1975] 
Peck — North American Brathinus 
65 
The genus had a continuous distribution from Asia through Berin- 
gia into and across North America in the Tertiary. The ancestral 
species nitidus-calif ornicus may have been limited to North America, 
but ancestral varicornis-oculatus ranged from Asia across Beringia to 
eastern North America. With the progressive deterioration of cli- 
mates in the Pliocene, the Beringian distributional link of this second 
ancestral species was broken, and the Asian population evolved into 
oculatus , and the North American populations into varicornis. The 
western North American populations of varicornis were eliminated 
by fluctuating Pleistocene climates, and the species became restricted 
to eastern North America. The range of ancestral nitidus-calif ornicus 
was formerly across North America, but it became broken into two, 
in the mountains of eastern and western North America, during the 
fluctuating climatic events of the Pleistocene. Population separation 
and subsequent speciation into nitidus and calif ornicus was facilitated 
by a dry-warm central continental climate in the Sangamon Inter- 
glacial or during an earlier interglacial. Later dispersal and expan- 
sion of ranges southwards was during the Wisconsin glacial. This is 
especially true for the expansion of nitidus south along the Appa- 
lachians. Both nitidus and varicornis have expanded northwards into 
formerly glaciated lands since deglaciation. Their southern limits 
may be contracting as warmer and drier interglacial conditions re- 
turn. B. nitidus , because of its preadaptation for cool and moist 
conditions, is now favoring caves in the southeast because they can 
serve as climatic refugia (Barr, 1968: 80). 
Acknowledgements 
I wish to thank J. F. Lawrence (MCZ), J. Milton Campbell and 
Ales Smetana (CNC), Henry Dybas (FMNH), Milton W. San- 
derson (INHS), J. M. Kingsolver (USNM), and Hugh B. Leech 
and David H. Kavanaugh (CAS) for permitting the examination of 
material in the collections under their care. Walter R. Suter, Thomas 
C. Barr, Jr., J. Milton Campbell, Ales Smetana, and M. W. San- 
derson gave or corresponded on material or on their field experiences 
with Brathinus. Most of my personal data on Brathinus were gath- 
ered during field work supported by NSF grants GB 3167 and GB 
7346 to the Evolutionary Biology Committee, Harvard University, 
Professor Reed C. Rollins, principal investigator, and by Canadian 
National Research Council operating grants. The manuscript was 
read by J. M. Campbell, M. W. Sanderson, and J. F. Lawrence. 
