Founding populations of non-native species typically contain a small subset of their home range populations, exhibiting a reduced subset of their genetic diversity. Many of these non-native species predominantly, or even solely, engage in asexual reproduction, but it is unclear whether asexual reproduction is linked with species invasion. We used a systematic review of peer-reviewed literature to investigate whether species with reproductive polymorphisms are more often asexual in their invaded than native range. We also investigated whether genetic diversity was higher in home than invaded ranges. We found 219 relevant studies, and those showed that asexual reproduction is three times more common in invaded than home ranges, and higher genetic diversity is 20 times more common in home than invaded ranges for these organisms (this difference highest in the more recently introduced species). Hence, asexual reproduction appears associated with species invasion. Whereas asexual reproduction lacks the genetic mixing needed to respond to heterogenous environments and natural enemies, it confers several advantages for small founding populations, including the ability to establish new populations from a single or very few founding members with no requirement for finding a mating partner or pollinator, and asexual species invasion often brings relatively low intraspecific competition (allowing monoculture domination). For non-native species, high phenotypic plasticity and a lack of natural enemies may offset the disadvantages of asexual reproduction, leading to enhanced success for asexual non-native plants and animals.
File name: Data.csv
Variables:
Ident = identifying line
Confidence = weighted confidence level (0 = not appropriate for the review; 1 = requires some inference to meet review objectives; 2 = mostly meets review objectives and 3 = meets review objectives)
Common = common name
Scientific = scientific name
First.report = first reported as an invader
Type = type of organism (Plant, invertebrate, fish, mammal, pathogen, other)
Invaded.rage = invaded range Origin.range = range of origin Origin = data for home or invaded range populations Reproduction = mode (asexual, sexual, both)
Higher.genetic = in which population (home or invaded) is genetic diversity higher (1,0) Polyploid = are they reported as polyploid?
Data.set = systematic review, 100 worst invaders or both
Missing data: NA
We followed the recommendations for reporting items for systematic review as outlined by Moher et al. (2009). We generated a list of peer-reviewed journal articles that reported results for asexual reproduction in non-native species using the search terms “non-native” or “invasive” with “asexual”, “apomixis,” “cleistogamy,” “self-fertilization,” “clone” or “parthenogenesis” in September-December 2020. We did not place date or language restrictions. We used the default search engine settings for the Science Citation Index Expanded (1970-present) but excluded the Social Sciences and Arts & Humanities citation indices. We also refined the search by “article.” We removed 70 results that were replicates between search terms. The search produced a master list of 409 articles. Graduate students (at least two students per article) examined each journal article and screened out reviews, meta-analyses, simulations, non-English papers, and papers with multiple species, leaving 132 papers for analysis. We note that, beyond initial training, the graduate students assessed the applicability of the reviewed articles independent of the authors of this review. We also note that more recent treatments often separate “non-native” and “invasive” descriptors but, as this review spans the transition in terminology, we included both terms as search items.
Given that a search directed toward asexual reproduction in non-native species risked overestimating asexuality in non-native species, we attempted to ameliorate this prejudice by using an independent compendium of species that focused on non-native status only, and then we investigated sexual polymorphism in all species on that list. We used the species list from the “100 of the worst invasive species” list (Lowe et al. 2004), which generated 98 additional records (we excluded two viruses). There were 13 species in common between the first “asexual” and second “worst” searches, leaving a total of 219 species records in the merged data set
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We categorized each species as fish, invertebrate, mammal, pathogen, plant, or ‘other.’ Fungi, herpetofauna, and birds were placed in the ‘other’ category as each was found in < 5 papers (n = 11 total), which was considered too few for meaningful interpretation. We also used these data to further investigate the literature for differences in genetic diversity between home and invaded ranges and whether the species was reported as being polyploid, but we did not assess the individual metrics of genetic diversity used in each paper – which might add error as the method of assessment could result in different predictions.
