No signs of inbreeding despite long-term isolation and habitat fragmentation in the critically endangered Montseny brook newt (Calotriton arnoldi)

Abstract

Endemic species with restricted geographic ranges potentially suffer the highest risk of extinction. If these species are further fragmented into genetically isolated subpopulations, the risk of extinction is elevated. Habitat fragmentation is generally considered to have negative effects on species survival, despite some evidence for neutral or even positive effects. Typically, non-negative effects are ignored by conservation biology. The Montseny brook newt (Calotriton arnoldi) has one of the smallest distribution ranges of any European amphibian (8 km) and is considered critically endangered by the International Union for Conservation of Nature. Here we apply molecular markers to analyze its population structure and find that habitat fragmentation owing to a natural barrier has resulted in strong genetic division of populations into two sectors, with no detectable migration between sites. Although effective population size estimates suggest low values for all populations, we found low levels of inbreeding and relatedness between individuals within populations. Moreover, C. arnoldi displays similar levels of genetic diversity to its sister species Calotriton asper, from which it separated around 1.5 million years ago and which has a much larger distribution range. Our extensive study shows that natural habitat fragmentation does not result in negative genetic effects, such as the loss of genetic diversity and inbreeding on an evolutionary timescale. We hypothesize that species in such conditions may evolve strategies (for example, special mating preferences) to mitigate the effects of small population sizes. However, it should be stressed that the influence of natural habitat fragmentation on an evolutionary timescale should not be conflated with anthropogenic habitat loss or degradation when considering conservation strategies.

Population genetic analysis of the recently rediscovered Hula painted frog (Latonia nigriventer) reveals high genetic diversity and low inbreeding

“…Similar surprising findings, i.e. high allelic richness, high genetic diversity and a very low inbreeding coefficient, were also observed in the Black toad and the Montseny brook newt 39 , 40 . This demonstrates that species with small N ad and N e are not necessarily genetically depauperate.…”

“…When we compared our results to those of two other studies focusing on similar systems, i.e. geographically very restricted amphibian species without viable metapopulation structures, we found that comparatively low N e values had also been reported (i) for the Black toad ( Anaxyrus exsul , formerly Bufo exsul ), a desert amphibian inhabiting four spring systems with a total range of only ~15 ha in California, for which N e values ranged between 7 and 30 39 , and (ii) for the Montseny brook newt ( Calotriton arnoldi ), one of the most endangered European vertebrate species with an overall distribution range of only 8 km², for which N e values ranged between 7.3 and 342.3 40 . These two species, however, already diverged from their sister species during the Pleistocene glaciations 39 – 41 and successfully persisted until today despite their isolation.…”

“…The explanations for this apparent contradiction are not easy to assess. For the Montseny brook newt, the authors speculate a possible preference of females to breed with (i) genetically more dissimilar partners or (ii) with several males in order to avoid low egg viability 40 . For the Hula painted frog, three further possible explanations may be speculated: (iii) recently metamorphosed (and potentially inbred) individuals could disperse 50 , which would give another explanation for the low number of juveniles observed by us, or (iv) there could be occasional immigrations of individuals from other yet unknown populations within the Hula Valley.…”

Jailed in the mountains: Genetic diversity and structure of an endemic newt species across the Pyrenees

“…asper populations across the Pyrenees (weighted average Ar = 2.930 and H E = 0.523) compared to its sister species, the Montseny brook newt, C . arnoldi (weighted average Ar = 3.398 and H E = 0.441)[ 26 ]. These values are also consistent compared to other mountain brook newts, such as Euproctus platycephalus on Sardinia (weighted average Ar = 2.376 and H E = 0.6 [ 65 ]) and are within the typical range of other urodeles and temperate amphibians (0.4–0.6; [ 66 ] and references therein).…”

“…Instead, highly phylopatric amphibian species with very restricted dispersal rates (e.g. Calotriton arnoldi ) present highly structured and isolated populations [ 26 ].…”