SELECTIVE PREDATION FOR VERTEBRAL PHENOTYPE INGASTEROSTEUS ACULEATUS: REVERSAL IN THE DIRECTION OF SELECTION AT DIFFERENT LARVAL SIZES

Abstract

Abstract. -Variation in the number of vertebrae is widespread in fishes, and is partly genetic in origin. The adaptive significance of this variation was tested by exposing larvae of the threespine stickleback (Gasterosteus aculeatus) to predation by sunfish iLepomis gibbosus). Two vertebral characters were considered: the total number (VN) and the ratio of abdominal to caudal vertebrae (VR), Predation was selective for both characters, but selection was more directly related to VR than to VN. The direction of selection depended on larval length: as length increased, optimal VR decreased. Total selection for VR was a combination of direct selection and an indirect effect of selection acting on a correlated trait, the ratio of precaudal to caudal length. Direct and indirect selection were in opposing directions at a given larval length. Variation in vertebral number may be maintained in populations partly because the strength of selection is reduced by opposing directions between direct and indirect selection, and between total selection at different larval lengths,

Locomotion in elongate fishes: A contact sport

“…Few studies have focused on how vertebral regionalization affects locomotory performance (Swain, 1992;Kelley et al, 1997). One compelling study that highlights the interaction between vertebral characteristics and survival performance with stickleback larvae (Gasterosteus aculeatus) revealed that selection was acting on the ratio of precaudal to caudal vertebrae and that as larvae increased in length, the optimal vertebral ratio decreased (Swain, 1992).…”

“…One compelling study that highlights the interaction between vertebral characteristics and survival performance with stickleback larvae (Gasterosteus aculeatus) revealed that selection was acting on the ratio of precaudal to caudal vertebrae and that as larvae increased in length, the optimal vertebral ratio decreased (Swain, 1992). Thus individuals with relatively more caudal vertebrae exhibit increased performance in their aquatic escape response (Swain, 1992). While some species exhibit dramatic anatomical differences between the major regions of the vertebral column, the functional implications of vertebral regionalization on locomotor performance have yet to be realized.…”

Effects of induced variation in anuran larval development on postmetamorphic energy reserves and locomotion

“…In ectotherms, temperature experienced during embryonic development has been shown to affect juvenile shape (Swain and Lindsey 1986;Shine and Harlow 1993;Blouin and Brown 2000), trunk segmentation (Tåning 1952;Lindsey and Harrington 1972) and muscle structure (Stickland et al 1988;. Moreover, phenotypic variation in these traits has a significant impact on locomotor performance (Swain 1992a;Shine and Harlow 1993;Tejedo et al 2000a) and is subjected to strong selection associated with predation (Swain and Lindsey 1984;Swain 1992aSwain , 1992b. Low temperatures retard differentiation more than growth, thereby increasing stage-specific size (Smith-Gill and Berven 1979).…”

Predator associated morphology in Galaxias platei in Patagonian lakes

“…Intraspecific morphological variability in fishes often results from competition for resources in heterogeneous environments (Robinson & Wilson, 1994;Bell & Andrews, 1997;Skú lason et al, 1999) or from spatial or temporal heterogeneity in predation intensity (Brö nmark & Miner, 1992;Swain, 1992;Hori, 1993). Trophic polymorphisms are relatively frequent in oligotrophic, post-glacial, temperate lakes with low species diversity, and have been reported for fishes in both the northern hemisphere [e.g.…”