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Signals and receiver responses often vary across a species' geographic range. Effective communication requires a match between signal and receiver response, so there is much interest in the developmental mechanisms that maintain this link. Two potential mechanisms are genetic covariance between signal and receiver response and plasticity where individuals adjust their phenotype based on their partner's phenotype. Here, we test how plasticity contributes to geographic variation in individual face recognition in Polistes fuscatus wasps. Previous work has shown that P. fuscatus from Michigan, USA (MI) have variable facial patterns used for individual recognition, while P. fuscatus from central Pennsylvania, USA (PA) lack variable facial patterns and are unable to learn individual conspecifics. We experimentally altered rearing environment, so wasps were either reared with their own population or in a common garden with wasps from both populations. Then, we tested the wasps' capacity to learn and remember individual conspecific faces. Consistent with previous work, MI wasps reared with MI wasps were adept at learning conspecific faces, while PA wasps reared with PA wasps were unable to learn conspecific faces. However, MI and PA wasps reared in a common garden developed similar, intermediate capacity for individual face learning. These results indicate that individual face learning in Polistes wasps is highly plastic and responsive to the social environment. Plasticity in receiver responses may be a common mechanism mediating geographic differences in non-sexual signaling systems and may play a role in maintaining links between signals and receiver responses in geographically variable communication systems. [ABSTRACT FROM AUTHOR]

Monarch butterflies, Danaus plexippus (L.), from eastern North America are well known for their incredible autumn migration to Mexico; however, not all monarchs follow this route. There is evidence of monarchs overwintering and reproducing in Florida, arriving to insular and continental Caribbean, and roosting by the thousands in the Yucatán, Mexico. This work aims to present evidence that these monarchs are part of two current migratory routes, that we consider as the south-eastern and the Atlantic routes, routes that were probably more prominent in the past. Monarchs were collected for 12 months in south Florida, for 4 years in Cuba in November and once in March, in the Yucatán and Guatemala at different times, and once in northern Venezuela. We used two independent techniques, stable hydrogen isotope (δ2H) analyses of the wings and/or thin layer chromatography (TLC), to trace the monarch's natal grounds. We analysed the DNA of monarchs collected in St. Marks in the Florida Panhandle, Cuba and Guatemala, and compared those data against previously-analysed DNA data from monarchs in the Americas to characterize their genetic structure and to assess the possible movement and presence of North American monarchs and/or their alleles outside the USA. Our results support the existence of south-eastern and Atlantic migratory routes. TLC, isotope and DNA analyses showed the arrival of likely North American monarchs in Cuba, Yucatán, Guatemala, Venezuela and other areas of the Americas. North American monarchs found in these areas have different natal grounds, phenotypic traits and DNA signature than Mexican migrants. Monarchs from the south-eastern route mostly originated in the south-east USA and fed on local Asclepias spp. such as Asclepias viridis , Asclepias humistrata , Asclepias perennis and Asclepias asperula. Butterflies from this migratory route move east, enter the Florida Peninsula, pass to Cuba, fly to the Yucatán and then to Guatemala where they appear to overwinter in the high mountains of Guatemala where Abies guatemalensis occurs. Monarchs that are part of the Atlantic route move east of the Appalachians, enter the Florida Peninsula, and from there pass to the insular and continental Caribbean. The main host plants for the Atlantic monarchs are A. perennis and A. humistrata ; in contrast, Mexican monarchs mainly feed on Asclepias syriaca. Some monarchs from these two proposed migratory routes, south-eastern and Atlantic, will stay in the places where they travelled and others will return via Florida and Mexico. We propose a scenario for how the different migratory routes evolved. [ABSTRACT FROM AUTHOR]