Dispersal strategies in sponge larvae: integrating the life history of larvae and the hydrologic component

While known to be uniformly non-feeding, short-lived, and potentially short dispersing, sponge larvae display different behaviours (swimming ability and taxis). Our aim was to show whether sponge larvae with different behaviours exhibit different dispersal strategies under variable intensity of water movements. We first assessed the distribution of larvae of six taxa: Dictyoceratida spp., Dysidea avara, Crambe crambe, Phorbas tenacior, Scopalina lophyropoda, and Cliona viridis, collected through plankton sampling, and the abundance of the corresponding adult sponges across three hard bottom communities and a sandy bottom from a north-west Mediterranean rocky shore. We then tested adult–larvae couplings (abundance of larvae vs abundance of adults) under increasing levels of water movements (surge) to assess the importance of this environmental factor in driving differences in dispersal strategies. Adults of Dictyoceratida spp., D. avara, and P. tenacior were most abundant in semi-dark caves (SDC), C. crambe and C. viridis in communities of sciaphilic algae (SA), whereas the distribution of S. lophyropoda was extremely patchy, being present almost only in the SA community of one of the five stations studied. Larvae of Dictyoceratida spp. and P. tenacior were more abundant in the SDC, whereas D. avara and C. crambe were homogeneously distributed across the communities. The larvae of C. viridis were more abundant in the SA communities and the S. lophyropoda larvae were mostly present in one station and one community (SA). Increased water movement did not modify the adult–larvae coupling for Dictyoceratida spp., D. avara, and C. crambe, whereas it broke up the positive association for P. tenacior and to some extent S. lophyropoda. For C. viridis, possible variability in adult–larvae coupling was not tested because the larvae were collected on only one day under calm sea conditions. We confirm that efficient-swimming larvae with some cue response can actively counteract hydrodynamic forces and highlight the importance of both larval behaviour and environmental conditions in determining small-scale patterns of dispersal.     

Heritability of progeny size in a terrestrial isopod: transgenerational environmental effects on a life history trait

Maternal effects, the environment that mothers provide to their offspring, their provision of nutrients and the environment that offspring of the same clutch share, have come to be recognized as an important influence on offspring fitness. In addition, in invertebrates, maternal effects and common environment may change according to a mother's diet. We tested for the changes in quantitative genetic parameters in a half-sib design where mothers were fed diets varying in nutrient content. Surprisingly, we found that not only maternal and common environmental variance changed with experimental diets but also there were significant changes in narrow-sense heritabilities, with corresponding h(2) values of 0.61 (high protein), 0.08 (high carbohydrate) and 0.001 (equal carbohydrate:protein). Our results show how an environmentally driven evolutionary process could occur in nature, since the response to selection could change dramatically according to the composition of the diet that females are ingesting.     

Changes in life history trait composition during undisturbed old-field succession

This paper describes the patterns of vegetation change by spontaneous succession on former agricultural land. In 1968, initiated by Heinz Ellenberg, an experimental study site was set up on an arable field in the new botanical garden of Göttingen University (Germany). The undisturbed successions on four plots of a long sere (since 1968/69) and on four additional plots of a shorter sere (since 1982) were evaluated. The seres were classified into stages by cluster analysis, which yield to four subsequent stages for the long sere and to three subsequent stages for the short sere. The early succession is characterized by a high proportion of species invasion, whereas with developing time species extinction increased. On all study plots undisturbed succession directed to the development of pioneer forests. Altogether 247 vascular plant species were recorded. The total species richness shows a fluctuating course during the successional seres, with significantly increased numbers shortly after succession has started and a decline in the pioneer-forest stage, when stands age and close down. The primary aim was to compare the characteristics (particular traits) of species occurring at different stages of succession. The majority of the traits concerned exhibited some clear trends in the course of succession. Exclusive reproduction by seeds decreased and the ability for additional vegetative reproduction increased. Anemochorous dispersal significantly decreased, whereas the importance of dispersal by animals, especially endochorous, dominates in the pioneer-forest stage. The mean seed weight significantly increased. During early succession, plant species staying green over winter dominated, but are of none relevance in the pioneer-forest stage, where summergreen plant species dominate. The change in strategy type features a significant increase of competitive species. The mean indicator value for light in the herb layer decreased significantly in the pioneer-forest stage.     

Spatial and environmental effects on Coho Salmon life history trait variation

Adult size, egg size, fecundity, and mass of gonads are affected by trade‐offs between reproductive investment and environmental conditions shaping the evolution of life history traits among populations for widely distributed species. Coho salmon Oncorhynchus kisutch have a large geographic distribution, and different environmental conditions are experienced by populations throughout their range. We examined the effect of environmental variables on female size, egg size, fecundity, and reproductive investment of populations of Coho Salmon from across British Columbia using an information theoretic approach. Female size increased with latitude and decreased with migration distance from the ocean to spawning locations. Egg size was lowest for intermediate intragravel temperature during incubation, decreased with migration distance, but increased in rivers below lakes. Fecundity increased with latitude, warmer temperature during the spawning period, and river size, but decreased in rivers below lakes compared with rivers with tributary sources. Relative gonad size increased with latitude and decreased with migration distance. Latitude of spawning grounds, migratory distance, and temperatures experienced by a population, but also hydrologic features—river size and headwater source—are influential in shaping patterns of reproductive investment, particularly egg size. Although, relative gonad size varied with latitude and migration distance, how gonadal mass was partitioned gives insight into the trade‐off between egg size and fecundity. The lack of an effect of latitude on egg size suggests that local optima for egg size related to intragravel temperature may drive the variation in fecundity observed among years.     

Effects of polyploidy and reproductive mode on life history trait expression

Ploidy elevation is increasingly recognized as a common and important source of genomic variation. Even so, the consequences and biological significance of polyploidy remain unclear, especially in animals. Here, our goal was to identify potential life history costs and benefits of polyploidy by conducting a large multiyear common garden experiment in Potamopyrgus antipodarum, a New Zealand freshwater snail that is a model system for the study of ploidy variation, sexual reproduction, host–parasite coevolution, and invasion ecology. Sexual diploid and asexual triploid and tetraploid P. antipodarum frequently coexist, allowing for powerful direct comparisons across ploidy levels and reproductive modes. Asexual reproduction and polyploidy are very often associated in animals, allowing us to also use these comparisons to address the maintenance of sex, itself one of the most important unresolved questions in evolutionary biology. Our study revealed that sexual diploid P. antipodarum grow and mature substantially more slowly than their asexual polyploid counterparts. We detected a strong negative correlation between the rate of growth and age at reproductive maturity, suggesting that the relatively early maturation of asexual polyploid P. antipodarum is driven by relatively rapid growth. The absence of evidence for life history differences between triploid and tetraploid asexuals indicates that ploidy elevation is unlikely to underlie the differences in trait values that we detected between sexual and asexual snails. Finally, we found that sexual P. antipodarum did not experience discernable phenotypic variance‐related benefits of sex and were more likely to die before achieving reproductive maturity than the asexuals. Taken together, these results suggest that under benign conditions, polyploidy does not impose obvious life history costs in P. antipodarum and that sexual P. antipodarum persist despite substantial life history disadvantages relative to their asexual counterparts.     

Dispersal and life history strategies in epiphyte metacommunities: alternative solutions to survival in patchy,dynamic landscapes

Host trees for obligate epiphytes are dynamic patches that emerge, grow and fall, and metacommunity diversity critically depends on efficient dispersal. Even though species that disperse by large asexual diaspores are strongly dispersal limited, asexual dispersal is common. The stronger dispersal limitation of asexually reproducing species compared to species reproducing sexually via small spores may be compensated by higher growth rates, lower sensitivity to habitat conditions, higher competitive ability or younger reproductive age. We compared growth and reproduction of different groups of epiphytic bryophytes with contrasting dispersal (asexual vs. sexual) and life history strategies (colonists, short- and long-lived shuttle species, perennial stayers) in an old-growth forest stand in the boreo-nemoral region in eastern Sweden. No differences were seen in relative growth rates between asexual and sexual species. Long-lived shuttles had lower growth rates than colonists and perennial stayers. Most groups grew best at intermediate bark pH. Interactions with other epiphytes had a small, often positive effect on growth. Neither differences in sensitivity of growth to habitat conditions nor differences in competitive abilities among species groups were found. Habitat conditions, however, influenced the production of sporophytes, but not of asexual diaspores. Presence of sporophytes negatively affected growth, whereas presence of asexual diaspores did not. Sexual species had to reach a certain colony size before starting to reproduce, whereas no such threshold existed for asexual reproduction. The results indicate that the epiphyte metacommunity is structured by two main trade-offs: dispersal distance vs. reproductive age, and dispersal distance vs. sensitivity to habitat quality. There seems to be a trade-off between growth and sexual reproduction, but not asexual. Trade-offs in species traits may be shaped by conflicting selection pressures imposed by habitat turnover and connectivity rather than by species interactions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A critique of life history approaches to human trait covariation

Covariation of life history traits across species may be organised on a ‘fast-slow’ continuum. A burgeoning literature in psychology and social science argues that trait covariation should be similarly organised across individuals within human populations. Here we describe why extrapolating from inter-species to inter-individual trait covariation is not generally appropriate. The process that genetically tailors species to their environments (i.e. Darwinian evolution) is fundamentally different from processes that tailor individuals to their environments (e.g. developmental plasticity), so their outcomes in terms of trait covariation need not be parallel or even related. We discuss why correlational selection, physical linkage, pleiotropy, and non-random mating do not substantively affect this claim in the context of complex human traits. We also discuss life history trade-offs and their relation to inter-individual trait covariation. We conclude that researchers should avoid hypotheses and explanations that assume trait covariation will correspond across and within species, unless they can mount a theoretically coherent argument to support this claim in the context of their research question.     

A functional trait approach to identifying life history patterns in stochastic environments

Temporal variation in demographic processes can greatly impact population dynamics. Perturbations of statistical coefficients that describe demographic rates within matrix models have, for example, revealed that stochastic population growth rates (log(λ_s)) of fast life histories are more sensitive to temporal autocorrelation of environmental conditions than those of slow life histories. Yet, we know little about the mechanisms that drive such patterns. Here, we used a mechanistic, functional trait approach to examine the functional pathways by which a typical fast life history species, the macrodetrivore Orchestia gammarellus, and a typical slow life history species, the reef manta ray Manta alfredi, differ in their sensitivity to environmental autocorrelation if (a) growth and reproduction are described mechanistically by functional traits that adhere to the principle of energy conservation, and if (b) demographic variation is determined by temporal autocorrelation in food conditions. Opposite to previous findings, we found that O. gammarellus log(λ_s) was most sensitive to the frequency of good food conditions, likely because reproduction traits, which directly impact population growth, were most influential to log(λ_s). Manta alfredi log(λ_s) was instead most sensitive to temporal autocorrelation, likely because growth parameters, which impact population growth indirectly, were most influential to log(λ_s). This differential sensitivity to functional traits likely also explains why we found that O. gammarellus mean body size decreased (due to increased reproduction) but M. alfredi mean body size increased (due to increased individual growth) as food conditions became more favorable. Increasing demographic stochasticity under constant food conditions decreased O. gammarellus mean body size and increased log(λ_s) due to increased reproduction, whereas M. alfredi mean body and log(λ_s) decreased, likely due to decreased individual growth. Our findings signify the importance of integrating functional traits into demographic models as this provides mechanistic understanding of how environmental and demographic stochasticity affects population dynamics in stochastic environments.     

Evolvability of an avian life history trait declines with father's age

Studies of laboratory organisms have suggested that parental age affects the genetic variance of offspring traits. This effect can engender age-specific variance in genetic contributions to evolutionary change in heritable traits under directional selection, particularly in age-structured populations. Using long-term population data of the blue-footed booby (Sula nebouxii), we tested whether genetic variance of recruiting age varies with parental age. Using robust quantitative genetic models fitted to pedigree, we found a significant genotype-by-paternal age interaction for recruiting age. Genetic potential for adaptive change in recruiting age was greater in progeny of young (age 1-6 years) fathers (males: CV(A)=6.68; females: CV(A)=7.59) than those of middle age (7-9 years) fathers (males: CV(A) = 4.64; females: CV(A)=5.08) and old (10-14 years) fathers (CV(A)=0 for both sexes). Therefore, parental age dependence of heritable variance, in addition to age-related variation in survival and fecundity, should affect the strength of natural selection for evolutionary changes. Our results provide rare evidence for the influence of parental age on the evolutionary potential of a life history trait in a wild population.     

Spatially and temporally varying selection on intrapopulation quantitative trait loci for a life history trade-off in Mimulus guttatus

Why do populations remain genetically variable despite strong continuous natural selection? Mutation reconstitutes variation eliminated by selection and genetic drift, but theoretical and experimental studies each suggest that mutation‐selection balance insufficient to explain extant genetic variation in most complex traits. The alternative hypothesis of balancing selection, wherein selection maintains genetic variation, is an aggregate of multiple mechanisms (spatial and temporal heterogeneity in selection, frequency‐dependent selection, antagonistic pleiotropy, etc.). Most of these mechanisms have been demonstrated for Mendelian traits, but there is little comparable data for loci affecting quantitative characters. Here, we report a 3‐year field study of selection on intrapopulation quantitative trait loci (QTL) of flower size, a highly polygenic trait in Mimulus guttatus. The QTL exhibit antagonistic pleiotropy: alleles that increase flower size, reduce viability, but increase fecundity. The magnitude and direction of selection fluctuates yearly and on a spatial scale of metres. This study provides direct evidence of balancing selection mechanisms on QTL of an ecologically relevant trait.     

Dispersal and vicariance: the complex evolutionary history of boid snakes

Since the early 1970s, boine snakes (Boidae: Boinae) have served as a prime example of a group whose current distribution was shaped by vicariant events associated with the fragmentation of the supercontinent Gondwana. Early phylogenetic treatments of this group, and what were thought to be closely related groups (Erycinae and Pythoninae) based on morphological features, produced a relatively stable view of relationships that has strongly influenced subsequent molecular-based work. We examined 4307 base pairs (bp) of nucleotide sequence data obtained from five nuclear loci (c-mos, NT3, BDNF, RAG1, and ODC) and one mitochondrial locus (cyt b) for all genera of erycines and boines, plus representatives of other groups, including those previously thought to be closely allied with boines (Ungaliophiidae, Loxocemidae, Xenopeltidae, and Pythoninae). Our results suggest that the Boidae is not monophyletic, and its current division into three subfamilies (Erycinae, Boinae, and Pythoninae) does not accurately reflect evolutionary history. We find that the evolutionary relationships are better reflected by current geographic distributions and tectonic history than by the morphological characters that have long served as the foundation of boid phylogeny. Divergence time estimates suggest that this strong congruence between geography and phylogeny is the result of several vicariant and dispersal events in the Late Cretaceous and Paleocene associated with the fragmentation of the Gondwanan supercontinent. Our results demonstrate the importance of both vicariance and dispersal in shaping the global distributions of terrestrial organisms.     

Patterns of life history among cyclopoid copepods of central Europe

• 1 Life history characters (body size of adults, egg diameter, egg sac length and breadth) of nineteen species of central European cyclopoid copepods were measured and sexual size dimorphism (adult female length x adult male length^?1), relative egg size (egg weight X body weight^?1), weight of adult females and of eggs, egg sac shape (egg sac length x egg sac breadth^?1), and reproductive effort (clutch weight produced per female weight per day) were calculated to detect trends in life history strategies.
• 2 Typical planktonic species exhibited the lowest reproductive effort. Among planktonic species, the value for egg sac shape increased with clutch size.
• 3 Large species and small species exhibited different trends in life history characters. Large species had larger clutches, larger eggs, and a greater sex size dimorphism than small species. However, small species had a greater relative egg size.
• 4 Large species live in cold water and reproduce during the spring bloom of phytoplankton where the production of large clutches with relatively small eggs is advantageous. Reserves are unnecessary for juveniles because food is abundant. Small species generally are most abundant during the warm season, when conditions are less predictable, and relatively large eggs, possibly provided with reserves, are advantageous.

     

Rapid independent trait evolution despite a strong pleiotropic genetic correlation

Genetic correlations are the most commonly studied of all potential constraints on adaptive evolution. We present a comprehensive test of constraints caused by genetic correlation, comparing empirical results to predictions from theory. The additive genetic correlation between the filament and the corolla tube in wild radish flowers is very high in magnitude, is estimated with good precision (0.85 ± 0.06), and is caused by pleiotropy. Thus, evolutionary changes in the relative lengths of these two traits should be constrained. Still, artificial selection produced rapid evolution of these traits in opposite directions, so that in one replicate relative to controls, the difference between them increased by six standard deviations in only nine generations. This would result in a 54% increase in relative fitness on the basis of a previous estimate of natural selection in this population, and it would produce the phenotypes found in the most extreme species in the family Brassicaceae in less than 100 generations. These responses were within theoretical expectations and were much slower than if the genetic correlation was zero; thus, there was evidence for constraint. These results, coupled with comparable results from other species, show that evolution can be rapid despite the constraints caused by genetic correlations.     

Macroevolution of panicoid inflorescences: a history of contingency and order of trait acquisition

Background and Aims

Inflorescence forms of panicoid grasses (Panicoideae s.s.) are remarkably diverse and they look very labile to human eyes; however, when performing a close inspection one can identify just a small subset of inflorescence types among a huge morphospace of possibilities. Consequently, some evolutionary constraints have restricted, to some extent, the diversification of their inflorescence. Developmental and genetic mechanisms, the photosynthetic type and plant longevity have been postulated as candidate constraints for angiosperms and panicoids in particular; however, it is not clear how these factors operate and which of these have played a key role during the grass inflorescence evolution. To gain insight into this matter the macroevolutionary aspects of panicoid inflorescences are investigated.

Methods

The inflorescence aspect (lax versus condensed), homogenization, truncation of the terminal spikelet, plant longevity and photosynthetic type were the traits selected for this study. Maximum likelihood and Bayesian Markov chain Monte Carlo methods were used to test different models of evolution and to evaluate the existence of evolutionary correlation among the traits. Both, models and evolutionary correlation were tested and analysed in a phylogenetic context by plotting the characters on a series of trees. For those cases in which the correlation was confirmed, test of contingency and order of trait acquisition were preformed to explore further the patterns of such co-evolution.

Key Results

The data reject the independent model of inflorescence trait evolution and confirmed the existence of evolutionary contingency. The results support the general trend of homogenization being a prerequisite for the loss of the terminal spikelet of the main axis. There was no evidence for temporal order in the gain of homogenization and condensation; consequently, the homogenization and condensation could occur simultaneously. The correlation between inflorescence traits with plant longevity and photosynthetic type is not confirmed.

Conclusions

The findings indicate that the lability of the panicoid inflorescence is apparent, not real. The results indicate that the history of the panicoids inflorescence is a combination of inflorescence trait contingency and order of character acquisition. These indicate that developmental and genetic mechanisms may be important constraints that have limited the diversification of the inflorescence form in panicoid grasses.Key words: Inflorescence, morphology, evolution, panicoids, Panicoideae, Poaceae     

Identification of a candidate adaptive polymorphism for Drosophila life history by parallel independent clines on two continents

Life history traits are critical components of fitness and frequently reflect adaptive responses to environmental pressures. However, few genes that contribute to natural life history variation have been identified. Insulin signalling mediates the determination of life history traits in many organisms, and single gene manipulation in Drosophila melanogaster suggests that individual genes in the pathway have the potential to produce major effects on these quantitative traits. We evaluated allelic variation at two insulin signalling genes, the Insulin‐like Receptor (InR) and its substrate, chico, in natural populations of D. melanogaster. We found different patterns of variation: InR shows evidence of positive selection and clines in allele frequency across latitude; chico exhibits neutral patterns of evolution. The clinal patterns at InR are replicated between North America and Australia, showing striking similarity in the distribution of specific alleles and the rate at which allele frequencies change across latitude. Moreover, we identified a polymorphism at InR that appears to be functionally significant and consistent with hypothetical patterns of selection across geography. This polymorphism provides new characterization of genic regions of functionality within InR, and is likely a component in a suite of genes and traits that respond adaptively to climatic variation.     

Muskrat life history: a comparison of a northern and southern population

Muskrats Ondatra zibethicus were studied at Old Crow flats Yukon Territory (68°05'N, 140°05W) and Tiny Marsh, Ontario (44°35'N, 79°52'W) during the summers of 1985 and 1986 Life–history traits of these two populations were compared Litter size was not significantly different between the two sites However average annual productivity was significantly greater at Tiny Marsh where individuals produced more litters per season Growth rates of juvenile and adult muskrats were significantly greater at Tiny Marsh, as was juvenile and adult weight However overwinter survival of juvenile muskrats was significantly greater at Old Crow than at Tiny Marsh We suggest that the shorter growing season and proximate energetic limitations on growth and reproduction favour a conservative reproductive strategy by the northern muskrat population For the southern muskrat population a long growing season and high quality food resources allow for a more productive reproductive strategy     

Dispersal history of a spider (Stegodyphus lineatus) across contiguous deserts: vicariance and range expansion

Israel marks a crossroads between three continents encompassing several phytogeographical and zoogeographical zones. In this complex area, the flow of species from different biogeographical regions creates opportunities to study how geographical division and colonization routes affect current distribution and structure of resident populations of organisms associated with desert and arid environments, habitats that may have persisted throughout Pleistocene glacial periods. The present paper analyses the population history of the spider Stegodyphus lineatus in the contiguous Negev and Judean deserts in Israel using allozyme and mtDNA variation. The distinct patterns of variation indicate that Judean and Negev populations are vicariant lineages. The residence time was longer in Judea, where populations were more polymorphic for mtDNA, showed isolation by distance and were less structured than in the Negev. The Negev population, possibly linked to other Mediterranean populations of S. lineatus , consisted of two subdivisions derived from a recent eastward expansion across the central Negev watershed. Despite differences in age and level of structure, all lineages show similar dispersal processes dominated by restricted gene flow. The distribution patterns of allozyme and mtDNA markers are unrelated to geographical patterns of precipitation and vegetation. Rather, they follow large-scale topographic features, namely the water divide between Mediterranean and Afro-Syrian rift drainages and between eastern and western Negev drainages.   © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 739–754.     

Mesosternal bristle number in a cosmopolitan drosophilid: an X-linked variable trait independent of sternopleural bristles

Mesosternal (MS) bristles in Drosophila are a pair of machrochaetae found at the sternal end of the sternopleural (STP) microchaetae, and are thought to be invariable. In a closely related drosophilid genus, Zaprionus, their number is four and, in contrast to Drosophila, they show interspecific and intraspecific variability. The genetic basis of MS bristle number variability was studied in Z. indianus, the only cosmopolitan species of the genus. The trait responded rapidly to selection and two lines were obtained, one lacking any bristles (0-0) and the other bearing the normal phenotype (2-2). Other symmetrical phenotypes, (1-1) and (3-3), could also be selected for, but with lesser success. By contrast, STP bristle number did not vary significantly between the two lines (0-0) and (2-2), revealing its genetic independence from MS bristle number. Reciprocal crosses between these two lines showed that MS bristle number is mainly influenced by a major gene on the X chromosome (i.e. F₁ males always resembled their mothers) with codominant expression (i.e. heterozygous F₁ females harboured an average phenotype of 2 bristles). However, trait penetrance was incomplete and backcrosses revealed that this variability was partly due to genetic modifiers, most likely autosomal. The canalization of MS bristle number was investigated under different temperatures, and the increased appearance of abnormal phenotypes mainly occurred at extreme temperatures. There was a bias, however, towards bristle loss, as shown by a liability (developmental map) analysis. Finally, when ancestral and introduced populations were compared, the latter were far less stable, suggesting that genetic bottlenecks may perturb the MS bristle number canalization system. MS bristle number, thus, appears to be an excellent model for investigating developmental canalization at both the quantitative and the molecular level.