A population of all-female A. tremblayi salamanders from Ginn-Nixon Woods (Delaware County, Indiana) was the subject of this study. These salamanders are members of the Ambystoma jeffersonianum complex which consists of two diploid species (the northern A. laterale and the southern A. jeffersonianum) and two all-female, triploid species (A. tremblayi and A. platineum). The triploid species are believed to be intermediate in range and tolerance to their diploid allies and are usually found associated with them (A. tremblayi with A. laterale and A. platineum with A. jeffersonianum). In this sympatric alliance, the all-female triploids rely on the diploid ales for sperm, which in this case, apparently only activate the eggs without fertilizing them.The population of A. tremblayi in Ginn-NixonWoods is allopatric to all other members of the complex and has evolved a method of reproduction in which no courtship occurs and no spermatophores are picked up. Apparently, however, these A. tremblayi females do require the presence of male A. texanum, a more distantly related ambystomatid, in order to deposit viable eggs.A - maculatum, A. texanum, A. tigrinum and A. tremblayi salamanders were captured in pitfalls along a drift fence as they migrated to the vernal breeding ponds.Pairings of A. tremblayi females with males of the sympatric species in the breeding cages established that the only successful reproduction (through metamorphosis) occurred in the presence of the male A. texanum, although no courtship behavior was observed and no spermatophores were deposited.Cytological studies of the A. tremblayi females in this population, including karyotyping, revealed that the animals are indeed triploid with a chromosome complement of 42 (N = 14). Two of the three chromosomes which were identified as belonging to group three possessed a distinct secondary constriction not previously reported in the literature. It is proposed that this cytological marker identifies these two chromosomes as being derived from A. laterale and lends further support to the hypothesis that A. tremblayi is 'two-thirds A. laterale and one-third A. jeffersonianum' as proposed by Uzzell inhis studies of the Ambystoma jeffersonianum complex.