The resident's dilemma: a female choice model for the evolution of alternative mating strategies in lekking male ruffs (Philomachus pugnax)

Previous models for the evolution of alternative male matingbehavior have virtually ignored the role of female choice. Wepresent a model in which female choice favors the evolutionand maintenance of alternative mating strategies in male ruffs,Philomachus pugnax. Resident male ruffe establish and defendcourts on leks against other residents, while non-territorialsatellite males move between leks and among courts on a lek.Residents appear to actively recruit satellites to their courts,even though satellites may mate with females once there. Residentbehavior toward satellites and data on female behavior suggestthat residents benefit from a satellite's presence due to somefemale preference for mating on co-occupied courts. However,if all residents accept satellites, none gains any relativeadvantage, yet all pay the costs of having satellites on theircourt. We present a game theoretical model that shows that therelative nature of female choice places residents in an evolutionarydilemma with respect to satellite acceptance. Although all residentswould benefit if satellites could be cooperatively excludedfrom leks, the only evolutionarily stable strategy for individualresidents is to defect and accept satellites. The model alsodemonstrates that this "resident's dilemma" likely exists onlyin a local sense, since the failure of residents to cooperativelyexclude satellites from leks need not result in globally lowerpayoffs, due to frequency-dependent selection on the proportionof satellites in the population. Our analysis suggests thatthe resident-satellite relationship in ruffs, despite its obviouscompetitive elements, is fundamentally a cooperative associationfavored by female choice. Female choice has also been proposedas the primary mechanism selecting for male association to formleks in ruffe. In this context, resident-satellite associationsmay be thought of as transitory "leks within a lek     

Steroid hormones in bluegill, a species with male alternative reproductive tactics including female mimicry

The proximate mechanisms underlying the evolution and maintenance of within-sex variation in mating behaviour are still poorly understood. Species characterized by alternative reproductive tactics provide ideal opportunities to investigate such mechanisms. Bluegill (Lepomis macrochirus) are noteworthy in this regard because they exhibit two distinct cuckolder (parasitic) morphs (called sneaker and satellite) in addition to the parental males that court females. Here we confirm previous findings that spawning cuckolder and parental males have significantly different levels of testosterone and 11-ketotestosterone. We also report, for the first time, that oestradiol and cortisol levels are higher in cuckolders than in parental males. The two cuckolder morphs did not differ in average levels of any of the four hormones. However, among satellite males which mimic females in appearance and behaviour, there was a strong negative relationship between oestradiol levels and body length, a surrogate for age. This finding suggests that for satellite males, oestradiol dependency of mating behaviour decreases with increasing mating experience. Although such decreased hormone dependence of mating behaviour has been reported in other taxa, our data represent the first suggestion of the relationship in fishes.     

Alternative routes to the leader male role in a multi-level society: follower vs. solitary male strategies and outcomes in hamadryas baboons

The nested one-male units (OMUs) of the hamadryas baboon are part of a complex social system in which "leader" males achieve near exclusive mating access by forcibly herding females into permanent consortships. Within this multi-level social system (troops, bands, clans and OMUs) are two types of prereproductive males--the follower and solitary male--whose different trajectories converge on the leader role. Here we compare OMU formation strategies of followers, who associate with a particular OMU and may have social access to females, with those of solitary males, who move freely within the band and do not associate regularly with OMUs. Data were derived from 42 OMU formations (16 by followers and 26 by solitary males) occurring over 8 years in a hamadryas baboon band at the Filoha site in Ethiopia. "Initial units" (IUs) with sexually immature females (IU strategy) were formed by 44% of followers and 46% of solitary males. The remaining followers took over mature females when their leader was deposed (challenge strategy) or disappeared (opportunistic strategy), or via a seemingly peaceful transfer (inheritance strategy). Solitary males took over mature females from other clans and bands, but mainly from old, injured or vanished leaders within their clan (via both the challenge and opportunistic strategies). Former followers of an OMU were more successful at taking over females from those OMUs than any other category of male. Despite this advantage enjoyed by ex-follower leaders, ex-solitary leaders were equally capable of increasing their OMU size at a comparable rate in their first 2 years as a leader. These results demonstrate the potential for males to employ both multiple roles (follower vs. solitary male) and multiple routes (IU, inheritance, challenge, opportunistic) to acquire females and become a leader male in a mating system characterized by female defense polygyny in a competitive arena.     

I'm sexy and I glow it: female ornamentation in a nocturnal capital breeder

In many species, males rely on sexual ornaments to attract females. Females, by contrast, rarely produce ornaments. The glow-worm (Lampyris noctiluca) is an exception where wingless females glow to attract males that fly in search of females. However, little is known about the factors that promote the evolution of female ornaments in a sexual selection context. Here, we investigated if the female ornament of the glow-worm is a signal of fecundity used in male mate choice. In support of this, we found brightness to correlate with female fecundity, and males to prefer brighter dummy females. Thus, the glow emitted by females is a reliable sexual signal of female fecundity. It is likely that male preference for the fecundity-indicating ornament has evolved because of large variation among females in fecundity, and because nocturnal males cannot directly assess female size and fecundity. These results indicate that female ornamentation may evolve in capital breeders (i.e. those in which stored resources are invested in reproduction) when females vary significantly in fecundity and this variation cannot be assessed directly by males.     

Frequency-dependent physiological trade-offs between competing colour morphs

Evolutionary theory suggests that alternative colour morphs (i.e. genetically controlled phenotypes) may derive similar fitness under frequency-dependent selection. Here we experimentally demonstrate opposing effects of frequency-dependent social environments on plasma hormone levels (testosterone and corticosterone) and immune function between red- and black-headed male morphs of the Gouldian finch (Erythrura gouldiae). Red-headed males are highly sensitive to changes in the social environment, especially towards the relative density of their own aggressive morph, exhibiting high stress responses and immunosuppression in socially competitive environments. In contrast, the non-aggressive black-headed males follow a more passive strategy that appears to buffer them against social stresses. The differential effect of hormones on aggressive behaviour and immune performance reinforces the contrasting behavioural strategies employed by these colour morphs, and highlights the importance of the social environment in determining the individual basis of behavioural and physiological responses.     

Molecular analysis of human leukocyte antigen class I and class II allele frequencies and haplotype distribution in Pakistani population

AIM:

Distribution of HLA class I and II alleles and haplotype was studied in Pakistani population and compared with the data reported for Caucasoid, Africans, Orientals and Arab populations.

MATERIALS AND METHODS:

HLA class I and II polymorphisms in 1000 unrelated Pakistani individuals was studied using sequence-specific primers and polymerase chain reaction and assay.

RESULTS:

The most frequent class I alleles observed were A*02, B*35 and CW*07, with frequencies of 19.2, 13.7 and 20%, respectively. Fifteen distinct HLA-DRB1 alleles and eight HLA-DQB1 alleles were recognized. The most frequently observed DRB1 alleles which represented more than 60% of the subjects were DRB1 *03, *07, *11 and *15. The rare DRB1 alleles detected in this study were HLADRB1 *08 and *09, having frequencies of 0.9 and 1.7%, respectively. In addition, at DRB1-DQB1 loci there were 179 different haplotypes and 285 unique genotypes and the most common haplotype was DRB1*15-DQB1*06 which represented 17% of the total DRB1-DQB1 haplotypes. In our population, haplotype A*33-B*58-Cw*03 comprised 2.8% of the total class I haplotypes observed. This haplotype was seen only in the oriental populations and has not been reported in the African or European Caucasoid.

CONCLUSION:

Our study showed a close similarity of HLA class I and II alleles with that of European Caucasoid and Orientals. In Pakistani population, two rare loci and three haplotypes were identified, whereas haplotypes characteristic of Caucasians, Africans and Orientals were also found, suggesting an admixture of different races due to migration to and from this region.     

Alternative mating tactics in the yellow dung fly: resolving mechanisms of small-male advantage off pasture

Recent work suggests that the yellow dung fly mating system may include alternative patroller–competitor mating tactics in which large males compete for gravid females on dung, whereas small, non-competitive males search for females at foraging sites. Small males obtain most matings off pasture, yet the behavioural mechanism(s) giving rise to this pattern are unknown. We investigated the male and female behaviours that determine mating success in this environment by conducting field mating experiments and found small males to benefit from several attributes specific to the off-pasture mating environment. First, small males from foraging sites exhibited higher mating propensity, indicating that large males away from dung may be depleted of energy and/or sperm. Second, small males were more discriminating, being significantly less likely to attempt with non-gravid females, which are absent on dung but common off pasture. Third, non-gravid females were generally more likely to actively struggle and reject mating attempts; however, such behaviours occurred disproportionately more often with large males. Female Scathophaga stercoraria thus appear to preferentially mate with small males when off pasture. These findings challenge assumptions about male–female interactions in systems with alternative mating tactics and reveal hidden processes that may influence selection patterns in the field.     

Disruptive sexual selection on male nuptial coloration in an experimental hybrid population of cichlid fish

Theory suggests that genetic polymorphisms in female mating preferences may cause disruptive selection on male traits, facilitating phenotypic differentiation despite gene flow, as in reinforcement or other models of speciation with gene flow. Very little experimental data have been published to test the assumptions regarding the genetics of mate choice that such theory relies on. We generated a population segregating for female mating preferences and male colour dissociated from other species differences by breeding hybrids between species of the cichlid fish genus Pundamilia. We measured male mating success as a function of male colour. First, we demonstrate that non-hybrid females of both species use male nuptial coloration for choosing mates, but with inversed preferences. Second, we show that variation in female mating preferences in an F2 hybrid population generates a quadratic fitness function for male coloration suggestive of disruptive selection: intermediate males obtained fewer matings than males at either extreme of the colour range. If the genetics of female mate choice in Pundamilia are representative for those in other species of Lake Victoria cichlid fish, it may help explain the origin and maintenance of phenotypic diversity despite some gene flow.     

The costs of risky male behaviour: sex differences in seasonal survival in a small sexually monomorphic primate

Male excess mortality is widespread among mammals and frequently interpreted as a cost of sexually selected traits that enhance male reproductive success. Sex differences in the propensity to engage in risky behaviours are often invoked to explain the sex gap in survival. Here, we aim to isolate and quantify the survival consequences of two potentially risky male behavioural strategies in a small sexually monomorphic primate, the grey mouse lemur Microcebus murinus: (i) most females hibernate during a large part of the austral winter, whereas most males remain active and (ii) during the brief annual mating season males roam widely in search of receptive females. Using a 10-year capture-mark-recapture dataset from a population of M. murinus in Kirindy Forest, western Madagascar, we statistically modelled sex-specific seasonal survival probabilities. Surprisingly, we did not find any evidence for direct survival benefits of hibernation-winter survival did not differ between males and females. By contrast, during the breeding season males survived less well than females (sex gap: 16%). Consistent with the 'risky male behaviour' hypothesis, the period for lowered male survival was restricted to the short mating season. Thus, sex differences in survival in a promiscuous mammal can be substantial even in the absence of sexual dimorphism.     

Xylan-degrading enzymes in male and female flower nectar of Cucurbita pepo

Background and Aims

Nectar is a very complex mixture of substances. Some components (sugars and amino acids) are considered primary alimentary rewards for animals and have been investigated and characterized in numerous species for many years. In contrast, nectar proteins have been the subject of few studies and little is known of their function. Only very recently have detailed studies and characterization of nectar proteins been undertaken, and then for only a very few species. This current work represents a first step in the identification of a protein profile for the floral nectar of Cucurbita pepo. In this regard, the species studied is of particular interest in that it is monoecious with unisexual flowers and, consequently, it is possible that nectar proteins derived from male and female flowers may differ.

Methods

Manually excised spots from two-dimensional (2-D) electrophoresis were subjected to in-gel protein digestion. The resulting peptides were sequenced using nanoscale LC–ESI/MS-MS (liquid chromatography–electrospray ionization/tandem mass spectrometry). An MS/MS ions search was carried out in Swiss-Prot and NCBInr databases using MASCOT software.

Key Results

Two-dimensional electrophoresis revealed a total of 24 spots and a different protein profile for male and female flower nectar. Four main proteins recognized by 2-D electrophoresis most closely resemble β-d-xylosidases from Arabidopsis thaliana and have some homology to a β-d-xylosidase from Medicago varia. They were present in similar quantities in male and female flowers and had the same molecular weight, but with slightly different isoelectric points.

Conclusions

A putative function for xylosidases in floral nectar of C. pepo is proposed, namely that they may be involved in degrading the oligosaccharides released by the nectary cell walls in response to hydrolytic enzymes produced by invading micro-organisms. Several types of oligosaccharides have been reported to increase the pathogenic potential of micro-organisms. Thus, it is possible that such a mechanism may reduce the virulence of pathogens present in nectar.     

Mitochondria-responsive signaling between egg and central cell controls their coordinated maturation

Recent studies suggest a complex regulatory network in female gametophyte of angiosperm. The cell-cell communication between female gametes was confirmed during their maturation and functional specialization. The mitochondria-responsive signaling may play a critical role in this process. Here, we briefly summarized the recent discussion on this topic and proposed a two-pathway’s mechanism for regulating coordinated development of the female gamete cells.     

Comparison of radiation-and chemically-induced dominant lethal mutations in male mice

Ionizing radiation-induced dominant lethal mutations in all spermatogenic stages. After irradiation of male mice with 200 R the yield of induced mutations in early spermatids was twice the yield in spermatozoa, late spermatids, and spermatocytes. After irradiation with 400 R or 800 R the spermatocytes were the most sensitive stage for the induction of dominant lethal mutations. The frequency of radiation-induced dominant lethal mutations in postspermatogonial stages was dose-dependent. The yield of dominant lethal mutations in spermatogonia was independent of the dose.     

Aurora A inhibition by MNL8054 promotes centriole elongation during Drosophila male meiosis

Aurora A kinase plays an important role in several aspects of cell division, including centrosome maturation and separation, a crucial step for the correct organization of the bipolar spindle. Although it has long been showed that this kinase accumulates at the centrosome throughout mitosis its precise contribution to centriole biogenesis and structure has until now not been reported. It is not surprising that so little is known, due to the small size of somatic centrioles, where only dramatic structural changes may be identified by careful electron microscopy analysis. Conversely, centrioles of Drosophila primary spermatocytes increase tenfold in length during the first prophase, thus making any change easily detectable. Therefore, we examined the consequence of the pharmacological inhibition of Aurora A by MLN8054 on centriole biogenesis during early Drosophila gametogenesis. Here, we show that depletion of this kinase results in longer centrioles, mainly during transition from prophase to prometaphase of the first meiosis. We also found abnormal ciliogenesis characterized by irregularly growing axonemal doublets. Our results represent the first documentation of a potential requirement of Aurora A in centriole integrity and elongation.     

Effects of floral display size on male and female reproductive success in Mimulus ringens

Background and Aims

The number of flowers blooming simultaneously on a plant may have profound consequences for reproductive success. Large floral displays often attract more pollinator visits, increasing outcross pollen receipt. However, pollinators frequently probe more flowers in sequence on large displays, potentially increasing self-pollination and reducing pollen export per flower. To better understand how floral display size influences male and female fitness, we manipulated display phenotypes and then used paternity analysis to quantify siring success and selfing rates.

Methods

To facilitate unambiguous assignment of paternity, we established four replicate (cloned) arrays of Mimulus ringens, each consisting of genets with unique combinations of homozygous marker genotypes. In each array, we trimmed displays to two, four, eight or 16 flowers. When fruits ripened, we counted the number of seeds per fruit and assigned paternity to 1935 progeny.

Key Results

Siring success per flower declined sharply with increasing display size, while female success per flower did not vary with display. The rate of self-fertilization increased for large floral displays, but siring losses due to geitonogamous pollen discounting were much greater than siring gains through increased self-fertilization. As display size increased, each additional seed sired through geitonogamous self-pollination was associated with a loss of 9·7 seeds sired through outcrossing.

Conclusions

Although total fitness increased with floral display size, the marginal return on each additional flower declined steadily as display size increased. Therefore, a plant could maximize fitness by producing small displays over a long flowering period, rather than large displays over a brief flowering period.     

Drosophila male sex peptide inhibits siesta sleep and promotes locomotor activity in the post-mated female

Quiescence, or a sleep-like state, is a common and important feature of the daily lives of animals from both invertebrate and vertebrate taxa, suggesting that sleep appeared early in animal evolution. Recently, Drosophila melanogaster has been shown to be a relevant and powerful model for the genetic analysis of sleep behaviour. The sleep architecture of D. melanogaster is sexually dimorphic, with females sleeping much less than males during day-time, presumably because reproductive success requires greater foraging activity by the female as well as the search for egg-laying sites. However, this loss of sleep and increase in locomotor activity will heighten the risk for the female from environmental and predator hazards. In this study, we show that virgin females can minimize this risk by behaving like males, with an extended afternoon ‘siesta’. Copulation results in the female losing 70 per cent of day-time sleep and becoming more active. This behaviour lasts for at least 8 days after copulation and is abolished if the mating males lack sex peptide (SP), normally present in the seminal fluid. Our results suggest that SP is the molecular switch that promotes wakefulness in the post-mated female, a change of behaviour compatible with increased foraging and egg-laying activity. The stress resulting from SP-dependent sleep deprivation might be an important contribution to the toxic side-effects of male accessory gland products that are known to reduce lifespan in post-mated females.     

Cryptic dioecy in Mussaenda pubescens (Rubiaceae): a species with stigma-height dimorphism

Background and Aims

Evolutionary transitions from heterostyly to dioecy have been proposed in several angiosperm families, particularly in Rubiaceae. These transitions involve the spread of male and female sterility mutations resulting in modifications to the gender of ancestral hermaphrodites. Despite sustained interest in the gender strategies of plants, the structural and developmental bases for transitions in sexual systems are poorly understood.

Methods

Here, floral morphology, patterns of fertility, pollen-tube growth and floral development are investigated in two populations of the scandent shrub Mussaenda pubescens (Rubiaceae), native to southern China, by means of experimental and open-pollinations, light microscopy, fluorescence microscopy and scanning electron microscopy combined with paraffin sectioning.

Key Results

Mussaenda pubescens has perfect (hermaphroditic) flowers and populations with two style-length morphs but only weak differentiation in anther position (stigma-height dimorphism). Experimental pollinations demonstrated that despite morphological hermaphroditism, the species is functionally dioecious. The long-styled (L) morph possesses sterile pollen and functions as a female, whereas the short-styled (S) morph is female sterile and functions as a male. Self- and intra-morph pollinations of the S-morph were consistent with those expected from dimorphic incompatibility. The two populations investigated were both S-morph (male) biased. Investigations of early stages of floral development indicated patterns typical of hermaphroditic flowers, with no significant differences in organ growth between the floral morphs. Meiosis of microspore mother cells was of the simultaneous type with tetrads isobilateral in shape. The tapetal cells in anther walls of the L-morph became vacuolized during meiosis I, ahead of the uninucleate microspore stage in the S-morph. In the L-morph, the microspore nucleus degenerated at the tetrad stage resulting in male sterility. Microsporogenesis and male gametophyte development was normal in the S-morph. Failure in the formation of megaspore mother cells and/or the development of megagametophytes resulted in female sterility in the S-morph, compared with normal megasporogenesis in the L-morph.

Conclusions

In M. pubescens, cryptic dioecy has evolved from stigma-height dimorphism as a result of morph-specific sterility mutations.     

Temporal and spatial characteristics of male cone development in Metasequoia glyptostroboides Hu et Cheng

Metasequoia glyptostroboides, a famous relic species of conifer that survived in China, has been successfully planted in large numbers across the world. However, limited information on male cone development in the species is available. In this study, we observed the morphological and anatomical changes that occur during male cone development in M. glyptostroboides using semi-thin sections and scanning electron microscopy. The male cones were borne oppositely on one-year-old twigs that were mainly located around the outer and sunlit parts of crown. Male cones were initiated from early September and shed pollen in the following February. Each cone consisted of spirally arranged microsporophylls subtended by decussate sterile scales, and each microsporophyll commonly consisted of three microsporangia and a phylloclade. The microsporangial wall was composed of an epidermis, endothecium, and tapetum. In mid-February, the endothecium and tapetum layers disintegrated, and in the epidermal layer the cell walls were thickened with inner protrusions. Subsequently, dehiscence of the microsporangia occurred through rupturing of the microsporangial wall along the dehiscence line. These results suggest that the structure, morphology, architecture and arrangement of male cones of M. glyptostroboides are mainly associated with the production, protection and dispersal of pollen for optimization of wind pollination.