Behavioural and life history traits in temporary and perennial waters: comparisons among three pairs of sibling dragonfly species

Identifying and examining traits that influence the distribution of species is crucial to the understanding of community structure. Theory predicts that traits should differ between species that live in temporary and permanent waters because of differing major environmental variables; viz drying out and predator presence, respectively. Species, however, will also be influenced by their evolutionary history, i.e. by the traits of their common ancestors. We studied differences in life history and behaviour traits in a series of laboratory experiments using pairs of dragonfly species out of three genera of Namibian Libellulidae (Odonata) with one species from each type of habitat. As predicted, growth rates were significantly higher in the temporary water species compared to the permanent water species. Activity and foraging, in contrast, differed between the genera, but did not differ between the habitat types. Hence, our study implies that the behavioural traits are influenced by phylogenetic inertia rather than by the habitat variables, while growth rate is adapted to the habitat. We argue that in all three genera one species has diverged recently from a sister species that lives in the original habitat of the genus, which may be temporary waters in Crocothemis Brauer and in Orthetrum Newman, and permanent waters in Trithemis Brauer. The behavioural traits may therefore be less well adapted. Rapid growth may be the more relevant trait because it is crucial to survival in temporary waters.     

A field study of larval development in a dragonfly assemblage in African desert ponds (Odonata)

Aquatic animals distributed along a 'habitat-permanence' gradient (HPG), differ in life history (Wellborn et al., 1996. Annual Revue of Ecology and Systematics 27: 337--363). Dragonflies that occur in hot arid regions often occur in temporary waters and consequently perform direct and rapid development. Dragonfly species of the Namibian desert do differ in their selection of habitats along the HPG and therefore may also differ in life cycle. Here, we attempt to monitor colonisation, larval growth and emergence in a temporary pond of known history. We studied the development of dragonfly species that laid eggs in artificial ponds constructed by us in March 2001. The assemblage consisted of species that originate from different habitats along the HPG. To obtain data on larval development we took samples from the ponds at 10-day intervals. Most species showed rapid development. By regressing the maximum sizes attained by larvae on each sampling date against time we estimated growth rates for five species and were thereby able to estimate that total duration of development from oviposition to emergence ranged between 38 and 70 days. Observation of first oviposition and first emergence for three of these species corroborated our estimates based on growth rate. Of few species, which laid eggs in the ponds no larvae or adults were found. For some this may have been the result of predation whereas others may not have grown fast enough to emerge before the ponds dried up. Our results indicate that dragonflies cannot recognise whether a pond will retain water long enough for full larval development and oviposit in waters that will not allow larval development.     

Integrating species life-history traits and patterns of deforestation in amphibian conservation planning

Aim  To identify priority areas for amphibian conservation in southeastern Brazil, by integrating species life-history traits and patterns of deforestation.
Location  State of São Paulo, Brazil.
Methods  We used the software M arxan to evaluate different scenarios of amphibian conservation planning. Our approach differs from previous methods by explicitly including two different landscape metrics; habitat split for species with aquatic larvae, and habitat loss for species with terrestrial development. We evaluated the effect of habitat requirements by classifying species breeding habitats in five categories (flowing water, still water permanent, still water temporary, bromeliad or bamboo, and terrestrial). We performed analyses using two scales, grid cells and watersheds and also considered nature preserves as protected areas.
Results  We found contrasting patterns of deforestation between coastal and inland regions. Seventy-six grid cells and 14 watersheds are capable of representing each species at least once. When accounting for grid cells already protected in state and national parks and considering species habitat requirements we found 16 high-priority grid cells for species with one or two reproductive habitats, and only one cell representing species with four habitat requirements. Key areas for the conservation of species breeding in flowing and permanent still waters are concentrated in southern state, while those for amphibians breeding in temporary ponds are concentrated in central to eastern zones. Eastern highland zones are key areas for preserving species breeding terrestrially by direct or indirect development. Species breeding in bromeliads and bamboos are already well represented in protected areas.
Main conclusions  Our results emphasize the need to integrate information on landscape configuration and species life-history traits to produce more ecologically relevant conservation strategies.     

Dragonfly associations (Insecta: Odonata) in relation to habitat variables: a multivariate approach

In a dragonfly survey, carried out in a lowland wetland area in eastern Austria, a total of 19 resident species was recorded. Multivariate statistical procedures were used to analyse the relationship between dragonfly assemblage patterns and environmental variables. Besides widespread and euryoecious species with unspecific habitat requirements two dragonfly associations were identified: on the one hand species mainly occurring at temporary natural and near-natural ponds characterised by rush and reed vegetation, on the other hand species preferring permanent waters such as the artificial waterbodies in the investigation area characterised by floating macrophytes. Water persistence and the existence of floating macrophytes determined the formation of species assemblages.     

Life history traits variation in heterogeneous environment: The case of a freshwater snail resistance to pond drying

Ecologists and population geneticists have long suspected that the diversity of living organisms was connected to the structure of their environment. In heterogeneous environments, diversifying selection combined to restricted gene flow may indeed lead to locally adapted populations. The freshwater snail, Galba truncatula, is a good model to address this question because it is present in a heterogeneous environment composed of temporary and permanent waters. In order to test the selective importance of those environments, we proposed here to measure survival of lineages from both habitats during drought episodes. To this purpose, we experimentally submitted adults and juveniles individuals from both habitats to drought. We found a difference in desiccation resistance between temporary and permanents waters only for adults. Adults from temporary habitats were found more resistant to drought. This divergence in desiccation resistance seems to explain the unexpected life history traits differences between habitats observed.     

Changing the habitat: the evolution of intercorrelated traits to escape from predators

Burst escape speed is an effective and widely used behaviour for evading predators, with burst escape speed relying on several different morphological features. However, we know little about how behavioural and underlying morphological attributes change in concert as a response to changes in selective predation regime. We studied intercorrelated trait differentiation of body shape and burst‐swim‐mediating morphology in response to a habitat shift‐related reduction in burst escape speed using larvae of the dragonfly genus Leucorrhinia. Species in this genus underwent a well‐known habitat shift from predatory fish lakes (fish lakes) to predatory fish‐free lakes dominated by large predatory dragonflies (dragonfly lakes) accompanied by relaxed selection on escape burst speed. Results revealed that species from fish lakes that possess faster burst speed have evolved a suite of functionally intercorrelated traits, expressing a wider abdomen, a higher abdominal muscles mass and a larger branchial chamber compared with species from dragonfly lakes. In contrast, populations within species did not show significant differences in muscle mass and branchial chamber size between lake types in three of the species. High multicollinearity among variables suggests that traits have evolved in concert rather than independently when Leucorrhinia shifted from fish lakes to dragonfly lakes. Thus, relaxed selection on burst escape speed in dragonfly‐lake species resulted in a correlated reduction of abdominal muscles and a smaller branchial chamber, likely to save production and/or maintenance costs. Our results highlight the importance of studying integrated behavioural and morphological traits to fully understand the evolution of complex phenotypes.     

On the habitats of three species of the genus Hygrotus Stephens (Coleoptera: Dytiscidae)

SUMMARY. 1. Adult Hygrotus beetles were collected from about 400 localities out of 621 sampled in the Netherlands. Distribution of the three Dutch species of this genus has been related to different environmental variables, principally by use of the Index of Representation (I.R.).
2. Hygrotus decoratus is an acidophilous and haloxenous species. It inhabits small water bodies such as peat-ditches, reed-lands and overgrown ditches where emergent plants are abundant. Hygrotus inaequalis occurs in all of the habitats studied and has no clear preferences or aversions with respect to the environmental variables examined. Hygrotus versicolor inhabits permanent water bodies such as clay- and sand-canals which have a rich growth of submerged plants and a weak current. The species has a significant preference for waters with a pH between 7.1 and 8.0 and a chlorinity between 60 and 200 mg 1-⁻¹.
3. H. decoratus and H. versicolor rarely co-exist because of their different environmental requirements, but both species often co-exist with H. inaequalis. Structural environmental variables such as water depth and abundance and growth-form of the aquatic plants play a greater role than chemical factors in habitat selection by Hygrotus spp.     

Dormancy, dispersal and the survival of cyclopoid copepods (Cyclopoida, Copepoda) in a lowland floodplain

1. The survival of cyclopoid copepods was investigated in a floodplain for 2 years where flooding occurred during the cold season. The cyclopoid community was studied in three waterbodies with distinct hydroperiods: a permanent pond connected to the flooded area during inundation, a temporary pool that is part of the flooded area and an isolated temporary pool.
2. Field studies, including data obtained from samples of water, sediment and soil, showed the overall predominance of species with a summer diapause over those with a winter diapause or without diapause. Emergence of cyclopoid copepods at the onset of flooding, examined using emergence traps and data from recently filled or still isolated temporary pools, showed that some species can survive several months of drying.
3. The ability of the diapausing fourth copepodid stages of Cyclops strenuus and C. insignis , the two cyclopoids most abundant during winter and spring flooding, to survive terrestrial conditions was tested in laboratory experiments. Both species survived for several months, but rates differed among the species. A higher percentage of C. strenuus survived for a longer period, possibly explaining why this species was relatively more abundant in more temporary habitats.
4. Both dormancy and dispersal facilitated survival of cyclopoid copepods in transient habitats connected to each other during flood periods. Dormancy was the most important survival strategy, whereas dispersal could be more important following prolonged periods without flooding.     

Survival of caddis larvae in relation to their case material in a group of temporary and permanent pools

1. The occurrence of larvae of Limnephilus coenosus and L. vittatus (Trichoptera) was recorded in 103 rock pools both before and after the dry periods in spring–summer (April–May and July–early August), when a great number of the pools dried out. In early spring, 84% of the pools sampled contained larvae of at least one of the species. Limnephilus coenosus larvae were present in a higher proportion of pools that later dried out than in the permanent ones, while L. vittatus larvae were predominantly found in permanent pools. Larvae of both species were found together in 31% of the inhabited pools.
2. Laboratory experiments, designed to elucidate differential survival under drought conditions, demonstrated that the organic cases of L. coenosus larvae held water more efficiently than did the mineral L. vittatus cases. Full-grown (fifth instar) L. coenosus larvae also survived dry conditions better than did L. vittatus larvae. The higher survival of L. coenosus was due to a combination of drought-resistant case material and a higher survival ability of the larvae themselves.
3. Limnephilus vittatus larvae were restricted by their low capability to withstand desiccation, although case material and food were available for L. vittatus larvae in all pools. Absence of case material and high-quality food in many pools, however, restricted the presence of L. coenosus larvae, but this species did not suffer from heavy mortality because of desiccation and all pool populations of L. coenosus survived until pupation.
4. The differences in species composition in these temporary and permanent pools can be explained by the differential site selection by ovipositing females, as well as by larval survival. The intrinsically greater survival of L. coenosus larvae during drought, together with the water-retaining properties of the cases, allowed this species to exploit stressful and risky habitats, such as temporary pools.     

Survival of caddis larvae in relation to their case material in a group of temporary and permanent pools

1. The occurrence of larvae of Limnephilus coenosus and L. vittatus (Trichoptera) was recorded in 103 rock pools both before and after the dry periods in spring–summer (April–May and July–early August), when a great number of the pools dried out. In early spring, 84% of the pools sampled contained larvae of at least one of the species. Limnephilus coenosus larvae were present in a higher proportion of pools that later dried out than in the permanent ones, while L. vittatus larvae were predominantly found in permanent pools. Larvae of both species were found together in 31% of the inhabited pools.
2. Laboratory experiments, designed to elucidate differential survival under drought conditions, demonstrated that the organic cases of L. coenosus larvae held water more efficiently than did the mineral L. vittatus cases. Full-grown (fifth instar) L. coenosus larvae also survived dry conditions better than did L. vittatus larvae. The higher survival of L. coenosus was due to a combination of drought-resistant case material and a higher survival ability of the larvae themselves.
3. Limnephilus vittatus larvae were restricted by their low capability to withstand desiccation, although case material and food were available for L. vittatus larvae in all pools. Absence of case material and high-quality food in many pools, however, restricted the presence of L. coenosus larvae, but this species did not suffer from heavy mortality because of desiccation and all pool populations of L. coenosus survived until pupation.
4. The differences in species composition in these temporary and permanent pools can be explained by the differential site selection by ovipositing females, as well as by larval survival. The intrinsically greater survival of L. coenosus larvae during drought, together with the water-retaining properties of the cases, allowed this species to exploit stressful and risky habitats, such as temporary pools.     

Shredder–collector interactions in temporary streams of western Oregon

1. Field data and results from laboratory rearing are combined to describe shredder–collector interactions in western Oregon temporary streams.
2. The composition of functional feeding groups in the temporary streams conforms to that predicted for permanent headwaters by the River Continuum Concept (RCC).
3. A distinct functional feeding group phenology was found, with shredders emerging first and collectors emerging last in the season. Scrapers were intermediate.
4. Presence of shredders enhanced collector growth in laboratory experiments ( P < 0.01; n = 12). The species reared in the study trials accounted for 67% of the shredder biomass and 76% of the collector biomass in the natural systems.
5. Field data and laboratory rearing trials both support the hypothesis of a close shredder–collector interaction in the processing of allochthonous material in the summer-dry headwaters studied.     

Role of epibiotic diatoms isolated from the barnacle shell in the cyprid metamorphosis of <Emphasis Type="Italic">Balanus amphitrite</Emphasis>

The mechanisms structuring aquatic communities across environmental gradients are often difficult to distinguish from one another and can produce similar patterns of species distributions. In freshwater systems, the amount of canopy cover from surrounding trees is often associated with transitions in local community structure. These community changes could be driven by habitat selection prior to colonization of the aquatic habitat and/or species-sorting post-colonization. To assess the contributions of pre- versus post-colonization processes in structuring larval dragonfly assemblages, we tested the impact of artificial and natural canopy cover on the selection of experimental aquatic mesocosms by adult dragonflies, and monitored the performance (i.e. growth and survival) of larval dragonflies that were placed in mesocosms under a gradient of natural canopy cover. We found that greater levels of canopy cover resulted in fewer adult visits to mesocosms, and more natural canopy cover decreased the species richness of visitors. There were no effects of canopy cover on the growth and survival of larvae added to the mesocosms. Our results suggest that adult habitat selection plays a dominant role in structuring larval dragonfly assemblages across a canopy cover gradient, and that canopy cover can be an important environmental filter on species distributions.     

Relaxed predation results in reduced phenotypic integration in a suite of dragonflies

Although changes in magnitude of single traits responding to selective agents have been studied intensively, little is known about selection shaping networks of traits and their patterns of covariation. However, this is central for our understanding of phenotypic evolution as traits are embedded in a multivariate environment with selection affecting a multitude of traits simultaneously rather than individually. Here, we investigate inter‐ and intraspecific patterns of trait integration (trait correlations) in the larval abdomen of dragonflies as a response to a change in predator selection. Species of the dragonfly genus Leucorrhinia underwent a larval habitat shift from predatory fish to predatory dragonfly‐dominated lakes with an associated relaxation in selection pressure from fish predation. Our results indicate that the habitat‐shift‐induced relaxed selection pressure caused phenotypic integration of abdominal traits to be reduced. Intraspecific findings matched patterns comparing species from both habitats with higher abdominal integration in response to predatory fish. This higher integration is probably a result of faster burst swimming speed. The abdomen holds the necessary morphological machinery to successfully evade predatory fish via burst swimming. Hence, abdominal traits have to function in a tight coordinated manner, as maladaptive variation and consequently nonoptimal burst swimming would cause increased mortality. In predatory dragonfly‐dominated lakes, no such strong link between burst swimming and mortality is present. Our findings highlight the importance of studying multivariate trait relationships as a response to selection for understanding patterns of phenotypic diversification.     

Crustacean zooplankton community structure in temporary and permanent grassland ponds

Lentic community structure varies across a size gradient of ponds and lakes with physical factors, such as pond drying, and biotic factors, such as fish predation, determining the species assemblage. We studied the effects of pond drying and fish absence on crustacean zooplankton across a gradient of pond sizes in a Texas grassland. We determined the species compositions and size distributions of crustacean zooplankton in 20 temporary and 18 permanent ponds in April after March rains had refilled the ponds. The surface areas of temporary and permanent ponds ranged from <0.01 to 0.21 ha and 0.04 to 13.8 ha, respectively, and temporary ponds were significantly smaller, on average, than permanent ponds. Fish were absent from all temporary ponds and present in all permanent ponds. We detected a difference in the zooplankton species assemblages of the temporary and permanent ponds. Out of 14 total zooplankton taxa that occurred in eight or more ponds, seven taxa were significantly more prevalent in temporary ponds and four taxa were significantly more prevalent in permanent ponds. The sizes of zooplankton in the temporary fishless ponds were greater than those in the permanent ponds with fish present. We concluded that pond size mediated susceptibility to pond drying, and pond drying determined the presence and absence of fish and their secondary trophic-level effect on zooplankton community structure. Handling editor: Steven Declerck     

Relationship between morphology,dispersal and habitat distribution in three species of Libellula (Odonata: Anisoptera)

Morphology is an important determinant of flight performance and can shape species’ dispersal behaviour. This study contrasted the morphology of flight-related structures in dragonfly species with different dispersal behaviours to gain insights into the relationship between morphology and dispersal behaviour. Specifically, wing size, wing shape and thorax size were compared in three co-occurring species from different clades within the genus Libellula (Odonata: Anisoptera: Libellulidae) to assess how these morphological traits are related to differences in dispersal behaviour and to how broadly their larvae occur across a habitat gradient. Two species had broad larval habitat distributions as well as high rates and distances of dispersal. These two species had relatively larger wings and thoraces than the third species, which was found only in permanent lakes and had limited dispersal. The hind-wings of more dispersive species also had lower aspect ratios and a relatively wider basal portion of the wing than the less dispersive species. Broad hind-wings may facilitate the use of gliding flight and reduce the energetic costs of dispersal. Determining the morphological traits associated with alternative dispersal behaviours may be a useful tool to assess the differential dispersal capacities of species or populations.     

Colonization of an artificial stream by fishes and aquatic macro-invertebrates

We examined colonization by fishes and macro-invertebrates from permanent streams into an artificial freshwater stream simulating lotic temporary bodies of water that exist for only a limited period each year. After introducing water, invertebrates such as chironomid larvae in mud increased in numbers rapidly in the experimental stream, although they were rare in mud in the permanent streams. Eleven of 12 fish species present in the permanent streams colonized the experimental stream and preyed upon invertebrates, although fish composition differed significantly between the two streams. About 100 days after the initiation of the experiment, both species richness and diversity in the experimental stream reached almost the same level as that in the permanent streams. More diverse fishes colonized the complex section where habitat diversity was high compared to the simple section in the experimental stream. Our study strongly suggests that lotic temporary waters such as temporary streams around main rivers have unique ecological characteristics and serve as valuable foraging sites for fish.     

High quantitative and no molecular differentiation of a freshwater snail (Galba truncatula) between temporary and permanent water habitats

We investigate the variation in quantitative and molecular traits in the freshwater snail Galba truncatula, from permanent and temporary water habitats. Using a common garden experiment, we measured 20 quantitative traits and molecular variation using seven microsatellites in 17 populations belonging to these two habitats. We estimated trait means in each habitat. We also estimated the distributions of overall genetic quantitative variation (QST), and of molecular variation (FST), within and between habitats. Overall, we observed a lack of association between molecular and quantitative variance. Among habitats, we found QST>FST, an indication of selection for different optima. Individuals from temporary water habitat matured older, at a larger size and were less fecund than individuals from permanent water habitat. We discuss these findings in the light of several theories for life-history traits evolution.     

Growth responses of 15 Salix genotypes to temporary water stress are different from the responses to permanent water shortage

Hybrids of willow (Salix spp.) are today grown as biomass crops for energy in several cool-temperate regions including Sweden. These trees have great growth potential also under warmer climates, but may suffer from drought and heat. Research on tree growth under drought has often focused on the responses to permanent water stress. Less attention has been paid to the effects of temporary water stress on tree growth, although periods of strong water shortage are recurrent in many regions of the world. We performed a greenhouse experiment to assess the impact of five treatments including permanent (PWS; 30 days of water shortage) and temporary (TWS; 4–12 days of water shortage followed by normal watering) water stress on growth and leaf traits of 15 Salix genotypes. Plant biomass and height increment decreased across treatments in the order control (well-watered) > TWS > PWS, but there was also a significant genotype × treatment interaction. The pattern in growth traits was not directly reflected by the leaf traits, for which there was no significant genotype × treatment interaction (except for leaf angle). The significant genotype × treatment interactions for growth traits indicate a potential for breeding. Permanent water shortage does not necessarily represent an appropriate environment for the selection of genotypes for environments characterised by temporary water stress.     

Foraging tactics in alternative heterochronic salamander morphs: trophic quality of ponds matters more than water permanency

1. In lentic freshwater habitats, the composition of animal assemblages shifts along a gradient from temporary to permanent basins. When habitats with different degrees of permanence are at the scale of the home range of species, they constitute alternatives in terms of energy acquisition through feeding. 2. In this context, previous studies showed an advantage of metamorphic over paedomorphic tiger salamanders (Ambystoma tigrinum) in temporary ponds which are only available to metamorphs. The aim of this study was to establish whether salamanders obtain similar benefits in ponds that do not differ in water permanence and whether salamanders shifted from detrimental to advantageous ponds. To this end, we determined the feeding habits, body condition and movement patterns of the two morphs in a complex of four permanent and four temporary ponds. 3. Consistent with previous studies, metamorphs consumed higher‐quality diets than paedomorphs in term of energy intake. However, these differences occurred because metamorphs consumed fairy shrimp in a single temporary pond. Individual movement patterns confirmed that most of the metamorphs used different aquatic habitats both within and between years and that most of them moved from permanent ponds for breeding towards the most profitable temporary pond in terms of foraging. 4. These results indicate that habitat selection by salamanders is optimal in term of energy intake in metamorphs that use high quality ponds independently of hydroperiod. It seems that both spatial and temporal variation can influence the relative foraging success of each morph.     

Adaptations to increasing hydraulic stress: morphology, hydrodynamics and fitness of two higher aquatic plant species

Sessile organisms often exhibit morphological changes in response to permanent exposure to mechanical stimulation (wind or water movements). The adaptive value of these morphological changes (hydrodynamic performance and consequences on fitness) has not been studied extensively, particularly for higher plants submitted to flow stress. The aim was to determine the adaptive value of morphological patterns observed within two higher aquatic plant species, Berula erecta and Mentha aquatica, growing along a natural flow stress gradient. The hydrodynamic ability of each ramet was investigated through quantitative variables (drag coefficient and E-value). Fitness-related traits based on vegetative growth and clonal multiplication were assessed for each individual. For both species, the drag coefficient and the E-value were explained only to a limited extent by the morphological traits used. B. erecta exhibited a reduction in size and low overall plant drag at higher flow velocities, despite high drag values relative to leaf area, due to a low flexibility. The plants maintained their fitness, at least in part, through biomass reallocation: one tall ramet at low velocity, but shorter individuals with many interconnected stolons when flow velocity increased. For M. aquatica, morphological differences along the velocity gradient did not lead to greater hydrodynamic performance. Plant size increased with increasing velocities, suggesting the indirect effects of current favouring growth in high velocities. The fitness-related traits did not demonstrate lower plant fitness for high velocities. Different developmental constraints linked to plant morphology and trade-offs between major plant functions probably lead to different plant responses to flow stress.