Morphological and life-history adaptations in sky island aquatic insects.

A.L. Pelegrin and D.A. Lytle.Department of Zoology, Oregon State University, Corvallis, OR, 97331

Paleohydrology indicates that during the Pleistocene era, southeastern corner of Arizona was home to a mesic network of interconnected waterways. Since the onset of the current geological era, open desert has replaced swamps, and aquatic habitats have become insular. In what ways have aquatic organisms changed their morphologies or life-history strategies to cope with highly localized conditions? The flightless giant waterbug Abedus herberti (Hemiptera: Belostomatidæ), now restricted to springs and mountain streams, comprises at least thirty disjunct populations. Significant morphological differences exist between mountain stream populations and spring populations. Common-garden rearing of six separate populations, three of each type, indicates these differences are genetic rather than environmental. Analyses of nymph body size and intermolt time suggest that spring-dwelling populations are particularly well-suited to take advantage of perennially stable water temperatures, while individuals from mountain streams are more adapted for overwintering in hibernal conditions.