Protamine-like sperm nuclear basic proteins in the primitive frog Ascaphustruei and histone reversions among more advanced frogs

Sperm nuclear basic proteins (SNBPs) that condense chromatin are very diver se. In animals, evolution of SNBPs has proceeded from lysine-rich histone H type in sponges to more arginine-rich protamine-like PL and protamine P ty pes. Yet sporadic PL/P to H reversions are known to occur in both protostom es and deuterostomes. To determine why this is the case, we have examined S NBPs in eleven anuran species. We find that sperm of the primitive, interna lly fertilizing archeobatrachian frog A. truei (family Ascaphidae) has PL/P type (42 mol % arginine), with an electrophoretic profile similar tot SNBP s in another archeobatrachian, externally fertilizing Leiopelma hochstetter i (family Leiopelmatidae). Cytochemistry of sperm nuclei in the advanced, e xternally fertilizing neobatrachian frogs Crinia signifera and C. desertico la (family Myobatrachidae) indicates that they have reverted to H type SNBP s. This is also known to be the case in externally fertilizing Rana (family Ranidae) and Silurana, a subgenus of Xenopus (family Pipidae). Such a tren d, from PL/P type SNBPs in two archeobatrachians to sporadic reversions to H type in more advanced frogs, parallels the ultrastructural simplification from complex A. truei introsperm to neobatrachian aquasperm that Jamieson et al. (1993. Herpetologica 49:52-65) attribute as a secondary reversion to external fertilization. (C) 1999 Wiley-Liss, Inc.