Greater Reproductive Capacity Research Articles

Morphometric changes on dung beetle Dichotomius problematicus (Coleoptera: Scarabaeidae: Scarabaeinae) related to conversion of forest into grassland: A case of study in the Ecuadorian Amazonia.

The conversion of forest into grassland can induce differentiation in the functional morphology of resilient species. To assess this effect, we have chosen a dung beetle Dichotomius problematicus, as a model species. We established 20 sampling points distributed along a transect for a forest and grassland located in the Podocarpus National Park in Ecuador. Four pit-fall traps were baited with pig feces per sample point and were left open for 48 h. We sexed and measured 13 morphological traits of 269 individuals. Nonmetric multidimensional scaling was carried out to evaluate the influence of habitat and sexual dimorphism on the traits. We applied a principal component analysis to evaluate the morphological features that best explain the differences between land use and sexual dimorphism. We used generalized linear models to evaluate the explanatory variables: habitat and sexual dimorphism with respect to morphological traits. Five traits contributed over 70% body thickness, Pronotum width, Pronotum length, Head width and Elytra length, following the results of a principal component analysis. Both habitat and sex influence traits. In the forest, the individuals are larger than grassland likely due to available resources, but in grassland, the structures in charge of the burial process head, protibia are larger, displaying a strong pronotum and possible a greater reproductive capacity given by spherecity. These patterns of changes in the size of beetles and their structures could reflect the conservation state of an ecosystem.

Life history mediates the trade-offs among different components of demographic resilience.

Accelerating rates of biodiversity loss underscore the need to understand how species achieve resilience—the ability to resist and recover from a/biotic disturbances. Yet, the factors determining the resilience of species remain poorly understood, due to disagreements on its definition and the lack of large‐scale analyses. Here, we investigate how the life history of 910 natural populations of animals and plants predicts their intrinsic ability to be resilient. We show that demographic resilience can be achieved through different combinations of compensation, resistance and recovery after a disturbance. We demonstrate that these resilience components are highly correlated with life history traits related to the species’ pace of life and reproductive strategy. Species with longer generation times require longer recovery times post‐disturbance, whilst those with greater reproductive capacity have greater resistance and compensation. Our findings highlight the key role of life history traits to understand species resilience, improving our ability to predict how natural populations cope with disturbance regimes.

SITUACIÓN ACTUAL DE LA MANCHA FOLIAR DEL TRIGO CAUSADA POR Zymoseptoria tritici EN MÉXICO

La mancha foliar causada por Zymoseptoria tritici es una enfermedad que ocasiona pérdidas económicas importantes en las zonas trigueras del mundo. Cambios en las prácticas culturales como la labranza mínima, aunadas al uso irracional de fungicidas y a la gran plasticidad genética y capacidad reproductiva del hongo son responsables, en parte, del desarrollo de nuevas epifitias por esta enfermedad. Para su manejo se requiere de la implementación de diversas estrategias, como la rotación de cultivos y la remoción de residuos de cosecha; sin embargo, el uso de variedades resistentes es clave para incrementar la productividad del trigo (Triticum aestivum L.). México cuenta con algunas variedades comerciales de trigo harinero moderadamente resistentes. El objetivo de esta revisión fue conocer la situación actual de la mancha foliar, para identificar líneas futuras de investigación que coadyuven al manejo de la enfermedad en el país.

Garden balsam optimization algorithm

SummaryThis paper introduces a method called garden balsam optimization algorithm (GBO) for optimization problems. Garden balsam randomly ejects the seeds within a certain range by virtue of mechanical force originating from cracking of mature seed pods. The seeds scattered to suitable growth area will have greater reproductive capacity in the next generation, followed by iteration until the most suitable point for growth in a particular space is eventually found. Mimicking the transmission of garden balsam seeds, GBO generates the seeds by the mechanical transmission and second transmission operator to search the global optimum in the problem space. The convergence of GBO is tested in details through a set of benchmark multi‐dimensional functions. Secondly, the effect of tuning parameters on algorithm performance is studied. Finally, several typical problems were selected in the standard test set to test the performance of GBO. The experimental results show that the algorithm has advantages in optimization problems. In conclusion, the performance of GBO has a reasonable performance for all the test functions.

Migratory Helicoverpa armigera (Lepidoptera: Noctuidae) Exhibits Marked Seasonal Variation in Morphology and Fitness.

Many insects adopt seasonal, trans-latitudinal migration in response to altering climatic conditions, resource availability or reproductive requirements. Though the migration behavior of the cotton bollworm, Helicoverpa armigera (Hübner)(Lepidoptera: Noctuidae), has been well-studied, little is known about the extent of intra-specific variation between northward- and southward-migrating individuals. In this study, we captured H. armigera adults along the species' migration route during 2017-2018 to determine seasonal variability in their morphology, flight capability, and reproductive performance. Northward migrants have broader, longer bodies and are 1.33 times heavier than southward migrants, hinting at a comparatively higher allocation of resources in the abdomen. Accordingly, the former migrants engaged in longer flights, had greater reproductive capacity and a longer lifespan than southward ones. As northward migrants originate from favorable environmental conditions, their fitness is higher than that of the southward cohorts that develop on less favorable host plants and in perhaps more adverse climatic or ecological conditions. Northward H. armigera migrants thus possess an advantageous morphology that benefits habitat colonization and resource exploitation. Our work offers a novel perspective on the ecological and reproductive benefits of long-distance migration and can aid the development of population monitoring and forecasting methods for this globally important agricultural pest.

Identification of SNPs and copy number variations in mitochondrial genes related to the reproductive capacity of the cultured Asian yellow pond turtle (Mauremys mutica)

Mitochondria function as an energy transfer organelle for cell metabolism with the energy being used for processes such as reproduction. To investigate whether mutations and copy number variations in mitochondrial genes are related to the reproductive capacity of the Asian yellow pond turtle, Mauremys mutica, there was exploration of the distribution frequency of 129 Single Nucleotide Polymorphism loci of six mitochondrial genes, ND1, ND2, COX2, ND4, Cytb andD-loop, of turtles from a relatively greater and lesser fecundity group by direct sequencing. The validation results for five candidate SNP loci in 83 female turtles indicated that only three SNP loci (C119T, A320G and A417C) in ND1 were positively correlated with reproductive capacity in M. mutica (P < 0.05). In addition, by constructing linear regression equations of the copy numbers of ND1, ND4, Cytb, D-loop, COX3, and ATP6 (log10 transformed) genes and the mean offspring number of different female turtles during a 4-year period, the copy numbers of ND4 and ATP6 (log10 transformed) genes were positively correlated (P < 0.05) with the fecundity of female turtles. Results from the present study may provide useful genetic markers for breeding M. mutica with greater reproductive capacity.

A novel numerical optimization algorithm inspired from garden balsam

This paper introduces a new evolutionary computing method inspired by the seed transmission process of garden balsam. Garden balsam, a beautiful and attractive flower, randomly ejects the seeds within a certain range by virtue of mechanical force originating from cracking of mature seed pods, which is different from natural expansion of most species of plants. The seeds scattered to suitable growth area will have greater reproductive capacity in the next generation, followed by iteration until the most suitable point for growth in a particular space is eventually found. This phenomenon can more intuitively show the process of searching the problem solution space in the optimization problem. The garden balsam optimization algorithm proposed in this paper incorporates two different types of search processes and has a mechanism to maintain population diversity. Through the optimization experiment on 24 constrained optimization problems, the results obtained by using this algorithm are compared with those of some known meta-heuristic search algorithms. The statistical analysis of the experimental results has been implemented by Friedman rank test and Holm–Sidak test. The comparison results verify the effectiveness of the algorithm.

Could enemy release explain invasion success of Sagittaria platyphylla in Australia and South Africa?

Sagittaria platyphylla (delta arrowhead) is an emergent aquatic macrophyte native to southeastern United States of America that has been introduced into Australia and South Africa as an ornamental pond and aquarium plant. Compared to plants in the native range, S. platyphylla in the introduced range have greater reproductive capacity and form extensive infestations that dominate shallow waterbodies. One explanation for the invasive success of S. platyphylla in introduced countries is that plants are devoid of biotic pressures that would regulate population abundance in their native range (the enemy release hypothesis). We previously reported on field surveys that documented the number of pathogens and insect herbivores associated with S. platyphylla in native and introduced ranges. Here, we quantify the damage caused by these natural enemies to S. platyphylla in the two ranges. As predicted, damage to plants caused by pathogens and insect herbivores was much greater in the native than the introduced range at both the plant and population level. In introduced regions herbivory was low (less than 10%) in every plant part, while in North America insect damage to fruiting heads was 46% (of fruiting heads attacked), damage to leaves was between 33 to 57%, and internal herbivore damage to petioles and the inflorescence scapes was 56% and 43% respectively. Pathogen damage to leaves was between 39 to 57% of leaves per plant affected, compared to 9% in Australia and 8% in South Africa. This lack of biotic resistance from herbivores and disease may have facilitated S. platyphylla invasion in Australia and South Africa.

Coupled, multi-strain epidemic models of mutating pathogens

We introduce and analyze coupled, multi-strain epidemic models designed to simulate the emergence and dissemination of mutant (e.g. drug-resistant) pathogen strains. In particular, we investigate the mathematical and biological properties of a general class of multi-strain epidemic models in which the infectious compartments of each strain are coupled together in a general manner. We derive explicit expressions for the basic reproduction number of each strain and highlight their importance in regulating the system dynamics (e.g. the potential for an epidemic outbreak) and the existence of nonnegative endemic solutions. Importantly, we find that the basic reproduction number of each strain is independent of the mutation rates between the strains — even under quite general assumptions for the form of the infectious compartment coupling. Moreover, we verify that the coupling term promotes strain coexistence (as an extension of the competitive exclusion principle) and demonstrate that the strain with the greatest reproductive capacity is not necessarily the most prevalent. Finally, we briefly discuss the implications of our results for public health policy and planning.

Motivação e inclusão para o sucesso numa unidade curricular basilar

Students begin higher education with great reproductive capacity with evidence of seriousflaws in analysis and reflection, as well as difficulty in adapting knowledge and competencesto new situations. This easily creates frustrating events leading to dropping out and failure. This manuscript addresses teaching methods in a Mathematics course in higher education degrees inEconomics and/or in Management, treating the problems of student motivation and student inclusionin the educational process. This pedagogical project, implemented with blended learning, isbased on the availability of a high number of resources of teaching-learning, pushing the studentstowards the creation of their own path according to their preferences. The way the information isperceived varies according to the means of support of the pedagogical resource and with each student’sprofile. The availability of various resources invites and promotes its adequate and selectiveusage. The dynamics created in the construction of the learning procedure values autonomy andrewards success. During three years, the students have been highly receptive and there is a clearincrease in success.

Relationship of molting, gonadosomatic index, and methyl farnesoate in male snow crab (Chionoecetes opilio) from the eastern Bering Sea

Snow crabs, Chionoecetes opilio (Fabricius, 1788), have a complex mating system, and understanding their reproductive physiology is paramount to crab fishery management. Mating and molting are inextricably linked, so the energetically demanding molting process may compromise male mating potential for some period prior to and after the molt. Recently molted, new-shell males are targeted preferentially during the commercially valuable eastern Bering Sea (EBS) fishery. Old-shell males, or males that have not molted within the last year, are not as visually appealing, but may have greater reproductive capacity and can contribute disproportionately to the genetic stock. We measured a crustacean reproductive hormone, methyl farnesoate (MF), and reproductive fitness, using gonadosomatic index (GSI) as a proxy, in EBS male snow crab to determine differences in reproductive potential between adolescents and adults. We compared these reproductive indices in new- and old-shell males as a broad estimate of the effect of molting biology on reproduction. Circulating MF was significantly higher in new-shell adolescent males compared to old-shell adolescent males and old-shell adult males, suggesting a juvenilizing rather than gonadotropic role for MF in C. opilio. New-shell males had a significantly lower GSI compared to old-shell males for both adolescent and adult males. The lower GSI measured in new-shell adults compared to the significantly higher GSI levels measured in old-shell adults suggests that new-shell males harvested during the commercial fishery lack the reproductive capacity of the old-shelled adults and therefore may not be contributing equally to the population.

Reproductive strategies of Datura ferox, an abundant invasive weed in agro-ecosystems from central Argentina

Crop weeds develop in highly modified environments and are one of the most severe threats to agriculture worldwide, because their invasive nature determines competition for resources with crops and at the same time they can be hosts for pests and diseases. The information provided in this work is relevant both in scientific and technical terms, contributing to the design of effective strategies for the control of Datura ferox (Solanaceae). The aims of this work were to: (a) evaluate the reproductive strategies of D. ferox relative to fruit and seed production, (b) analyze the relationship between reproductive traits and persistence of these populations in agro-ecosystems of central Argentina, and (c) discuss different strategies to control crop weeds based on the knowledge of their reproductive ecology. D. ferox presented a great reproductive capacity that would not be constrained by limited pollen availability or pollinators in the populations studied. Flowers were pollinated by sphingids, coleopterans and Apis mellifera. The populations were self-compatible and autogamous; however, they exhibited higher fruiting percentages by natural pollination. Fruits produced by autogamy and geitonogamy had larger size and lower seed number and mass than those derived from natural pollination and xenogamy. D. ferox has combinations of traits (i.e., two flowering peaks, interactions with different pollinators, seed production after autogamy or xenogamy) that provide ecological advantages for establishment and survival processes in agro-ecosystems, hindering the species’ control. Control strategies might be improved if D. ferox abundance would be reduced before flowering to avoid fruit and seed production. This management strategy should be consistent over several years because the soil seed bank would allow population recovery in subsequent years.

Genetic Control of Mosquitoes: population suppression strategies

Over the last two decades, morbidity and mortality from malaria and dengue fever among other pathogens are an increasing Public Health problem. The increase in the geographic distribution of vectors is accompanied by the emergence of viruses and diseases in new areas. There are insufficient specific therapeutic drugs available and there are no reliable vaccines for malaria or dengue, although some progress has been achieved, there is still a long way between its development and actual field use. Most mosquito control measures have failed to achieve their goals, mostly because of the mosquito's great reproductive capacity and genomic flexibility. Chemical control is increasingly restricted due to potential human toxicity, mortality in no target organisms, insecticide resistance, and other environmental impacts. Other strategies for mosquito control are desperately needed. The Sterile Insect Technique (SIT) is a species-specific and environmentally benign method for insect population suppression, it is based on mass rearing, radiation mediated sterilization, and release of a large number of male insects. Releasing of Insects carrying a dominant lethal gene (RIDL) offers a solution to many of the drawbacks of traditional SIT that have limited its application in mosquitoes while maintaining its environmentally friendly and species-specific utility. The self-limiting nature of sterile mosquitoes tends to make the issues related to field use of these somewhat less challenging than for self-spreading systems characteristic of population replacement strategies. They also are closer to field use, so might be appropriate to consider first. The prospect of genetic control methods against mosquito vectored human diseases is rapidly becoming a reality, many decisions will need to be made on a national, regional and international level regarding the biosafety, social, cultural and ethical aspects of the use and deployment of these vector control methods.

The opportunistic feeding and reproduction strategies of the annual fish Cynopoecilus melanotaenia (Cyprinodontiformes: Rivulidae) inhabiting ephemeral habitats on southern Brazil

Most Rivulidae fishes are popularly known as annual fishes which live in ephemeral environments such as pools, that obligatorily dry out seasonally causing the death of adult individuals. They have unique biological characteristics such as small body size, early sexual maturation, continuous reproduction, an elaborated courtship behavior, and a great reproductive capacity among fishes. The rivulids are widely distributed in North, Central and South America. In this study, the diet and reproductive biology of Cynopoecilus melanotaenia was analyzed. A total of 263 specimens were collected and the analysis of 233 gastrointestinal contents revealed an invertivorous diet composed mainly of small crustaceans (Cladocera, Amphipoda, and Ostracoda) and immature insects (Chaoboridae, Culicidae, Syrphidae, but mainly Chironomidae larvae). Lepidophagy on male's diet was also registered. Fecundity was estimated by analyzing 59 pairs of mature ovaries and ranged from 2 to 157 oocytes (mean, 19 ± 26[SD]). The species has fractional spawning, a strategy to increase the chance of survival to prolonged depletions. This study is the first to investigate the reproductive biology of C. melanotaenia. The results confirmed the opportunistic character of the rivulid C. melanotaenia and provided unreported reproductive information that may aid conservation of the species.

Harmonia axyridis: an environmental risk assessment for Northwest Europe

In this paper, we summarize the international situation with respect to environmental risk assessment for biological control agents. Next, we apply a recently designed, comprehensive risk evaluation method consisting of a stepwise procedure to evaluate the environmental risks of Harmonia axyridis in Northwest Europe. This resulted in the very clear conclusion that H. axyridis is a potentially risky species for Northwest Europe, because it is able to establish, it has a very wide host range including species from other insect orders and even beyond the class of Insecta, it may feed on plant materials, it can cover large distances (>50 km per year), it does move into non-target areas, it may attack many non-target species including beneficial insects and insects of conservation concern, its activities have resulted in the reduction of populations of native predators in North America, it is known as a nuisance in North America and recently also in Northwest Europe, and it may develop as a pest of fruit in North America. Considering the H. axyridis case, current knowledge would lead to the conclusion that, although the predator is capable to effectively control several pest species, its risks are manifold and it should, thus, not have been released in Northwest Europe. At the time of the first releases in Nortwest Europe in 1995, the available scientific literature made clear that H. axyridis is a large sized polyphagous predator and has a great reproductive capacity in comparison with other ladybird beetles, and that there was a need to study non-target effects because of its polyphagous behaviour. In retrospect, this information should have been sufficient to reject import and release of this species, but it was apparently ignored by those who considered release of this predator in Northwest Europe. The case of Harmonia releases in Northwest Europe underlines that there is an urgent need for harmonized, world-wide regulation of biological control agents, including an information system on risky natural enemy species.

Canada goldenrod (Solidago Canadensis): An invasive alien weed rapidly spreading in China

Invasive species pose a serious threat to native ecosystems and their biodiversity, and cause considerable economic loss to the regions they invade. In the case of Canada goldenrod (Solidago canadensis L.) (Compositae), a long-lived perennial plant native to North America, it was initially introduced as an ornamental plant to Shanghai in 1935, it then escaped into the wild and it is now spreading rapidly in China, especially in eastern China. We here describe briefly this species in relation to invasion biology. S. canadensis is actually a Canada-goldenrod complex that consists of at least six subspecies and varieties. S. canadensis has great reproductive capacity (through both seed production and clonal growth) and high genetic variation, both of which contribute to its great invasiveness. S. canadensis may outcompete or allelopathically exclude native plant species, resulting in monospecific stands with concomitant loss of plant and insect diversity, and ultimately alteration in ecosystem functioning. Lack of natural enemies in the invaded ecosystems makes this species highly invasive. Abiotic factors such as niche opportunities created by habitat disturbance and human activities, and nitrogen deposition, can promote S. canadensis’ establishment and spread through seed dispersal and vegetative structures. In addition, the species’ capacity for early season emergence and growth, rapid clonal growth, wide physiological tolerance, and high architectural plasticity make the species highly aggressive under a wide range of ecological conditions. Although commonly used control methods of weeds may also be suitable for S. canadensis, minimising its seed production seems to be critical to its effective control, which requires that all the control measures be taken during its vegetative growth.

Social dominance, task performance and nutrition: implications for reproduction in eusocial wasps.

Dominance status is associated with individual differences in reproductive capacity in many animal societies, but the mechanisms that link social dominance to reproductive physiology are poorly understood. We propose a model for social dynamics that incorporates the nutritional costs and benefits of behavior: dominant individuals avoid energy-expensive behavior and build their nutritional reserves, thereby increasing their potential for reproduction. Greater reproductive capacity, once achieved, favors increased social dominance. To test the model, we measured relationships of females' nutrient storage and reproductive capacities with dominance status and task performance in the eusocial wasp Mischocyttarus mastigophorus. Ovary development was positively related with high levels of nutrient storage and with high rates of dominance behavior, but was not correlated with task performance. In contrast, high levels of nutrient storage were positively related with the performance of nutrient garnering and conserving tasks, but not with dominance behavior. These data support a model which places the nutritional costs of task performance as an intermediate causal link that connects dominance status with the accumulation of nutrient stores. Nutrient flow may be a general causal mechanism linking dominance status to reproductive capacity in animal societies.

In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers

1. In situ exclosure experiments in the Mississippi and Ohio Rivers determined the importance of fish predation in regulating zebra mussels (Dreissena polymorpha), an increasingly important constituent of the benthic invertebrate assemblages in both rivers.2. We evaluated the effects of predatory fish on the density, biomass and size distribution of zebra mussels in a floodplain reach of the upper Mississippi River and in a naturally constrained reach of the Ohio River. Fifty, six‐sided, predator‐exclusion cages and fifty ‘partial’ cages (mesh at the upstream end only) were deployed, with half the cages containing willow snags and half clay tiles suspended 12–16 cm above the bottom. A single snag or tile sample unit was removed from each cage at approximately monthly intervals from July to October 1994. Types and relative abundances of molluscivorous fish were evaluated by electrofishing near the cages in both rivers. Actual and potential recruitment of young zebra mussels on to the substrata were measured using benthic samples in both rivers and estimated (Ohio River only) from counts of planktonic veligers.3. Zebra mussels were consumed by at least three fish species in the upper Mississippi River (mostly carp, Cyprinus carpio, and redhorse suckers, Moxostoma sp.) and five species in the Ohio River (primarily smallmouth buffalo, Ictiobus bubalus, and channel catfish, Ictalurus punctatus), but potential recruitment seemed adequate to replace consumed mussels, at least in the Ohio River. The number of juvenile benthic mussels showed no apparent link with the density of veligers soon after initiation of reproduction. Recruitment of juveniles on snags and tiles was not affected by cage type (thus eliminating a potentially confounding ‘cage effect’).4. Fish significantly influenced mussel populations, but the impact was often greatest among low density populations in the upper Mississippi. Density and biomass differed in both rivers for cage type (higher inside cages), substratum (greater on tiles), and date (increased over time). Presumed size‐selective predation was present in the Mississippi (greater on larger size classes) but was not evident in the Ohio. We hypothesize that fish in the Mississippi can more easily select larger prey from the low density populations; whereas size‐selective predation on tightly packed zebra mussels in the Ohio would be difficult.5. Although fish can reduce numbers of Dreissena polymorpha in the two rivers, current levels of fish predation seem insufficient to regulate zebra mussel densities because of its great reproductive capacity. The recent invasion of zebra mussels, however, could lead to larger fish populations while promoting greater carbon retention and overall ecosystem secondary production.

DISPLACEMENT OF BATHYPLECTES CURCULIONIS (THOMS.) (HYMENOPTERA: ICHNEUMONIDAE) BY B. ANURUS (THOMS.) IN EASTERN ONTARIO POPULATIONS OF THE ALFALFA WEEVIL, HYPERA POSTICA (GYLL.) (COLEOPTERA: CURCULIONIDAE)

AbstractBathyplectes anurus (Thoms.) has displaced B. curculionis (Thorns.) as the main larval parasitoid in populations of the alfalfa weevil, Hypera postica (Gyll.), in eastern Ontario. Following its belated spread to the Bay of Quinte dairy belt, it used a combination of r and K strategies to assert its superiority: a greater reproductive capacity, more rapid search and handling, and more aggressive behaviour. Also, it is not subject to encapsulation by the host and reduces direct competition with the entomopafhogenic fungus Zoophthora phytonomi (Arthur) by laying its eggs in older hosts that have a greater probability of escaping death from disease. Taken together, these factors have enabled it to perform better than B. curculionis and to displace it in the host–parasitoid community. Moreover, it may have the potential to stabilize weevil populations during years when the fungus is enzootic.

Reproductive Capacity of Dragraked and Non-Dragraked Irish Moss (Chondrus crispus Stackhouse) Beds in the Southern Gulf of St. Lawrence

A non-dragraked bed of Chondrus crispus Stackhouse (Rustico) showed a greater year-round carposporangial reproductive capacity than a dragraked bed (Miminegash). The former had a lower frond density but larger fronds which were the major sources of reproduction. Although carposporangial sori had a greater area and were more frequently full in Miminegash, reproductive capacity was higher in Rustico due to higher sorus densities per frond and sample unit. All the studied parameters did not show significant (P = 0.05) differences between the study sites for tetrasporophytes, resulting in similar overall tetrasporangial reproductive capacities. Reproductive capacity peaked in Miminegash prior to the harvesting season. Class 4 and 5 fronds (largest fronds) have the greatest reproductive capacity. To protect this source of spores and thus improve bed reproductive potential, a 1-mo delay in the present season opening date is suggested. The much higher tetrasporophyte reproductive capacity over that of carposporophytes is at least a partial explanation for the greater gametophytic abundance in some populations.