The selective constraints of ecological specialization in mustelidae on mitochondrial genomes

Effect of locomotor preference on the evolution of mitochondrial genes in Bovidae

Locomotor preferences and habitat types may drive animal evolution. In this study, we speculated that locomotor preference and habitat type may have diverse influences on Bovidae mitochondrial genes. We used selection pressure and statistical analysis to explore the evolution of mitochondrial DNA (mtDNA) protein-coding genes (PCGs) from diverse locomotor preferences and habitat types. Our study demonstrates that locomotor preference (energy demand) drives the evolution of Bovidae in mtDNA PCGs. The habitat types had no significant effect on the rate of evolution in Bovidae mitochondrial genes. Our study provides deep insight into the adaptation of Bovidae.

Different Evolutionary Trends of Galloanseres: Mitogenomics Analysis

The two existing clades of Galloanseres, orders Galliformes (landfowl) and Anseriformes (waterfowl), exhibit dramatically different evolutionary trends. Mitochondria serve as primary sites for energy production in organisms, and numerous studies have revealed their role in biological evolution and ecological adaptation. We assembled the complete mitogenome sequences of two species of the genus Aythya within Anseriformes: Aythya baeri and Aythya marila. A phylogenetic tree was constructed for 142 species within Galloanseres, and their divergence times were inferred. The divergence between Galliformes and Anseriformes occurred ~79.62 million years ago (Mya), followed by rapid evolution and diversification after the Middle Miocene (~13.82 Mya). The analysis of selective pressure indicated that the mitochondrial protein-coding genes (PCGs) of Galloanseres species have predominantly undergone purifying selection. The free-ratio model revealed that the evolutionary rates of COX1 and COX3 were lower than those of the other PCGs, whereas ND2 and ND6 had faster evolutionary rates. The CmC model also indicated that most PCGs in Anseriformes exhibited stronger selective constraints. Our study suggests that the distinct evolutionary trends and energy requirements of Galliformes and Anseriformes drive different evolutionary patterns in the mitogenome.

Mitochondrial Genomic Evidence of Selective Constraints in Small-Bodied Terrestrial Cetartiodactyla

Body size may drive the molecular evolution of mitochondrial genes in response to changes in energy requirements across species of different sizes. In this study, we perform selection pressure analysis and phylogenetic independent contrasts (PIC) to investigate the association between molecular evolution of mitochondrial genome protein-coding genes (mtDNA PCGs) and body size in terrestrial Cetartiodactyla. Employing selection pressure analysis, we observe that the average non-synonymous/synonymous substitution rate ratio (ω) of mtDNA PCGs is significantly reduced in small-bodied species relative to their medium and large counterparts. PIC analysis further confirms that ω values are positively correlated with body size (R2 = 0.162, p = 0.0016). Our results suggest that mtDNA PCGs of small-bodied species experience much stronger purifying selection as they need to maintain a heightened metabolic rate. On the other hand, larger-bodied species may face less stringent selective pressures on their mtDNA PCGs, potentially due to reduced relative energy expenditure per unit mass. Furthermore, we identify several genes that undergo positive selection, possibly linked to species adaptation to specific environments. Therefore, despite purifying selection being the predominant force in the evolution of mtDNA PCGs, positive selection can also occur during the process of adaptive evolution.

Analysis of the Complete Mitochondrial Genome of Pteronura brasiliensis and Lontra canadensis

P. brasiliensis and L. canadensis are two otter species, which successfully occupied semi-aquatic habitats and diverged from other Mustelidae. Herein, the full-length mitochondrial genome sequences were constructed for these two otter species for the first time. Comparative mitochondrial genome, selection pressure, and phylogenetic independent contrasts (PICs) analyses were conducted to determine the structure and evolutionary characteristics of their mitochondrial genomes. Phylogenetic analyses were also conducted to confirm these two otter species' phylogenetic position. The results demonstrated that the mitochondrial genome structure of P. brasiliensis and L. canadensis were consistent across Mustelidae. However, selection pressure analyses demonstrated that the evolutionary rates of mitochondrial genome protein-coding genes (PCGs) ND1, ND4, and ND4L were higher in otters than in terrestrial Mustelidae, whereas the evolutionary rates of ND2, ND6, and COX1 were lower in otters. Additionally, PIC analysis demonstrated that the evolutionary rates of ND2, ND4, and ND4L markedly correlated with a niche type. Phylogenetic analysis showed that P. brasiliensis is situated at the base of the evolutionary tree of otters, and then L. canadensis diverged from it. This study suggests a divergent evolutionary pattern of Mustelidae mitochondrial genome PCGs, prompting the otters' adaptation to semi-aquatic habitats.

The mitochondrial genome of the mountain wooly tapir, Tapirus pinchaque and a formal test of the effect of altitude on the adaptive evolution of mitochondrial protein coding genes in odd-toed ungulates

BACKGROUND

The harsh conditions of high-altitude environments are known to drive the evolution of physiological and morphological traits in endothermic animals. These conditions are expected to result in the adaptive evolution of protein coding genes encoded in mitochondrial genomes that are vital for the oxidative phosphorylation pathway. In this study, we formally tested for signatures of adaptive evolution on mitochondrial protein coding genes in Tapirus pinchaque and other odd-toed ungulates inhabiting high-elevation environments.

RESULTS

The AT-rich mitochondrial genome of T. pinchaque is 16,750 bp long. A phylomitogenomic analysis supports the monophyly of the genus Tapirus and families in the Perissodactyla. The ratio of non-synonymous to synonymous substitutions demonstrated that all mitochondrial genes undergo purifying selection in T. pinchaque and other odd ungulates living at high elevations. Over this negative background selection, Branch Models suggested that cox3 and nad6 might be undergoing stronger purifying selection than other mitochondrial protein coding genes. Furthermore, Site Models suggested that one and four sites in nad2 and nad5, respectively, could be experiencing positive selection. However, these results were supported by Likelihood Ratio Tests but not Bayesian Empirical Bayes posterior probabilities. Additional analyses (in DataMonkey) indicated a relaxation of selection strength in nad6, evidence of episodic diversifying selection in cob, and revealed episodic positive/diversifying selection signatures for two sites in nad1, and one site each in nad2 and nad4.

CONCLUSION

The mitochondrial genome of T. pinchaque is an important genomic resource for conservation of this species and this study contributes to the understanding of adaptive evolution of mitochondrial protein coding genes in odd-toed ungulates inhabiting high-altitude environments.

Genetic Drift and Purifying Selection Shaped Mitochondrial Genome Variation in the High Royal Jelly-Producing Honeybee Strain (Apis mellifera ligustica)

Mitochondrial genomes (mitogenomes) are involved in cellular energy metabolism and have been shown to undergo adaptive evolution in organisms with increased energy-consuming activities. The genetically selected high royal jelly-producing bees (RJBs, Apis mellifera ligustica) in China can produce 10 times more royal jelly, a highly nutritional and functional food, relative to unselected Italian bees (ITBs). To test for potential adaptive evolution of RJB mitochondrial genes, we sequenced mitogenomes from 100 RJBs and 30 ITBs. Haplotype network and phylogenetic analysis indicate that RJBs and ITBs are not reciprocally monophyletic but mainly divided into the RJB- and ITB-dominant sublineages. The RJB-dominant sublineage proportion is 6-fold higher in RJBs (84/100) than in ITBs (4/30), which is mainly attributable to genetic drift rather than positive selection. The RJB-dominant sublineage exhibits a low genetic diversity due to purifying selection. Moreover, mitogenome abundance is not significantly different between RJBs and ITBs, thereby rejecting the association between mitogenome copy number and royal jelly-producing performance. Our findings demonstrate low genetic diversity levels of RJB mitogenomes and reveal genetic drift and purifying selection as potential forces driving RJB mitogenome evolution.

High-altitude adaptation in vertebrates as revealed by mitochondrial genome analyses

The high-altitude environment may drive vertebrate evolution in a certain way, and vertebrates living in different altitude environments might have different energy requirements. We hypothesized that the high-altitude environment might impose different influences on vertebrate mitochondrial genomes (mtDNA). We used selection pressure analyses and PIC (phylogenetic independent contrasts) analysis to detect the evolutionary rate of vertebrate mtDNA protein-coding genes (PCGs) from different altitudes. The results showed that the ratio of nonsynonymous/synonymous substitutions (dN/dS) in the mtDNA PCGs was significantly higher in high-altitude vertebrates than in low-altitude vertebrates. The seven rapidly evolving genes were shared by the high-altitude vertebrates, and only one positive selection gene (ND5 gene) was detected in the high-altitude vertebrates. Our results suggest the mtDNA evolutionary rate in high-altitude vertebrates was higher than in low-altitude vertebrates as their evolution requires more energy in a high-altitude environment. Our study demonstrates the high-altitude environment (low atmospheric O2 levels) drives vertebrate evolution in mtDNA PCGs.

FGF gene family characterization provides insights into its adaptive evolution in Carnivora

Fibroblast growth factors (FGFs) encoded by the FGF gene family can regulate development and physiology in animals. However, their evolutionary characteristics in Carnivora are largely unknown. In this study, we identified 660 sequences of three types of FGF genes from 30 unannotated genomes of Carnivora animals (before 7th May 2020), and the FGF genes from 52 Carnivora species were analyzed through the method of comparative genomics. Phylogenetic and selective pressure analyses were carried out based on the FGF genes of these 52 Carnivora species. The phylogenetic analysis results demonstrated that the FGF gene family was divided into 10 subfamilies and that FGF5 formed one clade rather than belonging to the subfamilies of FGF4 and FGF6. The evolutionary analysis results showed that the FGF genes were prominently subjected to purifying selection and were highly conserved in the process of Carnivora evolution. We also carried out phylogenetic comparative analyses, which indicated that the habitat was one of the factors that shaped the evolution of Carnivora FGF genes. The FGF1 and FGF6 genes were positively selected in the Carnivora animals, and positive selection signals were detected for the FGF19 gene in semiaquatic Carnivora animals. In summary, we clarified the phylogenetic and evolutionary characteristics of Carnivora FGF genes and provided valuable data for future studies on evolutionary characterization of Carnivora animals.