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.

A populational survey of 45S rDNA polymorphism in the Jefferson salamander Ambystoma jeffersonianum revealed by fluorescence in situ hybridization (FISH)

The chromosomal localization of 45S ribosomal RNA genes in Ambystoma jeffersonianum was determined by fluorescence in situ hybridization with 18S rDNA fragment as a probe (FISH-rDNA). Our results revealed the presence of rDNA polymorphism among A. jeffersonianum populations in terms of number, location and FISH signal intensity on the chromosomes. Nine rDNA cytotypes were found in ten geographically isolated populations and most of them contained derivative rDNA sites. Our preliminary study provides strong indication of karyotypic diversification of A. Jeffersonianum that is demonstrated by intraspecific variation of 45S rDNA cytotypes. rDNA cytotype polymorphism has been described in many other caudate amphibians. We predict that habitat isolation, low dispersal ability and decline of effective population size could facilitate the fixation and accumulation of variable rDNA cytotypes during their chromosome evolution.

The influence of multi-stage predation on population growth and the distribution of the pond-breeding salamander, Ambystoma jeffersonianum

Understanding the drivers of distributional patterns is a fundamental goal of ecology. For many organisms, distributions are determined by the habitats in which breeding occurs. Therefore, determining the factors that limit post-ovipositional success in specific habitats is critical to deciphering the factors that shape distributions. Using field surveys and laboratory, mesocosm, and field experiments, we conducted a study of the breeding effort of the salamander Ambystoma jeffersonianum (Green, 1827) in sites of varying predation pressure and the susceptibility of its embryos and larvae to predators. We then used these data to parameterize a matrix model examining the effects of predation on population growth. We found that A. jeffersonianum egg masses were less abundant in ponds with higher predation pressure. Moreover, A. jeffersonianum performance was negatively affected by both embryonic and larval predators. The results of the model suggest that only predation acting upon multiple life-history stages can limit population growth for A. jeffersonianum. These data provide support for the hypothesis that multi-stage predation can shape breeding distributions by imposing strong selective costs in specific environments. Furthermore, these data highlight the importance of conducting multi-stage studies and utilizing multiple ecological methodologies when addressing the factors that limit the distribution and abundance of organisms.