Effects of Water Temperature Under Projected Climate Change on the Development and Survival of Enallagma civile (Odonata: Coenagrionidae)

Current climate projections for the Great Plains of North America indicate markedly increased air temperatures by the end of the current century. Because the Great Plains contains >80,000 intermittent wetlands that serve as irreplaceable wildlife habitat, this projected warming may have profound effects throughout a continental-scale trophic network. However, little research has been done to determine how projected warming may affect the growth, development, or survival of even common species in this region. We conducted laboratory warming experiments, using an abundant amphibious predatory insect, Enallagma civile (Hagen, 1861), as a model organism, to determine whether projected warming may affect development or survival. Eggs were collected and reared under four water temperature regimes representing current (26°C) and projected future conditions (32, 38, and 41°C). Nymph body size after each molt, development rate, and deaths were recorded. Elevated water temperatures were found to significantly affect the survivorship of E. civile eggs and nymphs as well as adult body size at emergence: an increase in temperature incurred a decrease in survival and size. Nymphs in the two hotter treatments were smaller and had low survivorship whereas individuals in the cooler temperatures generally survived to adulthood and were larger. Nymphs reared at 32°C experienced accelerated ontogenetic development compared with the other temperatures, going from egg to adult in 26 d. Projected elevated temperatures may, thus, be both advantageous and detrimental, causing concern for aquatic invertebrates in this region in the future.

Use of Saltmarsh by Dragonflies (Odonata) in the Baie des Chaleurs Region of Quebec and New Brunswick in Late Summer and Autumn

During late summer and autumn, in the Baie des Chaleurs region of Quebec, 18 species of adult dragonflies were recorded during one or more visits of at least 2 hours each to 14 saltmarshes. Three species, Aeshna canadensis, Sympetrum danae and S. internum, were present in more than half of the sites. The most abundant species was S. internum with over 100 seen at some locations. Adults of several species, including Aeshna canadensis, A. umbrosa, Enallagma civile, E. hageni, Ischnura verticalis, Lestes disjunctus, Libellula quadrimaculata, Sympetrum danae, S. internum and S. obtrusum, occurred in relatively high frequencies in both Baie des Chaleurs saltmarshes and in those elsewhere in Acadia. Within Baie des Chaleurs observations of emergence and/or presence of larvae, as well as regional abundance, were recorded for Aeshna canadensis, A. umbrosa, Ischnura verticalis, Sympetrum costiferum, S. internum and S. vicinum. Oviposition in saltmarsh pools was recorded for Aeshna canadensis, Enallagma civile, E, hageni, Ischnura verticalis, Lestes congener and Sympetrum danae. The saltmarsh dragonfly fauna of Baie des Chaleurs is significantly different from that of the rest of Acadia based on frequencies predicted from the latter region. To a large extent this difference is a result of significantly increased use of saltmarsh habitat by adults of six species including Lestes congener, Sympetrum danae, Aeshna canadensis, Sympetrum costiferum, Lestes disjunctus, and Sympetrum internum (in order of decreasing significance) in Baie des Chaleurs in comparison with saltmarshes elsewhere in Acadia. Local amelioration of salty conditions in certain saltmarshes, superimposed on regional amelioration as a result of protection from storms and saltwater dilution in the Baie des Chaleurs estuary, may contribute to an environment where adaptation can occur or where already tolerant species can exist. Dragonflies use saltmarsh habitat on the northeast coast of North America more extensively than is currently documented.