Evolution: sperm, cryptic choice, and the origin of species

Genome-Scale Phylogenetic and Population Genetic Studies Provide Insight Into Introgression and Adaptive Evolution of Takifugu Species in East Asia

As a typical marine adaptive radiation species, most Takifugu species are widely distributed in East Asian offshore, which have diversified morphological characteristics and different ecological habits. The phylogenetic relationship and population structure of the Takifugu species was complicated because of incomplete lineage sorting, widespread hybridization and introgression. Therefore, to systematically clarify the phylogenetic relationships of Takifugu genus, explore the introgression and natural hybridization between different Takifugu species, and detect the selective signatures in the adaptive evolution of diversified traits, whole-genome resequencing was used in 122 Takifugu samples from 10 species. Phylogenetic analysis showed solid sister-group relationships between Takifugu bimaculatus and Takifugu flavidus, Takifugu oblongus, and Takifugu niphobles, Takifugu rubripes, and Takifugu obscurus, Takifugu xanthoptreus, and Takifugu ocellatus. Further admixture analysis indicated the divergence of T. obscurus population and the bidirectional gene flow between T. bimaculatus and T. flavidus. Using species-specific homozygous genetic variance sites, we detected the asymmetric introgression between T. bimaculatus and T. flavidus at China East sea and southern Taiwan Strait. By genome-scale genetic diversity scanning, we detected two copies of syt1, zar1 and tgfbr1 related to the semilunar reproduction rhythm in T. niphobles, involved in memory formation, embryo maturation and female reproduction. Furthermore, we also found lots of T. niphobles specific mutations in CDS region of circadian rhythm related genes and endocrine hormone genes. For Takifugu species, our research provides reliable genetic resources and results for the phylogeny, introgression, hybridization and adaptive evolution, and could be used as a guide for the formulation of the protection and proliferation release policies.

Evolution of the elaborate male intromittent organ of Xiphophorus fishes

Internally fertilizing animals show a remarkable diversity in male genital morphology that is associated with sexual selection, and these traits are thought to be evolving particularly rapidly. Male fish in some internally fertilizing species have "gonopodia," highly modified anal fins that are putatively important for sexual selection. However, our understanding of the evolution of genital diversity remains incomplete. Contrary to the prediction that male genital traits evolve more rapidly than other traits, here we show that gonopodial traits and other nongonopodial traits exhibit similar evolutionary rates of trait change and also follow similar evolutionary models in an iconic genus of poeciliid fish (Xiphophorus spp.). Furthermore, we find that both mating and nonmating natural selection mechanisms are unlikely to be driving the diverse Xiphophorus gonopodial morphology. Putative holdfast features of the male genital organ do not appear to be influenced by water flow, a candidate selective force in aquatic habitats. Additionally, interspecific divergence in gonopodial morphology is not significantly higher between sympatric species, than between allopatric species, suggesting that male genitals have not undergone reproductive character displacement. Slower rates of evolution in gonopodial traits compared with a subset of putatively sexually selected nongenital traits suggest that different selection mechanisms may be acting on the different trait types. Further investigations of this elaborate trait are imperative to determine whether it is ultimately an important driver of speciation.