Pollen dispersal in Yucca filamentosa (Agavaceae): the paradox of self-pollination behavior by Tegeticula yuccasella (Prodoxidae)

We investigated pollen dispersal in an obligate pollination mutualism between Yucca filamentosa and Tegeticula yuccasella. Yucca moths are the only documented pollinator of yuccas, and moth larvae feed solely on developing yucca seeds. The quality of pollination by a female moth affects larval survival because flowers receiving small amounts of pollen or self-pollen have a high abscission probability, and larvae die in abscised flowers. We tested the prediction that yucca moths primarily perform outcross pollinations by using fluorescent dye to track pollen dispersal in five populations of Y. filamentosa. Dye transfers within plants were common in all populations (mean ± 1 SE, 55 ± 3.0%), indicating that moths frequently deposit self-pollen. Distance of dye transfers ranged from 0 to 50 m, and the mean number of flowering plants between the pollen donor and recipient was 5 (median = 0), suggesting that most pollen was transferred among near neighbors. A multilocus genetic estimate of outcrossing based on seedlings matured from open-pollinated fruits at one site was 94 ± 6% (mean ± 1 SD). We discuss why moths frequently deposit self-pollen to the detriment of their offspring and compare the yucca-yucca moth interaction with other obligate pollinator mutualisms in which neither pollinator nor plant benefit from self-pollination.     

Synchronized,mass-emergences of a yucca moth,Prodoxus Y-inversus (Lepidoptera: Prodoxidae), after 16 and 17 years in diapause

Summary In 1985 and 1986, more than 180 adults of Prodoxus y-inversus Riley eclosed from cocoons of the 1969 generation in Yucca baccata, after prepupal larvae spent 16 and 17 years in diapause, intervals prior to mass emergence that are unmatched by any other insect on record. The emergences, which occurred during 15- to 16-day periods, followed many years of virtually no maturation by other individuals of the colony, and the size of the moths was not diminished by the long wait. Successful delay of development and synchronous emergence by many individuals indicates that whole populations can postpone activities through long periods of conditions that would be adverse for adult activity.     

Host specificity and reproductive success of yucca moths (Tegeticula spp. Lepidoptera: Prodoxidae) mirror patterns of gene flow between host plant varieties of the Joshua tree (Yucca brevifolia: Agavaceae)

Coevolution between flowering plants and their pollinators is thought to have generated much of the diversity of life on Earth, but the population processes that may have produced these macroevolutionary patterns remain unclear. Mathematical models of coevolution in obligate pollination mutualisms suggest that phenotype matching between plants and their pollinators can generate reproductive isolation. Here, we test this hypothesis using a natural experiment that examines the role of natural selection on phenotype matching between yuccas and yucca moths (Tegeticula spp.) in mediating reproductive isolation between two varieties of Joshua tree (Yucca brevifolia var. brevifolia and Y. brevifolia var. jaegeriana). Using passive monitoring techniques, DNA barcoding, microsatellite DNA genotyping, and sibship reconstruction, we track host specificity and the fitness consequences of host choice in a zone of sympatry. We show that the two moth species differ in their degree of host specificity and that oviposition on a foreign host plant results in the production of fewer offspring. This difference in host specificity between the two moth species mirrors patterns of chloroplast introgression from west to east between host varieties, suggesting that natural selection acting on pollinator phenotypes mediates gene flow and reproductive isolation between Joshua‐tree varieties.     

Systematic revision of the yucca moths in the Tegeticula yuccasella complex (Lepidoptera: Prodoxidae) north of Mexico

The yucca moths (Tegeticula and Parategeticula) are of great importance in studies of coevolution because of their obligate mutualism with their yucca hosts. Historically, three species of Tegeticula have been recognized. One of them, T. yuccasella, has been regarded as the pollinator of all but two yucca species, but morphological, molecular and biological data show that this is a large complex of monophagous and oligophagous species that differ greatly in their biology. It also includes derived ‘cheater’ species that do not pollinate their hosts and oviposit into fruits rather than flowers. Here the yuccasella complex north of Mexico is revised. The nominotypic pollinator species yuccasella is redescribed, and ten new pollinator species described: altiplanella, baccatella, carnerosanella, cassandra, elatella, maderae, mojavella, rostratella, superficiella and treculeanella. Two non-pollinating cheater species are recognized. One such species originally misidentified as a Prodoxus species, then synonymised with yuccasella, is re-erected as the non-pollinating intermedia. In addition, the new non-pollinator species corruptrix is described.     

Phylogeny of the pollinating yucca moths, with revision of Mexican species (Tegeticula and Parategeticula; Lepidoptera, Prodoxidae)

The yucca moths ( Tegeticula and Parategeticula ; Lepidoptera, Prodoxidae) are well known for their obligate relationship as exclusive pollinators of yuccas. Revisionary work in recent years has revealed far higher species diversity than historically recognized, increasing the number of described species from four to 20. Based on field surveys in Mexico and examination of collections, we describe five additional species: T. californica Pellmyr sp. nov. , T. tehuacana Pellmyr & Balcázar-Lara sp. nov. , T. tambasi Pellmyr & Balcázar-Lara sp. nov., T. baja Pellmyr & Balcázar-Lara sp. nov. and P. ecdysiastica Pellmyr & Balcázar-Lara sp. nov . Tegeticula treculeanella Pellmyr is identified as a junior synonym of T. mexicana Bastida. A diagnostic key to the adults of all species of the T. yuccasella complex is provided. A phylogeny based on a 2104-bp segment of mitochondrial DNA (mtDNA) in the cytochrome oxidase I and II region supported monophyly of the two pollinator genera, and strongly supported monophyly of the 17 recognized species of the T. yuccasella complex. Most relationships are well supported, but some relationships within a recent and rapidly diversified group of 11 taxa are less robust, and in one case conflicts with a whole-genome data set (amplified fragment length polymorphism, AFLP). The current mtDNA-based analyses, together with previously published AFLP data, provide a robust phylogenetic foundation for future studies of life-history evolution and host interactions in one of the classical models of coevolution and obligate mutualism.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 297–314.     

Phylogeny and life history evolution of Prodoxus yucca moths (Lepidoptera: Prodoxidae)

Abstract. Yucca moths (Lep., Prodoxidae) are well‐known for their obligate pollination mutualism with yuccas. In addition to the pollinators, yuccas also host many non‐pollinating yucca moths. Here the genus Prodoxus, the non‐pollinating sister group of the pollinators, is revised using morphological and molecular data, their phylogenetic relationships are analysed, and the evolution of host tissue specialization explored. Twenty‐two species are recognized, including nine new species: Prodoxus gypsicolor sp.n. , P. sonorensis sp.n. , P. carnerosanellus sp.n. , P. tamaulipellus sp.n. , P. weethumpi sp.n. , P. tehuacanensis sp.n. , P. californicus sp.n. , P. mapimiensis sp.n. and P. atascosanellus sp.n. Prodoxus y‐inversus Riley, P. coloradensis Riley and P. sordidus Riley are redescribed. The genus Agavenema is synonymized with Prodoxus. Phylogenetic analyses indicated that stalk‐feeding is basal within the group, that there are three separate origins of fruit‐feeding, and one origin of leaf‐mining from a stalk‐feeding ancestor. Although species with different feeding habits often coexist within hosts, the analyses suggest that ecological specialization and diversification within a host only may have occurred within one or possibly two hosts.     

Genetic consequences of specialization: yucca moth behavior and self-pollination in yuccas

Reciprocal specialization in interspecific interactions, such as plant-pollinator mutualisms, increases the probability that either party can have detrimental effects on the other without the interaction being dissolved. This should be particularly apparent in obligate mutualisms, such as those that exist between yucca and yucca moths. Female moths collect pollen from yucca flowers, oviposit into floral ovaries, and then pollinate those flowers. Yucca moths, which are the sole pollinators of yuccas, impose a cost in the form of seed consumption by the moth larvae. Here we ask whether there also is a genetic cost through selfish moth behavior that may lead to high levels of self fertilization in the yuccas. Historically, it has been assumed that females leave a plant immediately after collecting pollen, but few data are available. Observations of a member of the Tegeticula yuccasella complex on Yucca filamentosa revealed that females remained on the plant and oviposited in 66% of all instances after observed pollen collections, and 51% of all moths were observed to pollinate the same plant as well. Manual cross and self pollinations showed equal development and retention of fruits. Subsequent trials to assess inbreeding depression by measuring seed weight, germination date, growth rate, and plant mass at 5 months revealed significant negative effects on seed weight and germination frequency in selfed progeny arrays. Cumulative inbreeding depression was 0.475, i.e., fitness of selfed seeds was expected to be less than half that of outcrossed seeds. Single and multilocus estimates of outcrossing rates based on allozyme analyses of open-pollinated progeny arrays did not differ from 1.0. The discrepancy between high levels of behavioral self-pollination by the moths and nearly complete outcrossing in mature seeds can be explained through selective foreign pollen use by the females, or, more likely, pollen competition or selective abortion of self-pollinated flowers during early stages of fruit development. Thus, whenever the proportion of pollinated flowers exceeds the proportion that can be matured to ripe fruit based on resource availability, the potential detrimental genetic effects imposed through geitonogamous pollinations can be avoided in the plants. Because self-pollinated flowers have a lower probability of retention, selection should act on female moths to move among plants whenever moth density is high enough to trigger abortion. Received: 18 March 1996 \Accepted: 30 July 1996     

Phylogeographic structure in the bogus yucca moth Prodoxus quinquepunctellus (Prodoxidae): comparisons with coexisting pollinator yucca moths

The pollination mutualism between yucca moths and yuccas highlights the potential importance of host plant specificity in insect diversification. Historically, one pollinator moth species, Tegeticula yuccasella, was believed to pollinate most yuccas. Recent phylogenetic studies have revealed that it is a complex of at least 13 distinct species, eight of which are specific to one yucca species. Moths in the closely related genus Prodoxus also specialize on yuccas, but they do not pollinate and their larvae feed on different plant parts. Previous research demonstrated that the geographically widespread Prodoxus quinquepunctellus can rapidly specialize to its host plants and may harbor hidden species diversity. We examined the phylogeographic structure of P. quinquepunctellus across its range to compare patterns of diversification with six coexisting pollinator yucca moth species. Morphometric and mtDNA cytochrome oxidase I sequence data indicated that P. quinquepunctellus as currently described contains two species. There was a deep division between moth populations in the eastern and the western United States, with limited sympatry in central Texas; these clades are considered separate species and are redescribed as P. decipiens and P. quinquepunctellus (sensu stricto), respectively. Sequence data also showed a lesser division within P. quinquepunctellus s.s. between the western populations on the Colorado Plateau and those elsewhere. The divergence among the three emerging lineages corresponded with major biogeographic provinces, whereas AMOVA indicated that host plant specialization has been relatively unimportant in diversification. In comparison, the six pollinator species comprise three lineages, one eastern and two western. A pollinator species endemic to the Colorado Plateau has evolved in both of the western lineages. The east-west division and the separate evolution of two Colorado Plateau pollinator species suggest that similar biogeographic factors have influenced diversification in both Tegeticula and Prodoxus. For the pollinators, however, each lineage has produced a monophagous species, a pattern not seen in P. quinquepunctellus.     

Variation in the costs and benefits of mutualism: the interaction between yuccas and yucca moths

Summary Yucca moths are both obligate pollinators and obligate seed predators of yuccas. I measured the costs and net benefits per fruit arising for eight species of yuccas from their interaction with the yucca moth Tegeticula yuccasella. Yucca moths decrease the production of viable seeds as a result of oviposition by adults and feeding by larvae. Oviposition through the ovary wall caused 2.3–28.6% of ovules per locule to fail to develop, leaving fruit with constrictions, and overall, 0.6–6.6% of ovules per fruit were lost to oviposition by yucca moths. Individual yucca moth larvae ate 18.0–43.6% of the ovules in a locule. However, because of the number of larvae per fruit and the proportion of viable seeds, yucca moth larvae consumed only 0.0–13.6% of potentially viable ovules per fruit. Given both oviposition and feeding effects, yucca moths decreased viable seed production by 0.6–19.5%. The ratio of costs to (gross) benefits varied from 0% to 30%, indicating that up to 30% of the benefits available to yuccas are subsequently lost to yucca moths. The costs are both lower and more variable than in a similar pollinator-seed predator mutualism involving figs and fig wasps.There were differences between species of yuccas in the costs of associating with yucca moths. Yuccas with baccate fruit experienced lower costs than species with capsular fruit. There were also differences in costs between populations within species and high variation in costs between fruit within populations. High variability was the result of no yucca moth larvae being present in over 50% of the fruit in some populations, while other fruit produced up to 24 larvae. I present hypotheses explaining both the absence and high numbers of larvae per fruit.     

Oviposition and pollination behavior of the yucca moth,Tegeticula maculata (Lepidoptera: Prodoxidae), and its relation to the reproductive biology of Yucca whipplei (Agavaceae)

Summary The adult behavior of the yucca moth, Tegeticula maculata Riley, is finely tuned to the reproductive biology of its specific host plant, Yucca whipplei Torr. The female moths oviposit in the ovaries of the yucca flowers and actively pollinate the same flowers with pollen which they have collected previously. The selective pressures imposed on the moths by 1) the plant's need for pollen transfer via an insect pollinating agent, 2) its partial self-incompatibility, and 3) its ability to regulate seed set by aborting excess fruits, have molded the pollinator's behavior in such a way that its offspring have the greatest possible chance of surviving through the early larval stages. The evolutionary responses of the pollinator include the following: 1) the female moths consistently fly to a different plant after collecting pollen, thus insuring cross-fertilization of the flowers, 2) they always pollinate after depositing the first egg in a flower, but not necessarily after subsequent ovipositions, and 3) females emerging near the end of the flowering season frequently oviposit in developing seed pods, as opposed to open flowers which are more likely to be aborted by the plants.     

Pedigree reconstruction from SNP data: parentage assignment,sibship clustering and beyond

Data on hundreds or thousands of single nucleotide polymorphisms (SNPs) provide detailed information about the relationships between individuals, but currently few tools can turn this information into a multigenerational pedigree. I present the r package sequoia , which assigns parents, clusters half‐siblings sharing an unsampled parent and assigns grandparents to half‐sibships. Assignments are made after consideration of the likelihoods of all possible first‐, second‐ and third‐degree relationships between the focal individuals, as well as the traditional alternative of being unrelated. This careful exploration of the local likelihood surface is implemented in a fast, heuristic hill‐climbing algorithm. Distinction between the various categories of second‐degree relatives is possible when likelihoods are calculated conditional on at least one parent of each focal individual. Performance was tested on simulated data sets with realistic genotyping error rate and missingness, based on three different large pedigrees (N = 1000–2000). This included a complex pedigree with overlapping generations, occasional close inbreeding and some unknown birth years. Parentage assignment was highly accurate down to about 100 independent SNPs (error rate <0.1%) and fast (<1 min) as most pairs can be excluded from being parent–offspring based on opposite homozygosity. For full pedigree reconstruction, 40% of parents were assumed nongenotyped. Reconstruction resulted in low error rates (<0.3%), high assignment rates (>99%) in limited computation time (typically <1 h) when at least 200 independent SNPs were used. In three empirical data sets, relatedness estimated from the inferred pedigree was strongly correlated to genomic relatedness.     

DNA条形码技术在北京百花山地区夜蛾科物种鉴定中的应用

为了探讨DNA条形码技术在夜蛾物种鉴定中的可行性, 本研究利用条形码通用引物扩增了北京百花山地区43种夜蛾75个样本的线粒体细胞色素C氧化酶亚基I （mitochondrial cytochrome c oxidase subunit I, COI）基因序列, 以Kimura双参数模型进行种内种间遗传距离分析、 使用邻接法（neighbor-joining, NJ）和最大简约法（maximum parsimony, MP）分别构建系统发育树, 并利用分子序列差异阈值对样本进行分子可操作分类单元（molecular defined operational taxonomic units, MOTU）划分。结果表明： 所有夜蛾种类通过系统发育树可以成功区分; 种内平均遗传距离(0.03%)远远小于种间平均遗传距离(11.29%); 采用较为保守的1%的序列差异阈值将75个夜蛾样本分为42个MOTU, 正确率为95%, 除了MOTU04包含2个物种外, 剩余41个MOTU与形态种呈现一一对应的关系。结果显示, 基于COI基因的DNA条形码对于本研究中所涉及的夜蛾具有较好的区分, 可以作为一种有效的工具在夜蛾科昆虫物种鉴定中进行应用。     

Genetic variability and individual assignment of Chinese indigenous sheep populations (Ovis aries) using microsatellites

The purpose of this study was to assess the genetic characteristics of six breeds of Chinese local sheep using 19 microsatellite loci and to effectively validate statistical methods for individual assignment based on informative microsatellites. All the six breeds deviated from Hardy–Weinberg equilibrium expectations, while the majority of markers complied. The polymorphism information content (PIC) of overall loci for the six populations ranged from 0.283 (SRCRSP5) to 0.852 (OarVH72). Tibetan sheep were the most diverse population with the highest mean allelic richness (6.895), while Ujmuqin (UQ) harboured the lowest allelic richness (6.000). The F‐statistics for the six populations were F_IS = ?0.172, F_IT = ?0.082 and F_ST = 0.077, respectively. Furthermore, the pair‐wise F_IS revealed a moderate genetic differentiation among populations (P < 0.01), indicating that all breeds can be considered genetically independent entities. The lowest genetic differentiation was between Tengchong (TC) and UQ (F_ST = 0.041), and the highest one was between TC and Fat‐tailed Han (F_ST = 0.111). In comparing the three statistical models, we note that the seven microsatellite loci (MAF65, OarJMP58, SRCRSP9, MCM140, OarAE129, BM8125 and SRCRSP5) commonly used for individual assignment will ensure a powerful detection of individual origin, with accuracy up to 91.87%, when the likelihood‐based method is used. Overall, these findings shed light onto the genetic characteristics of Chinese indigenous sheep and offer a set of microsatellite loci that is simple, economic and highly informative for individual assignment of Chinese sheep.     

Inbreeding and outcrossing in Yucca whipplei: consequences for the reproductive success of plant and pollinator

Unlike most pollinators, yucca moths are active pollinators of their host plants. Females lay their eggs in the flowers they pollinate, and their larvae feed solely on the resulting seeds. Previous evidence suggests that the yucca moth Tegeticula maculata avoids self-pollinating their host Yucca whipplei . Other yucca moths may self-pollinate more frequently. When pollinating, yucca moths are also reported to fly large distances between plants, bypassing neighbouring plants in the process. We experimentally verify the suggestion of Pellmyr et al . that yucca is more likely to retain fruits from self-pollination if overall fruit set is low. Thus, selection on moths to avoid self-pollinating should be density dependent. We found no evidence that mating with close neighbours resulted in inbreeding depression, thus the moth's long-distance flights between plants are yet to be explained.     

Potential of microsatellites for individual assignment: the North Atlantic redfish (genus Sebastes) species complex as a case study

We used the four redfish taxa (genus Sebastes) from the North Atlantic to evaluate the potential of multilocus genotype information obtained from microsatellites in assigning individuals at two different levels of group divergence. We first tested the hypothesis that microsatellites can diagnostically discriminate individual redfish from different groups. Second, we compared two different methods to quantify the effect of number of loci and likelihood stringency levels on the power of microsatellites for redfish group membership. The potential of microsatellites to discriminate individuals from different taxa was illustrated by a shared allele distance tree in which four major clusters corresponding to each taxa were defined. Concomitant with this strong discrimination, microsatellites also proved to be powerful in reclassifying specimens to the taxon of origin, using either an empirical or simulated method of estimating assignment success. By testing for the effect of both the number of loci and the level of stringency on the assignment success, we found that 95% of all specimens were still correctly reclassified with only four loci at the most commonly used criterion of log0. In contrast, the results obtained at the population level within taxa highlighted several problems of assignment that may occur at low levels of divergence. Namely, a drastic decrease of success with increasing stringency illustrated the lack of power of our set of loci. Strong discrepancy was observed between results obtained from the empirical and simulated methods. Finally, the highest assignment success was obtained when reducing the number of loci used, an observation previously reported in studies of human populations.     

Homoploid hybrid origin of Yucca gloriosa: intersectional hybrid speciation in Yucca (Agavoideae,Asparagaceae)

There is a growing appreciation for the importance of hybrid speciation in angiosperm evolution. Here, we show that Yucca gloriosa (Asparagaceae: Agavoideae) is the product of intersectional hybridization between Y. aloifolia and Y. filamentosa. These species, all named by Carl Linnaeus, exist in sympatry along the southeastern Atlantic coast of the United States. Yucca gloriosa was found to share a chloroplast haplotype with Y. aloifolia in all populations sampled. In contrast, nuclear gene‐based microsatellite markers in Y. gloriosa are shared with both parents. The hybrid origin of Y. gloriosa is supported by multilocus analyses of the nuclear microsatellite markers including principal coordinates analysis (PCO), maximum‐likelihood hybrid index scoring (HINDEX), and Bayesian cluster analysis (STRUCTURE). The putative parental species share only one allele at a single locus, suggesting there is little to no introgressive gene flow occurring between these species and Y. gloriosa. At the same time, diagnostic markers are segregating in Y. gloriosa populations. Lack of variation in the chloroplast of Y. aloifolia, the putative maternal parent, makes it difficult to rule out multiple hybrid origins of Y. gloriosa, but allelic variation at nuclear loci can be explained by a single hybrid origin of Y. gloriosa. Overall, these data provide strong support for the homoploid hybrid origin of Y. gloriosa.     

Phylogeography and host association in a pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae)

Inferring the historical context of ecological diversification is an important step in understanding the way that population-level processes result in a diversity of species and interactions in communities. We performed a phylogeographic analysis of mitochondrial DNA haplotypes from the pollinating seed parasite Greya politella (Lepidoptera: Prodoxidae) in order to determine the degree to which populations were structured according to geographical location and host-plant association. Ninety-eight individuals were sampled from 29 locations ranging from southern California to western Idaho. Restriction-site variation in 87 individuals (27 populations) was screened by digestion with 11 endonucleases, followed by Southern blotting; 38 restriction-site positions were mapped by double digests. Haplotypes were further defined by generating fragments 251 bases in length via PCR, screening them for sequence variation using denaturing gel gradient electrophoresis (DGGE), and sequencing the resulting variants. Parsimony analysis of the resulting 12 restriction-site and 15 sequence haplotypes indicated strong geographical structuring of populations: (i) most populations were monomorphic for haplotype; (ii) haplotypes from California and the Pacific Northwest (Oregon, Washington and Idaho) formed robust monophyletic groups. Population structure was significant both within and between the two regions, as reflected by N _ST. Patterns of host-plant association and haplotype phylogeny suggest that populations have recently undergone host-plant shifts in many different parts of the species range, although the direction and number of host shifts cannot be determined at the present level of sampling resolution.     

蛾翅数学形态特征用于夜蛾分类和鉴定的可行性研究

摘要: 为探讨蛾翅数学形态特征(MMC)在夜蛾科分类鉴定中的可行性, 本文利用数字化技术获得和处理昆虫图像, 对鳞翅目夜蛾科6种夜蛾的右前翅提取矩形度、 延长度、 叶状性、 偏心率、 球状性、 似圆度和不变矩Hu1、 Hu2等13项与大小尺度和方向均无关的数学形态特征, 并利用方差分析、 逐步判别分析和聚类分析等方法研究了各项数学形态特征在昆虫分类上作为分类特征的可行性、 可靠性和重要性, 并且从数学形态学角度对夜蛾科6个种的亲缘关系进行了分析。分析结果认为矩形度和延长度2个形态特征对这6种夜蛾的分类鉴定没有显著意义, 从而筛选出11个形态特征作为分类变量, 它们的作用大小依次为： （偏心率、 Hu5、 Hu7）＞Hu2＞似圆度＞球状性＞Hu3＞（叶状性、 Hu1、 Hu6）＞Hu4。利用蛾翅的这些特征参数成功地实现了对夜蛾科6种夜蛾的分类鉴定, 基于这些特征参数的6种夜蛾的亲缘关系远近与基于传统形态学的系统进化观点相同。研究表明蛾翅数学形态特征可应用于蛾类昆虫的快速鉴定, 为未来逐步实现蛾类昆虫的自动识别奠定了基础。     

Reproductive consequences of interactions between Yucca glauca (Agavaceae) and Tegeticula yuccasella (Lepidoptera) in Colorado

For over 100 years the association between Yucca (Agavaceae) and Tegeticula (Lepidoptera: Incurvariidae) has been accepted as a quintessential example of an obligate mutualism. The yucca moth is purported to be the sole pollinator of Yucca, while Yucca flowers provide courtship and mating arenas, and Yucca seeds provide food for developing Tegeticula larvae. We studied Yucca glauca in northern Colorado, comparing the reproductive ecology and breeding systems of Yucca in plains populations, the “preferred” habitat of Yucca, with “marginal” sites at the edge of the local elevational distribution. Tegeticula are abundant at plains sites, and fruit set is significantly higher than in the foothills, where fruit set is limited by the paucity of moths. The low frequency of moths at high elevation, coupled with behaviors of adult female Tegeticula which lead to self-pollination, failure to pollinate, and periodic overloading of fruits with eggs, may help explain why Yucca glauca appears to maintain alternative pollinators. Some fruits lack evidence of Tegeticula infestation, suggesting that larvae die before completing development, or that fertilization of Yucca sometimes occurs without the intervention of Tegeticula. Biochemical analyses of nectar and observations of floral visitors revealed that it is highly likely that the fly Pseudocalliope sp. nov. (Lauxaniidae), which congregates and mates on Yucca glauca blossoms, acts as a secondary pollinator. Autogamy appears to occur infrequently in natural populations. We therefore propose that the yucca-yucca moth symbiosis be viewed as a facultative mutualism.