Genomics-informed models reveal extensive stretches of coastline under threat by an ecologically dominant invasive species.

Explaining why some species are widespread, while others are not, is fundamental to biogeography, ecology, and evolutionary biology. A unique way to study evolutionary and ecological mechanisms that either limit species' spread or facilitate range expansions is to conduct research on species that have restricted distributions. Nonindigenous species, particularly those that are highly invasive but have not yet spread beyond the introduced site, represent ideal systems to study range size changes. Here, we used species distribution modeling and genomic data to study the restricted range of a highly invasive Australian marine species, the ascidian Pyura praeputialis This species is an aggressive space occupier in its introduced range (Chile), where it has fundamentally altered the coastal community. We found high genomic diversity in Chile, indicating high adaptive potential. In addition, genomic data clearly showed that a single region from Australia was the only donor of genotypes to the introduced range. We identified over 3,500 km of suitable habitat adjacent to its current introduced range that has so far not been occupied, and importantly species distribution models were only accurate when genomic data were considered. Our results suggest that a slight change in currents, or a change in shipping routes, may lead to an expansion of the species' introduced range that will encompass a vast portion of the South American coast. Our study shows how the use of population genomics and species distribution modeling in combination can unravel mechanisms shaping range sizes and forecast future range shifts of invasive species.

Contemporary climate change hinders hybrid performance of ecologically dominant marine invertebrates.

Human activities alter patterns of biodiversity, particularly through species extinctions and range shifts. Two of these activities are human mediated transfer of species and contemporary climate change, and both allow previously isolated genotypes to come into contact and hybridize, potentially altering speciation rates. Hybrids have been shown to survive environmental conditions not tolerated by either parent, suggesting that, under some circumstances, hybrids may be able to expand their ranges and perform well under rapidly changing conditions. However, studies assessing how hybridization influences contemporary range shifts are scarce. We performed crosses on Pyura herdmani and Pyura stolonifera (Chordata, Tunicata), two closely related marine invertebrate species that are ecologically dominant and can hybridize. These sister species live in sympatry along the coasts of southern Africa, but one has a disjunct distribution that includes northern hemisphere sites. We experimentally assessed the performance of hybrid and parental crosses using different temperature regimes, including temperatures predicted under future climate change scenarios. We found that hybrids showed lower performance than parental crosses at the experimental temperatures, suggesting that hybrids are unlikely to expand their ranges to new environments. In turn, we found that the more widespread species performed better at a wide array of temperatures, indicating that this parental species may cope better with future conditions. This study illustrates how offspring fitness may provide key insights to predict range expansions and how contemporary climate change may mediate both the ability of hybrids to expand their ranges and the occurrence of speciation as a result of hybridization.

Anthropogenic transport of species across native ranges: unpredictable genetic and evolutionary consequences.

Human activities are responsible for the translocation of vast amounts of organisms, altering natural patterns of dispersal and gene flow. Most research to date has focused on the consequences of anthropogenic transportation of non-indigenous species within introduced ranges, with little research focusing on native species. Here, we compared genetic patterns of the sessile marine invertebrate, Ciona intestinalis, which has highly restricted dispersal capabilities. We collected individuals in a region of the species' native range where human activities that are known to facilitate the artificial spread of species are prevalent. Using microsatellite markers, we revealed highly dissimilar outcomes. First, we found low levels of genetic differentiation among sites separated by both short and large geographical distances, indicating the presence of anthropogenic transport of genotypes, and little influence of natural geographical barriers. Second, we found significant genetic differentiation in pairwise comparisons among certain sites, suggesting that other factors besides artificial transport (e.g. natural dispersal, premodern population structure) may be shaping genetic patterns. Taken together, we found dissimilar patterns of population structure in a highly urbanized region that could not be predicted by artificial transport alone. We conclude that anthropogenic activities alter genetic composition of native ranges, with unknown consequences for species' evolutionary trajectories.

Secondary contacts and genetic admixture shape colonization by an amphiatlantic epibenthic invertebrate.

Research on the genetics of invasive species often focuses on patterns of genetic diversity and population structure within the introduced range. However, a growing body of literature is demonstrating the need to study how native genotypes affect both ecological and evolutionary mechanisms within the introduced range. Here, we used genotyping-by-sequencing to study both native and introduced ranges of the amphiatlantic marine invertebrate Ciona intestinalis. A previous study using microsatellites analysed samples collected along the Swedish west coast and showed the presence of genetically distinct lineages in deep and shallow waters. Using 1,653 single nucleotide polymorphisms (SNPs) from newly collected samples (285 individuals), we first confirmed the presence of this depth-defined genomic divergence along the Swedish coast. We then used approximate Bayesian computation to infer the historical relationship among sites from the North Sea, the English Channel and the northwest Atlantic and found evidence of ancestral divergence between individuals from deep waters off Sweden and individuals from the English Channel. This divergence was followed by a secondary contact that led to a genetic admixture between the ancestral populations (i.e., deep Sweden and English Channel), which originated the genotypes found in shallow Sweden. We then revealed that the colonization of C. intestinalis in the northwest Atlantic was as a result of an admixture between shallow Sweden and the English Channel genotypes across the introduced range. Our results showed the presence of both past and recent genetic admixture events that together may have promoted the successful colonizations of C. intestinalis. Our study suggests that secondary contacts potentially reshape the evolutionary trajectories of invasive species through the promotion of intraspecific hybridization and by altering both colonization patterns and their ecological effects in the introduced range.

Ultrasonic call characteristics of rat pups are altered following prenatal malnutrition.

The male offspring of rats provided with a protein deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy were subjected to a brief period of isolation and cooling at postnatal Days (P)7, 9, and 11, and their ultrasonic vocalizations were compared with those of well-nourished pups. Calls were categorized into 12 different types based upon their sonographic patterns. Although call rates were equal, the call characteristics of the prenatally malnourished pups differed significantly from those of well-nourished controls. At P7, their mean peak sound frequency (irrespective of call type) was significantly higher, and constant frequency calls were of both higher frequency and longer duration. Over the age range studied, prenatally malnourished pups emitted a smaller variety of calls, with significantly fewer ascending frequency vocalizations while producing either significantly fewer (P9) or greater (P11) descending frequency calls. Altered crying patterns have been related to brain damage in human babies, with more abnormal cries being associated with more severe neurological impairment. Therefore, the present results most likely reflect altered central nervous system development and function. Ultrasonic vocalization characteristics in rat pups may provide a useful early marker of the severity of disturbance to the development of the central nervous system following an insult, and offer the potential for predicting the degree of functional and behavioral deficits later in life.