Conservation genetics of yellow-bellied toads (Bombina variegata): a matter of geographical scale and isolation

Abstract

Amphibian populations world-wide are threatened by declines and extinctions mainly due to habitat loss and fragmentation. Habitat fragmentation threatens the yellow-bellied toad Bombina variegata in the northern and western regions of its distribution where it is strictly protected. We studied the genetic structure and diversity of populations at three geographical scales using microsatellite loci to detect potential threats for population persistence. At the local scale, we sampled four neighbouring localities at 1–2.6 km distance to detect effects of short-term (decades) fragmentation on connectivity. At the regional scale, five additional localities in the mountains of the Westerwald (Rhineland-Palatinate, Germany) were studied at up to 50.1 km distance to analyse genetic diversity and population structure. At the continental scale, we included data from regions in the northern distribution with fragmented populations (Hesse and Lower Saxony, Germany) and more continuous populations in the South (Alsace, France; Geneva, Switzerland; Trentino, Italy) to evaluate variation of genetic diversity. At the local scale, short-term fragmentation caused significant genetic differentiation between breeding assemblages only 1.4 km apart from each other. At the regional scale, we found notable genetic distance among localities. At the continental scale, we identified Alsace, Trentino and Geneva in the South as regions with low genetic structuring and high allelic richness, and the northern remaining regions in Germany as deeply structured with reduced allelic richness. We suggest that reduced genetic diversity and habitat fragmentation in northern regions makes these populations particularly vulnerable to decline. In conclusion, informed conservation management of B. variegata should focus on measures maintaining or improving connectivity among neighbouring populations.

Small monsters: Insect predation limits reproduction of yellow‐bellied toad Bombina variegata to ponds in their earliest successional stage

“…However, few of the 1,564 Natura 2000 sites intended to protect B. variegata are actually focused on the protection of this species. Whereas in western Europe the species is Critically Endangered (Kuzmin et al, 2009; Heatwole & Wilkinson, 2013; Hantzschmann et al, 2021), its status in the eastern part of the EU is regarded as favourable; but this is not so. In only two of the seven EU countries where the overall status of B. variegata was evaluated is its status favourable; in the other five the assessment is negative (European Environment Information and Observation Network, 2009).…”

Landscape Genetics of the Yellow-Bellied Toad (Bombina variegata) in the Northern Weser Hills of Germany

“…Intensive agriculture is a major threat to biodiversity, and adds to the impermeability of the landscape, resulting in decreased migration potential [59]. Wider grass verges between fields and steppingstone biotopes between isolated populations more than 5 km apart [16] can help loosen up the landscape and make it more permeable for amphibians. An additional aspect is the embarkment of rivers.…”

“…A significant positive correlation between genetic and geographic distance was found in this study. A distance between 1 and 2 km is recommended for a good connectivity between subpopulations of the yellow-bellied toad [53], as well as the implementation of steppingstone biotopes in between subpopulations 5 or more km apart [16]. All these findings and recommendations emphasize the importance of short scale reestablishment of connectivity in the conservation of this species.…”

“…In particular, the northern populations are endangered or have gone extinct due to habitat loss [15]. Since habitats are generally more isolated in north Germany, B. variegata shows greater genetic isolation in the northern federal provinces of Germany than in the south [14][15][16].…”

Importance of Genetic–Fitness Correlations for the Conservation of Amphibians

“…Higher genetic distances (F ST values) indicating population fragmentation have been found for amphibians (F ST = 0.32, N = 33 amphibian species) than for other taxa (e.g., F ST = 0.076 for birds and F ST = 0.26 for reptiles, [2]). For example, studies on the yellow-bellied toads Bombina variegata in Germany revealed highly structured populations with pairwise F ST values which were significantly different among most populations and an overall extremely low genetic diversity (as measured by heterozygosity, H O , H E and inbreeding F IS ) in most toad localities [24,25]. Other examples for highly structured amphibian species with low GD are the Oregon spotted frog Rana pretiosa from the Pacific Northwest [26], and the Arouss Al Ayn Salamandra inframaculata from northern Israel [27].…”