Patterns of sexual dimorphism in flight agility in territorial and non-territorial Odonata

Journal of Ethology - Adult dragonflies (Anisoptera) and damselflies (Zygoptera) are amongst the most accomplished flying insects on the planet. The main functions of spatial displacement by flight...     

中文蜻蜓常用名称考

在我国,蜻蜓有多种名称,目前仍在使用的有蜻蜓、蜻蛉、水虿、、豆娘等。它们当中,有些是源自蜻蜓类昆虫的体色,如“蜻、”;有些是由蜻蜓的身体形状而来,如“蜓、蛉、水虿”。而“豆娘”出现最晚,应用时间也最短。中文之“豆娘”与日文中的“豆娘”关系甚为复杂,目前尚无定论。     

Sexual selection, sexual size dimorphism and Rensch's rule in Odonata

Odonata (dragonflies and damselflies) exhibit a range of sexual size dimorphism (SSD) that includes species with male-biased (males > females) or female-biased SSD (males < females) and species exhibiting nonterritorial or territorial mating strategies. Here, we use phylogenetic comparative analyses to investigate the influence of sexual selection on SSD in both suborders: dragonflies (Anisoptera) and damselflies (Zygoptera). First, we show that damselflies have male-biased SSD, and exhibit an allometric relationship between body size and SSD, that is consistent with Rensch's rule. Second, SSD of dragonflies is not different from unit, and this suborder does not exhibit Rensch's rule. Third, we test the influence of sexual selection on SSD using proxy variables of territorial mating strategy and male agility. Using generalized least squares to account for phylogenetic relationships between species, we show that male-biased SSD increases with territoriality in damselflies, but not in dragonflies. Finally, we show that nonagile territorial odonates exhibit male-biased SSD, whereas male agility is not related to SSD in nonterritorial odonates. These results suggest that sexual selection acting on male sizes influences SSD in Odonata. Taken together, our results, along with avian studies (bustards and shorebirds), suggest that male agility influences SSD, although this influence is modulated by territorial mating strategy and thus the likely advantage of being large. Other evolutionary processes, such as fecundity selection and viability selection, however, need further investigation.     

Are all Mexican odonate species documented? An assessment of species richness

With the aim of protecting Mexican diversity, one current governmental task is to complete national biological inventories. In the case of odonate insects, several researchers have hypothesized that species richness is complete (205 dragonflies and 151 damselflies), but there has not been any formal exercise to test this. Thus, we have investigated whether odonate species richness (for Mexican endemics, dragonflies (suborder Anisoptera), damselflies (suborder Zygoptera) and total species) is complete using sample-based and coverage-based rarefaction curves. Along with this, we also showed how good distribution data are in the country. The rarefaction curves have indicated 100% completeness for all groups suggesting that the inventory is complete. However, species' distribution data is highly patchy regarding areas either well (e.g. central Mexico) or badly (e.g. coast of Guerrero and Oaxaca) collected. We encourage researchers to continue odonate sampling in order to support at least three conservation actions: (i) conservation assessment of endangered species; (ii) knowledge of range shifts given rising global temperatures; and (iii) increase public interest and awareness in protected, touristic areas.     

Beyond latitude: Temperature,productivity and thermal niche conservatism drive global body size variation in Odonata

Aim

So far, latitudinal body size clines have been discussed primarily in the context of thermoregulation, sensu Bergmann. However, body size patterns are ambiguous in ectotherms, and this heterogeneity remains poorly understood. We tested whether Bergmann's rule and the resource availability rule, which states that energetic requirements determine species body size, apply to damselflies and dragonflies (Odonata). Furthermore, we hypothesized that the contrasting effects of thermoregulation and resource availability (e.g., productivity) can obscure the overall gradient in body size variation.

Location

Global.

Time period

Contemporary.

Major taxa studied

Odonata.

Methods

Using data for 43% of all odonate species described so far, we tested our hypotheses in phylogenetically and spatially comparative analyses at assemblage and species levels. For the distribution data, we integrated expert range maps and ecoregional ranges based on all available occurrence records. To distinguish between long-term and evolutionarily recent responses of environmental drivers in body size, we constructed a phylogenetically informed classification of all odonate species and decomposed the body size into its phylogenetic and specific components for our subset of species.

Results

We documented a weak positive relationship between body length and latitude but found strong and contrasting effects for temperature between dragonflies and damselflies and consistent positive effects for productivity that explained 35–57% of body size variation. Moreover, we showed a strong phylogenetic signal in sized-based thermoregulation that shaped the distribution of dragonflies, but not of damselflies.

Main conclusions

We concluded that temperature, productivity and conservatism in size-based thermoregulation synergistically determine the distribution of ectotherms, while the taxon-specific importance of these factors can lead to contrasting and weak latitude–size relationships. Our results reinforce the importance of body size as a determinant of species distributions and responses to climate change.     

Genome size in arthropods; different roles of phylogeny,habitat and life history in insects and crustaceans

Despite the major role of genome size for physiology, ecology, and evolution, there is still mixed evidence with regard to proximate and ultimate drivers. The main causes of large genome size are proliferation of noncoding elements and/or duplication events. The relative role and interplay between these proximate causes and the evolutionary patterns shaped by phylogeny, life history traits or environment are largely unknown for the arthropods. Genome size shows a tremendous variability in this group, and it has a major impact on a range of fitness‐related parameters such as growth, metabolism, life history traits, and for many species also body size. In this study, we compared genome size in two major arthropod groups, insects and crustaceans, and related this to phylogenetic patterns and parameters affecting ambient temperature (latitude, depth, or altitude), insect developmental mode, as well as crustacean body size and habitat, for species where data were available. For the insects, the genome size is clearly phylogeny‐dependent, reflecting primarily their life history and mode of development, while for crustaceans there was a weaker association between genome size and phylogeny, suggesting life cycle strategies and habitat as more important determinants. Maximum observed latitude and depth, and their combined effect, showed positive, and possibly phylogenetic independent, correlations with genome size for crustaceans. This study illustrate the striking difference in genome sizes both between and within these two major groups of arthropods, and that while living in the cold with low developmental rates may promote large genomes in marine crustaceans, there is a multitude of proximate and ultimate drivers of genome size.     

MEASURING PHENOTYPIC SELECTION ON AN ADAPTATION: LAMELLAE OF DAMSELFLIES EXPERIENCING DRAGONFLY PREDATION

Previous studies suggest that the evolution of increased caudal lamellae size to increase swimming speed was an adaptation of Enallagma damselflies for coexisting with large, predatory dragonflies in fishless lakes. To test whether dragonfly predation still exerts selection pressures for increased lamellae size, I performed a field experiment in which I manipulated the abilities of dragonfly larvae to inflict mortality on Enallagma boreale larvae and compared differences in lamellae size and shape between treatments. In cages where dragonflies were free to forage on damselflies, surviving E. boreale larvae had lamellae that were larger in lateral surface area, and that were wider relative to their length, as compared with larvae recovered from treatments in which dragonflies were not permitted to forage on damselflies. Selection differentials of about 0.25 phenotypic standard deviation units were measured for both of these characters. These results indicate that dragonfly predation still exerts significant selection pressures on damselfly antipredator adaptations. The results of this study are discussed in the context of studies of adaptation.     

Body size evolution in an old insect order: No evidence for Cope's Rule in spite of fitness benefits of large size

We integrate field data and phylogenetic comparative analyses to investigate causes of body size evolution and stasis in an old insect order: odonates (“dragonflies and damselflies”). Fossil evidence for “Cope's Rule” in odonates is weak or nonexistent since the last major extinction event 65 million years ago, yet selection studies show consistent positive selection for increased body size among adults. In particular, we find that large males in natural populations of the banded demoiselle (Calopteryx splendens) over several generations have consistent fitness benefits both in terms of survival and mating success. Additionally, there was no evidence for stabilizing or conflicting selection between fitness components within the adult life‐stage. This lack of stabilizing selection during the adult life‐stage was independently supported by a literature survey on different male and female fitness components from several odonate species. We did detect several significant body size shifts among extant taxa using comparative methods and a large new molecular phylogeny for odonates. We suggest that the lack of Cope's rule in odonates results from conflicting selection between fitness advantages of large adult size and costs of long larval development. We also discuss competing explanations for body size stasis in this insect group.     

The Impacts of Introduced Poeciliid Fish and Odonata on the Endemic Megalagrion (Odonata) Damselflies of Oahu Island, Hawaii

Since the beginning of this century there have been substantial declines in the distribution and abundance of native Megalagrion damselflies on the Hawaiian Island of Oahu. Native damselflies have also vanished from most low elevation areas on other Hawaiian Islands, although historically, lotic and wetland dwelling damselfly species were once common throughout the archipelago. It is hypothesized that poeciliid fish introduced for biological control have caused the decline of four stream-breeding damselfly species on Oahu, and the extinction or near-extinction of two other species in Hawaii. This study documents the presence of remnant Megalagrion populations in Oahu streams, wetlands and estuaries, and records the elevational distributions of introduced fish in each waterbody surveyed. The distributions of introduced Odonata are also recorded, because the seven species of damselflies and dragonflies introduced to Oahu since 1936 present another potential threat to native Hawaiian damselflies. Native damselfly and introduced poeciliid fish distributions were mutually exclusive on Oahu, and it is concluded that this is probably due to predation by the introduced fish. By contrast, even the rarest native Megalagrion damselflies were found in areas containing introduced damselflies and dragonflies.     

Does the management of surrounding terrestrial habitats increase the tendency of odonates to leave aquatic habitats?

Generally, dragonflies and damselflies (odonates) are considered aquatic invertebrates. However, the ecological requirements of their adults are not different from those of fully, terrestrial insects. Surprisingly, there is a very little information on whether the management and structure of surrounding habitats has any influence on the diversity and seasonal dynamics of odonates. This is important to know because recently, a large proportion of freshwater habitats in Central Europe have becomes surrounded by intensively managed habitats. The aim of this study was to investigate the effects of different types of terrestrial habitats on their long-term utilization by dragonflies and damselflies. I assumed that this pattern varied over time; therefore, I used generalized additive mixed models to analyze the effects of management on seasonal changes in the abundance of individuals in terrestrial environments. From my results, it was evident that the management practices of surrounding terrestrial habitats had a significant impact on the population dynamics of dragonflies. The abundance of dragonfly adults in surrounding terrestrial habitats increased toward the end of the season. However, this was only, when the natal aquatic habitat was not affected by fish farming and was able to supply surrounding terrestrial habitats with offspring. This was evidenced by the fact that, compared to areas with extensive water management, in sites with fish farming, seasonal increases in abundance was negligible. There is no doubt that the structure of surrounding terrestrial habitats has a significant influence on the diversity of terrestrial invertebrates. However, we must not forget that terrestrial habitats, regardless of their management, are not able to replace the poor quality of the aquatic (natal) habitat. Interestingly, the abundance of damselflies decreased toward the end of the season, regardless of the management practices of the surrounding areas. This indicates that their dynamics is more controlled by time stress or other similar mechanisms than that of dragonflies.     

Evolutionary avenues for, and constraints on, the transmission of frog lung flukes (Haematoloechus spp.) in dragonfly second intermediate hosts

Metacercariae survival patterns and their distribution in second intermediate odonate hosts were examined for 4 species of frog lung flukes. Surveys of aquatic larvae and recently emerged teneral dragonflies and damselflies indicated that prevalence and mean abundance of Haematoloechus spp. metacercariae were significantly lower in teneral dragonflies than larval dragonflies, while there was no significant difference in prevalence or mean abundance of Haematoloechus spp. metacercariae among larval and teneral damselflies. Experimental infections of dragonflies indicated that metacercariae of Haematoloechus coloradensis and Haematoloechus complexus were located in the head, thorax, and branchial basket of dragonflies, whereas metacercariae of Haematoloechus longiplexus and Haematoloechus parviplexus were restricted to the branchial basket of these hosts. Metacercariae of H. coloradensis, H. complexus, and H. longiplexus infected the head, thorax, and abdomen of damselflies, but these insects were resistant to infection with H. parviplexus. Subsequent metamorphosis experiments on experimentally infected dragonflies indicated that most metacercariae of H. longiplexus were lost from the branchial basket during metamorphosis, but most metacercariae of H. coloradensis, H. complexus, and H. parviplexus survived dragonfly metamorphosis. These observations suggest that the observed ecological host specificity of H. longiplexus in semiterrestrial leopard frogs may be due to few metacercariae of H. longiplexus reaching these frogs in a terrestrial environment. Because of the uncertain validity of Haematoloechus varioplexus as a distinct species from its synonym H. parviplexus, their morphological characters were reevaluated. The morphological data on H. varioplexus and H. parviplexus indicate that they differ in their acetabulum length and width, ovary shape, testes length, and egg length and width. Experimental infections of plains leopard frogs, northern leopard frogs, and bullfrogs with worms from bullfrogs indicate that the synonymy of H. parviplexus with H. varioplexus is not warranted, and that these flukes are distinct species, i.e., H. parviplexus in bullfrogs and H. varioplexus in plains leopard frogs and northern leopard frogs.     

Wing length allometry in Odonata: differences between families in relation to migratory behaviour

In insects, wing shape and body size are correlated with several aspects of behaviour, and the optimal morphology of wings is a trade-off between a number of functional demands in relation to behaviour (e.g. foraging, migration and sexual display). Dragonflies are spectacularly skilful flyers and present a range of different wing shapes, but to date, no detailed studies have been conducted in this group on wing length allometry in relation to body size. In this paper, we use published data on body length and wing length in all European and North American dragonflies to investigate differences in wing length allometries among Odonata taxa (suborders and families) and to relate these to behavioural patterns. We found different wing allometries between Zygoptera and Anisoptera, which are probably related to the flight mode and wing form of the two suborders. Among the Anisoptera, the Libellulidae showed a distinct wing length allometry from all other anisopteran families and migrants differed from non-migrant species. The first dichotomy is likely to reflect the adaptation of wing morphology of Libellulidae to sit-and-wait behaviour and to brief foraging flights (most species of this family are perchers) with respect to all other families, members of which are typically flyers. The second dichotomy reflects the trend of migrating species to have relatively longer wings than non-migrating members of the same family. Finally, wing length allometry differed among all the zygopteran families analysed, and this pattern suggested that each family evolved a particular wing morphology in response to peculiarities in behaviour, habitat and flight mode.     

Changing temperature regimes have advanced the phenology of Odonata in the Netherlands

Abstract.  1. Responses of biota to climate change have been well documented for a restricted number of taxa. This study examined shifts in phenology of 37 species of the aquatic insect order Odonata in the Netherlands over the last decade.
2. The present study shows that adults of the Dutch dragonflies and damselflies have advanced their flight dates over recent years due to complex effects of changing temperature regimes on the timing of adult flight dates.
3. Flight dates did not respond to changes in autumn/winter temperatures, advanced with increases in spring temperatures of the focal and previous year, and delayed with increases in summer temperatures of the previous year. Climate change consequently advanced the flight dates of the Odonata because only spring temperatures have increased during the study period.
4. The findings imply that climate change can evoke strong phenological responses in aquatic insects. Moreover, shifts in phenology due to climate change are likely to vary both spatially or temporally, depending on the exact nature of climate change.     

A northward shift of range margins in British Odonata

Many species are predicted to shift their ranges to higher latitudes and altitudes in response to climate warming. This study presents evidence for 37 species of nonmigratory British dragonflies and damselflies shifting northwards at their range margins over the past 40 years, seemingly as a result of climate change. This response by an exemplar group of insects associated with fresh water, parallels polewards range changes observed in terrestrial invertebrates and other taxa.     

Genome size and developmental complexity

Haploid genome size (C-value) is correlated positively with cell size, and negatively with cell division rate, in a variety of taxa. Because these associations are causative, genome size has the potential to impact (and in turn, be influenced by) organism-level characters affected by variation in either of these cell-level parameters. One such organismal feature is development. Developmental rate, in particular, has been associated with genome size in numerous plant, vertebrate, and invertebrate groups. However, rate is only one side of the developmental coin; the other important component is complexity. When developmental complexity is held essentially constant, as among many plants, developmental rate is the visibly relevant parameter. In this case, genome size can impose thresholds on developmental lifestyle (and vice versa), as among annual versus perennial plants. When developmental rate is constrained (as during time-limited amphibian metamorphosis), complexity becomes the notable variable. An appreciation for this rate-complexity interaction has so far been lacking, but is essential for an understanding of the relationships between genome size and development. Moreover, such an expanded view may help to explain patterns of variation in taxa as diverse as insects and fish. In each case, a hierarchical approach is necessary which recognizes the complex interaction of evolutionary processes operating at several levels of biological organization.     

Peculiarities of structural-functional organization of the motor neuropil in the dragonfly thoracic ganglia

The study considers structural-functional relations in motor neuropil of the thoracic ganglia in dragonflies-insects capable of performing very complex and fast maneuvering in flight. The motor neuropil in dragonflies was shown to be more differentiated than in less mobile insects, while its motor nuclei are more outlined and approached to each other. There were revealed dendrites of the leg muscle motoneurons (intermediate nucleus), running to the anterior and posterior nuclei that contain dendrites of the wing muscle motoneurons. A possible role of such a dendrite approaching is discussed for close functional cooperation of wing and leg muscles essential for dragonflies to catch a large prey in flight by using their legs. Peculiarities of structural organization of the wing muscle motoneurons in dragonflies and locusts are considered to suggest the greater functional capabilities of motoneurons in the dragonfly motor apparatus.     

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.     

Bird predation selects for wing shape and coloration in a damselfly

Wing shape is related to flight performance, which is expected to be under selection for improving flight behaviours such as predator avoidance. Moreover, wing conspicuousness, usually involved in sexual selection processes, is also relevant in terms of predation risk. In this study, we examined how predation by a passerine bird, the white wagtail Motacilla alba, selects wing shape and wing colour patch size in males of the banded demoiselle Calopteryx splendens. The wing colour patch is intra‐ and intersexually selected in the study species. In a field study, we compared wings of live damselflies to wings of predated damselflies which are always discarded after predation. Based on aerodynamic theory and a previous study on wing shape of territorial tactics in damselflies, we predicted an overall short and broad wing, with a concave front margin shape to be selected by predation. This shape would be expected to improve escaping ability. Moreover, we predicted that wing patch size should be negatively selected by predation. We found that selection operated differently on fore‐ and hindwings. In contrast to our predictions, predation favoured a slender general forewing shape. However, the predicted wing shape was favoured in hindwings. We also found selection favouring a narrower wing colour patch. Our results suggest different roles of fore‐ and hindwings in flight, as previously suggested for Calopteryx damselflies and shown for butterflies and moths. Forewings would be more involved in sustained flight and hindwings in flight manoeuvrability. Our results differ somehow from a recently published work in the same study system, but using another population, suggesting that selection can fluctuate across space, despite the simplicity of this predator–prey system.