Degree Of Phenotypic Divergence Research Articles

Variation in egg size and offspring phenotype among and within seven Arctic charr morphs.

Maternal effects have the potential to alter early developmental processes of offspring and contribute to adaptive diversification. Egg size is a major contributor to offspring phenotype, which can influence developmental trajectories and potential resource use. However, to what extent intraspecific variation in egg size facilitates evolution of resource polymorphism is poorly understood. We studied multiple resource morphs of Icelandic Arctic charr, ranging from an anadromous morph—with a phenotype similar to the proposed ancestral phenotype—to sympatric morphs that vary in their degree of phenotypic divergence from the ancestral anadromous morph. We characterized variation in egg size and tested whether egg size influenced offspring phenotype at early life stages (i.e., timing of‐ and size at‐ hatching and first feeding [FF]). We predicted that egg size would differ among morphs and be less variable as morphs diverge away from the ancestral anadromous phenotype. We also predicted that egg size would correlate with offspring size and developmental timing. We found morphs had different egg size, developmental timing, and size at hatching and FF. Egg size increased as phenotypic proximity to the ancestral anadromous phenotype decreased, with larger eggs generally giving rise to larger offspring, especially at FF, but egg size had no effect on developmental rate. The interaction between egg size and the environment may have a profound impact on offspring fitness, where the resulting differences in early life‐history traits may act to initiate and/or maintain resource morphs diversification.

Phenotypic and genetic divergence among island populations of sika deer (Cervus nippon) in southern Japan: a test of the local adaptation hypothesis

AbstractTransplant and common garden experiments have been used in studies on local adaptation, but are difficult to be conducted for large animals with long life span. A previous study on the southern Japanese islands demonstrated that relative limb lengths of sika deer (Cervus nippon) were short on islands with steep slopes. We hypothesized that this morphological variation was evidence for local adaptation, and tested this hypothesis by comparing phenotypic divergence with neutral genetic divergence among eight populations of the sika deer in the southern Japanese islands. Divergence patterns differed between the phenotypic and neutral genetic features. Genetic similarity was high among individuals on Kyushu (OI, KGS, and KGK). Individuals on Tanegashima (TN) and Yakushima (YK) also constituted a group, whereas individuals on Tsushima (TS), Wakamatsujima (WM), and Kuchinoerabujima (KE) formed a genetically distinct group. Phenotypic data indicated that individuals from TS, OI, KGS, and KGK exhibited similarity, whereas individuals on YK formed an isolated group that was separated from the other populations. The degree of phenotypic divergence was larger than that of neutral genetic divergence between TN and YK. These results suggest that divergent selection worked between two of the eight island populations (TN and YK). The morphological trait of captive‐bred individuals from TN and YK, which had never experienced their original environments, retained their original morphological features. By combining the results of multiple analyses, we found that the difference in relative limb length between the two populations was consistent with local adaptation hypothesis, although conclusive results were not obtained for the other populations.

Rapid postglacial diversification and long-term stasis within the songbird genus Junco: phylogeographic and phylogenomic evidence.

Natural systems composed of closely related taxa that vary in the degree of phenotypic divergence and geographic isolation provide an opportunity to investigate the rate of phenotypic diversification and the relative roles of selection and drift in driving lineage formation. The genus Junco (Aves: Emberizidae) of North America includes parapatric northern forms that are markedly divergent in plumage pattern and colour, in contrast to geographically isolated southern populations in remote areas that show moderate phenotypic divergence. Here, we quantify patterns of phenotypic divergence in morphology and plumage colour and use mitochondrial DNA genes, a nuclear intron, and genomewide SNPs to reconstruct the demographic and evolutionary history of the genus to infer relative rates of evolutionary divergence among lineages. We found that geographically isolated populations have evolved independently for hundreds of thousands of years despite little differentiation in phenotype, in sharp contrast to phenotypically diverse northern forms, which have diversified within the last few thousand years as a result of the rapid postglacial recolonization of North America. SNP data resolved young northern lineages into reciprocally monophyletic lineages, indicating low rates of gene flow even among closely related parapatric forms, and suggesting a role for strong genetic drift or multifarious selection acting on multiple loci in driving lineage divergence. Juncos represent a compelling example of speciation in action, where the combined effects of historical and selective factors have produced one of the fastest cases of speciation known in vertebrates.

The tempo of trait divergence in geographic isolation: avian speciation across the Marañon Valley of Peru.

Geographic isolation is considered essential to most speciation events, but our understanding of what controls the pace and degree of phenotypic divergence among allopatric populations remains poor. Why do some taxa exhibit phenotypic differentiation across barriers to dispersal, whereas others do not? To test factors controlling phenotypic divergence in allopatry, we employed a comparative phylogeographic approach consisting of replicates of ecologically similar Andean bird species isolated across a major biogeographic barrier, the Marañon Valley of Peru. Our study design leverages variation among codistributed taxa in their degree of plumage, morphometric, and vocal differentiation across the Marañon to examine the tempo of phenotypic evolution. We found that substantial plumage differences between populations required roughly two million years to evolve. In contrast, morphometric trait evolution showed greater idiosyncrasy and stasis. Our results demonstrate that despite a large degree of idiosyncrasy in the relationship between genetic and phenotypic divergence across taxa and environments, comparative studies within regions may reveal predictability in the pace of phenotypic divergence. Our results also suggest that social selection is important for driving differentiation of populations found in similar environments.

Individuals in food webs: the relationships between trophic position, omnivory and among-individual diet variation.

Among-individual diet variation is common in natural populations and may occur at any trophic level within a food web. Yet, little is known about its variation among trophic levels and how such variation could affect phenotypic divergence within populations. In this study we investigate the relationships between trophic position (the population’s range and average) and among-individual diet variation. We test for diet variation among individuals and across size classes of Eurasian perch (Perca fluviatilis), a widespread predatory freshwater fish that undergoes ontogenetic niche shifts. Second, we investigate among-individual diet variation within fish and invertebrate populations in two different lake communities using stable isotopes. Third, we test potential evolutionary implications of population trophic position by assessing the relationship between the proportion of piscivorous perch (populations of higher trophic position) and the degree of phenotypic divergence between littoral and pelagic perch sub-populations. We show that among-individual diet variation is highest at intermediate trophic positions, and that this high degree of among-individual variation likely causes an increase in the range of trophic positions among individuals. We also found that phenotypic divergence was negatively related to trophic position in a population. This study thus shows that trophic position is related to and may be important for among-individual diet variation as well as to phenotypic divergence within populations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-014-3203-4) contains supplementary material, which is available to authorized users.

Ecological Niche Dimensionality and the Evolutionary Diversification of Stick Insects

The degree of phenotypic divergence and reproductive isolation between taxon pairs can vary quantitatively, and often increases as evolutionary divergence proceeds through various stages, from polymorphism to population differentiation, ecotype and race formation, speciation, and post-speciational divergence. Although divergent natural selection promotes divergence, it does not always result in strong differentiation. For example, divergent selection can fail to complete speciation, and distinct species pairs sometimes collapse (‘speciation in reverse’). Widely-discussed explanations for this variability concern genetic architecture, and the geographic arrangement of populations. A less-explored possibility is that the degree of phenotypic and reproductive divergence between taxon pairs is positively related to the number of ecological niche dimensions (i.e., traits) subject to divergent selection. Some data supporting this idea stem from laboratory experimental evolution studies using Drosophila, but tests from nature are lacking. Here we report results from manipulative field experiments in natural populations of herbivorous Timema stick insects that are consistent with this ‘niche dimensionality’ hypothesis. In such insects, divergent selection between host plants might occur for cryptic colouration (camouflage to evade visual predation), physiology (to detoxify plant chemicals), or both of these niche dimensions. We show that divergent selection on the single niche dimension of cryptic colouration can result in ecotype formation and intermediate levels of phenotypic and reproductive divergence between populations feeding on different hosts. However, greater divergence between a species pair involved divergent selection on both niche dimensions. Although further replication of the trends reported here is required, the results suggest that dimensionality of selection may complement genetic and geographic explanations for the degree of diversification in nature.

Three‐dimensional morphometric analysis of craniofacial shape in the unaffected relatives of individuals with nonsyndromic orofacial clefts: A possible marker for genetic susceptibility

Numerous studies have described altered patterns of craniofacial form in the unaffected relatives of individuals with nonsyndromic clefts. Unfortunately, results from such studies have been highly variable and have failed to provide a reliable method for differentiating "at-risk" relatives from controls. In the present study, we compared craniofacial shape between a sample of unaffected relatives (33 females; 14 males) from cleft multiplex families and an equal number of age/sex/ethnicity-matched controls. Sixteen x,y,z facial landmark coordinates derived from 3D photogrammetry were analyzed via Euclidean Distance Matrix Analysis, while 14 additional linear distances were analyzed via t tests. A subset of variables was then entered into a discriminant function analysis (DFA). Compared to controls, female unaffected relatives demonstrated increased upper facial width, midface reduction and lateral displacement of the alar cartilage. DFA correctly classified 70% of female unaffected relatives and 73% of female controls. Male unaffected relatives demonstrated increased upper facial and cranial base width, increased lower facial height and decreased upper facial height compared with controls. DFA correctly classified 86% of male unaffected relatives and 93% of male controls. In both sexes, upper facial width contributed most to group discrimination. Following DFA, unaffected relatives were assigned to risk/liability classes based on the degree of phenotypic divergence from controls. Results indicate that craniofacial shape differences characterizing unaffected relatives are partly sex-specific and are in broad agreement with previous reports. These findings further suggest that a quantitative assessment of the craniofacial phenotype may allow for the identification of susceptible individuals within nonsyndromic cleft families.

INHERITANCE OF ALBINISM IN THE GOLDFISH, <i>CARASSIUS AURATUS</i>

Albinism appeared in the globe-eyed goldfish (demekin) is not a simple Mendelian character but is the double recessive of two independently assorting autosomal genes since non-albino and albino types appear in the 15:1 ratio in the F2 generation. When scored on advanced embryos and larvae, however, the dark (normal), the light and the albino types appear in the 12:3:1 ratio, related in action of dominant epistasis.Symbol M is proposed for the epistatic dominant gene responsible for normal melanin deposition as well as normal melanophore development, S for the hypostatic dominant gene governing slower melanin formation and slower melanophore development. The effect of the S is masked in the combination M, S, because of epistasis of the M to the S (M>S). The dark type, thus, is represented by either M, S or M, s, the light one by m, S and the albino by m, s. The F2 ratio scored on embryos and larvae becomes 12 dark (M, S and M, s): 3 light (m, S):1 albino (m, s).In the light embryos and larvae, eyes darken slowly and melanophores are smaller in size and fewer in number, i.e., in earlier developmental stage. The degree of phenotypic divergence between the dark and the light types is gradually obliterated as development proceeds. Final melanin deposition as well as final state of melanophores become eventually the same since the two genes differ only in the time-relationships in the developmental process.The M and the S act in the same sense like duplicate genes. Since, however, M>S in epistasis but not M=S, the mode of non-allelic gene interaction in this case may be termed as a dominant epistasis akin to duplicate genes.The presence of the M and the S genes pertinent to melanin as well as melanophores in a number of the ordinary black-eyed varieties of the goldfish is pointed out.

Mendelian Genes and Rates of Development in Gammarus Chevreuxi

ABSTRACT In the present paper the following facts and theoretical considerations have been brought forward: (1) All the mutations so far examined which influence the colour of the facets (as opposed to total absences of black and red pigment) in the eyes of Gammarus chevreuxi appear to act by modifying the time relationships governing the deposition of melanin. (2) All coloured eyes are at first colourless, and then become scarlet owing to the formation of a red pigment soluble in alcohol; later they may darken by the deposition of melanin. (3) In the normal black eye (RR), melanin begins to be deposited about 2 days before hatching (at 23° C.); its deposition is very rapid, and complete saturation, giving a dense black colour, is reached at or about extrusion. (4) In red (rr) eyes the time of onset and the rate of melanin formation is always slower. The rate may be modified by a factor “s” slowing it down considerably, and a factor “m” slowing it down to a less degree. (5) At 23° C. rrSSMM eyes begin to darken at about 4 to 6 days after extrusion, and reach an equilibrium position (of a deep chocolate colour) in about 3 weeks. (6) Under the same conditions, rrssMM eyes begin to darken at about 4 to 8 days, and reach an equilibrium (of a lighter chocolate shade) in about 5 to 7 weeks. The degree of phenotypic divergence between the colours of rrSS and rrss is at first nil; it then increases to a maximum at about 212 to 3 weeks from extrusion, after which it diminishes once more. It is, however, not completely obliterated in the adult. (7) In addition a factor “d” has been found which delays the onset of rapid pigment development until sexual maturity. The rate of subsequent darkening is that characteristic of the other factors present. (8) Other agencies also influence melanin formation. In rr eyes melanin is formed rapidly at 23° C. (above which temperature the stocks are unhealthy), less rapidly at 20° C., and only to a slight extent, beginning after about four months, at or below 14° C. (9) In RR (wild type and black-no-white) eyes, however, low temperatures merely cause a slight delay in melanin formation. (10) The area of the eye also influences the colour. The eye facets continue to increase in size after the melanin has attained its equilibrium position. Thus the same amount of pigment is spread over a greater area, and the eye appears slightly paler. This again does not apply to RR eyes, presumably owing to the large quantity of black pigment formed. New facets are added so long as growth continues. Since they behave as distinct units in pigment formation, those which have appeared most recently will be bright red while the older ones are already blackish. (11) Other instances are given of genes which appear to control rates of development in various animals. (12) It is suggested that the effects of multiple allelomorph series (e.g. for eye-colour in Drosophila) may represent a cross-section through a series of developmental curves of one and the same substance, the curves differing as regards rates of formation of the substance, times of onset of deposition, and final level of the equilibrium position obtained.