Selective factors in the evolution of insect wings: response to Kukalová-Peck

Kukalová-Peck (J. Kukalová-Peck. 1987. Can. J. Zool. 65: 2327–2345) has recently criticized the hypothesis that selection for increased thermoregulatory capacity was important in the early evolution of wings from protowings. Here we argue that the current paleontological, embryological, and experimental evidence cannot be used to reject the thermoregulatory hypothesis. Experimental studies of aerodynamics and thermoregulation suggest that knowledge of the body size of ancestral pterygotes is crucial to evaluating the relative importance of aerodynamic and thermoregulatory factors in the evolution of flight.

Feeding strategy and the mechanics of blood sucking in insects

As a means of exploring foraging strategies of blood-feeding insects, we studied the mechanics of blood feeding. We develop a mechanistic model for the dynamics of non-Newtonian fluid flow to describe the feeding process for blood feeders. Using available feeding and morphological data, we examine the relationship of feeding time to proboscis design, and consider optimal foraging strategies for blood feeders. Because of the flow rates typical of many blood feeders, the non-Newtonian nature of blood is of little importance for flow dynamics. Observed feeding times and flow rates do not necessarily reflect the energy requirements for feeding. The radius of the food canal is the major morphological determinant of flow dynamics. Feeding time is a monotonically increasing function of blood hematocrit. There is an optimal blood hematocrit of 0.3 which maximizes the rate of total protein intake for blood feeders, regardless of the energy output or proboscis design. This hematocrit level is typical of humans with blood parasite infections. In contrast, the rate of red blood cell intake is maximized at a hematocrit of 0.4. We argue that the existence of such optima may be a general consequence of the mechanics of feeding on nutrients dissolved or suspended in a fluid medium. Results are discussed in relation to foraging strategy, proboscis design, and the coevolution among host, vector, and parasite in blood feeding insects.