Discovery of Novel Viruses Associated With the Invasive Cane Toad (Rhinella marina) in Its Native and Introduced Ranges

Cane toads (Rhinella marina) are notoriously successful invaders: from 101 individuals brought to Australia in 1935, poisonous toads now cover an area >1.2 million km2 with adverse effects on native fauna. Despite extensive research on the role of macroparasites in cane toad invasion, viral research is lagging. We compared viral prevalence and diversity between toads in their native range (French Guiana, n=25) and two introduced ranges: Australia (n=151) and Hawai’i (n=10) with a metatranscriptomic and metagenomic approach combined with PCR screening. Australian toads almost exclusively harbor one of seven viruses detected globally. Rhimavirus-A (Picornaviridae) exhibited low genetic diversity and likely actively infected 9% of sampled Australian toads extending across ~2,000km of Northern Australia and up to the current invasion front. In native range cane toads, we identified multiple phylogenetically distinct viruses (Iridoviridae, Picornaviridae, Papillomaviridae, and Nackedna-like virus). None of the same viruses was detected in both ranges, suggesting that Australian cane toads have largely escaped the viral infection experienced by their native range counterparts. The novel native range viruses described here are potential biocontrol agents, as Australian toads likely lack prior immunological exposure to these viruses. Overall, our evidence suggests that there may be differences between viruses infecting cane toads in their native vs. introduced ranges, which lays the groundwork for further studies on how these viruses have influenced the toads’ invasion history.

Development of a Set of Microsatellite Markers to Investigate Sexually Antagonistic Selection in the Invasive Ant Nylanderia fulva

Sexually antagonistic selection (SAS) occurs when distinct alleles are differentially selected in each sex. In the invasive tawny crazy ant, Nylanderia fulva, a genomic region is under SAS, while the rest of the genome is randomly selected in males and females. In this study, we designed a suite of 15 microsatellite markers to study the origin and evolution of SAS in N. fulva. These SAS markers were polymorphic, with allelic frequencies that are highly different between males and females. All haploid males carry only a subset of the alleles present in the population, while females are reliably heterozygous, with one allele from the male gene pool and a different allele inherited from their mother. In addition, we identified six polymorphic markers not associated with SAS and six markers yielding consistent, yet monomorphic, amplification in the introduced range of this species. Reaction condition optimizations allowed all retained markers to be co-amplified in four PCR mixes. The SAS markers may be used to test for the strength and the extent of the genomic regions under SAS in both the native and introduced ranges of N. fulva, while the set of non-SAS loci may be used to assess the invasion route of this species. Overall, the application of these microsatellite markers will yield insights into the origin and evolution of SAS within and among species of the genus Nylanderia.

Quo vadis? Historical distribution and impact of climate change on the worldwide distribution of the Australasian fungus Clathrus archeri (Phallales, Basidiomycota)

Clathrus archeri is a fungus native to Australia and New Zealand that has started to expand into Europe, and it is considered a potentially invasive species. In this study, we examine the historical occurrence, current geographical range and potential future changes in the distribution of C. archeri using worldwide distribution data. Ecological modelling was used to assess the locations of the potential climatic niches of C. archeri within both its native and introduced ranges in the past, present and future. Our study clearly shows that the coverage of suitable habitats of this fungus has decreased since the last glacial maximum, and anthropogenic climate changes are accelerating the process of niche loss. The highest rate of C. archeri range contraction is expected in Australia, where the fungus should be considered a threatened species in the future. Highly valuable habitats will be available in Tasmania and New Zealand. However, a significant expansion rate of C. archeri will still probably be observed in Europe, where the climatic conditions preferred by the fungus will allow its quick expansion northeast into the continent.

The unreliable concept of native range as applied to the distribution of the rusty crayfish (Faxonius rusticus) in North America

The concept of native range in invasion biology is difficult to define since, in many cases, this type of range is unknown and cannot be determined. We investigate the uncertainties related to this concept by focusing on the distribution of Faxonius rusticus (Girard, 1852), also known as the rusty crayfish, which is perceived as possibly the worst invasive crayfish species in North America. In this study, we undertake a comprehensive literature review, which includes 430 studies published between 1852 and 2018, in order to analyze the native and introduced ranges of this species. The rusty crayfish was reported to occur in 33 states in the U.S.A. and 3 Canadian Provinces. Ten of these U.S. states and one Canadian Province have been included multiple times in both the native and the non-native ranges of this crayfish. The confusion regarding the limits and history of the native range of the rusty crayfish has implications for the conservation of this species in various jurisdictions. This review also demonstrates that even for intensely studied species perceived as invasive, we often do not have a clear understanding of essential concepts such as native and non-native range.