. Boinski 《Behavioral ecology and sociobiology》1987,21(1):13-21
Summary The mating system of squirrel monkeys (Saimiri oerstedi) in Parque Nacional Corcovado, Costa Rica was studied and used to develop a model to interpret the evolution of seasonal sexual dimorphism in squirrel monkeys (Saimiri spp.). Adult male body weights in captivity and the wild may increase more than 20%, beginning approximately two months prior to and continuing through the annual two month, breeding season. Female inter-troop transfer was common in the study population, but male troop residence was stable. Instances of agression among adult males in the troop, even in sexual contexts, were rare. Reproductively mature males enlarged to varying degrees by the start of the breeding season and cooperated in mobbing females to olfactorily evaluate female, estrous condition. Female mate preference corresponded to a ranking based on relative male enlargement. The largest male obtained 70% of the copulations observed in the 1984 breeding season. Little evidence exists that females typically mate with more than one male during the period of peak receptivity. Seasonal enlargement in males is suggested to be the result, of both male intrasexual competition and female choice. 相似文献
14.
Mark R. Forbes Dean G. McCurdy Keiko Lui Selma I. Mautner J. Sherman Boates 《Behavioral ecology and sociobiology》2006,60(1):87-95
Potential rates of reproduction (PRR) differ between the sexes of many animal species. Adult sex ratios together with PRR
are expected to determine the operational sex ratio (OSR) defined as the ratio of fertilizable females to sexually active
males at any given time. OSR is expected to determine the degree to which one sex competes for another—the limiting sex. We
explored the potential for mate limitation in an intertidal amphipod, Corophium volutator (Pallas). Males have higher PRR than females, but males may be limiting because of extreme female-biased sex ratios observed
in this species. Consistent with this idea, late season females were less likely to be ovigerous and had smaller size-specific
clutches, both of which were associated with seasonal declines in availability of males of reproductive size. Seasonal changes
in ovigery could not be explained by seasonal changes across sites in other factors (e.g., female body size or phenology of
breeding). Smaller females were less likely to become ovigerous later in the season at three of four sites. Seasonal reductions
in clutch size also occurred among small females expected to be reproducing for their first time. In complimentary laboratory
experiments, reduced likelihood of ovigery and reduced fecundity occurred when the number of receptive females was increased
relative to availability of a reproductively active male. Our results suggest male mate limitation can occur seasonally in
this species and that male limitation is regionally widespread and may affect recruitment. 相似文献
15.
Male competition for mates and female mate choice are key mechanisms involved in sexual selection. Surprisingly, these mechanisms
have often been investigated separately although they appear to interact in many species. Male–male competition for territories
located at the best places or to establish dominance relationships often explain mating patterns. Such male behaviours may
affect and sometimes even hinder female mate choice, as in the case of sexual coercion. While in many species females are
able to exert cryptic control over paternity (i.e. a process allowing females to bias offspring production toward certain
males after intromission), in other species external fertilisation prevents females from doing so. This is the case in the
waterfrog hybridisation complex where the hybrid Pelophylax esculentus can only produce viable offspring by pairing with the parental species Pelophylax lessonae (hybridogenetic reproduction). We examined two potential processes that could enhance such mating combinations. Firstly,
by monitoring male spatial distribution within six choruses, we showed that the proportion of P. lessonae males located at the edge (in the best position to grasp females arriving at the chorus) cannot explain the frequency of
mating combinations observed. Secondly, an experimental approach emphasised a new way for anuran females to favour paternity
of a particular male in a sexual coercion context. When females are forcefully paired with an incompatible male, they cannot
remove the male grasped on their back by themselves. Nevertheless, by controlling the movement of the pair within the chorus,
these females often change mates by enhancing male competition instead of laying eggs. In many species with externally fertilised
eggs, it may be thus necessary to take into account this new possibility for females to control offspring paternity. 相似文献
16.
Jonathan N. Pruitt Susan E. Riechert David J. Harris 《Behavioral ecology and sociobiology》2011,65(10):1957-1966
Relatively few investigations explicitly test for concordant versus conflicting selection pressures from intrasexual versus
intersexual selection. Here, we examine the effects of male body mass and behavioral type (BT) on reproductive success in
the spider Anelosimus studiosus, with emphasis placed on the potential interaction between intrasexual and intersexual selection influences. Female A. studiosus exhibit either an aggressive-active or docile-passive BT, both of which co-occur in multifemale colonies. Males, in contrast, exhibit a more continuous distribution of
behavioral tendencies. We investigated the male traits favored by females in five trial types: one docile female, one aggressive
female, four docile females, four aggressive females, and two docile and two aggressive females. Male reproductive success
was estimated by the number eggs produced by females following staged mating trials. In previous work, it was established
that large aggressive males are favored in male–male contests, an intrasexual effect. However, large aggressive males were
not universally favored here. We failed to detect an effect of male body mass or aggressiveness on reproductive success in
trials with all docile females; however, in situations involving aggressive females, large aggressive males experienced diminished
reproductive success relative to small docile males. Large, aggressive males were also more likely to be attacked and killed
by aggressive females in the first 20 min of staged encounters and were more likely to be found dead after 72 h of unobserved
interactions. Taken together, our data suggest that the reproductive consequences of male traits differ based on (1) the aspect
of sexual selection being considered (intrasexual versus intersexual) and (2) the BT of their prospective mates: large aggressive
males enjoy advantages in intrasexual selection and when courting docile females and small docile males experience reduced
risk of cannibalism and increased reproductive success with aggressive females. 相似文献
17.
Amanda Vincent Ingrid Ahnesjö Anders Berglund 《Behavioral ecology and sociobiology》1994,34(6):435-442
In the pipefish Syngnathus typhle, only males brood embryos in specially developed brood pouches, supplying oxygen and nutrients. Laboratory studies have shown that this elaborate paternal care has led to sex-role reversal in this species: males limit female reproductive rate, females are the primary competitors for mates and males exercise greater selectivity in accepting mates. In the first field study of this pipefish, we describe mating behaviour in the wild and test the hypothesis that temporal variations in the operational sex ratio (OSR) determine sex differences in mating behaviour. Our study comprised two reproductive seasons of two sequential mating periods each, the latter separated by a lengthy interval of male brooding. During mating periods, females displayed to all males without wandering and males moved about searching for females, without reacting to all females. The OSR was least female-biased (or even male-biased) at the onset of the breeding season, when most pipefish were simultaneously available to mate, but became strikingly female-biased as males' pouches were filled. The OSR remained substantially female-biased during the second mating period, because few males became available to remate at any one time. As hypothesised, female-biased OSRs resulted in more female-female meetings. As well, females were above the eelgrass more often than brooding males, thus exposing themselves to conspecifics and/ or predators. In the second year, males arrived earlier than females on the breeding site and male pregnancies were shorter, because of higher water temperatures, so rematings occurred earlier. Males met more often during that year than the previous one, but male competitive interactions were still not observed. The field results support laboratory studies and demonstrate that behaviours associated with female-female competition are more prominent when the OSR is more female-biased.
Correspondence to: A. Vincent 相似文献
18.
Lekking behavior in the neotropical frog Ololygon rubra 总被引:2,自引:0,他引:2
Godfrey R. Bourne 《Behavioral ecology and sociobiology》1992,31(3):173-180
Summary This is the first study to document in detail the satisfaction of Bradbury's four criteria for categorizing any anuran as a classical lekking species. The paternal care of male neotropical frogs, Ololygon rubra, consisted of minimal contributions of their genes. Males competed acoustically at traditional, defended, clustered sites (Fig. 1, Table 3) to attract gravid females, who paired with the males at these locations but took the amplectant males to oviposition sites away from the pairing sites. Individual males apparently did not control resources necessary for attracting females, because there were no correlations between male numbers and measured habitat variables, or between male numbers and oviposition sites. On chorusing nights, males always arrived at their display arenas before any females were observed. Females moved freely among clusters and males, before making their choices of mates. However, males employed other mate acquisition strategies that tended to undermine the initial female choices. The predictions that lekking species should have a relatively extended breeding season, a highly biased operational sex ratio (OSR), and an absence of male control of resources essential for female acquisition were also evaluated and corroborated. These frogs have two long breeding seasons encompassing a total of about 6 months (Fig. 2). There were strongly male biased nightly OSRs (Table 1), that contributed to high variance in male reproductive success (RS), but reduced indices of sexual selection, and a relatively low coefficient of variation (CV) of male RS (Table 5) compared to other amphibians. Thus, all of this evidence supports the conclusion that O. rubra in coastal Guyana uses a lek mating system. 相似文献
19.
Kai Lindström Colette M. St. Mary Christophe Pampoulie 《Behavioral ecology and sociobiology》2006,60(1):46-51
Male parental care is typically thought to come at a cost to mate attraction and future mating success. However, it has also
been hypothesized that paternal care may be under sexual, as well as natural, selection, such that good fathers actually attract
more mates. Here we show experimentally that in the sand goby, Pomatoschistus minutus, females prefer to mate with males that provide higher levels of parental care. We manipulated male behavior using (1) different
nest sizes and (2) an application of low-O2 water in the nests, and found that females consistently preferred males with elevated levels of care in dichotomous mate
choice tests. This complements our earlier study in which we showed that males increase the amount and quality of care they
provide in the presence of females. Our results demonstrate that male care may have evolved as a result of sexual selection
rather than natural selection alone, and furthermore, that male care may not necessarily be in conflict with mate attraction. 相似文献
20.
Paul J. Watson 《Behavioral ecology and sociobiology》1990,26(2):77-90
Summary Two to five days before sexual maturation, female sierra dome spiders (Linyphia litigiosa: Linyphiidae) undergo a transformation in their behavior toward males that visit their webs. During this latter part of their penultimate instar, females change from consistently positioning themselves far away from males to actively maintaining close proximity, reactions I call avoidant and associative behavior, respectively. Consistent associative behavior ceases after the female's first mating and thus is limited to soon-to-mature penultimate females. When a mate-seeking male fords an associative female, he attempts to guard her until she matures; this is often a multi-day affair. In contrast, males guard immature avoidant and mature mated females for only a single day. This dichotomy in male guarding times can be understood by the fact that associative behavior signals that the female will soon develop peak reproductive value. Upon completion of their final molt, 98% of females immediately mate with the current guarding male. Secondary suitors are not as likely to achieve mating. Moreover, first mates father 1.8 times more offspring, on average, than secondary mates. Whenever they meet on any female's web, males fight until one of the contestants withdraws. Fights typically are intensive, occasionally deadly, and often result in usurpation of the web by the newly arriving male. Larger males win more fights, but other qualities (e.g., vigor and persistence) appear to be important when contestants differ by less than 10–20% in body weight. Prolonged (i.e., multi-day) guarding of associative females enhances the intrasexual selection process by ensuring that every male that arrives at the web finds it already guarded. Therefore every male that finds the web becomes a participant in a series of male-male conflicts and web usurpations which span the period between the resident female's commencement of associative behavior and her sexual maturation. Since unforced male departures from the webs of associative females are rare, victors are retained on the web until they themselves lose a fight. This facilitates a steady increase in the fighting ability of sequential guards throughout the associative period, up until female maturation and mating. On my study site, first mates represented the final winners in a combative sorting process based on a minimum average of 2 fights; they were heavier and larger than secondary mates and randomly sampled males. The combination of (1) associative behavior by nearly mature females, (2) high mating propensity of newly mature females, and (3) first male sperm priority, constitutes a system whereby females enhance male-male competition and boost the expected fighting prowess of the principal sire of their progeny. Since males appear to make no material contribution toward progeny, the female's behavior probably functions to improve the genetic constitution of the offspring. In addition, the timing of associative behavior may limit prolonged guarding by food-stealing males to a period (1) encompassing the female's pre-molt fast and (2) before the heavy yolking of eggs, thereby ameliorating the nutritional costs of intrasexual selection. 相似文献