Polyamines, which are small positively charge molecules present in all cells, play important roles in the replication of DNA and RNA viruses. Chikungunya virus (CHIKV) relies on polyamines for translation of the viral genome upon viral entry, and pharmacological depletion of polyamines limits viral replication. However, the potential development of antiviral resistance necessitates a better understanding of how polyamines function and can be targeted via compounds that alter polyamine levels. We have isolated CHIKV that is resistant to polyamine depletion and contains two mutations in the nonstructural protein 1 (nsP1)-coding region in combination with a mutation to the opal stop codon preceding nsP4. These mutations, in addition to promoting viral replication in polyamine-depleted cells, confer enhanced viral replication in vitro and in vivo. The nsP1 mutations enhance membrane binding and methyltransferase activities, while the stop codon mutation allows increased downstream translation. These mutations, when combined, enhance viral fitness, but individual mutants are attenuated in mosquitoes. Together, our results suggest that CHIKV can evolve resistance to polyamine depletion and that pharmaceuticals targeting the polyamine biosynthetic pathway may be best used in combination with other established antivirals to mitigate the development of resistance.IMPORTANCE Chikungunya virus is a mosquito-borne virus that has infected millions worldwide. Its expansion into the Americas and rapid adaptation to new mosquito hosts present a serious threat to human health, which we can combat with the development of antiviral therapies as well as understanding how these viruses will mutate when exposed to antiviral therapies. Targeting polyamines, small positively charged molecules in the cell, may be a potential strategy against RNA viruses, including chikungunya virus. Here, we have described a virus that is resistant to polyamine depletion and has increased fitness in cells and in full organisms. Mutations in viral genome capping machinery, membrane binding activity, and a stop codon arise, and their altered activities enhance replication in the absence of polyamines. These results highlight strategies by which chikungunya virus can overcome polyamine depletion and emphasize continued research on developing improved antiviral therapies.KEYWORDS antiviral, antiviral resistance, chikungunya virus, polyamines, viral replication C hikungunya virus (CHIKV) is an arthropod-borne virus (arbovirus) from the Alphavirus family that has caused several severe outbreaks worldwide. Clinical manifestations can be severe and long lasting, including fever and chronic joint pain, and rapid

Sexual dimorphism and specific patterns of development contribute in a great manner to the direction and degree of the sexual differences in body size and shape in many insects. Using a landmark-based geometric morpohometrics approach, we investigated sex-specific morphological size and shape variation in the seed beetle, Acanthoscelides obtectus. We also tested the functional hypothesis of the two morphological modules—thorax and abdomen in both sexes. Female-biased sexual dimorphism in size was shown, while differences in shape were reflected in the wider thorax and abdomen and shorter abdomen in females in comparison to males. The functional hypothesis of a two-module body was confirmed only in females before correction for size, and in both sexes after the allometry correction. Our results indicate that reproductive function has the central role in forming the patterns of modularity. We hypothesize that high morphological integration of the abdomen in females results from intense stabilizing selection, while the more relaxed integration in males is driven by the higher intensity of sexual selection.

1. Expansion of the host range in phytophagous insects, followed by the specialisation on novel hosts, encompasses changes in many aspects of insects' behaviour, physiology, and the interaction between their life-history features.2. Here, we analyse the roles of insects' developmental plasticity in the process of host shift. Using laboratory populations of the seed beetle (Acanthoscelides obtectus), which have evolved on both optimal (common beans) and suboptimal (chickpea) plant hosts for more than 35 years, we experimentally replicated the process of host shift and analysed the patterns of short-term and long-term life-history responses to host variation.3. In order to test whether selection for increased plasticity has an effect on host shifting processes, we used existing bean and chickpea adapted populations to establish new populations in which the host plant offered for insect development was changed each generation (for 13 generations). To test the potential for a shortterm plastic response, beetles from each laboratory population were raised on both hosts for one generation.4. Results showed that, in contrast to the populations that evolved on beans, which maintained high levels of developmental plasticity, long-term host switching to chickpeas was accompanied with specialisation of pre-adult viability with a simultaneous increase in fecundity. Populations evolved on alternate plant hosts that revealed similar plasticity patterns as their ancestral populations.5. These results suggest that short-term plastic responses could determine the paths of long-term evolution of life-history plasticity. However, more time could be needed for plasticity to evolve differently from the initial responses.