Effect of Host-Switching on the Ecological and Evolutionary Patterns of Parasites.

Speciation via host-switching is a macroevolutionary process that emerges from a microevolutionary dynamic where individual parasites switch hosts, establish a new association, and reduce reproductive contact with the original parasite lineage. Phylogenetic distance and geographic distribution of the hosts have been shown to be determinants of the capacity and opportunity of the parasite to change hosts. Although speciation via host-switching has been reported in many host-parasite systems, its dynamic on the individual, population and community levels is poorly understood. Here we propose a theoretical model to simulate parasite evolution considering host-switching events on the microevolutionary scale, taking into account the macroevolutionary history of the hosts, to evaluate how host-switching can affect ecological and evolutionary patterns of parasites in empirical communities at regional and local scales. In the model, parasite individuals can switch hosts under variable intensity and have their evolution driven by mutation and genetic drift. Mating is sexual and only individuals that are sufficiently similar can produce offspring. We assumed that parasite evolution occurs at the same evolutionary time scale as their hosts, and that the intensity of host-switching decreases as the host species differentiate. Ecological and evolutionary patterns were characterized by the turnover of parasite species among host species, and parasite evolutionary tree imbalance respectively. We found a range of host-switching intensity that reproduces ecological and evolutionary patterns observed in empirical communities. Our results showed that turnover decreased as host-switching intensity increased, with low variation among the model replications. On the other hand, tree imbalance showed wide variation and non-monotonic tendency. We concluded that tree imbalance was sensitive to stochastic events, whereas turnover may be a good indicator of host-switching. We found that local communities corresponded to higher host-switching intensity when compared to regional communities, highlighting that spatial scale is a limitation for host-switching. [Dispersal of parasites, opportunity and capacity of interaction, phylogenetic conservatism, and community structure.].

Effect of heat stress on the antioxidant defense system and erythrocyte morphology of Antarctic fishes.

This study analyzed the effect of thermal stress on erythrocytes of Notothenia rossii and Notothenia coriiceps, abundant notothenioids in Admiralty Bay, Antarctic Peninsula. In both species, the antioxidant defense system enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione-S transferase, glutathione reductase were punctually altered (8°C for 1, 3 and 6 days) in erythrocytes, indicating that these markers are not ideal for termal stress. However, under the influence of thermal stress, morphological changes in Notothenia coriiceps erythrocytes were observed at all exposure times (1, 3 and 6 days at 8°C), and in Notothenia rossii occurred in 6 days. These results suggest that Notothenia corriceps presents a lower tolerance to thermal stress at 8°C for up to 6 days, since the cellular and nuclear alterations recorded are pathological and may be deleterious to the cells. Among the morphological markers analyzed in this work, we believe that the shape change and nuclear bubble formation may be good stress biomarkers in erythrocytes of Notothenia rossii and Notothenia coriiceps.

Disentangling the beta-diversity in anuran parasite communities.

There is great heterogeneity in parasite communities among hosts, understanding the nature and drivers of such variations is still a great scientific quest. Here, we analyse the variation in parasite communities by addressing the following questions: (i) What is the beta-diversity component (nestedness or turnover) that most contributes to beta diversity in parasite communities among anuran species? (ii) Does the beta diversity of parasite communities follow a non-random pattern? (iii) Is the dissimilarity in composition of parasite communities related to the phylogenetic or functional dissimilarity among hosts? We found that turnover in parasite assemblages was the main component of beta diversity, but the variation observed both in the total beta diversity and in its components did not differ from the respective null models. The dissimilarity among parasite communities was not related to the phylogenetic species variability or functional dissimilarity among anuran species for most localities. In short, our findings may indicate a process of resource tracking by the parasite species, in which the resource may not necessarily be conserved phylogenetically in their hosts.

The role of ecological opportunity in shaping host-parasite networks.

Despite the great interest to quantify the structure of host-parasite interaction networks, the real influence of some factors such as taxonomy, host body size and ecological opportunity remains poorly understood. In this paper, we investigate the general patterns of organization and structure of interactions in two anuran-parasite networks in the Brazilian Pantanal (seasonally flooded environment) and Atlantic Forest (non-flooded forest). We present theoretical models to test whether the structures of these host-parasite interaction networks are influenced by neutrality, host taxonomy and host body size. Subsequently, we calculated metrics of connectance, nestedness and modularity to characterize the network structure. We demonstrated the structure networks were influenced mainly by body size and taxonomy of the host. Moreover, our results showed that the seasonally flooded environment present networks with higher connectance/nestedness and lower modularity compared to the other environment. The results also suggest that seasonal floods may promote ecological opportunities for new species associations.

How deadly sarcophagid fly larvae are for anurans? New interactions and review to Neotropical region.

Myiasis is defined as the infestation of living or necrotic tissues of vertebrates by dipteran larvae. In amphibians, it can be caused by fly larvae belonging to families Calliphoridae, Chloropidae, Muscidae, and Sarcophagidae. In this study, we report new records and infestation intensity of myiasis in anurans from two localities of the Atlantic Forest in southern Brazil, and also present a list with myiasis caused by flesh fly Sarcophagidae species in anurans of the Neotropical region. For this, we surveyed anuran communities during two breeding seasons, examined for myiasis signs, and when positive collected the specimens. We found infested individuals of 13 anurans of seven species. Different Sarcophagidae larva morphotypes were collected, and two of them emerged as adult flies of Lepidodexia (Notochaeta) fumipennis and Peckia (Sarcodexia) lambens, which were both found in the tree frog Bokermannohyla circumdata. We compiled 21 cases of myiasis in anurans in the Neotropical region from the literature reviewed. This data indicated that hosts of different lineages and modes of life can be affected and that death is often fast. The diversity of myiasis-causing flies in anurans in nature is probably a lot greater than expected, especially if we consider that the encounters are occasional, but at relatively high intensities, can cause rapid deaths.