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1.
Comparative analyses have found that relative testis size is a strong predictor of the prevalence of sperm competition for many taxa, including mammals, yet underlying this pattern is the assumption that intraspecific variation in testis size is related to individual fitness. Because intraspecific variation in ejaculate investment underlies interspecific patterns, it is critical to understand the causes and consequences of intraspecific variation in ejaculate investment. We examined relationships between ejaculate investment (testis size and sperm length) and reproductive success, body size and condition in the yellow-pine chipmunk (Tamias amoenus), a small ground squirrel in which sperm competition occurs. We examined genetic estimates of male reproductive success from a wild population of yellow-pine chipmunks and determined that males with large testes had higher annual reproductive success than males with small testes. This result provides empirical support for the numerous comparative studies that indicate testis size is associated with the intensity of sperm competition. In addition, males in good condition had relatively larger testes than males in poor condition, but there was no evidence of sperm length being dependent on condition. Finally, contrary to many predictions, males that invested more in sperm production (relatively heavy testes) produced shorter sperm, not longer sperm, than males that invested less.Communicated by P.M. Kappeler 相似文献
2.
Sperm competition models on the evolution of sperm size assume associations with another sperm quality trait, sperm longevity. Sperm length can also provide an indication of possible mechanisms affecting motility and thus fertilization success. Despite their importance, however, detailed mechanisms of sperm competition at the gamete level are poorly understood. In simultaneously hermaphroditic land snails, sperm traits and cryptic female choice are assumed to be crucial in determining fertilization success. We examined the variation in sperm length and number among individuals from four natural populations of the land snail Arianta arbustorum, a species with multiple mating and long-term sperm storage. We also assessed variation in velocity, motility and longevity of sperm in snails from two of the four populations. Independent of shell size, sperm length differed among populations and, to a minor extent, even among individuals within populations. Mean sperm length of a snail was not correlated with the number of sperm delivered in a spermatophore. The mean sperm velocity (=VCL) did not differ between snails from two populations. However, VCL varied among snails. Percentage motility and longevity of sperm differed between snails from the two populations. No correlations were found between length, velocity, percentage motility and longevity of sperm. To conclude, individual snails differed in sperm quality, and this variation may partly explain the differential fertilization success between A. arbustorum snails. Moreover, our findings did not support the positive association between sperm length and longevity assumed by sperm competition models for internally fertilizing species. 相似文献
3.
Sperm competition should select for increased sperm production if the probability of fertilization by a specific male is proportional to the relative number of sperm inseminated. A review of the literature generally supports the predicted positive association between sperm production or allocation and various measures of the presumed intensity of sperm competition. However, it is not clear how increased sperm competition is related to extra-pair paternity, and it remains unknown whether certainty of paternity should be associated with relative testis size. Based on a large sample of bird species with information on extra-pair paternity gathered from the literature, we demonstrate that testis mass is related positively to the level of extra-pair paternity, after controlling for body size and phylogeny. Although large testes may be necessary to avoid sperm depletion in species in which males frequently engage in multi-pair copulations, we argue that selection has favoured increased testis mass in situations of more intense sperm competition in order to retaliate against copulations by rival males. The fact the males are not always successful in retaliating against rival ejaculates further suggests that females may largely control the allocation of paternity in birds and that increased sperm production by males may simply be a male strategy to make the best of a bad situation. 相似文献
4.
Susanne P. A. den Boer Jacobus J. Boomsma Boris Baer 《Behavioral ecology and sociobiology》2008,62(12):1843-1849
The seminal fluid that accompanies sperm in ejaculates has been shown or suggested to affect sperm competition and paternity
success of insects by preventing female remating, inducing oviposition, and forming mating plugs. In Atta leafcutter ants, queens have multiple mates but never remate later in life, although they may live and produce fertilized
eggs for several decades. The mating biology and life history of these ants therefore suggests that the major function of
seminal fluid is to maximize sperm viability during copulation, sperm transfer, and initial sperm storage. We tested this
hypothesis by comparing the viability of testis sperm and ejaculated sperm (mixed with seminal fluid) and found a significant
positive effect of seminal fluid on sperm viability. We further quantified this positive effect by adding accessory gland
secretion (a major component of seminal fluid) in a dilution series, to show that minute quantities of accessory gland secretion
achieve significant increases in sperm viability. Sperm stored by queens for 1 year benefited in a similar way from being
exposed to accessory gland compounds after dissection in control saline solution. Our results provide the first empirical
evidence that seminal fluid is important for the production of viable ejaculates and that the accessory glands of Atta males—despite their small size—are functional and produce a very potent secretion. 相似文献
5.
Chiara Boschetto Clelia Gasparini Andrea Pilastro 《Behavioral ecology and sociobiology》2011,65(4):813-821
While both sperm number and quality are now recognized to be important in determining the outcome of sperm competition, very
few studies have experimentally assessed the influence of these two parameters simultaneously. We studied the effect of sperm
quality and number on competitive fertilization success in an internal-fertilizing fish, the guppy (Poecilia reticulata), which is characterized by high levels of sperm competition. We artificially inseminated virgin females with varying proportion
of sperm from two competing males, while holding constant the total number of sperm transferred to the female. Sperm morphology
and sperm swimming velocity were also determined prior to insemination. The paternity outcome of sperm competition trials
was assessed through molecular analyses of the resulting offspring using polymorphic microsatellite loci. We found that both
sperm number and sperm velocity affected the outcome of sperm competition, with males that contributed more and faster sperm
achieving a greater paternity share. 相似文献
6.
Under sperm competition, a males fertilization success depends largely on the ejaculate characteristics of competing males. Theoretical models predict that, in external fertilizers, increased risk of sperm competition should result in selection for increased sperm swimming speed. To test this prediction, we studied the behavior of sperm from parental and sneaker male bluegill (Lepomis macrochirus), a fish species characterized by high levels of cuckoldry due to alternative reproductive tactics of males (parentals and cuckolders). Because cuckolders (sneakers and satellites) always spawn in the presence of a parental male, but the reverse is not true, cuckolders experience the greater risk of sperm competition. We show here that the spermatozoa of sneakers have faster initial swimming speeds but shorter periods of motility than the sperm of parental males. Moreover, we show that sperm swimming speeds shortly after activation (when most fertilization occurs) are correlated with starting ATP levels in spermatozoa, suggesting that sperm competition has selected for higher energetic capacity in the sperm of sneakers. Thus, the higher energetic capacity and initial swimming speed of sneaker sperm may explain why, despite having fewer sperm per ejaculate than parentals, sneakers fertilize more eggs than parental males when they compete to fertilize a clutch of eggs.Communicated by L.W. Simmons 相似文献
7.
Eva Giacomello Francis C. Neat Maria B. Rasotto 《Behavioral ecology and sociobiology》2008,62(5):671-680
Sperm competition, cost of spermatogenesis and spawning frequency are known to influence ejaculate expenditure. Accordingly,
males, particularly those with high reproductive costs, are expected to have evolved mechanisms enabling them to prudently
allocate sperm, such as the fractioning of ejaculate expenditure or the semi-cystic type of spermatogenesis, hypothesised
to favour the production of small ejaculates. In this study, we investigate sperm competition risk, ejaculate size and mode
of ejaculate release in seven polygynous blenniid fish where males provide sole paternal care of eggs. In addition, we estimated
the relative size of the two parts composing the male gonad, the strictly testicular (testicular lobules or testis) and the
glandular (testicular gland), as the development of the latter is indicative of the level of semi-cystic spermatogenesis.
In all the examined species, eggs were laid one by one, and the sperm expenditure at mating, evaluated as the total number
of sperm released per mating, was parcelled out in several successive ejaculations, allowing males to adjust the release of
sperm to the duration of egg deposition. In accordance with sperm competition theory, species experiencing higher sperm competition
risk allocated more in sperm, both considering ejaculate size and ejaculate expenditure per mating. An increase in sperm expenditure
was paralleled by the development of the testis at the expense of the testicular gland. Smaller species, whose males do not
face sperm competition risk and fecundity is low, produced smaller ejaculates and exhibited a more developed testicular gland,
supporting the hypothesis that a semi-cystic type of spermatogenesis is a mechanism allowing sperm economy. 相似文献
8.
Experience affects mating behavior, but does not impact parental reproductive allocation in a lizard
Daniel A. Warner Clint D. Kelly Matthew B. Lovern 《Behavioral ecology and sociobiology》2013,67(6):973-983
Investment into reproduction is influenced by multiple factors and varies substantially between males and females. Theory predicts that males should adjust their ejaculate size or quality in response to variation in female experience or phenotypic quality. In addition, sperm investment by males may also be influenced by their own status and experience. Although such adjustments of male ejaculate size can impact reproductive success (via fertilization success), fitness returns from male sperm investment may be influenced (either limited or facilitated) by the level of maternal investment. To test this hypothesis, we conducted an experiment that simultaneously evaluated the effect of paternal and maternal experience (which incorporates mating status, age, body size, and other related variables) on paternal sperm investment and maternal reproductive allocation in the lizard Anolis sagrei. During staged mating trials, experienced males were more likely to copulate with females, but these individuals were less likely to transfer sperm during mating than were naïve individuals. Maternal experience had no impact on these mating behaviors. In contrast to expectations, experience and phenotypic quality (of both sexes) had no impact on male ejaculate size or quality (proportion of live sperm) or on maternal reproductive investment (in terms of egg size and yolk steroids). These findings were intriguing given the mating system and past evidence for differential maternal investment in relation to sire quality in A. sagrei. The results found in this study highlight the complexity of reproductive investment patterns, and we urge caution when applying general conclusions across populations or taxa. 相似文献
9.
Fabrice Helfenstein Murielle Podevin Heinz Richner 《Behavioral ecology and sociobiology》2010,64(4):557-565
Sperm competition exerts strong selection on males to produce spermatozoa with an optimal morphology that maximizes their
fertilization success. Long sperm were first suggested to be favored because they should swim faster. However, studies that
investigated the relationship between sperm length and sperm competitive ability or sperm swimming velocity yielded contradictory
results. More recently, ratios of the different sections of a spermatozoon (the head, midpiece, and flagellum) were suggested
to be more crucial in determining swimming velocity. Additionally, sperm ability to remain and survive in the female storage
organs may also influence fertilization success, so that optimal sperm morphology may rather maximize sperm longevity than
velocity. In this study, we investigated how sperm morphology is related to sperm velocity and sperm longevity in the house
sparrow Passer domesticus. Sperm velocity was found to be correlated with head/flagellum ratio. Sperm with small heads relative to their flagellum showed
higher swimming velocity. Additionally, shorter sperm were found to live longer. Finally, we found sperm morphological traits
to vary substantially within males and the head/flagellum ratio to be unrelated to total sperm length. We discuss the hypothesis
that the substantial within-male variation in sperm morphology reflects a male strategy to produce a diversity of sperm from
long, fast-swimming to short, long-living sperm to maximize their fertilization success in a context of sperm competition. 相似文献
10.
Sperm competition and sexual selection: a meta-analysis of paternity studies of birds 总被引:8,自引:0,他引:8
Sperm competition (the competition among the sperm of different males for fertilization of the eggs of a female) has been
suggested to be an important component of sexual selection, but no general assessment has been made of this proposition. We
used a meta-analytic approach to assess the extensive literature on paternity (the proportion of offspring in a focal nest
sired by an attending male) in birds based on allozyme and molecular techniques. The relative variance in male mating success
was on average increased by a factor of 4.6 over the variance in apparent male success. Males with more extravagant secondary
sexual characters had higher paternity in their own nests than less adorned males. There was a weak effect of male age being
positively associated with paternity in own nests. Male body size measured as the length of wing and tarsus was weakly positively
associated with paternity in own nests. Male survival prospect was positively associated with paternity in own nests. Polygynous
males generally had decreased paternity of their broods compared to monogamous males. Paternity of the resident male decreased
with increasing population density and breeding asynchrony. The intensity of paternity guards such as within-pair copulation
rate and mate guarding were not significantly related to extra-pair paternity. Sperm competition was thus an important component
of sexual selection by increasing the variance in male mating success, and by being associated with the expression of secondary
sexual characters, in particular in dense and asynchronously breeding populations of birds.
Received: 12 February 1998 / Accepted after revision: 31 May 1998 相似文献
11.
The Shiner Perch (Cymatogaster aggregata Gibbons) exhibits a viviparous reproductive mode and long-term female sperm storage, two biological features that may predispose
this fish species for both intense sperm competition and frequent multiple paternity within broods. To test these hypotheses,
we used polymorphic microsatellite markers to identify sires and quantify paternal contributions to the progeny arrays of
27 pregnant females from a natural population of C. aggregata. The number of sires per brood ranged from one to eight (mean 4.6), typically with skewed distributions of fertilization
success by the fathers but no correlation between sire number and brood size. The extraordinarily high incidences of multiple
paternity in this species probably are due in part to high rates of mate encounter, but selection pressures related to the
avoidance of maternal–fetal incompatibility may further have promoted the evolution of polyandrous mating behaviors in this
female-pregnant species. Our genetic data are consistent with the hypothesis that viviparity, long-term sperm storage, and
extreme polyandry are interrelated reproductive phenomena that should promote the evolution of post-copulatory sperm competition
and/or cryptic female choice in these fishes. 相似文献
12.
Multiple paternity and individual variation in sperm precedence in the simultaneously hermaphroditic land snail Arianta arbustorum 总被引:2,自引:0,他引:2
Bruno Baurl 《Behavioral ecology and sociobiology》1994,35(6):413-421
Intraspecific variation in the proportion of offspring sired by the second mate with a female (P2) is an aspect of sperm competition that has received little attention. I examined the effects of delay between copulations (range 9–380 days) and size of sperm donor on sperm precedence in double-mated individuals of the simultaneously hermaphroditic land snail Arianta arbustorum. Using shell colour as a genetic marker, paternity was analysed in 132 broods produced by 35 snails that had mated with two partners of different genotype. Sperm precedence (P2) was influenced by the time between the two matings when the mating delay exceeded 70 days (one reproductive season). P2 averaged 0.34 in the first brood of snails that mated twice within 70 days indicating first mate sperm precedence. In contrast, P2 averaged 0.76 in broods of snails that remated in the following season, indicating a decreased viability of sperm from the first mate. The size of sperm-donating individuals had no effect on the fertilization success of their sperm in the first brood produced after the second copulation. Analysis of long-term sperm utilization in 23 snails that laid three to nine egg batches over 2 years revealed striking differences among individuals. Five snails (21.7%) exhibited first-mate sperm precedence throughout, eight snails (34.8%) showed second-mate sperm precedence throughout, whereas ten snails (43.5%) exhibited sperm mixing in successive batches. It is suggested that the individual variation in sperm precedence in A. arbustorum may partly be due to differences in the amount of sperm transferred. Paternity analysis in 34 batches laid by 19 wild-caught individuals of A. arbustorum indicated that at least 12 snails (63.2%) used sperm from two or more mates for the fertilization of their eggs. This suggests a high incidence of multiple paternity in broods of A. arbustorum under field conditions. 相似文献
13.
Evolutionary theory predicts that more resources are allocated to sperm production when sperm competition is high. This prediction is supported by both comparative and experimental data on static measures of male allocation, such as testis and ejaculate size. However, resource allocation is a dynamic process, and it is therefore important to evaluate if the static measures reflect this. Such an evaluation has to our knowledge never been done. Immunocytochemical labelling with bromodeoxyuridine (BrdU) allows visualisation of cells in S-phase. BrdU becomes incorporated into cells if, and only if, they are actively undergoing DNA duplication, which is a dynamic process. The number of BrdU-positive cells in the testis can hence serve as a dynamic measure of male allocation, i.e. testicular activity. We evaluate the relationship between testis size and testicular activity in the marine flatworm Macrostomum sp. In a previous study, we showed that testis size is phenotypically plastic in this species, and that worms make larger testes when they are raised in larger groups. We use this plasticity to experimentally produce variation in testis size, and demonstrate that larger testes are associated with higher testicular activity. Moreover, testis size and testicular activity were related linearly. We have thus, for the first time, shown that testis size is a good measure of resource allocation to the male function. Moreover, increased testicular activity is probably one of the first steps in the upregulation of sperm production. It is thus expected that testicular activity is a more sensitive measure of short-term variation in male allocation than the commonly used static measures.Communicated by N. Wedell 相似文献
14.
Terje Laskemoen Oddmund Kleven Frode Fossøy Raleigh J. Robertson Geir Rudolfsen Jan T. Lifjeld 《Behavioral ecology and sociobiology》2010,64(9):1473-1483
Sperm competition is widespread among animal taxa and considered a major force in sperm evolution. Recent comparative studies have indicated that sperm competition selects for high sperm production capacity and long and fast-swimming spermatozoa across species. Here, we examine the role of sperm quantity and quality for fertilization success of individual males in a Canadian population of tree swallows Tachycineta bicolor, a socially monogamous, but highly promiscuous passerine. Male fertilization success (the sum of withinpair and extrapair young) was significantly associated with the size of the cloacal protuberance (a proxy for sperm quantity), but not with sperm size or in vitro sperm swimming speed. In a multivariate analysis, both cloacal protuberance volume and relative sperm midpiece size (i.e. high mitochondrial loading) had significant effects on male fertilization success. However, relative sperm midpiece size was not associated with fertilization success in a simple regression. Further, both cloacal protuberance volume and relative midpiece size had significant effects on sperm velocity, both in simple regressions and in a multivariate analysis. The finding that males with large relative midpiece size had both higher fertilization success and faster swimming sperm, suggests an indirect link between sperm morphology and male fertility mediated through sperm velocity. In conclusion, both quantitative and qualitative sperm traits seem to affect male fertilization success in tree swallows. 相似文献
15.
16.
Diego Rubolini Paolo Galeotti Gabriele Ferrari Michele Spairani Franco Bernini Mauro Fasola 《Behavioral ecology and sociobiology》2006,60(2):212-219
Sperm competition is a well-recognised agent in the evolution of sperm and ejaculate structure, as well as variation in female quality. Models of the evolution of ejaculate expenditure predict that male body condition, female fecundity and the risk and intensity of sperm competition may be the ultimate factors shaping optimal ejaculate size. We investigated sperm allocation in Austropotamobius italicus, a freshwater crayfish exhibiting a coercive mating system and external fertilisation, in relation to male and female traits and copulation behaviour under laboratory conditions. We found that mating males were sensitive to female size and produced larger ejaculates when mating with larger females, which were more fecund in terms of number of eggs produced. We found no evidence for female egg production being sperm-limited, as the number of eggs was not dependent on male sperm expenditure. Copulation duration and number of ejaculations reliably predicted the amount of sperm transferred, and both these behavioural measures positively covaried with female body size. These results indicate that male freshwater crayfish can modulate their sperm expenditure in accordance with cues that indicate female fecundity. In addition, a novel finding that emerged from this study is the decrease in sperm expenditure with male body size, which may either suggest that large, old male crayfish are better able than small males to economise sperm at a given mating to perform multiple matings during a reproductive season, or that they experience senescence of their reproductive performance. 相似文献
17.
Reproductive delays between mating and birth may provide a previously unconsidered avenue for post-copulatory sexual selection in mammals. In particular, delayed fertilization could provide an enhanced opportunity for sperm competition by extending the time for ejaculates to interact in the female reproductive tract. We tested the prediction that species with delayed fertilization exhibit greater degrees of sperm competition than those without delays by examining testis volume (a proxy for sperm competition) in 38 species of bats. Examination of fluid-preserved museum specimens of bat species with and without delays revealed that species with delays (in particular those with delayed fertilization) had significantly larger testes than species without them. Although it predicts the presence of delayed fertilization, hibernation did not predict relative testis size. We conclude that, once they evolve, reproductive delays may facilitate sperm competition. 相似文献
18.
Sperm traits often show extreme variation both between and within species. Between-species variation may often be interpreted
in the context of a sperm competition theory, but within-species variation has remained unexplained. Previous studies on intraspecific
variation in sperm traits have focused on a limited set of variables and may have failed to explain observed variation because
of potential trade-offs between different sperm traits. We report on variation in number, size, motility and longevity of
sperm in the frog Crinia georgiana, a species where sperm competition is common. We found intrapopulation variation in sperm size and motility and interpopulation
variation in relative sperm number and size. When we combined relative sperm number and size into one variable, and motility
and longevity into another, we found significant interpopulation variation in these variables as well. We also detected considerable
intra- and significant interpopulation variation in cumulative sperm quality, a combination of all four sperm traits. Furthermore,
a significant effect of the interaction between population origin and male size on sperm characteristics indicated interpopulation
variation in the strength of selection acting on sperm traits of males adopting different mating strategies. We discuss heterogeneity
in the reproductive environment, a complex genetic background in the determination of sperm characteristics and varying levels
of developmental noise as potential contributors to the observed variation in sperm traits. 相似文献
19.
Sperm competition or sperm selection: no evidence for female influence over paternity in yellow dung flies Scatophaga stercoraria 总被引:2,自引:0,他引:2
L. W. Simmons P. Stockley R. L. Jackson G. A. Parker 《Behavioral ecology and sociobiology》1996,38(3):199-206
Recent studies of non-random paternity have suggested that sperm selection by females may influence male fertilization success.
Here we argue that the problems originally encountered in partitioning variation in non-random mating between male competition
and female choice are even more pertinent to interpreting patterns of non-random paternity because of intense sperm competition
between males. We describe an experiment with the yellow dung fly, Scatophaga stercoraria, designed to partition variance in the proportion of offspring sired by the second male, P
2, between males and females, and to control for sperm competition. Large males were shown to have a higher P
2 than small males but P
2 was independent of the size of the female’s first mate. This result might suggest an absolute female preference for large
males via sperm selection. However, large males have a higher constant rate of sperm transfer and displacement. After controlling
for this effect of sperm competition, large males did not achieve higher paternity than small males. We argue that a knowledge
of the mechanism of sperm competition is essential so that male effects can be controlled before conclusions are made regarding
the influence of sperm selection by females in generating non-random paternity.
Received: 4 April 1995 / Accepted after revision: 17 October 1995 相似文献
20.
Testes mass in megachiropteran bats varies in accordance with sperm competition theory 总被引:4,自引:0,他引:4
D. J. Hosken 《Behavioral ecology and sociobiology》1998,44(3):169-177
Sperm competition is a widespread phenomenon influencing a range of characters, including investment in gonadal tissue. Conspecific
proximity is one factor which can influence the risk of sperm competition and hence testicular investment, and decreased confidence
of paternity may be one cost of group living. Aspects of female biology may also influence spermatogenic investment and sperm
morphology. This study examines the associations between relative testes mass and roost-group size across 17 species of Megachiroptera.
Associations between breeding season duration and investment in spermatogenesis are also examined, as are associations between
female reproductive tract dimensions and testes mass and dimensions of spermatozoa across all bats. Relative testes mass was
significantly positively associated with roost-group size at a species level and after appropriate phylogenetic control (pairwise
comparisons and comparison of independent contrasts). There were no significant relationships between breeding season duration
and relative testes mass. Across all bats, neither testes mass nor sperm length were significantly related to dimensions of
the female tract. The results are discussed in the context of sperm competition.
Received: 7 January 1998 / Accepted after revision: 8 August 1998 相似文献