Microevolutionary Changes Research Articles

The important choice of reference environment in microevolutionary climate response predictions.

It is well documented that individuals of wild populations can adjust to climate change by means of phenotypic plasticity, but few reports on adaptation by means of genetically based microevolution caused by selection. Disentanglement of these separate effects requires that the reference environment (the environmental zero point) is defined, and this should not be done arbitrarily. The problem is that an error in the reference environment may lead to large errors in predicted microevolution. Together with parameter values and initial mean trait values, the reference environment can be estimated from environmental, phenotypic and fitness data. A prediction error method for this purpose is described, with the feasibility shown by simulations. As shown in a toy example, an estimated reference environment may have large errors, especially for small populations. This may still be a better choice than use of an initial environmental value in a recorded time series, or the mean value, which is often used. Another alternative may be to use the mean value of a past and stationary stochastic environment, which the population is judged to have been fully adapted to, in the sense that the expected geometric mean fitness was at a global maximum. Exceptions are cases with constant phenotypic plasticity, where the microevolutionary changes per generation follow directly from phenotypic and environmental data, independent of the chosen reference environment.

Toxicological Implications of Biological Heterogeneity.

From a micro to macro scale of biological organization, macromolecular diversity and biological heterogeneity are fundamental properties of biological systems. Heterogeneity may result from genetic, epigenetic, and non-genetic characteristics (e.g., tissue microenvironment). Macromolecular diversity and biological heterogeneity are tolerated as long as the sustenance and propagation of life are not disrupted. They also provide the raw materials for microevolutionary changes that may help organisms adapt to new selection pressures arising from the environment. Sequence evolution, functional divergence, and positive selection of gene and promoter dosage play a major role in the evolution of life's diversity including complex metabolic networks, which is ultimately reflected in changes in the allele frequency over time. Robustness in evolvable biological systems is conferred by functional redundancy that is often created by macromolecular diversity and biological heterogeneity. The ability to investigate biological macromolecules at an increasingly finer level has uncovered a wealth of information in this regard. Therefore, the dynamics of biological complexity should be taken into consideration in biomedical research.

Random Genetic Drift: A Non-directional Force of Evolution

Evolution is a corner stone of biology. In terms of genetics, it is defined as a change in genetic composition of populations. A population has two attributes: Gene frequency proportion of different alleles of a gene in a population; Gene pool- sum total of genes in the reproductive gametes of a population (considered as gametic pool). When the population is evolving and under-going microevolutionary changes, different elemental forces operate to bring about these changes: mutation, natural selection, migration and random genetic drift. The first three forces have one quality in common, they usually operate in directional fashion to change allele frequencies progressively from one value to the other. When other factors are not opposing, these factors can lead to fixation of one allele and elimination of others. In case polymorphism is balanced, they can lead to equilibrium between two or more alleles. On the other hand, there is another factor that brings about the changes in allele frequency in nondirectional manner and has no predictive constancy from generation to generation. It is known as random genetic drift which arises from variable sampling of gene pool in each generation. It operates in small populations and causes allele frequency changes due to chance events causing random fluctuation in allele frequency occurring because of sampling errors. It may lead to fixation or elimination of a particular allele which causes increase in homozygosity. Sewall Wright discussed the role of genetic drift in small populations with particular

The stagnation paradox: the ever-improving but (more or less) stationary population fitness

Fisher's fundamental theorem states that natural selection improves mean fitness. Fitness, in turn, is often equated with population growth. This leads to an absurd prediction that life evolves to ever-faster growth rates, yet no one seriously claims generally slower population growth rates in the Triassic compared with the present day. I review here, using non-technical language, how fitness can improve yet stay constant (stagnation paradox), and why an unambiguous measure of population fitness does not exist. Subfields use different terminology for aspects of the paradox, referring to stasis, cryptic evolution or the difficulty of choosing an appropriate fitness measure; known resolutions likewise use diverse terms from environmental feedback to density dependence and ‘evolutionary environmental deterioration’. The paradox vanishes when these concepts are understood, and adaptation can lead to declining reproductive output of a population when individuals can improve their fitness by exploiting conspecifics. This is particularly readily observable when males participate in a zero-sum game over paternity and population output depends more strongly on female than male fitness. Even so, the jury is still out regarding the effect of sexual conflict on population fitness. Finally, life-history theory and genetic studies of microevolutionary change could pay more attention to each other.

Why the third way of evolution is necessary.

The Third Way of Evolution was founded in 2014 to make the public aware that contemporary evolution science is not limited to the neo-Darwinian Modern Synthesis of the past century. This was important to do because evolution was challenged as incapable of explaining biological complexity by the Intelligent Design movement. Expounding biological theories like the Modern Synthesis is always subject to limited empirical evidence, fundamental concepts that inevitably change over time, and conceptual preferences that often prove to be misleading. The Modern Synthesis was based on Darwin's preference for the phyletic gradualism necessary to elevate Natural Selection as the sole force determining the direction of evolutionary change. In contradiction to this principle, agricultural crop breeding, direct observation in nature, and genomics have shown that genome change following symbiogenetic cell fusions or interspecific hybridization, not selection, are empirically the most effective methods for originating novel life forms and new species. By asserting that the accumulation of random "slight" variations was the basic mode of both short-term and long-term evolutionary change, the Modern Synthesis also ignored the distinction between (1) microevolutionary change within species by localized mutations and (2) macroevolutionary origination of new species and taxa by genome restructuring. In so doing, the Modern Synthesis failed to recognize the evolutionary importance of cellular capacities to generate large-scale genome changes. By focusing on individual protein-coding genes as the fundamental units of genetic information, the Modern Synthesis did not successfully incorporate either the full non-coding informa tion content in genomes or the major evolutionary potential of mobile DNA elements to generate multisite intragenomic networks necessary for the development of complex organisms. When all of the phenomena overlooked by the Modern Synthesis are taken into consideration, it is not difficult to answer Intelligent Design arguments and show that science is making real progress in understanding the evolution of biological complexity.

What prevents mainstream evolutionists teaching the whole truth about how genomes evolve?

The common belief that the neo-Darwinian Modern Synthesis (MS) was buttressed by the discoveries of molecular biology is incorrect. On the contrary those discoveries have undermined the MS. This article discusses the many processes revealed by molecular studies and genome sequencing that contribute to evolution but nonetheless lie beyond the strict confines of the MS formulated in the 1940s. The core assumptions of the MS that molecular studies have discredited include the idea that DNA is intrinsically a faithful self-replicator, the one-way transfer of heritable information from nucleic acids to other cell molecules, the myth of “selfish DNA”, and the existence of an impenetrable Weismann Barrier separating somatic and germ line cells. Processes fundamental to modern evolutionary theory include symbiogenesis, biosphere interactions between distant taxa (including viruses), horizontal DNA transfers, natural genetic engineering, organismal stress responses that activate intrinsic genome change operators, and macroevolution by genome restructuring (distinct from the gradual accumulation of local microevolutionary changes in the MS). These 21st Century concepts treat the evolving genome as a highly formatted and integrated Read–Write (RW) database rather than a Read-Only Memory (ROM) collection of independent gene units that change by random copying errors. Most of the discoverers of these macroevolutionary processes have been ignored in mainstream textbooks and popularizations of evolutionary biology, as we document in some detail. Ironically, we show that the active view of evolution that emerges from genomics and molecular biology is much closer to the 19th century ideas of both Darwin and Lamarck. The capacity of cells to activate evolutionary genome change under stress can account for some of the most negative clinical results in oncology, especially the sudden appearance of treatment-resistant and more aggressive tumors following therapies intended to eradicate all cancer cells. Knowing that extreme stress can be a trigger for punctuated macroevolutionary change suggests that less lethal therapies may result in longer survival times.

Immigration counter-acts local micro-evolution of a major fitness component: Migration-selection balance in free-living song sparrows.

Ongoing adaptive evolution, and resulting “evolutionary rescue” of declining populations, requires additive genetic variation in fitness. Such variation can be increased by gene flow resulting from immigration, potentially facilitating evolution. But, gene flow could in fact constrain rather than facilitate local adaptive evolution if immigrants have low additive genetic values for local fitness. Local migration‐selection balance and micro‐evolutionary stasis could then result. However, key quantitative genetic effects of natural immigration, comprising the degrees to which gene flow increases the total local additive genetic variance yet counteracts local adaptive evolutionary change, have not been explicitly quantified in wild populations. Key implications of gene flow for population and evolutionary dynamics consequently remain unclear. Our quantitative genetic analyses of long‐term data from free‐living song sparrows (Melospiza melodia) show that mean breeding value for local juvenile survival to adulthood, a major component of fitness, increased across cohorts more than expected solely due to drift. Such micro‐evolutionary change should be expected given nonzero additive genetic variance and consistent directional selection. However, this evolutionary increase was counteracted by negative additive genetic effects of recent immigrants, which increased total additive genetic variance but prevented a net directional evolutionary increase in total additive genetic value. These analyses imply an approximate quantitative genetic migration‐selection balance in a major fitness component, and hence demonstrate a key mechanism by which substantial additive genetic variation can be maintained yet decoupled from local adaptive evolutionary change.

Daphnia depth selection in gradients of light intensity from different artificial sources: An evolutionary trap?

AbstractIt is well known that artificial light at night alters the natural patterns of light in space and time, which interrupts a variety of physiological processes of individuals, altering their life history and behavioral adjustments. However, much less is known about the effect of artificial light at night on their fitness. We tested the hypothesis that planktonic animals, such as Daphnia spp., are able to correctly assess light intensity‐ and spectrum‐dependent‐mortality risk due to predation by planktivorous fish and select depths offering the highest possible fitness gain in the vertical gradient of different artificial light sources (halogen, metal‐halide, cool white LEDs, and high pressure sodium lamps) commonly used in street lighting. To test this hypothesis, we compared the virtual distributions of three clones of Daphnia longispina from simulations based on an experimentally parameterized, optimizing individual‐based model with distributions observed in laboratory experiments performed with 5‐d‐old individuals in an experimental apparatus comprised of twin vertical columns. Our hypothesis was confirmed only partially, since the distributions obtained in the experiments overlapped the virtual distributions only in the gradient of LEDs and high pressure sodium light, which suggests that that the strength of the maladaptive response could depend on the type of artificial light (i.e., spectral composition) penetrating the water column. Moreover, the results revealed that the response to the presence of artificial light is clone‐specific, which suggest that it could be a selective factor for microevolutionary changes.

Strong survival selection on seasonal migration versus residence induced by extreme climatic events.

Elucidating the full eco-evolutionary consequences of climate change requires quantifying the impact of extreme climatic events (ECEs) on selective landscapes of key phenotypic traits that mediate responses to changing environments. Episodes of strong ECE-induced selection could directly alter population composition, and potentially drive micro-evolution. However, to date, few studies have quantified ECE-induced selection on key traits, meaning that immediate and longer-term eco-evolutionary implications cannot yet be considered. One widely expressed trait that allows individuals to respond to changing seasonal environments, and directly shapes spatio-seasonal population dynamics, is seasonal migration versus residence. Many populations show considerable among-individual phenotypic variation, resulting in 'partial migration'. However, variation in the magnitude of direct survival selection on migration versus residence has not been rigorously quantified, and empirical evidence of whether seasonal ECEs induce, intensify, weaken or reverse such selection is lacking. We designed full annual cycle multi-state capture-recapture models that allow estimation of seasonal survival probabilities of migrants and residents from spatio-temporally heterogeneous individual resightings. We fitted these models to 9years of geographically extensive year-round resighting data from partially migratory European shags Phalacrocorax aristotelis. We thereby quantified seasonal and annual survival selection on migration versus residence across benign and historically extreme non-breeding season (winter) conditions, and tested whether selection differed between females and males. We show that two of four observed ECEs, defined as severe winter storms causing overall low survival, were associated with very strong seasonal survival selection against residence. These episodes dwarfed the weak selection or neutrality evident otherwise, and hence caused selection through overall annual survival. The ECE that caused highest overall mortality and strongest selection also caused sex-biased mortality, but there was little overall evidence of sex-biased selection on migration versus residence. Our results imply that seasonal ECEs and associated mortality can substantially shape the landscape of survival selection on migration versus residence. Such ECE-induced phenotypic selection will directly alter migrant and resident frequencies, and thereby alter immediate spatio-seasonal population dynamics. Given underlying additive genetic variation, such ECEs could potentially cause micro-evolutionary changes in seasonal migration, and thereby cause complex eco-evolutionary population responses to changing seasonal environments.

POLYMORPHISM OF GROWTH HORMONE RECEPTOR GENE AND MYOGENIC FACTOR 5 GENE IN DAIRY CATTLE POPULATIONS

Investigations of the genetic structure features of the populations of Ukrainian Black-and-White and Red-and-White dairy breeds by polymorphism of growth hormone receptor (GHR) and myogenic factor 5 (MYF5) genes were carried out. AluI-polymorphism in the promoter fragment of the GHR gene and TaqI-polymorphism in the second intron of the MYF5 gene was detected using polymerase chain reaction and restriction analysis (PCR-RFLP). According to the research results, it was shown that the growth hormone receptor and myogenic factor 5 genes in the populations of Ukrainian Black-and-White and Red-and-White dairy breeds are polymorphic. In the population of the Ukrainian Black-and-White dairy breed at the GHR locus, the frequency of the AluI+ allele was 0.61; allele AluI- – 0.39; at the MYF5 locus, the TaqI+ allele frequency was 0.65; allele Taq- – 0.35, respectively. In the population of the Ukrainian Red-and-White dairy breed at the GHR locus, the frequency of the AluI+ allele was 0.54; allele AluI- – 0.46; at the MYF5 locus, the TaqI+ allele frequency was 0.64; allele Taq- – 0.36, respectively. Both experimental populations for GHR and MYF5 loci are in a genetic equilibrium state according to Hardy-Weinberg, which indicates the absence of microevolutionary changes in the process of their reproduction. There were no significant fluctuations in the genetic structure according to the revealed features of the genotype and allele frequencies distribution. The breeding work that is carried out on both populations does not affect marker alleles (which are described in the work), which is reflected in the features of the genetic-population structure of the experimental groups and their equilibrium state. The features of the distribution of individuals with different genotypes by GHR and MYF5 loci in the populations of both breeds make it possible to carry out further studies to determine the relationship between the identified allelic variants of polymorphic loci with parameters of animal productivity.

Microevolutionary changes during urbanization of “wild” bird species

Microevolutionary changes during urbanization of “wild” bird species

ENVIRONMENTAL, BIOLOGICAL AND GENETIC FEATURES OF CERTAIN POPULATIONS OF GREAT GERBIL (Rhombomys opius Licht., 1823) OF KAZAKHSTAN

The main host of a number of especially dangerous zoonotic infections in the arid zones of Kazakhstan, covering an area of about 1.1 million km2, is the great gerbil (Rhombomys opimus). In the process of formation in natural foci of the parasitic triad (pathogen-host-vector, mutual adaptation of all its members to environmental conditions and their coevolution occurs. The article presents the results of a study of the intraspecific, population heterogeneity of ecological-biological and some genomic features of the great gerbil in three foci of zoonotic Infections: Pribalkash, Betpakdala and Predustyurt. The features of climate, soil and vegetation cover, tendencies of their perennial and seasonal changes were studied. Differences in climatic conditions and characteristics of vegetation between the 3 foci were revealed at a rather high degree of synchronization of the trend of changes in air temperature and precipitation. Analysis of the cytB gene fragment from 88 individuals from three autonomous plague foci identified 19 haplotypes that form three haplogroups, one of which is represented by individuals from the populations of two autonomous plague foci Populations of great gerbils from Kazakhstan and China are included in the same cluster and are genetically distant from the populations of Iran. Geographic isolation, significant differences in climatic, landscape, and forage conditions, microevolutionary changes in the genomic status determined the heterogeneity of three described populations of the great gerbil. A growing negative impact on the population of the great gerbil and the epizootic status of natural foci of climate warming and an increasing anthropogenic pressure, primarily in the form of overgrazing, on natural phytocenoses was noted.

Microevolutionary change in mimicry? Potential erosion of rattling behaviour among nonvenomous snakes on islands lacking rattlesnakes

Batesian mimics – harmless species that converge on the warning signals of a dangerous species – are spectacular examples of adaptation, but few documented cases involve acoustic signals. Even fewer studies have documented microevolutionary change in mimicry of any kind. Here, we describe a potential evolutionary change in acoustic mimicry. Many nonvenomous snakes vibrate their tail tip when threatened, making a sound resembling venomous rattlesnakes, which can vibrate their tail rapidly and for a long duration. When we compared this behavior between Gophersnakes from mainland California (where rattlesnakes are present) versus nearby derived island populations (where rattlesnakes are absent), we found that mainland snakes vibrated their tail for a longer duration, thereby producing a signal more similar to rattlesnakes. At the same time, we did not find evidence that island snakes differ from mainland snakes in the rate at which they vibrate their tails, or their propensity to vibrate their tails. Taken together, these data lend some support to the longstanding hypothesis that defensive tail vibration by nonvenomous snakes represents acoustic mimicry of rattlesnakes. These data further suggest that this mimetic signal may be undergoing erosion in populations where rattlesnakes are absent.

Drimolen cranium DNH 155 documents microevolution in an early hominin species.

Paranthropus robustus is a small-brained extinct hominin from South Africa characterized by derived, robust craniodental morphology. The most complete known skull of this species is DNH 7 from Drimolen Main Quarry, which differs from P. robustus specimens recovered elsewhere in ways attributed to sexual dimorphism. Here, we describe a new fossil specimen from Drimolen Main Quarry, dated from approximately 2.04-1.95 million years ago, that challenges this view. DNH 155 is a well-preserved adult male cranium that shares with DNH 7 a suite of primitive and derived features unlike those seen in adult P. robustus specimens from other chronologically younger deposits. This refutes existing hypotheses linking sexual dimorphism, ontogeny and social behaviour within this taxon, and clarifies hypotheses concerning hominin phylogeny. We document small-scale morphological changes in P. robustus associated with ecological change within a short time frame and restricted geography. This represents the most highly resolved evidence yet of microevolutionary change within an early hominin species.

Genesis of the scientific discipline “Invasive Biology” in Russia

This article describes the chronology of scientific papers dealing with invasive biology. The genesis of this new discipline is characterized. The focus is on the study of invasions of plant organisms. The main tasks of the discipline are formulated and results are described. It is shown that over 40 years, single finds of alien plant species have turned into a list of invasive species in Russia, identifying the most significant invasion vectors, and determining the rate of microevolutionary changes in species of the secondary distribution range. The inventory data made it possible to conduct monitoring studies of biological invasions and alien species in general, which will help reduce the economic costs of combating invasive species. However, the dynamics of the invasive component determines the need to continue inventory work, especially in Siberia and the Far East.

Evolutionary ecology of Lyme Borrelia.

The bacterial genus, Borrelia, is comprised of vector-borne spirochete species that infect and are transmitted from multiple host species. Some Borrelia species cause highly-prevalent diseases in humans and domestic animals. Evolutionary, ecological, and molecular research on many Borrelia species have resulted in tremendous progress toward understanding the biology and natural history of these species. Yet, many outstanding questions, such as how Borrelia populations will be impacted by climate and land-use change, will require an interdisciplinary approach. The evolutionary ecology research framework incorporates theory and data from evolutionary, ecological, and molecular studies while overcoming common assumptions within each field that can hinder integration across these disciplines. Evolutionary ecology offers a framework to evaluate the ecological consequences of evolved traits and to predict how present-day ecological processes may result in further evolutionary change. Studies of microbes with complex transmission cycles, like Borrelia, which interact with multiple vertebrate hosts and arthropod vectors, are poised to leverage the power of the evolutionary ecology framework to identify the molecular interactions involved in ecological processes that result in evolutionary change. Using existing data, we outline how evolutionary ecology theory can delineate how interactions with other species and the physical environment create selective forces or impact migration of Borrelia populations and result in micro-evolutionary changes. We further discuss the ecological and molecular consequences of those micro-evolutionary changes. While many of the currently outstanding questions will necessitate new experimental designs and additional empirical data, many others can be addressed immediately by integrating existing molecular and ecological data within an evolutionary ecology framework.

Современная семья. Антропогенетические особенности репродуктивных процессов в популяциях малой и средней численности*

The report presents a comparative analysis of anthropogenetic parameters in the populations of ethnic Greeks and Albanians of the Azov region, which contrast with the Pamirs and Kyrgyzs of the Pamir Mountains. In the highland Pamir populations of the Pastuf and Khuf (Rushan district of Gorno-Badakhshan Administrative Division (GBAD) of Tajikistan) and the Kyrgyzs of Murghab (Murghab district of GBAD), the main factors of microevolutionary changes are environmental conditions along with the influence of ethnic and confessional attitudes and cultural traditions. The pattern of reproduction is natural with unregulated fertility. A decrease in fertility is associated with the height of populations’ habitats above sea level. The populations of Azov – Krasnaya Polyana (ethnic Greeks speaking Rumeíka), Starolaspe (Tatar-speaking Greeks), and compactly populated Albanians of Devninskoye and Georgievka settlements underwent a demographic transition to the family planning system and strict artificial birth control. Populations surrounded by other ethnic groups have an urbanized pattern of reproduction not typical for groups of small and medium size. This population suffers from the effect of abrupt “aging”, with a small proportion of pre-reproductive age and a significant number of post-reproductive cohorts. Reproductive rates are low and the number is supported by migrations from other groups. The anthropogenetic analysis demonstrated that reproduction processes in populations depend on a set of biological and social factors, geographical conditions and environment.

Recently increased prevalence of the human median artery of the forearm: A microevolutionary change.

The median artery has been considered as an embryonic structure, which normally regresses around the 8th week of gestation. However, various prevalences have been reported in adults since the 18th century. Furthermore, in a study by Henneberg and George (1995; Am J Phys Anthropol 96, 329-334), has suggested that increasing prevalence of the median artery during the 20th century was a 'possible secular trend'. The present study, conducted nearly a quarter of a century later, is a continuation of that study. A total of 26 median arteries were found in 78 upper limbs obtained from Australians aged 51 to 101years, who died in the period 2015-2016, a prevalence rate of 33.3%. Analysis of the literature showed that the presence of the median artery has been significantly increasing (p=.001) over time, from approximately 10% in people born in the mid-1880s to approximately 30% by the end of the 20th century. The significance of the prevalence increased to a p value <.0001, when the results of the present study and other studies conducted by our research team were combined. After removal of the studies that were possibly biased, because of their specific focus on the evolutionary aspects of the median artery, the significance remained at p=.018. The present study provides an example of microevolutionary changes in the internal anatomy of the human body. Second-order polynomial regression of the median artery's prevalence on dates of birth shows that it is now present in 35% of people and predicts that people born 80years from now will all carry a median artery if the trend continues. When the median artery prevalence reaches 50% or more, it should not be considered as a variant, but as a 'normal' human structure.

Genomic evidence for parallel adaptation to cities.

Urban evolutionary biology is the study of rapid evolutionary change in response to humans and our uses of land to support city dwellers. Because cities are relatively modern additions to the natural world, research on urban evolution tends to focus on microevolutionary change that has happened across a few to many hundreds of generations. These questions still fall under the broad purview of evolutionary ecology. However, the severity, rapidity and replication of environmental changes that drive evolution in this context make it worthy of specific attention. Urban evolution provides the opportunity to study the earliest stages of evolution in a context that is scientifically interesting and societally important. The newness of urban populations and their proximity to natural populations also creates challenges when trying to detect population genetic change. In a From the Cover article in this issue of Molecular Ecology, Mueller et al. use whole genome resequencing data to address some of these challenges while exploring genetic changes associated with urbanization in three replicate urban-rural burrowing owl (Athene cunicularia) populations. Combining multiple approaches across these sample sites Mueller et al. find evidence for selection on genes whose function is related to synapses, neuron projections, brain connectivity and cognitive function in general. That selection was parallel suggests that phenotypes related to brain processes were probably particularly important for urban adaptation.

Inferred genetic architecture underlying evolution in a fossil stickleback lineage.

Inferring the genetic architecture of evolution in the fossil record is difficult because genetic crosses are impossible, the acquisition of DNA is usually impossible and phenotype-genotype maps are rarely obvious. However, such inference is valuable because it reveals the genetic basis of microevolutionary change across many more generations than is possible in studies of extant taxa, thereby integrating microevolutionary process and macroevolutionary pattern. Here, we infer the genetic basis of pelvic skeleton reduction in Gasterosteus doryssus, a Miocene stickleback fish from a finely resolved stratigraphic sequence that spans nearly 17,000 years. Reduction in pelvic score, a categorical measure of pelvic structure, resulted primarily from reciprocal frequency changes of two discrete phenotypic classes. Pelvic vestiges also showed left-side larger asymmetry. These patterns implicate Pitx1, a large-effect gene whose deletion generates left-side larger asymmetry of pelvic vestiges in extant, closely related Gasterosteus aculeatus. In contrast, reductions in the length of the pelvic girdle and pelvic spines resulted from directional shifts of unimodal, continuous trait distributions, suggesting an additional suite of genes with minor, additive pelvic effects, again like G. aculeatus. Similar genetic architectures explain shared but phyletically independent patterns across 10 million years of stickleback evolution.