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Natural variation in cold tolerance in the nematode Pristionchus pacificus: the role of genotype and environment.

ABSTRACT: Low temperature is a primary determinant of growth and survival among organisms and almost all animals need to withstand temperature fluctuations in their surroundings. We used the hermaphroditic nematode Pristionchus pacificus to examine variation in cold tolerance in samples collected from 18 widespread locations. Samples were challenged by exposure to both direct and gradual low temperature after culture in the laboratory at 20°C. A short-term acclimation treatment was also applied to assess cold tolerance following a pre-exposure cold treatment. Finally, genotype-by-environment (G × E) analysis was performed on a subset of samples cultured at two additional temperatures (15°C and 25°C). P. pacificus displayed a high degree of natural variation in cold tolerance, corresponding to the presence of three distinct phenotypic classes among samples: cold tolerant, non-cold tolerant, cold tolerant plastic. Survival of gradual cold exposure was significantly higher than survival of direct exposure to low temperature and a cold exposure pre-treatment significantly enhanced cold tolerance in some samples. By focusing on a sub-set of well-sampled locations from tropical La Réunion Island, we found evidence of significant effects of genotype and environment on cold tolerance, and we also showed that, within the different Réunion locations sampled, all three phenotypic classes are generally well represented. Taken together, our results show that P. pacificus exhibits a highly plastic tolerance to cold exposure that may be partly driven by differential trait sensitivity in diverse environments.

SUBMITTER: McGaughran A

PROVIDER: S-EPMC4163660 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The nematode species Pristionchus pacificus has an androdioecious mating system in which populations consist of self-fertilizing hermaphrodites and relatively few males. The prevalence of males in such a system is likely to depend on the relative pros and cons of outcrossing. While outcrossing generates novel allelic combinations and can therefore increase adaptive potential, it may also disrupt the potentially beneficial consequences of repeated generations of selfing. These include purging of deleterious alleles, inheritance of co-adapted allele complexes, improved hermaphrodite fitness and increased population growth. Here we use experimental and population genetic approaches to test hypotheses relating to male production and outcrossing in laboratory and natural populations of P. pacificus sampled from the volcanic island of La Réunion.We find a significant interaction between sampling locality and temperature treatment influencing rates of spontaneous male production in the laboratory. While strains isolated at higher altitude, cooler localities produce a higher proportion of male offspring at 25 °C relative to 20 or 15 °C, the reverse pattern is seen in strains isolated from warmer, low altitude localities. Linkage disequilibrium extends across long physical distances, but fails to approach levels reported for the partially selfing nematode species Caenorhabditis elegans. Finally, we find evidence for admixture between divergent genetic lineages.Elevated rates of laboratory male generation appear to occur under environmental conditions which differ from those experienced by populations in nature. Such elevated male generation may result in higher outcrossing rates, hence driving increased effective recombination and the creation of potentially adaptive novel allelic combinations. Patterns of linkage disequilibrium decay support selfing as the predominant reproductive strategy in P. pacificus. Finally, despite the potential for outcrossing depression, our results suggest admixture has occurred between distinct genetic lineages since their independent colonization of the island, suggesting outcrossing depression may not be uniform in this species.

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Natural variation in cold tolerance in the nematode Pristionchus pacificus: the role of genotype and environment.

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