Anthony Zera

Anthony Zera Professor Faculty Ph.D. State University of New York - Stony Brook, 1984

Contact Information 228 Manter Hall 402.472.2768 azera1@unl.edu   Lab Website

Research Interests

Overview of research. My research focuses on the physiological, biochemical, molecular, and endocrine bases of adaptation. Since graduate school I have been working on two interrelated problems: (1) the evolution of the endocrine regulation of development and reproduction in insects, and (2) the physiological, biochemical, and endocrine bases of life history evolution, especially lipid metabolism and life-history trade-offs. A new research focus is the microevolution of circadian rhythms. This research has largely been undertaken in wing-polymorphic crickets of the genus Gryllus, and has resulted in the first detailed syntheses of evolutionary genetics, endocrinology, life history evolution, and metabolic biochemistry. My research has been supported continuously by NSF during the past 18 years, with multiple concurrent grants from the same or different panels during this entire period. The hallmarks of this research are its highly interdisciplinary, integrative nature, and its focus on the details of variation in proximate mechanisms that underlie adaptation.

Wing polymoprhism in Gryllus firmus. Dispersing (long-winged, LW) and flightless (short-winged, SW) morphs. Note reduced wing length (left panel), reduced flight muscles (middle panel), but increased ovaries (right panel) in flightless, SW morph.

Wing polymorphism experimental model. Research in my laboratory primarily uses wing polymorphism to investigate issues in evolutionary physiology. Wing polymorphism consists of a flight-capable morph that has fully developed wings and flight muscles, and a flightless morph with underdeveloped, non-functional wings and flight muscles. The flightless morph produces 100-400% more eggs than its flight-capable counterpart during early adulthood, and hence trades-off flight capability for early age fecundity. Wing polymorphism is the most extreme example of the trade-off between dispersal and reproduction, which occurs to some degree in most organisms, and is very common in many insects groups (crickets, grasshoppers, aphids, waterstriders, beetles). Since the 1960s, wing polymorphism has served as one of the premier examples of morphological evolution (wings and flight muscles) that results from evolutionary modification of endocrine regulation. This experimental model has also developed into a prominent model in studies of life history evolution, especially with respect to the trade-off between dispersal and reproduction.

Major research topics: (a) Evolutionary endocrinology of life history trade-offs, development and circadian rhythms.
Evolutionary biologists have been interested in identifying physiological processes responsible for life history trade-offs (negative genetic correlations between life history traits), which occur commonly in organisms. Because hormones regulate many important organismal traits, they are prime candidates as causal factors in life history trade-offs. Yet the hormonal basis of life history trade-offs is only recently beginning to be studied in any detail; my investigations of the endocrine regulation of the trade-off between reproduction and dispersal in Gryllus are spearheading such studies and are an important contributor to the new subdiscipline of evolutionary endocrinology (see Zera et al., 2007).

Morph-specific circadian rhythm of the blood level of juvenile hormone in adults. Note the high-amplitude cycle in the dispersing morph [LW(f)] but not in the flightless morph (SW).

Microevolution of endocrine circadian rhythms. For over six decades, insect physiologists and evolutionary biologists have postulated that the expression of morph adaptations for flight vs. reproduction in wing-polymoprhic insects is due to morph-differences in the level of juvenile hormone, a key regulator in insects. However, only recently has this hypothesis been directly tested in my laboratory by directly measuring blood JH levels in flightless/reproductive and flight-capble morphs. This work has resulted in an unexpected and surprising finding: a dramatic morph-specific circadian rhythm for the blood level of this hormone. The JH titer rises and falls 10-50-fold during a four-six hour period in the flight-capable morph during each day of early adulthood, but is temporally constant in the flightless morph. Subsequent studies have verified this morph-specific pattern in field populations of a variety of Gryllus species. This finding contrasts sharply with the widely held “classical” endocrine model of wing polymorphism mentioned above.
This finding has several important implications. It is the first example of a naturally-occurring, genetic polymorphism for a circadian rhythm for a hormone titer . This finding opens up a whole new area of research on the microevolution of functionally-important circadian rhythms in natural populations, a virtually unexplored area at the interface of evolutionary endocrinology, life history evolution, and chronobiology (biological rhythms).

Morph-specific circadian rhythm of the blood level of juvenile hormone in adults. Note the high-amplitude cycle in the dispersing morph [LW(f)] but not in the flightless morph (SW).

Microevolution of endocrine circadian rhythms. For over six decades, insect physiologists and evolutionary biologists have postulated that the expression of morph adaptations for flight vs. reproduction in wing-polymoprhic insects is due to morph-differences in the level of juvenile hormone, a key regulator in insects. However, only recently has this hypothesis been directly tested in my laboratory by directly measuring blood JH levels in flightless/reproductive and flight-capble morphs. This work has resulted in an unexpected and surprising finding: a dramatic morph-specific circadian rhythm for the blood level of this hormone. The JH titer rises and falls 10-50-fold during a four-six hour period in the flight-capable morph during each day of early adulthood, but is temporally constant in the flightless morph. Subsequent studies have verified this morph-specific pattern in field populations of a variety of Gryllus species. This finding contrasts sharply with the widely held “classical” endocrine model of wing polymorphism mentioned above.
This finding has several important implications. It is the first example of a naturally-occurring, genetic polymorphism for a circadian rhythm for a hormone titer . This finding opens up a whole new area of research on the microevolution of functionally-important circadian rhythms in natural populations, a virtually unexplored area at the interface of evolutionary endocrinology, life history evolution, and chronobiology (biological rhythms).

Left panel: Schematic diagram of lipid metabolism illustrating experiments in which incorporation of injected radioactive lipid precursors into end products of lipid metabolism was measured. Right panel: Schematic results of experiments showing greater biosynthesis of triglyceride (flight fuel) by the dispersing (LW) morph, and greater production of phospholipid (important in egg development) by the flightless, reproductive SW morph.

Ongoing research is breaking new ground by identifying specific alterations of intermediary metabolism that underlie increased accumulation of lipid (flight fuel) in the flight-capable morph. Using radiotracers, we have documented large-magnitude, genetically-based alterations in flux through pathways of fatty acid and triglyceride biosynthesis that account for the increased accumulation of triglyceride flight fuel in the flight-capable morph. This work is now being cited in basic textbooks on evolution as a classic example of a biochemically-based allocation trade-off that underlies a life history trade-off (e.g. Evolutionary Analysis by Freeman and Harron, 3 rd ed., 2004; pp 458-459). We have further documented that morph-specific differences in flux through pathways of lipid biosynthesis result from large-scale changes in the activities of enzymes that comprise these pathways. Finally, preliminary data suggest that that these large-scale alterations in lipid metabolism may be primarily caused by morph-specific alterations in the endocrine control of metabolism. This important result suggests that alterations in intermediary metabolism that underlie a key life history trade-off in G. firmus may be primarily due to alterations in regulation, rather than due to limited availability of internal resources, the most widely held explanation for life history trade-offs. These studies are beginning to open the black box of intermediary metabolism as it relates to life history trade-offs, and have resulted in the first detailed synthesis of evolutionary genetics, metabolic biochemistry, and endocrinology. A recently funded NSF grant expands above-mentioned research in new direction. We are currently investigating the the molecular/enzymatic mechanisms (gene transcription; post-translational modification) responsible for the elevated activities of lipogenic enzymes that cause the enhanced biosynthesis of triglyceride flight fuel in the flight-capable morph.