Asymmetric mating in the brachypterous grasshopper Podisma sapporensis

Crossing of genetically differentiated populations often results in assortative mating within populations. However, asymmetric sexual isolation or negative assortative mating has occasionally been reported. Previous studies suggested that sexual selection or sexual conflicts would lead to asymmetric mating when local populations are crossed. In order to evaluate the extent of assortative or disassortative mating in population crosses, we conducted laboratory crosses using the flightless grasshopper Podisma sapporensis. Crossing was conducted for all pairwise combinations of three populations, 150–240 km from one another – Teine, Shimokawa, and Akan. We found evidence for asymmetric mating for all the pairs of the populations. In particular, when the Teine and Akan populations were crossed, mating in the Teine male–Akan female cross was significantly more frequent than mating in both within‐population crosses, whereas mating in the Teine female–Akan male cross was significantly less frequent than mating in both within‐population crosses. We examined whether these results can be explained by any of the three hypotheses: (1) Kaneshiro's hypothesis, (2) differentiation in attractiveness, or (3) coevolution between male vigor and female receptivity. All the results were consistent with male vigor differing between populations balanced by different female potential to reject males. The available evidence suggests that antagonistic coevolution between the sexes has led local populations to different equilibria and that crossing of populations at different equilibria has resulted in asymmetry in mating frequencies.     

CROSS ABILITY OF MIMULUS GUTTATUS IN RELATION TO COMPONENTS OF GENE FIXATION

The joint effects of parental gene fixation and consanguinity of mates upon the fitness of matings was examined in Mimulus guttatus. Plants from four populations were crossed at five levels of genetic relatedness, and five viability characters were scored in progeny. Parental gene fixation at 12 polymorphic allozyme loci was partitioned into local, subpopulation, and population components. A model is proposed wherein parental gene fixation influences distance-dependent crossing success. At a fixed locus, inbreeding is favored if natural selection caused allele fixation, or is disfavored if gene fixation was random. The distance between mates required to eliminate gene fixation depends upon patch size of fixation. When selective fixation and patch size differ among loci, an optimal crossing distance is possible. In M. guttatus, progeny viability generally decreased with greater relatedness between mates, but this decrease was often heterogeneous among populations. The highest pollen viability and the lowest seed set were found at an intermediate relatedness between mates. To determine whether parental gene fixation influences these crossing patterns, a type of mutational-load analysis was performed. Progeny fitness was regressed on parent F and fitness estimated at F = 1. This was done for each component of F, for a) crosses that maintain gene fixation and b) crosses that eliminate gene fixation. A multiplicative, composite measure of fitness indicates that, in M. guttatus, genes fixed during local or population differentiation favor outbreeding, while genes fixed during subpopulation differentiation favor inbreeding. This predicts that random mating within subpopulations confers highest progeny fitness, exclusive of between-population matings. However, predictions did not fit the observed patterns of crossing success very well, perhaps because gene fixation was relatively low or was not adequately measured at loci influencing fitness.     

POLLEN AND OVULE SOURCES AFFECT SEED PRODUCTION OF LOBELIA CARDINALIS (LOBELIACE AE)

To examine the breeding system and components of male and female reproductive success in the hermaphroditic plant Lobelia cardinalis, we performed three crossing experiments with plants taken from natural populations. The experiments were designed to determine if the crossing success of plants as pollen and ovule parents was affected by the distance among mates, including self-pollinations and pollinations between populations; to determine if plants differed in their abilities to sire or mature seed; and to determine if there was a correlation between a plant's success at siring and maturing seed. Selfpollinations resulted in significantly fewer seeds per fruit and significantly smaller seeds. There were no significant differences in germinability between selfed and outcrossed seeds. Distance among parents within a population did not affect any of the traits. Outcrosses within and between population produced similar numbers of seeds per fruit, similar seed weights, and similar germination success. There were highly significant differences among maternal plants in all three experiments in the number of seeds they matured, mean seed weight, and seed germinability. The maternal parent was the most important factor determining seed production, but there were also significant differences among paternal plants in the number of seeds they sired (all three experiments), in the germinability of the seeds they sired (two experiments), and in the sizes of seeds they sired (one experiment). Our results indicate that differences in success of Lobelia plants as male parents cannot be due solely to their relatedness to the female parent.     

Reproductive consequences of mate quantity versus mate diversity in a wind-pollinated plant

Since most pollen travels limited distances in wind-pollinated plants, both the local quantity and diversity of mates may limit female reproductive success. Yet little evidence exists on their relative contribution, despite the importance of viable seed production to population dynamics.To study how variation in female reproductive success is affected by the quantity versus the diversity of surrounding mates contributing pollen, we integrated pollination experiments, data on natural seed set and seed viability, and AFLP genetic marker data in the wind-pollinated dioecious clonal forest herb Mercurialis perennis.Pollination experiments indicated weak quantitative pollen limitation effects on seed set. Among-population crosses showed reduced seed viability, suggesting outbreeding depression due to genetic divergence. Pollination with pollen from a single source did not negatively affect reproductive success. These findings were consistent with results of the survey of natural female reproductive success. Seed set decreased with the distance to males in a female plants’ local neighborhood, suggesting a shortage of pollen in isolated female plants, and increased with the degree of local genetic diversity. Spatial isolation to other populations and population size did not affect seed set. None of these variables were related to seed viability.We conclude that pollen movement in M. perennis is likely very limited. Both male proximity and the local degree of genetic diversity influenced female reproductive success.     

Male and female effects on fertilization success and offspring viability in the Peron's tree frog,Litoria peronii

Abstract There is increasing theoretical and empirical evidence that genetic compatibility among partners is an important determinant of fertilization success and offspring viability. In amphibians, females often actively choose partners from among a variety of males and polyandry is common. Genetic compatibility among partners may therefore be an important determinant of fertilization success and offspring viability in some amphibians. Amphibians also show some of the highest levels of genetic differentiation among neighbouring populations known in vertebrates, and as such, populations may have evolved different co‐adapted gene complexes. This means that offspring from among‐population crosses may have reduced fitness. It is therefore essential to understand to what extent crossings between and within populations may interfere with successful fertilization and offspring viability. Here, we test whether crossing individuals within and between two different populations of the Australian Peron's tree frog (Litoria peronii) using artificial fertilizations affect fertilization success and offspring viability. Fertilization success per se is strongly influenced by male identity, which is likely to depend at least to some extent on the experimental procedure (e.g. resulting in variation in sperm number per ejaculate), whereas there was no fertilization effect of female identity. More importantly, male and female identity, independently of each other, explained significant variation in offspring viability, whereas no such effect could be linked to population of origin. Thus, our experiments suggest that crossing populations may not always be the most significant factor affecting fertilization success or offspring viability, but may be more influenced by the genetic quality or the genetic compatibility of partners.     

THE EFFECT OF FLOWER PRODUCTION ON MALE REPRODUCTIVE SUCCESS IN WILD RADISH POPULATIONS

Flower production is the major determinant of pollen yield and an important component in pollinator attraction. Consequently differences among plants in flower production are expected to have a substantial impact on their relative success at fathering seed. We examined this prediction using one natural and three structured populations of wild radish. We found that a plant's relative success at fathering seed on another plant in the population (male fertility) increased with flower production. Nonetheless, the increase in fertility exhibited a diminishing marginal gain, with the relationship varying among populations. The relationship between the estimates of total number of seeds sired and flower production varied substantially among the populations examined, ranging from a weakly linear to strongly negative quadratic. Not surprisingly, the spatial structure of the population with respect to seed yield had a powerful effect on the total number of seeds sired because male fertility decreased exponentially with intermate distance. This exponential relationship occurred in all populations examined. Other covariates important to male fertility were flower color, time, the specific identity of the male parent, and male by female interaction. The identity of the male parent consistently accounted for a large portion of the variation in male fertility, indicating that other unmeasured features of the plant influenced its success.     

Evolution of intrinsic reproductive isolation among four North American populations of Rhagoletis pomonella (Diptera: Tephritidae)

Across its range in North America, four geographically separated, ecologically and genetically diverged populations of hawthorn (Crataegus)‐infesting Rhagoletis pomonella (Diptera: Tephritidae) flies inhabit the Eje Volcánico Trans Mexicano (EVTM), the Sierra Madre Oriental (SMO), the Chiapas Highlands (CHIS) and the USA. Here, we tested whether these four populations are reproductively isolated by any intrinsic, nonhost‐related, pre‐ or postmating barriers to gene flow. Crossing experiments suggested that a low level of host‐independent prezygotic isolation may exist between hawthorn flies from EVTM and the three other populations, but only with respect to a slight reduction in copulation duration in EVTM matings. Some evidence for postmating isolation was found, again primarily involving EVTM crossed to SMO, CHIS and US flies. Certain crosses produced no (SMO male × EVTM female) or few (EVTM male × CHIS female; CHIS male × SMO female) F1 hybrid offspring. F2 crosses were generally fertile, except for US male × CHIS female matings. Inherent reproductive isolation therefore appears to be quantitative rather than absolute between populations, as the possibility for gene flow exists through at least some combinations of mating among EVTM, SMO, CHIS and US flies. Our results are consistent with a recently advanced hypothesis that episodic introgression from Mexico into the USA has played a role in providing genetic variation, facilitating sympatric host race formation and the adaptive radiation of the R. pomonella sibling species' complex in the USA. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 213–223.     

Sequential variation in the components of reproductive success in the distylousJasminum fruticans (Oleaceae)

A 2-year study of three natural populations of the distylousJasminum fruticans showed that mean fruit and seed production were significantly greater in shortstyled plants (thrums) than in long-styled plants (pins). In this study, we investigated the role of four sequential factors which may differentially influence fruit and seed set in the two floral morphs: (1) differences in flowering phenology, (2) a limitation of pollen transfer towards pins, (3) a differential capacity of the two morphs to act through famale and male function and (4) differential fruit abortion in the two morphs. Fruit set was significantly influenced by differences in flowering phenology although there were no differences in flowering time between the two morphs. supplementary pollinations in a natural population significantly increased fruit set and reduced the difference in fruit set between the two morphs in relation to controls, indicating a limitation on pollen transfer which was most severe towards pin stigmas. In reciprocal crosses, seed set was significantly dependent on the paternal and maternal identity of the pin parent. There was no significant variation among thrums for their performance as male or female parent. Furthermore, individual pin plants with relatively high percentage seed set as female parents gave poor seed set as male parents and vice-versa. Whereas fruit removal had no effect on seed number in thrum plants, a greater proportion of viable seeds were produced on pin plants which were left to naturally mature their fruits than on pins which had fruits artificially removed, suggesting the occurrence of selective fruit abortion in pins but not in thrums. The initially greater maternal fitness of thrums due to their greater success as pollen recipients may thus be opposed by increased viable seed set in the pins due to factors acting after the pollination stage. The relative reproductive success of floral morphs in the distylousJ. fruticans is thus differentially influenced by ecological factors occurring at different stages of the reproductive process.     

FITNESS CONSEQUENCES OF OUTCROSSING IN A SOCIAL SPIDER WITH AN INBREEDING MATING SYSTEM

Inbreeding mating systems are uncommon because of inbreeding depression. Mating among close relatives can evolve, however, when outcrossing is constrained. Social spiders show obligatory mating among siblings. In combination with a female‐biased sex ratio, sib‐mating results in small effective populations. In such a system, high genetic homozygosity is expected, and drift may cause population divergence. We tested the effect of outcrossing in the social spider Stegodyphus dumicola. Females were mated to sib‐males, to a non‐nestmate within the population, or to a male from a distant population, and fitness traits of F1s were compared. We found reduced hatching success of broods from between‐population crosses, suggesting the presence of population divergence at a large geographical scale that may result in population incompatibility. However, a lack of a difference in offspring performance between inbred and outbred crosses indicates little genetic variation between populations, and could suggest recent colonization by a common ancestor. This is consistent with population dynamics of frequent colonizations by single sib‐mated females of common origin, and extinctions of populations after few generations. Although drift or single mutations can lead to population divergence at a relatively short time scale, it is possible that dynamic population processes homogenize these effects at longer time scales.     

Natural selection on floral traits through male and female function in wild populations of the heterostylous daffodil Narcissus triandrus

Measurements of natural selection in hermaphrodite populations require the analysis of performance through both female and male sex functions. Here, we investigate selection on three floral traits: flower number, flower length, and corona width through both sex functions in natural populations of the tristylous daffodil Narcissus triandrus . Selection through female function was examined in six populations, and in two of these we also estimated male selection gradients using multilocus microsatellite genotyping of parents and offspring. We detected significant directional selection for flower number through female function, and significant stabilizing selection for corona width and flower length through male function. Variation in male reproductive success was strongly influenced by the distance between mates and was significantly higher than variation in female reproductive success in one population, a result consistent with Bateman's principle. However, variation through both sex functions was similar in the other population and there was a significant negative correlation between female and male fitness indicating sex-specific trade-offs in reproductive success. Selection on floral design in N. triandrus was stronger through male than female function probably because floral morphology plays an important role in promoting effective cross-pollen transfer in populations of this heterostylous species.     

Variation in male effects on female fecundity in Drosophila melanogaster

In many species, males have the capacity to directly influence (either positively or negatively) the fitness of their mates and offspring, not only via parental care contributions and/or precopulatory resource provisioning, but also via the post‐copulatory activity of those substances passed on to their mates in their ejaculates. Here, we examine how an individual male's identity may be related to phenotypic variation in short‐term female fecundity in the model species, Drosophila melanogaster. The effect of male identity on short‐term fecundity stimulation of females was repeatable across time and accounted for over a fifth of the total observed phenotypic variation in fecundity in two independent populations. The functional explanations for these results and the implications for our understanding of the factors that contribute to the adaptive significance of mating preferences and/or sexual conflict are discussed.     

Sexual conflict and consistency of offspring desertion in Eurasian penduline tit <Emphasis Type="Italic">Remiz pendulinus</Emphasis>

Background  

The trade-off between current and future parental investment is often different between males and females. This difference may lead to sexual conflict between parents over care provisioning in animals that breed with multiple mates. One of the most obvious manifestations of sexual conflict over care is offspring desertion whereby one parent deserts the young to increase its reproductive success at the expense of its mate. Offspring desertion is a wide-spread behavior, and its frequency often varies within populations. We studied the consistency of offspring desertion in a small passerine bird, the Eurasian penduline tit Remiz pendulinus, that has an extremely variable breeding system. Both males and females are sequentially polygamous, and a single parent (either the male or the female) incubates the eggs and rears the young. About 28–40% of offspring are abandoned by both parents, and these offspring perish. Here we investigate whether the variation in offspring desertion in a population emerges either by each individual behaving consistently between different broods, or it is driven by the environment.     

Intrasexual selection and male mating strategies in baboons and macaques

If baboon and macaque mating systems constitute a form of female defense polygyny, male mating strategies should be intrasexually selected and should vary in predictable ways with female defensibility, and demographic factors which affect the numbers of competing males per estrous female in populations. Substantial behavioral evidence exists for intrasexual selection of male mating strategies in baboons and macaques. Limited evidence also offers tentative support for theorybased predictions about the relationship between male mating strategy and female defensibility. Although male dominance rank generally predicts mating success, there are a number of factors which tend to increase the success of subordinate males above that expected from a simple dominance-based model of priority of access to mates.     

Within/between population crosses reveal genetic basis for siring success in Silene latifolia (Caryophyllaceae)

Divergence at reproductive traits can generate barriers among populations, and may result from several mechanisms, including drift, local selection and co-adaptation between the sexes. Intersexual co-adaptation can arise through sexually antagonistic co-evolution, a timely hypothesis addressed in animals but, to our knowledge, not yet in flowering plants. We investigated whether male and female population of origin affected pollen competition success, offspring fitness and sex ratio in crosses within/between six genetically differentiated populations of the white campion, Silene latifolia. Each female was crossed with pollen from one focus male from the same population, and pollen from two focus males from two distinct populations, both as single-donor and two-donor crosses against a fixed tester male with a 2-h interpollination interval (n = 288 crosses). We analysed paternity with microsatellite DNA. Male populations of origin significantly differed for siring success and in vitro pollen germination rates. In vitro pollen germination rate was heritable. Siring success also depended on sex ratio in the female family of origin, but only in between-population crosses. In some female populations, two-donor crosses produced less female-biased sex ratios compared with single-donor crosses, yet in other female populations the reverse was true. Offspring sex ratio varied with donor number, depending on the female population. Within/between population crosses did not differ significantly in seed set or offspring fitness, nor were siring success and offspring fitness significantly correlated. Altogether this suggests reproductive divergence for traits affecting pollen competition in S. latifolia.     

Effects of Single Versus Multiple Mates: Monogamy Results in Increased Fecundity for the Beetle <Emphasis Type="Italic">Phoracantha semipunctata</Emphasis>

Effects of polyandry versus monogamy were assessed for the beetle Phoracantha semipunctata (Coleoptera: Cerambycidae) by comparing measures of female reproductive success, including fecundity, egg viability, time until eclosion, and clutch size. The effect of intermittent presence or absence of a male was also evaluated. Polyandry was detrimental to female reproductive success in comparison to monogamy. Fecundity, egg viability, and clutch size were lower, and time to eclosion were increased for eggs from females with multiple mates compared with monogamous females. Intermittent presence of males had no effect on female reproductive success. Possible explanations for the decreased fecundity experienced by females with multiple mates include sperm competition intensity, costs of male harassment, and exceeding the optimal mating frequency. Females may reduce costs associated with polyandry by spending less time on host logs where mating occurs.     

RAPID EVOLUTION OF ASYMMETRIC REPRODUCTIVE INCOMPATIBILITIES IN STALK‐EYED FLIES

The steps by which isolated populations acquire reproductive incompatibilities remain poorly understood. One potentially important process is postcopulatory sexual selection because it can generate divergence between populations in traits that influence fertilization success after copulation. Here we present a comprehensive analysis of this form of reproductive isolation by conducting reciprocal crosses between variably diverged populations of stalk‐eyed flies (Teleopsis dalmanni). First, we measure seven types of reproductive incompatibility between copulation and fertilization. We then compare fertilization success to hatching success to quantify hybrid inviability. Finally, we determine if sperm competition acts to reinforce or counteract any incompatibilities. We find evidence for multiple incompatibilities in most crosses, including failure to store sperm after mating, failure of sperm to reach the site of fertilization, failure of sperm to fertilize eggs, and failure of embryos to develop. Local sperm have precedence over foreign sperm, but this effect is due mainly to differences in sperm transfer and reduced hatching success. Crosses between recently diverged populations are asymmetrical with regard to the degree and type of incompatibility. Because sexual conflict in these flies is low, postcopulatory sexual selection, rather than antagonistic coevolution, likely causes incompatibilities due to mismatches between male and female reproductive traits.     

Pollen limitation in the endangered Chinese endemic species Sinocalycanthus chinensis

Pollen limitation negatively impacts endangered and endemic plants with small fragmented populations, such as Sinocalycanthus chinensis, an endangered plant endemic to China. In this study, we analyzed the pollen limitation of the S. chinensis Damingshan (DMS) population in 2006, 2009, and 2010, and crossed plants with mates separated by different distances, both within and between populations. The DMS population exhibited strong pollen limitation in fruit set, seed set, and seeds per fruit in 2006, 2009, and 2010. The average accumulated pollen limitation (for fruit set times seeds per fruit) was 0.510 ± 0.180. Progeny crossed with pollen from intermediate neighboring plants within the same population (separated by 30–50 m from pollen recipients) had the lowest fitness. No optimal outcrossing distance was found within the DMS population. Progeny from crosses with the Shunxiwu (SXW) and Daleishan (DLS) populations performed relatively better, while those from crosses with Qingliangfeng (QLF) and Longxushan (LXS) populations performed worse. Compared with average reproductive success, outbreeding depression was found in progeny from crosses with the LXS and QLF populations. Reproductive success from pure self‐pollination indicated S. chinensis is self‐compatible. Geitonogamous selfing increased reproductive success. Based on geitonogamous selfing, the proportion of selfed offspring was relatively high. These results provide basic references for the conservation of this species.     

Female Choice by Scent Recognition in the Spotted Cucumber Beetle

In species that demonstrate female choice, geographically distinct populations can vary in their signal‐response behaviors as a result of environmental differences or genetic drift. Observing whether or not females discriminate against males from allopatric populations can establish such signal deviations. Here we compare mating success within and between populations of the spotted cucumber beetle (Diabrotica undecimpunctata howardi) collected from Delaware, Tennessee, Missouri, and New Mexico, USA. A no‐choice cross‐mating experiment was employed to measure female preference for sympatric and allopatric males. While only two of the populations (Tennessee and Missouri) demonstrated statistically significant female preference for sympatric males, this trend was observed in all populations tested. Further, we show that (i) males from Tennessee, Missouri, and New Mexico differ in their scent, (ii) females may use population‐specific scents to discriminate among males, and (iii) females whose antennae have been surgically removed are unable to recognize acceptable mates. New Mexico males, which were never accepted by either Tennessee or Missouri females, became acceptable mates when crowded with Tennessee or Missouri males prior to copulation. We infer that male odor may be an important factor in determining cucumber beetle mating success.     

Parental effects on fertilization and hatching success and development of Atlantic halibut (Hippoglossus hippoglossus L.) embryos and larvae

The parental effects on fertilization and early life history traits were studied in Atlantic halibut, Hippoglossus hippoglossus L. Sperm from 12 different males were used to fertilize eggs of two females in separate crosses. The fertilization success were generally high, above 80% of developing embryos at 16-cell stage in 20 of 24 crosses with an average of 85.9+/-17.6% and 87.2+/-16.5% for female A and female B, respectively. Corresponding hatching success was 74.8+/-17.7% and 41.6+/-20.1%, respectively. The relationship between fertilization success and hatching success was positive. The parental influence on hatching was dominated by a strong and significant (p<0.001) maternal effect; however, the paternal effect was also significant (p<0.001). Furthermore, there was no relationship between fertilization success, hatching success and larvae viability as a high number of larvae developed locked jaws (i.e., were not functional). There was a significant (p<0.01) difference in yield of functional larvae of female A (43%) and female B (56%), and also between crosses sired by different males. The standard length of offspring of female A (12.4+/-0.5 mm) and B (12.6+/-0.6 mm) were significantly (p<0.001) different, and also significantly influenced by both the female (p<0.001) and the male (p<0.001). The present paper provides strong indications that not only the female, but also the male parent influences quantitative features of early development of their offspring.     

Plastid behavior in North AmericanEuoenotheras

Summary Extensive records of plastid behavior in the North American euoenotheras by the writer and students support in general the conclusions of Stubbe regarding the number of plastid and genome classes and their behavior relative to each other, except that our findings do not make it necessary to distinguish between classes II and III as defined byStubbe.Clarification of the plastid situation in the North American euoenotheras and their European derivatives makes it easier to visualize the precise manner in which the present groups of races in North America have come into existence. Parviflora I and parviflora II no doubt arose as a result of crosses between population 1 as female and populations 2 and 3 respectively as male.Biennis arose through hybridization between population 2 as female and population 3 as male. It has not been determined which population served as the female and which as the male parent in the crosses between populations 3 and 4 that gave rise to the strigosas.In honor of Professor Dr.E. G. Pringsheim on the occasion of his 80th birthday.Supported by a grant from the Rockefeller Foundation.