The enemy of my enemy: multiple interacting selection pressures lead to unexpected anti-predator responses

Spoilt for choice: Do female mosquitoes experience choice overload when deciding where to lay eggs?

Animals live in complex natural environments. Based on the effects of natural selection, theory on animal information use says that it is optimal for animals to make "rational" decisions, i.e., to choose alternatives which maximize fitness gains, irrespective of the number of alternatives presented to them. Yet, animals commonly make seemingly "irrational" choices in the face of complex and variable stimuli that challenge their cognitive machinery. Here, we test the choice overload hypothesis - decision-making is negatively affected when animals experience an overload of choice. Using simultaneous-choice trials that varied in choice repertoire size, we examined oviposition site selection behaviour in Aedes aegypti towards larval predators, the nymphs of Bradinopyga geminata. Based on the underlying fitness trade-offs of oviposition decision-making, we predicted that female oviposition preference would be weaker and variation in this response would be higher in complex, multiple-choice trials than in binary-choice trials. In partial support of our hypothesis, oviposition preference was weaker in the complex, multiple-choice trials, but the variation in response depended on predator density, and did not depend on choice repertoire size. We suggest that information overload can negatively affect certain aspects of animal decision-making, resulting in choices appearing as "irrational" if the complexity of the decision-making context is not incorporated. Information overload can potentially lead to alternative strategies, such as bet-hedging or decision-making with reduced discrimination.

Partitioning variance in immune traits in a zooplankton host-Fungal parasite system

Host immune traits arise from both genetic and environmental sources of variation. When immune traits have a strong genetic basis, the presence and severity of disease in a population may influence the distribution of those traits. Our study addressed how two immune-related traits (gut penetrability and the hemocyte response) are shaped by genetic and environmental sources of variation, and how the presence of a virulent disease altered the relative frequency of these traits in natural populations. Daphnia dentifera hosts were sampled from five Indiana lakes between June and December 2017 before and during epidemics of their fungal pathogen, Metschnikowia bicuspidata. Collected Daphnia were experimentally exposed to Metschnikowia and assayed for their gut penetrability, hemocyte response, and multi-locus genotype. Mixed-effects models were constructed to partition variance in immune traits between genetic and environmental sources. We then isolated the genetic sources to produce genotype-specific estimates of immune traits for each multi-locus genotype. Finally, we assessed the relative frequency and dynamics of genotypes during epidemics and asked whether genotypes with more robust immune responses increased in frequency during epidemics. Although genotype was an important source of variation for both gut penetrability and the hemocyte response, environmental factors (e.g., resource availability, Metschnikowia prevalence, and co-infection) still explained a large portion of observed variation, suggesting a high degree of flexibility in Daphnia immune traits. Additionally, no significant associations were detected between a genotype's immune traits and its frequency in a population. Our study highlights the power of variance partitioning in understanding the factors driving variation in Daphnia traits and motivates further research on immunological flexibility and the ecological drivers of immune variation.

Island biogeography and human practices drive ecological connectivity in mosquito species richness in the Lakshadweep Archipelago

Mosquitoes are globally distributed and adapted to a broad range of environmental conditions. As obligatory hosts of many infectious pathogens, mosquito abundance and distribution are primarily determined by the presence and quality of larval habitats. To understand the dynamics and productivity of larval habitats in changing island environments, we conducted a four-month mosquito survey across ten inhabited islands in the Lakshadweep archipelago. Using fine-resolution larval habitat mapping, we recorded 7890 mosquitoes representing 13 species and 7 genera. Of these, four species comprised 95% of the total collections—Aedes albopictus (Stegomyia) was the dominant species followed by Armigeres subalbatus, Culex quinquefasciatus and Malaya genurostris. We found larval species richness was positively associated with the island area and mosquito larval richness (Chao1 estimator) was higher in artificial habitats than in natural habitats. Furthermore, mosquito species composition did not deteriorate with distance between islands. Mosquito abundance by species was associated with microclimatic variables—pH and temperature. We detected co-existence of multiple species at a micro-habitat level with no evidence of interactions like competition or predation. Our study analyzed and identified the most productive larval habitats –discarded plastic container and plastic drums contributing to high larval indices predicting dengue epidemic across the Lakshadweep islands. Our data highlight the need to devise vector control strategies by removal of human-induced plastic pollution (household waste) which is a critical driver of disease risk.

Linking Mosquito Ecology, Traits, Behavior, and Disease Transmission

Mosquitoes are considered to be the deadliest animals on Earth because the diseases they transmit claim at least a million human lives every year globally. Here, we discuss the scales at which the effects of ecological factors cascade to influence epidemiologically relevant behaviors of adult mosquitoes. In particular, we focused our review on the environmental conditions (coarse-scale variables) that shape the life-history traits of larvae and adult mosquitoes (fine-scale traits), and how these factors and their association, in turn, modulate adult behaviors to influence mosquito-borne disease transmission. Finally, we explore the integration of physical, physiological, and behavioral information into predictive models with epidemiological applications.