A molecular screening method for unisexual <Emphasis Type="Italic">Ambystoma</Emphasis> using mitochondrial DNA

The geographical range of unisexual Ambystoma overlaps with four bisexual species that also breed in spring ponds. Several of these species are of conservation concern, and both adults and larvae can be difficult to distinguish morphologically from unisexuals. Here we present a rapid molecular method for screening unisexuals, whose mtDNA is most similar to Ambystoma barbouri. A 258 bp segment of the cytochrome b gene was amplified in six Ambystoma species and exemplar unisexuals by PCR using taxon-specific primers. An internal 113 bp segment was amplified only in unisexuals and A. barbouri using Universal forward and Hybrid reverse primers. Multisequence alignment comparing the nucleotide sequence where Hybrid reverse primer anneals revealed nucleotide diversity in this region among Ambystoma species. This simple method for discriminating between unisexuals and bisexuals, excluding A. barbouri, can be applied prior to further research on these declining species.     

Dispersal and Predation Behavior in Larvae of <Emphasis Type="Italic">Chrysomya albiceps</Emphasis> and <Emphasis Type="Italic">Chrysomya megacephala</Emphasis> (Diptera: Calliphoridae)

Chrysomya albiceps and Chrysomya megacephala are exotic blowfly species known by producing myiasis in humans and other animals and by transmitting pathogens mechanically. C. albiceps stand out by being a facultative predator of other dipteran larvae. In this paper we investigated the influence of larval predation on the dispersal of larvae of C. albiceps and C. megacephala single and double species for three photophases. An experimental acrylic channel graduated and covered with wood shavings was used to observe the larval dispersal. The results showed that C. albiceps attacks C. megacephala larvae during dispersal and keeps an aggregated pattern close to the release point, in single and double species, independently of the different photophases. Chrysomya megacephala single species exhibited the same pattern, but in double species this was changed to a random distribution.     

Fatal attack on a Rylands' bald-faced saki monkey (<Emphasis Type="Italic">Pithecia rylandsi</Emphasis>) by a black-and-white hawk-eagle (<Emphasis Type="Italic">Spizaetus melanoleucus</Emphasis>)

Predation risk has played an important role in primate behavioral evolution, yet natural primate–predator interactions are rarely observed. We describe the consumption and probable predation of an adult bald-faced saki monkey (Pithecia rylandsi) by a black-and-white hawk-eagle (Spizaetus melanoleucus) at the Los Amigos Biological Station in lowland Amazonian Peru. To our knowledge, this is the first published case of a black-and-white hawk-eagle consuming any primate species. We contend that while most reported observations of successful and attempted predation by raptors involves the largest and most notorious species (i.e. the harpy eagle), smaller and lesser known species like S. melanoleucus should be considered more seriously as a predator of neotropical primates. We discuss the predation event in the context of understanding what other neotropical primates might be vulnerable to S. melanoleucus predation given its body size and hunting tactic.     

Multiple defence strategies of <Emphasis Type="Italic">Daphnia</Emphasis><Emphasis Type="Italic">galeata</Emphasis> against predation in a weakly stratified reservoir

In the presence of size-selective fish daphnids were shown to exhibit two alternative inducible defence strategies: They may either escape predation by active migration or adopt a life history strategy, e.g., reproduce earlier and at a smaller size. Depending on the type of habitat, migration may either be vertically (in deep stratified lakes) or horizontally (in shallow lakes with macrophytes) oriented. Concerning behavioural defence strategies, daphnids living in medium-deep, weakly stratified water bodies with a poorly developed littoral face a dilemma, since the littoral provides no shelter and the availability of a deep-water refuge is unpredictable. We studied the population dynamics, life history changes (size at maturity) and daytime vertical distribution of Daphnia galeata in a weakly stratified reservoir in relation to predation by juvenile fish during 6 years. While temperature gradients were usually small, oxygen concentrations suggest that a low-oxygen refuge for daphnids was available in every year to some extent. Our results indicate that, depending on predation intensity and stratification patterns, daphnids exhibit both, behavioural and life history defences. In years with a high biomass of young-of-the-year (YOY) perch Daphnia abundance declined rapidly at the end of the clear water stage while at the same time the vertical distribution at daytime shifted to deep strata providing a low-oxygen refuge and the size at maturity decreased. However, while the life history response in some years lasted throughout most of the summer period, a shift in daytime vertical distribution was exhibited for much shorter periods. Both traits were much less expressed in years with low YOY fish densities and no negative correlation between them could be verified. We suggest that under high predation pressure in this relatively shallow reservoir no strictly alternative (either behavioural or life history) strategies exist, but that daphnids make use of the full range of possible anti-predator defences available, at least during short periods when predation is most intense. Guest editor: Piet Spaak Cladocera: Proceedings of the 7th International Symposium on Cladocera     

Predation capacity and prey preference of <Emphasis Type="Italic">Chrysoperla carnea</Emphasis> on <Emphasis Type="Italic">Pieris brassicae</Emphasis>

The predation capacity and prey preference of larvae of Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae) on eggs or larvae of Pieris brassicae (Linnaeus) (Lepidoptera: Pieridae) in the absence and presence of cabbage aphids as an alternative prey were evaluated in laboratory experiments at 25°C. Both instars preyed upon butterfly eggs and larvae as well as on cabbage aphids with the third instar being the most voracious. The lacewings had a strong preference for caterpillars to butterfly eggs. In the presence of the aphids the predation on P. brassicae eggs or larvae was either completely abandoned or reduced by about 70%, respectively, by second instar lacewings and either reduced by about 80% or maintained, respectively, by third instar lacewings. Both instars thus had a clear preference for aphids compared to eggs of P. brassicae. However, second instar lacewings preferred aphids to caterpillars whereas the opposite was the case for third instar lacewings. The results indicate that 3rd instar C. carnea has a potential as biocontrol agent against P. brassicae.     

Nonlethal indirect effects of a native predatory mite,<Emphasis Type="Italic"> Amblyseius womersleyi</Emphasis> Schicha (Acari:Phytoseiidae), on the phytophagous mite<Emphasis Type="Italic"> Tetranychus kanzawai</Emphasis> Kishida (Acari: Tetranychidae)

We experimentally tested the indirect and direct effects of Amblyseius womersleyi on Tetranychus kanzawai. The presence of A. womersleyi indirectly reduced egg production of T. kanzawai by 25.9%, although this effect had less impact than direct egg predation. The mechanism of this indirect effect could be explained by behavioral changes in T. kanzawai females; in the presence of A. womersleyi, T. kanzawai females allocated more time to seeking refuge on webs at the expense of feeding on leaves.     

Variation in hydraulic architecture and gas-exchange in two desert sub-shrubs,<Emphasis Type="Italic"> Hymenoclea salsola</Emphasis> (T. &; G.) and<Emphasis Type="Italic"> Ambrosia dumosa</Emphasis> (Payne)

Adjustment of hydraulic architecture in response to environmental conditions was studied in two warm-desert sub-shrubs, Hymenoclea salsola and Ambrosia dumosa, both at the level of genetic adaptation along a climatic gradient and plastic response to immediate growth conditions. Individuals of both species originating from southern populations developed higher leaf-specific hydraulic conductance in the common greenhouse than individuals from northern populations. Hydraulic conductance was higher in plants grown at high temperature, but did not vary as a function of growth relative humidity. Hydraulic conductance was not correlated within species with individual variation in vessel diameter, cavitation vulnerability, or root:shoot ratio, but was strongly, negatively correlated with the fraction of total plant biomass allocated to leaves. For both species, stomatal conductance (g _s) at high leaf-to-air vapor pressure difference (ν) was tightly correlated with variability in hydraulic conductance, as was the sensitivity of stomatal closure to increasing ν. Experimentally increasing shoot water potential by soil pressurization, under conditions where high ν had already caused stomatal closure, led to substantial stomatal reopening in both species, but recovery was significantly higher in H. salsola. Hydraulic conductance was higher in H. salsola than A. dumosa. H.salsola also differed from A. dumosa by being a representative of a highly specialised group of desert shrubs which use the twigs as a major photosynthetic organ. The southern population of H. salsola produced far fewer leaves and relied much more heavily on twig photosynthesis than the northern population. At the whole-plant level, increased reliance on twig photosynthesis was associated with higher leaf-specific hydraulic conductance, but equivalent whole-plant photosynthesis on either a dry weight (μmol CO₂ g^–1) or nitrogen basis (μmol CO₂ g^–1)). This suggests that twig photosynthesis might be one way of increasing hydraulic conductance per unit photosynthetic canopy by increasing allocation to an organ which simultaneously performs photosynthetic, support, and transport functions. Received: 13 December 1999 / Accepted: 31 March 2000     

<Emphasis Type="Italic">Drosophila</Emphasis> pupation behavior in the wild

We investigated pupa distributions of D. simulans, D. buzzatii, D. melanogaster, D. immigrans and D. hydei on a number of natural breeding sites. Pupae of all five species showed aggregated distributions, which prompted us to examine these aggregations in a more detail for two species that commonly co-occur in breeding sites, D. simulans and D. buzzatii. We found that pupae of both species tend to be aggregated in conspecific clusters. Subsequent experiments revealed that both species are attracted to the odors of other larvae, though only D. buzzatii differentiated between conspecifics and heterospecifics (they preferred conspecific). Furthermore, third instar larvae of both species preferred more alkaline substrates. Altogether, our results demonstrate that Drosophila species form conspecific pupa aggregations in natural breeding sites, and that pupation site selection depends on interactions among conspecific and heterospecific larvae and on chemical characteristics of the breeding sites.     

Fecundity and feeding of <Emphasis Type="Italic">Galerucella calmariensis</Emphasis> and <Emphasis Type="Italic">G. pusilla</Emphasis> on <Emphasis Type="Italic">Lythrum salicaria</Emphasis>

Fecundity and feeding of two introduced sibling biological control species, Galerucella calmariensis and G. pusilla (Coleoptera: Chrysomelidae) on purple loosestrife, Lythrum salicaria L. (Lythraceae) were compared at constant temperatures of 12.5, 15, 20, 25, and 27.5 °C. Larval feeding was also carried out at 30 °C, but at this temperature, larvae developed only to the L2 stage and none pupated. Thus, data for this temperature were not used in the analysis. There were significant species × temperature interactions in fecundity. Of the two species, Galerucella pusilla laid more eggs. Although egg production of both species was lowest at 12.5 °C and increased to 20 °C, at higher temperatures, the two species reacted differently. From 25 to 27.5 °C, egg production decreased for G. pusilla, but G. calmariensis fecundity peaked at 27.5 °C. Significant temperature × species × life-stage interactions were also observed in feeding. For each species, the amount of feeding varied with temperature and stage of development. Galerucella pusilla adults consumed more foliage at 15, 20, and 27.5 °C. However, at 12.5 °C G. calmariensis adults fed more than G. pusilla. G. pusilla larvae consumed an average of 25% less foliage than G. calmariensis. The lower larval consumption of G. pusilla suggests that when food is limited, G. pusilla larvae may have a higher survival rate because of its ability to complete larval development with less food and produce more progeny due to its greater fecundity. When food is not limited neither species would have a competitive advantage and both species could coexist temporally and spatially. However, since G. calmariensis larvae consumed more leaf material, the larval stage of this species would have a greater impact on purple loosestrife than G. pusilla.     

Behavioral responses to light gradients,olfactory cues,and prey in larvae of two North Pacific gadids (<Emphasis Type="Italic">Gadus macrocephalus</Emphasis> and <Emphasis Type="Italic">Theragra chalcogramma</Emphasis>)

The growth and survival of larvae can be significantly enhanced through close association with patches of high prey concentration. However, the taxis and kinesis responses used by larvae to locate and maintain residence in micro-patches remains poorly understood. In this study, the behavioral responses of Pacific cod (Gadus macrocephalus) and walleye pollock (Theragra chalcogramma) larvae (45–100 dph) to light, prey scent, and prey were examined. Both species displayed an ontogenetic shift in response to a horizontal light gradient, with small larvae (11–13 mm SL) exhibiting a positive phototaxis and large larvae (23–32 mm SL) exhibiting a negative phototaxis. Whether this reversal is related to ontogenetically appropriate foraging cues or some other aspect of the environment remains to be determined. Neither species displayed significant behavioral responsiveness to the introduction of olfactory prey cues at either size. The aggregating (taxis) response of large larvae to introduction of live prey was stronger than that of small larvae, possibly due to increased reaction distances and encounter rates. In addition, both species exhibited a kinesis response of reducing the frequency of swimming bouts in response to introduction of live prey. These results suggest that the scale of prey patchiness and the physical factors that determine patch encounter rates are a significant determinant of larval growth and survival in the early feeding stages of marine fishes.     

Dispersal and Burial Behavior in Larvae of <Emphasis Type="Italic">Chrysomya megacephala</Emphasis> and <Emphasis Type="Italic">Chrysomya albiceps</Emphasis> (Diptera,Calliphoridae)

Blowflies use discrete and ephemeral substrates to feed their larva. After they run out of food, the larvae begin to disperse in order to find adequate places for pupation or additional food sources, a process named post-feeding larval dispersal. Briefly state the aspects and why they are important were studied in a circular arena of 25 cm in diameter and covered with wood shavings to a height of 40 cm allowing post-feeding dispersal from the center of the arena. Larvae of both Chrysomya albiceps and C. megacephala were used in five experiments for each species. For each pupa location, determined as distance from the center, depth, and weight were evaluated. Statistical tests were done to verify the relation between weight, depth and distance for pupation and for larvae of two species shows that the media distance is significantly different for two species and for C. megacephala this distance is greater than the distance for C. albiceps. The depth too is different for each species, as the larvae of C. megacephala buries deeper than C. albiceps. With relation of weight, there is no statistic evidence that have any difference between weights for pupation for each species.     

High altitude mountain streams as a possible refuge habitat for the catfish <Emphasis Type="Italic">Amphilius uranoscopus</Emphasis>

Amphilius uranoscopus is a catfish species, restricted to rivers and streams in east, southern and central Africa. It is likely to be displaced due to both competition and predation by exotic trout and other introduced fish. In high altitude mountain streams it can be the only species occurring, which means that this habitat may act as a refuge for this species. Ecosystems like this are threatened by habitat alteration and are therefore in need of protection. The abiotic environment, population structure, behavior and feeding biology of Amphilius uranoscopus were studied in a small, high-altitude perennial tributary of the Limpopo River in the Soutpansberg mountain range, Limpopo Province, South Africa, during 2005–2006. Here A. uranoscopus showed nocturnal behavior. It used dark hollow crevices in rapids as shelters during the daytime. The rapids are characterized by a high flow rate, high dissolved oxygen content and coarse riverbed substrate consisting mainly of boulders without fallen leaves. In contrast to the adults, juveniles found shelter among the fallen leaves in pools. At night, A. uranoscopus moved out of the rapids into the open water of the pools. The main food of A. uranoscopus consisted of macroinvertebrates, mainly Trichoptera larvae. Amounts of algae and detritus in its diet were negligible. A. uranoscopus foraged mainly in rapids and on rock surfaces, spending less time foraging between the fallen leaves at the bottom of pools, in open water, at the surfaces of bottom and bank and near the water surface. At the water surface, it also fed opportunistically on terrestrial insects that dropped into the stream, like flying termites. A. uranoscopus was the top predator of the stream system and reached a high density (0.71 fish m⁻²). There was no competition from other fish species at the study site as they were lacking. A. uranoscopus showed a striking ability to climb and cling on to vertical substrates to conquer waterfalls and very shallow streams that sometimes become dry, using its fins, adhesive body and protruding mouth teeth.     

Intraguild predation and interference competition on the endangered dragonfly <Emphasis Type="Italic">Aeshna viridis</Emphasis>

We examined the effects of intraguild predation (IGP) and interference competition on an endangered dragonfly, Aeshna viridis Eversm. (Odonata: Anisoptera). A. viridis is rare in Europe due to the decrease in suitable habitats harboring the macrophyte Stratiotes aloides L. Stratiotes plants are the principal oviposition substrate for A. viridis females and protect the larvae of A. viridis from fish predation. In our study lakes A. viridis larvae are sympatric with larvae of Aeshna grandis and Aeshna juncea. The susceptibility of A. viridis larvae to IGP by similar-sized larvae of A. grandis and A. juncea was tested in a laboratory predation experiment. Microhabitat use of A. viridis and A. grandis was studied in the laboratory to determine the possible effects of interference competition on the spatial distribution of A. viridis larvae. Our results show that at least in laboratory conditions, A. viridis is susceptible to IGP and interference competition. In competition, A. grandis larvae dominated the middle and outer portion of S. aloides rosettes whereas A. viridis stayed in the inner parts. When A. grandis larvae were absent, A. viridis colonized the middle and outer parts of the rosettes. We conclude that asymmetric predation between odonate larvae of equal size can be intense, and that both IGP and interference competition affect A. viridis. Although natural habitat complexity diminishes their impact, these interactions may nevertheless influence the distribution of A. viridis in S. aloides waters and restrict its microhabitat use in S. aloides rosettes.     

Limitations of <Emphasis Type="Italic">Neoseiulus baraki</Emphasis> and <Emphasis Type="Italic">Proctolaelaps bickleyi</Emphasis> as control agents of <Emphasis Type="Italic">Aceria guerreronis</Emphasis>

Several predatory mites have been found in association with the coconut mite, Aceria guerreronis Keifer, in northeast Brazil. However, the latter still causes damage to coconut in that region. The objectives of this work were to compare the frequencies of occurrence of Neoseiulus (Phytoseiidae) and Proctolaelaps (Melicharidae) species on standing and aborted coconuts in coastal Pernambuco State, northeast Brazil and to analyze their possible limitations as control agents of the coconut mite, based on evaluations of the restrictions they may have to access the microhabitat inhabited by the pest and their functional and reproductive responses to increasing densities of the latter. Neoseiulus baraki (Athias-Henriot) was found mostly on standing coconuts whereas Proctolaelaps bickleyi (Bram) was found mostly on aborted coconuts. Measurements of the entrance to the microhabitat occupied by the coconut mite, between the bracts and the subjacent fruit surface, showed that this different pattern of predator prevalence could be related to predator sizes, although other environmental factors could not be disregarded. Progressively higher predation rate of N. baraki was observed up to an experimental density that corresponded to 1,200 coconut mites per fruit, which is close to the average number determined in northeast Brazil, reducing slightly afterwards. Predation rate of P. bickleyi reduced consistently but slightly with increasing prey densities, but in absolute values, rates were always much higher than determined for N. baraki. The excessively high killing capacity of P. bickleyi, probably related to its high feeding requirement, may be detrimental in terms of stability. In fact, such high requirement for food suggests that P. bickleyi might not have a strong relation with the coconut mite and that the latter may not be its main food source under natural conditions. It is concluded that body sizes of both predators and the exceedingly high feeding requirement of P. bickleyi may limit their performance as control agents of the coconut mite.     

Effects of Chemical Cues on Foraging in Damselfly Larvae, <Emphasis Type="Italic">Enallagma antennatum</Emphasis>

Animals experiencing a trade-off between predation risk and resource acquisition must accurately predict ambient levels of predation risk to maximize fitness. We measure this trade-off explicitly in larvae of the damselfly Enallagma antennatum, comparing consumption rates in the presence of chemical cues from predators and injured prey. Damselflies distinguished among types of chemical cues based on species of prey injured or eaten. Injured coexisting heterospecific and unknown heterospecific chemical cues did not reduce foraging relative to starved predator cues, while cues arising from predators eating a coexisting heterospecific did decrease foraging. This study shows a cost in terms of reduced foraging in response to chemical cues and further defines the ability of prey to respond discerningly to chemical cues.     

Plastic changes in head size during juvenile development of the butterfly <Emphasis Type="Italic">Pieris napi</Emphasis>

Among herbivorous insects, the ability to change adaptive traits plastically in response to novel host plants is advantageous for coping with sudden environmental shifts. The host plants in our study were two closely related species, viz., Arabis flagellosa (tougher leaves, i.e., they are physically defended) and A. gemmifera (softer leaves that are physiologically defended). We demonstrated that young larvae of the butterfly Pieris napi are able to plastically change head size during development in response to changes in food plant species. When larvae were fed the physically defended A. flagellosa, the head sizes of third instar larvae emerging from eggs originally collected from leaves of both A. flagellosa and A. gemmifera became identically larger. When larvae fed on the physiologically defended A. gemmifera, the head sizes of third instar larvae emerging from eggs originally collected from leaves of both A. flagellosa and A. gemmifera became identically smaller. When leaves of A. flagellosa were presented to fourth instars reared on A. flagellosa, larvae with larger heads consumed more food than those with smaller heads. In contrast, when leaves of the physiologically defended A. gemmifera were presented to fourth instar larvae reared on A. gemmifera, larvae with smaller heads processed more food than those with larger heads. Hence, larvae of P. napi retain the capacity for adaptive plastic responses to novel host plant species.     

Antennule shape and body size of <Emphasis Type="Italic">Bosmina</Emphasis>: key factors determining its vulnerability to predacious Copepoda

Cyclopoid copepods are common in lakes and ponds, and they have a significant predation impact on the communities of the small zooplankton species. To reduce the predation risk, some cladoceran zooplankters develop protuberant (defensive) morphologies in the presence of the copepods. In the case of the small cladoceran Bosmina, they elongate their appendages (antennule and mucrone) and change the antennule morphotype. However, information about the effectiveness of these defensive devices against copepod predation is still insufficient. In our study, to find the compositive effects of these appendages on the vulnerability of Bosmina, we exposed two bosminid species (B. longirostris and B. fatalis) of different body sizes and with appendages of different lengths and shapes to copepod (Mesocyclops) predation. The experiment revealed that the shape of the antennule is a main factor determining the bosminid’s vulnerability to copepod predation and indicated that the protection of the opened ventral carapace must be a key strategy by which Bosmina avoids copepod predation.     

Larvae and juveniles of the plunderfishes <Emphasis Type="Italic">Artedidraco shackletoni</Emphasis> and <Emphasis Type="Italic">A.</Emphasis><Emphasis Type="Italic">skottsbergi</Emphasis> (Notothenioidei,Artedidraconidae) from the Indian sector of the Southern Ocean

Early life stages of Artedidraco skottsbergi and A. shackletoni were collected off Adélie Land. The morphology and pigmentation pattern of nine larvae and juveniles of A. skottsbergi between 17.2 and 21.4 mm in standard length (SL), and of two juveniles of A. shackletoni measuring 25.1 mm SL were described. A. skottsbergi was characterized by a heavily pigmented body, except for the caudal peduncle, with distinctively dense pigmentation on the ventrolateral half of the body and caudal section (17.2–17.9 mm SL). Furthermore, they had no pigmentation on the pectoral fin base until they attained 21.4 mm SL. Juvenile A. shackletoni had a heavily pigmented body except for the ventral side of the abdomen and the anal fin base. The proximal part of the dorsal fin and most of the anal fin were covered with melanophores. Although knowledge of larval and juvenile Artedidraco species is limited, the distribution of melanophores on the fins, pectoral fin base and caudal peduncle at each developmental stage may be useful for species identification.     

Effects of structural heterogeneity provided by the floating macrophyte <Emphasis Type="Italic">Eichhornia azurea</Emphasis> on the predation efficiency and habitat use of the small Neotropical fish <Emphasis Type="Italic">Moenkhausia sanctaefilomenae</Emphasis>

Macrophytes have a fundamental structuring role in aquatic environments. Several authors have suggested that trophic interactions are particularly mediated by aquatic plants. In the current article, we evaluated the effects of the structural heterogeneity provided by Eichhornia azurea (Kunth) roots on predation and habitat use by the small fish Moenkhausia sanctaefilomenae (Steindachner). We tested the hypotheses that (i) high structural heterogeneity protects macroinvertebrates against predation by M. sanctaefilomenae; (ii) distinct prey types are differently protected by the refuge provided by roots; and (iii) the behavior of M. sanctaefilomenae is affected by the structural heterogeneity provided by macrophyte roots. To test these hypotheses, we performed an experiment in 20 l aquaria in which macroinvertebrates (Cypricercus sp. and Chironomus sp.) were exposed to M. sanctaefilomenae predation for 4 h under three structural heterogeneities, represented by different root densities. High structural heterogeneity protected macroinvertebrates against predation. Additionally, E. azurea roots similarly protected different prey species. The macrophyte spatial structure substantially changed the habitat use of M. sanctaefilomenae. In general, our results corroborated the hypothesis that the structural heterogeneity provided by E. azurea roots significantly affects predation and habitat use by M. sanctaefilomenae. Handling editor: S. Declerck