My work on Agathidium, an obscure genus of small, slime-mold-feeding beetles, is in collaboration with Dr. Quentin Wheeler (Cornell University).Together we revised the New World members of the genus which includes about 100 species (over 60 newly described by us).

We also began some work on the evolution of unusual asymmetrical horns on males of certain members of the genus. Males of some species exhibit large horns extending from the apex or surface of the left mandible (see Figs 1-2 below).Males use a head-thrusting behavior to dislodge other males from the surfaces of the slime-molds on which they feed, presumably increasing the opportunity for the winning male to mate. The horn apparently increases the efficacy of this head-thrust maneuver. Agathidium horns are unusual in that most male ornamentation in nature is bilaterally symmetrical, whereas Agathidium horns are distinctly asymmetrical.

Also, the horns in Agathidium males show strong allometry with a particular sigmoid relationship between ornament length and body size making for distinct majors and minors in populations of these beetles (see Figs 3-4 below).

What is not known is the distribution of features related to horn variation and behavior in the phylogeny of Agathidium. Presumably, the head thrusting behavior came first in the evolution of this scenario and one, or more, instances of horn evolution resulted. Male horns come in a variety of forms which may or may not be homologous, and not all Agathidium species in this group have male mandibular horns.

We are beginning work on the phylogeny and behavior of this group to attempt to answer the questions of order of evolution of head-thrusting behavior and horn morphology.

Fig. 1: pulchrum LeConte, lateral aspect
Fig. 2: Agathidium pulchrum LeConte, dorsal aspect
Fig. 3: Frequency histograms of greatest pronotal width and mandible height (measured as indicated on illustrations), and relationship between greatest pronotal width and left mandible height for Agathidium angulare (n=118). Arrows indicate individuals illustrated. Dashed line on X-axis indicates optimal inflexion (switch) point.
Fig. 4: Frequency histograms of greatest pronotal width and mandible height (measured as indicated on illustrations), and relationship between greatest pronotal width and left mandible height for Agathidium pulchrum (n=64). Arrows indicate individuals illustrated. Dashed line on X-axis indicates optimal inflexion (switch) point.