Loss of genetic diversity and fitness in Common Toad (Bufo bufo) populations isolated by inimical habitat

Abstract

Measures of genetic diversity (including heterozygosity), survival and developmental homeostasis were found to be significantly lower in small, urban populations of the Common Toad (Bufo bufo) than in larger, rural populations of the same region. The autecology and genetic analysis of this relatively sedentary species suggested that the causal mechanism was genetic drift, arising from barriers to migration created by urban development. The pre-metamorphic survival of larvae cultured in identical conditions increased positively with the mean number of alleles at a locus and the percentage of polymorphic loci. Observed heterozygosity in urban garden and rural populations was correlated inversely with the number of observed physical abnormalities (used as a measure of developmental homeostasis) in the developing tadpoles. Genetic distances between town sites of mean 2.2 km separation were significantly higher than those between rural sites of mean 37 km separation. Genetic data were based on allozyme analysis of 27 loci in 8 urban and 4 rural populations. A subset of these sites (3 urban, 2 rural) were also assessed at 3 minisatellite loci and a positive correlation found between the average number of alleles per locus detected by the two methods. Estimates of Nei's 1972 genetic distance, derived separately from the DNA and protein data, were not, however, correlated. The reduction in genetic diversity and fitness observed in these urban toads provides an example of the effect on population persistence that longer term depletion in numbers and habitat fragmentation can have in the wider environment.

Genetic diversity and condition factor: a significant relationship in Flemish but not in German populations of the European bullhead (Cottus gobio L.)

“…This is in accordance with population genetics theory, inbreeding experiments and empirical studies of natural populations (Gjerde et al, 1983;Hartl and Clark, 1997;Meffe and Carroll, 1997;Hitchings and Beebee, 1998;Keller and Waller, 2002). Nevertheless, our results also suggest that there may be different associations between levels of genetic diversity and the condition factor at the population level, even within a single species.…”

“…Moreover, empirical evidence is accumulating that small and isolated populations that have been depleted of genetic variation often suffer a decreased fitness. Fragmented populations of the common toad (Bufo bufo) for example are characterised by significantly lower genetic diversity, survival and developmental homeostasis, compared to larger toad populations (Hitchings and Beebee, 1998). Similarly, remnant populations of the Florida panther (Puma concolor coryi) have, compared with larger populations of the species in western United States, low levels of genetic variation, poor sperm quality and high susceptibility to parasites (Roelke et al, 1993;O'Brien, 1994).…”

The spatial genetic structure of the yellow-necked mouse in an urban environment – a recent invader vs. a closely related permanent inhabitant

“…amphibians), often related to a specific environment, such as water bodies, exhibit decreased genetic variability due to isolation and intensified genetic drift (Hitchings and Beebee 1998;Noël et al 2007;Noël and Lapointe 2010;Mikulič and Pišút 2012;Munshi-South et al 2013;Zak and Pehek 2013, but see also Saarikivi et al 2013); (ii) mobile species able to cross environmental barriers seem to maintain a high level of genetic variability, probably avoiding complete isolation between patches of habitat within the city as well as between urban and rural areas (Desender et al 2005;Gardner-Santana et al 2009;Rutkowski et al 2009;Bj rklund et al 2010;Munshi-South and Kharchenko 2010); (iii) urban populations, usually fragmented into local subpopulations inhabiting small patches of suitable habitats (e.g. green spaces), exhibit pronounced genetic structure (Rubin et al 2001;Wood and Pullin 2002;Wandeler et al 2003;Desender et al 2005;Gardner-Santana et al 2009;Bj rklund et al 2010;Delaney et al 2010;Munshi-South and Kharchenko 2010;Vangestel et al 2011;Gortat et al 2013Gortat et al , 2015aMunshi-South et al 2013;Unfried et al 2013).…”

Fine-scale population genetic structure and sex-biased dispersal in the smooth snake (Coronella austriaca) in southern England

“…However, habitat change can result in the creation of dispersal barriers (Hitchings and Beebee, 1998), which can alter patterns of gene flow and lead to the isolation of remnant populations (Gerlach and Musolf, 2000). Such small and isolated populations may continue to lose genetic variation as a consequence of genetic drift (Reed and Frankham, 2003), and become inbred (Madsen et al, 1996).…”