| Summary: | Thesis (Ph.D.)--Memorial University of Newfoundland, 1991. Biology Bibliography: leaves 300-324 The S. venustum/verecundum complex (Avalon Peninsula,Newfoundland) was examined to ascertain if individualcytotypes had unique and predictable ecological characteristics. Emphasis was placed on larval spatial-temporal distribution. Six cytotypes were found: EFG/C venustum, CC2-3 venustum (combined CC2 and CC3), AC(gb) venustum. AA verecundum and ACD verecundum. -- Larval cytotypes selected different macrohabitats. EFG/C and ACD were sublacustrine species; CC2-3 and AC(gb) preferred downstream sites. Within downstream habitats CC3 usually occurred in large streams and AC(gb) in cool canopied sites with a bed of small stones or rubble; CC2 was ubiquitous. AA preferred outlets and trickles. Cytotype fauna changed in a continuous, directional and predictable manner with increased distance from outlets. -- Abundance of CC2-3 increased with increasing seston and- discharge, and decreasing conductivity. AC(gb) abundance increased with increasing stream width. -- Larval cytotypes also selected different microhabitats. Optimal velocity for EFG/C and ACD was 0.36 and 0.71 m/s, respectively. EFG/C preferred shallow water but ACD showed no depth preference. These differences were not related to larval size. Maximum abundance of EFG/C occurred 10.5 - 16.O m from outlets; ACD was most abundant just below outlets. Proportionally more ACD and AA were found on vegetation than rocks; the reverse was true for EFG/C. The density of ACD and AA was higher on vegetation than rocks. -- Seasonal occurrence of cytotypes overlapped but population peaks were typically asynchronous. EFG/C appeared 1-5 weeks earlier than other cytotypes. ACD and AA appeared later and remained longer than other cytotypes. EFG/C was univoltine. AC(gb) may have a limited second generation. CC2-3 was bi- or multivoltine. ACD and AA were multivoltine. -- EFG/C complete larval development from 5 - 30°C with maximum survival between 15 - 20°C (68.0 - 73.5%). An ACD-AA mixed population completed development between 5 - 25°C with maximum survival between 15 - 25°C (55.3 - 61,0%) . The temperature survival curve of EFG/C was significantly different from ACD-AA. Threshold temperature was 0°C. Degree- days to complete larval development varied with temperature, cytotype and sex. Temperature also affected larval size. -- It was concluded that each cytotype examined was a distinct species with a unique and predictable ecological profile, supporting the hypothesis of widespread sibling speciation within the S. venustum/verecundum complex.
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