BMC Ecology and Evolution

The remarkable structural and functional diversity of the avian bill serves as an ideal system to understand how ecological and environmental factors influence morphological diversification under physically demanding tasks. For example, in cavity-excavating birds where the bill experiences tremendous physical stresses, climate and habitat affect the mechanical properties of available nesting substrates and therefore can potentially influence the shape and performance of bills. Few studies have focused on the entire avian bill, a complex structure consisting of the rhamphotheca and bony core of the upper and lower mandibles, which may evolve as independent modules or as a single integrated unit. Here, we examined patterns and drivers of bill shape diversification in barbets using micro-computed tomography of museum study skins. We employed landmark-based geometric morphometrics and phylogenetic comparative methods to study the influence of climatic conditions, integration and phylogenetic constraints on bill shape diversification. Asian and African barbets have explored distinct maxillary shape spaces without corresponding change in mandibular shape after correcting for phylogenetic non-independence. Additionally, maxillary shape for both rhamphotheca and bony components was significantly correlated with climate variables and exhibited signatures of allometric scaling. All four bill components, however, covaried with each other and have evolved in a gradual and integrated fashion, exhibiting late-stage shape disparity. Through these findings, our study offers crucial insights into how ecological behaviors impact morphological evolution of complex, multifunctional features.

Male crickets belonging to the tribe Lebinthini (Eneopterinae) produce high-frequency, sometimes ultrasonic, calling songs characterized by a dominant harmonic frequency -a phenomenon known as harmonic hopping. While cricket sound production is well understood, the mechanism allowing the dominant frequency to move to the harmonics of the spectrum is little studied. The wing region known as the harp corresponds to the primary resonator of the cricket tegmina. Here we hypothesize that the surface ultrastructure of this region could play a role in the physical properties of the wings and in their vibratory behavior. In this study, we used scanning electron microscopy to explore the diversity of wing membrane ultrastructure in the harp region of 33 species of Eneopterinae, including species producing both low-frequency and high-frequency calling songs. We highlighted a great diversity of ultrastructure within the subfamily. We defined and measured 5 morphological traits concerning the hexagonal cells visible on the dorsal face of the wing, and the microtrichia, filiform sensory structures present on the ventral face. Significant differences are found in hexagonal cell size and density between males and females, and between the males of the species of the Lebinthini tribe and the non-Lebinthini species. These results suggest a link between the presence of these hexagonal structures and the song frequency value. Surfacic structures could play a role in the stiffening of the wing, a property directly related to vibration frequency of the wing. The observation of these structure and more precisely their size and distribution between high-frequency songs producing species and Low-frequency species constitute a new avenue for the understanding of harmonic-hoppings in Lebinthini crickets.

Trophic diversification is one of the main mechanisms driving the adaptive radiation. The polyploid lineage of the cyprinid genus Labeobarbus represent an excellent model for studying the trophically-based adaptive radiation in either lacustrine or riverine environments. Recently discovered four diversifications in rivers of the Ethiopian Highlands (East Africa) demonstrate independently evolved repeated mouth polymorphisms each represented by four core mouth phenotypes: (i) generalized, (ii) thick-lipped, (iii) scraping, and iv) large-mouthed. Mouth phenotypes in some radiations can be further divided to subtypes representing from four to eight sympatric ecomorphs. Using the stable isotope and gut content analyses we tested hypothesis on trophic resource partitioning within each radiation, revealed disparity in degree of diversification between radiations and tried to reconstruct the process of trophic diversification. Three of four radiations demonstrated partitioning of trophic resources within five trophic niches: i) detritophagy, ii) macrophytophagy, iii) invertivorous benthophagy, iv) periphyton feeding, and v) piscivory. The studied riverine radiations were likely at the different stages of the diversification. One radiation having a similar set of mouth phenotypes was not trophically divergent displaying a remarkable decouple of form and function. A unique case of ecologically non-functional mouth polymorphism at an incipient stage of trophic diversification supports a concept of the plasticity-first evolution. This phenomenon stems from the pre-existing genomic templates of mouth polymorphism ancestrally inherited upon the allopolyploid origin of the Labeobarbus lineage. The predetermined and preadaptive mouth polymorphism can be considered a key innovation of the Labeobarbus that promoted to resource-based diversification via adaptive radiation.

Climate change exposes populations to more frequent periods of extreme temperatures and faster temperature fluctuations. Theoretical models suggest that different types of adaptations should occur in constant versus fluctuating environments of varying frequency. Furthermore, evolutionary adaptation to one environment may weaken the adaptations to alternative environments due to antagonistically pleiotropic alleles. However, fitness trade-offs are rarely observed in experiments and it has been hypothesized that the number and severity of trade-offs evolving in fluctuating environments might depend on population size. To evaluate whether specific types of adaptations evolve at fluctuating temperatures and how population size affects the evolution of trade-offs, we performed an evolution experiment with fission yeast (Schizosaccharomyces pombe). The small and large populations evolved for 500 generations at constant and fluctuating temperatures, after which the evolved strains competed against ancestral strains in respective selection environments and in alternative environments to detect trade-offs. We observed significant adaptation and maladaptation only to constant heat, but not to fluctuating temperatures. Overall, the population size did not have significant effects on adaptation capacity or trade-offs in alternative environments. Our results suggest that constant extreme temperatures may act as stronger selective pressures than temperature variation and that trade-offs are unlikely to constrain adaptation to fluctuating temperatures.

In modern evolutionary theory, the mechanism of sympatric speciation is still an unsolved mystery. Ecological niche specialization and the subsequent premating reproductive isolation (RI) are the putative initial steps of sympatric speciation, even though the exact mechanism of how the former leads to the latter remains unclear. This study aims to develop a simple, intuitive, and realistic model ecosystem that uses the fewest variables possible but is still comprehensive enough to uncover the fundamental mechanisms of sympatric speciation. Applying the concept of an adaptive fitness landscape, the study used an individual-based computer simulation to investigate how ecological selection and sexual selection may interact to produce sympatric premating RI. Mathematical models were derived to describe the nonlinear adaptive dynamics of the system. A user-friendly computer application was able to solve, numerically, all the trajectories, fixed points, and bifurcation points of the models and display the solutions as phase portraits. The findings reveal that under favorable conditions, fixed points may emerge in the systems phase portraits to create stable mating-bias-allele polymorphisms and varying degrees of premating RI between niche ecotypes. Solving the nonlinear equations of the mathematical models establishes the precise parametric values required to produce such fixed points. It also specifies the conditions necessary for high-mating-bias mutant alleles to invade and produce, or enhance, premating RI. Restricting migration between niches impedes mutant invasion in parapatric and allopatric populations. Multi-locus mating traits may produce hybrids that prevent speciation. Simulation results of a gonochoric, multi-niche system demonstrate that linkage disequilibrium can emerge spontaneously among ecological, male-trait, and female-preference genotypes to produce premating RI. From these results, a five-stage mechanism of sympatric speciation is formulated: Initially, disruptive ecological selection creates selection pressure for high-mating-bias alleles to invade and rapidly establish premating RI. This then paves the way for the recruitment of late-stage mechanisms, such as adaptive coupling and post-zygotic isolation, to complete the speciation process. Applying nonlinear dynamics theories to model and analyze sympatric speciation has yielded novel findings that support and extend the results of prior studies. These new discoveries may help to overcome the theoretical objections to sympatric speciation and establish it as a prevalent mode of speciation in nature.

Long-distance avian migration is thought to be under strong natural selection. Facing geographical barriers, migrants display various patterns considered to be adaptive. For example, they may detour along either side around the barrier or cross it, requiring specialized behavioral adaptations. Variations within closely related taxa are excellent sources for understanding the evolutionary background of migration and how barriers are shaping migration routes. In Asia, some species are assumed to have a migratory divide in response to the major geographical barrier, the Qinghai-Tibet Plateau (QTP), including the stonechat taxa (Siberian Stonechat Saxicola maurus maurus and Amur Stonechat S. stejnegeri). As they detour along either side of the QTP, these taxa are believed to disfavor a crossing over the highland. However, the more southernly distributed Tibetan Stonechat (S. m. przewalskii) breeds on the QTP, suggesting adaptation to high elevation. To investigate migration patterns and the potentially associated genetic differences, we studied migration routes and population genetics of four populations around the assumed migratory divide in Russia and Mongolia, and of one from the QTP in China. Our results confirmed the existence of a migratory divide between maurus and stejnegeri, albeit with extensive hybridization. We observed both the hypothesized western and eastern routes, but also found individuals employing intermediate routes crossing the QTP, of which two-thirds were clear hybrids. Meanwhile, przewalskii followed a highland-crossing route and was genetically differentiated from maurus and stejnegeri. The diverse migration routes among Asian stonechats show differential responses towards the geographical barrier. The intermediate route may be associated with hybridization, and its conditional viability may facilitate gene flow between maurus and stejnegeri. The Asian stonechat complex thus offers great opportunities for novel research of the genetics and evolution of migration. The specific evolutionary background associated with inhabiting and crossing the QTP can offer new perspectives in this field. Teaser textMigratory divides can arise in birds because alternative routes around migratory barriers would select for behaviors to restrict hybridization. Hybrids of parental types that employ alternative routes are hypothesized to embark on intermediate routes that would expose them to suboptimal conditions, resulting in post-zygotic reproductive isolation. However, this hypothesis is challenged when a sister taxon actually breeds on the geographical barrier. This is the case in the Asian stonechat complex that breeds near or on the Qinghai-Tibet Plateau (QTP), the roof of the world. We demonstrated a migratory divide in central Siberia to Mongolia for race maurus and stejnegeri, yet showed also evidence for extensive hybridization. Hybrids migrated along a newly discovered intermediate route, seemingly viable and overlaps with the migration trajectory of race przewalskii over the eastern part of the QTP. The Asian migratory divide relative to the QTP thus provided new insights to the evolution of landbird migration.

Understanding how chromosomal rearrangements (CRs) interact with epigenetic changes to drive speciation is a fundamental question in evolutionary biology. CRs are key contributors to chromosome evolution and can play a pivotal role in reproductive isolation. The Drosophila nasuta-albomicans species complex presents an ideal model to explore this, as D. albomicans possesses neo-sex chromosomes formed by Robertsonian fusion of chr3L, chr3R, and a sex chromosome, unlike its sister species D. nasuta. In this study, we investigate CRs influence on accessible chromatin (AC) and its relationship with genetic differentiation. We used ATAC-seq to decipher ACs of testis in two hybrids of D. albomicans and D. nasuta, and genome-wide fixation index (FST) scans of D. albomicans and D. nasuta to identify regions of genetic differentiation. Our analyses revealed that chromosome 4 (Muller F) harbors the largest number of differentially accessible regions ([~]97 Kb), which coincide with peaks in FST. Moreover, changes in ACs were associated with differential transcription factor (TF) binding across the genome. These results suggest that CRs can drive epigenomic divergence in hybrids, particularly on Muller F, and chromatin-level changes may play a key role in reproductive isolation. Our study provides an example of how chromosomal and epigenetic architecture interact in the early stages of speciation.

The size and shape of Red Blood Cells (RBC) can provide key information on life history strategies in vertebrates. However, little is known about how RBC shape evolved in response to environmental factors and the role of phylogenetic relationship. Here, we analyzed RBC morphometrics in a continental radiation of fishes testing the hypothesis that phylogenetic relationship determines species occupation of morphospace. We collected blood samples of five specimens of 15 freshwater fish species from six orders and used basic stereological methods to measure cell and nucleus area, perimeter, and diameter, cell and nucleus volume, nucleus:cytoplasm ratio, and shape factor of 50 cells per specimen. Then, we conducted a phylogenetic Principal Components Analysis using a dated phylogeny and built a phylomorphospace. To test if the phylogenetic relationship predicted the phenotypic similarity of species, we calculated multivariate phylogenetic signal. We also estimated the evolution rate of RBC shape for each node and tip using ridge regression. Finally, we tested if the position in the water column influenced RBC shape using a phylogenetic GLS. RBC shape seems to have evolved in a non-stationary way because the distribution pattern of species in the phylomorphospace is independent of the phylogeny. Accordingly, the rate of evolution for shape was highly heterogeneous, with an increase in the genus Pygocentrus. Water column position does not influence RBC shape. In conclusion, RBC shape seem to have evolved in response to multiple selective pressures independent of life history characters.

The ability of interlocus sexual conflict to facilitate reproductive isolation is widely anticipated. However, very few experimental evolutionary studies have convincingly demonstrated the evolution of reproductive isolation due to sexual conflict. Recently a study on replicate populations of Drosophila melanogaster under differential sexual conflict found that divergent mate preference evolved among replicate populations under high sexual conflict regime. The precopulatory isolating mechanism underlying such divergent mate preference could be sexual signals such as cuticular hydrocarbons since they evolve rapidly and are involved in D. melanogaster mate recognition. Using D. melanogaster replicates used in the previous study, we investigate whether cuticular hydrocarbon divergence bears signatures of sexually antagonistic coevolution that led to reproductive isolation among replicates of high sexual conflict regime. We found that D. melanogaster cuticular hydrocarbon profiles are sexually dimorphic. Although replicate populations under high sexual conflict displayed assortative mating, we found no significant differences in the cuticular hydrocarbon profile between the high and low sexual conflict regimes. Instead we find cuticular hydrocarbon divergence patterns to be suggestive of the Buridans Ass regime which is one of the six possible mechanisms to resolve sexual conflict. Sexual selection that co-vary between populations under high and low sexual conflict regimes may also have contributed to the evolution of cuticular hydrocarbons. This study indicates that population differentiation as a result of cuticular hydrocarbon divergence cannot be credited to sexual conflict despite high sexual conflict regime evolving divergent cuticular hydrocarbon profiles.

Ecomorphs result from divergent natural selection, leading to species-rich adaptive radiations. Identifying ecomorphs and the resulting adaptive radiations in frogs is challenging due to conserved morphology and high species diversity. In this study, we demonstrate the ecological and climate specializations that have driven the diversification of shrub frogs of the genus Pseudophilautus in Sri Lanka, a tropical continental island. We use a time-calibrated phylogeny, morphometric analyses, and climate-niche evolution, and identify five ecomorphological categories, including Tree-shrub, Rock-boulder, Leaf-litter, Habitat Generalists, and Canopy forms, and describe their evolution. Body size is the primary factor separating species, and specific body features correlate with habitat type. Ecomorphs likely evolved multiple times in disparate lineages, and in different regions and altitudes, during cold climatic periods owing to monsoon cycles resulting from the Himalayan-Tibetan orogeny. The common ancestor was a medium-sized, wet-adapted, tree-shrub habitat specialist which originated in the late Oligocene. Extreme size classes (diminutive leaf litter forms and large canopy forms) evolved recently and suggest that morphological disparity arose late in diversification, possibly aided by favorable climates. This work will facilitate understanding of adaptive radiations in frogs, which possibly will help uncover the prevalence of subtle adaptive radiations in frogs, just as in tailed-vertebrates.

Conspicuous colors have fascinated biologists for centuries, leading to much research on the evolution and functional significance of color traits. However, some authors have critiqued the adaptationist dogma amongst color researchers. When investigating a color trait, researchers often exclusively consider the alternative hypotheses--they assume color is adaptive. The null hypothesis of animal color--that coloration is non-adaptive or evolutionary neutral, is rarely considered. Here, we use phylogenetic comparative methods to investigate color evolution throughout freshwater crayfishes. Within the taxa we analyzed, conspicuous colors have evolved independently over 50 times. The intuitive, but not evolutionary-justified assumption when presented these results is to assume that these colors are an adaptation. But contrary to this intuition, our work might support the hypothesis that coloration in crayfish is neutral; because we show that conspicuous colors are evolutionary correlated to a semi-terrestrial burrowing lifestyle. Conspicuous coloration being common in semi-terrestrial burrowers is paradoxical, because these species are nocturnal, and rarely leave their burrows. Overall, our work brings into question to traditional view of animal coloration as a perfectly adapted phenotype.

Non-genetic variation is the phenotypic variation induced by the differential expression of a genotype in response to varying environmental cues and is broadly categorized into two types: phenotypic plasticity and developmental noise. These variation aspects have been suggested to play an important role in adaptive evolution; however, the mechanisms by which these two types of non-genetic variations influence the evolutionary process are currently poorly understood. Using a machine-learning based phenotyping tool, we independently quantified the phenotypic plasticity and developmental noise in the wing morphological traits of a fruit fly Drosophila simulans. Utilizing a rearing experiment, we demonstrated plastic responses in both wing size and shape as well as non-zero heritability of both phenotypic plasticity and developmental noise, which suggests that adaptive phenotypic plasticity can evolve via genetic accommodation in the wing morphology of D. simulans. We found a positive correlation between phenotypic plasticity and developmental noise, while the correlation between the plastic response to three kinds of environmental factors that were examined (nutrient condition, temperature, and light-dark cycle) were poor. These results suggest that phenotypic plasticity and developmental noise contribute to evolvability in a similar manner, however, the mechanisms that underlie the correspondence between these two variation types remains to be elucidated. Lay SummaryNon-genetic variations consist of phenotypic plasticity and developmental noise, and these variations have been suggested to influence the direction and the rate of evolution. However, the role of phenotypic plasticity and developmental noise in evolutionary process is still poorly understood. Using a rearing experiment, we examined the heritability of plasticity and developmental noise, the correlation of the strength of plastic response to three kinds of environmental factors, and the relationship between plasticity and developmental noise in wing size and wing shape in Drosophila simulans. We found that the degree of phenotypic plasticity and developmental noise were heritable, and positively correlated with each other. Our results suggest that there two non-genetic variations dependently affect the direction and the rate of evolution together.

Homoploid hybrid speciation (HHS) is an enigmatic evolutionary process where new species arise through hybridization of divergent lineages without changes in chromosome number. Although increasingly documented in various taxa and ecosystems, convincing cases of HHS in marine fishes have been lacking. This study presents evidence of HHS in Torpedo scad Megalaspis cordyla based on comprehensive genomic, morphological, and ecological analyses. A Principal Component Analysis using thousands of SNPs identified three sympatric clusters in the western Pacific. Genome-wide differentiation between the clusters and the admixed nature of a cluster between the others were evident from population genomic analyses, species tree estimation, mitochondrial DNA divergence, and tests of introgression. Multiple statistical methods for hybrid detection also supported the admixed ancestry of this cluster. Moreover, model-based demographic inference favored a hybrid speciation scenario over introgression. Examination of occurrence data and ecologically relevant morphological characters suggested ecological differences between the clusters, potentially contributing to reproductive isolation and niche partitioning in sympatry. The clusters are morphologically distinguishable and thus can be taxonomically recognized as separate species. The hybrid cluster is restricted to the coasts of Taiwan and Japan, where all three clusters coexist. The parental clusters are additionally found in lower latitudes such as the coasts of the Philippines, Vietnam, Thailand, and Malaysia, where they display non-overlapping distributions. Given the geographical distributions, estimated times of the species formation, and patterns of historical demographic changes, we propose that the Pleistocene glacial cycles were the primary driver of HHS in this system. Based on this argument, we develop an ecogeographic model of HHS in marine coastal ecosystems, including a novel hypothesis to explain the initial stages of HHS.

To test the hypothesis that high speciation rate in groups is coupled with high rate of karyotype evolution but also that younger groups having a higher rate of karyotypic diversity, I estimated rates of speciation and rates of karyotype evolution in 1,177 species belonging to 26 families in the insect order Orthoptera. Rates of karyotype evolution were estimated using the diploid number and the number of chromosome arms (fundamental number) from published karyotypes of Orthoptera. Rates of speciation were quantified considering the number of species examined karyotypically in each family, the most recent common ancestor of each family and the information about extinction rate. The rate of speciation was strongly correlated with rate of karyotype evolution and the average rates of speciation was nearly ~177 times higher than the background rate estimated for Orthoptera based on acoustic communication using phylogenomic data, as well as 8.4 and 35.6 times higher than the estimated speciation rate in vertebrates and bivalve mollusks respectively, indicating that Orthoptera has evolved very fast at chromosomal level. The findings supported the hypothesis of a high speciation rate in lineages with high rate of chromosomal evolution but there were not evidences that younger groups tended to have higher rate of karyotypic diversity. Furthermore, rates of karyotype evolution most closely fitted the punctuational evolutionary model indicating the existence of long periods of stasis of karyotype change with most karyotype change occurring quickly over short evolutionary times. I discussed genetic drift, divergent selection and meiotic drive as potential biological mechanisms to explain karyotype evolution allowing or impeding for the fixation of chromosomal rearrangements and in turn speciation in orthopterans lineages.

Insights into ecomorphology are enriched when investigating evolutionary correlations between ecologically and functionally important traits. However, tools currently available to model patterns of shape covariation limit researchers to either assume that trait covariances between taxa are independent of, or completely described by, their shared evolutionary history. Using a novel approach to incorporate phylogenetic signal in trait covariance analysis, we aim to solve this long-standing problem in phylogenetic comparative methods and investigate ecological associations and evolutionary shape covariation in the ecological and morphological diverse case study of surgeonfishes (Acanthuridae). By revising acanthurid phylogenetic relationships and analyzing the geometric morphometrics of their body, head, and fins, we found that head and body shape were significantly associated with dietary ecotype. Surgeonfishes showed a significant negative correlation between caudal fin and pectoral fin shape; high/low aspect ratio (AR) tails are associated with low/high AR pectoral fins, respectively, suggesting locomotor tradeoffs. With our new methodology to estimate the influence of phylogeny on trait covariances between taxa, we found that the caudal fin covaried with both the body and pectoral fin due to dietary and locomotor demands, respectively and exhibited the highest evolutionary variance along the primary axis of integration in all trait covariance comparisons.

Cold stress is a critical environmental challenge that affects an organisms fitness-related traits. In Drosophila, increased resistance to specific environmental stress may lead to increased resistance to other kinds of stress. In the present study, we aimed to understand whether increased cold stress resistance in Drosophila melanogaster can facilitate their ability to tolerate other environmental stresses. For the current study, we used successfully selected replicate populations of D. melanogaster against cold shock and their control population. These selected populations have evolved several reproductive traits, including increased egg viability, mating frequency, male mating ability, ability to sire progenies, and faster recovery for mating latency under cold shock conditions. In the present work, we investigated egg viability and mating frequency with and without heat and cold shock conditions in the selected and their control populations. We also examined resistance to cold shock, heat shock, desiccation, starvation, and survival post-challenge with Staphylococcus succinus subsp. succinus PK-1 in the selected and their control populations. After cold-shock treatment, we found a 1.25 times increase in egg viability and a 1.57 times increase in mating frequency in the selected populations compared to control populations. Moreover, more males (0.87 times) and females (1.66 times) of the selected populations survived under cold shock conditions relative to their controls. After being subjected to heat shock, the selected populations egg viability and mating frequency increased by 0.30 times and 0.57 times, respectively, compared to control populations. Additionally, more selected males (0.31 times) and females (0.98 times) survived under heat shock conditions compared to the control populations. Desiccation resistance slightly increased in the females of the selected populations relative to their control, but we observed no change in the case of males. Starvation resistance decreased in males and females of the selected populations compared to their controls. Our findings suggest that the increased resistance to cold shock correlates with increased tolerance to heat stress, but this evolved resistance comes at a cost, with decreased tolerance to starvation.

Convergent evolution of similar phenotypes suggests some predictability in the evolutionary trajectories of organisms, due to strong and repeated selective pressures, and/or developmental constraints. In adaptive radiations, particularly in cichlid fish radiations, convergent phenotypes are commonly found within and across geographical settings. There are some main axes of cichlid morphological diversification. Recurrent changes in body patterns reveal adaption to alternative habitats, and modifications of the trophic apparatus respond to the exploitation of different food resources. Here we compare two Neotropical cichlid assemblages, the Mexican desert cichlid, and the Nicaraguan Midas cichlid, with similar polymorphic body and trophic apparatus patterns despite their independent evolution and evaluate morphological and gene expression convergence and divergence. We found a single morphological axis of differentiation in pharyngeal jaws with equivalent papilliform and molariform morphotypes in both cichlid radiations. In contrast, we found two different axes of differentiation in the shape of the body, defining two alternative limnetic body patterns. Genetic differences between morphotypes seem to be specific to each radiation, with no clear patterns of convergence.

The ability to thermal adaptation can alter insects reproductive traits and physiologic response. A number of studies in Drosophila documented the higher expression levels of heat shock proteins (Hsps) and Frost (Fst) genes during the recovery phase of cold shock treatment and suggested that higher expression levels of these genes and lipids can protect from cold stress. However, these genes expression and cold adaptation have not been well studied. Therefore, understanding the molecular and biochemical basis of cold adaptation, we examined the levels of lipid and expression patterns of Hsp22, Hsp23, Hsp40, Hsp68, Hsp70, Hsp 83, and Fst genes under the cold stress or benign condition in the populations of Drosophila melanogaster selected for increased resistance to cold shock. We observed the significant up-regulation of Hsp22, Hsp23, Hsp40, Hsp68, and Fst genes in the FSB and FCB populations during the recovery phase post cold shock compared to the no shock condition. However, there was not a significant change in the transcript levels of these genes between FSB and FCB under both the cold stress or no shock condition. Additionally, we noticed higher total lipid levels in the females from cold shock treatment than those from no shock treatment. This finding suggests that cold selected populations have different mechanisms to sustain cold stress.

Sperm competition drives the plasticity of sperm quality and seminal fluid. However, how environmental and behavioral factors influence sperm competition and its outcome on the plasticity of sperm quality are unknown. In this study, we show males can asses the sperm competition level, and their fertilization-promoting sperm traits changes according to intensity. The promiscuous Tanganyikan cichlids Ophthalmotilapia ventralis perform their fertilization in the female mouth cavity. Sperm competition occurs in the female mouth as sperm is collected from multiple males. Behavioral (i.e., courtship success rates [CSR]) and environmental (density of spawning sites [DS]) factors are related to sperm collection. Seminal plasma glycoprotein 120 (SPP120) aids in sperm immobilization and aggregation, and sperm quality (longevity and velocity) could increase the probability of siring offspring. Based on an assumption of the involvement of DS and CSR on sperm collection, DS and CSR could influence the expression of SPP120 and sperm quality. We examined how sperm quality and SPP120 affect sperm competition-associated CSR and DS. Sperm longevity and velocity were positively correlated with DS. SPP120 expression was also positively correlated with CSR and DS. The plasticity of sperm quality and amount of SPP120 result in high fertilization competency according to sperm competition level.

Mitochondrial energy metabolism may be directly influenced by natural selection pressures in response to the energy demands of an organisms specific ecological niche. Here, we hypothesized that the mitochondrial genome of turbellarian animals was influenced by the metabolic requirements of various habitats We used selection pressure and phylogenetic independent contrasts (PIC) analyses to detect the selection pressure of protein-coding genes in the mitochondrial genome of turbellarian living in aquatic and terrestrial habitats. The results indicated turbellarians in aquatic habitats experienced greater selection pressure, resulting in the evolution of several genes at a lower {omega} value compared to their terrestrial counterparts. The NAD4 was identified as having positive selection sites in all site models analyzed. Among all genes, the equilibrium constant (ionization of COOH) was the most frequently detected amino acid characteristic with significant positive selection changes, followed by hydropathy and molecular volume. The equilibrium constant (ionization of COOH) was found to be the amino acid characteristic with the greatest magnitude of change in NAD4. This suggests that it plays a crucial role in the adaptive evolution of turbellarians to varying habitats. The study found a significant positive correlation (R = 0.61, p < 0.05) between the {omega} value of turbellarian and their habitats by PIC analysis. These findings shed light on the adaptive evolution of turbellarian mtDNAs and their influence on the oxidative phosphorylation molecular mechanism. 0. Significance statementThe adaptive evolution of mitochondrial genes is closely related to environmental temperature, high energy metabolism demand, altitude, and oxygen availability. Mitochondrial energy metabolism may be directly influenced by natural selection pressures in response to the energy demands of an organisms specific ecological niche. Here, we investigated the evolution of mtDNA PCGs in turbellarians across different habitats, and identified purifying selection as the main evolutionary pattern of the turbellarian mitochondrial genome. Additionally, we found that NAD4 played an important role in the adaptive evolution of turbellarians to different habitats.