Leslie A. Lowcock

Genome size and metabolic rate in salamanders

Abstract 1. 1. The relationship between genome size (C-value) and metabolic rate in salamanders was examined by correlation analyses. 2. 2. The C-values of 48 species of salamanders were determined by flow cytometry measurement of DNA quantity in erythrocyte nuclei; C-values of 88 species were taken from the literature. 3. 3. Standard metabolic rates for salamanders at 5, 15, 20 and 25°C were taken from the literature. 4. 4. Only at 25°C is there a robust, significant correlation between C-value and metabolic rate, and the hypothesis of a frugal metabolic strategy and genome size effect on metabolic rates in salamanders is discussed.

The Ambystoma laterale-jeffersonianum Complex in Central Ontario: Ploidy Structure, Sex Ratio, and Breeding Dynamics in a Bisexual-unisexual Community

Ploidy ratio was investigated in six Ontario populations of the Ambystoma laterale-jeffersonianum complex by collecting blood from individual salamanders during spring migrations, and analyzing the nuclear DNA content of erythrocytes by flow cytometry. All populations contained diploid male and female A. laterale as well as a potential mixture of diploid, triploid, and tetraploid female hybrids, which occurred at variable frequencies. Triploid males, pentaploid females and possible polyploid A. laterale (3n and 4n) were found in one extensively sampled population. Initial separation of A. laterale from hybrids based on morphological criteria was tested for accuracy by comparison with the cytometric results and found to be exceptionally high (99.6%). Sex ratios in all populations were biased overwhelmingly towards females, primarily because female hybrids accounted for up to 84% of a breeding aggregate; however, diploid female A. laterale outnumbered males in several populations and in two instances, near the northern limit of hybrid biotypes, these account for much of the biased sex ratio. Timing of breeding, always triggered by precipitation (rain or snow), varied between sites and was correlated with altitude/latitude. Initial immigrations at all sites contained biotypes indicative of local primary composition with respect to both ploidy and hybridity. The breeding dynamics of one population were investigated by daily sampling throughout the breeding period. Migration occurred in distinct waves. In A. laterale, frequency of immigrating males declined over the breeding period while frequency of females increased, a pattern conforming to the typical Ambystoma breeding dynamic. Within hybrids, the percentage of tetraploids increased over the breeding period. Within waves, there was a general increase in hybrids over time.

Flow cytometry in biodiversity surveys: methods, utility, and constraints

Flow cytometry of blood is a powerful tool for rapidly sorting individual specimens on the basis of cellular DNA content. During biodiversity surveys, the method enabled the early identification of both cryptic sympatric and allopatric species of Vietnamese ranid frogs. This method may be extremely valuable in sorting individuals from other taxa and geographic regions, especially when cellular DNA content is known to vary among closely related taxa, and in tropical situations where crypsis is a relatively common phenomenon. Protocols for preparation of freezing solution, field procedures, preparation of reference standards, and flow cytometric analysis are provided. The best method for field preservation of blood is freezing in liquid nitrogen; field fixation of blood in ethanol was less efficient and resulted in drastically increased coefficients of variation. Once samples have been transferred to freezer storage, they should not be returned to a lower storage temperature in liquid nitrogen.

Size in Relation to Sex, Hybridity, Ploidy, and Breeding Dynamics in Central Ontario Populations of the Ambystoma laterale-jeffersonianum Complex

We examined the relationship of size to sex, hybridity, and ploidy in five central Ontario populations of the Ambystoma laterale-jeffersonianum complex. For one extensively sampled population, we also considered time-related changes in size for each class of biotype during the breeding period. In addition, we compared the efficiency of visual and mathematical discrimination between hybrid and non- hybrid biotypes via linear discriminant function and subsequent analysis of error rates. Our results dem- onstrate that: (1) there is no significant sexual dimorphism in A. laterale; (2) there are some size differences among populations in both A. laterale and hybrids; (3) changes in mean size in all classes of biotypes are correlated with timing of breeding; (4) rates of maturation of wild polyploids are identical to those of lab-reared forms; and (5) hybrid: non-hybrid ratios can be estimated reliably for populations, either by eye or by discriminant function analysis of three simple morphological variables. In an earlier paper (Lowcock et al., 1991), we reported on the inter-relationships of ploidy structure, sex ratio, and breeding dynamics in six bisexual-unisexual communities of the Am- bystoma laterale-jeffersonianum complex of sala- manders in central Ontario, Canada. We found that unisexuals affect population structure and breeding dynamics of syntopic bisexuals, and that the biotype composition of breeding mi- grants changes over time. We suggested that similar effects may obtain for other ecological considerations. One such variable is individual

Pentaploidy in hybrid salamanders demonstrates enhanced tolerance of multiple chromosome sets

Breeding populations of unisexual hybrid salamanders (genusAmbystoma) are dominated by allotriploid (3n) and allotetraploid (4n) forms, however, sexually mature allopentaploids (5n) may also occur. These are the first known naturally-occurring pentaploid vertebrates, and their genesis differs from that of previously studied autopentaploid urodeles induced or observed in the laboratory. The latter always suffered severely deleterious effects in development, and could not attain sexual maturity.