75 Years Ago in Bee Systematics: Cockerell on “The Evolution of the Bees”

Abstract

Theodore D.A. Cockerell (1866–1948) was one of the great melittologists of all time. Indeed, he was one of the greatest of biological systematists, one of the last of the polyhistors and comfortable working on taxa as diverse as sunflowers, protists, and insects, among many others (Weber, 1965, 1976, 2000, 2004). While most remember him for the mountain of new taxa he described and named, it is oft overlooked that he had a remarkably synthetic mind and was quite conversant in the modern methods and theories of his day. It was for these reasons that he was heralded as the ‘‘Huxley of America’’ (Weber, 2000), and was widely regarded as an outstanding evolutionary biologist. His careful observation and insights into innumerable aspects of evolutionary biology are frequently buried in his taxonomic accounts and therefore ignored by many modern students. Herein we wish to draw attention to one small section of a partial monograph on the African bee fauna (encompassing the genera Halictus, Ceratina, and Megachile), in which Cockerell provided a reflective and insightful introduction (Cockerell, 1937). Herein he muses on issues such as dramatic shifts in climate and their effects on local bee populations, the possibility of shifting continents and changing sea levels (or as he terms it, ‘‘permanence of the oceans’’), the historical biogeography of genera and even alludes to austral disjunct distributions, the floral associations of bees, and even some key themes in evolutionary developmental biology much before the establishment of the field, among other topics. While it is too much to reproduce the entirety of his introductory discourse, we here present Cockerell’s brief section on the evolution of bees. This small account highlights several of Cockerell’s more remarkable qualities (including his ability to write clearly and engagingly), perhaps inspiring JKES readers to seek out his work and give its entirety greater attention. At the time this material was published Cockerell was 71 years old, and it is clear he was very well cognizant of the latest advances in biology as well as their possible implications for understanding observed patterns and phenomena. It is reasonably clear that the bees are derived from the fossorial wasps, but whether from a single stock, or more than once, is not definitely known. Extensive morphological studies of the lower bees and digger wasps would doubtless throw fresh light on this question. There are certain lines of development among the bees which undoubtedly indicate evolutionary sequence, or levels of departure from the original types. Thus it cannot be doubted that primitively the maxillary palpi had six joints, and the labial palpi four similar joints. The tongue was short, and probably emarginated. The wings possessed three submarginal or cubital cells. Such characters still exist in many genera of bees. With these facts in mind, it is comparatively easy to sort out any collection of bees into groups representing various degrees of departure from the archetype, various degrees of specialisation. The maxillary palpi lose one joint after another, and in one South American genus disappear. The labial palpi become enormously elongated, but the two apical joints remain small. The tongue may be so elongated, with the supporting parts, that it cannot be folded away, but is held under the body like the beak of an hemipteron. The venation may be considerably reduced, as seen in the social bees of the genus Trigona. Such studies are fascinating, and seem to reveal to us the processes of Nature through the ages. But certain complications arise. The same kind of modification may occur more than once; thus it is quite evident that types with only two cubital cells in the front wings have arisen in several groups independently. This modification may even be found occasionally as an individual aberration in species normally having three cubitals. The parasitic bees are undoubtedly derived from the working kinds; it could not be otherwise. But no one would pretend that such