Reticulate evolution in Conidae: Evidence of nuclear and mitochondrial introgression

The role of Pleistocene dispersal in shaping species richness of sky island wintergreens from the Himalaya-Hengduan Mountains

In addition to topography and climate, biogeographic dispersal has been considered to influence plant diversity in the Himalaya-Hengduan Mountains (HHM), yet, the mode and tempo of sky island dispersal and its influence on species richness has been little explored. Through phylogenetic analysis of Gaultheria ser. Trichophyllae, a sky island alpine clade within the HHM, we test the hypothesis that dispersal has affected current local species richness. We inferred the dynamics of biogeographic dispersal with correlation tests on direction, distance, occurrence time, and regional species richness. We found that G. ser. Trichophyllae originated at the end of the Miocene and mostly dispersed toward higher longitudes (eastward). In particular, shorter intra-regional eastward dispersals and longer inter-regional westward dispersals were most frequently observed. We detected a prevalence of eastward intra-region dispersals in both glacial periods and interglacials. These dispersals may have been facilitated by the reorganization of paleo-drainages and monsoon intensification through time. We suggest that the timing of dispersal corresponding to glacial periods and the prevalence of intra-region dispersal, rather than dispersal frequency, most influenced the pattern of species richness of G. ser. Trichophyllae. This study facilitates a more comprehensive understanding of biodiversity in the sky islands within the HHM.

Systematic dissection of genomic features determining the vast diversity of conotoxins

BACKGROUND

Conus, a highly diverse species of venomous predators, has attracted significant attention in neuroscience and new drug development due to their rich collection of neuroactive peptides called conotoxins. Recent advancements in transcriptome, proteome, and genome analyses have facilitated the identification of conotoxins within Conus' venom glands, providing insights into the genetic features and evolutionary patterns of conotoxin genes. However, the underlying mechanism behind the extraordinary hypervariability of conotoxins remains largely unknown.

RESULTS

We analyzed the transcriptomes of 34 Conus species, examining various tissues such as the venom duct, venom bulb, and salivary gland, leading to the identification of conotoxin genes. Genetic variation analysis revealed that a subset of these genes (15.78% of the total) in Conus species underwent positive selection (Ka/Ks > 1, p < 0.01). Additionally, we reassembled and annotated the genome of C. betulinus, uncovering 221 conotoxin-encoding genes. These genes primarily consisted of three exons, with a significant portion showing high transcriptional activity in the venom ducts. Importantly, the flanking regions and adjacent introns of conotoxin genes exhibited a higher prevalence of transposon elements, suggesting their potential contribution to the extensive variability observed in conotoxins. Furthermore, we detected genome duplication in C. betulinus, which likely contributed to the expansion of conotoxin gene numbers. Interestingly, our study also provided evidence of introgression among Conus species, indicating that interspecies hybridization may have played a role in shaping the evolution of diverse conotoxin genes.

CONCLUSIONS

This study highlights the impact of adaptive evolution and introgressive hybridization on the genetic diversity of conotoxin genes and the evolution of Conus. We also propose a hypothesis suggesting that transposable elements might significantly contribute to the remarkable diversity observed in conotoxins. These findings not only enhance our understanding of peptide genetic diversity but also present a novel approach for peptide bioengineering.

Hidden species diversity and mito-nuclear discordance within the Mediterranean cone snail, Lautoconus ventricosus

The Mediterranean cone snail, Lautoconus ventricosus, is currently considered a single species inhabiting the whole Mediterranean basin and the adjacent Atlantic coasts. Yet, no population genetic study has assessed its taxonomic status. Here, we collected 245 individuals from 75 localities throughout the Mediterranean Sea and used cox1 barcodes, complete mitochondrial genomes, and genome skims to test whether L. ventricosus represents a complex of cryptic species. The maximum likelihood phylogeny based on complete mitochondrial genomes recovered six main clades (hereby named blue, brown, green, orange, red, and violet) with sufficient sequence divergence to be considered putative species. On the other hand, phylogenomic analyses based on 437 nuclear genes only recovered four out of the six clades: blue and orange clades were thoroughly mixed and the brown one was not recovered. This mito-nuclear discordance revealed instances of incomplete lineage sorting and introgression, and may have caused important differences in the dating of main cladogenetic events. Species delimitation tests proposed the existence of at least three species: green, violet, and red+blue+orange (i.e., cyan). Green plus cyan (with sympatric distributions) and violet, had West and East Mediterranean distributions, respectively, mostly separated by the Siculo-Tunisian biogeographical barrier. Morphometric analyses of the shell using species hypotheses as factor and shell length as covariate showed that the discrimination power of the studied parameters was only 70.2%, reinforcing the cryptic nature of the uncovered species, and the importance of integrative taxonomic approaches considering morphology, ecology, biogeography, and mitochondrial and nuclear population genetic variation.

Comparative Venomics of C. flavidus and C. frigidus and Closely Related Vermivorous Cone Snails

Cone snail venom biodiversity reflects dietary preference and predatory and defensive envenomation strategies across the ≈900 species of Conidae. To better understand the mechanisms of adaptive radiations in closely related species, we investigated the venom of two phylogenetically and spatially related species, C. flavidus and C. frigidus of the Virgiconus clade. Transcriptomic analysis revealed that the major superfamily profiles were conserved between the two species, including 68 shared conotoxin transcripts. These shared transcripts contributed 90% of the conotoxin expression in C. frigidus and only 49% in C. flavidus, which showed greater toxin diversification in the dominant O1, I2, A, O2, O3, and M superfamilies compared to C. frigidus. On the basis of morphology, two additional sub-groups closely resembling C. flavidus were also identified from One Tree Island Reef. Despite the morphological resemblance, the venom duct proteomes of these cryptic sub-groups were distinct from C. flavidus. We suggest rapid conotoxin sequence divergence may have facilitated adaptive radiation and the establishment of new species and the regulatory mechanisms facilitating species-specific venom evolution.

Comparative Venomics of the Cryptic Cone Snail Species Virroconus ebraeus and Virroconus judaeus

The venom duct transcriptomes and proteomes of the cryptic cone snail species Virroconus ebraeus and Virroconus judaeus were obtained and compared. The most abundant and shared conotoxin precursor superfamilies in both species were M, O1, and O2. Additionally, three new putative conotoxin precursor superfamilies (Virro01-03) with cysteine pattern types VI/VII and XVI were identified. The most expressed conotoxin precursor superfamilies were SF-mi2 and M in V. ebraeus, and Cerm03 and M in V. judaeus. Up to 16 conotoxin precursor superfamilies and hormones were differentially expressed between both species, and clustered into two distinct sets, which could represent adaptations of each species to different diets. Finally, we predicted, with machine learning algorithms, the 3D structure model of selected venom proteins including the differentially expressed Cerm03 and SF-mi2, an insulin type 3, a Gastridium geographus GVIA-like conotoxin, and an ortholog to the Pionoconus magus ω-conotoxin MVIIA (Ziconotide).