ANALYSIS OF REPRODUCTIVE SYSTEM ONTOGENY AND HOMOLOGY IN NASSARIUS VIBEX (GASTROPODA: BUCCINIDAE: NASSARIINAE)

The post-larval development of the reproductive system in Nassariusvibex was investigated using a histological approach, to establishthe sequence of organogenesis and the contribution of differentorganogenetic components to the adult system. This researchis part of a broader investigation with two primary objectives.The first is to provide a detailed analysis of reproductivesystem development that can be used to re-evaluate existingcharacter sets and generate new characters for reconstructing gastropodphylogenies. The reproductive tract has always been a promisingbut problematic system to work with in phylogenetic research,because of the uncertain homology of many parts of the system.Most of the reproductive system itself develops during post-larvalontogeny, a phase of gastropod development that has been investigatedin very few taxa; thus this line of research has the potentialto provide a wealth of new information. The second objective isto establish comparable organogenetic series for representative gastropodtaxa that can be used to investigate the significance of heterochronicprocesses in the evolution of gastropod organ systems. The reproductive system in Nassarius vibex develops very latein ontogeny from two ontogenetic components in the male andthree in the female. Development and differentiation of theorgan system is not completed until near maturity. In both sexes,ductal components develop first and fuse to form the rudimentaryreproductive tract. Gonads and accessory reproductive structuresdevelop after the ductal components are fused, and glandulartissues do not appear until near maturity. The penis does notdevelop until near maturity. The capsule and albumen glandsin this species are broadly conjoined, unlike the situationin other members of Nassarius. The ingesting gland developsbetween them as a dorsal outgrowth of the glandular lumen. (Received 25 April 2000; accepted 1 July 2000)     

Development of indices for nonsacrificial sexing of imposex-affected Hexaplex (Trunculariopsis) Trunculus (Gastropoda: Muricidae)

The muricid Hexaplex (Trunculariopsis) trunculus lacks externalsexual dimorphism and is highly affected by imposex, which furthercomplicates its sexual identification. In this context, theaim of this study was to develop sexual indices based on thedimensions of male and imposex-affected female penis, whichcould constitute a useful, simple and nonsacrificial tool forsexing live specimens of T. trunculus. The adoption of sexualindices consisting of penis dimensions of both sexes relativeto individual size revealed a high accuracy in the sexual identificationof sacrificed specimens (>95% correct sexing). Additionally,multivariate discriminant analysis allowed correct sexing of98.8% of the original 1053 sacrificed individuals, with accuratesexual identification being higher for males (99.5%) than forimposex-affected females (97.7%). An anaesthetization experimentwas performed to investigate the effects produced by the anaesthetic(MgCl₂) on penis measurements, to test this nonsacrificial approachand to validate the previously developed sexual indices. Theanaesthetic provoked an expected enlargement in penis dimensionsbut, despite this side effect, the sexual indices developedfor sacrificed specimens were still highly successful in sexinganaesthetized T. trunculus (generally more than 95% correctsexual identification). The practical application and some limitationsof developing and employing this kind of index for the sexualidentification of T. trunculus and other imposex-affected gastropodspecies are discussed. (Received 30 May 2005; accepted 17 January 2006)     

稻褐飞虱雄虫第二种鸣声及其生殖竞争意义

本文研究了稻褐飞虱Nilaparvata lugens雄虫第二种鸣声(SMVS)及其生殖竞争意义,结果如下：1.SMVS是2头或2头以上同种雄虫共栖一处时才产生的特殊信号,不同密度, 不同虫龄雄虫SMVS的呜叫习性不同,虫龄和温度对SMVS有明显影响。2.具SMVS行为的雄虫在求偶、交配系列行为中的优势逐步明显,最终成功交配的SMVS雄虫达70.2%,而非SMVS雄虫仅“14.9%。3.回放SMVS录音可以显著降低稻褐飞虱交配率(下降41.0%)。 SMVS是一种生殖竞争信号,具种的专一性。     

Size, operational sex ratio, and mate-guarding success of the carrion beetle, Necrophila americana

When male insects guard females until oviposition, the benefitsfrom last-male sperm precedence must outweigh the costs of relinquishingadditional fertilizations. The profitability of guarding isincreased when males guard large, fecund females and when femalesare scarce because fewer fertilizations are sacrificed. However,the male reproductive success is not only determined by theprofitability of guarding but also by his ability to maintainguarding. In this study, we used male carrion beetles (Necrophilaamericana) to examine the effects of sex ratio, male relativesize, and female quality on the ability to guard. First, wepresent a model of mate guarding that explores factors, suchas sperm precedence, sex ratio, male size, and female quality,that influence the profitability of postcopulatory riding. Ourmodel predicts that large N. americana males should preferentiallyguard the largest female only when the sex ratio is male biasedand sperm precedence is above 80%. In contrast, small malesgain little from guarding because they are not likely to maintainit and be the last male to mate. Then, we tested these predictionsby manipulating sex ratio, relative male size, and female quality.All males in equal sex ratio and large males in male-biasedsex ratio guarded females significantly longer than did malesin female-biased sex ratio. In male-biased sex ratio, largemales guarded significantly longer and achieved more takeoversthan small males. Large females were guarded longer. The successof guarding males in this beetle depends on their size relativeto other males and the operational sex ratio.     

Male courtship signals and female signal assessment in Photinus greeni fireflies

The evolutionary dynamic of courtship signaling systems is drivenby the interaction between male trait distributions and femalepreferences. This interaction is complex because females maychoose mates based on multiple components of male signals, andfemale preference functions may vary depending on mate availability,female reproductive state, and environmental conditions. InPhotinus fireflies (Coleoptera: Lampyridae), flying males emitbioluminescent flash signals to locate sedentary females, whichreply selectively to attractive male flash signals with theirown response flash. In this study, we first examined temporalvariation in the paired-pulse flash patterns produced by Photinusgreeni males in the field and found significant among-male variation(70% of total variation) in interpulse intervals (IPIs). Therewas no significant relationship between male IPI and spermatophoresize, suggesting that P. greeni male courtship signals do notprovide females with reliable indicators of male material resources.In laboratory playback experiments, we presented P. greeni femaleswith simulated flash signals to assess how IPI and pulse durationindependently affected the likelihood of female flash response.We also examined the effects of female body mass and time duringthe mating season on female preference functions, hypothesizingthat females would be less discriminating when they were heavier(more fecund) and when mate availability declined. We foundthat P. greeni females discriminated among signals within theirspecies' range based primarily on flash pattern IPI. Neitherthe time during the mating season nor female weight alteredfemale preference functions for IPI, although season did influencefemale response to pulse duration. These results reveal thatP. greeni females discriminate among conspecific males basedprimarily on male IPIs, the same signal character previouslyshown to be important for firefly species recognition. Fieldplayback experiments indicated that female responsiveness peakednear the average IPI given by males at different ambient temperatures,suggesting that fireflies exhibit temperature coupling similarto that seen in many acoustically signaling animals.     

Paternal care as a conditional strategy: distinct reproductive tactics associated with elaboration of plumage ornamentation in the house finch

When individuals in a population differ in physiological conditionand residual reproductive value, selection should favor phenotypicplasticity in reproductive investment such that individualsare able to adopt the reproductive tactic that results in thehighest fitness under given conditions. Here we examined reproductivetactics in relation to the elaboration of condition-dependentsexual ornamentation (carotenoid breast coloration) in a Montanapopulation of the house finches (Carpodacus mexicanus). Malesused distinct reproductive tactics depending on elaborationof their sexual ornamentation. Males with red pigmentation (maximum ornament elaboration) paired with females that nestedearlier, but these males did little provisioning of incubatingfemales and nestlings. In contrast, males with yellow colorationpaired with females that nested later, but these males fedfemale and nestlings more. Consequently, for red males offspringrecruitment was primarily affected by earlier nest initiation, whereas in yellow males it was affected most by male provisioning.In males with intermediate plumage coloration, all measuredcomponents, nest initiation, provisioning of incubating female,and nestling feeding, strongly contributed to offspring recruitment.The fitness consequences of alternative reproductive tacticsof males were influenced by breeding experience and fidelityof their mates. Among first-time breeders, red males achievedthe highest fecundity because of the advantage gained throughearly nesting and pairing with more experienced females andbecause of compensation by their mates for low male provisioningof nestlings. Among experienced breeders, males with intermediateplumage coloration achieved the highest fecundity because ofthe combined benefits of relatively early pairing and high parental care. High variation in sexual ornamentation in a Montana populationof house finches may favor distinct associations of sexualdisplays with a particular set of reproductive behaviors.     

Sexual signaling in the European bitterling: females learn the truth by direct inspection of the resource

In many taxa females appear to base their mate choice on multipletraits. But the relative importance of different traits inmate choice has rarely been determined. Here we show that femalesof a freshwater fish, the European bitterling, Rhodeus sericeus,base their mate choice on multiple traits that differ in theirreliability as indicators of expected reproductive successand are used at different stages of the decision process. Theinitial decision to inspect a male is based on male behaviorand red coloration, whereas the final spawning decision isbased on the quality of the live unionid mussel, Anodonta anatina,that the male is defending as an oviposition site. Male traitsmay indicate which males are worth inspecting by reflectingmale quality, such as reproductive condition and genetic constitution.Male traits do not, however, reflect mussel quality, as bright males also court females vigorously toward mussels that yielda low probability of survival of the offspring. Females, onthe other hand, are choosier than males in their choice ofspawning site and seem to gain reliable information about thesurvival probability of the eggs by inspecting the mussel directly.     

The Red Queen Visits Sage Grouse Leks

Coevolution between parasites and host is a sufficient althoughnot necessary condition for the evolution of secondary sexualcharacteristics. I review evidence supporting the role of parasitesin the maintenance of lek behavior in Sage Grouse (Centrocercusurophasianus). Males bearing avianmalaria (Plasmodium pediocetii)or lice (Lagopoecus gibsoni or Goniodes centrocerci) have significantlylower reproductive success than noninfected males. Malaria-infectedmales attend leks significantly less frequently and lek attendanceis highly correlated with male reproductive success. Inaddition,males with malaria secured copulations later in the breedingseason with hens that wereyounger, in poorer condition, andless successful than mates of malaria-free males. Lice createhematomas on the air sacs of males which females can detectto avoid lousy males. Results of our field studies are reinforcedby experiments; captive males given antibiotics to reduce parasiteloads are chosen more often by females in arena trials. Ourresults lend empirical support for Hamilton and Zuk's (1982)interpretation of the RedQueen's hypothesis, although many unknownsremain in our understanding of the interaction between parasitesand Sage Grouse.     

THE ESTUARINE MUD SNAIL, NASSARIUS OBSOLETUS: ABNORMALITIES IN THE REPRODUCTIVE SYSTEM

Females of the dioecious snail Nassarius obsoletus may havethree male characteristics: a penis, a vas deferens, and theconvolution of a normally straight gonadial oviduct to resemblea stunted mimic of the vesicula seminalis in the male. The firstcharacteristic is the most common and the last is the leastcommon. Collectively these characteristics were called imposex.A system for evaluating its frequency of occurrence and intensityof expression was developed. The frequency and intensity ofimposex was similar among different age groupings of snails,though there may be a trend towards less imposex in juveniles.The differences in the frequency and intensity of imposex betweengroups of parasitized and unparasitized females were very small.In males the reduction of penis size due to parasites was muchlarger. This pattern ofimposition of male characteristics onfemales is a new syndrome which does not resemble reported formsof hermaphroditism or pseudohermaphroditism related to age orparasitism. ^*Current address: Community Health Program, Electric Power ResearchInstitute, P.O. Box 10412, Palo-Alto, California 94303, U.S.A. (Received 28 August 1979;     

Proximate developmental mediators of sexual dimorphism in size: case studies from squamate reptiles

Sexual dimorphism in size (sexual size dimorphism; SSD) is nearlyubiquitous, but the relative importance of genetic versus environmentalcontrol of SSD is not known for most species. We investigatedproximate determinants of SSD in several species of squamatereptiles, including three species of Sceloporus lizards andthe diamond-backed rattlesnake (Crotalus atrox). In naturalpopulations of these species, SSD is caused by sexual differencesin age-specific growth. Males and females, however, may oftenshare similar potentials for growth: growth is strongly responsiveto the availability of food, and sexual differences in growthcan be greatly suppressed or completely absent under commonenvironmental conditions in the laboratory. Sexually divergentgrowth is expressed in natural environments because of inherentecological differences between males and females and becauseof potential epigenetic effects of sex-specific growth regulators.In field-active Sceloporus, sexual differences in growth rateare associated with sexual divergence in plasma testosterone.Experiments confirm that testosterone inhibits growth in speciesin which females are larger (for example, S. undulatus and S.virgatus) and stimulates growth in those in which males arelarger (for example, S. jarrovii). Interestingly, however, sexualdivergence in plasma testosterone is not accompanied by divergencein growth in S. jarrovii or in male-larger C. atrox in the laboratory.Furthermore, experimental effects of castration and testosteronereplacement on growth are not evident in captive S. jarrovii,possibly because growth effects of testosterone are supersededby an abundant, high-quality diet. In female-larger S. undulatus,growth may be traded-off against testosterone-induced reproductivecosts of activity. In male-larger species, costs of reproductionin terms of growth are suggested by supplemental feeding ofreproductive female C. atrox in their natural environment andby experimental manipulation of reproductive cost in femaleS. jarrovii. Growth costs of reproduction, however, do not contributesubstantially to the development of SSD in male-larger S. jarrovii.We conclude that the energetic costs of testosterone-induced,male reproductive behavior may contribute substantially to thedevelopment of SSD in some female-larger species. However, despitestrong evidence that reproductive investment exacts a substantialcost in growth, we do not support the reproductive cost hypothesisas a general explanation of SSD in male-larger species.     

Allometry and sexual selection of male weaponry in Wellington tree weta, Hemideina crassidens

Both male and female Wellington tree weta, Hemideina crassidens,use cavities in trees as diurnal shelters. That these galleriesare often limiting in nature offers males the opportunity toincrease their reproductive success by monopolizing galleriesand the females residing in them. Male H. crassidens, can matureat either the 8th, 9th, or 10th instar, whereas females matureat the 10th instar only, and male head (and mandible) size positivelycovaries with ultimate instar number. It has been suggestedthat males fight for control of galleries by using their enlargedmandibles as weapons, and males with larger mandibles controlgalleries with more females. In the present study, I presenta statistical examination of sexual dimorphism, showing thattraits related to head size are on average significantly largerin males, whereas traits related to body size are on averagesignificantly larger in females. I tested three predictionsaddressing the hypothesis that sexual selection is driving megacephalyin male H. crassidens. First, as predicted, traits related tohead size show a positive allometric relationship with bodysize in males but not in females. Second, adapting a novel statisticaltechnique based on maximum likelihood and bootstrapping revealedthat males, but not females, exhibit a multimodal distributionin head and body size traits. This is likely a consequence ofmales maturing at one of three instars, which results in positivecovariance between the ultimate instar number and morphologicaltraits. Third, as predicted, single adult males with largerheads reside in galleries housing larger groups of adult females.     

The effect of age on encounters between male crab spiders

In males that compete aggressively for females, size and agemay determine which males obtain access to these females. Inthe present study, we use the crab spider, Misumena vatia, aspecies with males that do not grow after becoming sexuallymature adults, to test the hypothesis that age affects the successof males competing for access to females. M. vatia is an excellentspecies to test this hypothesis because it is possible to disentangleage from size, characters that typically vary together in thespecies usually tested. We staged encounters between similar-sizedolder and younger adult male M. vatia in the presence of a femaleto determine the role of age in male access to females. Encountersbetween the males occurred during 63.3% of these pairings. Youngermales won significantly more (70.2%) of the encounters thandid older ones, but did not initiate significantly more encountersthan did older ones (62.5%). Although older males won only 29.8%of these encounters, they initiated significantly more (76.5%)of them than predicted by chance. This design also allowed usto test Parker's hypothesis that older individuals should exhibita higher level of aggression than younger ones. However, attacksby younger males were most likely to include extensive bodilycontact, whereas attacks by older males involved significantlyless contact. These results counter the frequent assertion thatolder individuals usually prevail over younger ones in contestsfor access to females, and that older males are more likelyto engage in highly overt aggression than are younger ones.Aging may decrease reproductive opportunities and success ratesof male M. vatia, affecting as many as nearly one-fourth oftheir encounters.     

The Neuropeptide APGWamide as a Penis Morphogenic Factor (PMF) in Gastropod Mollusks

The goal of this study was to further investigate the role ofendogenous APGWamide levels in imposex induction in snails.APGWamide is a common neurotransmittor/neuromodulator peptidefound in many species of molluscs, and is often related to sexorgan growth or reproductive behavior. Mud snails (Ilyanassaobsoleta) were collected from the Rachel Carson Estuarine Reservenear Beaufort, NC, and were dosed with the environmental contaminanttributyltin (TBT), testosterone (T), or solvent vehicle (EtOH/saline) controls. Both TBT and T have been shown previouslyto induce female snails to grow penises (a condition termedimposex), and to increase male penis size. Male normalized penislength was correlated to endogenous APGWamide levels (as measuredby Western blotting of whole animal homogenates, r² = 0.475),and control males had significantly higher APGWamide levelsthan control females. All TBT-treated animals, (male, female,and imposex) had levels of APGWamide similar to control malesand significantly higher than control females. In testosteronetreated animals, APGWamide levels were the same as controlsand it is likely that testosterone interferes with a downstreamsignaling event to induce imposex. In addition, immunohistochemistryfor APGWamide expression in abdominal areas was done on female,male and imposex snails collected from the wild. The patternof APGWamide in imposex snails was similar to male snails, showinglarge patches of immuno-reactive areas in the top portion ofthe visceral mass. In female snails, no areas of cross-reactivitywere found.     

Sexual selection for large male size in a polyandrous butterfly: the effect of body size on male versus female reproductive success in Pieris napi

Sexual selection theory predicts that the larger sex shouldbe that for which fitness increases at the faster rate withsize. In butterflies, as in most invertebrates, females areusually the larger sex, but previous comparative analysis hasshown that relative male size increases with female polyandryamong butterflies. In agreement with this pattern, males arelarger than females in the strongly polyandrous green-veinedwhite butterfly, Pieris napi L., and in this article we assessthe size dependence of reproductive success in both sexes. Inan experiment where virgin males and females were released inthe field, we found no strong association between size and malemating success. However, laboratory experiments showed thatthere was a strong correlation between size and the ejaculatethat the male delivered to the female at mating and that largeejaculates delayed female remating for a longer time comparedto small ejaculates. Moreover, female P. napi utilize male-derivednutrients received at mating to increase their fecundity. Hence,large males sire more offspring both by way of donating morenutrients to female egg production and by way of delaying femaleremating (given that the last male to mate with the female willfather most of the offspring). Laboratory experiments showedthat the association between size and fecundity was low, ornonexistent, among P. napi females allowed to mate only once.However, weak size dependence was found for polyandrous females.We hypothesize that size dependence of female fecundity maybe especially weak among polyandrous butterflies because a fundamentalsource of variation in fecundity relates to their ability tofind nutrient giving males, an ability which may be unrelatedto female size. According to this hypothesis there is a causalassociation between weak size dependence of female fecundityand polyandry, and a strong size dependence of male reproductivesuccess that may underlie the comparative pattern of positivecorrelation between relative male size and polyandry.     

Sexual harassment in live-bearing fishes (Poeciliidae): comparing courting and noncourting species

Sexual harassment by males has been reported from several live-bearingfishes (Poeciliidae) and has been shown to inflict costs onfemales. For example, poeciliid females have reduced feedingopportunities when accompanied by a male because females dedicateattention to avoiding male copulation attempts. Poeciliid speciesdiffer considerably in male mating behavior, such as the presenceor absence of courtship. Courting males display in front ofthe females, but males attempting to sneak-copulate approachfemales from behind, that is, in the blind portion of theirvisual field, and force copulations, which can be viewed asa male persistence trait. We predicted that poeciliid femalesneed to be more vigilant in the presence of noncourting males,and costs of harassment by noncourting males might be stronger.In a comparative approach we examined the costs of male sexualharassment for females as reduced feeding time in 9 speciesof live-bearing fishes, including courting (Poecilia latipinna,Poecilia reticulata, Xiphophorus cortezi, Xiphophorus variatus)and noncourting species (Poecilia mexicana [surface- and cave-dwellingform], Poecilia orri, Gambusia affinis, Gambusia geiseri, Heterandriaformosa). In all species examined except for the cave form ofP. mexicana, focal females spent significantly less time feedingin the presence of a male than when together with another female.The time females spent feeding was found to significantly declinewith increasing male mating activity (sum of all sexual behaviors),but there was no support for the idea that females would spendmore time feeding in the presence of courting males comparedwith noncourting ones.     

Food availability and parasite infection influence mating tactics in guppies (Poecilia reticulata)

Despite the important effects of diet and parasite infectionon male reproductive behavior, few studies have simultaneouslyaddressed their influence on intrasexual selection (male–malecompetition). We examined the synergistic effects of 2 naturallyvarying environmental factors, lifetime food intake and infection,with the monogenean parasite Gyrodactylus turnbulli on the matingtactics and foraging behavior of male guppies (Poecilia reticulata).We allowed fish to interact directly with each other duringobservations and found that unparasitized males won more intermalecontests, courted females more frequently, and received positiveresponses to courtship displays more frequently than males thathad been infected. Infected males devoted more time to foragingand less time to courtship and competition than uninfected males,suggesting that they were energetically limited and could notincrease reproductive effort despite their reduced expectedlifespan. This interpretation was supported by the observationthat greater food intake ameliorated the negative effects ofparasite infection on courtship effort. Our results have bearingon how natural variation in food availability and parasite prevalenceinfluence geographic variation in reproductive behavior.     

You Are What You Eat: Food Limitation Affects Reproductive Fitness in a Sexually Cannibalistic Praying Mantid

Resource limitation during the juvenile stages frequently results in developmental delays and reduced size at maturity, and dietary restriction during adulthood can affect longevity and reproductive output. Variation in food intake can also result in alteration to the normal pattern of resource allocation among body parts or life-history stages. My primary aim in this study was to determine how varying juvenile and/or adult feeding regimes affect particular female and male traits in the sexually cannibalistic praying mantid Pseudomantis albofimbriata. Praying mantids are sit-and-wait predators whose resource intake can vary dramatically depending on environmental conditions within and across seasons, making them useful for studying the effects of feeding regime on various facets of reproductive fitness. In this study, there was a significant trend/difference in development and morphology for males and females as a result of juvenile feeding treatment, however, its effect on the fitness components measured for males was much greater than on those measured for females. Food-limited males were less likely to find a female during field enclosure experiments and smaller males were slower at finding a female in field-based experiments, providing some of the first empirical evidence of a large male size advantage for scrambling males. Only adult food limitation affected female fecundity, and the ability of a female to chemically attract males was also most notably affected by adult feeding regime (although juvenile food limitation did play a role). Furthermore, the significant difference/trend in all male traits and the lack of difference in male trait ratios between treatments suggests a proportional distribution of resources and, therefore, no trait conservation by food-limited males. This study provides evidence that males and females are under different selective pressures with respect to resource acquisition and is also one of very few to show an effect of juvenile food quantity on adult reproductive fitness in a hemimetabolous insect.     

Male tactics and reproductive success in the harem polygynous bat Saccopteryx bilineata

Alternative tactics in reproductive behavior enable individualsto maximize their fitness in relation to competitors in thesame population. In many taxa, territoriality is a common tacticof males to increase their reproductive success. In the batSaccopteryx bilineata, territorial males defend roosting areasfor females against other males and court females throughout the year. Peripheral males in the same colonies do not defendterritories but compete with territorial males for reproductionwith females. In this study, we monitored the behavior of themales in a natural colony over three reproductive seasons.We compared morphological and age data and measured the reproductiveoutput of males adopting the territorial or peripheral tactic.No differences in body size or weight were detected betweenmale types, but the probability of adopting a tactic seemedto be age dependent. Peripherals were often young males andreplaced territorials in several cases, whereas the oppositecase was not observed. Peripherals were not excluded from reproduction,but territorials were more likely to reproduce. Variation in reproductive success was high within both male tactics, andthe reproductive success of some peripherals was comparableto territorials, but, on average, the reproductive successof territorials was more than twice as high. Therefore, behavioraltactics do not seem to be equally profitable in general butmay represent different phases in the reproductive life of manyS. bilineata males.     

Male insemination decisions and sperm quality influence paternity in the golden orb-weaving spider

In polyandrous species, paternity may be influenced by the timingand frequency of mating. Female spiders possess 2 genital openingsthat lead to separate sperm-storage structures. Thus, even whenmating with a previously mated female, a male may reduce directsperm competition by inseminating the opposite opening to herfirst mate. Such morphology may provide females with greatercontrol over paternity. We examined simultaneously whether malesavoided already inseminated female genital openings and whetherthis behavior varied with the time between successive matings.To explore these questions, we mated female golden orb weaverspiders, Nephila edulis, each to 2 males and manipulated thetiming of their second mating. We documented male inseminationpatterns and explored the influence of male mating decisionson paternity success using the irradiated male technique. Wefound that 60% of males avoided sperm competition by discriminatingagainst inseminated genital openings. Moreover, male matingbehavior had a dramatic impact on the paternity success of irradiatedmales. When males inseminated the same genital opening, thecompetitive ability of the irradiated male's sperm was dramaticallyreduced resulting in lower paternity success. In contrast, whenthe 2 males inseminated opposite genital openings both malessired equal proportions of offspring regardless of their radiationstatus. There was no evidence that the timing of the secondmating affected patterns of paternity. Our data suggest thatdifferences in sperm quality may influence paternity successof N. edulis males under a sperm-competitive scenario. In contrast,females appear to have limited postmating control over paternity.     

The influence of environmental quality on sexual selection in Nauphoeta cinerea (Dictyoptera: Blaberidae)

We examined the impact of environmental conditions on the sexpheromone and mating behavior of the cockroach, Nauphoeta cinerea.Previous research on this species has shown that female behaviorduring courtship reflects female mate choice, male behaviorcorrelates with male social status, and the male sex pheromoneis the character used by females to assess males. In the presentstudy, males and females were allowed to develop from adultemergence to sexual maturity in either a high- or low-qualityenvironment. The environment affected the quantities of sexpheromone components. We found significantly less 3-hydroxy-2-butanoneand 4-ethyl-2-methoxyphenol, but not 2-methylthiazolidine, inthe pheromone glands of males from a poor environment. Pheromonequality was also affected; the ratios involving 2-methylthiazolidinewere altered, while the ratio 3-hydroxy-2-butanone to 4-ethyl-2-methoxyphenoldid not change. Development to sexual maturity under these environmentalconditions also influenced male and female sexual behavior.Male courtship activity reflected environmental influences;males from the low-quality environment took longer to initiatecourtship and spent more time copulating with females from allenvironments. Male quality, as assessed by females, was alsoaffected by their environment. Females were slower to respondto the courtship of males from the poor environment, regardlessof the females' own rearing environments. However, females fromthe low-quality environment also took longer to respond to thecourtship, and required more courtship, regardless of the males'rearing environments. Thus, poor environments also increasefemale choosiness. However, there was only one significant interactionterm, suggesting that the environmental effects are generaland that females do not show adaptive plasticity in mate choice.Studies of sexual selection that consider the effects of variableenvironments on behavior as well as the sexually selected morphologyin other systems are likely to provide new insights into thisevolutionary process