Post-emergence survival and dispersal of juvenile Jefferson salamander (Ambystoma jeffersonianum) and their unisexual dependents

Understanding population demography and dispersal of species at risk is integral for evaluating population viability, identifying causes of decline, and assessing the effectiveness of recovery actions. In pond-breeding amphibians, juvenile survival and dispersal are key components linked to population and metapopulation stability but little is known about this life stage. We use mark-recapture methods to estimate juvenile daily apparent survival, dispersal distance, and initial dispersal orientation during summer and fall dispersal of endangered Ambystoma jeffersonianum and their unisexual dependents (Ambystoma laterale – jeffersonianum). Over four years (2015-2018), 1018 juveniles (612 bisexual, 406 unisexual) were marked and 192 (19%) were recaptured at least once. Total captures varied widely between years, with the highest number of captures (88% of all individuals) occurring in 2017. Cormack-Jolly-Seber estimates of daily apparent survival were low in all years (0.76-0.95) but was higher for unisexuals than bisexuals. The majority of juveniles (71%) did not disperse further than 10-40 m after which movement appeared to cease. While most juveniles remained close to their natal pond, at least 2% of juveniles in 2017 travelled further than 100 m. Dispersal orientation varied by year and there was no difference in either dispersal orientation or distance between bisexual and unisexual individuals. This work is the first to estimate and compare juvenile survival and dispersal of sympatric A. jeffersonianum and A. laterale – jeffersonianum individuals, the results of which help inform population viability assessment and increase our understanding of juvenile dispersal dynamics and habitat use.

Estimating critical habitat based on year-round movements of the endangered Jefferson Salamander (Ambystoma jeffersonianum) and their unisexual dependents

Habitat protection is a key component of endangered species conservation, but critical habitat designations are often based on limited data or habitat use during only a portion of a species’ life cycle. Protected habitat around breeding pools for the endangered Jefferson Salamander (Ambystoma jeffersonianum (Green, 1827)) and their unisexual dependents (Ambystoma laterale – (2) jeffersonianum) is based upon limited movement data from primarily spring and summer seasons. Furthermore, despite their treatment as distinct species under Canada’s Species at Risk Act, differences in habitat use have not been directly compared in areas where they co-occur. We used radiotelemetry to track A. jeffersonianum (JJ) and A. laterale – jeffersonianum (LJJ and LJJJ) during fall migrations to overwintering sites. We used these data and summarized available movement data from past studies that tracked movements in other periods of the annual cycle to estimate year-round critical habitat. Ambystoma jeffersonianum travelled significantly longer distances to overwintering locations than unisexuals. Individuals were more likely to overwinter next to a similar genomotype individual than not. Critical habitat encompassing the entire annual cycle of A. jeffersonianum extends up to 400–450 m from breeding ponds indicating existing regulatory habitat protections in Canada do not currently protect sufficient habitat.

Taxonomic status of male salamanders of the Ambystoma jeffersonianum complex from an Ontario population, with the first record of the Jefferson salamander, A. jeffersonianum (Green), from Canada

Nine morphological criteria were used to determine the taxonomic status of the male salamanders of the Ambystoma jeffersonianum complex from a population near Streetsville, Toronto Township, Peel County, Ontario: (a) snout–vent length; (b) ratio of tail length to snout–vent length; (c) internarial width; (d) extent of separation or overlap of the toes of adpressed limbs; (e) total length; (f) ratio of tail length to total length; (g) ratio of internarial width to snout–vent length; (h) colouration of dorsal, lateral, and ventral body surfaces; and, (i) extent and distribution of the bluish spotting. The results indicate that all of these males resemble A. jeffersonianum or A. platineum rather than A. latérale. Since A. platineum males occur very rarely in nature, these Streetsville individuals are logically assigned to A. jeffersonianum. This represents the first record of this species from Canada. Based upon this new distributional datum of A. jeffersonianum and of the two Diploid species from the literature, we suggest that these triploid species may have originated in post-Wisconsin times and subsequently dispersed northward.