Density-Dependent Physiological Phase in Insects

Abstract

Insects respond to crowding in a variety of ways that are usually exemplified by rapid changes in behavior and culminate in enduring long-term morphological and/or chromatic responses. A common feature of both short-term and long-term effects is that they are graded, dependent not only on density but also on the duration and on phase history of the maternal generation. Because of their exoskeletons, which are persistent for the duration of each instar and endure throughout adult life, overt changes in morphology or coloration are restricted to the molting period and shortly afterward, when cuticular hardening and pigmentation are expressed. Changes in internal organs or metabolism elicited by population density, being independent of integumental constraints, are not restricted to the molting period, but the temporal difference between internal and external responses is not of fundamental significance. Intraspecific responses to the presence of sibling insects are of apparent ecological significance and often involve directional movement and/or migration. They are mediated via the sensory system, involve signal transduction, and elicit downstream biochemical and physiological changes.

The locust foraging gene

“…The major behavioral characteristic of gregarious-phase locusts is their strong attraction to conspecifics, which translates into active aggregation behavior (Ellis, 1959(Ellis, , 1963Uvarov, 1966). The phase transformation is thought to be a positive feedback process, with changes in behavior preceding and facilitating other phasechanges including biochemical, physiological, and morphological ones (Pener, 1991;Pener and Yerushalmi, 1998;Applebaum and Heifetz, 1999;Pener and Simpson, 2009). Recent findings have identified the primary sensory inputs inducing a densitydependent phase change in locusts .…”

Developmental and epigenetic pathways to obesity: an evolutionary-developmental perspective

“…The most obvious examples are those where there are distinct polyphenismsFfor example in the locust, which may 'choose' at the larval stage to develop as either a solitary or a migratory morph based on tactile or pheromonic signals that indicate population density and food availability. 12 Such morphs are very different anatomically, behaviorally and physiologically. Generally, however, adaptive developmental plasticity produces a more continuous range of phenotypes.…”

BARD workshop: “Insect reproductive molecules: From model systems to agricultural applications”

“…He played a principal role in the field of locust reproduction: he and his colleagues isolated the oocyte protein vitellogenin Lubzens et al, 1981;Asher et al, 1983) and identified the physiological mechanisms that regulate and mediate its production and action. Dr. Applebaum was also intrigued by the locust phase transition-physiological changes that are expressed in coloration, morphology, developmental rate, metabolism, and behavior in response to increased population density (Applebaum and Heifetz, 1999)-and carried out important research into the mechanism of this phenomenon (Heifetz et al, 1996;Applebaum et al, 1997;Heifetz et al, 1997). His interest in insect hormones, such as juvenile hormone, diuretic hormone, and adipokinetic hormone, produced important results (Pines et al, 1981;Gadot et al, 1987;Applebaum et al, 1990;Zhou et al, 2000) and led to a breakthrough in juvenile hormone research in Drosophila (Richard et al, 1989).…”