Genome Analysis of Lagocephalus sceleratus: Unraveling the Genomic Landscape of a Successful Invader

The Tetraodontidae family encompasses several species which attract scientific interest in terms of their ecology and evolution. The silver-cheeked toadfish (Lagocephalus sceleratus) is a well-known “invasive sprinter” that has invaded and spread, in less than a decade, throughout the Eastern and part of the Western Mediterranean Sea from the Red Sea through the Suez Canal. In this study, we built and analysed the first near-chromosome level genome assembly of L. sceleratus and explored its evolutionary landscape. Through a phylogenomic analysis, we positioned L. sceleratus closer to T. nigroviridis, compared to other members of the family, while gene family evolution analysis revealed that genes associated with the immune response have experienced rapid expansion, providing a genetic basis for studying how L. sceleratus is able to achieve highly successful colonisation. Moreover, we found that voltage-gated sodium channel (NaV 1.4) mutations previously connected to tetrodotoxin resistance in other pufferfishes are not found in L. sceleratus, highlighting the complex evolution of this trait. The high-quality genome assembly built here is expected to set the ground for future studies on the species biology.

On the reproductive biology of the invasive Armoured Sailfin Catfish Pterygoplicthys pardalis (Castelnau, 1855) (Siluriformes: Loricariidae) from the natural drainages in Thiruvananthapuram, India

The present paper deals with the breeding biology of the invasive fish Pterygoplicthys pardalis from the natural drainages of Thiruvananthapuram, Kerala. The specimens were collected from Amayizhanchan Thodu, a natural drainage running through the heart of the city. A total of 145 males and 142 females were collected from January to December 2018. The sex ratio was determined monthly as the percentage of males to females (M: F). Monthly mean gonadosomatic index (GSI) values were compared using R stat, and GSI was plotted monthly to identify the spawning seasons. The gonads were examined and different stages of maturity were noted using standard methods. The length at first maturity was also found out. The fish exhibit courtship behaviour and the eggs are deposited in burrows and also along the crevices in the granite walls; the burrows are guarded by the male fish till the young ones are hatched out. The sex ratio showed an average mean value of 1.04: 1 and showed no significant departure. The size at first maturity was 23.9 cm standard length. The ova diameter studies show the presence of ripe ovaries throughout the year, with peaks during March and April and between August and September and in December, indicating the fish is a batch spawner. The absolute fecundity ranges from 923 to 14,777 eggs, and the relative fecundity ranges 0.0142–0.0015. Regression analysis showed a significant relationship (P <0.001) between absolute fecundity and the total length, the total body weight, and ovary weight. The strong breeding behaviour, the presence of accessory respiratory organs, the absence of natural enemies and parental care makes Pterygoplichthys pardalis a successful invader in the natural drainage. More biological studies are needed for the successful eradication of the species from the invaded ecosystem.

Invasion and Extirpation Potential of Native and Invasive Spartina Species Under Climate Change

Coastal areas host some of the planet’s most productive ecosystems, providing life-sustaining ecological services and several benefits to humankind, while also being some of the most threatened areas (e.g., by globalization, climate change, and biological invasion). Salt marshes are coastal habitats with a key role in food and shelter provisioning, sediment deposition, nutrient cycling and carbon storage. Spartina spp. is a genus of grass halophytes which occurs in salt marshes worldwide, and includes species with different invasive potential. We evaluated the effect of climate change in the distribution and invasion potential of five Spartina species (S. anglica, S. alterniflora, S. densiflora, S. patens, and S. maritima) at a global scale. Species distribution models (SDMs) were applied on species occurrence data and atmospheric environmental predictors (WorldClim 2.1) to project potential changes in habitat suitability and associated changes in distribution and species co-occurrence until the end of the century, across four Shared Socioeconomic Pathway scenarios (i.e., SSP1-2.6 to SSP5-8.5). Projections showed a global trend for increasing species co-occurrence, with a general range expansion potentiated by increasing pathway severity. This study suggests that Spartina species can potentially benefit from climate change, predicting poleward expansions in the Northern Hemisphere for most species, with results pointing at increased conflict and invasion potential in Northern Europe and East Asian shorelines, already under strong invasive pressure. S. anglica is projected to remain a successful invader, with more severe scenarios likely favoring greater expansions. S. alterniflora exhibits very low expansion comparatively, despite exhibiting the same northward distribution shift. SSP1-2.6 produced the smallest change to species co-occurrence, suggesting a smaller potential for invasion-related conflicts, although still registering a potential net expansion for the Genus. Despite their limitations, SDMs can help establish general trends in climate change ecology and inform policymakers and environmental agents to ensure the correct management of these habitats and, ultimately, ecosystems.

Genetic diversity and relatedness in aquaculture and marina populations of the invasive tunicate Didemnum vexillum in the British Isles

Introductions of invasive, non-native species in the marine environment are increasing as human activity within coastal areas rises. Genetic datasets are useful tools to identify source populations, track routes of invasions, and illuminate the role of genetic variation in the establishment and subsequent spread of novel introductions. Here, a microsatellite dataset is used to estimate the genetic diversity and population structure of 7 introduced Didemnum vexillum populations in Britain and Ireland, 4 of which are associated with aquaculture and 3 with marinas. Genetic differentiation observed between these populations indicates human-mediated transport as the main mechanism underlying the population structure of D. vexillum in Britain and Ireland. In addition to elucidating patterns of population structure we found that aquaculture sites showed significantly higher genetic diversity (measured as allelic richness) in comparison to the marina sites. We discuss these findings in relation to the history of each invasion, the complex life history of D. vexillum, and available evidence of the relative invasiveness of these populations. Our results show numerous interesting patterns which highlight further research avenues to elucidate the complex factors underlying the global spread of this successful invader.

Impatiens parviflora (small balsam).

I. parviflora is an exceptionally successful invader of many European countries. Its spread has been rapid, it is abundant in many parts of its exotic range and is one of few plants to successfully invade undisturbed forest vegetation. It is consequently regarded as undesirable by some, though there is little evidence of negative economic, social or environmental impacts. Further spread in central Europe is not likely as the species is already very abundant. In North America, on the other hand, it is still very localized. Even without clear evidence for impacts, a further spread there should not be encouraged by deliberate or careless transport of the species.

Lymantria dispar (gypsy moth).

The gypsy moth is likely to ultimately occupy virtually all portions of the temperate world where oaks and other suitable host plants occur. Consequently, the northern hemisphere is more at risk for establishment than the southern hemisphere though some suitable hosts do occur in these areas. The gypsy moth is apparently not able to persist in very cold (e.g. Finland) or warm (subtropical to tropical) regions. The gypsy moth is a 'proven' invader. The broad range of host plants that it utilizes (Liebhold et al. 1995), along with its high reproductive rate combine to make this insect a very successful invader of many types of forest and urban landscapes. Another characteristic that contributes to the gypsy moth's invasiveness is its propensity to be transported on human-made objects (e.g., egg masses can be laid on vehicles, logs, etc.). Perhaps the greatest limitation this species has as an invader is that females (of the European strain) are incapable of flight and this limits its rate of unassisted range expansion. However, as females of the Asian strain are capable of flight and all strains can lay their eggs on human-made objects, established populations are nevertheless able to spread.

Thermoregulation comparisons between a threatened native and an invasive lizard species

Lizard thermoregulation is costly and is largely behavioural. Podarcis raffonei, endemic of few islets of the Aeolian archipelago (southern Italy), is one of the most threatened lizards in Europe, its survival being under threat also due to the presence of the congeneric P. siculus, a successful invader characterised by behavioural plasticity and effectiveness and precision at regulating body temperature (Tb). We tested whether thermoregulation behaviour diverges between the two species by analysing (i) the heating rates under a standard thermal condition, and (ii) the temperature at which lizards ended basking (Tfinal) along a thermal gradient. Overall, we found behavioural differences between the two lizards (i.e. P. siculus exhibited lower Tfinal), although both species had comparable heating rates and thermoregulated in the same thermal conditions. The invasive P. siculus had lower Tfinal and, since heating rates were similar between species, it expended less time basking than native P. raffonei. We speculate that the observed thermal ecology differences could provide a selective advantage to P. siculus in the harsh island environment.

Setaria verticillata (bristly foxtail).

S. verticillata is listed by Holm et al. (1979) as a 'serious' or 'principal' weed in 11 countries in Europe, Asia, Africa, South America and the Pacific. From its origins in Europe and perhaps Africa, it has been accidentally introduced to many other countries across the world. It is often listed as one of the two or three most important weeds in a wide range of crops, within and outside its native range, and it can also become dominant in grassland. The combination of ready dispersal by its 'sticky' seed and seed-heads, and its C4 physiology and rapid growth make it an extremely successful invader. It adapts to local conditions rapidly and has developed resistance to atrazine and other herbicides.

Megathyrsus maximus (Guinea grass).

M. maximus is a highly successful invader in tropical and warm temperate areas after introduction as fodder. It can spread from seed, is highly competitive with native flora, and while it is highly fire resistant it can quickly spread to invade gaps left in natural vegetation after fire.