Graduate Studies

My dissertation research at Stony Brook University was not tightly linked to any professor’s research.  This was a more common model for PhD students then than now.  Such research ideally needed to be inexpensive and close to the campus.  I’m grateful to Ron Carroll, who suggested that I consider beach populations of the common cocklebur, Xanthium strumarium, on the North Shore of Long Island, New York (Figs. 1 and 2) and two species of internal seed predator.  One was the Tephritid fly, Euaresta aequalis (Fig. 3) and the other was a Tortricid moth, Phaneta imbridana [1] (now Eucosma ochrocephala) (Fig. 4). For both species, the adult insects oviposit on or through the burr, and their offspring consume one of the two seeds within a burr (Fig. 5).

Figure 1.  Typical population of Xanthium Strumarium on a beach of the north shore of Long Island.

Figure 2.  X. strumarium with full-sized but immature burrs.

Figure 3.  Female Euaresta aequalis ovipositing through a burr of Xanthium strumarium.

Figure 4.  Eucosma ochrocephala adult resting on a leaf of Xanthium strumarium.

Figure 5.  Mature larvae of E. aequalis (left cell) and E. ochrocephala (right cell) within a burr of X. strumarium.  Both seeds of the burr were completely consumed.

I studied ten plant populations within a few km of each other and the Stony Brook campus (Fig. 6).  Adults of both insect species were found in all plant populations, but their progeny were not. 

Figure 6.  Map of the northeastern United States showing the portion of the north shore of Long Island where the study was conducted (circled), and a more detailed map of the shoreline showing the location of the individual populations. NIS, Nissequogue River Beach; LB, Long Beach; WMB, West Meadow Beach; SUN, Sunwood Estate beach ; CNS, Crane Neck - Sunwood beach; CNP, Crane Neck Point; CNF, Crane Neck - Flax Pond beach; OF, Old Field beach; HH, Harbor Hills beach; MTS, Mount Sinai Harbor beach; and LRB, Landing Road Beach..

Figure 7.  Rates of seed predation by the moth (E. Ochrocephala ) or the fly (E. aequalis) in 1975.  Population code as per Fig. 6.  From Hare & Futuyma, 1978.

Figure 8.  Schematic of a burr showing the morphological characters measured.

Rates of seed predation by both insects varied among populations (Fig. 7) [2].  I therefore attempted to determine if the rates of seed predation might be related to the variation in the morphological and chemical characteristics of the burrs produced by plants in the different populations.  Measurements taken on burrs are shown in Fig. 8. 

Figure 9.  Mean (+ s.e.) burr length from field-grown plants protected from attack.  From Hare 1980.

Figure 10.  Relationship between burr size and probability of attack.  From Hare 1980.

Figure 11.  Mean (+ s.e.) burrs produced by field-grown plants protected from attack.  From Hare 1980.

Burr size and other morphological and chemical characteristics varied significantly among plant populations (Fig. 9) , and this variation was heritable in that it persisted when plants were grown under uniform greenhouse conditions [3].  Seed predation declined with increasing burr length, suggesting that plants may be under selection for increased burr size in populations experiencing high seed predation (Fig. 10) [3].  The advantage of producing larger, more protective burrs in response to high seed predation occurred at a slight expense of total seed production (Fig. 11), such that plants producing a large number of small burrs may have the advantage where seed predation is low or absent but plants producing few, better protected burrs may have the advantage where seed predation is high [3].  The dramatic variation in the interactions among a single plant species and its two seed predator herbivores among closely adjacent populations and the possible trade-off between plant reproduction and defense against herbivores set the stage for much of my future research.

1 Hare, J.D. (1977) The Biology of Phaneta imbridana (Lepidoptera: Tortricidae), a Seed Predator of Xanthium Strumarium (Compositae). Psyche 84, 179-182.   DOI:  10.1155/1977/75959

2 Hare, J.D. and Futuyma, D.J. (1978) Different Effects of Variation in Xanthium strumarium L (Compositae) on Two Insect Seed Predators. Oecologia 37, 109-120.  DOI:  10.1007/bf00349997

3 Hare, J.D. (1980) Variation in Fruit Size and Susceptibility to Seed Predation Among and Within Populations of the Cocklebur, Xanthium strumarium L. Oecologia 46, 217-222.  DOI: 10.1007/bf00540129

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