Test for latitudinal variation of life history,behavior and mortality in the strictly univoltine damselfly Sympecma fusca (Zygoptera: Lestidae)

A wealth of evidence shows that combinations of ecological stressors interact in shaping life history traits, but little is known about how ecological stressors combine with different seasonal time constraints to shape life history, behavior and mortality across populations. We studied life history, behavior and mortality rate in two latitudinally distant populations of the strictly univoltine, adult‐overwintering damselfly Sympecma fusca. Results from laboratory common‐garden and outdoor experiments indicated countergradient variation of larval development time and growth rate: the more time‐constrained larvae showed faster development and a higher growth rate. This finding led to larger size at emergence in the more time‐constrained individuals. Under conditions of intraspecific interaction (outdoor experiment), northern individuals showed lower survival than southern ones, presumably due to cannibalism. In the absence of intraspecific interactions (laboratory experiment), northern and southern larvae did not differ in survival. Finally, laboratory‐grown northern and southern larvae did not differ in activity level. This is the first time that compensation for seasonal time constraints has been shown in a temperate odonate species that overwinters in the adult stage.     

Intraspecific variation influences natural settlement of eastern oysters

As populations decline, their intraspecific diversity also diminishes. Population decline may be exacerbated if a decrease in intraspecific diversity also reduces important ecological functions that maintain population numbers. Oyster reefs are severely overharvested, declining by ~85 % worldwide. We tested how increasing within-species diversity of eastern oysters (Crassostrea virginica) using transplants would affect recruitment of oyster larvae, a key function necessary to maintain future populations. If harvesting reduces population numbers, within-species diversity, and connectivity, then oysters may lose the ability to adapt to changing environmental conditions as well as incur lower levels of recruitment that may hasten their decline. Results from laboratory and field studies indicated that oyster larvae use chemical cues from adult oysters and not from associated fouling communities to select settlement sites. To test how increasing within-species diversity of oysters affected recruitment, we collected oysters from three distinct bay systems in Texas, USA, and compared natural settlement in treatments where all oysters were from a single bay to a mixture of all three bays. Significantly greater recruitment occurred in mixed treatments in 2010, 2011, and 2012 even though oyster recruitment varied by order of magnitude during this time. The net biodiversity effect was positive in all 3 years, indicating that increased recruitment in mixed treatments can be greater than the additive effect of the single bay treatments. Losing intraspecific diversity may reduce recruitment and lead to further declines in oyster populations, illustrating the need for understanding how intraspecific diversity influences ecological functions.     

Laboratory maintenance does not alter ecological and physiological patterns among species: a Drosophila case study

Large comparative studies in animal ecology, physiology and evolution often use animals reared in the laboratory for many generations; however, the relevance of these studies hinges on the assumption that laboratory populations are still representative for their wild living conspecifics. In this study, we investigate whether laboratory‐maintained and freshly collected animal populations are fundamentally different and whether data from laboratory‐maintained animals are valid to use in large comparative investigations of ecological and physiological patterns. Here, we obtained nine species of Drosophila with paired populations of laboratory‐maintained and freshly collected flies. These species, representing a range of ecotypes, were assayed for four stress‐tolerance, two body‐size traits and six life‐history traits. For all of these traits, we observed small differences in species‐specific comparisons between field and laboratory populations; however, these differences were unsystematic and laboratory maintenance did not eclipse fundamental species characteristics. To investigate whether laboratory maintenance influence the general patterns in comparative studies, we correlated stress tolerance and life‐history traits with environmental traits for the laboratory‐maintained and freshly collected populations. Based on this analysis, we found that the comparative physiological and ecological trait correlations are similar irrespective of provenience. This finding is important for comparative biology in general because it validates comparative meta‐analyses based on laboratory‐maintained populations.     

Intrinsic and extrinsic drivers of recruitment across the distribution range of a seed-dimorphic herb

Recruitment of new individuals, through germination and seedling survival, is a key process for short-lived plants. Here, we analyzed intraspecific variation in recruitment across the latitudinal range of Plantago coronopus, a widespread herb that produces both large basal seeds with a mucilaginous coat and small apical seeds without coat. We experimentally tested the effects of seed traits and water availability on recruitment, by using seeds from a wide environmental stress gradient from N Africa to N Europe. Our experiments were carried out in controlled environmental conditions and in dunes where the species naturally occurs. Water shortage decreased seed germination and seedling survival for all populations, showing the importance of water supply for P. coronopus. Basal seeds showed higher and faster germination rates than apical seeds. Since among-population variation in seed mass was not related to potential germination rate, it is the mucilaginous coat rather than size difference that likely drives the differential success between seed morphs. Seed mass positively affected seedling survival instead, but only in controlled conditions with regular water supply. An experiment in a dune showed indeed that the highest survival corresponded to the local population and not the one with the largest seeds. Our results demonstrate that both intrinsic and extrinsic factors drive inter-population variation in the early life stages of this short-lived plant, allowing it to adapt across the environmentally heterogeneous distribution range. Gathering information on intraspecific variation in recruitment-related traits will help us to understand and predict plant responses in a context of climatic change.     

The interaction effect between intraspecific competition and seed quality on the life‐history traits of the seed‐feeding beetle Acanthoscelides macrophthalmus

It has been shown that intraspecific competition and resource quality may affect life‐history traits of insects, such as body size, fecundity, and survival. However, intraspecific competition and resource quality may interact with each other. The study of such interacting effects is crucial for understanding the influence of these ecological variables on the selection of specific life‐history traits. Here, we investigated whether the interaction between intraspecific larval competition and variation in resource quality affects adult emergence and survival, egg size, fecundity, body size, and sexual size dimorphism (SSD) of the seed‐feeding beetle Acanthoscelides macrophthalmus (Schaeffer) (Coleoptera: Chrysomelidae: Bruchinae) when infesting Leucaena leucocephala (Lam.) De Wit (Fabaceae), its host plant. In the laboratory, beetles were reared on seeds that differed in quality (e.g., different hardness, seed size, water content), in the presence or absence of larval competition. Body size and SSD did not differ between treatments (with and without competition), nor were they affected by varying resource quality. Females subjected to competition during the larval stage and females emerging from seeds of higher quality, displayed the highest fecundity. The proportion of emergent adults was higher in the absence of competition. In addition, larger eggs were laid on the low‐quality resource in the absence of competition, showing a trade‐off between egg size and egg number. Adult survival differed among treatments and resource qualities, suggesting a higher investment in adult survival for individuals emerging from seeds of low quality in the presence of competition. Whether changes in specific traits could be selected for in detriment of others will depend on the strength of intraspecific competition, the variation in resource quality, and the plasticity in the life‐history traits investigated. This needs further clarification.     

The most variable vertebrate on Earth

In the search for the most variable non-human vertebrate on Earth, intraspecific variation of ten variable traits was compared among ten highly variable species. Mammals, birds and many reptiles, amphibians and fishes were excluded because most of the variation is among, and not within species. The focus was on northern fishes, where high intraspecific variation is well documented. The ten selected species were European whitefish Coregonus lavaretus, chinook salmon Oncorhyncus tshawytscha, sockeye salmon O. nerka, rainbow trout O. mykiss, atlantic salmon Salmo salar, brown trout S. trutta, arctic charr Salvelinus alpinus, brook charr S. fontinalis, dolly varden charr S. malma and threespine stickleback Gasterosteus aculeatus. Variation included not only size and phenotype, but also ecology, behaviour and life history. The traits were geographic range, migration, habitat, adult size, colour, body form, polymorphism, diet, reproduction and genetics. Arctic charr came on top in the final ranking, followed by dolly varden charr and rainbow trout. The two least variable were chinook salmon and threespine stickleback. It is proposed that arctic charr, which is also the northernmost fish on Earth, has evolved its unique variability in range, size, phenotype, ecology and life history by adapting to the extreme and highly unpredictable ecological conditions of arctic and other northern lakes for many glacial periods.     

The genetic variance but not the genetic covariance of life‐history traits changes towards the north in a time‐constrained insect

Seasonal time constraints are usually stronger at higher than lower latitudes and can exert strong selection on life‐history traits and the correlations among these traits. To predict the response of life‐history traits to environmental change along a latitudinal gradient, information must be obtained about genetic variance in traits and also genetic correlation between traits, that is the genetic variance‐covariance matrix, G . Here, we estimated G for key life‐history traits in an obligate univoltine damselfly that faces seasonal time constraints. We exposed populations to simulated native temperatures and photoperiods and common garden environmental conditions in a laboratory set‐up. Despite differences in genetic variance in these traits between populations (lower variance at northern latitudes), there was no evidence for latitude‐specific covariance of the life‐history traits. At simulated native conditions, all populations showed strong genetic and phenotypic correlations between traits that shaped growth and development. The variance–covariance matrix changed considerably when populations were exposed to common garden conditions compared with the simulated natural conditions, showing the importance of environmentally induced changes in multivariate genetic structure. Our results highlight the importance of estimating variance–covariance matrixes in environments that mimic selection pressures and not only trait variances or mean trait values in common garden conditions for understanding the trait evolution across populations and environments.     

Ecological and social effects on reproduction and local recruitment in the red-backed shrike

Numerous hypotheses have been proposed to explain variation in reproductive performance and local recruitment of animals. While most studies have examined the influence of one or a few social and ecological factors on fitness traits, comprehensive analyses jointly testing the relative importance of each of many factors are rare. We investigated how a multitude of environmental and social conditions simultaneously affected reproductive performance and local recruitment of the red-backed shrike Lanius collurio (L.). Specifically, we tested hypotheses relating to timing of breeding, parental quality, nest predation, nest site selection, territory quality, intraspecific density and weather. Using model selection procedures, predictions of each hypothesis were first analysed separately, before a full model was constructed including variables selected in the single-hypothesis tests. From 1988 to 1992, 50% of 332 first clutches produced at least one fledgling, while 38.7% of 111 replacement clutches were successful. Timing of breeding, nest site selection, predation pressure, territory quality and intraspecific density influenced nest success in the single-hypothesis tests. The full model revealed that nest success was negatively associated with laying date, intraspecific density, and year, while nest success increased with nest concealment. Number of fledglings per successful nest was only influenced by nest concealment: better-camouflaged nests produced more fledglings. Probability of local recruitment was related to timing of breeding, parental quality and territory quality in the single-hypothesis tests. The full models confirmed the important role of territory quality for recruitment probability. Our results suggest that reproductive performance, and particularly nest success, of the red-backed shrike is primarily affected by timing of breeding, nest site selection, and intraspecific density. This study highlights the importance of considering many factors at the same time, when trying to evaluate their relative contributions to fitness and life history evolution.Electronic supplementary material Supplementary material is available for this article at     

Genotype-environment interactions for insect growth in constant and fluctuating temperature regimes

Experiments on life history genetics are usually performed using constant temperature environments in the laboratory. However, the dynamics of insect growth can be influenced profoundly by daily fluctuations in temperature such as those which characterize field environments. We report here on experiments using different stocks and selected lines of a tropical butterfly, Bicyclus anynana, to examine whether genotype-environment interactions occur for three traits describing pre-adult growth. These traits were measured over two pairs of environments differing in mean temperature, each of which had a constant, and a cycling temperature regime. Development time, pupal weight and growth rate show genotype-environment interactions, especially at comparatively low average temperatures. Researchers should, therefore, take care when extrapolating from the form of genetic covariance matrices and ''trade-offs'' among life history traits found in constant temperature environments to those likely to occur in nature. <br>     

Intraspecific variations in life history traits of two pecky rice bug species from Japan: Mapping emergence dates and number of annual generations

The mirid bugs Stenotus rubrovittatus and Trigonotylus caelestialium, which cause pecky rice, have become a threat to rice cultivation in Asia. Damage caused by these pests has rapidly become frequent since around 2000 in Japan. Their expansion pattern is not simple, and predicting their future spread remains challenging. Some insects with wide ranges have locally adapted variations in life‐history traits. We performed laboratory rearing experiments to assess the geographical scale of intraspecific variations in life‐history traits of S. rubrovittatus and T. caelestialium. The experiments were aimed at increasing the accuracy of occurrence estimates and the number of generations per year. These results were compared with previous research, and differences in development rates were observed between populations of different latitudes, but not of the same latitude. Finally, plotting the timing of adult emergence and the potential number of generations per year on maps with a 5‐km grid revealed that they differed greatly locally at the same latitude. These maps can be used for developing more efficient methods of managing mirid bugs in integrated pest management.     

Intraspecific phenotypic variability of plant functional traits in contrasting mountain grasslands habitats

Empirical studies that link plants intraspecific variation to environmental conditions are almost lacking, despite their relevance in understanding mechanisms of plant adaptation, in predicting the outcome of environmental change and in conservation. Here, we investigate intraspecific trait variation of four grassland species along with abiotic environmental variation at high spatial resolution (n = 30 samples per species trait and environmental factor per site) in two contrasting grassland habitats in Central Apennines (Italy). We test for phenotypic adaptation between habitats, intraspecific trait-environment relationships within habitats, and the extent of trait and environmental variation. We considered whole plant, clonal, leaf, and seed traits. Differences between habitats were tested using ANOVA and ANCOVA. Trait-environment relationships were assessed using multiple regression models and hierarchical variance partitioning. The extent of variation was calculated using the coefficient of variation. Significant intraspecific differences in trait attributes between the contrasting habitats indicate phenotypic adaptation to in situ environmental conditions. Within habitats, light, soil temperature, and the availability of nitrate, ammonium, magnesium and potassium were the most important factors driving intraspecific trait-environment relationships. Leaf traits and height growth show lower variability than environment being probably more regulated by plants than clonal traits which show much higher variability. We show the adaptive significance of key plant traits leading to intraspecific adaptation of strategies providing insights for conservation of extant grassland communities. We argue that protecting habitats with considerable medium- and small-scale environmental heterogeneity is important to maintain large intraspecific variability within local populations that finally can buffer against uncertainty of future climate and land use scenarios.     

Comparative phylogeography of diadromous and freshwater daces of the genus <Emphasis Type="Italic">Tribolodon</Emphasis> (Cyprinidae)

Far Eastern daces, genus Tribolodon (Cyprinidae), are thought to have diversified and developed unique diadromous life histories under changing conditions in the Sea of Japan and the surrounding environment. To examine the relationships between life history traits, distribution, and genetic population structures, we conducted a comparative phylogeographic analysis using partial mtDNA sequence data from samples collected over almost the full ranges of all four Tribolodon species. Phylogenetic analyses revealed several intraspecific haplotype groups that differentiated in the early Pleistocene to the Pliocene with or without geographic overlaps. A time-calibrated phylogeny suggested that the relatively smaller geographic ranges of the strictly freshwater species, T. sachalinensis and T. nakamurai, were explained not by the recent origins of these species, but by their limited dispersal abilities and smaller historical population sizes. The wider-ranging diadromous species, T. brandtii and T. hakonensis, exhibited similar major phylogeographic structures in their distributions, but the chronological order and timing of formation of this structure largely differed between the two species. In addition to those differences, the overlapping patterns of the differentiated intraspecific lineages in these species suggest dynamic, but somewhat restricted dispersal during the Plio-Pleistocene. Tribolodon hakonensis, one of the most widespread species of East Asian freshwater fishes, included both common and unique phylogeographic patterns compared to other fish species; the unique patterns (i.e., its wide range across freshwater biogeographic boundaries like the sea and mountains) would reflect its ecological features as a remarkable generalist inhabiting lakes, upper and lower reaches of rivers, and even coastal areas.     

Dispersal of sea lamprey larvae during early life: relevance for recruitment dynamics

Dispersal is an important early life history process that influences fish population dynamics and recruitment. We studied larval sea lamprey (Petromyzon marinus) dispersal by combining spatially explicit field sampling, genetic methods, and laboratory experiments to investigate how far sea lamprey larvae can disperse away from nests during their first growing season; subsequent dispersal by age 1 of sea lamprey; and the effect of density on larval dispersal. In two study streams sea lamprey larvae were observed to have moved >150 m downstream from the most likely source nest within 2–3 weeks of hatching. Conversely, randomization trials suggested that for both streams age 0 larvae were found closer to full siblings than would be expected if dispersal was not constrained by distance. Restricted dispersal was also observed for age 1 larvae in five streams, although for this age class full siblings were more commonly found to be separated by >1,000 m. Laboratory experiments indicated a significant effect of density on the movement of larval sea lamprey, with more larval movement at higher densities. Temperature also affected movement significantly, with reduced larval movements at cooler temperatures. Our findings suggest that larval sea lamprey dispersal is sufficient to minimize the likelihood of strong density-dependent effects on recruitment, even with large population sizes.     

Identifying sources of variation in reproductive and life-history traits among five populations of a Chinese lizard (Takydromus septentrionalis, Lacertidae)

Research on life-history traits of squamate reptiles has focused on North American species, while Asian taxa have been virtually ignored. In order to understand general patterns in reptile life histories, we need a broader data base. Our study on the slender-bodied lacertid lizard Takydromus septentrionalis provides the first detailed information on factors responsible for intraspecific variation in reproductive output and life history in a Chinese reptile. Clutches of recently collected lizards from five widely separated localities in China revealed major divergences in female body size at maturation, mean adult female body size, body condition after oviposition, size-adjusted fecundity, relative clutch mass, and mass and shape of eggs. Most of these geographical differences persisted when the same groups of females were maintained in identical conditions in captivity. Additionally, reproductive frequency during maintenance under laboratory conditions differed according to the animals' place of origin. Thus, the extensive geographical variation in reproductive and life-history traits that occurs within T. septentrionalis is exhibited even in long-term captives, suggesting that proximate factors that vary among localities (local conditions of weather and food supply) are less important determinants of life-history variation than are intrinsic (presumably genetic) influences. The maternal abdominal volume available to hold the clutch may be one such factor, based on low levels of variation in Relative Clutch Mass among populations, and geographical variation in the position of trade-off lines linking offspring size to fecundity.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 443–453.     

Genetics, recruitment, and migration patterns of Arctic cisco (Coregonus autumnalis) in the Colville River, Alaska, and Mackenzie River, Canada

Arctic cisco Coregonus autumnalis have a complex anadromous life history, many aspects of which remain poorly understood. Some life history traits of Arctic cisco from the Colville River, Alaska, and Mackenzie River basin, Canada, were investigated using molecular genetics, harvest data, and otolith microchemistry. The Mackenzie hypothesis, which suggests that Arctic cisco found in Alaskan waters originate from the Mackenzie River system, was tested using 11 microsatellite loci and a single mitochondrial DNA gene. No genetic differentiation was found among sample collections from the Colville River and the Mackenzie River system using molecular markers (P > 0.19 in all comparisons). Model-based clustering methods also supported genetic admixture between sample collections from the Colville River and Mackenzie River basin. A reanalysis of recruitment patterns to Alaska, which included data from recent warm periods and suspected changes in atmospheric circulation patterns, still finds that recruitment is correlated to wind conditions. Otolith microchemistry (Sr/Ca ratios) confirmed repeated, annual movements of Arctic cisco between low-salinity habitats in winter and marine waters in summer.     

Matching field and laboratory environments: effects of neglecting daily temperature variation on insect reaction norms

The tropical butterfly, Bicyclus anynana, exhibits seasonal polyphenism. The wet season form has large eyespots and a pale band while these characters are much less conspicuous or absent in the dry season form. This plasticity is induced in the laboratory by use of a standard series of constant temperatures in the larval stage yielding a continuous norm of reaction. Butterflies in this study were reared from hatchling larvae in seven regimes which differed with respect to thermoperiod or photoperiod. The effect of rearing treatment on the phenotypic plasticity of the adult wing pattern, on life history traits and on larval feeding rhythms was investigated. Photoperiod had little effect except that constant light produced a higher mortality and tended to produce a longer development time. Thermoperiod had a major effect on the life history traits in comparison to a constant temperature regime with the same daily mean: development time was shorter with higher growth rates. The faster development was associated with a substantial shift in the wing pattern towards the wet season form. Larvae feed mostly at night both under constant and thermoperiod (cool nights) conditions. The results are discussed with respect to the necessity of matching field and laboratory environments in studies of norms of reaction or of life history traits where the adaptive significance of the variation is important. Fluctuating conditions in nature, especially with respect to thermoperiod, must be taken into account.     

Effects of assay conditions in life history experiments with Drosophila melanogaster

Selection experiments with Drosophila have revealed constraints on the simultaneous evolution of life history traits. However, the responses to selection reported by different research groups have not been consistent. Two possible reasons for these inconsistencies are (i) that different groups used different environments for their experiments and (ii) that the selection environments were not identical to the assay environments in which the life history traits were measured. We tested for the effect of the assay environment in life history experiments by measuring a set of Drosophila selection lines in laboratories working on life history evolution with Drosophila in Basel, Groningen, Irvine and London. The lines measured came from selection experiments from each of these laboratories. In each assay environment, we measured fecundity, longevity, development time and body size. The results show that fecundity measurements were particularly sensitive to the assay environment. Differences between assay and selection environment in the same laboratory or differences between assay environments between laboratories could have contributed to the differences in the published results. The other traits measured were less sensitive to the assay environment. However, for all traits there were cases where the measurements in one laboratory suggested that selection had an effect on the trait, whereas in other laboratories no such conclusion would have been drawn. Moreover, we provide good evidence for local adaptation in early fecundity for lines from two laboratories.     

Measuring Daphnia life history in the wild: The efficacy of individual field cages

Life‐history studies are often conducted in a laboratory environment where it is easy to assay individual animals. However, factors such as temperature, photoperiod, and nutrition vary greatly between laboratory and field environments, making it difficult to compare results. Consequently, there is a need to study individual life histories in the field, but this is currently difficult in systems such as Daphnia where it is not possible to mark and track individual animals. Here, we present a proof of principle study showing that field cages are a reliable method for collecting individual‐level life‐history data in Daphnia magna. As a first step, we compared the life history of paired animals reared outside and inside cages to test the hypothesis that cages allow free flow of algal food resources. We then used a seminatural mesocosm setting to compare the performance of individual field cages versus glass jars refilled with mesocosm water each day. We found that cages did not inhibit food flow and that differences in life histories between three clones detected in the jar assays were also detectable using the much less labor‐intensive field cages. We conclude that field cages are a feasible approach for collecting individual‐level life‐history data in systems such as Daphnia where individual animals cannot be marked and tracked.     

Biological influences on inter- and intraspecific isotopic variability among paired chondrostome fishes

This study aimed at examining resource partitioning both at the inter- and intraspecific levels between paired chondrostome fishes: Chondrostoma nasus, the nase, C. toxostoma, the sofie, and their hybrid. The study was performed in the south of France and concerned a main river (the Durance River) and a tributary (the Buech River). In these rivers, C. nasus was an introduced species, originating in central Europe, and C. toxostoma was an endemic congener, in the south of France. Stable isotope analysis was used to analyse trophic and spatial niches. Isotopic differences indicated that individuals from the three taxa (C. nasus, C. toxostoma and their hybrid) have different spatial origins. At the interspecific level, the different chondrostomes originating from the Buech River showed a high level of trophic niche overlap. At the intraspecific level, nase individuals originating from the different spatial origins showed a resource polymorphism; differences in morphology were associated with variation in behaviour and life history traits. Their coexistence was a likely outcome of resource polymorphism. This study provides an example of the importance of considering the link between intra- and interspecific interactions to gain an understanding of the mechanisms driving the coexistence of species-pairs.