Early development of the northern logperch, Percina caprodes semifasciata, according to the theory of saltatory ontogeny

Synopsis

The early development of northern logperch, Percina caprodes semifasciata, was examined from an ecological perspective and in relation to the theory of saltatory ontogeny. Steps, the intervals of relative homeostasis, separated by thresholds, rapid switches to new form and function resulting from canalization of changes in the preceeding step, are described and related to environmental factors. Adaptive shifts in growth allometries provided further evidence of the saltatory nature of ontogeny. Logperch eggs are small (1.2 mm diameter), demersal, and adhesive. The simple embryonic respiratory system reflects high oxygen availability on the lotic spawning grounds. Hatching occurs early, relative to other darters, and free embryos are pelagic. The small free embryos presumably drift downstream to lentic areas, where small planktonic food is more abundant. Logperch are therefore nonguarding, open substrate spawning lithopelagophils and, along with other Percina species, have not advanced from ancestral percid reproductive styles. Percina species have generally remained in ancestral habitats-rivers and lakes. The close correlation between developmental patterns of logperch and environmental factors is therefore interpreted as a restriction based on retention of ancestral characteristics, not as evidence of novel adaptations to new habitats.