Michael L. May

Simple rules guide dragonfly migration

Every year billions of butterflies, dragonflies, moths and other insects migrate across continents, and considerable progress has been made in understanding population-level migratory phenomena. However, little is known about destinations and strategies of individual insects. We attached miniaturized radio transmitters (ca 300 mg) to the thoraxes of 14 individual dragonflies (common green darners, Anax junius) and followed them during their autumn migration for up to 12 days, using receiver-equipped Cessna airplanes and ground teams. Green darners exhibited distinct stopover and migration days. On average, they migrated every 2.9±0.3 days, and their average net advance was 58±11 km in 6.1±0.9 days (11.9±2.8 km d−1) in a generally southward direction (186±52°). They migrated exclusively during the daytime, when wind speeds were less than 25 km h−1, regardless of wind direction, but only after two nights of successively lower temperatures (decrease of 2.1±0.6 °C in minimum temperature). The migratory patterns and apparent decision rules of green darners are strikingly similar to those proposed for songbirds, and may represent a general migration strategy for long-distance migration of organisms with high self-propelled flight speeds.

A Phylogenetic Perspective on Habitat Shifts and Diversity in the North American Enallagma Damselflies

Community ecologists are increasingly aware that the regional history of taxon diversification can have an important influence on community structure. Likewise, systematists recognize that ecological context can have an important influence on the processes of speciation and extinction that create patterns of descent. We present a phylogenetic analysis of 33 species of a North American radiation of damselflies (Zygoptera: Coenagrionidae: Enallagma Selys), which have been well studied ecologically, to elucidate the evolutionary mechanisms that have contributed to differences in diversity between larval habitats (lakes with and without fish predators). Analysis of molecular variation in 842 bp of the mitochondrial cytochrome oxidase I and II subunit and of the intervening Leu-tRNA and 37 morphological characters resulted in three well-defined clades that are only partially congruent with previous phylogenetic hypotheses. Molecular and morphological data partitions were significantly incongruent (p < .01). Lack of haplotype monophyly within species and small amounts of sequence divergence (< 1%) between related species in three of the four clades suggest that recent, and parallel, speciation has been an important source of community diversity. Reconstruction of habitat preference over the phylogeny suggests that the greater species diversity in fish-containing lake habitats reflects the recency of shifts into the fishless lake habit, although a difference in speciation or extinction rates between the two habitats is difficult to exclude as an additional mechanism.

Massive Swarm Migrations of Dragonflies (Odonata) in Eastern North America

Abstract We describe massive autumn migrations of dragonflies (Odonata) which occurred at Chicago, Illinois (14 September 1978), Cape May, New Jersey (11 September 1992), and Crescent Beach, Florida (3–5 September 1993). Estimated numbers of migrant dragonflies involved in these flights were approximately 1.2 million, >400,000, and 200,000, respectively. We also document other recent observations of large swarm migrations of dragonflies in eastern North America, review previous reports of this phenomenon, and compare these events to the flights at Chicago, Cape May and Crescent Beach. Records of large dragonfly migrations show several distinct patterns: (1) all reports fell between late July and mid-October, with a peak in September; (2) most of the large flights occurred along topographic leading lines such as coastlines and lakeshores; (3) massive swarm migrations generally followed the passage of synoptic-scale cold fronts; and (4) the common green darner (Anax junius) was the principal species involved in the majority of these flights. Striking parallels between the patterns of seasonal timing, geographical distribution, and meteorological context of dragonfly migrations and those of birds suggest that similar causal factors are involved.

Fliers and perchers among Odonata: dichotomy or multidimensional continuum? A provisional reappraisal

Abstract We revisit the hypothesis, first advanced in 1962, that, with regard to their means of thermoregulation and overt behaviour, two types of Odonata can be recognised: fliers, when active (during reproductive activity, primarily, or foraging) remain on the wing, whereas perchers, when similarly engaged, spend most of the time on a perch from which they make short flights. First, in light of the available data, we restrict the hypothesis to apply primarily to activity at the rendezvous. Next, we review evidence, including direct measurements of body temperature coupled with activity budgets, to test the proposition that the hypothetical classification constitutes a dichotomy rather than a continuum. We conclude: (1) that there is merit in retaining the dichotomous classification into fliers and perchers, together with the thermoregulatory capabilities assigned to each category; (2) that the distinction between fliers and perchers is sufficiently discrete to be a useful predictor of the suite of thermoregulatory strategies and energy demands characteristic of representatives of each category; and (3) that, within each category a continuum exists such that the capacity to heat the body by irradiation (i.e. ectothermically) or by metabolic heat production (endothermy) increases with body size. Some departures from expectation based on the percher/flier dichotomy reflect the increased flight activity that occurs at the rendezvous under conditions of heightened conspecific or interspecific interference. Other apparent anomalies are identified as topics for potentially fruitful research.

PARALLEL EVOLUTION IN ECOLOGICAL AND REPRODUCTIVE TRAITS TO PRODUCE CRYPTIC DAMSELFLY SPECIES ACROSS THE HOLARCTIC

Abstract The damselfly genus Enallagma originated in the Nearctic, and two Nearctic lineages recently underwent radiations partly associated with multiple independent habitat shifts from lakes dominated by fish predators into lakes dominated by dragonfly predators. A previous molecular study of four Palearctic morphospecies and all representative Nearctic species identified the presence of two cryptic species sets, with each set having Palearctic and Nearctic representatives. However, the cryptic species within each set are not sibling species. Here, we present quantitative data on ecologically important larval morphologies and behaviors involved in predator avoidance and on adult male morphological structures involved in mate recognition to quantify the phenotypic relationships among these cryptic species sets. For the adult stage, our data indicate strong parallel evolution of the structures involved in specific mate recognition—the male cerci. For the larval stage, morphometric analyses show that the Palearctic species evolved a nearly identical morphology to the sibling‐clade members in the Nearctic that live in waters where dragonflies are the top predators. This implicates the importance of dragonfly predation in the history of the Palearctic clade. Behavioral analyses suggest population differentiation in response to the actual predator environment in the Palearctic clade, consistent with the species differentiation seen in the Nearctic. Our results suggest parallel evolution of adult traits that influence specific mate choice and larval traits that influence ecological performance underlie the striking similarity of Enallagma species across continents. This concurrent parallel evolution in both stages of a complex life cycle, especially when both stages do not share the same selective environment, may be a very unusual mechanism generating cryptic species.

A phylogenetic reassessment of the subfamilies of Coenagrionidae (Odonata: Zygoptera)

We reanalyzed subfamily divisions of Coenagrionidae phylogenetically using morphological characters. Characters historically and currently used to divide Coenagrionidae, as well as previously unpublished characters, were carefully defined or redefined and coded. Many characters traditionally used in coenagrionoid taxonomy were found to be continuously distributed rather than falling into discrete states. Nevertheless, it is just these characters on which most subfamily distinctions are based, we regarded it as essential to try to assess their effects in phylogenetic analysis. Therefore, character states for continuously distributed morphometric characters were determined using a clustering algorithm. We also present trees that exclude these characters, however. Cladistic analysis indicates that, of the existing subfamilies, only the apophyletic Agriocnemidinae is monophyletic. Shortest trees were markedly shorter than ones in which all current subfamilies were constrained to be monophyletic. Cladistic analysis using characters of Davies and Tobin (1984) and Fraser (1957) alone to define subfamilies resulted in poorer resolution and failed to support monophyly of any of the current subfamilies, as did alternative character weightings. Even a phenetic comparison using discriminant analysis failed to support the existing taxonomy. Our phylogeny suggests the existence of several possible clades within Coenagrionidae, but none are strongly supported by bootstrap analysis or decay index values. Coenagrionidae as a whole is polyphyletic in our shortest trees, although trees supporting amonophyletic Coenagrionidae are only slightly longer. We conclude that subfamilies should not be recognized within Coenagrionidae until well-supported subdivisions are demonstrated.

Phylogeny and taxonomy of the damselfly genus Enallagma and related taxa (Odonata: Zygoptera: Coenagrionidae)

Abstract The zygopteran genus Enallagma has been the subject of numerous behavioural and ecological studies, but phylogenetic relationships among species have been examined only within eastern North America, and even the composition and diagnosis of the genus are unclear on a world‐wide basis. Most authorities currently recognize about seventy species within Enallagma, comprising two major radiations, in North America and Africa. This study, using morphological data, demonstrates that the North American and a few related Palaearctic species form a monophyletic group that is quite distinct from the African species. The latter are themselves divided into at least three, and probably four, separate clades, one of which may be related to E. parvum of India. Consequently, three of Kennedys long disused genera, Africallagma, Amphiallagma and Proischnura ( Kennedy, 1920 ) are resurrected and two new genera, Azuragrion gen.n. and Pinheyagrion gen.n. are established for the remaining African taxa. Finally, Enallagma is divided into two subgenera, Enallagma s.s., the typical ‘bluets’, including many North American, Holarctic and Palaearctic species, and Chromatallagma subgen.n., comprising a group of species of more variable colour that is confined to North America, the Caribbean and northernmost South America.

Pamita hannahdaltonae gen. nov., sp. nov. from Baltic amber (Odonata: Amphipterygida)

Abstract The first known amphipterygid-like zygopteran from amber is described. Although its provenance is not known with certainty, we feel confident in attributing it to the Baltic amber deposits of northern Europe. It thus represents the first Old World Tertiary amphipterygidan and substantially extends the known geographic range of the taxon. Based on current knowledge its phylogenetic position cannot be ascertained reliably, but its possible relationships are discussed. It shares a mixture of characters with extant species including Amphipterygidae, Diphlebiidae, Thaumatoneurinae and Lestoideinae.

Phylogenetic relationships of North American Gomphidae and their close relatives

Intrafamilial relationships among clubtail dragonflies (Gomphidae) have been the subject of many morphological studies, but have not yet been systematically evaluated using molecular data. Here we present the first molecular phylogeny of Gomphidae. We include six of the eight subfamilies previously suggested to be valid, and evaluate generic relationships within them. We have included examples of all genera reported from the Nearctic except Phyllocycla. This sample includes all North American species of Ophiogomphus, which has allowed us to explore intrageneric relationships in that genus. Our particular focus is on the closest relatives of the genus Gomphus, especially those North American species groups that have been commonly treated as subgenera of Gomphus. The Gomphus complex is split into additional genera, supported by molecular and morphological evidence: Phanogomphus, Stenogomphurus, Gomphurus and Hylogomphus are here considered to be valid genera. The genus Gomphus, in our restricted sense, does not occur in the western hemisphere; in addition, G. flavipes is transferred to Stylurus.

Case 3584 Erythemis Hagen, 1861: proposed precedence over Lepthemis Hagen, 1861 (Insecta, Odonata)

Abstract. The purpose of this application, under Articles 23.9.3 and 81.1 of the Code, is to conserve the widespread usage of the generic name Erythemis Hagen, 1861 for a group of common dragonflies from the New World over the simultaneously published nominal genus Lepthemis Hagen, 1861, selected to take precedence by the First Reviser action (Article 24.2), whenever these names are considered to be synonyms. This proposal seeks to achieve the least change in the nomenclature of the species currently placed in these two genera, in strict accordance with Principle 4 of the Code.