Rapid turnover of a pea aphid superclone mediated by thermal endurance in central Chile.

Global change drivers are imposing novel conditions on Earth's ecosystems at an unprecedented rate. Among them, biological invasions and climate change are of critical concern. It is generally thought that strictly asexual populations will be more susceptible to rapid environmental alterations due to their lack of genetic variability and, thus, of adaptive responses. In this study, we evaluated the persistence of a widely distributed asexual lineage of the alfalfa race of the pea aphid, Acyrthosiphon pisum, along a latitudinal transect of approximately 600 km in central Chile after facing environmental change for a decade. Based on microsatellite markers, we found an almost total replacement of the original aphid superclone by a new variant. Considering the unprecedented warming that this region has experienced in recent years, we experimentally evaluated the reproductive performance of these two A. pisum lineages at different thermal regimes. The new variant exhibits higher rates of population increase at warmer temperatures, and computer simulations employing a representative temperature dataset suggest that it might competitively displace the original superclone. These results support the idea of a superclone turnover mediated by differential reproductive performance under changing temperatures.

Phenotypic specialization of the pea aphid in its southern limit of distribution.

The success of biological invasions ultimately relies on phenotypic traits of the invasive species. Aphids, which include many important pests worldwide, may have been successful invading new environments partly because they can maximize reproductive output by becoming parthenogenetic and losing the sexual phase of their reproductive cycle. However, invasive populations of aphids invading wide ranges can face contrasting environmental conditions and requiring different phenotypic strategies. Besides transitions in their reproductive cycle, it is only partially known which phenotypic traits might be associated to the invasion success of aphid populations in extended novel ranges. Here, we used four genotypes of the pea aphid Acyrthosiphon pisum from two localities in Chile to test for phenotypic specialization that might explain their establishment and spread in habitats exhibiting contrasting environmental conditions. We show that lineages living at a higher latitude with low temperatures show, in addition to facultative sexual reproduction, smaller body sizes, lower metabolic rates and a higher tolerance to the cold than the obligate asexual lineages living in a mild weather, at the expense of fecundity. Conversely, at higher temperatures only asexual lineages were found, which exhibit larger body sizes, higher reproductive outputs and consequently enhanced demographic ability. As a result, in conjunction with the reproductive mode, lineage specialization in physiological and life-history traits could be taken into account as an important strategy for populations of pea aphid to effectively invade extended novel ranges comprising different climatic conditions.