BIPARENTAL INBREEDING DEPRESSION IN THE SELF-INCOMPATIBLE ANNUAL PLANT GAILLARDIA PULCHELLA (ASTERACEAE)

Biparental inbreeding is thought to be a common feature of plant populations with restricted pollen dispersal. It is generally assumed that the inbreeding depression frequently observed to accompany self-fertilization can be extrapolated to the lesser degrees of consanguinity involved in biparental inbreeding, but this is virtually untested. To test this assumption, seeds collected from a single natural population of the self-incompatible annual Gaillardia pulchella were used to generate full-sib families derived by crossing either noninbred full-sibs (inbred families) or noninbred nonrelatives (outbred families). Members of each family were divided between high-stress and low-stress treatments that differed in soil volume and nutrient level. Inbred seedlings had a lower chance of survival, were more likely to be morphologically abnormal, and grew more slowly than outbred seedlings, indicating the presence of biparental inbreeding depression. Stress treatment had no significant effect on inbreeding depression, and no family stress-environment interactions were detected. Inbreeding did not increase the among-family variance in growth rate, suggesting that inbreeding depression of growth rate is caused by many genes with small individual effects. Relative to direct estimates of inbreeding depression, observed levels of near-neighbor outcrossing depression, presumed to be biparental inbreeding depression, are surprisingly high in many plant species.     

A Biosemiotic Perspective of the Resource Criterion: Toward a General Theory of Resources

Describing resources and their relationships with organisms seems to be a useful approach to a ‘unified ecology’, contributing to fill the gap between natural and human oriented processes, and opening new perspectives in dealing with biological complexity. This Resource Criterion defines the main properties of resources, describes the mechanisms that link them to individual species, and gives a particular emphasis to the biosemiotic approach that allows resources to be identified inside a heterogeneous ecological medium adopting the eco-field model. In particular, this Criterion allows to couple matter, structured energy and information composing the ecological systems to the biosemiotic and cognitive mechanisms adopted by individual species to track resources, transforming neutral surroundings into meaningful species-specific Umwelten. The expansion of the human semiotic niche that is a relevant evolutionary process of the present time, assigns the role of powerful and efficient agency to the Resources Criterion to evaluate the effect of human intrusion into the natural systems with habits of key stone species, under the challenge of a growing use of alloctonous, immaterial and symbolic resources of the actual globalized societal models. The Resource Criterion interprets the ecological dynamics contributing to complete the epistemology of the ecology, to open a bridge toward economy and other societal sciences, and to contribute to formulate a General Theory of Resources.     

Putting the Biological Species Concept to the Test: Using Mating Networks to Delimit Species

Although interfertility is the key criterion upon which Mayr’s biological species concept is based, it has never been applied directly to delimit species under natural conditions. Our study fills this gap. We used the interfertility criterion to delimit two closely related oak species in a forest stand by analyzing the network of natural mating events between individuals. The results reveal two groups of interfertile individuals connected by only few mating events. These two groups were largely congruent with those determined using other criteria (morphological similarity, genotypic similarity and individual relatedness). Our study, therefore, shows that the analysis of mating networks is an effective method to delimit species based on the interfertility criterion, provided that adequate network data can be assembled. Our study also shows that although species boundaries are highly congruent across methods of species delimitation, they are not exactly the same. Most of the differences stem from assignment of individuals to an intermediate category. The discrepancies between methods may reflect a biological reality. Indeed, the interfertility criterion is an environment-dependant criterion as species abundances typically affect rates of hybridization under natural conditions. Thus, the methods of species delimitation based on the interfertility criterion are expected to give results slightly different from those based on environment-independent criteria (such as the genotypic similarity criteria). However, whatever the criterion chosen, the challenge we face when delimiting species is to summarize continuous but non-uniform variations in biological diversity. The grade of membership model that we use in this study appears as an appropriate tool.     

Mating system contributes only slightly to female maintenance in gynodioecious Geranium maculatum (Geraniaceae)

Gynodioecy, the co-occurrence of female and hermaphroditic individuals within a population, is an important intermediate in the evolution of separate sexes. The first step, female maintenance, requires females to have higher seed fitness compared with hermaphrodites. A common mechanism thought to increase relative female fitness is inbreeding depression avoidance, the magnitude of which depends on hermaphroditic selfing rates and the strength of inbreeding depression. Less well studied is the effect of biparental inbreeding on female fitness. Biparental inbreeding can affect relative female fitness only if its consequence or frequency differs between sexes, which could occur if sex structure and genetic structure both occur within populations. To determine whether inbreeding avoidance and/or biparental inbreeding can account for female persistence in Geranium maculatum, we measured selfing and biparental inbreeding rates in four populations and the spatial genetic structure in six populations. Selfing rates of hermaphrodites were low and did not differ significantly from zero in any population, leading to females gaining at most a 1–14% increase in seed fitness from inbreeding avoidance. Additionally, although significant spatial genetic structure was found in all populations, biparental inbreeding rates were low and only differed between sexes in one population, thereby having little influence on female fitness. A review of the literature revealed few sexual differences in biparental inbreeding among other gynodioecious species. Our results show that mating system differences may not fully account for female maintenance in this species, suggesting other mechanisms may be involved.     

Estimating selfing rates from reconstructed pedigrees using multilocus genotype data

Several methods have been developed to estimate the selfing rate of a population from a sample of individuals genotyped for several marker loci. These methods can be based on homozygosity excess (or inbreeding), identity disequilibrium, progeny array (PA) segregation or population assignment incorporating partial selfing. Progeny array-based method is generally the best because it is not subject to some assumptions made by other methods (such as lack of misgenotyping, absence of biparental inbreeding and presence of inbreeding equilibrium), and it can reveal other facets of a mixed-mating system such as patterns of shared paternity. However, in practice, it is often difficult to obtain PAs, especially for animal species. In this study, we propose a method to reconstruct the pedigree of a sample of individuals taken from a monoecious diploid population practicing mixed mating, using multilocus genotypic data. Selfing and outcrossing events are then detected when an individual derives from identical parents and from two distinct parents, respectively. Selfing rate is estimated by the proportion of selfed offspring in the reconstructed pedigree of a sample of individuals. The method enjoys many advantages of the PA method, but without the need of a priori family structure, although such information, if available, can be utilized to improve the inference. Furthermore, the new method accommodates genotyping errors, estimates allele frequencies jointly and is robust to the presence of biparental inbreeding and inbreeding disequilibrium. Both simulated and empirical data were analysed by the new and previous methods to compare their statistical properties and accuracies.     

The Great Chain of Semiosis. Investigating the Steps in the Evolution of Semiotic Competence

Based on the conception of life and semiosis as co-extensive an attempt is given to classify cognitive and communicative potentials of species according to the plasticity and articulatory sophistication they exhibit. A clear distinction is drawn between semiosis and perception, where perception is seen as a high-level activity, an integrated product of a multitude of semiotic interactions inside or between bodies. Previous attempts at finding progressive trends in evolution that might justify a scaling of species from primitive to advanced levels have not met with much success, but when evolution is considered in the light of semiosis such a scaling immediately catches the eye. The main purpose of this paper is to suggest a scaling of this progression in semiotic freedom into a series of distinct steps. The elleven steps suggested are: 1) molecular recognition, 2) prokaryote-eukaryote transformation (privatization of the genome), 3) division of labor in multicellular organisms (endosemiosis), 4) from irritability to phenotypic plasticity, 5) sense perception, 6) behavioral choice, 7) active information gathering, 8) collaboration, deception, 9) learning and social intelligence, 10) sentience, 11) consciousness. In light of this, the paper finally discusses the conceptual framework for biosemiotic evolution. The evolution of biosemiotic capabilities does not take the form of an ongoing composition of simple signs (icons, indices, signals, etc.) into composite wholes. Rather, it takes the shape of the increasing subdivision and control of a primitive, holophrastic perception-action circuit already committed to “proto-propositions” (dicisigns) reliably guiding action already in the most primitive species.     

Species as historical individuals

The species category is defined as thesmallest historical individual within which there is a parental pattern of ancestry and descent. The use of historical individual in this definition is consistent with the prevailing notion that speciesper se are not involved in processes — they are effects, not effectors. Reproductive isolation distinguishes biparental historical species from their parts, and it provides a basis for understanding the nature of the evidence used to discover historical individuals.     

Direct Familiarity Does Not Alter Mating Preference for Sisters in Male Pelvicachromis taeniatus (Cichlidae)

In social species, individuals who grew up together are usually relatives. Therefore, direct familiarity is normally a reliable kin recognition mechanism that is used in many species to discriminate kin from non‐kin. It has been shown in animals and in humans that familiar individuals are rejected as mating partners in order to circumvent potential costs of inbreeding. Here, we tested whether direct familiarity also leads to inbreeding avoidance behaviour in male Pelvicachromis taeniatus, a small socially monogamous cichlid with biparental brood care. In mate choice experiments, reproductively active males were given the choice between familiar sisters and unfamiliar, unrelated females. In a previous study, both sexes of P. taeniatus had preferred unfamiliar full‐sibs over unfamiliar unrelated individuals as mating partners. Here, we show that direct familiarity does not alter the male preference for closely related females. This result is in accordance with theoretical predictions, that inbreeding can be advantageous under certain conditions, and confirms previous findings, that active inbreeding is an adaptive strategy in P. taeniatus.     

Role of evolutionary and ecological factors in the reproductive success and the spatial genetic structure of the temperate gorgonian Paramuricea clavata

Dispersal and mating features strongly influence the evolutionary dynamics and the spatial genetic structure (SGS) of marine populations. For the first time in a marine invertebrate, we examined individual reproductive success, by conducting larval paternity assignments after a natural spawning event, combined with a small‐scale SGS analysis within a population of the gorgonian Paramuricea clavata. Thirty four percent of the larvae were sired by male colonies surrounding the brooding female colonies, revealing that the bulk of the mating was accomplished by males from outside the studied area. Male success increased with male height and decreased with increasing male to female distance. The parentage analyses, with a strong level of self‐recruitment (25%), unveiled the occurrence of a complex family structure at a small spatial scale, consistent with the limited larval dispersal of this species. However, no evidence of small scale SGS was revealed despite this family structure. Furthermore, temporal genetic structure was not observed, which appears to be related to the rather large effective population size. The low level of inbreeding found suggests a pattern of random mating in this species, which disagrees with expectations that limited larval dispersal should lead to biparental inbreeding. Surface brooding and investment in sexual reproduction in P. clavata contribute to multiple paternity (on average 6.4 fathers were assigned per brood), which enhance genetic diversity of the brood. Several factors may have contributed to the lack of biparental inbreeding in our study such as (i) the lack of sperm limitation at a small scale, (ii) multiple paternity, and (iii) the large effective population size. Thus, our results indicate that limited larval dispersal and complex family structure do not necessarily lead to biparental inbreeding and SGS. In the framework of conservation purposes, our results suggested that colony size, proximity among colonies and the population size should be taken into consideration for restoration projects.     

Change and aging senescence as an adaptation

Understanding why we age is a long-lived open problem in evolutionary biology. Aging is prejudicial to the individual, and evolutionary forces should prevent it, but many species show signs of senescence as individuals age. Here, I will propose a model for aging based on assumptions that are compatible with evolutionary theory: i) competition is between individuals; ii) there is some degree of locality, so quite often competition will be between parents and their progeny; iii) optimal conditions are not stationary, and mutation helps each species to keep competitive. When conditions change, a senescent species can drive immortal competitors to extinction. This counter-intuitive result arises from the pruning caused by the death of elder individuals. When there is change and mutation, each generation is slightly better adapted to the new conditions, but some older individuals survive by chance. Senescence can eliminate those from the genetic pool. Even though individual selection forces can sometimes win over group selection ones, it is not exactly the individual that is selected but its lineage. While senescence damages the individuals and has an evolutionary cost, it has a benefit of its own. It allows each lineage to adapt faster to changing conditions. We age because the world changes.     

River alteration and niche overlap among three native minnows (Cyprinidae) in the Missouri River hydrosystem

The influence of physical and hydrologic stabilization on habitat niche overlap among three native cyprinid species: flathead chub Platygobio gracilis , sicklefin chub Macrhybopsis meeki and sturgeon chub Macrhybopsis gelida , in riverine segments of the Missouri and Yellowstone Rivers in western North Dakota and eastern Montana, was evaluated. Collectively the three species exhibited higher niche overlap in quasi‐natural river segments than in segments highly altered by a mainstem dam based on relatively high percentages of individuals in quasi‐natural river segments that were classified correctly, according to species, in discriminant function analyses of resource use, compared to lower percentages of individuals classified correctly in the altered river segments. The lower niche overlap in altered river segments resulted primarily from the lower overlap between flathead chub and the remaining species; this appears to be related to a decline in the diversity of natural habitats and conditions that provided a wide range of habitat conditions suitable for all three species. Results from this study suggest that selective segregation and habitat changes, rather than interactive segregation and competition, is probably the mechanism responsible for the pattern of habitat use and niche overlap among the three species in the altered segments.     

Integrating across life-history stages: consequences of natal habitat effects on dispersal

Ecological and evolutionary processes are affected by forces acting at both local and regional scales, yet our understanding of how these scales interact has remained limited. These processes are fundamentally linked through individuals that develop as juveniles in one environment and then either remain in the natal habitat or disperse to new environments. Empirical studies in a diverse range of organisms have demonstrated that the conditions experienced in the natal habitat can have profound effects on the adult phenotype. This environmentally induced phenotypic variation can in turn affect the probability that an individual will disperse to a new environment and the ecological and evolutionary impact of that individual in the new environment. We synthesize the literature on this process and propose a framework for exploring the linkage between local developmental environment and dispersal. We then discuss the ecological and evolutionary implications of dispersal asymmetries generated by the effects of natal habitat conditions on individual phenotypes. Our review indicates that the influence of natal habitat conditions on adult phenotypes may be a highly general mechanism affecting the flow of individuals between populations. The wealth of information already gathered on how local conditions affect adult phenotype can and should be integrated into the study of dispersal as a critical force in ecology and evolution.     

Sex and aging: A comparison between two phenoptotic phenomena

Phenoptosis is a phenomenon that is genetically programmed and favored by natural selection, and that determines death or increased risk of death (fitness reduction) for the individual that manifests it. Aging, here defined as agerelated progressive mortality increase in the wild, if programmed and favored by natural selection, falls within the definition of phenoptosis. Sexual reproduction (sex), as for the involved individuals determines fitness reduction and, in some species, even certain death, also falls within the definition of phenoptosis. In this review, sex and aging are analyzed as phenoptotic phenomena, and the similarities between them are investigated. In particular, from a theoretical standpoint, the genes that cause and regulate these phenomena: (i) require analyses that consider both individual and supra-individual selection because they are harmful in terms of individual selection, but advantageous (that is, favored by natural selection) in particular conditions of supra-individual selection; (ii) determine a higher velocity of and greater opportunities for evolution and, therefore, greater evolutionary potential (evolvability); (iii) are advantageous under ecological conditions of K-selection and with finite populations; (iv) are disadvantageous (that is, not favored by natural selection) under ecological conditions of r-selection and with unlimited populations; (v) are not advantageous in all ecological conditions and, so, species that reproduce asexually or species that do not age are predicted and exist.     

Degree of social contact affects the emission of food calls in the common marmoset (Callithrix jacchus)

The aim of this study was to investigate whether the emission of food calls in common marmosets (Callithrix jacchus) is influenced by different social contexts. Food calls are emitted by this species only in the presence of preferred food. If these calls have any communicative function, it may be that individuals produce food calls in order to call family mates toward the food source. If this is the case, the number of calls produced should vary in accordance with the number of family mates present at the moment of the discovery of the food, i.e., the fewer family mates nearby, the more food calls are emitted. This hypothesis was tested with five pairs of common marmosets, by recording the number of food calls emitted in four experimental conditions: 1). isolation: completely isolated from the family mates; 2). visual isolation: separated by a wooden panel from the family mates; 3). visual contact: separated by a wire-mesh from the family mates; and 4). physical interaction: together with the family mates. The results show that the proportion of intervals during which food calls were produced by the pairs was significantly different in the four experimental conditions. It decreased from the isolation and visual isolation condition, through the visual contact condition, reaching the lowest value in the physical interaction condition. The variation observed in the proportion of intervals during which food calls were emitted, in relation to different social contexts, is an indication in favor of the communicative function of this vocalization.     

Sexual selection and simultaneous hermaphroditism among the Unionidae (Bivalvia: Mollusca)

Simultaneous hermaphroditism is an infrequent mode of reproduction among bivalves of the family Unionidae: only five of the 220 North American species are simultaneous hermaphrodites. However, hermaphroditic individuals of otherwise predominantly dioecious species have been encountered in 30 of I01 species examined. These hermaphroditic individuals as well as simultaneous hermaphrodites can exhibit considerable variability in the ratio of spermatogenic: oogenic tissue within the gonad, and the purposes of this paper are to determine the underlying causes of both this variability and the occurrence of occasional hermaphroditic individuals among dioecious species. Results indicate that the ratio of male: female gonodal tissue of a simultaneous hermaphrodite is bimodally distributed, and several hypotheses to account for this observation are presented. It is proposed that populations occurring in different habitats and under conditions of different individual density are subject to fundamentally different sexual selection pressures acting on ratios of allocation to male and female gametes. Occasional hermaphroditism among otherwise predominantly dioecious species was in this study associated with infection of the gonads by digenean trematodes. A model of sexual determination among unionids presented in this paper proposes that sex is determined by genetically controlled hormone levels: occasional hermaphrodites result from alterations in these hormone levels caused by developmental errors and trematodal infections which mimic the results of such errors. Predictions of this model are consistent with observed levels of variability in male: females gonadal tissue among occasional hermaphrodites.     

Culturing Mammalian Tissues for Cytogenetic Investigations

Biologists often tend to assume that natural selection acts fundamentally on individuals or on species. It is now appreciated that this is an oversimplification. Present understanding of the unit of natural selection, with its pivotal importance in evolution, largely derives from a consideration of the problem of why altruism exists. This paper reviews evidence for and against the theories that evolution acts essentially on genes, on individuals, on kin, or on larger groups.     

Quantifying gene flow from spatial genetic structure data in a metapopulation of Chamaecrista fasciculata (Leguminosae)

Abstract An extensive allozyme survey was conducted within a natural "meta" population of the native North American annual legume, Chamaecrista fasciculata (Leguminosae) to quantify genetic structure at different spatial scales. Gene flow was then estimated by a recently developed indirect method based on a continuous population model, using pairwise kinship coefficients between individuals. The indirect estimates of gene flow, quantified in terms of neighborhood size, with an average value on the order of 150 individuals, were concordant among different spatial scales (subpopulation, population, metapopulation). This gene-flow value lies within the range of direct estimates previously documented from observations of pollen and seed dispersal for the same metapopulation. Monte Carlo simulations using the direct measures of gene flow as parameters further demonstrated that the observed spatial pattern of allozyme variation was congruent with a model of isolation by distance. Combining previously published estimates of pollen dispersal distances with kinship coefficients from this study, we quantified biparental inbreeding relative to either a single subpopulation or the whole metapopulation. At the level of a neighborhood, little biparental inbreeding was observed and most departure from Hardy-Weinberg genotypic proportions was explained by self-fertilization, whereas both selfing and biparental inbreeding contributed to nonrandom mating at the metapopulation level. Gene flow was also estimated from indirect methods based on a discontinuous population structure model. We discuss these results with respect to the effect of a patchy population structure on estimation of gene flow.