Neotropical dragonflies (Insecta: Odonata) as indicators of ecological condition of small streams in the eastern Amazon

Sensitive and cost‐effective indicators of aquatic ecosystem condition in Amazon streams are necessary to assess the effects of anthropogenic disturbances on those systems in a viable and ecologically meaningful manner. We conducted the present study in the municipality of Paragominas, state of Pará, northern Brazil, where we sampled adult dragonflies in 50 100‐m‐long wadeable stream sites in 2011. We collected 1769 specimens represented by 11 families, 41 genera and 97 species. The suborder Zygoptera contributed 961 individuals and Anisoptera 808. Among the 97 recorded species, nine were classified as useful indicators of ecological condition, with four species being associated with more degraded streams (three Anisoptera, one Zygoptera) and five with more preserved streams (all were Zygoptera). Anisoptera (dragonflies) tend to provide more useful indicators of more degraded environments because they have more efficient homeostatic mechanisms and are more mobile, enabling them to tolerate a wider range of environmental conditions. By contrast, Zygoptera (damselflies) tend to provide a more useful role as indicators of more preserved environments and high levels of environmental heterogeneity because of their smaller body sizes and home ranges and greater ecophysiological restrictions. We conclude from our assessment of this low‐order Amazonian stream system that (i) the occurrence of specific odonate species is strongly associated with the configuration of riparian vegetation, (ii) agricultural activities appear to be the main factor determining changes in the composition of odonate assemblages and (iii) these insects can act as useful indicators of the ecological consequences of riparian habitat loss and disturbance. Because generalist species invade moderately degraded areas, those areas may have high species richness but host few species of Zygoptera. Therefore, preserving dense riparian vegetation is necessary to maintain aquatic ecological condition, and that condition can be rehabilitated by planting new trees. Both require enforcing existing environmental regulations, various types of incentives and educating local communities.     

A catalogue of the West Indian dragonflies (Insecta: Odonata)

Summary. Compilation and analysis of the existing literature together with the results of our research carried out since 2000 makes possible an updated catalogue of the West Indian Odonata. Such a catalogue has not previously been available, and dispersed and multilingual literature did not facilitate odonatological studies. The odonate fauna of the Caribbean is currently composed of 108 valid species, of which 36 (32%) are endemic to one or a few islands. The most species-rich families are Libellulidae and Coenagrionidae, together comprising 65% of the total fauna.     

The Australian monsoon tropics as a barrier for exchange of dragonflies (Insecta: Odonata) between New Guinea and Australia

Recent studies show a remarkable scarcity of faunal exchange events between Australia and New Guinea in the Pleistocene despite the presence of a broad land connection for long periods. This is attributed to unfavourable conditions in the connecting area associated with the long established northern Australian Monsoon Climate. This would be expected to have impacted strongly on freshwater faunas with the following results: (1) limited overlap in species, (2) most higher taxonomic groups present in both areas sharing no species or even genera and (3) shared species dominated by lentic species with high dispersal capacity. Testing these predictions for dragonflies showed the turnover in the family, genus and species composition between Australia and New Guinea to be higher than anywhere in the world with only 50% of families and subfamilies, 33% of the genera and 8% of the species being shared. Only one of the 53 shared species favors lotic waters compared with 64% of the 652 combined Australian–New Guinean species. These results agree with our predictions and indicate that the dragonfly fauna of Australia and New Guinea have effectively been separated during the Pleistocene probably due to the prolonged unfavourable climatic conditions in the intervening areas.     

An exploration of genome size diversity in dragonflies and damselflies (Insecta: Odonata)

Like most insect orders, the Odonata (dragonflies and damselflies) remain poorly studied from the perspective of genome size. They exhibit several characteristics that make them desirable targets for analysis in this area, for example a large range in body size, differences in developmental rate, and distinct modes of flight – all of which are related to genome size in at least some animal taxa. The present study provides new genome size estimates and morphometric data for 100 species of odonates, covering about 1/5 of described North American diversity. Significant relationships are reported between genome size and body size (positive in dragonflies, negative in damselflies), and there is also indication that developmental rate and flight are related to genome size in these insects. Genome size is also positively correlated with chromosome number across the order. These findings contribute to an improved understanding of genome size evolution in insects, and raise several interesting questions for future research.     

Identifying habitat linkages to maintain connectivity for corridor dwellers in a fragmented landscape

Anthropogenic habitat fragmentation typically precedes conservation planning; maintaining remaining linkages among core habitat areas can thus become a key conservation objective. Identifying linkages for dispersal and ensuring those linkages have long-term protection and management are challenging tasks for wildlife managers. These tasks can be especially daunting for smaller species with low mobility, termed corridor dwellers, which must maintain sustainable populations within corridors. Between May 2007 and June 2009, we collected occurrence locations for a corridor dweller, the Palm Springs pocket mouse (Perognathus longimembris bangsii), from museums, previous research, and our own field sampling. We used those data to model their suitable niche space and then identify suitable linkages between proposed conservation areas. We used a partitioned Mahalanobis D² statistic to create a spatially explicit niche model describing the distribution of a suitable niche space, and we validated the model statistically, with live trapping and with burrowing owl (Athene cunnicularia) diets. Our model identified soil characteristics, topographic ruggedness, and vegetation as variables delimiting Palm Springs pocket mouse habitat; sand content of the soils was an especially important characteristic. Our historic distribution model identified 120,000–90,000 ha as historically potential Palm Springs pocket mouse habitat; roughly 39% of that has been lost to more recent development. Most of the remaining suitable habitat occurred in the northwestern portion of the valley. We modeled habitat within core reserves as well as within proposed linkages between those reserves as having high similarity to known occupied habitats. Live trapping in areas with high (≥0.95) Habitat Suitability Index (HSI) values resulted in captures at 66% of those locations and, along with burrowing owl diets, refined a qualitative model as to what constituted a suitable Palm Springs pocket mouse corridor. While most corridor analyses have focused on mobile species which may traverse corridors in hours, days, or weeks, linkages for corridor dwellers must include habitat for sustaining multi-generational populations. This requires evaluating whether continuous suitable habitat exists within proposed corridors. Our research demonstrates how niche modeling can provide a landscape-scale view of the distribution of suitable habitat to evaluate conservation objectives for connectivity. © 2011 The Wildlife Society.     

Crevice organs: Sensory structures on the wings of dragonflies (Insecta,Odonata)

Summary Crevice organs are small, elongate, innervated indentations in the hard cuticle of one wing vein of aeshnid dragonflies. There are four groups on each wing. The structure and orientation of crevice organs suggest that they detect strains in the cuticle during wing movements.I wish to thank Mr. R. Whitty and staff for technical assistance with the scanning electron microscope and Dr. E.E. Ball for helpful discussion     

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.     

Heterogeneity and homologies of the repeating and unique DNA of dragonflies (Odonata, Insecta)

A relative content of unique and reiterated nucleotide sequences in DNA of eleven dragonfly species was estimated. The degree of intra- and intergenomic divergence of these DNA sequences was determined by means of DNA-DNA hybridization. Species from different genera share 40-45% of the repetitive sequences and those from different families--from 11 to 20% only. Data on the thermostability of homo- and heteroduplexes suggest that new families of the repetitive sequences have arisen repeatedly during dragonflies evolution. The quality of homologous unique sequences in the DNA compared (20-97%) correlates with the taxonomic relationships of species. Phylogenesis of some dragonfly families is discussed in view of the results obtained.     

Odonata (dragonflies and damselflies) as a bridge between ecology and evolutionary genomics

Odonata (dragonflies and damselflies) present an unparalleled insect model to integrate evolutionary genomics with ecology for the study of insect evolution. Key features of Odonata include their ancient phylogenetic position, extensive phenotypic and ecological diversity, several unique evolutionary innovations, ease of study in the wild and usefulness as bioindicators for freshwater ecosystems worldwide. In this review, we synthesize studies on the evolution, ecology and physiology of odonates, highlighting those areas where the integration of ecology with genomics would yield significant insights into the evolutionary processes that would not be gained easily by working on other animal groups. We argue that the unique features of this group combined with their complex life cycle, flight behaviour, diversity in ecological niches and their sensitivity to anthropogenic change make odonates a promising and fruitful taxon for genomics focused research. Future areas of research that deserve increased attention are also briefly outlined.     

The role of habitat connectivity and landscape geometry in experimental zooplankton metacommunities

Theory predicts that inter-patch dispersal rates and patterns of patch heterogeneity both have the potential to alter patterns of local and regional species diversity. To test this, we manipulated both rates of habitat connectivity and the geometric arrangement of habitat heterogeneity within regions of experimental zooplankton communities. We found no effects of habitat geometry on any metric of species diversity or composition. Additionally, we found no effect of habitat connectivity rate on local species diversity. We did, however, find that increasing connectivity led to a decrease in regional diversity, as well as an increase in the percent similarity of local communities within regions. Of all of the species in these communities, the relatively large cladoceran Ceriodaphnia reticulata significantly responded to the treatments, and had a higher probability of achieving high densities when connectance was high. As such, we suggest that this species played a large role in driving the increased local community similarity and decreased regional species richness as connectivity increased. These findings are in opposition to previous experimental studies of metacommunities, but support the notion that increased connectance among local patches may decrease regional diversity when patches are heterogeneous.     

Odonata (Insecta) as a tool for the biomonitoring of environmental quality

Despite the fundamental dependence of human populations on water resources, a range of anthropogenic impacts, in particular the removal of riparian vegetation, threaten freshwater environments. One of the most effective means of evaluating the effects of anthropogenic disturbance in aquatic ecosystems is the use of bioindicators, and the insects of the order Odonata are among the most efficient indicators, due to their enormous sensitivity to environmental changes. In this context, the present study aimed to verify which parameters of the odonate community (species richness, abundance/biomass, composition, taxonomic diversity and taxonomic/phylogenetic distinctness) are most effective for the evaluation of the loss of environmental integrity. The study focused on 50 streams in the northeast of the Brazilian state of Pará. The streams were sampled during the dry season, between June and August 2011. The physical characteristics of each stream were evaluated using a Habitat Integrity Index (HII). The species composition provided the best parameter for the evaluation of ecological integrity, providing a relatively accurate assessment at a lower mean research cost than other parameters. Taxonomic diversity and distinctness also provided relatively reliable results, contributed additional information on the evolutionary relationships among the odonate taxa, and also provided a low-cost approach. Deconstructing communities is necessary to detect impacts, considering the considerable variation in the environmental requirements of the different species. Overall, the parameter that best responded to gradients of disturbance was species composition, followed by diversity and taxonomic distinctness. Given these findings, odonate-based biomonitoring should focus on these parameters to guarantee the optimal detection and evaluation of habitat alterations.     

Global diversity of dragonflies (Odonata) in freshwater

Larvae of almost all of the 5,680 species of the insect order Odonata (dragonflies and damselflies) are dependent on freshwater habitats. Both larvae and adults are predators. The order is relatively well studied, and the actual number of species may be close to 7,000. Many species have small distributional ranges, and are habitat specialists, including inhabitants of alpine mountain bogs, seepage areas in tropical rain forests, and waterfalls. They are often successfully used as indicators for environmental health and conservation management. The highest diversity is found in flowing waters in rain forests of the tropics, the Oriental and Neotropical regions being the most speciose. This paper discusses diversity, summarises the biogeography of dragonflies in the different biogeographical regions and gives the total number of species and genera per family per biogeographical region. Examples are given of areas of particular diversity, in terms of areas of endemism, presence of ancient lineages or remarkable recent radiations but no well-based review of areas with high endemism of dragonflies is available so far. The conservation status of dragonflies is briefly discussed. Species confined to small remnants of forest in the tropics are most under threat of extinction by human activities. Guest editors: E. V. Balian, C. Lévêque, H. Segers and K. Martens Freshwater Animal Diversity Assessment     

Export of biomass and metals from aquatic to terrestrial ecosystems via the emergence of dragonflies (Insecta: Odonata)

Long-term monitoring of the abundance and spatial distribution of 18 widespread species of Odonata has made it possible to assess their contribution to the export of aquatic productivity that entered the Barabinsk forest-steppe ecosystem. The annual emergence of Odonata varies from 0.8 to 4.9 g/m² of the land area and from 2.3 to 13.3 g/m² of the water area, which is 4–5 times larger than that in Diptera. The total flux of organic matter from water to terrestrial ecosystems remains relatively stable (sixfold interannual variability) irrespective of large interannual variations in the abundance of separate species (e.g., 42-fold interannual variability in Libellula quadrimaculata). The metal content was determined in nine Odonata species. Export of metals by dragonflies decreases in the series K > Na > Mg > Ca > Fe > Zn > Cu > Mn > Pb > Ni > Cr > Cd. Therefore, odonates appear to be quantitatively and qualitatively important providers of aquatic resources to the forest-steppe landscape of Western Siberia.     

The distribution patterns of dragonflies (Insecta: Odonata) along the Kiewa River,Australia, and their relevance in conservation assessment

Sampling of larval and adult Odonata from 16 sites along the Kiewa River, Victoria, yielded 34 species: 10 Zygoptera, 24 Anisoptera. Patterns of larval and adult incidence were appraised, and showed that most species were restricted in incidence to several consecutive sites along the river, and that there is clear distinction also between the faunas of the potamon, rhithron and eucrenon regions. Different species of some genera of Anisoptera displayed different zonational distributions, and patterns of incidence and relative abundance of larvae and adults confirmed zonational occupancy. For larvae, these distribution patterns transcended the mode of collection, although many species were found most abundantly in one microhabitat or by one of several sampling methods employed at each site. Sampling of the two stages separately showed considerable concurrence of distributional patterns, so that either stage alone may provide data of value in faunal and conservation assessment. This revised version was published online in July 2006 with corrections to the Cover Date.     

The population of Odonata (dragonflies) in small tropical rivers with reference to asynchronous growth patterns

The odonate larval communities in three small rivers in Penang Island were studied. More species of dragonflies were found in the Botanical Garden and Titi Teras rivers (13 and 11 respectively) of relatively similar environmental parameters. Fewer (nine) dragonfly species were collected from the Youth Park River which has a lower dissolved oxygen (DO) and a higher biological oxygen demand (BOD), conductivity and turbidity. A mixture of sand, gravel and pebble substrate of Botanical Garden River with dense growth of submerged Hydrilla, grasses and Cladias (Araceae) provided suitable habitats for the dragonflies. The sandy substrate and relatively fast flowing water of Titi Teras River was highly preferred by gomphids. In the Youth Park River, the small community of dragonfly larvae was dominated by tolerant Pseudagrion rubriceps, P. microcephalum, Orthetrum chrysis and Crocothemis servilia. Based on the larval instar distribution of Ictinogomphus decoratus and O. chrysis, very asynchronous populations of these dragonflies occurred in each river. Young larvae were continuously introduced into the populations resulting in undulating growth rate curves. The growth rates of these two species were higher in the Titi Teras River when compared to those in other rivers. Density-dependent mortality, asynchronous cannibalism and fish predation could play important roles in regulating the larval dragonfly population in these rivers.     

Evolution of reproductive strategies in libellulid dragonflies (Odonata: Anisoptera)

In Libellulidae, oocyte production has been assumed to be continuous, with periods of egg-laying interspersed with periods of resting/eating; however, recent work suggests that two types of oocyte production are common: either (a) continuous or (b) step-wise. These are mirrored in the arrangement of the ovarioles in the ovaries. Likewise, two types of mate-guarding behavior have been observed in Libellulidae: (1) non?Ccontact guarding and (2) tandem guarding in which the male either hovers above the female or is physically attached to her during oviposition. Using molecular (mitochondrial and nuclear) data we explored the evolution of female reproductive traits, focusing on ovariole morphology, as well as guarding behavior, in Libellulidae. Continuous egg production appears to have evolved more than once, as have tandem and non-contact guarding. We discuss how the evolution of different ovariole types and guarding behavior may have been influenced by habitat instability, dispersal and crowded oviposition sites; thus, migratory behavior or habitat availability may have been the driving force of ovariole evolution.     

A phylogeny of anisopterous dragonflies (Insecta,Odonata) using mtRNA genes and mixed nucleotide/doublet models

The application of mixed nucleotide/doublet substitution models has recently received attention in RNA‐based phylogenetics. Within a Bayesian approach, it was shown that mixed models outperformed analyses relying on simple nucleotide models. We analysed an mt RNA data set of dragonflies representing all major lineages of Anisoptera plus outgroups, using a mixed model in a Bayesian and parsimony (MP) approach. We used a published mt 16S rRNA secondary consensus structure model and inferred consensus models for the mt 12S rRNA and tRNA valine. Secondary structure information was used to set data partitions for paired and unpaired sites on which doublet or nucleotide models were applied, respectively. Several different doublet models are currently available of which we chose the most appropriate one by a Bayes factor test. The MP reconstructions relied on recoded data for paired sites in order to account for character covariance and an application of the ratchet strategy to find most parsimonious trees. Bayesian and parsimony reconstructions are partly differently resolved, indicating sensitivity of the reconstructions to model specification. Our analyses depict a tree in which the damselfly family Lestidae is sister group to a monophyletic clade Epiophlebia + Anisoptera, contradicting recent morphological and molecular work. In Bayesian analyses, we found a deep split between Libelluloidea and a clade ‘Aeshnoidea’ within Anisoptera largely congruent with Tillyard’s early ideas of anisopteran evolution, which had been based on evidently plesiomorphic character states. However, parsimony analysis did not support a clade ‘Aeshnoidea’, but instead, placed Gomphidae as sister taxon to Libelluloidea. Monophyly of Libelluloidea is only modestly supported, and many inter‐family relationships within Libelluloidea do not receive substantial support in Bayesian and parsimony analyses. We checked whether high Bayesian node support was inflated owing to either: (i) wrong secondary consensus structures; (ii) under‐sampling of the MCMC process, thereby missing other local maxima; or (iii) unrealistic prior assumptions on topologies or branch lengths. We found that different consensus structure models exert strong influence on the reconstruction, which demonstrates the importance of taxon‐specific realistic secondary structure models in RNA phylogenetics.