Genetic detection of sperm from forced copulations between sympatric populations of Poecilia reticulata and Poecilia picta

The reproductive success of the sneaky mating tactic is difficult to determine in fish with internal fertilization. We approached this problem by developing an assay that allows the recovery of sperm DNA from the reproductive tract of females. This assay was used to test whether sperm transfer occurs between sympatric populations of the guppy, Poecilia reticulata , and its putative sister species, Poecilia picta . Six hundred females of both species from two sympatric sites in Trinidad were collected, and then the contents of the females' reproductive tracts were analysed using reciprocally diagnostic microsatellite markers. Conspecific sperm occurred in approximately 86% of females, whereas heterospecific sperm were found in only 4% of females. Because females of either species do not mate willingly with heterospecific males, the results indicate that sneaky mating results in the transfer of sperm. The data are consistent with the idea that sexual conflict can result in differences in the strength of behavioural isolation between the sexes, and they suggest that behavioural isolation is unlikely to have driven speciation between the guppy and P. picta .  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 397–402.     

Life History Effects Upon Contest Behaviour: Age as a Predictor of Territorial Contest Dynamics in Two Populations of the Speckled Wood Butterfly, Pararge aegeria L.

Although empirical studies of life history effects upon sexually selected phenomena have largely overlooked contest behaviour, recent research suggests that territorial contest participation in butterflies may be mediated by ageing per se. Verbal and mathematical arguments predict lifetime increases in the expression of risky male reproductive behaviours, such as fighting, under a range of ecological conditions. Here we explored the relevance of ageing per se to contest dynamics in two phenologically distinct populations of the speckled wood butterfly, Pararge aegeria. We established 160 experimental like‐population contests among naïve south Swedish and Madeiran dyads, 112 of which we varied the age difference between combatants by 3–4 d. Although this age asymmetry did not influence contest outcome in either population, we found weak positive covariance between the loser's age and contest duration amongst Madeiran males. This is consistent with a slight lifetime increase in aggression because the duration of these aerial persistence contests is a sensitive measure of the losing male's level of aggressive intent. However, the size of this effect (semi‐partial correlation = 0.281) suggests age is not as strongly relevant to contest behaviour in P. aegeria as in other territorial butterflies. We discuss the ways in which ecological differences between butterfly species, particularly with respect to predation risk, may have influenced the evolution of lifetime aggressive strategies in this group.     

Genital variation in a dimorphic moth Selenia tetralunaria (Lepidoptera, Geometridae)

Insect genitals vary greatly among species and provide a key tool for species-level taxonomy. Insects differing in the genitalia are often treated as discrete, reproductively isolated species. This principle dates back to the lock-and-key hypothesis, which states that genitalia vary between species in order to provide a mechanical reproductive isolation system. Thus, the hypothesis assumes low within-species variability in genital traits. However, recent studies suggest that sexual selection may be responsible for the evolution of insect genitalia. We studied allometry and genital size and shape variation in a dimorphic moth Selenia tetralunaria . We found that the genitalia showed negative allometry in relation to body size as reported in many insect and spider species. This allometry was stronger in internal genital structures than it was in external genitalia. We also found that there was more variation in internal compared with external genitalia. Finally, we found that the shape of genital structures differed between morphs in all three examined areas. S. tetralunaria is among the first reported cases of genitally dimorphic insect species. Considerable variation in internal genitalia and especially the presence of genital shape differences between morphs were not consistent with the predictions of the lock-and-key hypothesis.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 297–307.     

Mating distribution and its temporal dynamics affect operational sex ratio: a simulation study

The present study investigated how variation in mating distribution in time and among males influences the operational sex ratio (OSR) with a simulation inspired by paternally caring fish. Varying (1) the potential reproductive rate of each sex, (2) the mating distribution among males, and (3) the length of male mating phase, we created different mating patterns. In each case, we searched for the adult sex ratio that resulted in an OSR of 50% (where sex-roles switch). This approach enabled a comparison with a previous model. We found that the OSR was influenced by the distribution of matings in time and among males when the male mating phase was limited by a parental phase. Furthermore, the mating dynamics were shaped by the fact that the numbers of males and females and their capacities for collateral investment affected OSR immediately from the start of the reproductive season, whereas their times-out had a delayed effect on OSR.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 551–559.     

Parasite-mediated sexual selection and species divergence in Lake Victoria cichlid fish

We investigate the role of parasite-mediated sexual selection in the divergence of two species of Lake Victoria cichlids. Pundamilia pundamilia and Pundamilia nyererei represent a common pattern of male nuptial colour divergence between haplochromine sister species: metallic grey–blue in P. pundamilia and bright yellow and red in P. nyererei . Female mating preferences for different male colours maintain the genetic and phenotypic differentiation of the two species in clear water. Previous work indicated that the red coloration of P. nyererei males, which is subject to directional sexual selection, may be a carotenoid-dependent signal of parasite infestation rate. In the present study, we find a parallel result for P. pundamilia : bright blue males are infected with fewer species of parasites. We also find that parasite infestation rates differ quantitatively between the two species in a way that is consistent with species differences in diet and microhabitat. We conclude that parasite-mediated sexual selection may have contributed to the divergence of female mating preferences between P. pundamilia and P. nyererei , and may currently strengthen reproductive isolation between these species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94 , 53–60.     

Antler size and fluctuating asymmetry in red deer (Cervus elaphus) stags and probability of becoming a harem holder in rut

Red deer hinds play a significant role in selecting stags for mating. We tested the hypotheses that in red deer ( Cervus elaphus ) the probability of becoming a harem holder (and hence achieving reproductive success) occurs in stags bearing larger, branched antlers and showing low fluctuating asymmetry (FA). Eleven antler characteristics were measured; absolute and relative FA were calculated on 51 cast antler sets from 19 individually recognized stags. Probability of becoming a harem holder (PBHH) was originally analysed separately, i.e. for antler size and FA of each antler characteristic and calculated factors for both antler size and FA. If analysed separately, large antler size and low relative but high absolute FA increased PBHH. When we combined antler size and FA of antler characteristics in one model using antler size and FA factors, however, PBHH and achieving reproductive success were mainly dependent on increasing antler size and enhanced antler branching rather than on FA. We conclude that in contrast to antler size, FA is unlikely to play any significant role in sexual selection as an indicator of individual quality.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 59–68.     

Reproductive characters in a gynodioecious species, Silene italica (Caryophyllaceae), with attention to the gynomonoecious phenotype

Gynodioecious populations (i.e. populations with female and hermaphrodite individuals) often contain a third phenotype with an intermediate sex expression. In Silene italica , this phenotype is characterized by a mixture of pistillate and perfect flowers and is thus gynomonoecious. To characterize sexual functions of these gynomonoecious individuals and their potential influence in the maintenance of gynodioecy, reproductive characters of the three sexual phenotypes were compared over 2 years in several families of S. italica produced by crossing. We found that gynomonoecious individuals were intermediate for flower production and female fertility characters, although they did not always significantly differ from female individuals. Perfect flowers of gynomonoecious and hermaphrodite plants were similar in size and pollen production. Gynomonoecious individuals were thus intermediate in female and in male functions. Family effects were found for most of the characters. The female advantage (i.e. the fertility of females compared to the female fertility of pollen producing plants) was not dramatically different when gynomonoecious plants were taken into account.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 583–591.     

Female morphology,web design,and the potential for multiple mating in Nephila clavipes: do fat‐bottomed girls make the spider world go round?

In animal species where females mate with multiple males, female mating success might be expected to covary with aspects of female morphology, such as size or shape. Spiders are especially interesting in this regard, as the females of several spider groups weave intricate webs that often accommodate multiple male spiders, all of whom are potential mates. Because web design is likely to be dependent on female size/shape, we use multivariate methods to assess the relationships among female morphology, web design, and reproductive ecology over a range of body sizes in the orb-weaving spider Nephila clavipes . Of the measured variables, only abdomen size explained a significant amount of the variation in number of males on a web, and this relationship holds even after statistically accounting for body size. Because abdomen size is an indicator of body condition in spiders, we suggest that condition is likely to be an important factor relating to potential mating success in female spiders. We found no evidence for an association between web design and number of males on a web, although our data indicate that larger females build webs that are both larger and further from the ground than those of smaller females.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 95−102.     

Asynchronous arrival pattern, operational sex ratio and occurrence of multiple paternities in a territorial breeding anuran, Rana dalmatina

Understanding why females mate multiply is a major issue in evolutionary ecology. We investigated the consequences of an asynchronous arrival pattern on male competition and multiple paternity in the apparently monoandrous agile frog ( Rana dalmatina ). The largest frogs arrived first and both males and females lost weight significantly during the spawning period. Asynchronous arrival at breeding sites resulted in a male-biased operational sex ratio (OSR). The OSR was more strongly male-biased at the beginning and at the end of the breeding period when the number of satellite males increased. All females mated only once, but multiple paternity within clutches occurred at the beginning and the end of the breeding period. The influence of asynchronous arrival and biased sex ratio suggests that reduced variance or bet-hedging promoting female fitness had only a reduced role in the evolution of polyandry, and polyandry is likely to be associated with male benefits. Polyandry in frogs can be explained either by forced mating as a result of sexual conflict or by clutch piracy. By modifying intrasexual competition, asynchronous arrival and changes in OSR may have a decisive influence upon the evolution of mating systems and favour both polyandry and stable coexistence of alternative mating behaviour.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 191–200.     

Impaired sperm quality,delayed mating but no costs for offspring fitness in crickets winning a fight

The outcome of male–male contest competition is known to affect male mating success and is believed to confer fitness benefits to females through preference for dominant males. However, by mating with contest winners, females can incur significant costs spanning from decreased fecundity to negative effects on offspring. Hence, identifying costs and benefits of male dominance on female fitness is crucial to unravel the potential for a conflict of interests between the sexes. Here, we investigated males' pre‐ and post‐copulatory reproductive investment and its effect on female fitness after a single contest a using the field cricket Gryllus bimaculatus. We allowed males to fight and immediately measured their mating behaviour, sperm quality and offspring viability. We found that males experiencing a fight, independently of the outcome, delayed matings, but their courtship effort was not affected. However, winners produced sperm of lower quality (viability) compared to losers and to males that did not experience fighting. Results suggest a trade‐off in resource allocation between pre‐ and post‐mating episodes of sexual selection. Despite lower ejaculate quality, we found no fitness costs (fecundity and viability of offspring) for females mated to winners. Overall, our findings highlight the importance of considering fighting ability when assessing male reproductive success, as winners may be impaired in their competitiveness at a post‐mating level.     

The evolution of sexual size dimorphism in cottontail rabbits (Sylvilagus,Leporidae)

In mammals, ‘female‐biased’ sexual size dimorphism (SSD), in which females are larger than males, is uncommon. In the present study, we examined Sylvilagus, a purported case of female‐biased SSD, for evolutionary correlations among species between SSD, body‐size, and life‐history variables. We find that: (1) although most species are female‐biased, the degree and direction of SSD vary more than was previously recognized and (2) the degree of SSD decreases with increasing body size. Hence, Sylvilagus provides a new example, unusual for a female‐biased taxon, in which allometry for SSD is consistent with ‘Rensch's Rule’. As a corollary to Rensch's Rule, we observe that changes in SSD in Sylvilagus are typically associated with larger, more significant changes in males than females. Female‐biased SSD could be produced by selection for larger females, smaller males, or both. Although larger female size may be related to high fecundity and the extremely rapid fetal and neonatal growth in Sylvilagus, we find little evidence for a correlation between SSD and various fecundity‐related traits in among‐species comparisons. Smaller male size may confer greater reproductive success through greater mobility and reduced energetic requirements. We propose that a suite of traits (female dispersion, large male home ranges, reduced aggression, and a promiscuous mating system) has favoured smaller males and thus influenced the evolution of SSD in cottontails. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 141–156.     

The secondary copulatory organ in female ground weta (Hemiandrus pallitarsis,Orthoptera: Anostostomatidae): a sexually selected device in females?

Secondary sexual devices in female insects, primarily abdominal modifications, appear to function as a means of thwarting coercive mating attempts by males or are, in rare cases, sexually selected adaptations. Female ground weta, Hemiandrus pallitarsis (Orthoptera: Anostostomatidae), have an elaborate elbowed device on the underside of the mid-abdomen. Experimental removal of this accessory organ shows that it does not increase the probability of mating as predicted by the thwart-copulation hypothesis. Instead, removal prevents copulation, thus demonstrating that it is a secondary copulatory device. The male attaches to the organ both at the beginning of copulation and at the end, when he positions himself to adhere a spermatophylax food gift onto the mid-ventral region of his mate. The female accessory organ does not function to manipulate eggs or larvae (females provide care to their single clutch of offspring) and is unlikely to be a copulatory structure that prevents hybridization. The great extent of the modification of the ventral abdominal segments of H. pallitarsis females compared to other Hemiandrus species is consistent with a history of sexual selection on the accessory organ. Taken together, these results and the finding that the length of the accessory organ of H. pallitarsis correlates with female fecundity, suggest that this structure evolved under sexual selection to acquire nuptial gifts from males.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 463–469.     

Mate location, antennal morphology, and ecology in two praying mantids (Insecta: Mantodea)

The sensory systems employed by animals to locate potential mates are diverse. Among insects, chemical and acoustic signals are commonly used over long distances, with visual signals playing a role in close-range orientation and courtship. Within groups that exhibit a scramble competition mating system, selection on mate searching ability will be particularly strong. Clearly, aspects of the species ecology, such as habitat complexity and population density, will be crucial in the evolution of mate searching systems and sexual signals. Praying mantids exhibit both chemical and visual sexual signalling behaviour, and also vary in their ecology. This study employs scanning electron microscopy of antennal sensory morphology and behavioural assays to investigate the relative importance of chemical and visual signalling in two Australian praying mantid species: Pseudomantis albofimbriata and Ciulfina biseriata . As predicted, the high level of habitat complexity, low population density and strong male dispersal capability of P. albofimbriata corresponded to the use of airborne sex pheromones. Conversely, the open habitat, high population density, and poor dispersal of C. biseriata corresponded to a greater reliance on short-range visual cues for mate location.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 307–313.     

Changes in sperm stores, ejaculate size, fertilization success, and sexual motivation over repeated matings in the common toad, Bufo bufo (Anura: Bufonidae)

Fertilization is of central importance in the determination of reproductive success for both males and females. In species where males have the chance to mate repeatedly within a short period of time, sperm stocks may become depleted and males may have to carefully economize on their sperm reserves. Also, intensive intrasexual competition for females and repeated matings may lead to exhaustion on the behavioural level. To determine whether the reproductive potential of males is limited and if such a limitation is due to behavioural exhaustion or sperm depletion, we experimentally investigated changes in sperm stores, sperm expenditure, fertilization success, and sexual motivation over three repeated matings in the common toad, Bufo bufo , where the breeding season is short and sequential polygyny occurs. At the end of the breeding season, the number of sperm stored in the testes of males mated repeatedly was close to 50% lower than in testes of unmated males. Ejaculate size, which was estimated by applying a novel method allowing direct quantification, decreased by 88% from first to third matings. We also observed a drop in fertilization success from the first two to third matings by 65%, which was largest in males that had started the reproductive season in bad body condition. Some of these males also showed a decreased interest in females in the third mating round. Our results suggest that sperm depletion and loss of sexual motivation may together set a limit to the reproductive potential of common toad males. The present study draws attention to a limitation in reproductive potential, which may occur more often than currently anticipated and has the potential to strongly influence several aspects of reproductive behaviour.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 361–371.     

Identifying sources of variation in reproductive and life-history traits among five populations of a Chinese lizard (Takydromus septentrionalis, Lacertidae)

Research on life-history traits of squamate reptiles has focused on North American species, while Asian taxa have been virtually ignored. In order to understand general patterns in reptile life histories, we need a broader data base. Our study on the slender-bodied lacertid lizard Takydromus septentrionalis provides the first detailed information on factors responsible for intraspecific variation in reproductive output and life history in a Chinese reptile. Clutches of recently collected lizards from five widely separated localities in China revealed major divergences in female body size at maturation, mean adult female body size, body condition after oviposition, size-adjusted fecundity, relative clutch mass, and mass and shape of eggs. Most of these geographical differences persisted when the same groups of females were maintained in identical conditions in captivity. Additionally, reproductive frequency during maintenance under laboratory conditions differed according to the animals' place of origin. Thus, the extensive geographical variation in reproductive and life-history traits that occurs within T. septentrionalis is exhibited even in long-term captives, suggesting that proximate factors that vary among localities (local conditions of weather and food supply) are less important determinants of life-history variation than are intrinsic (presumably genetic) influences. The maternal abdominal volume available to hold the clutch may be one such factor, based on low levels of variation in Relative Clutch Mass among populations, and geographical variation in the position of trade-off lines linking offspring size to fecundity.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 443–453.     

Plant clonality, mutation, diplontic selection and mutational meltdown

Apomixis is a very common characteristic in vascular plants. It occurs in two general forms: either subversion of the sexual system (agamospermous seeds or apogamous sporophytes in non-seed plants) or vegetative reproduction. In this communication, only the mutational consequences of vegetative reproduction are considered. Vegetative reproduction involves the replication of apical meristems, especially shoot apical meristems. Three general types of shoot apical meristems occur in the vascular plants: single tetrahedral apical initial, unstratified with impermanent initials and stratified with impermanent initials. Each meristem type has different consequences with regard to mutation, diplontic selection and the possibility of mutational meltdown.  © 2003 The Linnean Society of London. Biological Journal of the Linnean Society , 2003, 79 , 61–67.     

Chromosome study of the fern genus Cyrtomium (Dryopteridaceae)

Cyrtomium (Dryopteridaceae) is an Asiatic genus comprising about 40 species characterized by having anastomosing veins that form areolae with included veinlets. Twelve chromosome counts representing 11 taxa were made in the present study. The chromosome numbers of six species endemic to China are reported for the first time: C. uniseriale , 2 n  = 164; C. guizhouense , 2 n  = 82; C. shingianum , n  = 82, 2 n  =  c .164; C. chingianum , 2 n  = 164; C. urophyllum , 2 n  = 82 and C. aequibasis , 2 n  = 123. The results were used to show that (1) C. uniseriale should be reduced to varietal status under C. balansae ; (2) subseries Balansana is not closely related to any other Cyrtomium species and should be separated from Cyrtomium ; and (3) C. guizhouense and C. lonchitoides are basal groups when subseries Balansana is not considered. These results were also supported by morphology. A high level of differentiation is a distinct characteristic in Cyrtomium . The genus has two reproductive types: sexual and apogamous. Sexual species are distributed mostly in China. Southwestern China is a modern diversity centre of Cyrtomium , with 80.6% of known species occurring there. Many species are endemic, most of which are sexual tetraploids or apogamous triploids. Both the apogamous reproductive type and polyploid species are adaptions to limestone habitats.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 221–228.     

Functional males in pair‐mating outcrossing hermaphrodites

In the mating system of simultaneously hermaphroditic animals, sexual allocation is predicted to vary as a function of the number of potential mates. According to the Hermaphrodite's Dilemma, sexual conflict over the preferred sexual role in hermaphroditic animals is resolved by reciprocity (i.e. by alternating sexual roles), accompanied by the animals' occasional cheating in the preferred role at a relatively low frequency. In a 350‐generation‐old laboratory strain of the pair‐mating outcrossing hermaphroditic polychaete worm Ophryotrocha diadema, we show that 9% of the individuals mated only in the male role over long periods, indicating a male‐role preference (temporary functional males). Furthermore, 2% of the individuals mated for their whole lifetime exclusively as males (permanent functional males). These findings indicate that the sex allocation of some individuals may vary from the predicted optimal sex allocation for the population. Morphologically, functional males exhibited a hermaphroditic phenotype (i.e. they matured a single batch of oocytes that they never laid and acted as functional males). We show that temporary functional males appeared in hermaphroditic populations under promiscuous mating regimes significantly more often than under monogamous ones. Indeed, under promiscuity, there are many mating opportunities and O. diadema hermaphrodites compete for mates, whereas, under monogamy, the two partners regularly take turns in laying cocoons and fertilizing their partner's cocoon. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 451–456.     

Testing the role of coadapted genes versus bet-hedging for mating strategies in colour polymorphic pygmy grasshoppers

Recent investigations of mate choice indicate that the genetic effect of sires on offspring fitness may depend on the interaction between maternal and paternal genotypes and the environmental conditions experienced by the offspring. Alternative colour morphs of the pygmy grasshopper, Tetrix subulata , represent ecological strategies that differ in body size, life history, thermoregulatory behaviour, and habitat selection. The hypothesis that selection promotes behaviours maintaining coadapted gene complexes predicts individuals to mate assortatively with respect to colour morph. On the other hand, the bet-hedging hypothesis predicts that the temporal variability of the environment inhabited by these animals may select for disassortative mating behaviour resulting in heterogeneous offspring. To distinguish between these competing hypotheses, we investigated mating behaviours using dual-choice experiments. Our results were not in agreement with the prediction of assortative mating but suggest instead that matings were random with regard to colour morph. Polyandry was common, and females mated with the second male regardless of whether the first mating was assortative or disassortative. Polyandry also was equally frequent among females in triads in which the two males belonged to different colour morphs as in triads where both males belonged to the same colour morph. A field experiment confirmed that polyandry occurred also among free-ranging individuals, and uncovered variation in mating success among male colour morphs, probably due to indirect effects of coloration on activity or habitat use. The consequences of this random and polyandrous mating strategy for the evolutionary dynamics of the colour polymorphism remain to be explored.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 491–499.     

The molecular systematics of Leiopotherapon unicolor (Günther, 1859): testing for cryptic speciation in Australia's most widespread freshwater fish

Leiopotherapon unicolor is the most widespread freshwater fish species in Australia. A comprehensive allozyme and mitochondrial DNA 16S rRNA data set was assembled from 141 specimens of L. unicolor collected Australia-wide in order to test for cryptic speciation in this far-ranging species. Surprisingly, little genetic diversity was observed within L. unicolor and provided no evidence for the existence of cryptic species within this lineage. In contrast, a small sample set of L. aheneus used as the outgroup showed two highly divergent haplotypes strongly suggestive of cryptic speciation. L. unicolor has a number of ecological and life history attributes that may explain the lack of significant genetic divergence over substantial geographical distances. The occurrence of other widespread fish and crustacean species that also display only limited genetic diversity indicate that climate conditions more favourable to dispersal across central and northern Australia than is suggested by the extent of present-day aridity have occurred in the relatively recent geological past.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 537–552.