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PATTERNS OF MORPHOLOGICAL AND REPRODUCTIVE VARIATION IN STENONEMA MAYFLIES (EPHEMEROPTERA: HEPTAGENIIDAE) IN EASTERN LAKE HURON

Published online by Cambridge University Press:  31 May 2012

Ian D. Martin  and
Michael A. Gates
Ian D. Martin
Affiliation:
Biological Research Section, Ontario Hydro
Michael A. Gates
Affiliation:
Department of Zoology, University of Toronto
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Abstract

Significant variation in the morphology of late-instar nymphs of Stenonema tripunctatum (Banks) in Lake Huron could not be ascribed to their proximity to warm-water plumes originating from the Bruce Nuclear Power Development, by either multivariate or univariate analyses of size and shape. Major sources of variation in S. tripunctatum were developmental state and sex. Nymphs collected just prior to emergence had low values of transverse measurements in anterior regions (inter-orbital width, prothoracic width), whereas males and females were separated by these measurements and other components of head geometry.

No significant effects of thermal exposure were found in the reproductive development of S. tripunctatum, but this species is most commonly found below depths at which thermal-plume effects are expected. Based on a small but representative sample, ultimate-instar nymphs of Stenonema vicarium (Walker) from a depth of 3 m contained significantly fewer eggs and allocated a significantly lower proportion of biomass (dry weight) to reproduction in locations with higher temperatures.

Résumé

D'après des analyses uni- ou multivariates de grandeur et de forme, la variation significative dans la morphologie des stades tardifs des nymphes de Stenonema tripunctatum (Banks) dans le lac Huron n'a pas pu être attribuée à leur proximité aux panaches d'eau chaude provenant du développement de la centrale nucléaire Bruce. Les sources principales de variation dans S. tripunctatum étaient dans le stade de développement et le sexe. Les valeurs des mesures transverses des régions antérieures (largeur inter-orbital et largeur prothoracique) des nymphes prélevées juste avant emergence étaient basses, tandis que les mâles et les femelles étaient séparés par ces mesures et d'autres composants de la géométrie de la tête.

Aucun effet significatif à l'exposition thermale sur le développement reproductif de S. tripunctatum n'a été trouvé, cependant cet espèce est trouvée le plus souvent sous la profondeur où les effets de la panache thermale sont attendus. Basé sur un petit échantillon représentif, les nymphes de Stenonema vicarium (Walker) provenant d'une profondeur de 3 m contenaient significativement moins d'oeufs et allouaient une proportion significativement plus basse de biomasse (poids sec) à la reproduction dans des endroits à températures plus élevées.

Type
Articles
Information
The Canadian Entomologist , Volume 116 , Issue 12 , December 1984 , pp. 1591 - 1603
Copyright
Copyright © Entomological Society of Canada 1984

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