Within-lake isolation and reproductive strategy of Stuckenia pectinata (L.) Börner at Lake Naivasha (Kenya): About water level fluctuations and alien species

Abstract

Submerged aquatic plants with mixed reproduction mode may show enhanced clonal growth explained by environmental conditions. For Stuckenia pectinata (L.) Börner this has been linked to within-lake factors, both biotic (tuber predation, herbivory, periphyton shading) and abiotic (hydrological connectivity, sediment type). We investigated the S. pectinata population from Lake Naivasha, where submerged aquatic plants tolerated strong historical water level fluctuations until introduced crayfish, shading by floating exotic weeds and increased turbidity nearly eradicated them, although some stands now rebounded in various lake areas. Using 13 nuclear microsatellite loci, we analyzed genetic diversity and structure of S. pectinata subpopulations along the southeastern shoreline of the main lake and inside Crescent Island Crater, a peripheral lake basin enclosed within the rim of an extinct volcano. Results revealed a predominantly sexual reproductive strategy with limited clonal expansion in the main lake contrasting with pronounced clonal growth in the crater basin. Each subpopulation experienced recent bottlenecks. Crater basin subpopulations exhibited the strongest divergence, lower clonal diversity and larger-sized clones. We explain this differentiation by the exposed crater rim acting as barrier, isolating the crater basin from the main lake during recent decades when low water levels prevailed, accompanied with less negative impact from alien species than in the main lake. Clonal extension occurred on steep-sloping hard sandy substrates, that likely prompted local reproductive adaptations. Genetic diversity, clonal structure and connectivity patterns are discussed in the light of the specific history and features of Lake Naivasha.