Occurrence of the Salamander Ambystoma platineum (Cope) in Southern Ontario

Abstract

Ambystoma platineum is reported from Peel County, Ontario, Canada, on the basis of four females. Identification was made using standard morphological analyses, measurement of erythrocyte area, and electrophoretic separation of blood plasma proteins. The silvery salamander, Ambystoma platineum (Cope), is a triploid (3n = 42), essentially all-female species of the Ambystoma jeffersonianum complex. Like the related triploid, all-female Ambystoma tremblayi Comeau, this species is believed to have arisen by hybridization between the diploid, dioeceous ambystomatids Ambystoma jeffersonianum (Green) and Ambystoma laterale Hallowell (Uzzell, 1964). The triploid forms are gynogenetic, and depend on males of the parental species for activating their eggs. Ambystoma platineum is typically associated with A. jeffersonianum, while A. tremblayi occurs with A. laterale. Although the triploid types are morphologically intermediate between the diploid species, each more closely resembles the parental form with which it typically associates. A. platineum attains a greater snout-vent length and has a wider snout relative to snout-vent length than A. tremblayi (Uzzell, 1964). Because of the overlap of these morphological charcters, however, the triploid forms can only be conclusively distinguished by electrophoretic patterns of blood plasma proteins (Uzzell and Goldblatt, 1967). The range of the species complex extends from Manitoba and Minnesota in the west to Labrador and Nova Scotia in the east, and south to Kentucky and Virginia (Uzzell, 1967a, b, c). Ambystoma laterale and A. tremblayi are more northern in distribution, while A. jeffersonianum and A. platineum range to the south. Until recently, only A. laterale and A. tremblayi have been known from Canada. Ambystoma platineum has been discovered at Waterloo, Ontario (Campbell, Menzel, and Pratt, unpublished), and A. jeffersonianum occurs in Peel County, Ontario (Weller and Sprules, 1976). In the present paper, we document the existence of A. platineum at this same Peel County locality and discuss the zoogeographic significance of these records. MATERIAL AND METHODS Breeding salamanders were collected from a temporary pond in a woodlot near Streetsville, Peel County, Ontario (43?34'N, 79?41'W) between 30 March and 30 April 1974. Of 433 specimens examined during an ecological study (Weller, in progress), 50 were morphologically identified as A. jeffersonianum (Weller and Sprules, 1976). Four female specimens were identified as A. platineum on the basis of morphology, pigmentation, erythrocyte size and electrophoretic patterns of blood plasma proteins. Measurements of snout-vent length, tail length and internarial width were taken with vernier calipers from living specimens using standard procedures. Colouration of living animals was determined with the specimens submerged in water. Erythrocyte area was calculated by direct measurement of fresh cells with an ocular micrometer. For each specimen, 30 erythrocytes were measured on two independent occasions and a mean value determined from the 60 observations.