Optimum reproduction and dispersal strategies of a clonal plant in a metapopulation: a simulation study with Hieracium pilosella

Clonal spread is favoured in many plants at the expense of seed production in order to expand rapidly into open habitats or to occupy space by forming dense patches. However, for the dynamics of a population in a patchy landscape seed dispersal remains important even for clonal plants. We used a spatially explicit individual-based metapopulation model to examine the consequences of two trade-offs in Hieracium pilosella L: first, between vegetative and sexual reproduction, and second, between short and far-distance dispersal of seeds. Our main question was, what are the environmental conditions that cause a mixed strategy of vegetative and sexual reproduction to be optimal. The model was parameterised with field data on local population dynamics of H. pilosella. Patch dynamics were given firstly by disturbance events that opened patches in a matrix of a clonal grass that were colonisable for H. pilosella, and secondly by the gradual disappearance of H. pilosella patches due to the expanding grass. Simulations revealed opposing selection pressures on traits determined by the two trade-offs. Vegetative reproduction is favoured by local dynamics, i.e. the need for maintenance and expansion of established populations, whereas seed production is favoured by the necessity to colonise empty habitats. Similar pressures act on the proportion of seeds dispersed over short and far distances. Optimum reproductive and dispersal strategies depended on habitat quality (determined by seedling establishment probability), the fraction of dispersed seeds, and the fraction of seeds lost on unsuitable ground. Under habitat conditions supporting moderate to low seedling establishment, between 20% and 40% of reproductive effort in H. pilosella should be devoted to sexual reproduction with at least 10% of the seeds dispersed over distances suitable to attain empty patches. We conclude that in a spatially heterogeneous landscape sexual seed production in a clonal plant is advantageous even at the expense of local vegetative growth.     

Transport of juvenile clams: effects of species and sediment grain size

Erosion and transport of juvenile benthic invertebrates, including bivalves, have the potential to alter patterns of distribution and abundance during the early post-settlement period. However, the factors influencing rates of postlarval dispersal are not well understood. Both hydrodynamics and behaviour (e.g. burrowing) are likely to play a role in determining patterns of transport of juvenile bivalves. To determine the relationship between sediment transport and bivalve dispersal, experiments were conducted in a racetrack flume to examine the effect of grain size, flow, and clam size on rates of erosion of two species of juvenile clams (Mya arenaria and Mercenaria mercenaria). Results of the experiments were compared to predictions of erosion thresholds based on the physical characteristics of the sediment and clams. Erosion of Mercenaria was greater than Mya, the opposite of predictions based on Mercenaria's greater density, indicating the importance of burrowing behaviour. In most cases, erosion also was greater in the finer sand, in contrast to the predicted similarity of erosion thresholds of the two sediments. However, clam erosion did increase with increasing shear velocity and decrease with clam size, as expected. The results of this study indicate that both hydrodynamics and behaviour play roles in the transport of these two species of juvenile bivalves and that their vulnerability to passive erosion cannot be predicted solely from knowledge of sediment transport.     

Extended parental care and delayed dispersal: northern, tropical, and southern passerines compared

Using modern comparative methods, we found that both time toindependence and time with parents were significantly longerin southern hemisphere and tropical birds than in northern hemisphereones. These differences held even after removing Australianpasserines or cooperatively breeding species, and they do notdepend on habitat, diet, or migration pattern. In southern hemisphereand tropical regions, both cooperative breeding and non-cooperativeparents continue to feed their young for a similar length oftime, but cooperative breeders allow them to stay longer intheir natal territory after they become nutritionally independent.Nevertheless, the young of non-cooperative species stay longerwith their parents than do the young of non-cooperative speciesin the temperate northern hemisphere. The fact that extendedperiods of post-fledging parental care are widespread amongpasserines provides further empirical support for the view thatlife histories of southern and tropical birds are ‘slow,’with small clutches, extended parental care, and long lifespan;parents take care of fewer young for longer. These results supportrecent theoretical models that predict that high adult survivaland low turnover of territory owners generally favor natal philopatry.We suggest that the reasons why some species (with or withoutcooperative breeding) exhibit natal philopatry and others donot lie in the balance between productivity and survival ofadults and of retained or dispersing offspring.     

Kinship in colonial tuco-tucos: evidence from group composition and population structure

Kinship plays a significant role in shaping the social and geneticstructures of many vertebrate populations. Evidence of kinship,however, may be substantially influenced by the spatial andtemporal scales over which co-ancestry is monitored. For example,while data on social group composition may yield little indicationof relatedness among reproductive partners, data on the demographicstructure of a population may reveal considerable shared ancestryamong mates. We explored relationships among social group composition,individual movements, and population-level patterns of kinshipusing data from a 7-year field study of the colonial tuco-tuco(Ctenomys sociabilis), a group-living subterranean rodent thatis endemic to southwestern Argentina. Our analyses indicatethat social groups are composed of 1–4 generations ofclosely related females and a single, immigrant male, suggestingthat reproductive partners are not related to one another. Monitoringindividual movements, however, revealed that (1) most male dispersaloccurs within the local population and (2) most new social groupsare founded by females born in the study population, indicatingthat individuals reared in different burrow systems may shareconsiderable co-ancestry. Simulation analyses revealed thatup to 67% of reproductive partnerships consist of animals thatshare co-ancestry within the last 5–7 generations. Thus,while analyses of social group composition provide little evidenceof kinship among reproductive partners, population-level analysesof dispersal and group formation suggest that co-ancestry amongmates is common. These findings have important implicationsfor interpreting social interactions and genetic structure inthis species.     

Molecular-genetic systems of development: Functional dynamics and molecular evolution

This work for the first time compares results obtained with studies of parametric robustness of the Hh- and Dpp/BMP signal cascades responsible for morphogenesis and molecular evolution of the Hh- and Dpp/BMP cascade genes. There is a link between adaptive evolution of genes and those changes in kinetic parameters of the signal cascade models, which are critical for normal functioning of these cascades. Special attention is paid to events of the molecular evolution of the Hh- and Dpp/BMP cascade genes that matched with the emergence of the major taxonomic types and classes of Bilateria.     

Vertical stratification of figs and fig-eaters in a Bornean lowland rain forest: how is the canopy different?

Fig trees (Ficus spp; Moraceae) are a common constituent of many tropical forests, where they produce figs that are eaten by a wide range of bird and mammal species. In our Bornean field site six Ficus seed dispersal guilds can be recognised, differentially attracting subsets of the frugivore community. Guild membership appears to be determined by figs' size, colour, crop size and height above ground, and frugivores' size, sensory and locomotory physiology and foraging height. Vertical stratification therefore appears to be an important determinant of fig and frugivore partitioning. The guild structure observed is discussed with respect to implications for seed dispersal and the differences between the canopy and understorey. Regarding figs eaten primarily by birds, larger fruit and crops can be found in the canopy where they are exposed to larger assemblages of potential frugivores than those presented in the understorey.     

Exotic Lepidopteran Leafminers in North American Apple Orchards: Rise to Prominence, Management, and Future Threats

The European tentiform leafminers, Phyllonorycter blancardella (Fabricius) and P. mespilella (Hübner) (Lepidoptera: Gracillariidae), have infested apple, Malus domestica Borkhausen, in North America for at least 60–70 years. Unreliable taxonomic methods and lack of voucher specimens, however, have contributed to poor understanding of precisely when, where, and how these leafminers were introduced. Tentiform leafminers developed into significant foliar pests at about the time when adult resistance to broad-spectrum insecticides was detected in the 1970s and 1980s. At present, growers manage leafminers with insecticides and, to a lesser extent, with biological control. Most management programs for orchard pests rely on insecticides that are highly toxic to parasitic wasps, which hampers biological control. New techniques promoted in the context of integrated pest management (IPM) may improve biological control by reducing insecticidal use, but their adoption will depend on cost, labor, need to control other pests, and demands of the marketplace. Management programs must be flexible enough to accommodate changes in the species composition of leafminers and their parasitoids. Procedures to exclude pests may slow the rate of new introductions of leafminers and other pests, but they will not entirely protect the North American apple industry. Once new apple pests reach North America, they face few obstacles to further dispersal. The abundance of potential host plants, the lack of rigorous inspections, and new retail practices may facilitate the dispersal of exotic pests.