Types Of Evolutionary Change Research Articles

An integrated, multi-level analysis of thermal effects on intertidal molluscs for understanding species distribution patterns.

Elucidating the physiological mechanisms that underlie thermal stress and discovering how species differ in capacities for phenotypic acclimatization and evolutionary adaptation to this stress is critical for understanding current latitudinal and vertical distribution patterns of species and for predicting their future state in a warming world. Such mechanistic analyses require careful choice of study systems (species and temperature-sensitive traits) and design of laboratory experiments that reflect the complexities of in situ conditions. Here, we critically review a wide range of studies of intertidal molluscs that provide mechanistic accounts of thermal effects across all levels of biological organization - behavioural, organismal, organ level, cellular, molecular, and genomic - and show how temperature-sensitive traits govern distribution patterns and capacities for coping with thermal stress. Comparisons of congeners from different thermal habitats are especially effective means for identifying adaptive variation. We employ these mechanistic analyses to illustrate how species differ in the severity of threats posed by rising temperature. Counterintuitively, we show that some of the most heat-tolerant species may be most threatened by increases in temperatures because of their small thermal safety margins and minimal abilities to acclimatize to higher temperatures. We discuss recent molecular biological and genomic studies that provide critical foundations for understanding the types of evolutionary changes in protein structure, RNA secondary structure, genome content, and gene expression capacities that underlie adaptation to temperature. Duplication of stress-related genes, as found in heat-tolerant molluscs, may provide enhanced capacity for coping with higher temperatures. We propose that the anatomical, behavioural, physiological, and genomic diversity found among intertidal molluscs, which commonly are of critical importance and high abundance in these ecosystems, makes this group of animals a highly appropriate study system for addressing questions about the mechanistic determinants of current and future distribution patterns of intertidal organisms.

PAMPs, DAMPs and SAMPs: Host Glycans are Self‐Associated Molecular Patterns, but subject to Microbial Molecular Mimicry

It has long been known that Pathogen-Associated Molecular Patterns (PAMPs, e.g., lipo-oligosaccharides, LOS) and Danger-Associated Molecular Patterns (DAMPs, e.g., fragments of endogenous hyaluronan) can be glycans or modified glycans. We have more recently emphasized that host glycans can also serve as Self-Associated Molecular Patterns (SAMPs), e.g., sialic acid-bearing glycans that are recognized by CD33-related Siglecs on innate immune cells to dampen responses, or by complement Factor H to dampen complement-mediated activation. However, several commensal or pathogenic organisms have evolved successful molecular mimicry of sialylated SAMPs, so as to hijack these mechanisms and suppress innate immune responses against them. Paired activating CD33rSiglecs have emerged in some lineages, presumably to counter hijacking by microbial molecular mimicry of sialylated SAMPs. Meanwhile, sialylated host SAMPs also have to evolve rapidly to escape from other pathogens that utilize them as targets to initiate infection. The ongoing pressures of these often-competing selection forces can explain our finding that the sialic-acid binding domains of CD33rSiglecs and Factor H show much higher than expected Ka/Ks ratios (an excess of non-synonymous substitutions changing encoded amino acids, over synonymous substitutions). Examples can also be found of lineage-specific complete loss of sialic binding e.g., via mutation of an essential arginine residue in some CD33rSiglec binding pocket––or even whole-sale elimination of the binding domain e.g., alternate splicing out of the amino-terminal V-set domain of CD33/Siglec-3. Such evolutionary changes can be either fixed or polymorphic within a given species. Further complexity arises because CD33rSiglec and Factor H can be directly engaged via protein:protein interactions, both with endogenous proteins such as Hsp70 and Vimentin, and with surface proteins of commensals e.g., the PorB protein of N. gonorrhea. The overall outcome is inter-species or intra-species variations in the intensity of innate immune responses, which can be reflected in relative susceptibility or resistance to infectious agents and/or harmful aggravation of endogenous inflammatory diseases. Perhaps because of the major changes in the sialome resulting from inactivation of the CMAH gene in the Homo lineage leading to humans, these and many other types of evolutionary changes appear to be very prominent in our species and in our pathogen regimes. This presentation will provide an overview of these topics and examples of our recent work in these areas. Varki, A.: Since there are PAMPs and DAMPs, there must be SAMPs? Glycan “self-associated molecular patterns” dampen innate immunity, but pathogens can mimic them. Glycobiology, 21:1121-1124, 2011. Padler-Karavani, V., Hurtado-Ziola, N., Chang, Y.-C., Sonnenburg, J., Ronaghy, A., Yu, H., Verhagen, A., Nizet, V., Chen, X., Varki, N., Varki, A., Angata, T.: Rapid Evolution of Binding Specificities and Expression Patterns of Inhibitory CD33-related Siglecs in Primates. FASEB J. 28:1280-93, 2014. Laubli, H. and Varki, A. Sialic acid–binding immunoglobulin-like lectins (Siglecs) detect self-associated molecular patterns to regulate immune responses. Cell. Mol. Life Sci. Springer, International. 2019.

The dynamics of export-import interaction

This work is devoted to the dynamic interpretation of the basic provisions of the quantitative theory of money. Namely, the construction of models of price changes for marketable products in the performance of export-import activities both in discrete and continuous time. A number of hypotheses are used to determine the conditions for the violation of the equilibrium states of the trade balance using the classical macroeconomic Fisher equation. An overview of scientific works is presented, which highlights the main factors for the implementation of foreign economic activity: exchange rates and devaluation. The analysis of the considered sources testifies to the presence of the problem of stability of the observed dynamic processes in the vicinity of the state of equilibrium, which have the traditional name of the Marshall-Lerner condition. A detailed study of the stability criteria of a discrete dynamic model with quadratic nonlinearity demonstrates a significant variety of trajectories of the studied process. These are, in particular, increasing or decreasing aperiodic behavior, oscillating processes of a fixed period, bifurcations of doubling the period and chaotic trajectories. The limits of distribution of various types of evolutionary changes in terms of elasticities as important indicators of export-import operations are indicated. For models of pricing dynamics in continuous time, a detailed analysis of the structural instability of equilibrium states was performed. Saddle-nodal bifurcation and no less important Andronov-Hopf bifurcation, which is associated with the formation of a boundary cycle around the equilibrium state, are distinguished. It is proved that the found cycle is unique and stable. For a discrete model of price formation, appropriate calculations are performed to demonstrate different types of evolutionary behavior. The given discrete model based on the Fisher equation can be used for qualitative forecasting (by trajectories) of the dynamics of internal pricing without the use of traditional methodology of econometric analysis of time series. This model is characterized by the fact that it is reduced to a single complex parameter and this greatly simplifies the definition of the corresponding types of dynamical regimes in the vicinity of equilibrium states.

PAMPs, DAMPs and SAMPs: Host Glycans are Self‐Associated Molecular Patterns, but subject to Microbial Molecular Mimicry

It has long been known that Pathogen‐Associated Molecular Patterns (PAMPs, e.g., lipooligosaccharides, LOS) and Danger‐Associated Molecular Patterns (DAMPs, e.g., fragments of endogenous hyaluronan) can be glycans or modified glycans. We have more recently emphasized that host glycans can also serve as Self‐Associated Molecular Patterns (SAMPs), e.g., sialic acid‐bearing glycans that are recognized by CD33‐related Siglecs on innate immune cells to dampen responses, or by complement Factor H to dampen complement‐mediated activation. However, several commensal or pathogenic organisms have evolved successful molecular mimicry of sialylated SAMPs, so as to hijack these mechanisms and suppress innate immune responses against them. Paired activating CD33rSiglecs have emerged in some lineages, presumably to counter hijacking by microbial molecular mimicry of sialylated SAMPs. Meanwhile, sialylated host SAMPs also have to evolve rapidly to escape from other pathogens that utilize them as targets to initiate infection. The ongoing pressures of these often‐competing selection forces can explain our finding that the sialic‐acid binding domains of CD33rSiglecs and Factor H show much higher than expected Ka/Ks ratios (an excess of non‐synonymous substitutions changing encoded amino acids, over synonymous substitutions). Examples can also be found of lineage‐specific complete loss of sialic binding e.g., via mutation of an essential arginine residue in some CD33rSiglec binding pocket—or even whole‐sale elimination of the binding domain e.g., alternate splicing out of the amino‐terminal V‐set domain of CD33/Siglec‐3. Such evolutionary changes can be either fixed or polymorphic within a given species. Further complexity arises because CD33rSiglec and Factor H can be directly engaged via protein:protein interactions, both with endogenous proteins such as Hsp70 and Vimentin, and with surface proteins of commensals e.g., the PorB protein of N. gonorrhea. The overall outcome is inter‐species or intra‐species variations in the intensity of innate immune responses, which can be reflected in relative susceptibility or resistance to infectious agents and/or harmful aggravation of endogenous inflammatory diseases. Perhaps because of the major changes in the sialome resulting from inactivation of the CMAH gene in the Homo lineage leading to humans, these and many other types of evolutionary changes appear to be very prominent in our species and in our pathogen regimes. This presentation will provide an overview of these topics and examples of our recent work in these areas.

Role of heterochronies in the morphogenesis of paleozoic ammonoids

Various types of evolutionary changes related to shifts in the appearance or order of formation of characters, i.e., heterochronies are shown. The most common such changes in Paleozoic ammonoids was the appearance of mosaic forms combining conservative and advanced characters resulting from recapitulation and paedomorphosis. These phenomena are related to certain phylogenetic stages in each group: the growth stage predominantly showed recapitulations; the diversification stage showed the appearance of many mosaic forms; the decline stage commonly shows paedomorphosis connected with retardation.

Past climate change on Sky Islands drives novelty in a core developmental gene network and its phenotype.

BackgroundA fundamental and enduring problem in evolutionary biology is to understand how populations differentiate in the wild, yet little is known about what role organismal development plays in this process. Organismal development integrates environmental inputs with the action of gene regulatory networks to generate the phenotype. Core developmental gene networks have been highly conserved for millions of years across all animals, and therefore, organismal development may bias variation available for selection to work on. Biased variation may facilitate repeatable phenotypic responses when exposed to similar environmental inputs and ecological changes. To gain a more complete understanding of population differentiation in the wild, we integrated evolutionary developmental biology with population genetics, morphology, paleoecology and ecology. This integration was made possible by studying how populations of the ant species Monomorium emersoni respond to climatic and ecological changes across five ‘Sky Islands’ in Arizona, which are mountain ranges separated by vast ‘seas’ of desert. Sky Islands represent a replicated natural experiment allowing us to determine how repeatable is the response of M. emersoni populations to climate and ecological changes at the phenotypic, developmental, and gene network levels.ResultsWe show that a core developmental gene network and its phenotype has kept pace with ecological and climate change on each Sky Island over the last ∼90,000 years before present (BP). This response has produced two types of evolutionary change within an ant species: one type is unpredictable and contingent on the pattern of isolation of Sky lsland populations by climate warming, resulting in slight changes in gene expression, organ growth, and morphology. The other type is predictable and deterministic, resulting in the repeated evolution of a novel wingless queen phenotype and its underlying gene network in response to habitat changes induced by climate warming.ConclusionOur findings reveal dynamics of developmental gene network evolution in wild populations. This holds important implications: (1) for understanding how phenotypic novelty is generated in the wild; (2) for providing a possible bridge between micro- and macroevolution; and (3) for understanding how development mediates the response of organisms to past, and potentially, future climate change.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0448-4) contains supplementary material, which is available to authorized users.

Kenneth Boulding's Theories of Evolutionary Economics and Organizational Change: A Reconstruction

:I identify a discrepancy between Kenneth Boulding's wide-ranging contributions to evolutionary economics and his professed ecological approach to it. I argue that Boulding has undersold his true contributions to evolutionary economics by trying to embed them into the ecological approach. I endeavor to overcome this discrepancy by differentiating between two types of evolutionary change analyzed in Boulding's writings: ecological change and civilizational change. In contrast to ecological change, civilizational change entails the possibility for the evolving system to overstrain the carrying capacity of the environment, thus suggesting the precarious relationship between civilizational complexity and sustainability. This argument sheds new light on Boulding's theory of “social organizers,” such as exchange, threat, and the integrative system. Boulding's understanding of civilizational change envisages the key role of threat and exchange in enabling civilizational complexity, while the integrative system is called upon to make this complexity sustainable.

Interstitial telomere-like repeats in the monocot family Araceae

Combining molecular cytogenetics and phylogenetic modelling of chromosome number change can shed light on the types of evolutionary changes that may explain the haploid numbers observed today. Applied to the monocot family Araceae, with chromosome numbers of 2n = 8 to 2n = 160, this type of approach has suggested that descending dysploidy has played a larger role than polyploidy in the evolution of the current chromosome numbers. To test this, we carried out molecular cytogenetic analyses in 14 species from 11 genera, using probes for telomere repeats, 5S rDNA and 45S rDNA and a plastid phylogenetic tree covering the 118 genera of the family, many with multiple species. We obtained new chromosome counts for six species, modelled chromosome number evolution using all available counts for the family and carried out fluorescence in situ hybridization with three probes (5S rDNA, 45S rDNA and Arabidopsis-like telomeres) on 14 species with 2n = 14 to 2n = 60. The ancestral state reconstruction provides support for a large role of descending dysploidy in Araceae, and interstitial telomere repeats (ITRs) were detected in Anthurium leuconerum, A. wendlingeri and Spathyphyllum tenerum, all with 2n = 30. The number of ITR signals in Anthurium (up to 12) is the highest so far reported in angiosperms, and the large repeats located in the pericentromeric regions of A. wendlingeri are of a type previously reported only from the gymnosperms Cycas and Pinus.

Human vs. Computer Diagnosis of Students’ Natural Selection Knowledge: Testing the Efficacy of Text Analytic Software

Our study examines the efficacy of Computer Assisted Scoring (CAS) of open-response text relative to expert human scoring within the complex domain of evolutionary biology. Specifically, we explored whether CAS can diagnose the explanatory elements (or Key Concepts) that comprise undergraduate students’ explanatory models of natural selection with equal fidelity as expert human scorers in a sample of >1,000 essays. We used SPSS Text Analysis 3.0 to perform our CAS and measure Kappa values (inter-rater reliability) of KC detection (i.e., computer–human rating correspondence). Our first analysis indicated that the text analysis functions (or extraction rules) developed and deployed in SPSSTA to extract individual Key Concepts (KCs) from three different items differing in several surface features (e.g., taxon, trait, type of evolutionary change) produced “substantial” (Kappa 0.61–0.80) or “almost perfect” (0.81–1.00) agreement. The second analysis explored the measurement of human–computer correspondence for KC diversity (the number of different accurate knowledge elements) in the combined sample of all 827 essays. Here we found outstanding correspondence; extraction rules generated using one prompt type are broadly applicable to other evolutionary scenarios (e.g., bacterial resistance, cheetah running speed, etc.). This result is encouraging, as it suggests that the development of new item sets may not necessitate the development of new text analysis rules. Overall, our findings suggest that CAS tools such as SPSS Text Analysis may compensate for some of the intrinsic limitations of currently used multiple-choice Concept Inventories designed to measure student knowledge of natural selection.

Developmental aspects of morphological disparity dynamics: a simple analytical exploration

We have devised a simple model for assessing the role of development in shaping the evolution of morphological disparity. Disparity of a clade at any given time is expressed in terms of the developmental dynamics that lead to the variety of adult morphotypes observed. We use assumed phenotypic manifestations of developmental processes, as they could be detected from allometric characterizations, to distinguish a few, nonexclusive types of evolutionary changes in ontogeny. On the basis of this formalization, we describe the diversification of hypothetical clades, using the standard curve of adult morphological disparity, the curve of juvenile disparity, and the curve of allometric disparity, the latter quantifying the diversification of clades in allometric space. Contrasts of these curves reflect the underlying developmental scheme that drives temporal changes in disparity. We then vary the parameters of the model to assess the expected signature of each metric under specific conditions: changes in the relative frequencies of the types of evolutionary developmental changes, changes in the transition magnitude attached to each of them, and effects of temporal variation in average adult size on disparity curves and patterns of morphospace occupation. Results emphasize the potential contribution of these proxies for developmental dynamics—juvenile morphological disparity, allometric disparity, and average adult size—in enriching the interpretation of standard disparity curves and the description of clade histories, with possible process-oriented inferences.

Components meet aspects: Assessing design stability of a software product line

Context It is important for Product Line Architectures (PLA) to remain stable accommodating evolutionary changes of stakeholder’s requirements. Otherwise, architectural modifications may have to be propagated to products of a product line, thereby increasing maintenance costs. A key challenge is that several features are likely to exert a crosscutting impact on the PLA decomposition, thereby making it more difficult to preserve its stability in the presence of changes. Some researchers claim that the use of aspects can ameliorate instabilities caused by changes in crosscutting features. Hence, it is important to understand which aspect-oriented (AO) and non-aspect-oriented techniques better cope with PLA stability through evolution. Objective This paper evaluates the positive and negative change impact of component and aspect based design on PLAs. The objective of the evaluation is to assess how aspects and components promote PLA stability in the presence of various types of evolutionary change. To support a broader analysis, we also evaluate the PLA stability of a hybrid approach (i.e. combined use of aspects and components) against the isolated use of component-based, OO, and AO approaches. Method An quantitative and qualitative analysis of PLA stability which involved four different implementations of a PLA: (i) an OO implementation, (ii) an AO implementation, (iii) a component-based implementation, and (iv) a hybrid implementation where both components and aspects are employed. Each implementation has eight releases and they are functionally equivalent. We used conventional metrics suites for change impact and modularity to measure the architecture stability evaluation of the 4 implementations. Results The combination of aspects and components promotes superior PLA resilience than the other PLAs in most of the circumstances. Conclusion It is concluded that the combination of aspects and components supports the design of high cohesive and loosely coupled PLAs. It also contributes to improve modularity by untangling feature implementation.

A PHYLOGENETIC HOT SPOT FOR EVOLUTIONARY NOVELTY IN MIDDLE AMERICAN TREEFROGS

Among the various types of evolutionary changes in morphology, the origin of novel structures may be the most rare and intriguing. Here we show statistically that the origins of different novel structures may be correlated and phylogenetically clustered into "hot spots" of evolutionary novelty, in a case study involving skull elements in treefrogs. We reconstruct phylogenetic relationships within a clade of Middle American treefrogs based on data from 10 nuclear and four mitochondrial genes and then analyze morphological evolution across this tree. New cranial elements are rare among anurans and tetrapods in general, but three novel elements have evolved within this clade, with a 40% increase in the number of skull roof elements in some species. Two of these elements also evolved in a related clade of treefrogs, and these two novel elements may have each evolved repeatedly within one or both clades. The molecular phylogeny suggests striking homoplasy in cranial morphology and shows that parsimony and Bayesian analyses of the morphological data have produced misleading results with strong statistical support. The origins of the novel elements are associated with an overall increase in the ossification of dermal skull roof elements (suggesting peramorphosis) and with the evolution of a novel adaptive behavior. Our study may be the first to statistically document significant phylogenetic clustering and correlation in the origins of novel structures, and to demonstrate the strongly misleading effects of peramorphosis on phylogenetic analysis.

Assessment of the probabilities for evolutionary structural changes in protein folds

The evolution of protein sequences can be described by a stepwise process, where each step involves changes of a few amino acids. In a similar manner, the evolution of protein folds can be at least partially described by an analogous process, where each step involves comparatively simple changes affecting few secondary structure elements. A number of such evolution steps, justified by biologically confirmed examples, have previously been proposed by other researchers. However, unlike the situation with sequences, as far as we know there have been no attempts to estimate the comparative probabilities for different kinds of such structural changes. We have tried to assess the comparative probabilities for a number of known structural changes, and to relate the probabilities of such changes with the distance between protein sequences. We have formalized these structural changes using a topological representation of structures (TOPS), and have developed an algorithm for measuring structural distances that involve few evolutionary steps. The probabilities of structural changes then were estimated on the basis of all-against-all comparisons of the sequence and structure of protein domains from the CATH-95 representative set. The results obtained are reasonably consistent for a number of different data subsets and permit the identification of several 'most popular' types of evolutionary changes in protein structure. The results also suggest that alterations in protein structure are more likely to occur when the sequence similarity is >10% (the average similarity being approximately 6% for the data sets employed in this study), and that the distribution of probabilities of structural changes is fairly uniform within the interval of 15-50% sequence similarity. The algorithms have been implemented on the Windows operating system in C++ and using the Borland Visual Component Library. The source code is available on request from the first author. The data sets used for this study (representative sets of protein domains, matrices of sequence similarities and structural distances) are available on http://bioinf.mii.lu.lv/epsrc_project/struct_ev.html.

Development and evolution of a heterogeneous continuous media server: a case study: Practice Articles

Media server software is significantly complicated to develop and maintain, due to the nature of the many interface aspects which must be considered. This paper provides a case study of the design, implementation, and evolution of a continuous media file server. We place emphasis on the evolution of the software and our approach to maintainability. The user interface is a major consideration, even though the server software would appear isolated from that factor. Since continuous media servers must send the raw data to a client application over a network, the protocol considerations, hardware interface, and data storage/retrieval methods are of the paramount importance. In addition, the application programmer's interface to the server facilities has an impact on both the internal design and the performance of such a server. We discuss our experiences and insight into the development of such software products within a small research-based university environment. We experienced two main types of evolutionary change: requirements changes from the limited user community and performance enhancements/corrections. While the former were anticipated via a generic interface and modular design structure, the latter were surprising and substantially more difficult to solve. Copyright © 2005 John Wiley & Sons, Ltd.

TRANSLATING BETWEEN MICROEVOLUTIONARY PROCESS AND MACROEVOLUTIONARY PATTERNS: THE CORRELATION STRUCTURE OF INTERSPECIFIC DATA.

As species evolve along a phylogenetic tree, we expect closely related species to retain some phenotypic similarities due to their shared evolutionary histories. The amount of expected similarity depends both on the hierarchical phylogenetic structure, and on the specific magnitude and types of evolutionary changes that accumulate during each generation. In this study, we show how models of microevolutionary change can be translated into the resulting macroevolutionary patterns. We illustrate how the structure of phenotypic covariances expected in interspecific measurements can be derived, and how this structure depends on the microevolutionary forces guiding phenotypic change at each generation. We then explore the covariance structure expected from several simple microevolutionary models of phenotypic evolution, including various combinations of random genetic drift, directional selection, stabilizing selection, and environmental change, as well as models of punctuated or burst-like evolution. We find that stabilizing selection leads to patterns of exponential decrease of between species covariance with phylogenetic distance. This is different from the usual linear patterns of decrease assumed in most comparative and systematic methods. Nevertheless, linear patterns of decrease can result from many processes in addition to random genetic drift, such as directional and fluctuating selection as well as modes of punctuated change. Our framework can be used to develop methods for (1) phylogenetic reconstruction; (2) inference of the evolutionary process from comparative data; and (3) conducting or evaluating statistical analyses of comparative data while taking phylogenetic history into account.

The population biology of transposable elements.

A transposable element can be defined as a DNA sequence capable of moving to new sites in the genome. Such DNA sequences have been described in a wide range of organisms. The evolutionary processes affecting transposable elements can thus be divided into two categories: changes in sequence and changes in genomic location. As with other types of evolutionary change, the nature of the evolutionary process will be reflected in the extent and type of genetic variation existing in wild populations. Quantitative models of the evolution of transposable element sequences and positions will be outlined, and related to relevant data. The extent to which models designed to describe obvious transposable elements such as the mobile sequences of Drosophila are also applicable to interspersed repetitive DNAs from other species will be discussed.

Postembryonic nongonadal cell lineages of the nematode Panagrellus redivivus: Description and comparison with those of Caenorhabditis elegans

The postembryonic nongonadal cell lineages of the nematode Panagrellus redivivus are described and compared with those of Caenorhabditis elegans. The newly hatched larvae of P. redivivus females and males and C. elegans hermaphrodites and males are very similar. An almost identical set of blast cells divides postembryonically in P. redivivus and C. elegans to produce similar changes in the neuronal, muscular, hypodermal, and digestive systems. Most of these cell lineages are invariant; however, there is substantial variability in the number of cell divisions in the relatively extensive lineages of the lateral hypodermis of P. redivivus. Typically, in P. redivivus females, 55 blast cells generate 635 surviving progeny and 29 cell deaths; in P. redivivus males, 59 blast cells generate 758 surviving progeny and 35 cell deaths. The lineages generating the cells of the male tails of P. redivivus and C. elegans are almost identical; thus, the grossly different characteristics of these structures must reflect differences in the morphogenesis of cells equivalent in lineage history. Laser ablation experiments demonstrate that the gonad induces vulva development and that cell-cell interactions are important in specifying the fates of hypodermal precursor cells. The lateral hypodermal lineages provide striking examples of the apparent construction of complex lineages from modular sublineages; one simple pattern of cell divisions and cell fates occurs 70 times in the P. redivivus female. The differences in cell lineage between P. redivivus and C. elegans are relatively minor, and many appear to have involved two types of evolutionary change: the replacement of sublineages, and the modification of sublineages by the four classes of lineage transformations previously proposed based on a comparison of P. redivivus and C. elegans gonadal cell lineages (Sternberg and Horvitz, 1981). These types of differences suggest that the genetic programming of cell lineage includes instructions specifying where and when a particular sublineage is utilized, and other instructions specifying the nature of that sublineage.

POPULATION DIFFERENTIATION IN EUPHYDRYAS EDITHA BUTTERFLIES: LARVAL ADAPTATION TO DIFFERENT HOSTS.

Adaptation of phytophagous insects to novel larval host plants can involve changes in at least three different suites of characters: those associated with female oviposition behavior, with larval feeding behavior, and with larval digestive physiology (Dethier, 1954, 1970; Bush, 1974; Feeny, 1975). Differences between closely related insect species and between conspecific populations indicate that evolutionary change in oviposition behavior is common (Singer, 1971; Smiley, 1978; Jones and Ives, 1979). Moreover, similar differences in larval growth rates and survivorship when different species or populations are reared on the same host plant indicate that larval adaptation often accompanies changes in oviposition behavior (Smiley, 1978; Futuyma et al., in press). However, few investigations have explicity attempted to separate the contributions of differences in larval feeding behavior and digestive physiology to observed differences in growth performance. Because both the number and type of characters involved in larval adaptation will presumably influence the probability that a newlyfounded insect population will successfully adapt to a novel host before becoming extinct, it seems desirable to characterize the types of changes that occur during adaptation of a population to its host plants. This study was conducted to provide such a characterization for the checkerspot butterfly, Euphydryas editha. In western North America, E. editha exists as a series of discrete populations (White and Singer, 1971; Ehrlich et al., 1975). In most populations, females oviposit on only one or perhaps two different plant species in the family Scrophulariaceae or the genus Plantago (Plantaginaceae), even though other species used by other populations may be available. Although populations differ both in acceptance responses of females to a standard array of host species (Singer, 1971, and pers. comm.) and in electrophoretically detectable patterns of enzyme variation (McKechnie et al., 1975), little is known about variation among populations in characters associated with larval adaptation. Although populations are normally highly localized and dispersal between them is low (Ehrlich, 1961; Ehrlich et al., 1975), population extinction and refounding by occasional migrants is probably fairly common (Ehrlich et al., 1980). Moreover, because populations specializing on one host species interdigitate geographically with populations specializing on others (White and Singer, 1974), it is likely that the founding of a new population often involves colonization of a novel host. A comparison of populations using different host species may elucidate the types of evolutionary changes that accompany such colonization. In this study I compare the growth performances of larvae from two E. editha populations that use different hosts. Specifically, I ask (1) Do larvae from different populations exhibit differential adaptation to their own host plants, as measured by growth rates and survivorship? and (2) If so, are observed differences due to differences in digestive physiology, feeding behavior, or both?

Non-adaptive or Neutral Characters in Evolution

I AM glad that Cain admits that genetic drift may be a real factor in evolution, even though he may not be willing to admit that its effect is significant. Since I have not wished to express an opinion on the relative importance of selection and drift, it seems that the only point at issue between us is that I do not accept the present evidence as being so strongly against drift that we should not, when dealing with some types of evolutionary change—especially trivial changes in micro-evolution—regard it and selection as equally possible explanations when neither is proved. If we do so regard them, it seems as much a fallacy to assume selection alone where there is no disproof of drift, as to assume drift wherever there is no proof of selection. If in any case analysis of selective effects is incomplete, this fact cannot be used as evidence against drift as the efficient cause.