Chromosome association and pollen fertility of parental and interspecific hybrids of Lycopersicon esculentum X L. hirsutum and L. pennellii

Cytological studies were carried out on two wild species (L. hirsutum and L. pennellii) and the cultivated species (L. esculentum) of tomato and their F1 hybrids. Both parents and hybrids show a diploid chromosome number of 2n=24. The meiotic behaviour of the cultivated species showed a high degree of chromosome homology resulting in a high level of chiasmata frequency per bivalent. In contrast, the two wild species showed a slight increase in uniyalent frequency and a decrease in bivalent formation and chiasmata frequency. The meiotic behaviour of the hybrids showed a high level of univalents and low levels of bivalents as well as trivalents. Highly significant decreases in chiasmata frequency and increases in meiotic abnormalities, especially in the L. esculentum X L. pennellii hybrid, also were detected. The high meiotic irregularity and low chiasmata frequency recorded in the second hybrid indicated the disharmony and difference between its parental genomes and also served to predict its sterility. With regard to degree of pairing recorded in the hybrids, there is a possibility that sterility in such cases may refer to genetic factors in addition to the previously mentioned reasons. Pollen fertility showed no great difference between L. esculentum and L. hirsutum and their F1 hybrid, but a significant decrease was recorded in the L. esculentum X L. pennellii hybrid, which was clearly associated with high meiotic irregularity, low chiasmata frequency and chromosome association.     

ESTIMATING THE MATING BEHAVIOR OF A PAIR OF HYBRIDIZING HELICONIUS SPECIES IN THE WILD

Premating isolation between incipient species is rarely studied in nature, even though mating tests in captivity may give an inaccurate picture of natural hybridization. We studied premating barriers between the warningly colored butterflies Heliconius erato and H. himera (Lepidoptera) in a narrow contact zone in Ecuador, where hybrids are found at low frequency. Eggs obtained from wild-mated females, supplemented with eggs and young larvae collected from the wild, were reared to adulthood. Adult color patterns of these progeny were then used to infer how their parents must have mated. Likelihood was used to estimate both the frequencies of potential parental genotypes from adult phenotypes collected in the wild, and the degree of assortative mating from the inferred parents. The frequencies of parental genotypes varied across the hybrid zone, but our statistical method allowed estimates of hybrid deficit and assortative mating to be integrated across all sites sampled. The best estimate of the frequency of F₁ and backcross hybrid adults in the center of the hybrid zone was 10%, with support limits (7.1%, 13.0%; support limits are asymptotically equivalent to 95% confidence limits). Mating was highly assortative: in the center of the hybrid zone the cross-mating probability between H. erato and H. himera was only 5% (0.3%, 21.4%). Wild hybrids themselves mated with both pure forms, and the probabilities that they mated in any direction were not significantly lower than those among conspecifics. These results are consistent with earlier laboratory studies on mate choice, and suggest that selection against hybrids must be strong to prevent formation of a hybrid swarm. Unfortunately, the wide support limits on mating behavior precluded a measure of the strength of selection from these data alone. Our statistical approach provides a useful general method for estimating mate choice in the wild.     

Stipa×brozhiana (Poaceae) nothosp. nov. from the western Pamir Alai Mts (middle Asia) and taxonomical notes on Stipa×tzvelevii

Stipa ×brozhiana M. Nobis nothosp. nov. (Poaceae) is described and illustrated. The taxon belongs to sect. Smirnovia Tzvel. and originated from the hybridization of species belonging to sect. Smirnovia and Barbatae Junge. Stipa ×brozhiana is morphologically close to Stipa lipskyi Roshev., but is easily distinguished by its much shorter hairs on the seta, thinner, uni‐ or indistinctly bigeniculate awns, differently shaped callus and longer ligules of vegetative shoots. Characters distinguishing S. ×brozhiana from the parental species and other similar hybrid taxa belonging to sect. Smirnovia and occurring in the Pamir Alai Mts are discussed. In addition, the taxonomical status of S. ×tzvelevii Ikonn. pro sp., another taxon that has originated from hybridization between species belonging to sect. Smirnovia and Barbatae, is discussed. The taxon was originally described as a distinct species, but is now considered to be the hybrid S. caucasica×S. orientalis. The main characters distinguishing S. ×tzvelevii from parental species are given.     

PATTERNS OF MATING IN WILD SUNFLOWER HYBRID ZONES

Theory predicts that homoploid hybrid speciation will be facilitated by selfing, yet most well-documented hybrid species are outcrossers. One possible explanation for this puzzle is that conditions in hybrid populations may favor selfing, even in otherwise outcrossing species. For example, in self-incompatible plants, mixtures of self and interspecific pollen often induce selfing. Here, we examine patterns of mating in three hybrid zones and four “pure” populations of Helianthus annuus and H. petiolaris, wild, self-incompatible sunflower species that are thought to have parented three homoploid hybrid species. Fourteen to 16 maternal families from each pure population and 44–46 maternal families from each hybrid zone were analyzed for seven polymorphic isozyme loci. Maximum-likelihood (ML) methods were used to estimate multilocus outcrossing rates (T_m) and hybridization frequencies for each maternal family, each phenotypic group within each hybrid zone (annuus-like, hybrid, and petiolaris-like), and each population. As predicted for self-incompatible species, all four parental populations have outcrossing rate ML estimates of 1.0. Within the hybrid zones, outcrossing rates were lowest in the H. annuus–like fraction of the population (0.73, 0.72, and 0.74 in the three hybrid zones, respectively), largely intermediate in the H. petiolaris–like group (0.94, 0.90, and 0.94), and highest in the hybrid group (0.97, 0.93, and 0.97). Although outcrossing rates are lower in hybrid zones than in pure populations, it is unlikely that the observed decrease facilitates hybrid speciation because outcrossing rates in the critical hybrid fraction of the population do not differ significantly from 1.0. Dividing the outcrossed pollen pool into intraspecific and interspecific components revealed that maternal plants are largely fertilized by conspecific pollen, confirming an important role for pollen competition as a reproductive barrier. Highly sterile hybrid plants do not appear to discriminate between parental species pollen, but hybrids with higher fertility tend to be fertilized by pollen from the parental group they resemble genetically. Thus, gametic selection leads to substantial assortative mating in these hybrid zones.     

Populations composed entirely of hybrid colonies: bidirectional hybridization and polyandry in harvester ants

In eusocial Hymenoptera, haplodiploid life cycles, obligate sterile castes, and polyandry may facilitate selection for hybridization. We analyzed a broad hybrid zone between the ecologically distinct seed‐harvester ants Pogonomyrmex occidentalis (Cresson) and Pogonomyrmex maricopa (Wheeler) using mitochondrial (mt)DNA sequence data, eight morphological markers, and 14 random amplified polymorphic DNA (RAPD) markers. Average mtDNA sequence divergence among parental species was 11.34%, indicating secondary contact. RAPD markers were significantly correlated with morphological variation, confirming the interspecific hybrid origin of all morphologically putative hybrid colonies. A morphological hybrid index indicates an abundance of both F₁ hybrids and parental morphotypes within colonies. Individual character frequencies plotted against distance show coincident and concordant clines, suggesting little to no introgression. The structure of the hybrid zone is two‐fold. Within the western region, stark reversals in character frequencies coincide with overt soil differences, indicating a mosaic hybrid zone structure. The eastern region is a riparian habitat where four adjacent populations were composed entirely of hybrid colonies. These habitat associations suggest that hybrid worker genomes permit dispersal into intermediate environments that select against one or both parental species. The present study suggests that, in addition to retaining reproductive compatibility, ecologically distinct species of ants may generate hybrid colonies maintained by environmental selection. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 320–336.     

Chiasmata and the breeding system in wild populations of diploid wheats

Seven populations of the selfer Triticum longissimum (= Aegilops longissima) and five populations of the closely related outbreeder T. speltoides (= Ae. speltoides) were scored for chiasma frequencies in pollen mother cells. The populations of the selfer have significantly higher frequencies of chiasmata than the outbreeding populations. This difference becomes even clearer when interstitial chiasmata alone are compared. It is argued that an optimal degree of effective recombination is achieved by the balance between outbreeding and interstitial chiasmata. — There are wider differences between the selfing populations than between the outbreeding populations, but the differences between families (within populations) are small in both species. Variation between plants within families seems to be lower in the selfer, but nevertheless high enough to be inexplicable on the basis of selfing alone. — Small populations subject to hardship conditions show a higher frequency of chiasmata than others.     

Studies on trisomics in a Jute hybrid

Fifteen red pigmented trisomics were isolated in the F₂ generation from the cross Corchorus olitorius L. x C. capsularis L. In the F₃ generation a few green trisomics were obtained; more of these were isolated from the backcross generation. A detailed morphological and cytological analysis of the trisomic hybrid populations derived from the F₃ and F₄ generations is presented. The trisomics were scored for several morphologically differentiating characters and most of them were intermediate between the parental species, a few resembling the olitorius parent more. Cytological studies showed the formation of abnormal sporads in trisomics with different frequencies indicating a misdivision at meiosis. This imbalance at meiosis results in a higher percentage of pollen sterility in the trisomics as compared with the parents. Analysis of M₁ of meiosis showed that there were: differences in the frequencies of the various chromosome configurations between the two categories of trisomics; significantly higher trivalent frequencies per PMC in the green trisomics; in contrast significantly hihger univalent frequencies per PMC in the red trisomics. No significant difference in chiasma formation was observed between red and green trisomics, nor between trisomics and their parental species. It appears that segmental homology in the parental chromosomes has probably resulted in varying degrees of preferential pairing in the trisomic hybrid.     

The use of genomic in situ hybridization (GISH) to show transmission of recombinant chromosomes by a partially fertile bigeneric hybrid, Gasteria lutzii ×Aloe aristata (Aloaceae), to its progeny

Genomic in situ hybridization (GISH) was used to study somatic chromosomes of parental and progeny plants (all 2n=2x=14) of the bigeneric hybrid between Gasteria lutzii and Aloe aristata (Aloaceae), which is partially fertile, a rare occurrence in plants. GISH successfully distinguished between the two parental genomes in the F1 hybrid and revealed numerous genomic recombinations in chromosomes transmitted by the F1 to the back-cross progeny. The results indicate high levels of meiotic compatibility between the parental genomes, even though they differ in size by 20%. Recombination occurred at a frequency that was higher than that expected from the analysis of orcein-stained meiosis in the F1. The discrepancy suggests that terminalization may occur prior to or during metaphase I, reducing the apparent chiasma frequency, or possibly reveals an under-estimation caused by difficulties in resolving closely grouped chiasmata by eye. Received: 9 September 1996; in revised form: 21 October 1996 / Accepted: 21 October 1996     

Niche partitioning between close relatives suggests trade‐offs between adaptation to local environments and competition

Niche partitioning among close relatives may reflect trade‐offs underlying species divergence and coexistence (e.g., between stress tolerance and competitive ability). We quantified the effects of habitat and congeneric species interactions on fitness for two closely related herbaceous plant species, Mimulus guttatus and Mimulus laciniatus, in three common habitat types within their sympatric range. Drought stress strongly reduced survival of M. guttatus in fast‐drying seeps occupied by M. laciniatus, suggesting that divergent habitat adaptation maintains this niche boundary. However, neither seedling performance nor congeneric competition explained the absence of M. laciniatus from shady streams where M. guttatus thrives. M. laciniatus may be excluded from this habitat by competition with other species in the community or mature M. guttatus. Species performance and competitive ability were similar in sympatric meadows where plant community stature and the growing season length are intermediate between seeps and streams. Stochastic effects (e.g., dispersal among habitats or temporal variation) may contribute to coexistence in this habitat. Habitat adaptation, species interactions, and stochastic mechanisms influence sympatric distributions for these recently diverged species.     

Frequency of spontaneous amphiploids in Gilia (Polemoniaceae) hybrids

This paper reports the frequency of spontaneous amphiploids or neopolyploids in experimental interspecific hybrids in two annual sections of Gilia (Polemoniaceae, sects. Arachnion and Gilia, x = 9). In each section the species were intercrossed in numerous hybrid combinations to obtain an array of F1 hybrid types; seven of the hybrid types spontaneously produced new amphiploid progeny in F2. In sect. Arachnion the parental species and F1s were all diploids and the amphiploids were tetraploid; in sect. Gilia the parental species were diploids or tetraploids and the amphiploids were tetraploid or hexaploid. Two measures were used to express the frequency of spontaneous amphiploid formation. The first is the proportion of the F1 hybrid combinations that yielded any amphiploid progeny at all. In sect. Arachnion this proportion is 3/39 or 7.7%; in sect. Gilia it is 4/16 or 25%. A second measure is needed to express the variation in productivity among the seven amphiploid-producing hybrid types. The measure adopted is the mean number of new amphiploids per single F1 hybrid plant. The productivity numbers for the three hybrid combinations in sect. Arachnion are 0.25, 0.67, and 2.0; and those for four hybrid combinations in sect. Gilia are 0.15, 0.62, 2.25, and 12.62. There are large differences from one hybrid combination to another in rate of amphiploid formation, and the rate is quite high in some hybrids. The factors affecting these differences are discussed.     

Interspecific hybridization in natural populations ofCyrtandra (Gesneriaceae) on the Hawaiian Islands: Evidence from RAPD markers

Interspecific hybridization among Hawaiian species ofCyrtandra (Gesneriaceae) was investigated using randomly amplified polymorphic DNA (RAPD) markers. Thirty-three different primers were used to investigate interspecific hybridization for 17 different putative hybrids based on morphological intermediacy and sympatry with putative parental species. RAPD data provided evidence for the hybrid origin of all putative hybrid taxa examined in this analysis. However, the patterns in the hybrid taxa were not found to be completely additive of the patterns found in the parental species. Markers missing in the hybrid taxa can be attributed to polymorphism in the populations of the parental species and the dominant nature of inheritance for RAPD markers. Unique markers found within hybrid taxa require further explanation but do not necessarily indicate that the taxa are not of hybrid origin. The implications suggest that these interspecific hybridization events had, and continue to have, an effect on the adaptive radiation and conservation biology ofCyrtandra.     

Studies on chiasma distribution and chiasma movement in Zoniopoda tarsata (Orthoptera: Romaleidae)

A sample of 27 males of Zoniopoda tarsata from Argentina was studied cytologically. The three largest autosomal pairs and the X were characterized by the presence of interstitial C-bands. Chiasma position relative to the bands was analyzed at diplotene and diakinesis. The frequency of interstitial, terminal and total chiasmata per cell was studied for the whole autosomal bivalent set, analysing the variations between stages and among individuals. The comparison of interstitial chiasma frequencies between stages and among individuals and the study of chiasma position relative to the bands in pairs 1, 2 and 3 indicated that chiasma distribution varied from diplotene to diakinesis. Therefore, terminalization does exist in this species and the movement may occur towards the centromere. The frequency of terminal associations at diplotene showed a high negative correlation (r=-0.89; p<10^-5) with the number of interstitial chiasmata. This correlation would not be expected if the two kinds of association were produced by different (independent) mechanisms. Consequently, terminal associations were considered genuine chiasmata. The correlation between interstitial and total chiasmata was very much lower then the former (r=0.39; p=0.04). This fact, besides the relatively low variation for chiasma number, observed among individuals suggests that in this species the number of interestitial chiasmata, which are the most important in controlling the genetical recombination, is mainly regulated by changes in chiasma distribution, while variations in total chiasma frequency are of much lower magnitude.Member of Carrera del Investigador del Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET)     

Are hybrid species more fit than ancestral parent species in the current hybrid species habitats?

Hybrid speciation is thought to be facilitated by escape of early generation hybrids into new habitats, subsequent environmental selection and adaptation. Here, we ask whether two homoploid hybrid plant species (Helianthus anomalus, H. deserticola) diverged sufficiently from their ancestral parent species (H. annuus, H. petiolaris) during hybrid speciation so that they are more fit than the parent species in hybrid species habitats. Hybrid and parental species were reciprocally transplanted into hybrid and parental habitats. Helianthus anomalus was more fit than parental species in the H. anomalus actively moving desert dune habitat. The abilities to tolerate burial and excavation and to obtain nutrients appear to be important for success in the H. anomalus habitat. In contrast, H. deserticola failed to outperform the parental species in the H. deserticola stabilized desert dune habitat, and several possible explanations are discussed. The home site advantage of H. anomalus is consistent with environmental selection having been a mechanism for adaptive divergence and hybrid speciation and supports the use of H. anomalus as a valuable system for further assessment of environmental selection and adaptive traits.     

Comparative chiasma analysis using a computerised optical digitiser

A new computerised technique has been devised for measuring the distribution of chiasmata along diplotene bivalents. The method involves the introduction into the field of view of the microscope, of a fine light spot which can be accurately manipulated along the chromosomes of each bivalent. The data recorded include (a) the positions of the chiasmata along the bivalent in terms of their relative distances from the centromere and (b) the individual bivalent and cellular chiasma frequencies. — The method has been applied to the analysis of chiasma distribution patterns in the two known species of the genus Caledia, C. species nova 1 and C. captiva and in two chromosomal races of the latter. Statistical tests indicate that within bivalents at least 40% of the comparative distribution patterns of chiasmata between races and species are significantly different. Similar comparisons between populations within races reveal only 18% significant differences. — The observed distribution patterns of chiasmata in this genus suggest that chiasma formation is sequential from centromere to telomere. — The variation in the frequency and distribution of chiasmata between races and species suggests that the interference distances between successive chiasmata are, at least partially, independent of chiasma frequency and position. — The interracial and interspecific differences in chromosome structure are correlated with changes in chiasma pattern.     

ECOLOGICAL AND GENETIC ASSOCIATIONS IN AN IRIS HYBRID ZONE

Chloroplast DNA (cpDNA) markers and 12 nuclear (random amplified polymorphic DNA, or RAPD) markers were used to examine the distribution of genetic variation among individuals and the genetic and ecological associations in a hybrid iris population. Plants in the population occurred at various distances from the edge of a bayou in a relatively undisturbed mixed hardwood forest and in an adjacent pasture dominated by herbaceous perennials with interspersed oak and cypress trees. The majority of plants sampled possessed combinations of markers from the different Iris species. Genetic markers diagnostic for Iris fulva and I. brevicaulis occurred at high frequencies, whereas markers diagnostic for I. hexagona were infrequent. For the majority of the nuclear markers, significant levels of cytonuclear disequilibria existed because of intraspecific associations among the markers in both the pasture and the forest. The distribution of nuclear markers among individuals was bimodal; intermediate genotypes were absent and the majority of RAPD markers were associated with their intraspecific cpDNA haplotypes. Strong intraspecific associations existed among RAPD markers in the forest, but associations tended to be weaker in the pasture area. Ecological correlations were detected for all but one of the I. fulva and I. brevicaulis RAPD markers. The ecological associations of hybrids similar to I. brevicaulis resembled associations of I. brevicaulis parental genotypes, suggesting that these hybrid genotypes may be relatively fit in the same habitats. The hybrids similar to I. fulva, however, were distributed in habitats that were unique relative to the parental species. The patterns of genetic and environmental associations along with other available data suggest that (1) only advanced generation hybrids were present in the population; (2) formation of F₁ hybrids among Louisiana irises is rare, leading to sporadic formation of hybrid populations; and (3) selection and assortative mating have contributed to the formation of hybrid genotypes that tend to be similar to parental genotypes. The patterns of ecological and genetic associations detected in this population suggest that assortative mating and environmental and viability selection are important in the structuring and maintenance of this hybrid zone.     

A comparison of chiasma frequency and distribution between sexes in three species of grasshoppers

Chiasma frequency and distribution have been compared in both sexes of the grasshoppers Chortoicetes terminifera (n=11+X) (Oedipodinae) Parapleurus alliaceus (n=11+X) (Oedipodinae) and Chrysochraon dispar (n=8+X) (Gomphocerinae). In the last two species, chiasmata in the males are terminally localised in all except the shortest bivalents. Strict chiasma localisation was not found in the females but chiasmata were rare near to the centromere. The sexes had different autosomal mean chiasma frequencies. Cell means were: C. terminifera Males 13.07, Females 13.02; P. alliaceus Males 12.32, Females 14.47; C. dispar Males 12.56, Females 13.57. Possible mechanisms affecting the distribution of chiasmata, and the significance of the intersex and interspecies difference, are discussed.     

Seed beetle survivorship,growth and egg size plasticity in a paloverde hybrid zone

1. Although numerous studies have examined the ecology of plant resistance to herbivores and the distribution of herbivores within plant hybrid zones, few have examined how plant hybridization influences herbivore growth, development, or life history. The experiment reported here examines variation in survivorship, development time, and final adult body size of Stator limbatus reared on seeds of parental and hybrid Cercidium floridum-×-C. microphyllum trees from a paloverde hybrid zone in eastern California. Because S. limbatus exhibits egg size plasticity in response to host species, the size of eggs that females lay on hybrid and parental plants is also examined. 2. The hypotheses (a) that seeds of hybrid trees are intermediate between those of the two parental species in their resistance to penetration by S. limbatus larvae; (b) that seeds of hybrid trees are intermediate in their suitability for the growth of larvae that successfully penetrate the seed-coat; (c) that female S. limbatus can distinguish between hybrid trees and pure-bred trees, as quantified by the size of eggs they lay on seeds of each taxon, and (d) that female S. limbatus can distinguish among individual hybrid trees, are tested. 3. On average, S. limbatus survivorship was lower, development time longer, and emergence body mass lower on seeds of C. floridum than on seeds of C. microphyllum. Seeds of hybrid trees were, on average (across trees), intermediate between seeds of the parental species in the resistance of their seed-coats to penetration by S. limbatus larvae and in their suitability for larval growth. Individual hybrid trees also varied in the resistance of their seeds to, and the suitability of their seeds for, S. limbatus larvae. 4. Female S. limbatus laid significantly larger eggs on seeds of C. floridum than on seeds of C. microphyllum, and, on average, intermediate size eggs on hybrid trees. The size of eggs laid by females also varied among hybrid trees, with females laying C. floridum-sized eggs on some trees, and C. microphyllum-sized eggs on other trees. These results suggest that females have at least some ability to distinguish among hybrid trees, but there was no evidence that females laid larger eggs on poorer quality hybrid trees.     

Arthropod communities on hybrid and parental cottonwoods are phylogenetically structured by tree type: Implications for conservation of biodiversity in plant hybrid zones

Although hybridization in plants has been recognized as an important pathway in plant speciation, it may also affect the ecology and evolution of associated communities. Cottonwood species (Populus angustifolia and P. fremontii) and their naturally occurring hybrids are known to support different plant, animal, and microbial communities, but no studies have examined community structure within the context of phylogenetic history. Using a community composed of 199 arthropod species, we tested for differences in arthropod phylogenetic patterns within and among hybrid and parental tree types in a common garden. Three major patterns emerged. (1) Phylogenetic diversity (PD) was significantly different between arthropod communities on hybrids and Fremont cottonwood when pooled by tree type. (2) Mean phylogenetic distance (MPD) and net relatedness index (NRI) indicated that communities on hybrid trees were significantly more phylogenetically overdispersed than communities on either parental tree type. (3) Community distance (D_pw) indicated that communities on hybrids were significantly different than parental species. Our results show that arthropod communities on parental and hybrid cottonwoods exhibit significantly different patterns of phylogenetic structure. This suggests that arthropod community assembly is driven, in part, by plant–arthropod interactions at the level of cottonwood tree type. We discuss potential hypotheses to explain the effect of plant genetic dissimilarity on arthropod phylogenetic community structure, including the role of competition and environmental filtering. Our findings suggest that cottonwood species and their hybrids function as evolutionarily significant units (ESUs) that affect the assembly and composition of associated arthropod communities and deserve high priority for conservation.     

Analysis of the genetic diversity and relationships among and within species of Hippophae (Elaeagnaceae) based on RAPD markers

RAPD markers were used to assess the genetic diversity and inter- and intra-specific relationships of the genus Hippophae L. and to study the correlation between genetic distances and geographic distances among populations of H. rhamnoides ssp. sinensis. The results analyzed by the percentage of polymorphic loci and Shannon information index indicated that a high level of genetic diversity existed both among and within species of the genus Hippophae. In the UPGMA dendrogram, the species or subspecies were clustered into two main groups but not strictly grouped according to sect. Hippophae and sect. Gyantsensis Lian. The multiple regression analysis and Mantel test both indicated a significant correlation between genetic distance and altitude distance among populations of H. rhamnoides ssp. sinensis, and the cluster analysis suggested that the genetic variation among populations of H. rhamnoides ssp. sinensis was linked to their monophyletic origin. Moreover, some degree of genetic differentiation was found among samples collected at different times.     

Three-trophic-level interactions in cattail hybrid zones

Plant-herbivore and herbivore-parasitoid wasp interactions were examined in three hybrid zones of the cattails Typha latifolia and T. angustifolia in south-eastern Michigan over a 2-year period. Patterns of resource use by two lepidopteran species of seed-eating herbivores were studied and herbivore densities sustained by the hybrid cattail T. x glauca and its parental species were determined. Densities of the commoner seed-eating lepidopteran, Lymnaecia phragmitella, were found to be highest in seed heads of both parental species and lowest in hybrid seed heads in zones of hybridization, thus supporting the hybrid resistance hypothesis of Fritz et al. (1994). Densities of the second herbivore, Dicymolomia julianalis, on the hybrid were lower than on the parental T. latifolia, but did not differ from the mean of the combined herbivore densities of the two parental species. D. julianalis in cattails appears to fit the additive hypothesis (Fritz et al. 1994). Parasitism of L. phragmitella by four species of parasitoid wasp, Itoplectis conquisitor (Ichneumonidae), Scambus hispae (Ichneumonidae), Macrocentrus delicatus (Braconidae), and Temelucha gracilipes (Ichneumonidae), was studied to determine if rates of parasitization by these natural enemics on the different cattails were similar to the patterns of plant exploitation exhibited by their hosts. Parasitism rates of L. phragmitella were significantly higher in larvae reared on hybrid cattails. This study reveals two different patterns of hybrid utilization by two very similar herbivores. Opposite patterns of plant utilization were found for the parasitoids compared with their host (L. phragmitella) in cattail hybrid zones.