Population variation and ecological correlates of tychoparthenogenesis in the mayfly, Stenonema femoratum

Species in which both sex and parthenogenesis co‐occur are extremely valuable for investigating ecological conditions favouring sex. Tychoparthenogenesis is a breeding system characterized by hatching of a small proportion of unfertilized eggs (typically < 10%) from females of sexually reproducing species. With tychoparthenogenesis, both sexual and parthenogenetic reproduction co‐occur within the same population. To identify ecological conditions that may favour this breeding system, I quantified population variation in females’ capacity for tychoparthenogenesis and investigated biotic and abiotic correlates of tychoparthenogenesis. I estimated tychoparthenognetic capacity (proportion of unfertilized eggs hatching) for females from 12 Missouri populations of the mayfly, Stenonema femoratum (Ephemeroptera: Heptageniidae), across three different habitat types – temporary streams, permanent streams and lakes. Tychoparthenogenetic capacity, measured as the population mean hatch success of unfertilized eggs, ranged from 3.8 to 10.7%. Tychoparthenogenetic capacity varied among habitats in 1996, but not in 1997. In 1996, temporary streams showed hatch success of unfertilized eggs twice that of permanent streams and lakes. Tychoparthenogenetic capacity also varied among sampling dates within years. Temporary streams also showed extremely low nymph densities compared to the other two habitats. However, habitats did not differ in adult density. Furthermore, in all populations nymphs showed significantly female‐biased sex ratios. In contrast, adult sex ratios were equal or slightly male biased. Tychoparthenogenetic capacity was negatively correlated with nymph density in 1996, but not in 1997, suggesting possible reproductive assurance in some years. Adult densities also suggested that there may be certain times of year when tychoparthenogenesis may provide benefits of reproductive assurance. Although habitats differed significantly in their abiotic characteristics, tychoparthenogenetic capacity was correlated significantly with water temperature only. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75 , 101–123.     

Plant mimicry: evolutionary constraints

Because plants are sessile and their flowers and fruits are aggregated, plant mimics are less likely to be mistaken for their models than animal mimics which are mobile and dispersed among their models. Therefore, operator species are more likely to be deceived by animal mimics than plant mimics. In addition, the autonomy of plant appendages implies that warning mimicry provides less advantage to plants than to animals because plants suffer less from sampling by naive operators. Therefore, the advantage of warning mimicry is much greater for animals than plants. These reasons may explain why plant mimicry is less common than animal mimicry, based on attraction of rather than avoidance by operator species, and limited to the class of aggressive mimicry.     

The fate of Mus domesticus demes after destruction of their habitats

To test our hypothesis that gene flow has the potential to prevent genetic isolation of crib populations separated by several kilometres, we caught and marked 137 house mice leaving six cribs being emptied of corn. In an attempt to recapture the mice, we set traps just after crib emptying and again, where feasible, 1–2 months later, in areas surrounding cribs (trap-nights/trap-area in hectares:cultivated fields, 3834/29.4; non-cultivated areas, 2238/4). Additional trapping was carried out near nine empty cribs and in eight cultivated fields (3304 trap-nights, 17.7 ha trap-area), each more than 120 m from cribs. After the six cribs were emptied, we recaptured 11% of the crib mice (distance from the crib:mean 81 m, range 0–570 m). In refuge habitats, away from cribs, a breeding population existed and three crib females bred there after emptying of cribs. In demonstrating long dispersal distances and breeding populations away from cribs, our data support the hypothesis that gene flow is potentially large enough to prevent genetic isolation of crib populations separated by expanses of cultivated and uncultivated terrain. The influence of decreased recruitment on gene migration is unclear. Potential predators on nestlings, such as Norway rats, deermice, shrews and voles, escaped from and were trapped outside cribs.     

AIRBORNE ALGAE: THEIR PRESENT STATUS AND RELEVANCE1

Ongoing climatic changes coupled with various natural processes and the outcomes of human activities are not only loading the atmosphere with diverse kinds of biological particles but also changing their prevalence and spatial distribution. Despite having considerable ecological and economic significance, including their possible impact on human health, airborne algae are the least‐studied organisms in both aerobiological and phycological studies. The present review has been written to bring together all available information, including a brief survey of the literature, the ecology of airborne algae, mechanisms involved in their aerosolization, the role of environmental factors in shaping the structure and composition of aero‐algal flora, and other significant information associated with airborne algae. This review provides information on methodological approaches and related problems, along with suggestions for areas of future research on airborne algae.     

POPULATION GENETIC STRUCTURE OF COASTAL BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) IN THE NORTHERN BAHAMAS

Population substructure has important implications for a species' ecology and evolution. As such, knowledge of this structuring is critical for the conservation and management of natural populations. Among marine mammals, many examples exist of species that enjoy a broad geographical distribution, yet are characterized by fine‐scale population subdivisions. Coastal bottlenose dolphins have been studied extensively in a few regions globally, and these studies have highlighted a great diversity in both social strategies and demographic isolation. Here we use molecular genetic markers to examine the degree of population subdivision among three study sites separated by less than 250 km on Little Bahama Bank in the northern Bahamas. Mitochondrial DNA (mtDNA) sequence variation and microsatellite genotypes were used to assess partitioning of genetic variance among 56 individually recognized coastal ecotype bottlenose dolphins. Although resolved levels of genetic differentiation suggest gene flow among the three study sites, both nuclear and mitochondrial data indicate a significant degree of subdivision within the Little Bahama Bank population, and sex‐based analyses suggest that patterns of dispersal may not be strictly biased toward males. These results corroborate the site fidelity documented through long‐term photo‐identification studies in the NE Bahamas, and highlight the need to consider independent subpopulation units for the conservation and management of coastal bottlenose dolphins in the Bahamas.     

REPRODUCTIVE LONGEVITY OF DRIFTING KELP MACROCYSTIS PYRIFERA (PHAEOPHYCEAE) IN MONTEREY BAY,USA1

Drifting Macrocystis pyrifera (L.) C. Agardh sporophytes have long been viewed as the primary long‐distance dispersal vector; yet, few data exist that support the ability of reproductive viable sporophytes to actually travel the presumed hundreds to thousands of kilometers. This study addressed the reproductive longevity of experimental and naturally occurring M. pyrifera drifters. Temporal variability in sporophyte size and reproduction was estimated for experimental drifting sporophytes that were tethered to surface buoys and compared with attached plants (controls). Reproductive viability was also studied for beach‐cast drifters (BCD), and naturally drifting sporophytes observed during field surveys in Monterey Bay. Detached drifting sporophytes were tracked with radio transmitters to follow drifter trajectories and to measure drifting speed. Experimental drifters (ED) experienced a 74% reduction in frond length after 35 days, a 76% reduction in average frond number after 70 days, and a reduction in average sorus area by 83% after 28 days. Although zoospore production was reduced following detachment, sporophytes remained fertile with high zoospore germination success as long as sori were present (125 days). Zoospore production and germination success for natural and BCD was similar to ED. The average displacement of radio‐tagged drifters was 7.12 km·day^?1, suggesting that a sporophyte adrift for 125 days disperses viable propagules (zoospores) over 890 km (±363). Dispersal of propagules is important for population restoration, distribution, and genetic diversity. Such dispersal distances are long enough to connect potentially all Northern Hemisphere Macrocystis populations across a generational timescale and may facilitate inter‐hemispheric gene flow.     

Seed Rain Produced by Bats and Birds in Forest Islands in a Neotropical Savanna1

The high degree of isolation of forest “islands” relative to “continental” forested areas creates a naturally fragmented landscape in the savanna ecosystem. Because fragmentation can affect the intensity and quality of biological interactions (e.g., seed dispersal) we examined the abundance and species richness of seed rain produced by birds and bats in three different parts of forest islands (center, edge, and exterior) located at the Estación Biológica del Beni, Bolivia. Despite the fact that we found higher species density of seeds in the seed rain at the center of forest islands, when comparing species richness corrected for observed differences in density, species richness was higher at the edge of islands. The three parts of the islands did not differ in total number of seeds. Three genera (Byrsonima, Ficus, and Piper) contributed the most seeds to the seed rain. We found differences in the abundance of dispersed seeds probably because of the variation related with the disturbance line, where the savanna matrix interacts with the forest islands. Carollia perspicillata, Carollia brevicauda, and Sturnira lilium were the bats that contributed most to seed dispersal within forest islands, and Schistochlamys melanopis and Tyranneutes stolzmanni were the most important birds. The movement of seeds produced by bats and birds within forest islands of the savanna is crucial to assure the continuity of ecological process and dynamics of these forest islands.     

Restoration of Araucaria Forest: The Role of Perches, Pioneer Vegetation, and Soil Fertility

The Araucaria forest is Brazil's highly threatened subtropical forest ecosystem that has been disappearing in recent decades. Restoration programs involving this forest type are scarce, and there is a lack of scientific information on how ecological processes such as competition, facilitation, and seed dispersal influence natural forest restoration. This work aims to investigate how use of perches to attract seed dispersers and the influence of pioneer vegetation and soil fertilization could affect the colonization of woody species in a degraded area. An experiment was conducted in an abandoned field where the natural establishment of seeds and seedlings of woody species was monitored under factorial combinations of the following treatments: (1) pioneer vegetation (presence and absence); (2) soil fertility (addition of NPK and control); and (3) perches (presence and absence). Seed and seedling abundance, seed and seedling species richness, and seedling mortality were recorded monthly during 12 months. Seed abundance and species richness were significantly greater in places with perches than in control plots. These results were consistent over the year and more pronounced when the surrounding forest produced a higher amount of fruit. Species richness and abundance of seedlings were significantly greater in places with perches than in control plots, and in places with vegetation than without. Soil fertility did not influence seedling establishment. Facilitation and seed dispersal are important factors affecting the colonization of woody species in this subtropical area. Nutrient availability neither regulates the facilitation process nor influences species replacement during the early stages of Araucaria forest succession.     

Suitability of different fluorescent powders for mass-marking the Chrysomelid, Diabrotica virgifera virgifera LeConte

Abstract:  The Western Corn Rootworm, Diabrotica virgifera virgifera LeConte (Col., Chrysomelidae), is an invasive alien pest of maize, Zea mays , in Europe. The suitability of 14 fluorescent powders for mass-marking the adults was studied in laboratory and in field cages. The visual discrimination between remaining spots of each colour on the beetles was investigated under ultraviolet (UV) light, as well as their retention time and the influences of those colours on the beetle survival and flight take-off response. The two best recognizable orange colours (i.e. of Radiant Colour and of Fiesta Colours Swada) were proposed for field experiments in first priority, followed by an orange and a yellow (both Magruder Colour), another yellow (Fiesta) and a pink (Radiant), as all did not affect beetle survival and flight take-off response and were recognizable under UV light for at least 10 days in the field. In contrast, the colours yellow and green (Radiant), red and blue (Magruder), yellow (Ciba Geigy) and pink (Fiesta) were unsuitable, because they either quickly disappeared from the beetles or adversely affected beetle survival or flight take-off response. For mass releases with differently marked beetles, only the use of a single orange colour together with a single yellow colour or the use of a pink colour together with a yellow colour can be used since few spots can clearly be discriminated from each other under UV light.