Libri novi

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Do reproductive activities compromise immunological competence as measured by phenoloxidase activity? Field and experimental manipulation in females of two damselfly species

Recent studies of female insects indicate that reproductive activities, such as mating and oviposition, can impair immune ability. Using the two tropical damselfly species Argia anceps Garrison and Hetaerina americana (Fabricius), egg production and phenoloxidase (PO) activity, a key enzyme in insect immunity, are measured in mating, ovipositing and perching females in December and March. Perching females of both species have fewer eggs compared with mating and ovipositing females, which suggests that perching females are not engaged in reproduction. There is seasonal variation in egg number for the three categories in H. americana but not in A. anceps, which can be interpreted in terms of adaptive changes in egg production depending on female–male interactions in the former species but not in the latter species. There is no difference in PO activity among mating, ovipositing or perching females within either species, although measurements in December and March indicate distinct seasonal changes. Juvenile Hormone (JH) is known to reduce the effectiveness of the immune system by favouring the use of resources for reproduction. A possible role for JH is examined in H. americana, using the JH analogue methoprene to manipulate hormone activity, revealing that PO activity is reduced in methoprene‐treated H. americana females. Thus, although the results of the present study are indicative of possible hormone‐driven changes in PO, there is not necessarily a down‐regulation of immune function (as determined by PO activity) during mating or oviposition. The results complement some recent studies countering the idea that reproductive activities reduce the immune ability in insects.     

Suitability of woodlice prey for generalist and specialist spider predators: a comparative study

1. Predators select a prey according to its energetic and nutritional composition. Generalist predators avoid, whereas specialists often specialise on well‐defended prey. The aim of this study was to find the suitability of woodlice prey for generalist and specialist predators by comparing their handling efficiency. 2. Laboratory experiments were performed in which specialist and generalist predators were reared on monotypic diets comprising one or other of two woodlice species that differ in their defensive strategies: rollers (Armadillidium) and clingers (Porcellio). A control group was reared on a mixture of arthropods (excluding woodlice). Three spider predators were used that differ in their adaptations to deal with woodlice prey: a woodlice specialist, Dysdera crocata; an oligophagous generalist, Pholcus phalangioides, that also captures woodlice; and a euryphagous generalist, Tegenaria domestica, that does not feed on woodlice. The frequency of capture was recorded and various fitness parameters were measured, namely survival, growth rate, and ontogenetic development. 3. It was found that the specialist, D. crocata, performed best on the Porcellio diet, and similarly well on Armadillidium and mixed diets. The two generalists, P. phalangioides and T. domestica, had poor performance on both woodlice diets but performed well on the mixed diet. 4. The results show that woodlice are unsuitable prey for both oligophagous and euryphagous generalist predators.     

Carrion flies of forensic interest: a study of seasonal community composition and succession in Lisbon,Portugal

Information on Diptera community, seasonality and successional patterns in every geographical region is fundamental for the use of flies as forensic indicators of time of death. In order to obtain these data from the Lisbon area (Portugal), experiments were conducted during the four seasons of the year, using piglet carcasses as animal models. Five stages were recognized during the decomposition process. The stages, besides visually defined, could be separated taking into account the occurrence and abundance of the specific groups of Diptera collected. In general, the bloated stage recorded higher abundance and species‐richness values. Seventy‐one species were identified, belonging to 39 families, in a total of 20 144 adult Diptera collected. Autumn yielded the highest values of species richness, whereas winter had the lowest. In all seasons of the year, Calliphoridae was the dominant family; Muscidae and Fanniidae were very abundant as well. Calliphora vicina Robineau‐Desvoidy, Calliphora vomitoria (Linnaeus), Chrysomya albiceps (Wiedemann), Lucilia ampullacea Villeneuve, Lucilia caesar (Linnaeus), Lucilia sericata (Meigen) (Calliphoridae), Hydrotaea ignava (Harris), Muscina prolapsa (Harris), Synthesiomyia nudiseta (van der Wulp) (Muscidae), Piophila megastigmata McAlpine, Stearibia nigriceps (Meigen) (Piophilidae) and Nemopoda nitidula (Fallén) (Sepsidae) were revealed to be very important members of the Diptera community collected. The necrophagous behaviour, demonstrated by their immatures, using carrion as a food source makes them useful forensic indicator species. Also of relevance is the presence of Chrysomya megacephala (Fabricius), S. nudiseta and P. megastigmata, foreign species established in the local carrion communities. This study also marks the first record of S. nudiseta in Portugal.     

A 3d-fem Simulation of Highest Stress Lines in Mandible Fractures by Elastic Impact

Abstract

In this article, the more usual mandible fracture areas are located by identifying the highest stress lines using a three-dimensional (tetrahedral) finite element method. By taking into account the temporomandibular contact and the inertia effects, the mathematical model is considered to be a dynamic Signorini's problem, that is, a dynamic variational inequality which is discretized in time following Newmark's method. So, in each time step a stationary variational inequality is solved by a penalty-duality algorithm. Finally, some numerical results obtained by simulating the more usual fractures in the human mandible are presented and compared with clinical experimental information.     

Plant species variation in bottom‐up effects across three trophic levels: a test of traits and mechanisms

1. An increasing number of studies have addressed the mechanisms by which plant inter‐specific variation influence interactions at higher trophic levels, but little is known about the underlying plant traits driving these dynamics. 2. Here we investigated the effects of host plant species on herbivore‐parasitoid interactions and the underlying traits driving such effects. For this, we measured the abundance of seed‐eating bruchids and their parasitoids across seven sympatric populations of the bean species Phaseolus coccineus and Phaseolus vulgaris in Central Mexico. To investigate the mechanisms underlying differences between bean species in bruchid‐parasitoid interactions, we carried out two laboratory experiments to test whether bruchid and parasitoid performance differed between plant species. We also measured seed size and phenolic compounds to investigate if seed traits mediate bruchid‐parasitoid interactions by influencing herbivore susceptibility or resistance to parasitoids. 3. Field surveys revealed that the rate of parasitoid recruitment to bruchids was significantly higher on P. vulgaris than on P. coccineus. Subsequent laboratory bioassays indicated that bruchids developed more slowly and exhibited lower fitness on P. vulgaris seeds than on P. coccineus seeds. Accordingly, we found that bean species differed in seed size, with P. vulgaris having smaller (less nutritious) seeds, which explains why bruchid development was slower on this plant species. 4. These results provide a mechanism for why bruchids exhibited higher parasitism rates on seeds of P. vulgaris in the field which could be due to Slow‐Growth/High‐Mortality effects, a smaller physical refuge provided by the seed, or both factors. The roles of these mechanisms remain inconclusive without further study.     

Community assembly and inventory efficiency at a regional scale: the case of terrestrial Heteroptera (Insecta) in northern Patagonia,Argentina

The first step to understanding the species present in a particular area is to perform inventory and assemblage studies. To obtain a species inventory, it is important to determine parameters such as species richness and relative abundance. This information can be useful for future studies and decision-making purposes in the conservation area. Despite the fundamental role of the terrestrial Heteroptera in ecosystems, they remain poorly known. We expected that the terrestrial Heteroptera species assemblage would be strongly associated with plant communities. Presently, 840 samples were collected in northern Argentine Patagonia during two years, 2013 and 2014. A total of 1950 adults of terrestrial Heteroptera belonging to 12 families, 32 species, and 8 morphospecies were found. Various statistical techniques were applied to correct the observed data for undersampling bias. These suggested that the lower boundary of the summer Heteroptera species richness in northern Patagonia was about 44–54 species. We concluded that the high regional habitat heterogeneity along the west-to-east and south-to-north gradients was paralleled by the turnover of Heteroptera. However, the Patagonian steppe shared a high number of species with the Monte and Subantarctic provinces. The suction sampling technique is an efficient technique to collect Heteroptera in environments with different plant structure and should thus be used in a complementary way with the sweeping technique.     

Discriminating species of Sinipta Stål (Orthoptera: Acrididae) from Uruguay based on morphological,ethological and molecular data

Two species of the genus Sinipta, S. dalmani and S. hectorisperonii, exist in Uruguay, the latter reported here for the first time. Both species have quite similar morphological features and can only be distinguished by slight details, which have led to misidentifications in the past. Specimens from both taxa were studied in order to detect suitable characters to distinguish them and to clarify their taxonomic status, by integrating previously unstudied morphological, biological and molecular characteristics. Detailed structures of the stridulatory file of both sexes were studied and described for the first time, and the sounds produced by both species were studied and described on the basis of recordings made in captivity with an analog recorder. The signal was digitized and analyzed using Avisoft software. Three different types of sound were described for both species: calling song, courtship song and disturbance song. Oscillograms and frequency spectra were provided, and the physical characteristics of the sounds of interest for species identification were established. Finally, molecular studies showed that the two taxa are reciprocally monophyletic groups. The combined results of the analyses suggest that the two studied taxa are distinct species, and point to features suitable for their identification.     

Landscape and anti-predation determinants of nest-site selection, nest distribution and productivity in a Mediterranean population of Long-eared Owls Asio otus

Nest predation is an important determinant of owl breeding success. We studied Long-eared Owl Asio otus productivity and attributes of nest-sites at the microhabitat and landscape scales in a Mediterranean locality over an 8-year period. We examined the effect on nest location and productivity of protective cover in concealing the nest from aerial and terrestrial predators. A dense cover of ivy and tree-foliage at canopy level favoured nest location but not productivity. By contrast, high shrub cover beneath the nest was selected by Owls and was positively related to both the site reoccupancy rate and the overall number of young fledged. Pre-fledging Owls use the ground, where they are exposed to terrestrial predators, which are much more abundant in the study area than are aerial predators. Our results therefore support the hypothesis that Owls adapt nest-site choice to local sources of predation risk. As reported elsewhere, Long-eared Owls in our study area showed restricted territoriality and nested in clusters. As active nest-sites during the same breeding season were more than 1 km apart on average, and their productivity was never greater for clustered nests than for more isolated nests, nest aggregation could not be interpreted as a case of facultative colonial breeding, which has been reported for this species in other areas. Neither landscape variables indicative of the availability of foraging areas nor structural attributes that protect young from predators explained the remarkable scarcity of nests in half of the study area. Unmeasured factors such as human disturbance could explain the pattern of distribution of Long-eared Owl nests.     

Multi-scale analysis of responses of stream macrobenthos to forestry activities and environmental context

1. Forestry activities can greatly modify the structure and function of invertebrate communities in streams, but the ability to detect effects of forestry may depend on the spatial scale considered, the choice of response metric and the environmental context. In this study, a multi‐scale, multi‐metric approach was used to compare the usefulness of proximate and larger‐scale measurements of forestry activity for understanding the impacts of forestry on stream macrobenthos. 2. Site‐specific responses of macrobenthic communities to forestry activities measured at four spatial scales (sub‐basin and 8‐, 2‐ and 0.5‐km radii upstream of study sites) were examined for 90 riffle sites distributed among 22 tributary streams (Strahler order 1–5) of the Cascapedia River basin, Quebec, Canada. 3. Multiple regression models and canonical correspondence analysis were used to relate six biological metrics (taxonomic richness, numerical density, biomass density, normalised biomass spectrum, individual body mass and community structure) to variables quantifying logging 1–19 years prior to the study and road density. Environmental predictors (variables quantifying local habitat or landscape features) were included in all analyses to statistically account for environmental context and increase the likelihood of detecting potentially subtle forestry impacts. 4. Forestry activities measured at the larger (sub‐basin and 8 km) scales were linked to decline in taxonomic richness, increase in numerical and biomass densities and shift in size structure of benthic macroinvertebrates, indicating that analyses encompassing larger areas, up to the full basin, may allow for more sensitive detection of effects than those of more limited span. 5. These responses primarily reflected marked increases in the abundance of chironomids and decline in the number of trichopteran taxa with increasing areal coverage of recent (≤2–4 years) cuts, suggesting that larger, longer‐lived and possibly more specialised taxa were more vulnerable to forestry impacts than smaller, multivoltine, generalist invertebrates. After partialling out the influence of other variables, rapid decline in richness occurred even when <1% of the basin had been clear cut in the year prior to the study. 6. Effects of forestry were detected after statistically accounting for natural environmental variability, which may have otherwise concealed those effects. The combined use of multiple biological metrics, partialling out of environmental effects and measurement of impacts at multiple spatial scales may be a broadly applicable approach for enhancing sensitivity and facilitating interpretation in studies of anthropogenic effects on macroinvertebrate communities.