Nestmate recognition in a Neotropical swarm-founding wasp: no effect of seasonality on tolerance of alien conspecifics

Previous study revealed that the swarm-founding wasp Polybia paulista is accurately able to distinguish nestmates from non-nestmates in the summer. However, the risk of accepting alien intruders is considered to be low in winter colonies, and additionally brood production is limited in 30-40% of colonies during the winter in this species. Thus, it is expected that colonies might lower their acceptance threshold and accept some conspecific wasps from alien colonies in winter. We conducted field experiments to examine tolerance of conspecific (nestmate and non-nestmate) females in winter. In contrast to our prediction, our colonies did not accept any individuals from alien colonies. We suggest that P. paulista exhibits the colony-specific acceptance threshold in winter, and colonies that produced brood in their nests may have raised the acceptance threshold even if the risk of accepting alien intruders is low in winter.

Colonization and extinction of land planarians (Platyhelminthes, Tricladida) in a Brazilian Atlantic Forest regrowth remnant

Long-term assessments of species assemblages are valuable tools for detecting species ecological preferences and their dispersal tracks, as well as for assessing the possible effects of alien species on native communities. Here we report a 50-year-long study on population dynamics of the four species of land flatworms (Platyhelminthes, Tricladida, Terricola) that have colonized or become extinct in a 70-year-old Atlantic Forest regrowth remnant through the period 1955-2006. On the one hand, the two initially most abundant species, which are native to the study site, Notogynaphallia ernesti and Geoplana multicolor have declined over decades and at present do not exist in the forest remnant. The extinction of these species is most likely related with their preference for open vegetation areas, which presently do not exist in the forest remnant. On the other hand, the neotropical Geoplaninae 1 and the exotic Endeavouria septemlineata were detected in the forest only very recently. The long-term study allowed us to conclude that Geoplaninae 1 was introduced into the study area, although it is only known from the study site. Endeavouria septemlineata, an active predator of the exotic giant African snail, is originally known from Hawaii. This land flatworm species was observed repeatedly in Brazilian anthropogenic areas, and this is the first report of the species in relatively well preserved native forest, which may be evidence of an ongoing adaptive process. Monitoring of its geographic spread and its ecological role would be a good practice for preventing potential damaging effects, since it also feeds on native mollusk fauna, as we observed in lab conditions.

Effects of Prepartum Ingestion of Ipomoea carnea on Postpartum Maternal and Neonate Behavior in Goats

Ipomoea carnea is a toxic plant that grows in tropical areas, and is readily consumed by grazing goats. The plant contains the alkaloids swainsonine and calystegines, which inhibit cellular enzymes and cause systematic cell death. This study evaluated the behavioral effects on dams and kids of prenatal ingestion of this plant. Freshly harvested leaves of I. carnea (10 g/kg body weight) were fed daily to nine pregnant goats from the fifth to the 16th week of gestation; five pregnant goats were controls. Dam and kid behavior were evaluated during 2-hr postpartum. Further evaluation of the offspring was performed using various tests after birth: (1) reaching and discriminating their dam from an alien doe (two tests at 12-hr postpartum), and (2) navigating a progressive maze (2, 4, and 6 days postpartum). Postnatal (n=2) and fetal (n=2) mortality were observed in the treated group. Intoxicated kids had difficulty in standing at birth, and only one was able to suckle within 2 hr of birth. Treated kids were slower than controls to arrive at their dam in the discrimination test; treated kids often (seven of nine completed tests) incorrectly chose the alien dam (controls: 0/10 tests). During some runs on days 2, 4, and 6 postpartum, treated kids were slower to leave the starting point of the maze, and were slower to arrive at the dam on all test days. This study suggests that the offspring of pregnant goats given I. carnea during gestation have significant behavioral alterations and developmental delays. Birth Defects Res (Part B) 92:131-138, 2011. (C) 2011 Wiley-Liss, Inc.

Phytophagous insect fauna tracks host plant responses to exotic grass invasion

The high dependence of herbivorous insects on their host plants implies that plant invaders can affect these insects directly, by not providing a suitable habitat, or indirectly, by altering host plant availability. In this study, we sampled Asteraceae flower heads in cerrado remnants with varying levels of exotic grass invasion to evaluate whether invasive grasses have a direct effect on herbivore richness independent of the current disturbance level and host plant richness. By classifying herbivores according to the degree of host plant specialization, we also investigated whether invasive grasses reduce the uniqueness of the herbivorous assemblages. Herbivorous insect richness showed a unimodal relationship with invasive grass cover that was significantly explained only by way of the variation in host plant richness. The same result was found for polyphagous and oligophagous insects, but monophages showed a significant negative response to the intensity of the grass invasion that was independent of host plant richness. Our findings lend support to the hypothesis that the aggregate effect of invasive plants on herbivores tends to mirror the effects of invasive plants on host plants. In addition, exotic plants affect specialist insects differently from generalist insects; thus exotic plants affect not only the size but also the structural profile of herbivorous insect assemblages.

Invasive grasses and native Asteraceae in the Brazilian Cerrado

Anthropogenic disturbances frequently modify natural disturbance regimes and foster the invasion and spread of nonindigenous species. However, there is some dispute about whether disturbance events or invasive plants themselves are the major factors promoting the local extinction of native plant species. Here, we used a set of savanna remnants comprising a gradient of invasive grass cover to evaluate whether the species richness of Asteraceae, a major component of the Brazilian Cerrado, is affected by invasive grass cover, or alternatively, whether variation in richness can be directly ascribed to disturbance-related variables. Furthermore, we evaluate whether habitat-specialist Asteraceae differ from habitat generalist species in their responses to grass invasion. Abundance and species richness showed unimodal variation along the invasive grass gradient for both total Asteraceae and habitat-generalists. The cerrado-specialist species, however, showed no clear variation from low-to-intermediate levels of grass cover, but declined monotonically from intermediate-to-higher levels. Through a structural equation model, we found that only invasive grass cover had significant effects on both abundance and species density of Asteraceae. The effect of invasive grass cover was especially high on the cerrado-specialist species, whose proportion declined consistently with increasing invasive dominance. Our results support the prediction that invasive grasses reduce the floristic uniqueness of pristine vegetation physiognomies.

Invasive plants: representativeness of research from tropical countries in the global context

Biological invasions threaten the native biota of several countries and this threat is even greater in the tropical regions that have the greatest biodiversity. In order to evaluate the representativeness of studies on invasive plants in tropical countries compared to the world, as well as the region of origin and habits of the most reported invasive plants in research, we analyzed the publications from eight of the most important international journals that address the theme, from January 1995 to December 2004. The articles on biological invasions were classified as theoretical or as case studies, and according to their approach, main question, where the study was conducted, region of origin and habit of the invasive plant. Case studies predominated, as did questions about the environment`s susceptibility to the invasion, the species` invasive power and the impacts it had. The most reported invasive species were herbaceous plants from Asia and Europe. Few articles address tropical environments and only one referred to Brazil. Most referred to North America and Europe. This small number of publications in the tropics indicates the need for a global projection on this subject and underscores the lack of consistent and organized data to understand the phenomenon and propose effective strategies to combat biological invasion.