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

   https://doi.org/10.1111/eva.13637  

   Cheek, Rebecca G. ; McLaughlin, Jessica F. ; Gamboa, Maybellene P. ; Marshall, Craig A. ; Johnson, Brett M. ; Silver, Douglas B. ; Mauro, Alexander A. ; Ghalambor, Cameron K. ( January 2024 , Evolutionary Applications)

   The successes of introduced populations in novel habitats often provide powerful examples of evolution and adaptation. In the 1950s, 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.Mysiswere 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, test for genetic divergence between populations, and for evidence of adaptive evolution within the introduced populations in Colorado. We found 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 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 at least one undocumented introduction from an unknown source population hybridized with the population in Gross Reservoir. Despite the overall low genetic diversity we observed,F_SToutlier 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. From an applied perspective, the observed patterns of divergence between populations suggest that genetic analysis can be a useful forensic tool to determine likely sources of invasive species.

    

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2. Rapid establishment of a flowering cline in Medicago polymorpha after invasion of North America

   https://doi.org/10.1111/mec.14898  

   Helliwell, Emily E. ; Faber‐Hammond, Joshua ; Lopez, Zoie C. ; Garoutte, Aaron ; von Wettberg, Eric ; Friesen, Maren L. ; Porter, Stephanie S. ( December 2018 , Molecular Ecology)

   To establish and spread in a new location, an invasive species must be able to carry out its life cycle in novel environmental conditions. A key trait underlying fitness is the shift from vegetative to reproductive growth through floral development. In this study, we used a common garden experiment and genotyping‐by‐sequencing to test whether the latitudinal flowering cline of the North American invasive plantMedicago polymorphawas translocated from its European native range through multiple introductions, or whether the cline rapidly established due to evolution following a genetic bottleneck. Analysis of flowering time in 736 common garden plants showed a latitudinal flowering time cline in both the native and invaded ranges where genotypes from lower latitudes flowered earlier. Genotyping‐by‐sequencing of 9,658SNPs in 446 individuals revealed two major subpopulations ofM. polymorphain the native range, only one of which is present in the invaded range. Additionally, native range populations have higher genetic diversity than invaded range populations, suggesting that a genetic bottleneck occurred during invasion. All invaded range individuals are closely related to plants collected from native range populations in Portugal and southern Spain, and population assignment tests assigned invaded range individuals to this same narrow source region. Taken together, our results suggest that latitudinal clinal variation in flowering time has rapidly evolved across the invaded range despite a genetic bottleneck following introduction.

    

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3. Genomics reveal the origins and current structure of a genetically depauperate freshwater species in its introduced Alaskan range

   https://doi.org/10.1111/eva.13556  

   Campbell, Matthew A. ; Hale, Matthew C. ; Jalbert, Chase S. ; Dunker, Kristine ; Sepulveda, Adam J. ; López, J. Andrés ; Falke, Jeffrey A. ; Westley, Peter A. H. ( May 2023 , Evolutionary Applications)

   Invasive species are a major threat to global biodiversity, yet also represent large‐scale unplanned ecological and evolutionary experiments to address fundamental questions in nature. Here we analyzed both native and invasive populations of predatory northern pike (Esox lucius) to characterize landscape genetic variation, determine the most likely origins of introduced populations, and investigate a presumably postglacial population from Southeast Alaska of unclear provenance. Using a set of 4329 SNPs from 351 individual Alaskan northern pike representing the most widespread geographic sampling to date, our results confirm low levels of genetic diversity in native populations (average 𝝅 of 3.18 × 10⁻⁴) and even less in invasive populations (average 𝝅 of 2.68 × 10⁻⁴) consistent with bottleneck effects. Our analyses indicate that invasive northern pike likely came from multiple introductions from different native Alaskan populations and subsequently dispersed from original introduction sites. At the broadest scale, invasive populations appear to have been founded from two distinct regions of Alaska, indicative of two independent introduction events. Genetic admixture resulting from introductions from multiple source populations may have mitigated the negative effects associated with genetic bottlenecks in this species with naturally low levels of genetic diversity. Genomic signatures strongly suggest an excess of rare, population‐specific alleles, pointing to a small number of founding individuals in both native and introduced populations consistent with a species' life history of limited dispersal and gene flow. Lastly, the results strongly suggest that a small isolated population of pike, located in Southeast Alaska, is native in origin rather than stemming from a contemporary introduction event. Although theory predicts that lack of genetic variation may limit colonization success of novel environments, we detected no evidence that a lack of standing variation limited the success of this genetically depauperate apex predator.

    

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4. Tracking invasions of a destructive defoliator, the gypsy moth (Erebidae: Lymantria dispar ): Population structure, origin of intercepted specimens, and Asian introgression into North America

   https://doi.org/10.1111/eva.12962  

   Wu, Yunke ; Bogdanowicz, Steven M. ; Andres, Jose A. ; Vieira, Kendra A. ; Wang, Baode ; Cossé, Allard ; Pfister, Scott E. ( April 2020 , Evolutionary Applications)

   Genetic data can help elucidate the dynamics of biological invasions, which are fueled by the constant expansion of international trade. The introduction of European gypsy moth (Lymantria dispar dispar) into North America is a classic example of human‐aided invasion that has caused tremendous damage to North American temperate forests. Recently, the even more destructive Asian gypsy moth (mainlyL. d. asiaticaandL. d. japonica) has been intercepted in North America, mostly transported by cargo ships. To track invasion pathways, we developed a diagnostic panel of 60 DNA loci (55 nuclear and 5 mitochondrial) to characterize worldwide genetic differentiation withinL. disparand its sister speciesL. umbrosa. Hierarchical analyses supported strong differentiation and recovered five geographic groups that correspond to (1) North America, (2) Europe plus North Africa and Middle East, (3) the Urals, Central Asia, and Russian Siberia, (4) continental East Asia, and (5) the Japanese islands. Interestingly,L. umbrosawas grouped withL. d. japonica, and the introduced North American population exhibits remarkable distinctiveness from contemporary European counterparts. Each geographic group, except for North America, shows additional lower‐level structures when analyzed individually, which provided the basis for inference of the origin of invasive specimens. Two assignment approaches consistently identified a coastal area of continental East Asia as the major source for Asian invasion during 2014–2015, with Japan being another source. By analyzing simulation and laboratory crosses, we further provided evidence for the occurrence of natural Asian–North American hybrids in the Pacific Northwest, raising concerns for introgression of Asian alleles that may accelerate range expansion of gypsy moth in North America. Our study demonstrates how genetic data contribute to bio‐surveillance of invasive species with results that can inform regulatory management and reduce the frequency of trade‐associated invasions.

    

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5. Stronger evidence for genetic ancestry than environmental conditions in shaping the evolution of a complex signalling trait during biological invasion

   https://doi.org/10.1111/mec.17123  

   Pita‐Aquino, Jessica N. ; Bock, Dan G. ; Baeckens, Simon ; Losos, Jonathan B. ; Kolbe, Jason J. ( September 2023 , Molecular Ecology)

   Introductions of invasive species to new environments often result in rapid rates of trait evolution. While in some cases these evolutionary transitions are adaptive and driven by natural selection, they can also result from patterns of genetic and phenotypic variation associated with the invasion history. Here, we examined the brown anole (Anolis sagrei), a widespread invasive lizard for which genetic data have helped trace the sources of non‐native populations. We focused on the dewlap, a complex signalling trait known to be subject to multiple selective pressures. We measured dewlap reflectance, pattern and size in 30 non‐native populations across the southeastern United States. As well, we quantified environmental variables known to influence dewlap signal effectiveness, such as canopy openness. Further, we used genome‐wide data to estimate genetic ancestry, perform association mapping and test for signatures of selection. We found that among‐population variation in dewlap characteristics was best explained by genetic ancestry. This result was supported by genome‐wide association mapping, which identified several ancestry‐specific loci associated with dewlap traits. Despite the strong imprint of this aspect of the invasion history on dewlap variation, we also detected significant relationships between dewlap traits and local environmental conditions. However, we found limited evidence that dewlap‐associated genetic variants have been subject to selection. Our study emphasizes the importance of genetic ancestry and admixture in shaping phenotypes during biological invasion, while leaving the role of selection unresolved, likely due to the polygenic genetic architecture of dewlaps and selection acting on many genes of small effect.

    

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