A lack of genetic diversity and minimal adaptive evolutionary divergence in introduced Mysis shrimp after 50 years

The successes of introduced populations in novel habitats often provide
powerful examples of evolution and adaptation. In the 1950’s, opossum
shrimp (Mysis diluviana) individuals from Clearwater Lake in Minnesota,
USA were transported and introduced to Twin Lakes in Colorado, USA by
fisheries managers to supplement food sources for trout. Shrimp were
subsequently introduced from Twin Lakes into numerous lakes throughout
Colorado. Because managers kept detailed records of the timing of the
introductions, we had the opportunity to test for evolutionary divergence
within a known time interval. Here, we used reduced representation genomic
data to investigate patterns of genetic diversity and test for genetic
divergence between populations and for evidence of adaptive evolution
within the introduced populations in Colorado. We found overall very low
levels of genetic diversity across all populations, with evidence for some
genetic divergence between the Minnesota source population and the
introduced populations in Colorado. There was also little differentiation
among the Colorado populations, consistent with the known provenance of a
single founding population, with the exception of the population from
Gross Reservoir, Colorado. Demographic modeling suggests that the
population in Gross Reservoir is of hybrid origin, with an earlier
founding population from an unknown source being later supplemented from
another population. Despite the overall low genetic diversity we observed,
FST outlier and environmental association analyses identified multiple
loci exhibiting signatures of selection and adaptive variation related to
elevation and lake depth. The success of introduced species is thought to
be limited by genetic variation, but our results imply that populations
with limited genetic variation can become established in a wide range of
novel environments.