MATING PROPENSITY AND COURTSHIP BEHAVIOR IN SERIALLY BOTTLENECKED LINES OF THE HOUSEFLY

The efficacy of bottlenecks to stimulate divergence in courtship behavior and consequent premating isolation was tested by serial founder-flush episodes of three sizes (one, four, or 16 pairs) on a population of houseflies established in the laboratory from a single field population. After the fifth founder-flush episode, intraline and interline crosses were performed to detect divergence in mating propensities and patterns of assortative mating. Videotapings of intraline courtships for the bottleneck lines and the control were evaluated for changes in courtship repertoire. All bottleneck lines showed significant divergence from the control in male and/or female mating propensity and in courtship behavior. Divergence from the control was bidirectional for both male and female mating propensities as well as for courtship element utilization. Out of 15 tests for assortative mating between bottleneck lines and between bottleneck lines and the control, only two cases of positive assortative mating and one case of negative assortative mating were detected. Because some bottleneck lines showed increased courtship element utilization and because decreased courtship utilization in some bottleneck lines was related to higher male mating success, the mechanisms behind the Kaneshiro model (which is based upon ancestral females discriminating against bottleneck males that had “lost” courtship elements) were not supported in general. A partitioning effect of the bottlenecks upon the intrinsic variation in the ancestral population for courtship pattern appeared to explain a large component of the directions of divergence from the control. Still, the pattern of divergence of some bottleneck lines apparently was not constrained by the intercorrelation structure of courtship behaviors detected in the control. Because previous studies showed that the bottleneck lines had rebounded from inbreeding depression to fitness levels of the control, this study documents nondebilitating differentiation in the courtship repertoire that can account for divergent mating propensities and premating isolation.     

笼养太行山猕猴的理毛行为

动物行为的归宿 ,无非是获取食物 ,避免伤害或得到最大的繁殖机会[1] 。当今 ,行为生态学已成为灵长类学研究中最为活跃的一个领域。在猕猴的种群生态[2～4 ] 、繁殖行为[5,6 ] 、取食行为[7] 及社会行为[1,8] 等方面的研究已经取得了较大的进展。理毛行为作为猕猴日常社会行为结构的一个重要补充已有一些定性描述[4 ,9～ 11] 。作者对笼养太行山猕猴的理毛行为做了长期观察 ,现将研究结果予以报道。1　材料与方法1 1　研究对象与设施选取河南师范大学生命科学学院猕猴养殖场笼养且具有档案记录的 38只太行山猕猴为观察对象。成年猕猴为野…     

EFFECTIVENESS OF SELECTION IN REDUCING THE GENETIC LOAD IN POPULATIONS OF PEROMYSCUS POLIONOTUS DURING GENERATIONS OF INBREEDING

It has been hypothesized that natural selection reduces the “genetic load” of deleterious alleles from populations that inbreed during bottlenecks, thereby ameliorating impacts of future inbreeding. We tested the efficiency with which natural selection purges deleterious alleles from three subspecies of Peromyscus polionotus during 10 generations of laboratory inbreeding by monitoring pairing success, litter size, viability, and growth in 3604 litters produced from 3058 pairs. In P. p. subgriseus, there was no reduction across generations in inbreeding depression in any of the fitness components. Strongly deleterious recessive alleles may have been removed previously during episodes of local inbreeding in the wild, and the residual genetic load in this population was not further reduced by selection in the lab. In P. p. rhoadsi, four of seven fitness components did show a reduction of the genetic load with continued inbreeding. The average reduction in the genetic load was as expected if inbreeding depression in this population is caused by highly deleterious recessive alleles that are efficiently removed by selection. For P. p. leucocephalus a population that experiences periodic bottlenecks in the wild, the effect of further inbreeding in the laboratory was to exacerbate rather than reduce the genetic load. Recessive deleterious alleles may have been removed from this population during repeated bottlenecks in the wild; the population may be close to a threshold level of heterozygosity below which fitness declines rapidly. Thus, the effects of selection on inbreeding depression varied substantially among populations, perhaps due to different histories of inbreeding and selection.     

FITNESS CONSEQUENCES OF MATERNAL AND NONMATERNAL COMPONENTS OF INBREEDING IN THE GYNODIOECIOUS PHACELIA DUBIA

I assessed the relationship between the level of inbreeding, F, and fitness, and the effects of nonmaternal and maternal components of inbreeding on fitness in Phacelia dubia. I conducted two generations of controlled crosses and tested the performance of the F₂ progeny in field and artificial conditions covering the whole life cycle. Inbreeding significantly decreased the individual contribution of seeds to the next generation in the field, but this decrease apparently is not enough to explain the maintenance of gynodioecy. The inbred progeny contributes significantly to the population genetic structure of P. dubia. Fitness estimates and fitness components tended to decrease, usually monotonically, with F. However, nonmonotonic relationships were found in male fitness components and, in some families, in fitness estimates, seed production per fruit, and establishment. Most of the inbreeding depression takes place at the level of seed establishment in the field, but, in artificial conditions the effects of inbreeding were similar at fecundity and establishment. I studied maternal and nonmaternal components of inbreeding by testing the effects of the relatedness of maternal grandparents and parents on the performance of the progeny. Both components affected fitness. Inbreeding depression was conditioned by the level of inbreeding of the maternal plant, but this interaction varied at different fitness components. Also, the magnitude and even the direction of the relationship between fitness and F changed as a result of the combined effects of maternal and nonmaternal components of inbreeding. Such interactions can render convex or concave fitness functions, giving in the latter case the appearance of a false purging. Maternal effects of inbreeding can result from several processes: maternal investment perhaps with serial adjustments during seed development, purging of recessive deleterious genes, and nucleocytoplasmic interactions. These results illustrate the importance of maternal effects of inbreeding, and the complex effects of inbreeding on fitness. A full understanding of the fitness consequences of inbreeding and, therefore, their potential implications in the evolution of breeding systems, should take into account male and female components as well as transgenerational effects in the context of the particular environment in which fitness is evaluated.     

CULTURAL INHERITANCE OF SONG AND ITS ROLE IN THE EVOLUTION OF DARWIN'S FINCHES

Songs of Darwin's finches were studied on the Galápagos Island of Daphne Major from 1976 to 1995. A single, structurally simple, and unvarying song is sung throughout life by each male of the two common species, Geospiza fortis (medium ground finch) and G. scandens (cactus finch). Songs of the two species differ strongly in quantitative features, and individual variation among males is much broader in G. fortis than in G. scandens. Although there are exceptions, songs of sons strongly resemble the songs of their fathers. They also resemble the songs of their paternal grandfathers, but not their maternal grandfathers, indicating that they are culturally inherited and not genetically inherited. Female G. fortis display a tendency to avoid mating with males that sing the same type of song as their father. They also avoid mating with males that sing heterospecific song, with very rare exceptions. Thus song, an evolving, culturally inherited trait, is an important factor in species recognition and mate choice. It constrains the mating of females to conspecifics, even when there is no genetic penalty to interbreeding, and thus may play a crucial role in species formation by promoting genetic isolation on secondary contact. The barrier is leaky in that occasional errors in song transmission result in misimprinting, which leads to a low incidence of hybridization and introgression. Introgression slows the rate of postzygotic isolation, but can produce individuals in novel genetic and morphological space that can provide the starting point of a new evolutionary trajectory.     

EPISTASIS AND THE EVOLUTION OF ADDITIVE GENETIC VARIANCE IN POPULATIONS THAT PASS THROUGH A BOTTLENECK

Traditional models of genetic drift predict a linear decrease in additive genetic variance for populations passing through a bottleneck. This perceived lack of heritable variance limits the scope of founder-effect models of speciation. We produced 55 replicate bottleneck populations maintained at two male-female pairs through four generations of inbreeding (average F = 0.39). These populations were formed from an F₂ intercross of the LG/J and SM/J inbred mouse strains. Two contemporaneous control strains maintained with more than 60 mating pairs per generation were formed from this same source population. The average level of within-strain additive genetic variance for adult body weight was compared between the control and experimental lines. Additive genetic variance for adult body weight within experimental bottleneck strains was significantly higher than expected under an additive genetic model This enhancement of additive genetic variance under inbreeding is likely to be due to epistasis, which retards or reverses the loss of additive genetic variance under inbreeding for adult body weight in this population. Therefore, founder-effect speciation processes may not be constrained by a loss of heritable variance due to population bottlenecks.     

夏秋两季饲养条件下扬子鳄的行为谱和活动节律初步研究

2003年夏秋两季(7-11月间),采用扫描取样法和目标动物取样法,对饲养条件下扬子鳄的个体行为和活动 节律进行了研究。结果表明:夏秋两季饲养条件下扬子鳄的个体行为主要包括休息行为(水中休息、陆地休息、晒 太阳、挠痒、打哈欠、伸懒腰);运动行为(游泳、潜水、爬行、摆尾);摄食行为(摄食、漱口);冲突行为(打斗、对视);嬉 戏行为(嬉戏、堆积);吼叫行为;排泄行为等。 夏季,扬子鳄休息行为的时间最多,日变化规律显示:早晨6:00-7:00为休息高峰期;下午12:30-13:30为潜 水高峰期。秋季,用于晒太阳的时间最多,秋季早晨6:00-7:30为潜水高峰期,且一天中扬于鳄晒太阳活动出现三 次高峰即10:30-11:00,13:30-14:00,16:30-17:00。统计结果表明,夏秋两季潜水、晒太阳和休息3种个体行为差 异性较为显著。在30℃-36℃之间,扬子鳄潜水时间和温度之间呈线性关系。研究结果同时表明,长期人工饲养 对扬子鳄的某些弹性行为如摄食行为等产生了较大影响。在行为描述的基础上,对扬子鳄的有关行为机制进行了 探讨。而影响扬子鳄行为表达的生物因素主要包括年龄和食物资源;非生物因素主要包括空间和生境等。     

THE SIGNIFICANCE OF GENETIC EROSION IN THE PROCESS OF EXTINCTION. IV. INBREEDING LOAD AND HETEROSIS IN RELATION TO POPULATION SIZE IN THE MINT SALVIA PRATENSIS

If, because of genetic erosion, the level of homozygosity in small populations is high, additional selfing will result in small reductions of fitness. In addition, in small populations with a long inbreeding history selection may have purged the population of its genetic load. Therefore, a positive relationship between population size (or level of genetic variation) and level of additional inbreeding depression, here referred to as inbreeding load, may be expected. In a previous study on the rare and threatened perennial Salvia pratensis, a positive correlation between population size and level of allozyme variation has been demonstrated. In the present study, the inbreeding load in six populations of varying size and allozyme variation was investigated. In the greenhouse, significant inbreeding load in mean seed weight, proportion of germination, plant size, regenerative capacity, and survival was demonstrated. In a field experiment with the two largest and the two smallest populations, survival of selfed progeny was 16% to 63% lower than survival of outcrossed progeny. In addition, survival of outcrossed progeny was, with the exception of the largest population, lower (16% to 37%) than of hybrid progeny, resulting from crosses between populations. Effects on plant size were qualitatively similar to the effects on survival, but these effects were variable in time because of differential survival of larger individuals. In all populations the total inbreeding load, that is, the effects on size and survival multiplicated, increased in time. It was demonstrated that inbreeding load in different characters may be independent. At no time and for no character was inbreeding load or the heterosis effect correlated to the mean number of alleles per locus, indicating that allozyme variation is not representative for variation at fitness loci in these populations. Combined with results of previous investigations, these results suggest that the small populations are in an early phase of the genetic erosion process. In this phase, allozyme variation, which is supposed to be (nearly) neutral, has been affected by genetic erosion but the selectively nonneutral variation is only slightly affected. These results stress the need for detailed information about the inbreeding history of small populations. The relative performance of selfed progeny was lowest in all populations, in the greenhouse as well as in the field, and inbreeding depression could still influence the extinction probabilities of the small populations.     

THE SIGNIFICANCE OF GENETIC EROSION IN THE PROCESS OF EXTINCTION. IV. INBREEDING DEPRESSION AND HETEROSIS EFFECTS CAUSED BY SELFING AND OUTCROSSING IN SCABIOSA COLUMBARIA

The effects of self-fertilization, within-population crosses (WPC) and between-population crosses (BPC) on progeny fitness were investigated in the greenhouse for Scabiosa columbaria populations of varying size. Plants grown from field collected seeds were hand pollinated to produce selfed, WPC, and BPC progeny. The performance of these progenies was examined throughout the entire life cycle. The different pollination treatments did not significantly affect germination, seedling-to-adult survival, flowering percentage and the number of flower heads. But severe inbreeding depression was demonstrated for biomass production, root development, adult survival, and seed set. Additionally, multiplicative fitness functions were calculated to compare relative fitnesses for progeny. On average, WPC progeny showed a more than 4-fold, and BPC progeny an almost 10-fold, advantage over selfed progeny, indicating that S. columbaria is highly susceptible to inbreeding. No clear relationship was found between population size and level of inbreeding depression, suggesting that the genetic load has not yet been reduced substantially in the small populations. A significant positive correlation was found between plant dry weight and total fitness. In two out of six populations, the differences between the effects of the pollination treatments on dry weight increased significantly when seedlings were grown under competitive conditions. This result is interpreted as an enhancement of inbreeding depression under these conditions. It is argued that improvement of the genetic exchange between populations may lower the probability of population extinction.     

豢养条件下白鱀豚雌雄个体的感情协调及其行为分

为独居6年的雄性白鱀豚“淇淇”成功地介绍了雌性白鱀豚“珍珍”。通过近两年的驯养,已使雌雄豚生活融洽。本文还对不同个体之间的行为关系作了仔细的观察和研究,特别对白鱀豚的性行为和人工饲养条件下繁殖的可行途径作了探讨。     

A COMPARISON OF INBREEDING DEPRESSION IN LIFE-HISTORY AND MORPHOLOGICAL TRAITS IN ANIMALS

The current study tests the hypothesis that life-history traits (closely related to fitness) show greater inbreeding depression than morphological traits (less closely related to fitness). The mean and median slope of the standardized coefficient of inbreeding depression (the slope of the linear relationship between F and the trait value) for life-history and morphological traits were compared. Slopes for life-history traits were higher than those for morphological traits. At F = 0.25 (full-sibling mating), life-history traits experienced a median reduction of 11.8% in trait value, whereas morphological traits showed a depression in trait value of approximately 2.2%.     

EVOLUTIONARY PATTERNS OF ALTERED BEHAVIOR AND SUSCEPTIBILITY IN PARASITIZED HOSTS

Adaptation is the usual context for interpreting parasite-host interactions. For example, altered host behavior is often interpreted as a parasite adaptation, because in some cases it enhances parasite transmission. Resistance to parasites also has obvious adaptive value for hosts. However, it is difficult to evaluate the adaptive significance of host-parasite interactions without considering the historical context in which these traits have evolved and if they can be predicted by host (or parasite) phylogeny. We examined the influence of host phylogeny on patterns of altered behavior and resistance to parasitism in a cockroach-acanthocephalan system. A consensus cladogram for cockroach subfamilies was produced from the morphological data of McKittrick. We used this cladogram to predict patterns of altered host behavior in seven cockroach host species. Each species was experimentally infected with a single species of acanthocephalan, Moniliformis moniliformis, a parasite that is transmitted when cockroaches are eaten by rodent final hosts. Activity patterns, substrate choices, and responses to light were measured for control and infected animals. These data were recoded into a behavioral matrix of discrete characters. We determined the most parsimonious distribution of the behavioral characters on the tree obtained from McKittrick's data. We then measured the concordance between the behavioral data and the cockroach cladogram with the consistency index (CI). We compared the observed CI to the expected value based on a randomization of observed character states. For three different models of evolutionary character change, there was no evidence of strong concordance (significantly large CI) between altered host behavior and host relationships. Parsimony analysis of the interior nodes of the phylogenetic reconstruction suggested that unaltered behavior was the ancestral state for most host behaviors. We also compared host phylogeny to a data set on the susceptibility of 29 cockroach species to infection with M. moniliformis. At the species level, there was a significant concordance between susceptibility and host phylogeny. This pattern was consistent with the finding that susceptibility of species varied significantly among different subfamilies. However, at the subfamily level, susceptibility was not strongly concordant with phylogeny. We predict that, given enough time, resistance should be lost in subfamilies that are currently resistant to parasitism. In spite of the potential importance of phylogeny in the evolution of behavior and susceptibility, we found little evidence for phylogenetic effects in this system. We conclude that changes in the behavioral responses of hosts to parasites and, to a lesser extent, changes in susceptibility are more frequent than cockroach speciation events in different cockroach lineages. This finding strengthens the assertion that at least some of the altered behaviors are adaptive for host and/or parasite.     

THE EFFECTS OF FIVE GENERATIONS OF ENFORCED SELFING ON POTENTIAL MALE AND FEMALE FUNCTION IN MIMULUS GUTTATUS

In prior work we detected no significant inbreeding depression for pollen and ovule production in the highly selfing Mimulus micranthus, but both characters showed high inbreeding depression in the mixed-mating M. guttatus. The goal of this study was to determine if the genetic load for these traits in M. guttatus could be purged in a program of enforced selfing. These characters should have been under much stronger selection in our artificial breeding program than previously reported characters such as biomass and total flower production because, for example, plants unable to produce viable pollen could not contribute to future generations. Purging of genetic load was investigated at the level of both the population and the individual maternal line within two populations of M. guttatus. Mean ovule number, pollen number, and pollen viability declined significantly as plants became more inbred. The mean performance of outcross progeny generated from crosses between pairs of maternal inbred lines always exceeded that of self progeny and was fairly constant for each trait through all five generations. The consistent performance of outcross progeny and the universally negative relationships between performance and degree of inbreeding are interpreted as evidence for the weakness of selection relative to the quick fixation of deleterious alleles due to drift during the inbreeding process. The selective removal (purging) of deleterious alleles from our population would have been revealed by an increase in performance of outcross progeny or an attenuation of the effects of increasing homozygosity. The relationships between the mean of each of these traits and the expected inbreeding coefficient were linear, but one population displayed a significant negative curvilinear relationship between the log of male fertility (a function of pollen number and viability) and the inbreeding coefficient. The generally linear form of the responses to inbreeding were taken as evidence consistent with an additive model of gene action, but the negative curvilinear relationship between male fertility and the inbreeding coefficient suggested reinforcing epistasis. Within both populations there was significant genetic variation among maternal lineages for the response to inbreeding in all traits. Although all inbred lineages declined at least somewhat in performance, several maternal lines maintained levels of performance just below outcross means even after four or five generations of selfing. We suggest that selection among maternal lines will have a greater effect than selecting within lines in lowering the genetic load of populations.     

THE ROLE OF INBREEDING DEPRESSION IN MAINTAINING THE MIXED MATING SYSTEM OF THE COMMON MORNING GLORY,IPOMOEA PURPUREA

Theoretical studies show that, although inbreeding depression (ID) will counterbalance the transmission advantage of selfing, it can only maintain a mixed mating system in plants when at least one of the following two conditions is met: (1) there is a positive association between selfing rates and the level of ID; and (2) ID is greater than 0.5 for the female component of fitness, while the average ID for male and female fitness is less than 0.5. This study tests whether these two conditions hold in the common morning glory, Ipomoea purpurea, which has a mixed mating system with 30% self-fertilization. Inbreeding depression was found in all but one fitness component measured in two groups of plants with distinct anther-stigma distances (ASD), a character that influences selfing rates. However, when examined separately, a negative association was found between selfing rates and ID; plants with large ASD (low-selfing-rate genotypes) tended to have higher ID than ones with small ASD (high-selfing-rate genotypes). Furthermore, the overall lifetime ID for male (12.5%) and female (24%) components of fitness, averaged across two ASD groups, were lower than what is necessary for ID to maintain an evolutionarily stable mixed mating system. Therefore, although inbreeding depression contributes to balancing the transmission advantage of selfing, it is not likely to be the primary mechanism maintaining the mixed mating system of I. purpurea. The contribution of other mechanisms is discussed.     

THE USEFULNESS OF BEHAVIOR FOR PHYLOGENY ESTIMATION: LEVELS OF HOMOPLASY IN BEHAVIORAL AND MORPHOLOGICAL CHARACTERS

It is widely believed that behavior is more evolutionarily labile and/or more difficult to characterize than morphology, and thus that behavioral characters are not as useful as morphological characters for estimating phylogenetic relationships. To examine the relative utility of behavior and morphology for estimating phylogeny, we compared levels of homoplasy for morphological and behavioral characters that have been used in systematic studies. In an analysis of 22 data sets that contained both morphological and behavioral characters we found no significant difference between mean consistency indices (CIs, which measure homoplasy) within data sets for the two types of characters. In a second analysis we compared overall CIs for 8 data sets comprised entirely of behavioral characters with overall CIs for 32 morphological data sets and found no significant difference between the two types of data sets. For both analyses, 95% confidence limits on the difference between the two types of characters indicate that, even if given the benefit of the doubt, morphological characters could not have substantially higher mean CIs than behavioral characters. These results do not support the idea that behavioral characters are less useful than morphological characters for the estimation of phylogeny.     

ECOLOGICAL GENETICS OF GYNODIOECY IN SILENE VULGARIS: RELATIVE FITNESS OF FEMALES AND HERMAPHRODITES DURING THE COLONIZATION PROCESS

Recent theoretical models have addressed the influence of metapopulation dynamics on the fitness of females and hermaphrodites in gynodioecious plants. In particular, selection is thought to favor hermaphrodites during population establishment because that sex should be less prone to pollen limitation, especially if self-fertilization is possible. However, inbreeding depression could limit this advantage. In this experimental study of Silene vulgaris, a weedy gynodioecious plant, the fitness of females and hermaphrodites was estimated from seed production in both mixed-sex populations and for individuals isolated from these populations by 20, 40, 80, or 160 m. In mixed populations females display statistically significant greater per capita seed production owing to higher capsule production and higher rates of seed germination. The fitness of both sexes declines with increasing isolation, but at different rates, such that in the 160-m treatment hermaphrodites are by far the more fit sex. Allozyme studies suggest that this differential decline is because the selfing rate in hermaphrodites increases as a function of isolation, at least partially compensating for a decline in the availability of outcross pollen. Overall, the negative effects of pollen limitation on females far outweighs the negative effects of inbreeding depression following selfing in hermaphrodites. Thus, extinction/recolonization dynamics would appear to favor hermaphrodites as long as seed dispersal events exceed some critical distance.     

RECONSTRUCTING ORIGINS OF LOSS OF SELF‐INCOMPATIBILITY AND SELFING IN NORTH AMERICAN ARABIDOPSIS LYRATA: A POPULATION GENETIC CONTEXT

Theoretical and empirical comparisons of molecular diversity in selfing and outcrossing plants have primarily focused on long‐term consequences of differences in mating system (between species). However, improving our understanding of the causes of mating system evolution requires ecological and genetic studies of the early stages of mating system transition. Here, we examine nuclear and chloroplast DNA sequences and microsatellite variation in a large sample of populations of Arabidopsis lyrata from the Great Lakes region of Eastern North American that show intra‐ and interpopulation variation in the degree of self‐incompatibility and realized outcrossing rates. Populations show strong geographic clustering irrespective of mating system, suggesting that selfing either evolved multiple times or has spread to multiple genetic backgrounds. Diversity is reduced in selfing populations, but not to the extent of the severe loss of variation expected if selfing evolved due to selection for reproductive assurance in connection with strong founder events. The spread of self‐compatibility in this region may have been favored as colonization bottlenecks following glaciation or migration from Europe reduced standing levels of inbreeding depression. However, our results do not suggest a single transition to selfing in this system, as has been suggested for some other species in the Brassicaceae.