Climate change and an invasive, tropical milkweed: an ecological trap for monarch butterflies.

While it is well established that climate change affects species distributions and abundances, the impacts of climate change on species interactions has not been extensively studied. This is particularly important for specialists whose interactions are tightly linked, such as between the monarch butterfly (Danaus plexippus) and the plant genus Asclepias, on which it depends. We used open-top chambers (OTCs) to increase temperatures in experimental plots and placed either nonnative Asclepias curassavica or native A. incarnata in each plot along with monarch larvae. We found, under current climatic conditions, adult monarchs had higher survival and mass when feeding on A. curassavica. However, under future conditions, monarchs fared much worse on A. curassavica. The decrease in adult survival and mass was associated with increasing cardenolide concentrations under warmer temperatures. Increased temperatures alone reduced monarch forewing length. Cardenolide concentrations in A. curassavica may have transitioned from beneficial to detrimental as temperature increased. Thus, the increasing cardenolide concentrations may have pushed the larvae over a tipping point into an ecological trap; whereby past environmental cues associated with increased fitness give misleading information. Given the ubiquity of specialist plant-herbivore interactions, the potential for such ecological traps to emerge as temperatures increase may have far-reaching consequences.

Cannibalism and Infectious Disease: Friends or Foes?

Cannibalism occurs in a majority of both carnivorous and noncarnivorous animal taxa from invertebrates to mammals. Similarly, infectious parasites are ubiquitous in nature. Thus, interactions between cannibalism and disease occur regularly. While some adaptive benefits of cannibalism are clear, the prevailing view is that the risk of parasite transmission due to cannibalism would increase disease spread and, thus, limit the evolutionary extent of cannibalism throughout the animal kingdom. In contrast, surprisingly little attention has been paid to the other half of the interaction between cannibalism and disease, that is, how cannibalism affects parasites. Here we examine the interaction between cannibalism and parasites and show how advances across independent lines of research suggest that cannibalism can also reduce the prevalence of parasites and, thus, infection risk for cannibals. Cannibalism does this by both directly killing parasites in infected victims and by reducing the number of susceptible hosts, often enhanced by the stage-structured nature of cannibalism and infection. While the well-established view that disease should limit cannibalism has held sway, we present theory and examples from a synthesis of the literature showing how cannibalism may also limit disease and highlight key areas where conceptual and empirical work is needed to resolve this debate.

The Invasion History of Diaphorina citri (Hemiptera: Liviidae) in Puerto Rico: Past, Present, and Future Perspectives.

The Asian citrus psyllid, Diaphorina citri Kuwayama, 1908 (Hemiptera: Liviidae), is a phloem-feeding insect pest of Citrus L. ( Sapindales: Rutaceae), Murraya J. Koenig ex L. (Sapindales: Rutaceae), and other Rutaceae, native to the Indian subcontinent and transmits the citrus greening pathogens (huanglongbing). We herein evaluate the occurrence of D. citri in Puerto Rico at a fine scale and the potential invasion history of the Caribbean from the native range. We found that the genetic diversity of D. citri in Puerto Rico, using the mitochondrial genetic marker CO1, indicated that the Caribbean haplotype is unique and more related to Southwest Asia haplotypes than other groups. Results then suggest that the invasion of the Caribbean did not occur from the United States. Also, we found that isothermality was the abiotic variable that influenced D. citri species distribution model performance the most in current and future climate change scenarios. Given the data available from the Global Biodiversity Information Facility (GBIF) for present D.citri reported occurrence, future projections suggest that climate change might promote an expansion of the pest to other Caribbean islands and Latin American countries. Still, it might elicit a range contraction across the Cordillera Central in Puerto Rico, possibly promoting citriculture. Regarding pest management strategies, we must consider a holistic approach to understanding D. citri invasion and resilience in novel habitats by including broader and more robust genetic population structure studies and if its current distribution reflects projected models across the neotropics.

Virulence-driven trade-offs in disease transmission: A meta-analysis.

The virulence-transmission trade-off hypothesis proposed more than 30 years ago is the cornerstone in the study of host-parasite co-evolution. This hypothesis rests on the premise that virulence is an unavoidable and increasing cost because the parasite uses host resources to replicate. This cost associated with replication ultimately results in a deceleration in transmission rate because increasing within-host replication increases host mortality. Empirical tests of predictions of the hypothesis have found mixed support, which cast doubt about its overall generalizability. To quantitatively address this issue, we conducted a meta-analysis of 29 empirical studies, after reviewing over 6000 published papers, addressing the four core relationships between (1) virulence and recovery rate, (2) within-host replication rate and virulence, (3) within-host replication and transmission rate, and (4) virulence and transmission rate. We found strong support for an increasing relationship between replication and virulence, and replication and transmission. Yet, it is still uncertain if these relationships generally decelerate due to high within-study variability. There was insufficient data to quantitatively test the other two core relationships predicted by the theory. Overall, the results suggest that the current empirical evidence provides partial support for the trade-off hypothesis, but more work remains to be done.